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Améliorer le dépistage du cancer : L’IA au service des radiologues

Le cancer est l'une des principales causes de morbidité et de mortalité à l'échelle mondiale, avec une personne sur cinq en moyenne développant un cancer au cours de sa vie (The Burden of Cancer, n.d.). Le dépistage du cancer cible les individus asymptomatiques et vise à identifier soit un cancer à un stade précoce, soit des affections précancéreuses. Dans de nombreux cas, cela permet une intervention rapide et de meilleurs résultats du traitement. En général, le dépistage peut être considéré comme jouant un rôle préventif ou de détection précoce. Le dépistage préventif vise à détecter les affections bénignes pouvant devenir cancéreuses, ce qui n'est possible que pour certains cancers, tandis que les approches de détection précoce visent à détecter un cancer à un stade précoce. Il est important de noter que le dépistage ne doit pas être considéré comme un test unique, mais comme un processus qui comprend l'identification de la population cible, la réalisation de tests de diagnostic et la planification d'un examen plus approfondi, y compris un traitement si nécessaire (Organisation mondiale de la santé. Bureau régional pour l’Europe, 2022). 

La radiologie joue depuis longtemps un rôle essentiel dans la détermination de l’étendue de la propagation locale et à distance des tumeurs après l’établissement d’un diagnostic de cancer. Cependant, elle est également indispensable dans le cadre du dépistage de plusieurs cancers courants. Dans ces cas, les examens d’imagerie médicale constituent soit le principal outil de dépistage, soit sont utilisées pour décider d’un examen plus approfondi après le dépistage à l’aide d’autres méthodes, telles que des analyses de sang. Selon le type de cancer, le dépistage peut faire appel à des techniques d'imagerie médicale telles que la mammographie, la tomodensitométrie (TDM), l'imagerie par résonance magnétique (IRM) ou l'échographie. Des programmes nationaux de dépistage utilisant l’imagerie médicale ont été mis en place pour certains des cancers les plus courants. La plupart de ces programmes ciblent des populations spécifiques à risque du cancer spécifique en question, identifiées à l'aide de facteurs de risque modifiables ou non modifiables.

Étant donné que le dépistage du cancer cible les personnes en bonne santé, il est particulièrement essentiel que les avantages d'un programme de dépistage l'emportent sur ses inconvénients. Cela doit être soigneusement établi pour chaque programme et est parfois controversé (Lam et al., 2014). Cependant, certains avantages et inconvénients du dépistage du cancer s'appliquent à toutes les techniques de dépistage et à tous les cancers (Kramer, 2004 ; Organisation mondiale de la santé. Bureau régional pour l’Europe, 2022). Le dépistage peut réduire les coûts des soins de santé et améliorer la qualité de vie des patients. Cela améliore également souvent le pronostic et les résultats du traitement des personnes diagnostiquées comme atteintes d'un cancer et peut rassurer les personnes chez lesquelles le cancer n'est pas détecté. Cependant, parfois, une détection précoce ne modifie pas le pronostic et, chez ces personnes, le dépistage peut donner lieu à un traitement inutile, entraînant une diminution de la santé ou de la qualité de vie. En fait, le dépistage permet parfois de détecter des cancers qui n'auraient jamais entraîné de problèmes de santé ou la mort d'une personne. De plus, les faux positifs et les faux négatifs sont inévitables avec tout test de dépistage. Les premiers conduisent à un surtraitement, avec les effets secondaires psychosociaux et physiques qui en résultent, et les deuxièmes à une fausse assurance et à un retard du traitement. 

Cancer du sein

Le cancer du sein est la deuxième cause de décès par cancer chez les femmes (Bray et al., 2018) et l'un des cancers les plus courants dans le monde (Sung et al., 2021). La détection et le traitement précoces peuvent améliorer les résultats, et des études ont révélé une mortalité jusqu'à 20 % inférieure dans les populations dépistées par rapport aux populations auxquelles le dépistage n’est pas proposé. Des études estiment qu’un décès par cancer du sein est évité en moyenne pour 250 à 414 femmes dépistées (Marmot et al., 2013 ; Tabár et al., 2011). Plus de 100 pays dans le monde ont mis en œuvre des programmes de dépistage du cancer du sein à grande échelle (Existence of National Screening Program for Breast Cancer, n.d.). Le début du dépistage est recommandé entre 40 et 50 ans (Ren et al., 2022) et se fait presque exclusivement par mammographie, qui utilise des rayons X à faible dose pour obtenir une image des seins, ou par tomosynthèse mammaire numérique, une technique similaire qui utilise plusieurs projections pour créer une série d’images empilées du sein.

 

breast cancer ebook

L’algorithme a augmenté la détection du cancer du sein de 12 à 27 % en triant les mammographies qui ont été évaluées comme négatives après une double lecture mais qui ont été considérées comme suspectes par l’algorithme pour une évaluation plus approfondie par IRM ou échographie.

La précision de la mammographie varie considérablement et même les lectures des radiologues les plus expérimentés présentent des taux élevés de faux positifs et de faux négatifs (Elmore et al., 2009 ; Lehman et al., 2015). On estime qu’au moins une femme dépistée sur trois aura un résultat faussement positif à la mammographie au cours de sa vie (Castells et al., 2006). La mammographie est particulièrement difficile dans le cas des seins denses (Boyd et al., 2007) et chez les femmes sous traitement hormonal substitutif (Banks et al., 2006). Le dépistage par mammographie est également un processus à forte intensité de main-d'oeuvre. Dans de nombreux pays européens, la norme de soins est la double lecture consensuelle, dans laquelle deux radiologues lisent consécutivement chaque cas et résolvent les désaccords par consensus (Giordano et al., 2012). Il existe malheureusement également une pénurie de radiologues et de manipulateurs en radiologie spécifiquement formés à la mammographie dans de nombreux pays (Moran & Warren-Forward, 2012 ; Rimmer, 2017 ; Wing & Langelier, 2009). 

Des systèmes basés sur l’intelligence artificielle (IA) ont été intégrés à différentes étapes du processus de dépistage du cancer du sein. Dans une étude portant sur près de 30 000 femmes aux États-Unis et au Royaume-Uni ayant subi des mammographies de dépistage à des intervalles de 1 à 3 ans et une période de suivi allant jusqu'à 39 mois, un ensemble de trois modèles d'apprentissage profond a été comparé à l'histopathologie et aux interprétations de radiologues certifiés (McKinney et al., 2020). L'algorithme avait une spécificité 1,2 à 5,7 % plus élevée et une sensibilité 2,7 à 9,4 % plus élevée que celles des radiologues qui ont effectué la première lecture. Les auteurs ont estimé que l’utilisation de l’algorithme pourrait rendre inutiles les secondes lectures dans jusqu’à 88 % des cas de dépistage tout en maintenant la précision, libérant ainsi des ressources indispensables. 

Des résultats toujours prometteurs ont été rapportés dans des études utilisant des systèmes basés sur l’IA en collaboration avec des radiologues. Une étude portant sur près de 16 000 femmes subissant une mammographie numérique ou une tomosynthèse mammaire numérique en Espagne a estimé que l'utilisation d'un algorithme basé sur l'apprentissage profond entraînerait une charge de travail inférieure de 72,5 % par rapport à la double lecture tout en maintenant la sensibilité (Raya-Povedano et al., 2021). Dans ce modèle, les examens les moins suspects seraient uniquement lus par l'algorithme et les 2 % d'examens les plus suspects, tels que jugés par l'algorithme, seraient signalés pour un examen plus approfondi, quelle que soit l'interprétation des radiologues. De même, une étude portant sur 7 354 femmes en Suède a révélé qu’un algorithme d’apprentissage profond disponible sur le marché classifiait avec précision les mammographies les moins suspectes, et que ces femmes n’avaient subi aucun examen supplémentaire (Dembrower et al., 2020). Ceci a été réalisé avec un taux de faux négatifs de 0 à 2,6 %. L'algorithme a également augmenté la détection du cancer du sein de 12 à 27 % en triant les mammographies qui ont été évaluées comme négatives après une double lecture, mais qui ont été considérées comme suspectes par l'algorithme pour une évaluation plus approfondie par IRM ou échographie. 

D’autres études ont utilisé des systèmes basés sur l’IA comme étape d’orientation décisionnelle. Dans une étude portant sur plus d’un million de mammographies en Allemagne, un réseau neuronal convolutif profond (CNN) a attribué un score de confiance à chaque mammographie (Leibig et al., 2022). Les évaluations réalisées avec un niveau de confiance élevé par l'algorithme n'ont fait l'objet d'aucun traitement supplémentaire, tandis que les évaluations à faible niveau de confiance ont été renvoyées au radiologue. Cette approche était associée à une augmentation de 4 % de la sensibilité et de 0,5 % de la spécificité par rapport à l'évaluation d'un seul radiologue sans l'aide de l'algorithme. Dans ce scénario, 63 % des mammographies ont été automatiquement triées par l'algorithme, et l'amélioration des performances par rapport à la lecture d'un seul radiologue était cohérente sur huit sites de dépistage et trois fabricants de dispositifs. 

Cancer du poumon

Le cancer du poumon est la principale cause de décès par cancer dans le monde, causant près de 1,8 million de décès en 2020 (Sung et al., 2021). Un exemple d’approche de dépistage ciblé, le dépistage du cancer du poumon, est recommandé en fonction du risque individuel. Le dépistage des adultes âgés de 50 à 80 ans ayant fumé pendant 20 paquets-années par tomodensitométrie à faible dose (LDCT) est recommandé aux États-Unis depuis 2013, après que des études initiales ont révélé une réduction relative de 20 % de la mortalité par la cancer du poumon (Lung Cancer: Screening, 2021 ; National Lung Screening Trial Research Team et al., 2011). Un programme de dépistage similaire est en cours de déploiement au Royaume-Uni (NHS England, 2022). Chez les patients qui qui bénéficient d’un dépistage du cancer du poumon par la LDCT, l’IA s’est révélée prometteuse pour la détection automatique des nodules pulmonaires susceptibles de représenter une tumeur maligne. Ceci est important car la détection des nodules pulmonaires par les radiologues est fastidieuse, prend du temps et est sujette aux erreurs (Al Mohammad et al., 2019 ; Armato et al., 2009 ; Gierada et al., 2017 ; Leader et al., 2005). Dans une étude portant sur près de deux mille patients, un algorithme basé sur le CNN conçu pour détecter automatiquement les nodules pulmonaires a été testé comme deuxième lecteur (Katase et al., 2022). Les cas témoins étaient constituée de nodules identifiés par deux radiologues expérimentés comme étant à haut risque selon l'histoire clinique ainsi que la morphologie du nodule. L'étude a révélé que l'utilisation de l'algorithme était associée à une sensibilité améliorée aux nodules à différents niveaux d'expérience du premier lecteur. Bien que la sensibilité globale soit plus faible pour les nodules en verre dépoli et les nodules de moins de 1 cm de diamètre, la sensibilité de ceux-ci était beaucoup plus élevée lorsque l'algorithme était utilisé que lorsque le radiologue interprétait seul les images. Les faux positifs incluaient des zones d'inflammation pleurale ou des vaisseaux périphériques, tandis que les faux négatifs étaient souvent des nodules en verre dépoli faibles ou mal délimités ou des nodules proches du diaphragme. Il est important de noter que les auteurs ont constaté des performances de modèle cohérentes sur une gamme de doses de rayonnement TDM dans une étude fantôme, ce qui indique que leurs résultats pourraient être généralisables à d’autres protocoles de TDM thoracique (Katase et al., 2022). Une autre étude a trouvé une sensibilité de 93 % et une spécificité de 96 % d'un algorithme basé sur le CNN pour la détection des nodules pulmonaires sur la LDCT par rapport au consensus de deux radiologues (Chamberlin et al., 2021). Les faux positifs dans cette étude comprenaient des zones d'atélectasie, des modifications parenchymateuses associées à une infection et des ostéophytes faisant saillie dans les champs pulmonaires à partir des vertèbres thoraciques. 

lung cancer ebook

L’étude a révélé que l’utilisation de l’algorithme était associée à une sensibilité améliorée aux nodules à différents niveaux d’expérience du premier lecteur.

Au-delà de la simple identification des nodules pulmonaires, certaines études ont tenté de classer le risque de malignité des nodules identifiés. Un algorithme à plusieurs composants comprenant des modèles de segmentation pulmonaire, de détection des régions cancéreuses et de prédiction du cancer a été testé sur 6 716 LDCT et validé sur un ensemble de données indépendant de 1 139 LDCT (Ardila et al., 2019). L'algorithme génère une probabilité de malignité basée soit sur des LDCT uniques, soit, lorsqu'elles sont disponibles, sur des LDCT antérieures du même patient. En utilisant des cas de cancer du poumon prouvé par biopsie, l’algorithme a fonctionné aussi bien que six radiologues lorsque des LDCT antérieures étaient disponibles. Dans les cas sans LDCT préalable, l’algorithme avait un taux de faux positifs inférieur de 11 % et un taux de faux négatifs inférieur de 5 % à celui des radiologues. 

Une évaluation du parenchyme pulmonaire sur la LDCT au-delà de la présence de nodules pulmonaires est une approche récente et prometteuse pour identifier le risque futur de cancer du poumon. Une étude a révélé qu'un algorithme 3D-CNN, testé sur plus de 15 000 LDCT, présentait une aire sous la courbe caractéristique de fonctionnement du récepteur (ASC) de 0,86 à 0,94 (selon l'ensemble de données) pour prédire le cancer du poumon à un an (Mikhael et al., 2023). Il est intéressant de noter que l’ASC de l’algorithme, après exclusion des cas où des nodules visibles étaient présents à la référence au même endroit que les futurs cancers, était de 0,82. L'algorithme a également montré un taux de faux positifs inférieur aux scores de malignité établis sur la base de la morphologie des nodules lorsque le volume total de la LDCT a été évalué par l'algorithme. Ces résultats suggèrent que d'autres caractéristiques au-delà des nodules suspects contribuaient à la prédiction de l'algorithme. Surtout, cela signifie que l’algorithme détecte des caractéristiques de la LDCT au-delà de ce que les radiologues considèrent généralement comme pertinents pour prédire le risque de cancer du poumon. 

Aux États-Unis, les critères d'éligibilité au dépistage du cancer du poumon, qui émanent des Centers for Medicare et Medicaid Services (CMS), négligent plus de la moitié des cas de cancer du poumon (Y. Wang et al., 2015). Bien qu’il existe d’autres outils de « pré-dépistage » plus complexes, basés sur des scores, les informations qu’ils nécessitent, comme le nombre de paquets-années, sont souvent inexactes ou indisponibles (Kinsinger et al., 2017). L’IA a ainsi été utilisée pour identifier davantage de personnes à haut risque de cancer du poumon afin de les inclure dans les programmes de dépistage. Une étude portant sur 5 615 personnes a révélé qu'une combinaison de radiographies thoraciques simples, d'âge, de sexe et de statut tabagique actuel permet une sélection plus ciblée de patients pour le dépistage par la LDCT (Lu et al., 2020). Le modèle dans cette étude avait une ASC de 0,7 pour prédire un cancer du poumon incident sur 12 ans, contre une ASC de 0,63 pour les critères CMS, ce qui se traduit par 30,7 % de cas de cancer du poumon en moins manqués avec l'algorithme. Le modèle prédit également une mortalité par le cancer du poumon sur 12 ans avec une ASC de 0,76. Les auteurs ne recommandent pas les radiographies thoraciques de routine à des fins de pré-dépistage, mais préconisent l'utilisation de ce modèle chez les patients subissant des radiographies thoraciques pour d'autres indications cliniques.

Cancer colorectal

Le cancer colorectal est le troisième cancer le plus répandu chez les femmes et les hommes et constitue une cause majeure de décès par le cancer dans le monde (Sung et al., 2021). Il se développe comme une cascade d’événements à mesure que les cellules de la muqueuse intestinale accumulent des mutations génétiques, se transformant d’abord en muqueuse hyperproliférative, puis en adénome bénin et, dans certains cas, en adénocarcinome (Kuipers et al., 2015). Le dépistage du cancer colorectal est avant tout préventif : il vise à détecter les adénomes potentiellement cancéreux afin de pouvoir les éliminer, une approche qui réduit la mortalité de la maladie (Zauber et al., 2012).

Colorectal cancer ebook

Une récente étude de validation de principe a utilisé une approche entièrement automatisée utilisant les CNN pour la segmentation des polypes et la distinction entre les polypes bénins et précancéreux.

Le dépistage du cancer colorectal est régulièrement effectué soit en recherchant du sang dans les selles à l'aide de tests très sensibles, soit en visualisant la lumière de l'intestin par coloscopie optique (Helsingen Lise M. & Kalager Mette, 2022). La coloscopie optique est une méthode établie et fiable pour identifier les adénomes colorectaux et permet de les éliminer immédiatement. Cependant, ses principaux inconvénients sont la faible observance du patient et la nécessité d'une sédation (Inadomi et al., 2012 ; Joseph et al., 2012 ; OECD, 2012 ; Stock et al., 2011 ; Use of Colorectal Cancer Screening Tests, 2023).

Une alternative émergente et prometteuse à la coloscopie optique est le coloscanner. Cette technique a une précision diagnostique similaire à celle de la coloscopie optique (Pickhardt et al., 2003, 2011, 2018), est préférée par les patients (Ristvedt et al., 2003) et offre une meilleure observance (Moawad et al., 2010). Elle ne nécessite pas non plus de sédation et peut détecter des résultats cliniquement pertinents en dehors de l'intestin qui sont invisibles à la coloscopie optique (Smyth et al., 2013). En revanche, la colonographie TDM nécessite une préparation intestinale (comme la coloscopie optique), expose le patient à certains rayonnements ionisants et ne permet pas la résection simultanée des polypes. Malgré ces inconvénients, l'American College of Radiology recommande la colonographie TDM pour le dépistage des patients présentant un risque moyen ou modéré de cancer colorectal (Expert Panel on Gastrointestinal Imaging: et al., 2018).

Les images de colonographie TDM subissent une série d’étapes de préparation avant d’être interprétées. Celles-ci incluent un prétraitement pour éliminer les artefacts, l’extraction du côlon du reste des structures abdominales, la reconstruction 3D du côlon et la visualisation de la lumière du côlon. Une étude récente a combiné une nouvelle méthode de segmentation et de reconstruction du côlon avec la détection des polypes à l'aide d'un CNN (Alkabbany et al., 2022). La segmentation automatisée du côlon a montré un chevauchement de plus de 90 % avec la segmentation manuelle experte dans 70 % des cas et des polypes du côlon ont été détectés avec une ASC de 0,93, une sensibilité de 97 % et une spécificité de 79 %. 

La différenciation entre les polypes bénins et ceux potentiellement malins est un défi à la fois en coloscopie optique et en colonographie TDM et a fait l'objet de plusieurs études utilisant l'IA. Les approches basées sur la radiomique pour classer les polypes bénins et précancéreux sur la colonographie TDM ont montré des ASC allant jusqu'à 0,91, mais nécessitent une segmentation manuelle des polypes (Grosu et al., 2021 ; Song et al., 2014). Une récente étude de validation de principe a utilisé une approche entièrement automatisée utilisant les CNN pour la segmentation des polypes et la distinction entre les polypes bénins et précancéreux (Wesp et al., 2022). Les auteurs ont formé le CNN sur les données de 63 patients et l'ont testé sur un ensemble de données indépendant de 59 patients, montrant une ASC allant jusqu'à 0,83 et une sensibilité et une spécificité allant jusqu'à 80 % et 69 % respectivement. De telles approches basées sur l’IA peuvent potentiellement être utilisées comme deuxième lecteur pour aider à orienter la décision concernant l’élimination des polypes.

Carcinome hépatocellulaire

Le carcinome hépatocellulaire (CHC) est l’une des causes les plus courantes de décès par cancer dans le monde (Sung et al., 2021). Les personnes atteintes d’une cirrhose du foie ou d’une infection chronique par le virus de l’hépatite B ou C courent un risque élevé de développer un CHC (Vogel et al., 2022). Le dépistage de ces patients est associé à une réduction de la mortalité par CHC (Singal et al., 2022 ; Zhang et al., 2004). Le dépistage est généralement réalisé par échographie abdominale tous les six mois (Association européenne pour l'étude du foie, 2018 ; Frenette et al., 2019 ; Marrero et al., 2018) avec ou sans mesure des taux d'alpha-foetoprotéine dans le sang (Colli et al., 2006 ; Tzartzeva et al., 2018). Les lésions suspectes identifiées par échographie sont ensuite caractérisées par TDM, IRM ou les deux. La pathogenèse du CHC implique une interaction complexe entre les nodules hépatiques qui existent à différents stades de lésions hépatiques chroniques. Des nodules régénératifs se forment en réponse à des lésions hépatocytaires et sont fréquemment observés dans les foies cirrhotiques. Les mutations génétiques peuvent s'accumuler au fil du temps dans ces nodules régénératifs, les convertissant en nodules dysplasiques avec un risque élevé d'évolution vers un CHC à mesure que davantage de mutations s'accumulent (Kudo, 2009). Faire la différence entre les nodules dysplasiques et malins à l’aide de l’imagerie est difficile (Park et al., 2017). En outre, les caractéristiques d'imagerie du CHC se confondent parfois avec celles d'autres lésions hépatiques, notamment les hémangiomes, les kystes hépatiques simples et l'hyperplasie nodulaire focale (Heiken, 2007). 

Hepatocellular cancer ebook

Les techniques d’apprentissage profond ont également été largement appliquées à l’imagerie hépatique à l’aide de l’échographie en mode B, montrant des résultats prometteurs pour détecter et classer les lésions focales du foie comme bénignes ou malignes.

En utilisant une approche radiomique combinant des informations de perfusion et une analyse de texture en échographie avec contraste amélioré, une étude portant sur 72 patients a trouvé une précision équilibrée de 0,84 pour distinguer les lésions hépatiques bénignes et malignes (Turco et al., 2022). Une autre étude utilisant l'échographie avec contraste amélioré a révélé une sensibilité de 94,8 % et une spécificité de 93,6 % pour distinguer le CHC de l'hyperplasie nodulaire focale à l'aide d'une approche d'apprentissage automatique à vecteurs de support (Huang et al., 2020), d'autres études trouvant des résultats similaires (Gatos et al., 2015 ; Kondo et al., 2017). Dans une étude multicentrique examinant la différenciation de 11 types différents de lésions focales du foie en utilisant l'échographie avec contraste amélioré et l'histopathologie comme référence, l'apprentissage automatique des vecteurs de support (ASC = 0,883) a surpassé un réseau neuronal artificiel (ASC = 0,829) et les deux approches ont surpassé un radiologue expérimenté (ASC = 0,702) (Ta et al., 2018). 

Les techniques d’apprentissage profond ont également été largement appliquées à l’imagerie hépatique utilisant l’échographie en mode B. Ces études ont montré des résultats prometteurs pour détecter (Brehar et al., 2020 ; Schmauch et al., 2019 ; Tiyarattanachai et al., 2022) et classer les lésions focales hépatiques comme bénignes ou malignes (Schmauch et al., 2019) ou les classer en entités spécifiques (Hassan et al., 2017 ; Virmani et al., 2014). En utilisant une approche d'apprentissage profond, une étude a révélé que la combinaison d'informations sur les données démographiques des patients et les résultats de laboratoire avec des images échographiques en mode B améliorait l'ASC pour classer les lésions hépatiques comme bénignes ou malignes de 0,721 (en utilisant uniquement l'échographie) à 0,994 (Sato et al., 2022). Une autre étude portant sur 334 patients a révélé que le taux de détection des lésions focales du foie par échographie en mode B utilisant un CNN était plus élevé pour le CHC que pour les autres lésions focales du foie et que le CNN surpassait les experts humains (avec un taux de détection d'algorithme de 100 % contre 39,1 % pour les non-radiologues et 69,6 % pour les radiologues) (Tiyarattanachai et al., 2022). 

Cancer de la prostate

Le cancer de la prostate est le cancer le plus répandu chez les hommes en Europe et aux États-Unis (Ferlay et al., 2018 ; Siegel et al., 2021) et le troisième cancer le plus répandu dans le monde (Sung et al., 2021). Dans les pays où des programmes existent, le dépistage repose généralement sur la mesure des taux sériques d’antigène spécifique de la prostate (PSA). Le PSA sérique a une sensibilité élevée mais une faible spécificité pour le cancer de la prostate (Merriel et al., 2022). Le dépistage basé sur le PSA seul conduit ainsi à de nombreuses biopsies inutiles, avec jusqu'à 75 % des biopsies systématiques de la prostate - celles réalisées sans cibler un endroit spécifique de la prostate, mais en prenant plusieurs biopsies dans différentes parties de la glande - étant négatives (Ahmed et al., 2017). De plus, le dépistage du PSA a tendance à détecter un cancer à faible risque et à croissance plus lente, considéré comme cliniquement insignifiant car il ne menace pas la survie du patient (US Preventive Services Task Force et al., 2018 ; Welch & Albertsen, 2020). Un dépistage basé sur le taux sérique de PSA suivi d'une biopsie systématique présente donc un bénéfice globalement discutable. L’approche idéale consisterait plutôt à détecter le cancer et à caractériser simultanément sa signification clinique. 

prostate cancer ebook

Une étude utilisant un classificateur basé sur les forêts aléatoires pour détecter les zones suspectes sur l’IRM multiparamétrique de la prostate a été associée à des temps de lecture plus courts et à une spécificité améliorée.

L’IRM multiparamétrique joue un rôle de plus en plus important dans le traitement des cas de cancer de la prostate dépistés et comprend des séquences pondérées en diffusion et pondérées T2, avec ou sans séquence dynamique à contraste amélioré pondérée T1 (Walker et al., 2020). Les faux positifs et la détection d’un cancer de la prostate cliniquement insignifiant peuvent être réduits grâce à l’IRM, ce qui peut contribuer à réduire le surtraitement (Drost et al., 2019). Des études suggèrent que l'IRM avant la biopsie peut réduire d'un tiers le nombre de biopsies inutiles (Elwenspoek et al., 2019), et cette approche a été incluse dans plusieurs lignes directrices sur la prise en charge du cancer de la prostate (Leitlinienprogramm Onkologie: Prostatakarzinom, n.d., Overview | Prostate Cancer: Diagnosis and Management | Guidance | NICE, n.d. ; Mottet et al., 2017). L’IRM peut également aider à orienter les biopsies ciblées chez les patients présentant des biopsies systématiques négatives de la prostate (Hoeks et al., 2012 ; Hugosson et al., 2022 ; Penzkofer et al., 2015 ; Siddiqui et al., 2015 ; Sonn et al., 2014). . Chez les patients présentant un risque de cancer de la prostate à très faible ou faible risque, l’IRM peut être utile pour surveiller activement la maladie, une approche associée à de bons résultats à long terme (Klotz et al., 2015). La lecture des IRM de la prostate est cependant difficile et même les systèmes de rapports standardisés ont une courbe d'apprentissage abrupte, et les performances diagnostiques varient considérablement entre les radiologues et les établissements (Kohestani et al., 2019 ; Muller et al., 2015 ; Rosenkrantz et al., 2017 ; Smith et al., 2019 ; Westphalen et al., 2020).

La segmentation de l'ensemble de la prostate permet de déterminer le volume de la glande qui est utilisé pour calculer la densité de PSA (une mesure qui permet de différencier l'hypertrophie bénigne de la prostate et le cancer de la prostate) et pour planifier la radiothérapie. La segmentation manuelle de la prostate par les radiologues prend cependant du temps et est sujette à des erreurs (Garvey et al., 2014). La segmentation automatisée de la prostate à l'aide d'outils basés sur l'IA est réalisable et précise, et plusieurs outils commerciaux sont actuellement disponibles à cet effet (AI for Radiology, n.d. ; Bardis et al., 2021 ; Belue & Turkbey, 2022 ; Sanford et al., 2020 ; Sunoqrot et al., 2022 ; Turkbey & Haider, 2022 ; Ushinsky et al., 2021 ; van Leeuwen et al., 2021 ; B. Wang et al., 2019). 

Plusieurs études utilisant des approches d'apprentissage profond ont atteint des ASC allant jusqu'à 0,89 pour la détection du cancer de la prostate par IRM multiparamétrique (Arif et al., 2020 ; Saha et al., 2021). Un algorithme basé sur l'apprentissage profond disponible dans le commerce a amélioré la détection par les radiologues du cancer de la prostate cliniquement significatif (en utilisant le consensus de trois radiologues expérimentés comme référence), a augmenté la fiabilité entre les lecteurs et a réduit le temps de lecture médian (Winkel et al., 2021). Comme dans le cas du cancer du sein, la précision du diagnostic est plus élevée lorsque les outils basés sur l'IA et les interprétations des radiologues sont considérés ensemble plutôt que de s'appuyer sur l'évaluation de l'un ou de l'autre (Cacciamani et al., 2023). 

L’IA a également été utilisée pour classer l’agressivité du cancer de la prostate. Dans une étude radiomique basée sur l’IRM, un classificateur de machine à vecteurs de support a été utilisé pour segmenter les zones de cancer de la prostate, suivi d’une analyse de texture et d’une extraction de caractéristiques quantitatives (Giannini et al., 2021). Dans la même étude, un autre classificateur de machine à vecteurs de support a utilisé les caractéristiques extraites pour classer l’agressivité des tumeurs en utilisant le classement histopathologique comme référence. Basée sur les données de 72 patients, l'étude a trouvé une ASC de 0,81 dans un ensemble de données de validation de 59 patients (valeur prédictive positive = 81 %, valeur prédictive négative = 71 %). Dans une autre étude portant sur les IRM multiparamétriques de la prostate de 107 patients, les classifications PI-RADS des radiologues ont été combinées avec un score de vraisemblance dérivé d'un classificateur en forêts aléatoires, et toutes les régions suspectes ainsi identifiées ont été biopsiées (Litjens et al., 2015). L'inclusion du score de l'algorithme était associée à une probabilité plus élevée de détecter un cancer de la prostate (ASC = 0,88 avec et 0,81 sans l'algorithme) et de détecter des cancers plus agressifs (ASC = 0,87 avec et 0,78 sans l'algorithme). Dans une étude portant sur 417 patients, un CNN a atteint une ASC de 0,81 pour classer le cancer de la prostate cliniquement significatif à l'aide d'une IRM multiparamétrique avec une sensibilité légèrement inférieure à celle des radiologues hautement expérimentés (Cao et al., 2019). 

Comme pour de nombreuses autres applications de l’IA en radiologie, le manque d’interprétabilité des modèles d’apprentissage profond de l’IRM de la prostate entrave et retarde leur mise en oeuvre dans la pratique clinique (Aristidou et al., 2022 ; Reddy et al., 2020 ; Reyes et al., 2020 ; Vayena et al., 2018). Une étude utilisant un CNN sur l'IRM de la prostate de 1 224 patients et l'histopathologie comme référence a trouvé une ASC de 0,89 pour distinguer le cancer de la prostate cliniquement significatif des autres modifications de la prostate (Hamm et al., 2023). En outre, ils comprenaient une carte thermique voxelwise des zones suspectes de cancer de la prostate cliniquement significatif et des explications descriptives inspirées de PI-RADS sur la façon dont le CNN est arrivé à sa conclusion. L'algorithme a été associé à une réduction du temps de lecture de 85 secondes à 47 secondes et à une augmentation de la confiance en lecture chez les lecteurs non experts.

Conclusion

L’imagerie médicale joue un rôle central dans le dépistage de plusieurs des cancers les plus courants. La lecture des examens de dépistage nécessite des compétences et une expérience considérables, et la demande actuelle dépasse de loin l'offre de radiologues qualifiés (AAMC Report Reinforces Mounting Physician Shortage, 2021, Clinical Radiology UK Workforce Census 2019 Report, 2019). L’utilisation d’outils basés sur l’IA pour le dépistage du cancer est extrêmement prometteuse pour atténuer ces problèmes. Les avantages de ces approches comprennent une meilleure identification des personnes éligibles au dépistage, une meilleure précision du diagnostic, des délais de rapports réduits et une confiance accrue des radiologues dans leurs propres décisions diagnostiques. Les résultats les plus prometteurs ont été obtenus lorsque les systèmes basés sur l’IA et les radiologues ont pris ensemble des décisions concernant les examens de dépistage. La prise de décision collaborative entre les outils basés sur l’IA et les radiologues peut ainsi ouvrir la voie à une ère de transformation dans le dépistage du cancer. 

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Guide to Artificial Intelligence in Radiology

    Artificial intelligence (AI) is playing a growing role in all our lives and has shown promise in addressing some of the greatest current and upcoming societal challenges we face. The healthcare industry, though notoriously complex and resistant to disruption, potentially has a lot to gain from the use of AI. With an established history of leading digital transformation in healthcare and an urgent need for improved efficiency, radiology has been at the forefront of harnessing AI’s potential.

    This book covers how and why AI can address challenges faced by radiology departments, provides an overview of the fundamental concepts related to AI, and describes some of the most promising use cases for AI in radiology. In addition, the major challenges associated with the adoption of AI into routine radiological practice are discussed. The book also covers some crucial points radiology departments should keep in mind when deciding on which AI-based solutions to purchase. Finally, it provides an outlook on what new and evolving aspects of AI in radiology to expect in the near future.

    The healthcare industry has experienced a number of trends over the past few decades that demand a change in the way certain things are done. These trends are particularly salient in radiology, where the diagnostic quality of imaging scans has improved dramatically while scan times have decreased. As a result, the amount and complexity of medical imaging data acquired have increased substantially over the past few decades (Smith-Bindman et al., 2019; Winder et al., 2021) and are expected to continue to increase (Tsao, 2020). This issue is complicated by a widespread global shortage of radiologists (AAMC Report Reinforces Mounting Physician Shortage, 2021, Clinical Radiology UK Workforce Census 2019 Report, 2019). Healthcare workers, including radiologists, have an increasing workload (Bruls & Kwee, 2020; Levin et al., 2017) that contributes to burnout and medical errors (Harry et al., 2021). Being an essential service provider to virtually all other hospital departments, staff shortages within radiology have significant effects that spread throughout the hospital and to society as a whole (England & Improvement, 2019; Sutherland et al., n.d.).

    With an ageing global population and a rising burden of chronic illnesses, these issues are expected to pose even more of a challenge to the healthcare industry in the future.

    AI-based medical imaging solutions have the potential to ameliorate these challenges for several reasons. They are particularly suited to handling large, complex datasets (Alzubaidi et al., 2021). Moreover, they are well suited to automate some of the tasks traditionally performed by radiologists and radiographers, potentially freeing up time and making workflows within radiology departments more efficient (Allen et al., 2021; Baltruschat et al., 2021; Kalra et al., 2020; O’Neill et al., 2021; van Leeuwen et al., 2021; Wong et al., 2019). AI is also capable of detecting complex patterns in data that humans cannot necessarily find or quantify (Dance, 2021; Korteling et al., 2021; Kühl et al., 2020).

    The term “artificial intelligence” refers to the use of computer systems to solve specific problems in a way that simulates human reasoning. One fundamental characteristic of AI is that, like humans, these systems can tailor their solutions to changing circumstances. Note that, while these systems are meant to mimic on a fundamental level how humans think, their capacity to do so (e.g. in terms of the amount of data they can handle at one time, the nature and amount of patterns they can find in the data, and the speed at which they do so) often exceeds that of humans.

    AI solutions come in the form of computer algorithms, which are pieces of computer code representing instructions to be followed to solve a specific problem. In its most fundamental form, the algorithm takes data as an input, performs some computation on that data, and returns an output.

    An AI algorithm can be explicitly programmed to solve a specific task, analogous to a step-by-step recipe for baking a cake. On the other hand, the algorithm can be programmed to look for patterns within the data in order to solve the problem. These types of algorithms are known as machine learning algorithms. Thus, all machine learning algorithms are AI, but not all AI is machine learning. The patterns in the data that the algorithm can be explicitly programmed to look for or that it can “discover” by itself are known as features. An important characteristic of machine learning is that such algorithms learn from the data itself, and their performance improves the more data they are given.

    One of the most common uses of machine learning is in classification - assigning a piece of data a particular label. For example, a machine learning algorithm might be used to tell if a photo (the input) shows a dog or a cat (the label). The algorithm can learn to do so in a supervised or unsupervised way.

    Supervised learning

    In supervised learning, the machine learning algorithm is given data that has been labelled with the ground truth, in this example, photos of dogs and cats that have been labelled as such. The process then goes through the following phases:

    1.Training phase: The algorithm learns the features associated with dogs and cats using the aforementioned data (training data).
    2.Test phase: The algorithm is then given a new set of photos (the test data), it labels them and the performance of the algorithm on that data is assessed.

    In some cases, there is a phase in between training and test, known as the validation phase. In this phase, the algorithm is given a new set of photos (not included in either the training or test data), its performance is assessed on this data, and the model is tweaked and retrained on the training data. This is repeated until some predefined performance-based criterion is reached, and the algorithm then enters the test phase.

    Unsupervised learning

    In unsupervised learning, the algorithm identifies features within the input data that allow it to assign classes to the individual data points without being told explicitly what those classes are or should be. Such algorithms can identify patterns or group data points together without human intervention and include clustering and dimensionality reduction algorithms. Not all machine learning algorithms perform classification. Some are used to predict a continuous metric (e.g. the temperature in four weeks’ time) instead of a discrete label (e.g. cats vs dogs). These are known as regression algorithms.

    Neural networks and deep learning

    A neural network is made up of an input layer and an output layer, which are themselves composed of nodes. In simple neural networks, features that are manually derived from a dataset are fed into the input layer, which performs some computations, the results of which are relayed to the output layer. In deep learning, multiple “hidden” layers exist between the input and output layers. Each node of the hidden layers performs calculations using certain weights and relays the output to the next hidden layer until the output layer is reached.

    In the beginning, random values are assigned to the weights and the accuracy of the algorithm is calculated. The values of the weights are then iteratively adjusted until a set of weight values that maximize accuracy is found. This iterative adjustment of the weight values is usually done by moving backwards from the output layer to the input layer, a technique called backpropagation. This entire process is done on the training data.

    Performance evaluation

    Understanding how the performance of AI algorithms is assessed is key to interpreting the AI literature. Several performance metrics exist for assessing how well a model performs certain tasks. No single metric is perfect, so a combination of several metrics provides a fuller picture of model performance.

    In regression, the most commonly used metrics include:

    • Mean absolute error (MAE): the average difference between the predicted values and the ground truth.
    • Root mean square error (RMSE): the differences between the predicted values and the ground truth are squared and then averaged over the sample. Then the square root of the average is taken. Unlike the MAE, the RMSE thus gives higher weight to larger differences.
    • R2: the proportion of the total variance in the ground truth explained by the variance in the predicted values. It ranges from 0 to 1.

    The following metrics are commonly used in classification tasks:

    • Accuracy: this is the proportion of all predictions that were predicted correctly. It ranges from 0 to 1.
    • Sensitivity: also known as the true positive rate (TPR) or recall, this is the proportion of true positives that were predicted correctly. It ranges from 0 to 1.
    • Specificity: Also known as the true negative rate (TNR), this is the proportion of true negatives that were predicted correctly. It ranges from 0 to 1.
    • Precision: also known as positive predictive value (PPV), this is the proportion of positive classifications that were predicted correctly. It ranges from 0 to 1.

    An inherent trade-off exists between sensitivity and specificity. The relevant importance of each, as well as their interpretation, highly depends on the specific research question and classification task.

    Importantly, although classification models are meant to reach a binary conclusion, they are inherently probability-based. This means that these models will output a probability that a data point belongs to one class or another. In order to reach a conclusion on the most likely class, a threshold is used. Metrics such as accuracy, sensitivity, specificity and precision refer to the performance of the algorithm based on a certain threshold. The area under the receiver operating characteristic curve (AUC) is a threshold-independent performance metric. The AUC can be interpreted as the probability that a random positive example is ranked higher by the algorithm than a random negative example.

    In image segmentation tasks, which are a type of classification task, the following metrics are commonly used:

    • Dice similarity coefficient: a measure of overlap between two sets (e.g. two images) that is calculated as two times the number of elements common to the sets divided by the sum of the number of elements in each set. It ranges from 0 (no overlap) to 1 (perfect overlap).
    • Hausdorff distance: a measure of how far two sets (e.g. two images) within a space are far from each other. It is basically the largest distance from one point in one set to the closest point in the other set.

    Internal and external validity

    Internally valid models perform well in their task on the data being used to train and validate them. The degree to which they are internally valid is assessed using the performance metrics outlined above and depends on the characteristics of the model itself and the quality of the data that the model was trained and validated on.

    Externally valid models perform well in their tasks on new data (Ramspek et al., 2021). The better the model performs on data that differs from the data the models were trained and validated on, the higher the external validity. In practice, this often requires the performance of the models to be tested on data from hospitals or geographical areas that were not part of the model’s training and validation datasets.

    Guidelines for evaluating AI research

    Several guidelines have been developed to assess the evidence behind AI-based interventions in healthcare (X. Liu et al., 2020; Mongan et al., 2020; Shelmerdine et al., 2021; Weikert et al., 2021). These provide a template for those doing AI research in healthcare and ensure that relevant information is reported transparently and comprehensively, but can also be used by other stakeholders to assess the quality of published research. This helps ensure that AI-based solutions with substantial potential or actual limitations, particularly those caused by poor reporting (Bozkurt et al., 2020; D. W. Kim et al., 2019; X. Liu et al., 2019; Nagendran et al., 2020; Yusuf et al., 2020), are not prematurely adopted (CONSORT-AI and SPIRIT-AI Steering Group, 2019). Guidelines have also been proposed for evaluating the trustworthiness of AI-based solutions in terms of transparency, confidentiality, security, and accountability (Buruk et al., 2020; Lekadir et al., 2021; Zicari et al., 2021).

    Over the past few years, AI has shown great potential in addressing a broad range of tasks within a medical imaging department, including many that happen before the patient is scanned. Implementations of AI to improve the efficiency of radiology workflows prior to patient scanning are sometimes referred to as “upstream AI” (Kapoor et al., 2020; M. L. Richardson et al., 2021).

    Scheduling

    One promising upstream AI application is predicting whichpatients arelikelytomisstheirscanappointments. Missed appointments are associated with significantly increased workload and costs (Dantas et al., 2018). Using a Gradient Boosting approach, Nelson et al. predicted missed hospital magnetic resonance imaging (MRI) appointments in the United Kingdom’s National Health Service (NHS) with high accuracy (Nelson et al., 2019). Their simulations also suggested that acting on the predictions of this model by targeting patients who are likely to miss their appointments would potentially yield a net benefit of several pounds per appointment across a range of model thresholds and missed appointment rates (Nelson et al., 2019). Similar results were recently found in a study of a single hospital in Singapore. For the 6-month period following the deployment of the predictive tool they were able to significantly reduce the no show rate from 19.3 % tp 15.9 % which translated into a potential economic benefit of $180,000 (Chong et. al., 2020).

    Scheduling scans in a radiology department is a challenging endeavour because, although it is largely an administrative task, it depends heavily on medical information. The task of assigning patients to specific appointments thus often requires the input of someone with domain knowledge, which stipulates that either the person making the appointments must be a radiologist or radiology technician, or these people will have to provide input regularly. In either scenario, the process is somewhat inefficient and can potentially be streamlined using AI-based algorithms that check scan indications and contraindications and provide the people scheduling the scans with information about scan urgency (Letourneau-Guillon et al., 2020).

    Protocolling

    Depending on hospital or clinic policy, the decision on what exact scan protocol a patient receives is usually made based on the information on the referring physician’s scan request and the judgement of the radiologist. This is often supplemented by direct communication between the referring physician and radiologist and the radiologist’s review of the patient’s medical information. This process improves patient care (Boland et al., 2014) but can be time-consuming and inefficient, particularly with modalities like MRI, where a large number of protocol permutations exist. In one study, protocolling alone accounted for about 6 % of the radiologist’s working time (Schemmel et al., 2016). Radiologists are also often interrupted by tasks such as protocolling when interpreting images, despite the fact that the latter is considered a radiologist’s primary responsibility (Balint et al., 2014; J.-P. J. Yu et al., 2014).

    Interpretation of the narrative text of the referring physician’s scan request has been attempted using natural language classifiers, the same technology used in chatbots and virtual assistants. Natural language classifiers based on deep learning have shown promise in assigning patients to either a contrast-enhanced or non-enhanced MRI protocol for musculoskeletal MRI, with an accuracy of 83 % (Trivedi et al., 2018) and 94 % (Y. H. Lee, 2018). Similar algorithms have shown an accuracy of 95 % for predicting the appropriate brain MRI protocol using a combination of up to 41 different MRI sequences (Brown & Marotta, 2018). Across a wide range of body regions, a deep-learning-based natural language classifier decided based on the narrative text of the scan requests whether to automatically assign a specific computed tomography (CT) or MRI protocol (which it did with 95 % accuracy) or, in more difficult cases, recommend a list of three most appropriate protocols to the radiologist (which it did with 92 % accuracy) (Kalra et al., 2020).

    AI has also been used to decide whether already protocolled scans need to be extended, a decision which has to be made in real-time while the patient is inside the scanner. One such example is in prostate MRI, where a decision on whether to administer a contrast agent is often made after the non-contrast sequences. Hötker et al. found that a convolutional neural network (CNN) assigned 78 % of patients to the appropriate prostate MRI protocol (Hötker et al., 2021). The sensitivity of the CNN for the need for contrast was 94.4 % with a specificity of 68.8 % and only 2 % of patients in their study would have had to be called back for a contrast- enhanced scan (Hötker et al., 2021).

    Image quality improvement and monitoring

    Many AI-based solutions that work in the background of radiology workflows to improve image quality have recently been established. These include solutions for monitoring image quality, reducing image artefacts, improving spatial resolution, and speeding up scans.

    Such solutions are entering the radiology mainstream, particularly for computed tomography, which for decades used established but artefact-prone methods for reconstructing interpretable images from the raw sensor data (Deák et al., 2013; Singh et al., 2010).

    These are gradually being replaced by deep-learning- based reconstruction methods, which improve image quality while maintaining low radiation doses (Akagi et al., 2019; H. Chen et al., 2017; Choe et al., 2019; Shan et al., 2019). This reconstruction is performed on supercomputers on the CT scanner itself or on the cloud. The balance between radiation dose and image quality can be adjusted on a protocol-specific basis to tailor scans to individual patients and clinical scenarios (McLeavy et al., 2021; Willemink & Noël, 2019). Such approaches have found particular use when scanning children, pregnant women, and obese patients as well as CT scans of the urinary tract and heart (McLeavy et al., 2021).

    AI-based solutions have also been used to speed up scans while maintaining diagnostic quality. Scan time reduction not only improves overall efficiency but also contributes to an overall better patient experience and compliance with imaging examination. A multi- centre study of spine MRI showed that a deep-learning- based image reconstruction algorithm that enhanced images using filtering and detail-preserving noise reduction reduced scan times by 40 % (Bash, Johnson, et al., 2021). For T1-weighted MRI scans of the brain, a similar algorithm that improves image sharpness and reduces image noise reduced scan times by 60 % while maintaining the accuracy of brain region volumetry compared to standard scans (Bash, Wang, et al., 2021).

    In routine radiological practice, images often contain artefacts that reduce their interpretability. These artefacts are the result of characteristics of the specific imaging modality or protocol used or factors intrinsic to the patient being scanned, such as the presence of foreign bodies or the patient moving during the scan. Particularly with MRI, imaging protocols that demand fast scanning often introduce certain artefacts to the reconstructed image. In one study, a deep-learning- based algorithm reduced banding artefacts associated with balanced steady-state free precession MRI sequences of the brain and knee (K. H. Kim & Park, 2017). For real-time imaging of the heart using MRI, another study found that the aliasing artefacts introduced by the data undersampling were reduced by using a deep-learning-based approach (Hauptmann et al., 2019). The presence of metallic foreign bodies such as dental, orthopaedic or vascular implants is a common patient-related factor causing image artefacts in both CT and MRI (Boas & Fleischmann, 2012; Hargreaves et al., 2011). Although not yet well established, several deep-learning-based approaches for reducing these artefacts have been investigated (Ghani & Clem Karl, 2019; Puvanasunthararajah et al., 2021; Zhang & Yu, 2018). Similar approaches are being tested for reducing motion-related artefacts in MRI (Tamada et al., 2020; B. Zhao et al., 2022).

    AI-based solutions for monitoring image quality potentially reduce the need to call patients back to repeat imaging examinations, which is a common problem (Schreiber-Zinaman & Rosenkrantz, 2017). A deep-learning-based algorithm that identifies the radiographic view acquired and extracts quality-related metrics from ankle radiographs was able to predict image quality with about 94 % accuracy (Mairhöfer et al., 2021). Another deep-learning-based approach was capable of predicting nondiagnostic liver MRI scans with a negative predictive value of between 86 % and 94 % (Esses et al., 2018). This real-time automated quality control potentially allows radiology technicians to rerun scans or run additional scans with greater diagnostic value.

    Scan reading prioritization

    With staff shortages and increasing scan numbers, radiologists face long reading lists. To optimize efficiency and patient care, AI-based solutions have been suggested as a way to prioritize which scans radiologists read and report first, usually by screening acquired images for findings that require urgent intervention (O’Connor & Bhalla, 2021). This has been most extensively studied in neuroradiology, where moving CT scans that were found to have intracranial haemorrhage by an AI-based tool to the top of the reading list reduced the time it took radiologists to view the scans by several minutes (O’Neill et al., 2021). Another study found that the time-to diagnosis (which includes the time from image acquisition to viewing by the radiologist and the time to read and report the scans) was reduced from 512 to 19 minutes in an outpatient setting when such a worklist prioritization was used (Arbabshirani et al., 2018). A simulation study using AI-based worklist prioritization based on identifying urgent findings on chest radiographs (such as pneumothorax, pleural effusions, and foreign bodies) also found a substantial reduction in the time it took to view and report the scans compared to standard workflow prioritization (Baltruschat et al., 2021).

    Image interpretation

    Currently, the majority of commercially available AI- based solutions in medical imaging focus on some aspect of analyzing and interpreting images (Rezazade Mehrizi et al., 2021; van Leeuwen et al., 2021). This includes segmenting parts of the image (for surgical or radiation therapy targeting, for example), bringing suspicious areas to radiologists’ attention, extracting imaging biomarkers (radiomics), comparing images across time, and reaching specific imaging diagnoses.

    Neurology

    ¡ 29–38 % of commercially available AI-based applications in radiology (Rezazade Mehrizi et al., 2021; van Leeuwen et al., 2021).

    Most commercially available AI-based solutions targeted at neuroimaging data aim to detect and characterize ischemic stroke, intracranial haemorrhage, dementia, and multiple sclerosis (Olthof et al., 2020). Several studies have shown excellent accuracy of AI- based methods for the detection and classification of intraparenchymal, subarachnoid, and subdural haemorrhage on head CT (Flanders et al., 2020; Ker et al., 2019; Kuo et al., 2019). Subsequent studies showed that, compared to radiologists, some AI-based solutions have substantially lower false positive and negative rates (Ginat, 2020; Rao et al., 2021). In ischemic stroke, AI-based solutions have largely focused on the quantification of the infarct core (Goebel et al., 2018; Maegerlein et al., 2019), the detection of large vessel occlusion (Matsoukas et al., 2022; Morey et al., 2021; Murray et al., 2020; Shlobin et al., 2022), and the prediction of stroke outcomes (Bacchi et al., 2020; Nielsen et al., 2018; Y. Yu et al., 2020, 2021).

    In multiple sclerosis, AI has been used to identify and segment lesions (Nair et al., 2020; S.-H. Wang et al., 2018), which can be particularly helpful for the longitudinal follow-up of patients. It has also been used to extract imaging features associated with progressive disease and conversion from clinically isolated syndrome to definite multiple sclerosis (Narayana et al., 2020; Yoo et al., 2019). Other applications of AI in neuroradiology include the detection of intracranial aneurysms (Faron et al., 2020; Nakao et al., 2018; Ueda et al., 2019) and the segmentation of brain tumours (Kao et al., 2019; Mlynarski et al., 2019; Zhou et al., 2020) as well as the prediction of brain tumour genetic markers from imaging data (Choi et al., 2019; J. Zhao et al., 2020)

    Chest

    ¡ 24 %–31 % of commercially available AI-based applications in radiology (Rezazade Mehrizi et al., 2021; van Leeuwen et al., 2021).

    When interpreting chest radiographs, radiologists detected substantially more critical and urgent findings when aided by a deep-learning-based algorithm, and did so much faster than without the algorithm (Nam et al., 2021). Deep-learning-based image interpretation algorithms have also been found to improve radiology residents’ sensitivity for detecting urgent findings on chest radiographs from 66 % to 73 % (E. J. Hwang, Nam, et al., 2019). Another study which focused on a broader range of findings on chest radiographs also found that radiologists aided by a deep-learning-based algorithm had higher diagnostic accuracy than radiologists who read the radiographs without assistance (Seah et al., 2021). The uses of AI in chest radiology also extend to cross-sectional imaging like CT. A deep learning algorithm was found to detect pulmonary embolism on CT scans with high accuracy (AUC = 0.85) (Huang, Kothari, et al., 2020). Moreover, a deep learning algorithm was 90 % accurate in detecting aortic dissection on non-contrast-enhanced CT scans, similar to the performance of radiologists (Hata et al., 2021).

    Outside the emergency setting, AI-based solutions have been widely tested and implemented for tuberculosis screening on chest radiographs (E. J. Hwang, Park, et al., 2019; S. Hwang et al., 2016; Khan et al., 2020; Qin et al., 2019; WHO Operational Handbook on Tuberculosis Module 2: Screening – Systematic Screening for Tuberculosis Disease, n.d.). In addition, they have been useful for lung cancer screening both in terms of detecting lung nodules on CT (Setio et al., 2017) and chest radiographs (Li et al., 2020) and by classifying whether nodules are likely to be malignant or benign (Ardila et al., 2019; Bonavita et al., 2020; Ciompi et al., 2017; B. Wu et al., 2018). AI-based solutions also show great promise for the diagnosis of pneumonia, chronic obstructive pulmonary disease, and interstitial lung disease (F. Liu et al., 2021).

    Breast

    ¡ 11 % of commercially available AI-based applications in radiology (Rezazade Mehrizi et al., 2021; van Leeuwen et al., 2021).

    So far, many of the AI-based algorithms targeting breast imaging aim to reduce the workload of radiologists reading mammograms. Ways to do this have included using AI-based algorithms to triage out negative mammograms, which in one study was associated with a reduction in radiologists’ workload by almost one-fifth (Yala et al., 2019). Other studies that have replaced second readers of mammograms with AI- based algorithms have shown that this leads to fewer false positives and false negatives as well as reduces the workload of the second reader by 88 % (McKinney et al., 2020).

    AI-based solutions for mammography have also been found to increase the diagnostic accuracy of radiologists (McKinney et al., 2020; Rodríguez-Ruiz et al., 2019; Watanabe et al., 2019) and some have been found to be highly accurate in independently detecting and classifying breast lesions (Agnes et al., 2019; Al- Antari et al., 2020; Rodriguez-Ruiz et al., 2019).
    Despite this, a recent systematic review of 36 AI- based algorithms found that these studies were of poor methodological quality and that all algorithms were less accurate than the consensus of two or more radiologists (Freeman et al., 2021). AI-based algorithms have nonetheless shown potential for extracting cancer-predictive features from mammograms beyond mammographic breast density (Arefan et al., 2020; Dembrower et al., 2020; Hinton et al., 2019). Beyond mammography, AI-based solutions have been developed for detecting and classifying breast lesions on ultrasound (Akkus et al., 2019; Park et al., 2019; G.- G. Wu et al., 2019) and MRI (Herent et al., 2019).

    Cardiac

    ¡ 11 % of commercially available AI-based applications in radiology (Rezazade Mehrizi et al., 2021; van Leeuwen et al., 2021).

    Cardiac radiology has always been particularly challenging because of the difficulties inherent in acquiring images of a constantly moving organ. Because of this, it has benefited immensely from advances in imaging technology and seems set to benefit greatly from AI as well (Sermesant et al., 2021). Most of the AI-based applications of the cardiovascular system use MRI, CT or ultrasound data (Weikert et al., 2021). Prominent examples include the automated calculation of ejection fraction on echocardiography, quantification of coronary artery calcification on cardiac CT, determination of right ventricular volume on CT pulmonary angiography, and determination of heart chamber size and thickness on cardiac MRI (Medical AI Evaluation, n.d., The Medical Futurist, n.d.). AI-based solutions for the prediction of patients likely to respond favourably to cardiac interventions, such as cardiac resynchronization therapy, based on imaging and clinical parameters have also shown great promise (Cikes et al., 2019; Hu et al., 2019). Changes in cardiac MRI not readily visible to human readers but potentially useful for differentiating different types of cardiomyopathies can also be detected using AI through texture analysis (Neisius et al., 2019; J. Wang et al., 2020) and other radiomic approaches (Mancio et al., 2022).

    Musculoskeletal

    ¡ 7–11 % of commercially available AI-based applications in radiology (Rezazade Mehrizi et al., 2021; van Leeuwen et al., 2021).

    Promising applications of AI in the assessment of muscles, bones and joints include applications where human readers generally show poor between- and within-rater reliability, such as the determination of skeletal age based on bone radiographs (Halabi et al., 2019; Thodberg et al., 2009) and screening for osteoporosis on radiographs (Kathirvelu et al., 2019; J.-S. Lee et al., 2019) and CT (Pan et al., 2020). AI- based solutions have also shown promise for detecting fractures on radiographs and CT (Lindsey et al., 2018; Olczak et al., 2017; Urakawa et al., 2019). One systematic review of AI-based solutions for fracture detection in several different body parts showed AUCs ranging from 0.94 to 1.00 and accuracies of 77 % to 98 % (Langerhuizen et al., 2019). AI-based solutions have also achieved accuracies similar to radiologists for classification of the severity of degenerative changes of the spine (Jamaludin et al., 2017) and extremity joints (F. Liu et al., 2018; Thomas et al., 2020). AI-based solutions have also been developed to determine the origin of skeletal metastases (Lang et al., 2019) and the classification of primary bone tumours (Do et al., 2017).

    Abdomen and pelvis

    ¡ 4 % of commercially available AI-based applications in radiology (Rezazade Mehrizi et al., 2021; van Leeuwen et al., 2021).

    Much of the efforts in using AI in abdominal imaging have thus far concentrated on the automated segmentation of organs such as the liver (Dou et al., 2017), spleen (Moon et al., 2019), pancreas (Oktay et al., 2018), and kidneys (Sharma et al., 2017). In addition, a systematic review of 11 studies using deep learning for the detection of malignant liver masses showed accuracies of up to 97 % and AUCs of up to 0.92 (Azer, 2019).

    Other applications of AI in abdominal radiology include the detection of liver fibrosis (He et al., 2019; Yasaka et al., 2018), fatty liver disease, hepatic iron content, the detection of free abdominal gas on CT, and automated volumetry and segmentation of the prostate (AI for Radiology, n.d.).

    Despite the great potential of AI in medical imaging, it has yet to find widespread implementation and impact in routine clinical practice. This research-to- clinic translation is being hindered by several complex and interrelated issues that directly or indirectly lower the likelihood of AI-based solutions being adopted. One major way they do so is by creating a lack of trust in AI- based solutions by key stakeholders such as regulators, healthcare professionals and patients (Cadario et al., 2021; Esmaeilzadeh, 2020; J. P. Richardson et al., 2021; Tucci et al., 2022).

    Generalizability

    One major challenge is to develop AI-based solutions that continue to perform well in new, real-world scenarios. In a large systematic review, almost half of the studied AI-based medical imaging algorithms reported a greater than 0.05 decrease in the AUC when tested on new data (A. C. Yu et al., 2022). This lack of generalizability can lead to adverse effects on how well the model performs in a real-world scenario.

    If a solution performs poorly when tested on a dataset with a similar or identical distribution to the training dataset, it is said to lack narrow generalizability and is often a consequence of overfitting (Eche et al., 2021). Potential solutions for overfitting are using larger training datasets and reducing the model’s complexity. If a solution performs poorly when tested on a dataset with a different distribution to the training dataset (e.g. a different distribution of patient ethnicities), it is said to lack broad generalizability (Eche et al., 2021). Solutions to poor broad generalizability include stress-testing the model on datasets with different distributions from the training dataset (Eche et al., 2021).

    AI solutions are often developed in a high-resource environment such as large technology companies and academic medical centres in wealthy countries. It is likely that findings and performance in these high-resource contexts will fail to generalize to lower- resource contexts such as smaller hospitals, rural areas or poorer countries (Price & Nicholson, 2019), which complicates the issue further.

    Risk of bias

    Biases can arise in AI-based solutions due to data or human factors. The former occurs when the data used to train the AI solution does not adequately represent the target population. Datasets can be unrepresentative when they are too small or have been collected in a way that misrepresents a certain population category. AI solutions trained on unrepresentative data perpetuate biases and perform poorly in the population categories underrepresented or misrepresented in the training data. The presence of such biases has been empirically shown in many AI-based medical imaging studies (Larrazabal et al., 2020; Seyyed-Kalantari et al., 2021).

    AI-based solutions are prone to several subjective and sometimes implicitly or explicitly prejudiced decisions during their development by humans. These human factors include how the training data is selected, how it is labelled, and how the decision is made to focus on the specific problem the AI-based solution intends to solve (Norori et al., 2021). Some recommendations and tools are available to help minimize the risk of bias in AI research (AIF360: A Comprehensive Set of Fairness Metrics for Datasets and Machine Learning Models, Explanations for These Metrics, and Algorithms to Mitigate Bias in Datasets and Models, n.d., IBM Watson Studio - Model Risk Management, n.d.; Silberg & Manyika, 2019).

    Data quantity, quality and variety

    Problems such as bias and lack of generalizability can be mitigated by ensuring that training data is of sufficient quantity, quality and variety. However, this is difficult to do because patients are often reluctant to share their data for commercial purposes (Aggarwal, Farag, et al., 2021; Ghafur et al., 2020; Trinidad et al., 2020), hospitals and clinics are usually not equipped to make this data available in a useable and secure manner, and organizing and labelling the data is time- consuming and expensive.

    Many datasets can be used for a number of different purposes, and sharing data between companies can help make the process of data collection and organization more efficient, as well as increase the amount of data available for each application. However, developers are often reluctant to share data with each other, or even reveal the exact source of their data, to stay competitive.

    Data protection and privacy

    The development and implementation of AI-based solutions require that patients are explicitly informed about, and give their consent to, the use of their data for a particular purpose and by certain people. This data also has to be adequately protected from data breaches and misuse. Failure to ensure this greatly undermines the public’s trust in AI-based solutions and hinders their adoption. While regulations governing health data privacy state that the collection of fully anonymized data does not require explicit patient consent (General Data Protection Regulation (GDPR) – Official Legal Text, 2016; Office for Civil Rights (OCR), 2012) and in theory protects from the data being misused, whether or not imaging data can be fully anonymized is controversial (Lotan et al., 2020; Murdoch, 2021). Whether consent can be truly informed considering the complexity of the data being acquired, and the resulting myriad of potential future uses of the data, is also disputed (Vayena & Blasimme, 2017).

    IT infrastructure

    Among hospital departments, radiology has always been at the forefront ofdigitalization. AI-based solutions that focus on image processing and interpretation are likely to find the prerequisite infrastructure in most radiology departments, for example for linking imaging equipment to computers for analysis and for archiving images and other outputs. However, most radiology departments are likely to require significant infrastructure upgrades for other applications of AI, particularly those requiring the integration of information from multiple sources and having complex outputs. Moreover, it is important to keep in mind that the distribution of necessary infrastructure is highly unequal across and within countries (Health Ethics & Governance, 2021).

    In terms of computing power, radiology departments will either have to invest resources into the hardware and personnel necessary to run these AI-based solutions or opt for cloud-based solutions. The former comes with an extra cost but allows data processing within the confines of the hospital or clinic’s local network. Cloud-based solutions for computing (known as “infrastructure as a service” or “IaaS”) are often considered the less secure and less trustworthy option, but this depends on a number of factors and is thus not always true (Baccianella & Gough, n.d.). Guidelines on what to consider when procuring cloud-based solutions in healthcare are available (Cloud Security for Healthcare Services, 2021).

    Lack of standardization, interoperability, and integrability

    The problem of infrastructure becomes even more complicated when considering how fragmented the AI medical imaging market currently is (Alexander et al., 2020). It is therefore likely that in the near future a single department will have several dozen AI-based solutions from different vendors running simultaneously. Having a separate self-contained infrastructure (e.g. a workstation or server) for each of these would be incredibly complicated and difficult to manage. Suggested solutions for this have included AI solution “marketplaces”, similar to app stores (Advanced AI Solutions for Radiology, n.d., Curated Marketplace, 2018, Imaging AI Marketplace - Overview, n.d., Sectra Amplifier Marketplace, 2021, The Nuance AI Marketplace for Diagnostic Imaging, n.d.), and development of an overarching vendor-neutral infrastructure (Leiner et al., 2021). The successful implementation of such solutions requires close partnerships between AI solution developers, imaging vendors and information technology companies.

    Interpretability

    It is often impossible to understand exactly how AI- based solutions come to their conclusions, particularly with complex approaches like deep learning. This reduces how transparent the decision-making process for procuring and approving these solutions can be, makes the identification of biases difficult, and makes it harder for clinicians to explain the outputs of these solutions to their patients and to determine whether a solution is working properly or has malfunctioned (Char et al., 2018; Reddy et al., 2020; Vayena et al., 2018; Whittlestone et al., 2019). Some have suggested that techniques that help humans understand how AI- based algorithms made certain decisions or predictions (“interpretable” or “explainable” AI) might help mitigate these challenges. However, others have argued that currently available techniques are unsuitable for understanding individual decisions of an algorithm and have warned against relying on them for ensuring that algorithms work in a safe and reliable way (Ghassemi et al., 2021).

    Liability

    In healthcare systems, a framework of accountability ensures that healthcare workers and medical institutions can be held responsible for adverse effects resulting from their actions. The question of who should be held accountable for the failures of an AI- based solution is complicated. For pharmaceuticals, for example, the accountability for inherent failures in the product or its use often lies with either the manufacturer or the prescriber. One key difference is that AI-based systems are continuously evolving and learning, and so inherently work in a way that is independent of what their developers could have foreseen (Yeung, 2018). To the end-user such as the healthcare worker, the AI- based solution may be opaque and so they may not be able to tell when the solution is malfunctioning or inaccurate (Habli et al., 2020; Yeung, 2018).

    Brittleness

    Despite substantial progress in their development over the past few years, deep learning algorithms are still surprising brittle. This means that, when the algorithm faces a scenario that differs substantially from what it faced during training, it cannot contextualize and often produces nonsensical or inaccurate results. This happens because, unlike humans, most algorithms learn to perceive things within the confines of certain assumptions, but fail to generalize outside these assumptions. As an example of how this can be abused with malicious intent, subtle changes to medical images, imperceptible by humans, can render the results of disease-classifying algorithms inaccurate (Finlayson et al., 2018). The lack of interpretability of many AI-based solutions compounds this problem because it makes it difficult to troubleshoot how they reached the wrong conclusion.

    So far, more than 100 AI-based products have gained conformité européenne (CE) marking or Food and Drug Adminstration (FDA) clearance. These products can be found in continuously updated and searchable online databases curated by the FDA (Center for Devices & Radiological Health, n.d.), the American College of Radiology (Assess-AI, n.d.), and others (AI for Radiology, n.d., The Medical Futurist, n.d.; E. Wu et al., 2021). The increasing number of available products, the inherent complexity of many of these solutions, and the fact that many people who usually make purchasing decisions in hospitals are not familiar with evaluating such products make it important to think carefully when deciding on which product to purchase. Such decisions will need to be made after incorporating input from healthcare workers, information technology (IT) professionals, as well as management, finance, legal, and human resources professionals within hospitals.

    Deciding on whether to purchase an AI-based solution in radiology, as well as which of the increasing number of commercially available solutions to purchase, includes considerations of quality, safety, and finances. Over the past few years, several guidelines have emerged to help potential buyers make these decisions (A Buyer’s Guide to AI in Health and Care, 2020; Omoumi et al., 2021; Reddy et al., 2021), and these guidelines are likely to evolve in the future with changing expectations from customers, regulatory bodies, and stakeholders involved in reimbursement decisions.

    First of all, it has to be clear to the potential buyer what the problem is and whether AI is the appropriate approach to this solution, or whether alternatives exist that are more advantageous on balance. If AI is the appropriate approach, buyers should know exactly what a potential AI-based product’s scope of the solution is - i.e. what specific problem the AI-based solution is designed to solve and in what specific circumstances. This includes whether the solution is intended for screening, diagnosis, monitoring, treatment recommendation or another application. It also includes the intended users of the solution and what kind of specific qualifications or training they are expected to have in order to be able to operate the solution and interpret its outputs. It needs to be clear to buyers whether the solution is intended to replace certain tasks that would normally be performed by the end-user, act as a double-reader, as a triaging mechanism, or for other tasks like quality control. Buyers should also understand whether the solution is intended to provide “new” information (i.e. information that would otherwise be unavailable to the user without the solution), improve the performance of an existing task beyond a human’s or other non-AI-based solution’s performance or if it is intended to save time or other resources.

    Buyers should also have access to information that allows them to assess the potential benefits of the AI solution, and this should be backed up by published scientific evidence for the efficacy and cost-efficiency of the solution. How this is done will depend highly on the solution itself and the context in which it is expected to be deployed, but guidelines for this are available (National Institute for Health and Care Excellence (NICE), n.d.). Some questions to ask here would be: How much of an influence will the solution have on patient management? Will it improve diagnostic performance? Will it save time and money? Will it affect patients’ quality of life? It should also be clear to the buyer who exactly is expected to benefit from the use of this solution (Radiologists? Clinicians? Patients? The healthcare system or society as a whole?).

    As with any healthcare intervention, all AI-based solutions come with potential risks, and these should be made clear to the buyer. Some of these risks might have legal consequences, such as the potential for misdiagnosis. These risks should be quantified, and potential buyers should have a framework for dealing with them, including identifying a framework for accountability within the organizations implementing these solutions. Buyers should also ensure they clearly understand the potential negative effects on radiologists’ training and the potential disruption to radiologists’ workflows associated with the use of these solutions.

    Specifics of the AI solution’s design are also relevant to the decision on whether or not to purchase it. These include how robust the solution is to differences between vendors and scanning parameters, the circumstances under which the algorithm was trained (including potential confounding factors), and the way that performance was assessed. It should also be clear to buyers if and how potential sources of bias were accounted for during development. Because a core characteristic of AI-based solutions is their ability to continuously learn from new data, whether and how exactly this retraining is incorporated into the solution with time should also be clear to the buyer, including whether or not new regulatory approval is needed with each iteration. This also includes whether or not retraining is required, for example, due to changes in imaging equipment at the buyer’s institution.

    The main selling points of many AI-based solutions are ease-of-use and improved workflows. Therefore, potential buyers should carefully scrutinize how these solutions are to be integrated into existing workflows, including inter-operability with PACS and electronic medical record systems. Whether or not the solution requires extra hardware (e.g. graphical processing units) or software (e.g. for visualization of the solution’s outputs), or if it can readily be integrated into the existing information technology infrastructure of the buyer’s organization influences the overall cost of the solution for the buyer and is therefore also a critical consideration. In addition, the degree of manual interaction required, both under normal circumstances and for troubleshooting, should be known to the buyer. All potential users of the AI solution should be involved in the purchasing process to ensure that they are familiar with it and that it meets their professional ethical standards and suits their needs.

    From a regulatory perspective, it should be clear to the buyer whether the solution complies with medical device and data protection regulations. Has the solution been approved in the buyer’s country? If so, under which risk classification? Buyers should also consider creating data flow maps that display how the data flows in the operation of the AI-based solution, including who has access to the data.

    Finally, there are other factors to consider which are not necessarily unique to AI-based solutions and which buyers might be familiar with from purchasing other types of solutions. This includes the licensing model of the solution, how users are to be trained on using the solution, how the solution is maintained, how failures in the solution are dealt with, and whether additional costs are to be expected when scaling up the solution’s implementation (e.g. using the solution for more imaging equipment or more users). This allows the potential buyer to anticipate the current and future costs of purchasing the solution.

    The past decade of increasing interest and progress in AI-based solutions for medical imaging has set the stage for a number of trends that are likely to appear or intensify in the near future.

    Firstly, there is an increasing sentiment that, although AI holds a great deal of promise for interpretive applications (such as the detection of pathology), non-interpretive AI-based solutions might hold the most potential in terms of instilling efficiency into radiology workflows and improving patient experiences. This trend towards involving AI earlier in the patient management process is likely to extend to AI increasingly acting as a clinical decision support system to guide when and which imaging scans are performed.

    For this to happen, AI needs to be integrated into existing clinical information systems, and the specific algorithms used need to be able to handle more varied data. This will likely pave the way for the development of algorithms that are capable of integrating demographic, clinical, and laboratory patient data to make recommendations about patient management (Huang, Pareek, et al., 2020; Rockenbach, 2021). The previously mentioned natural language processing algorithms that have been used to interpret scan requests may be useful candidates for this.

    In addition, we are likely to see AI algorithms that can interpret multiple different types of imaging data from the same patient. Currently, less than 5 % of commercially available AI-based solutions in medical imaging work with more than one imaging modality (Rezazade Mehrizi et al., 2021; van Leeuwen et al., 2021) despite the fact that the typical patient in a hospital receives multiple imaging scans during their stay (Shinagare et al., 2014). With this, it is also likely that more AI-based solutions will be developed that target hitherto neglected modalities such as nuclear imaging techniques and ultrasound.

    The current market for AI-based solutions in radiology is spread across a relatively large number of companies (Alexander et al., 2020). Potential users are likely to expect a streamlined integration of these products in their workflows, which can be challenging in such a fragmented market. Improved integration can be achieved in several different ways, including with vendor-neutral marketplaces or by the gradual consolidation of providers of AI-based solutions.

    With the expanding use of AI, the issue of trust between AI developers, healthcare professionals, regulators, and patients will become more relevant. It is therefore likely that efforts will intensify to take steps towards strengthening that trust. This will potentially include raising the expected standards of evidence for AI- based solutions (Aggarwal, Sounderajah, et al., 2021; X. Liu et al., 2019; van Leeuwen et al., 2021; Yusuf et al., 2020), making them more transparent through the use and improvement of interpretable AI techniques (Holzinger et al., 2017; Reyes et al., 2020; “Towards Trustable Machine Learning,” 2018), and enhancing techniques for maintaining patient data privacy (G. Kaissis et al., 2021; G. A. Kaissis et al., 2020).

    Furthermore, while most existing regulations stipulate that AI-based algorithms cannot be modified after regulatory approval, this is likely to change in the future. The potential for these algorithms to learn from data acquired after approval and adapt to changing circumstances is a major advantage of AI. Still, frameworks for doing so have thus far been lacking in the healthcare sector. However, promising ideas have recently emerged, including adapting existing hospital quality assurance and improvement frameworks to monitor AI-based algorithms’ performance and the data they are trained on and update the algorithms accordingly (Feng et al., 2022). This will likely require the development of multidisciplinary teams within hospitals consisting of clinicians, IT professionals, and biostatisticians who closely collaborate with model developers and regulators (Feng et al., 2022).

    While the obstacles discussed in previous sections might slow down the adoption of AI in radiology somewhat, the fear of AI potentially replacing radiologists is unlikely to be one of them. A recent survey from Europe showed that most radiologists did not perceive a reduction in their clinical workload after adopting AI-based solutions (European Society of Radiology (ESR), 2022), likely because, at the same time, demand for radiologists’ services has been continuously rising. Studies from around the world have shown that radiology professionals, particularly those with AI exposure and experience, are generally optimistic about the role of AI in their practice (Y. Chen et al., 2021; Huisman et al., 2021; Ooi et al., 2021; Santomartino & Yi, 2022; Scott et al., 2021).

    AI has shown promise in positively impacting virtually every facet of a radiology department’s work - from scheduling and protocolling patient scans to interpreting images and reaching diagnoses. Promising research on AI-based tools in radiology has not yet been widely translated to adoption in routine practice, however, because of a number of complex, partially intertwined issues. Potential solutions exist for many of these challenges, but many of these solutions require further refinement and testing. In the meantime, guidelines are emerging to help potential users of AI-based solutions in radiology navigate the increasing number of commercial products. This encourages their adoption in real-world scenarios, thus allowing their true potential to be uncovered, as well as their weaknesses to be identified and addressed in a safe and effective way. As these incremental improvements are made, these tools will likely evolve to handle more varied data, become integrated into consolidated workflows, become more transparent, and ultimately more useful for increasing efficiency and improving patient care.

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