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Contrast Thresholds for Detection of Low Iodine Concentrations In Subtraction CT and Dual Energy CTSystems

A Heshmat*, I Barreto, L Rill, M Arreola, University of Florida College of Medicine, Gainesville, FL

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(Saturday, 3/26/2022)   [Central Time (GMT-5)]

Purpose: To estimate the contrast thresholds of minimum iodine concentrations in variety of vessel diameters for subtraction CT (SCT) and dual-energy CT (DECT) systems.

Methods: Different sized vessels (Diameters: 1 mm, 3 mm, 5mm) were filled with a variety of iodine concentrations (Range: 0 - 20 mg/mL) and were placed in the center of twenty-seven cylindrical rods surrounded with water. Rods were placed in a 20 cm cylindrical solid-water phantom to simulate administration of iodine in a variety of vessel diameters. The phantom was scanned with SCT and DECT head protocols to assess the detection of minimum iodine concentrations in both systems. The SCT and DECT images were evaluated quantitatively with a Matlab script to extract region of interest (ROIs) of each vessel diameters. ROIs measurements were gathered in order to calculate the limit of detectability, and signal-to-noise ratio of Rose criteria for the assessment of the contrast thresholds.

Results: Both detectability methods agreed with determining the minimum detectable concentration of 0.4 mg/mL in the 5 mm vessel diameter for the SCT While, the minimum detectable concentration in the 5 mm vessel diameter of the DECT was 1 mg/mL. The 3 mm vessel diameter had the minimum detectable concentration of 0.8 mg/mL for SCT and 2 mg/mL for DECT. Lastly, the minimum detectable iodine concentration for the 1mm vessel diameter was 5 mg/mL for SCT and 10 mg/mL for DECT.

Conclusion: The SCT has the capability to detect a lower iodine concentrations compared to the DECT. Contrast thresholds vary for different vessel diameters and the smaller vessel diameters require a higher iodine concentration. Based on these knowledge radiologists can modify their protocols to increase contrast enhancement.

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