Synergistic Radiation Dose Reduction by Combining Automatic Tube Voltage Selection and Iterative Reconstruction

The aim of the study was to evaluate radiation dose and image quality in computed tomographic pulmonary angiography (CTPA) scans performed with automatic tube voltage selection (ATVS, CarekV) before and after implementation of iterative reconstruction (IR, Safire).

This IRB-approved study was conducted with waiver of informed consent. The cohort included 100 consecutive "standard protocol" CTPAs performed using ATVS and 100 consecutive "combined protocol" CTPAs performed using ATVS with a 33% reduction in reference mAs and IR. CTDIvol and main pulmonary artery enhancement, noise, and signal-to-noise ratio were recorded, along with blinded grading of subjective image quality. Dose and image quality were compared between cohorts with univariate analyses and linear regression models.

The 33% reduction in reference mAs with the combined protocol allowed ATVS to select reduced kVp more often than with the standard protocol, with a reduction in 120 and 100 kVp scans (26% to 0% and 61% to 51%, respectively) and an increase in 80 kVp scans (13% to 49%). The combined protocol yielded a CTDIvol reduction of 43% (P<0.0001) and increases in main pulmonary artery enhancement (57 HU, P=0.005) and noise (P=0.019) with unchanged signal-to-noise ratio (P=0.17). With the combined protocol, subjective image quality was unchanged for evaluation of vascular structures but was decreased for evaluation of soft tissues and lung parenchyma.

The combination of ATVS and IR resulted in a 43% dose reduction, greater than the 33% reduction that would be achieved by reducing the reference mAs alone. This was accomplished with preserved vascular image quality.