Radiation dose reduction in extremity multi-detector CT: A comparison of image quality with a standard dose protocol

Purpose: To analyze the quantitative and qualitative image quality of computed tomography (CT) of the extremities (shoulder, wrist, pelvis, and ankle joints) with low-dose radiation and standard-dose radiation.Materials and methods: In this study, we included 400 individuals who underwent CT of the extremities, comprising 50 cases of each joint (shoulder, wrist, pelvis, and ankle) at low and standard dose regimens. Low-dose CTs were performed using identical voltage and parameters with the exception of decreased (half of standard dose) tube current. Low-dose and standard-dose images were compared in terms of radiation dose, objective image quality according to the standard deviation (SD) of the Hounsfield unit value of the medulla, cortex, muscle, subcutaneous fat, and air, and subjective image quality according to noise, sharpness, diagnostic acceptability, and artifacts.Results: In the shoulder and pelvis, the mean value of the SD for all tissue on low dose CT images was significantly higher than that of standard dose CT, except for the SD of cortex in the shoulder joint and marrow in the pelvis. In the wrist, the mean value of the SD for all tissue was not significantly different between low dose and standard CT (p > 0.05). In the ankle, the mean value of the SD of the medulla and cortex was not different (p > 0.05), but the remaining measurements were significantly higher in low dose CT. Subjective image quality in the shoulder and pelvis were significantly reduced in low dose CT. In the wrist, all categories of subjective image quality except artifacts were similar. In the ankle, all categories of subjective image quality except for artifacts were degraded in low dose CT.Conclusions: Objective image noise is more increased in low dose CT images of the shoulder and pelvis. Although diagnostic performance was acceptable, mean subjective image quality also decreased. In the wrist, objective image noise and subjective image quality were not degraded in low dose CT. In the ankle, some measurements of objective and subjective image quality were similar between low dose and standard dose CT.