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Effect of Contrast Agent Administration On Water Equivalent Diameter in CT

B Viggiano*, T Szczykutowicz, University Wisconsin-Madison, Madison, WI


(Sunday, 7/12/2020)   [Eastern Time (GMT-4)]

Room: AAPM ePoster Library

Purpose: Water equivalent diameter (WED) is the preferred surrogate for patient size in CT. It is better than geometric size surrogates and patient weight/height/BMI/age because it correlates the best with x-ray attenuation. Here we study the clinically relevant effect of oral and IV contrast agent on WED.

Methods: We pulled 1,783 routine adult abdominal/pelvis cases from our PACS under retrospective IRB approval. 141 cases had no oral or IV contrast, 342 had just IV contrast, 108 had just oral contrast, and 1,192 had both oral and IV contrast. For each case, we measured the water equivalent and effective diameter (ED) over the middle 80% of the scan range from axial CT images. We plotted the WED versus the effective diameter for each class of contrast (non-con, IV, oral, both).

Results: All 4 classes of contrast administration had WED vs. ED that were indistinguishable of each other; the 95% confidence intervals for the linear fits of all four cases overlapped.

Conclusion: The use of WED as a metric for patient size is not effected by contrast agent for adult routine abdominal/pelvis scanning. Further work remains to generalize this result to all patient populations, IV contrast phases, and scan regions.

Funding Support, Disclosures, and Conflict of Interest: TPS receives research support GE Healthcare. TPS is a consultant and on an advisory board to GE Healthcare and Imalogix LLC. TPS is a consultant to Takeda Pharmaceuticals.


CT, Dose


IM- CT: Radiation dosimetry & risk

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