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. 2015 Jul-Aug;39(4):619-23.
doi: 10.1097/RCT.0000000000000245.

Assessment of Low-Contrast Resolution for the American College of Radiology Computed Tomographic Accreditation Program: What Is the Impact of Iterative Reconstruction?

James M Kofler  1 , Lifeng Yu, Shuai Leng, Yi Zhang, Zhoubo Li, Rickey E Carter, Cynthia H McCollough
Affiliations

Assessment of Low-Contrast Resolution for the American College of Radiology Computed Tomographic Accreditation Program: What Is the Impact of Iterative Reconstruction?

James M Kofler et al. J Comput Assist Tomogr. 2015 Jul-Aug.

Abstract

Objective: To compare contrast-to-noise ratio (CNR) thresholds with visual assessment of low-contrast resolution (LCR) in filtered back projection (FBP) and iteratively reconstructed (IR) computed tomographic (CT) images.

Methods: American College of Radiology (ACR) CT accreditation phantom LCR images were acquired at CTDIvol levels of 8, 12, and 16 mGy using 2 scanner models and reconstructed using one FBP and 2 IR kernels. Acquisitions were repeated 100 times. Three board-certified medical physicists blindly reviewed the LCR section images. Pass-percentage rates (PPRs) using previous and current ACR CT accreditation criteria were compared.

Results: Observer PPRs for FBP images were less than 32%. For IR images, 5 of 18 settings/dose/model configurations had PPRs greater than 32% (maximum 76.3%). For CNR evaluation of FBP images, PPRs for 15 configurations were greater than 70%. For IR images, all PPRs were at least 96%.

Conclusions: The CNR threshold used by the ACR CT accreditation program yields higher PPRs than visual assessment of LCR, potentially resulting in lower-quality images passing the ACR CNR criteria.

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Figures

Figure 1
Figure 1
The low contrast resolution section of the ACR CT accreditation phantom.
Figure 2
Figure 2
The distribution of mean human observer scores for image acquisitions from a) Vendor 1 and b) Vendor 2; and the distribution of CNR measurements for c) Vendor 1 and d) Vendor 2. The dashed line represents the “pass” level for each method.
Figure 2
Figure 2
The distribution of mean human observer scores for image acquisitions from a) Vendor 1 and b) Vendor 2; and the distribution of CNR measurements for c) Vendor 1 and d) Vendor 2. The dashed line represents the “pass” level for each method.
Figure 2
Figure 2
The distribution of mean human observer scores for image acquisitions from a) Vendor 1 and b) Vendor 2; and the distribution of CNR measurements for c) Vendor 1 and d) Vendor 2. The dashed line represents the “pass” level for each method.
Figure 2
Figure 2
The distribution of mean human observer scores for image acquisitions from a) Vendor 1 and b) Vendor 2; and the distribution of CNR measurements for c) Vendor 1 and d) Vendor 2. The dashed line represents the “pass” level for each method.
Figure 3
Figure 3
Vendor 1 pass-percentage results as determined by 2 of 3 human observers assigning a passing score, and as determined by the ACR criteria of CNR≥1.0. Error bars indicate the Wilcox 95% confidence intervals. Images acquired at a CTDIvol of a) 8 mGy, b) 12 mGy, and c) 16 mGy.
Figure 3
Figure 3
Vendor 1 pass-percentage results as determined by 2 of 3 human observers assigning a passing score, and as determined by the ACR criteria of CNR≥1.0. Error bars indicate the Wilcox 95% confidence intervals. Images acquired at a CTDIvol of a) 8 mGy, b) 12 mGy, and c) 16 mGy.
Figure 3
Figure 3
Vendor 1 pass-percentage results as determined by 2 of 3 human observers assigning a passing score, and as determined by the ACR criteria of CNR≥1.0. Error bars indicate the Wilcox 95% confidence intervals. Images acquired at a CTDIvol of a) 8 mGy, b) 12 mGy, and c) 16 mGy.
Figure 4
Figure 4
Vendor 2 pass-percentage results as determined by 2 of 3 human observers assigning a passing score, and as determined by the ACR criteria of CNR≥1.0. Error bars indicate the Wilcox 95% confidence intervals. Images acquired at a CTDIvol of a) 8 mGy, b) 12 mGy, and c) 16 mGy.
Figure 4
Figure 4
Vendor 2 pass-percentage results as determined by 2 of 3 human observers assigning a passing score, and as determined by the ACR criteria of CNR≥1.0. Error bars indicate the Wilcox 95% confidence intervals. Images acquired at a CTDIvol of a) 8 mGy, b) 12 mGy, and c) 16 mGy.
Figure 4
Figure 4
Vendor 2 pass-percentage results as determined by 2 of 3 human observers assigning a passing score, and as determined by the ACR criteria of CNR≥1.0. Error bars indicate the Wilcox 95% confidence intervals. Images acquired at a CTDIvol of a) 8 mGy, b) 12 mGy, and c) 16 mGy.
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