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The Effect of Model Based Iterative Reconstruction (GE-VEO) On the CT Numbers and Noise of Both Small Lung Nodules and Large Homogeneous (heart and Spongiosa) Regions in An Anthropomorphic Chest Phantom

M Goodsitt

M Goodsitt*, H Chan, E Christodoulou, S Larson, Univ Michigan, Ann Arbor, MI

TH-E-217BCD-10 Thursday 1:00:00 PM - 2:50:00 PM Room: 217BCD

Purpose: To investigate the effect of Model-Based Iterative Reconstruction (MBIR) on CT#s and noise (standard deviation, SD) of both nodules and homogeneous regions (heart and vertebra spongiosa) in an anthropomorphic chest phantom.

Methods: A Lungman phantom (Kyoto-Kagaku Co. Japan) was imaged with a GE Discovery CT750 HD CT scanner using our clinical lung nodule protocol (120kVp,80mA,0.5s,1.375:1pitch,1.25mm-slice,0.625mm-interval,40%ASIR) and lower dose protocols (20mA and 10mA), different %ASIR (0%,70%), and MBIR (VEO). A variety of 5mm-diameter simulated nodules (-630HU,100HU,water equivalent, etc.) were placed in the vasculature insert in the phantom. CT#s were measured within 7.9mm² ROIs at the centers of the nodules and within larger ROIs in the heart and vertebra regions.

Results: For nodules, on average, the CT#s are 18HU, 25HU, and 30HU greater for VEO than for 0%, 40% and 70%ASIR, respectively. The ratios of the SDs for VEO to those for 0%, 40% and 70%ASIR are 0.60, 0.77, and 0.93, respectively. For the heart region, the CT#s are independent of %ASIR at a given mA, and the CT#s for VEO are smaller than those for all ASIR blends by 10HU at 10mA, 3HU at 20mA, and 1HU at 80mA. The ratios of the SDs for VEO to those for ASIR blends increase with %ASIR and mA ranging from 0.14 for 0%ASIR/10 mA to 0.47 for 70%ASIR/80mA. Corresponding values in the spongiosa region show similar trends, with CT# differences of 35HU, 12HU, and 2HU, and SD ratios ranging from 0.13 to 0.40.

Conclusions: The effect of MBIR on mean CT#s and noise depends on object size. The CT#s are greater for MBIR than ASIR blends in nodules; whereas, they are smaller for MBIR in large homogeneous regions. The noise is almost always lower for MBIR, but the degree of smoothing is much greater in large homogeneous regions than in small nodules

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