[Optimization of Tube Voltage and Number of Signal Averages Based on Dose Efficiency in Late Iodine Enhancement CT].

Purpose

This study aimed to determine the optimal tube voltage and number of image averages for late iodine enhancement CT (LIE-CT) using physical image quality metrics.

Methods

A water phantom containing diluted contrast media (approx. 30 HU at 120 kV) was scanned under ECG gating. Tube voltage was varied (70, 80, 100, and 120 kV), and image averaging was performed for 1 to 6 scans, based on a CTDIvol of 3.7 mGy per scan. CT numbers, standard deviation (SD), and noise power spectrum (NPS) were measured for each image. The low-contrast object-specific CNR (CNRLO) was calculated, and the figure of merit (FOM) was derived using the size-specific dose estimate (SSDE) at a spatial frequency of 0.1 cycles/mm.

Results

CNRLO increased as tube voltage decreased and the number of averages increased, reaching a maximum at 70 kV. CT numbers and NPS also showed an upward trend with decreasing tube voltage. In contrast, the FOM peaked at 3 to 4 averages across all tube voltages and declined from the 5th scan onward due to decreased dose efficiency.

Conclusion

For LIE-CT, 4-scan image averaging at 70 kV can be a useful protocol balancing image quality and radiation dose.