X-ray dose quantification for various scanning protocols with the GE eXplore 120 micro-CT

The aim of this study was to quantify the dose delivered by several standard protocols on a GE eXplore 120 micro-CT (Gamma Medica I GE Healthcare) using the computed tomography dose index over 100 mm (CTDI₁₀₀). Four different protocols with tube voltages of 70 kVp and 80 kVp were investigated by measuring the spatial dose distribution over 100 mm in the axial direction for 9 transaxial positions inside a custom-built cylindrical PMMA phantom. All dose measurements were performed using a mobileMOSFET Dose Verification System (Best Medical Canada, Canada). The axial dose profile of the transaxial center position was used for the CTDl₁₀₀ calculation. The Fast scan (70 kVp, 0.512 mAs, 192°) delivered a mean dose of 13.92 ± 0.10 mGy, the Fast scan 360 (70 kVp, 0.512 mAs, 360°) 21.24 ± 0.26 mGy, the Soft Tissue Fast scan (70 kVp, 1.6 mAs, 192°) 38.37 ± 0.97 mGy and the Soft Tissue (80 kVp, 0.512 mAs, 192°, step & shoot) 19.63 ± 0.17 mGy. In order to compare the X-ray tube dose output per mAs the CTDI₁₀₀ of the protocols with 192° were normalized to 360° gantry rotation. At 70 kVp tube voltage the dose output was 45.81 ± 3.92 mGy/mAs across all protocols and 71.89 mGy/mAs at 80 kVp. Protocols with 192° gantry rotation showed inhomogeneity of the dose distribution in the transaxial direction.