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Session: Imaging: CT Image Quality, Protocol Optimization, and Dose Reduction [Return to Session]

A New Approach for Low Dose Low KVp Coronary Artery Calcium Scoring

D Zhang*, A Scott, C Lee, N Gellada, M Hyun, Y Zhou, Cedars-Sinai Medical Center, Los Angeles, CA


TH-IePD-TRACK 1-5 (Thursday, 7/29/2021) 3:00 PM - 3:30 PM [Eastern Time (GMT-4)]

Purpose: Dose reduction using lower kVp in coronary artery calcium scoring (CACs) CT is appealing due to the population dose concern from the wide use. Previously we proposed a vendor-independent approach for low dose low kVp CACs without changing the Agatston thresholds. This study was to further validate the approach by incorporating a large phantom size.

Methods: By applying consistent calcium contrast-to-noise ratio (CNR) to two anthropomorphic heart phantoms (medium and large) with 3-cm hydroxyapatite (HA) inserts, scanned using a dual-source CT, the relationship was derived between the volume CT dose index (CTDIvol) at lower tube voltages and the baseline CTDIvol at 120 kVp based on consistent CNR. The baseline CTDIvol was obtained using the specified noise thresholds from the images acquired at 120 kVp. To preserve the conventional Agatston thresholds, down-scaling with the found calcium HU enhancement factors was applied to images acquired at lower voltages with a dynamic heart module in 3D motion simulating heart movement at 60 beats per minute with 1.2-5 mm calcium inserts (50- 400 mg/cc) on the coronary tracks. Scores were evaluated on the scaled images by six readers and compared against the ground truth scores at high CTDIvol.

Results: The CTDIvol at lower voltages was related to the baseline CTDIvol following a power form of the voltage (index 1.246), regardless of the phantom size. The baseline CTDIvol was found to be 1.5 and 4.5 mGy, for the medium and large phantoms, respectively. Correspondingly, the reduced CTDIvol at 100-70 kVp were 1.28-0.76 mGy, and 3.57-2.32 mGy. The downscaling factors were 0.88-0.63. The calcium scores at lower voltages were found within 12% of the ground-truths.

Conclusion: A vendor- and patient size-independent approach was established to obtain the reduced dose and correct coronary calcium scores at lower tube voltages. Up to 50% dose reduction was achieved.



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