Ms. Karen L. Dobeli Profile

Karen L. Dobeli

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Proceedings Article | 22 February 2012 Paper

Dose-optimized slice thickness for routine multislice computed tomography liver examinations

K. Dobeli, S. Lewis, S. Meikle, D. Thiele, P. Brennan

Proceedings Volume 8318, 831812 (2012) https://doi.org/10.1117/12.910452

KEYWORDS: Opacity, Computed tomography, Liver, Diagnostics, Medical imaging, Medical research, Image filtering, Health sciences, Image visualization, Visualization

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The need to optimize CT protocols with respect to radiation dose is widely recognized. This study uses phantom-based methodology to investigate the affect of changes in exposure and slice thickness on observer performance for the detection of low contrast opacities with multislice computed tomography to determine dose- optimized slice thickness and image noise for routine liver imaging. Methods: A phantom containing an opacity with diameter 9.5mm and density 10HU below background was scanned at various exposure and slice thickness settings (range 50-125mAs and 1-3mm). An image set consisting of 120 images containing background-only and 60 images containing the opacity in random locations was created. Following Institutional Review Board approval, nine experienced observers viewed the images and scored opacity visualization using a four-point confidence scale. Noise, contrast-to-noise ratio (CNR), sensitivity, specificity and area under the curve (AUC) were calculated. Comparisons between exposure and slice thickness settings were performed using ROC, Spearman and Wilcoxon techniques. Results: Significant (p<0.05) reductions in AUC and sensitivity occurred when CNR dropped to 0.71 or below and 0.68 or below, respectively. There was strong correlation between noise and AUC (r = -0.79, p<0.01), noise and sensitivity (r = -0.92, p<0.001), CNR and AUC (r = -0.90, p<0.001) and CNR and sensitivity (r = 0.61, p<0.05). Conclusion: Observer performance for the detection of opacities is strongly related to quantum noise and CNR. Dose optimized lesion detection was achieved with 5mm slice thickness and CNR of 0.72 and noise of 9.05.

Proceedings Article | 3 March 2011 Paper

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

K. Dobeli, S. Lewis, S. Meikle, D. Thiele, P. Brennan

Proceedings Volume 7966, 79661I (2011) https://doi.org/10.1117/12.877917

KEYWORDS: Computed tomography, Diagnostics, Medical imaging, Image processing, Visualization, Health sciences, Cancer, Liver, Spherical lenses, Image visualization

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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.

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