Optimization of hepatic lesion detection with computed tomography (CT): Is randomization of lesion location necessary?

Abstract

Purpose: The purpose of this study was to compare observer performance for the detection of randomly-positioned lesions to that of location-known lesions to determine if randomization of lesion placement is necessary for optimization of hepatic lesion detection with CT. A phantom containing fixed lesions (diameter 2.4mm, 4.8mm and 9.5mm) was scanned at various exposure and slice thickness settings. A second image set was created by electronically cutting lesions from the phantom images and pasting them into background-only images. Nine observers, blinded to lesion location in the second image set, reviewed all images under standardized viewing conditions. Visualization of lesions was scored using a four-point scale. Observer scores for the two methods were correlated for all lesions, and for each lesion size using Spearman's rank correlation coefficient (r). There was very high correlation between the observer scores for all lesions (r=0.919, p<0.0001) and for the 9.5mm lesion (r=0.963, p<0.0001). There was moderate correlation for the 4.8mm and 2.4mm lesions (r=0.509, p=0.084, r=0.640, p=0.028). Discussion: When considering all lesions, or the 9.5mm lesion independently, randomization did not alter observer scores, suggesting random location of large lesions is unnecessary for dose optimization. For the smaller lesion sizes correlation between the two methods is less robust. Conclusion: If lesion size is large or unimportant, dose optimization can be performed using a phantom with fixed lesions. For small lesions, randomized lesion location may be warranted, thus having implications for phantom design.