SU‐GG‐I‐44: Real‐Time Dose Measurements of Automatic Tube Current Modulation in Multislice CT

Abstract

Purpose: To estimate real‐time doses which are controlled by automatic tube current modulation (ATCM) in multidetector computed tomography (MDCT), and to verify the dose decrease with the prediction by software. Method and Materials: Brilliance 40 MDCT scanner (Philips) provides five ATCM methods. Those are automatic current selection (ACS), xy‐plane dose modulation (D‐DOM), z‐axial dose modulation (Z‐DOM), ACS combined D‐DOM, and ACS combined Z‐DOM. Real‐time doses were measured by two CT pencil‐type detectors operating with a Barracuda (RTI‐e) electrometer connected to a PC running the software oRTIgo2002 (RTI‐e). One detector is DCT10 CTDI ion chamber (RTI‐e) with 100 mm sensitive length. The other is CT‐SD16 CT slice detector (RTI‐e) with 160 mm sensitive length. Several geometric phantoms, which are circular, oval, and elliptic cylinders with 15 cm height, were fabricated to simulate body shapes and to verify the xy‐plane dose modulation. An Apollo phantom was also fabricated to verify the z‐axial dose modulation. Results: For circular cylindrical phantoms with 16–24 cm diameter, doses decreased 28–69% for ACS, 28–67% for ACS combined D‐DOM, and 24–66% for ACS combined Z‐DOM. But dose increased 13–20% for 32 cm diameter. For oval and elliptic cylindrical phantoms, doses decreased 17–27% for ACS, 15–40% for D‐DOM, 31–39% for ACS combined D‐DOM, and 15–28% for ACS combined Z‐DOM. D‐DOM and Z‐DOM real‐time dose variation curves were similar for circular cylindrical phantoms. However, real‐time dose variation curves got closed along with increasing diameter. For oval and elliptic cylindrical phantoms, ACS and ACS combined Z‐DOM real‐time dose variations were resembling. But Z‐DOM real‐time dose variations were remarkable for the Apollo phantom. Conclusion: The methods established by this study could investigate the real‐time dose variations. Using ATCM techniques in MDCT scanning could decrease patient doses. However, it needs to pay more attention to use ATCM techniques for obese patients.