Purpose: As we experienced in clinical practice, the default automatic tube voltage selection may not be optimal in coronary artery CT angiogram (CCTA). This study was designed to find alternative tube voltages that are optimal in CCTA with dual-source CT.
Methods: Iodine targets of different diameters and densities (3 -5mm and 0.5–10 mg/cc) were inserted on the coronary artery track of a medium size anthropomorphic heart phantom. Large and extra-large phantom sizes were made by adding additional fat layers. The heart module in the phantoms was set in 3-dimensional motion by an ECG signal of 60 beats-per-minute. A Siemens Force CT was used to acquire CCTA with prospective gating at 65-75% of R-to-R peaks. The vendor CarekV was used first (with a typical CNR strength 9 for CCTA). Additional kVp (+/- 10) were manually selected with the scanner’s automatic mA compensation for CNR maintenance. Images were reconstructed to thickness of 0.5 mm (Bv40 and ADMIRE 3). Cylindrical voxels of interest were placed inside the targets of 5 mg/cc and 10 mg/cc and nearby blood pool to measure the contrast-to-noise ratio (CNR). The figure-of-merit (FOM) was defined by the CNR normalized to the square root of volume CT dose index to focus on the impact of kVp selection.
Results: On average the FOM was found 12% higher when the kVp was lowered by one step (10 kVp) from the machine auto-selection for all three phantom sizes. Visual comparison of image quality of the coronary iodine targets at different kVp values was consistent with the FOM results. 150 kVp was not found optimal for the extra-large phantom.
Conclusion: When the kVp was lowered by one step (10 kVp) from the machine auto-selection, the CCTA with dual-source CT delivers better performance.
Not Applicable / None Entered.