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Mathematical model observers to objectively optimize CT radiation exposure with respect to the clinical question

English title Mathematical model observers to objectively optimize CT radiation exposure with respect to the clinical question
Applicant Verdun Francis
Number 163344
Funding scheme Project funding (Div. I-III)
Research institution Institut de Radiophysique Département de Radiologie Université de Lausanne/CHUV
Institution of higher education University of Lausanne - LA
Main discipline Clinical Cancer Research
Start/End 01.02.2016 - 31.01.2019
Approved amount 266'678.00
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Keywords (5)

iterative reconstruction CT; Abdominal CT; image quality; patient exposure; Mathematical model observer

Lay Summary (French)

Lead
Réduction des doses en imagerie CT
Lay summary
En Suisse, comme dans la plupart des pays Occidentaux, l'exposition aux rayonnements ionisants de la population augmente de manière significative du fait de l’utilisation croissante de l’imagerie scanner (CT). À titre d'exemple, de 2008 à 2013 la dose moyenne par habitant suisse a augmenté de 0.8 à 1.0 mSv.  Les examens CT abdominaux sont responsables de près d’un tiers de cette exposition, avec une large variation des doses délivrées pour des questions cliniques similaires. Deux raisons expliquent cette variabilité : d’une part la grande différence du plateau technique permettant l’accès à des algorithmes de reconstruction plus efficaces (reconstructions itératives) et d’autre part une optimisation des paramètres dose – niveau de qualité d’image requis insuffisante.
Le problème majeur  que pose l’optimisation est qu’à présent on peut fortement diminuer les doses sans que l’aspect de l’image n’indique au radiologue que des lésions peu contrastées ne peuvent être détectées.  En effet les nouveaux algorithmes de reconstruction d’image améliorent le rendu mais n’assurent pas un transfert complet de l’information.  Dans un tel contexte il est nécessaire de qualifier de manière objective la détection de structures peu contrastées pour que les réductions de dose n’hypothèquent le diagnostic du radiologue. 
L’objectif de ce projet est de d’adapter des modèles d’observateur mathématiques (qui miment la détection de l’œil humain) pour que l’optimisation des protocoles CT abdominaux se fassent en toute sécurité.
Direct link to Lay Summary Last update: 28.09.2015

Responsible applicant and co-applicants

Employees

Publications

Publication
Effects of various generations of iterative CT reconstruction algorithms on low-contrast detectability as a function of the effective abdominal diameter: A quantitative task-based phantom study
Viry Anais, Aberle Christoph, Racine Damien, Knebel Jean-François, Schindera Sebastian T., Schmidt Sabine, Becce Fabio, Verdun Francis R. (2018), Effects of various generations of iterative CT reconstruction algorithms on low-contrast detectability as a function of the effective abdominal diameter: A quantitative task-based phantom study, in Physica Medica, 48, 111-118.
Multi-energy spectral photon-counting CT in crystal-related arthropathies: initial experience and diagnostic performance in vitro
Combes Christele, Viry Anais, Verdun Francis R., Becce Fabio, Anderson Nigel G., Raja Aamir Y., Kirkbride Tracy E., Choi Chloe, Stamp Lisa K., Dalbeth Nicola (2018), Multi-energy spectral photon-counting CT in crystal-related arthropathies: initial experience and diagnostic performance in vitro, in Physics of Medical Imaging, Houston, United StatesSPIE, USA.
Characterization of a CT unit for the detection of low contrast structures
Viry Anais, Racine Damien, Ba Alexandre, Becce Fabio, Bochud François O., Verdun Francis R. (2017), Characterization of a CT unit for the detection of low contrast structures, in SPIE Medical Imaging, Orlando, Florida, United StatesSPIE, USA.

Collaboration

Group / person Country
Types of collaboration
University of Otago New Zealand (Oceania)
- in-depth/constructive exchanges on approaches, methods or results
- Publication
- Research Infrastructure
Swiss Society of Radiology (SSR) Switzerland (Europe)
- in-depth/constructive exchanges on approaches, methods or results

Scientific events

Active participation

Title Type of contribution Title of article or contribution Date Place Persons involved
Journée Française de Radiologie Talk given at a conference Optimisation de procoles CT abdominaux à l’aide de modèle d’observateurs : une étude multicentrique 12.10.2018 Paris, France Becce Fabio; Racine Damien; Verdun Francis; Viry Anaïs;
EFOMP meeting Copenhagen Individual talk Image quality in CT: From physical measurements to model observers 23.08.2018 Copenhague, Denmark Verdun Francis;
Journées scientifiques de la SFPM, Société Française de Physique Médicale Talk given at a conference Impact des différentes générations d’algorithmes itératifs sur la détectabilité à bas contraste en tomodensitométrie abdominale 13.06.2018 Toulouse, France Racine Damien; Becce Fabio; Verdun Francis; Viry Anaïs;
SPIE Medical Imaging Talk given at a conference Multi-energy spectral photon-counting CT in crystal-related arthropathies: initial experience and diagnostic performance in vitro 09.03.2018 Houston, United States of America Becce Fabio; Verdun Francis; Viry Anaïs;
Journées scientifiques de la SFPM, Société Française de Physique Médicale Talk given at a conference Comparison of abdominal CT protocols: a multi-center study on image quality and radiation dose levels 14.06.2017 Lyon, France Verdun Francis; Viry Anaïs; Racine Damien; Becce Fabio;
SSR - SCR annual meeting Talk given at a conference Impact of various iterative reconstruction algorithms on low-contrast detectability in patients with varying abdominal diameters: A CT phantom study 08.06.2017 Berne, Switzerland Verdun Francis; Racine Damien; Becce Fabio; Schindera Sebastian; Viry Anaïs;
SSR - SCR annual meeting Talk given at a conference Evaluation of low contrast detectability and patient exposure using abdominal CT protocols: A multicentre study 08.06.2017 Berne, Switzerland Viry Anaïs; Racine Damien; Becce Fabio; Verdun Francis;
SPIE Medical Imaging Talk given at a conference Characterization of a CT unit for the detection of low contrast structures 10.03.2017 Orlando, United States of America Becce Fabio; Racine Damien; Bochud François; Verdun Francis; Viry Anaïs;
European Congress of Radiology, ECR Talk given at a conference Optimization of abdominal CT protocols using a mathematical model observer 01.03.2017 Vienne, Austria Viry Anaïs; Becce Fabio; Racine Damien; Verdun Francis;
European Congress of Radiology Individual talk Image quality assessment via model observers: connecting objective and subjective perspectives 01.03.2017 Vienne, Austria Verdun Francis;
European Congress of Radiology, ECR Talk given at a conference Effects of various generations of iterative reconstruction algorithms on low-contrast detectability in patients with varying abdominal diameters: A CT phantom study 01.03.2017 Vienne, Austria Becce Fabio; Schindera Sebastian; Racine Damien; Verdun Francis; Viry Anaïs;
European Congress of Radiology, ECR Talk given at a conference Objective comparison of high and low contrast detectability for three clinical protocols on eight CT scanners 01.03.2017 Vienne, Austria Verdun Francis; Racine Damien; Bochud François; Becce Fabio; Viry Anaïs;
50th Annual Meeting of SSRMP Talk given at a conference Benchmarking of abdominal CT protocols using a Channelized Hotelling Observer 25.08.2016 Sursee, Switzerland Viry Anaïs; Becce Fabio; Racine Damien; Verdun Francis;
The 4th International Conference on Image Formation in X-Ray Computed Tomograph Talk given at a conference Characterization CT unit using a dose efficiency index concept 22.07.2016 Bamberg, Germany Viry Anaïs; Verdun Francis; Racine Damien;


Associated projects

Number Title Start Funding scheme
140995 Iterative reconstruction in CT: by how much can we divide the doses delivered to children and young adults? 01.01.2013 Project funding (Div. I-III)

Abstract

In Switzerland, as in most Western countries, the radiation exposure of the population is steadily increasing due to an increasing utilization of computed tomography (CT). As an example, from 2008 to 2013 the average dose per Swiss inhabitant increased from 0.8 to 1.0 mSv. Abdominal CT scans are responsible for almost a third of that exposure, with a wide variation in doses for the same clinical question. There are two main explanations for the wide dose variability for abdominal CT in the clinical practice. Firstly, large differences in regards to the technical equipment for dose reduction exists in Switzerland, particularly on the background that very effective techniques were introduced recently by the CT manufacturers for dose reduction (e.g. iterative reconstruction (IR) techniques). Secondly, it has to be assumed that numerous CT scanners are not applied in a dose-efficient approach. In other words, the protocols are insufficiently optimized. The optimization process should begin by making sure that a CT unit is as efficient as possible to convert the radiation received by the detectors into useful image information. Then, one should ensure that the level of image quality produced allows the clinical question to be answered (i.e. diagnostic accuracy) avoiding unnecessary patient exposure. In the past, standard image quality assessment used metrics based on information theory that requires linear data processes. The introduction of IR, which includes highly non-linear processes, introduces a new challenge in the field of image quality assessment. As a matter of fact, although highly noise-suppressed CT images obtained with IR may exhibit a higher contrast-to-noise ratio than conventional filtered-back projection (FBP) images, the detection of low-contrast structures/lesions might still not be possible, thereby reducing the diagnostic value of the examination. Thus, the use of new clinically-relevant metrics controlling low-contrast detectability is required.At the moment, the use of mathematical model observers (MO) to predict low-contrast detectability of simple structures has been proposed by several groups worldwide. This approach is quite enticing since it is a task-based method that satisfies the pre-requisite of an actual optimization procedure of clinical protocols. Manufacturers have started to use these methods to benchmark their CT units, although many questions about the correct use of a CT unit in the clinical world remain unanswered. The choice of the most adequate model observer, phantom geometry, and low-contrast structures to be used in relation to specific clinical CT protocols has to be made. In summary, one needs to define a sound methodology that can be trusted by radiologists to ensure a safe process of patient dose reduction.
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