Effects of acquisition method and reconstruction algorithm for CT number measurement on standard-dose CT and reduced-dose CT: a QIBA phantom study

Purpose: To compare the effect of different acquisition and reconstruction methods on the radiation dose and accuracy of CT number measurements, using a 320-detector row CT and a Quantitative Imaging Biomarker Alliance (QIBA) recommended phantom. Materials and methods: Acquisitions were performed on a 320-detector row CT, as 64- and 80-detector row helical and wide detector step-and-shoot (i.e., wide volume) acquisitions with tube currents of 400 mA, 100 mA, 50 mA, 20 mA, and 10 mA. Image was reconstructed with the filtered back projection (FBP), adaptive iterative dose reduction using 3D processing (AIDR 3D), and forward projected model-based iterative reconstruction (FIRST) methods. The difference between measured CT numbers and the actual -856HU value of the phantom insert was determined by each CT acquisition protocol. Differences in actual and measured CT numbers were compared among acquisitions and among reconstruction methods by means of Tukey’s HSD test. Results: The CT number obtained with 64-detector row helical acquisition was significantly larger than that obtained with others (p < 0.0001). At each tube current, the CT number reconstructed with FIRST was significantly smaller than that with others (p < 0.0001). Conclusion: Acquisition and reconstruction methods are significantly affecting radiation dose reduction and accuracy of CT number measurements on a phantom study.