Toward a comparison and an optimization of CT protocols using new metrics of dose and image quality part I: prediction of human observers using a model observer for detection and discrimination tasks in low-dose CT images in various scanning conditions

Nadia Othman (1) , Anne-Catherine Simon (1) , Thierry Montagu (1) , Laureline Berteloot (2) , David Grévent (2) , Bouchra Habib Geryes (2) , Mohamed Benkreira (3) , Emeline Bigand (3) , Sophie Capdeville (3) , Julie Desrousseaux (3) , Bardia Farman (3) , Eloise Garnier (3) , Stephanie Gempp (3) , Jean-Marc Nigoul (3) , Natacha Nomikossoff (3) , Marion Vincent (3)

1 LM2S (CEA, LIST) - Laboratoire Modélisation et Simulation de Systèmes (CEA, LIST)
2 Service de radiologie pédiatrique [CHU Necker]
3 APHM - Assistance Publique - Hôpitaux de Marseille

In the context of reducing the patient dose coming from CT scanner examinations without penalizing the diagnosis, the assessment of both patient dose and image quality (IQ) with relevant metrics is crucial. The present study represents the first stage in a larger work, aiming to compare and optimize CT protocols using dose and IQ new metrics. We proposed here to evaluate the capacity of the Non-PreWhitening matched filter with an eye (NPWE) model observer to be a robust and accurate estimation of IQ. We focused our work on two types of clinical tasks: a low contrast detection task and a discrimination task. We designed a torso-shaped phantom, including Plastic Water® slabs with cylindrical inserts of different diameters, sections and compositions. We led a human observer study with 13 human observers on images acquired in multiple irradiation and reconstruction scanning conditions (voltage, pitch, slice thickness, noise level of the reconstruction algorithm, energy level in dual-energy mode and dose), to evaluate the behavior of the model observer compared to the human responses faced to changing conditions. The model observer presented the same trends as the human observers with generally better results. We rescaled the NPWE model on the human responses by scanning conditions (kVp, pitch, slice thickness) to obtain the best agreement between both observer types, estimated using the Bland-Altman method. The impact of some scanning parameters was estimated using the correct answer rate given by the rescaled NPWE model, for both tasks and each insert size. In particular, the comparison between the dual-energy mode at 74 keV and the single-energy mode at 120 kVp showed that, if the 120 kVp voltage provided better results for the smallest insert at the lower doses for both tasks, their responses were equivalent in many cases.

Mots clés: Bland-Altman method; discrimination; data processing; phantom; reconstruction; dual-energy; low contrast detection; model observer; Non-PreWhitening matched filter; CT protocol optimization; computed tomography; Medical imaging; CT scanner; Particle transport; diagnosis; diagnostic imaging; image quality; low dose level; patient dose; irradiation; Radioactivity; Ionizing radiation; Dosimetry

Domaines: Physique Médicale [physics.med-ph]; Traitement du signal et de l'image [eess.SP]; Physique Nucléaire Expérimentale [nucl-ex]

Nadia Othman, Anne-Catherine Simon, Thierry Montagu, Laureline Berteloot, David Grévent, et al.. Toward a comparison and an optimization of CT protocols using new metrics of dose and image quality part I: prediction of human observers using a model observer for detection and discrimination tasks in low-dose CT images in various scanning conditions. Physics in Medicine and Biology, 2021, 66 (11), pp.115003. ⟨10.1088/1361-6560/abfad8⟩. ⟨cea-03249922⟩