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.