Abstract
ObjectivesTo evaluate the effects of anatomical phantom structure on task-based image quality assessment compared with a uniform phantom background.MethodsTwo neck phantom types of identical shape were investigated: a uniform type containing 10-mm lesions with 4, 9, 18, 30, and 38 HU contrast to the surrounding area and an anatomically realistic type containing lesions of the same size and location with 10, 18, 30, and 38 HU contrast. Phantom images were acquired at two dose levels (CTDIvol of 1.4 and 5.6 mGy) and reconstructed using filtered back projection (FBP) and adaptive iterative dose reduction 3D (AIDR 3D). Detection accuracy was evaluated by seven radiologists in a 4-alternative forced choice experiment.ResultsAnatomical phantom structure impaired lesion detection at all lesion contrasts (p < 0.01). Detectability in the anatomical phantom at 30 HU contrast was similar to 9 HU contrast in uniform images (91.1% vs. 89.5%). Detection accuracy decreased from 83.6% at 5.6 mGy to 55.4% at 1.4 mGy in uniform FBP images (p < 0.001), whereas AIDR 3D preserved detectability at 1.4 mGy (80.7% vs. 85% at 5.6 mGy, p = 0.375) and was superior to FBP (p < 0.001). In the assessment of anatomical images, superiority of AIDR 3D was not confirmed and dose reduction moderately affected detectability (74.6% vs. 68.2%, p = 0.027 for FBP and 81.1% vs. 73%, p = 0.018 for AIDR 3D).ConclusionsA lesion contrast increase from 9 to 30 HU is necessary for similar detectability in anatomical and uniform neck phantom images. Anatomical phantom structure influences task-based assessment of iterative reconstruction and dose effects.Key Points• A lesion contrast increase from 9 to 30 HU is necessary for similar low-contrast detectability in anatomical and uniform neck phantom images.• Phantom background structure influences task-based assessment of iterative reconstruction and dose effects.• Transferability of CT assessment to clinical imaging can be expected to improve as the realism of the test environment increases.
Highlights
MethodsImage properties of clinical computed tomography (CT) images vary significantly due to differences between vendors, scanner generations, software versions, imaging techniques, and reconstruction methods
Readings of images of the uniform phantom yielded high detection accuracy already at relatively low lesion contrast of 9 HU (89.5%, 95% CI: 82.9 to 96%), which improved to 99.6% at 18 HU and perfect detection at 30 and 38 HU contrast
Readings of images of the uniform phantom with 4 HU lesion contrast originating from a previous study yielded an average detection accuracy of 62.9%
Summary
Image properties of clinical computed tomography (CT) images vary significantly due to differences between vendors, scanner generations, software versions, imaging techniques, and reconstruction methods. This diversity affects the diagnostic quality of CT images [1], and differences are likely to increase further as CT techniques evolve. The authors of another CT study report only negligible texture effects, concluding that uniform phantoms may allow sufficient assessment of clinical performance [9]. Both of these CT studies investigated cropped images mimicking vessel-free liver textures. In order to better understand the validity of CT assessment with uniform phantoms for clinical imaging, it would be desirable to evaluate how such assessments relate to CT images obtained in phantoms with full anatomical detail
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