Y Zhou*, E Eastman, C Lee, A Scott, Cedars-Sinai Medical Center, Los Angeles, CA

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  Y Zhou

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MO-C930-IePD-F8-6 (Monday, 7/11/2022) 9:30 AM - 10:00 AM [Eastern Time (GMT-4)]

Exhibit Hall | Forum 8

Purpose: Coronary artery calcium scoring (CACs) CT is performed at 120 kVp in patients with borderline risk. Hence efforts should be made to alleviate the population dose concern. General dose modulations do not consider the CACs specific quality requirement, resulting in significant dose variations in practice. We propose a new dose modulation based on the patient size adjusted noise thresholds in the ascending aorta.

Methods: Noises were measured retrospectively in the ascending aorta from 262 clinical studies acquired on Siemens Force using a general dose modulation with a reference effective mAs of 80 or 100. The patient effective diameters (L) were measured from the topograms. The dose indices (CTDIvol) were recorded. It was found that the noise(σ) can be fitted to α₁exp(β₁L)/CTDIvol^γ₁ (R² = 0.78). To find the optimal dose modulation, specific CTDIvol were extracted from the cases where the noise reached the SCCT’s recommended thresholds of 20 HU and 23 HU for the small/medium, and large patient sizes, respectively. The threshold noise was formulated as σt = α₂exp(β₂L)/CTDIvol^γ₂. The parameters were obtained from the known CTDIvol and noise thresholds at the three patient sizes. The CTDIvol for any L was derived by assuming σt be proportional to exp(λL).

Results: It was found that α₂= 9.072, β₂= 0.037/cm, γ₂=0.326, λ = 0.023/cm. The new modulation reduces the dose by 14.6% as compared to the modulation using reference mAs of 100, whereas the dose is close (5.7%) to that using the reference mAs of 80. The noise in the aorta is much more consistent than in the general modulation.

Conclusion: With the consistent noise performance and potential dose reduction, an optimal dose modulation is established for coronary artery calcium scans based on patient-size adjusted noise thresholds. The result can serve as the baseline for further dose reduction at lower kVp values.

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