Reduction of image noise in high-pitch CT imaging of the abdomen using a first generation iterative reconstruction algorithm - a phantom study

Abstract

Purpose: Evaluation of different high-pitch dual-source settings and the influence of iterative reconstruction (IRIS) on image noise in abdominal CT-scanning of a phantom – feasible study.

Materials and Methods: The institutional review board has approved this study. To evaluate whether the dual-source high-pitch mode (Somatom Definition FLASH, Siemens) is feasible for abdominal imaging, we took an Alderson RANDO Phantom and reduced the pitch in 0.2 steps from 3.2 to 1.6. The Care Dose was switched on. The current tube voltage was 100 kV in one group and 120 kV in the other. The Ref.mAS for each scan was 210 for both groups. The images were reconstructed in slices/increments of 1 mm/1 mm, 2 mm/2 mm and 5 mm/5 mm with and without IRIS [B30 kernel or I30 kernel (the IRIS kernel)]. In one defined slice position, we measured four defined and constant-sized ROIs, and evaluated the standard deviation as the image noise marker. To analyze the data statistically, we used a step-wise estimation approach for a linear model with interactions.

Results: IRIS significantly decreases the standard deviation as the image noise marker, especially in thin slices. The image noise was decreased by a factor of 0.716 (p < 0.001), 0.733 (p < 0.001) and 0.784 (p < 0.001) in 1 mm, 2 mm and 5 mm slices, respectively.

Conclusion: In our study, using IRIS we managed to reduce image noise significantly (all p-values < 0.001) compared to the normal reconstruction mode, especially in thin slices (scans performed in 1 mm, 2 mm and 5 mm slices). We may therefore be able to reduce the radiation dose applied to patients whilst obtaining the same image quality using IRIS.