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On the Relationship of Minimum Required Dose to Low Contrast Detectability and Blending Fractions With Adaptive Statistical Iterative Reconstruction (ASIR) in Abdominal CT
Y Zhou*, A Scott , J Allahverdian , C Lee , Cedars-Sinai Medical Center, Los Angeles, CA
Presentations
SU-F-207-11 (Sunday, July 12, 2015) 4:00 PM - 6:00 PM Room: 207
Purpose: It is of practical use to obtain the dose for a specified low contrast lesion detectability and a given ASIR fraction before the scan. To achieve the goal, we investigated the relationship of the minimum required dose to low contrast detectability and ASIR blending fraction in abdominal CT scans.
Methods: A realistically shaped abdomen phantom (CIRS TE-07) with an embedded vertebral bone rod was utilized. Helical CT scans were performed on a GE 750 HD at two dose levels of 8 mGy and 18 mGy. The images were reconstructed using different ASIR fractions (0 - 100%). The noise images, obtained using subtraction from adjacent slices, were partitioned into different scales using matrices of square cells sized differently. The noise at each cell size can be quantified by the standard deviation (sd) of the cell mean pixel values distribution. Upon verifying that the distributions follow Gaussian, we proposed that the statistically defined minimum detectable contrast (MDC) can be applied to ASIR reconstructed images, i.e., MDC = 3.29sd. We then defined the normalized MDC (N_MDC) as the ratio of the MDC with ASIR to the MDC with filtered backprojection and postulated that N_MDC is dose independent. N_MDC was obtained at each cell size from different ASIR blending fractions at different dose levels.
Results: The matrix cell means distribution was verified following Gaussian. N_MDC was found to linearly decrease as the ASIR blending fraction increases. The relationship is the same with two distinct doses. For the specified MDC at lesion size d and ASIR blending fraction (s), the minimum required dose D = [14.05(1-bs)/(MDC*d^1.12)]^2.03, where b = 0.005/d^0.784.
Conclusion: The relationship of the minimum required dose to low contrast detectability and ASIR blending fraction was obtained. It can be used to adjust the scan parameters corresponding to the calculated minimum required dose.
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