Iterative Reconstruction Algorithm for Abdominal Multidetector CT at Different Tube Voltages: Assessment of Diagnostic Accuracy, Image Quality, and Radiation Dose in a Phantom Study

Abstract

To assess the diagnostic accuracy, image quality, and radiation dose of an iterative reconstruction algorithm compared with a filtered back projection (FBP) algorithm for abdominal computed tomography (CT) at different tube voltages. A custom liver phantom with 45 simulated hypovascular liver tumors (diameters of 5, 10, and 15 mm; tumor-to-liver contrast of 10, 25, and 50 HU) was placed in a cylindrical water container that mimicked an intermediate-sized patient. The phantom was scanned at 120, 100, and 80 kVp. The CT data sets were reconstructed with FBP and iterative reconstruction. The image noise was measured, and the contrast-to-noise ratio (CNR) of the tumors was calculated. The radiation dose was assessed with the volume CT dose index. Tumor detection was independently performed by three radiologists. Statistical analysis included analysis of variance. Compared with the FBP data set at 120 kVp, the iterative reconstruction data set collected at 100 kVp demonstrated significantly lower mean image noise (20.9 and 16.7 HU, respectively; P < .001) and greater mean CNRs for the simulated tumors (P < .001). The iterative reconstruction data set collected at 120 kVp yielded the highest sensitivity for tumor detection, while the FBP data set at 80 kVp yielded the lowest. The sensitivity for the iterative reconstruction data set at 100 kVp was comparable with that for the FBP data set at 120 kVp (79.3% and 74.9%, respectively; P > .99). The volume CT dose index decreased by 39.8% between the 120-kVp protocol and the 100-kVp protocol and by 70.3% between the 120-kVp protocol and the 80-kVp protocol. Results of this phantom study suggest that a 100-kVp abdominal CT protocol with an iterative reconstruction algorithm for simulated intermediate-sized patients increases the image quality and maintains the diagnostic accuracy at a reduced radiation dose when compared with a 120-kVp protocol with an FBP algorithm.