Objective comparison of high‐contrast spatial resolution and low‐contrast detectability for various clinical protocols on multiple CT scanners

Abstract

Purpose: We sought to compare objectively computed tomography (CT) scanner performance for three clinically relevant protocols using a task-based image quality assessment method in order to assess the potential for radiation dose reduction. Methods: Four CT scanners released between 2003 and 2007 by different manufacturers were compared with four CT scanners released between 2012 and 2014 by the same manufacturers using ideal linear model observers (MO): prewhitening (PW) MO and channelized Hotelling (CHO) MO with Laguerre-Gauss channels for high-contrast spatial resolution and low-contrast detectability (LCD) performance, respectively. High-contrast spatial resolution was assessed using a custom-made phantom that enabled the computation of the target transfer function (TTF) and noise power spectrum (NPS). Low-contrast detectability was assessed using a commercially available anthropomorphic abdominal phantom providing equivalent diameters of 24, 29.6, and 34.6 cm. Three protocols were reviewed: a head (trauma) and an abdominal (urinary stones) protocol were applied to assess highcontrast spatial resolution performance; and another abdominal (focal liver lesions) protocol was applied for LCD. The liver protocol was tested using fixed and modulated tube currents. The PW MO was proposed for assessing high-contrast detectability performance of the various CT scanners. Results: Compared with older generation CT scanners, three newer systems displayed significant improvements in high-contrast detectability over that of their predecessors. A fourth, newer system had lower performance. The CHO MO was appropriate for assessing LCD performance and revealed that an excellent level of image quality could be obtained with newer scanners at significantly lower dose levels. Conclusions: This study shows that MO can objectively benchmark CT scanners using a task-based image quality method, thus helping to estimate the potential for further dose reductions offered by the latest systems. Such an approach may be useful for adequately and quantitatively comparing clinically relevant image quality among various scanners.

Task-based quantification of image quality using a model observer in abdominal CT: a multicentre study

“…Therefore, in the end, the challenge is to establish a link between the different clinical tasks and the surrogates used to assess image quality [ 32 ]. These task-based image quality criteria (for example the LCD requirements) should be initiated for a few morphology types and a standardisation process concerning image quality requirements as a function of the common clinical indications [ 33 ]. Indeed, IR provide images that look satisfying in a larger dose range than with the standard FBP reconstruction algorithm, since the amount of noise does not alert the radiologist.…”

Characterisation and mapping of scattered radiation fields in interventional radiology theatres

“…Our second reason for wanting to characterise the radiation field is related to the evolution of imaging systems. Medical imaging experts are permanently optimising the dose received by patients 8 , as well as using increasingly sophisticated imaging systems and improved image reconstruction algorithms. Additional filters are used to optimise the procedures (patient morphology, paediatric, etc.).…”

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

“…Previous studies have assessed the potential improvement of LCD with IR algorithms for one single phantom size, and often applied subjective and/or objective image quality parameters based on the technical efficacy (image noise, contrast-to-noise ratio (CNR), and spatial resolution) [9][10][11]. However, since it is difficult to correlate these image quality metrics with an accurate assessment of diagnostic performance, it is of paramount importance to use image quality criteria linked to a specific and clinically relevant task, such as LCD, for different phantom sizes [12,13].…”