Performance Evaluation of the GE eXplore CT 120 Micro-CT for Various Scanning Protocols

The aim of this study was to evaluate the performance of the General Electric (GE) eXplore CT 120 micro-CT using the same methodology and image quality assurance vmCT phantom developed for the GE eXplore Ultra. In addition, Quality assurance in Radiology and Medicine (QRM) low contrast and bar pattern phantoms were used. The phantoms were imaged using the six protocols regularly used in our laboratory (Fast scan 220 (P1) or 360 (P2): 70 kV, 32 mA, 220 or 360 views; Soft tissue fast scan (P3): 70 kV, 50 mA, 220 views, Soft tissue step & shoot (P4): 80 kV, 32 mA, 220 views; Low Noise (P5): 100 kV, 50 mA, 720 views and In Vivo Bone scan (P6): 100 kV, 50 mA, 360 views). Data were reconstructed with an isotropic voxel size of 100 µm (50 µm when protocol detector-binning was reduced to 2x2). The MTF obtained with the slanted edge and coil methods agreed very well. A 10% modulation transfer function (MTF) was observed in the range 3.6-4.8 mm-1 (P1&2 = 4.2; P3&4 = 4.8; P5 = 3.6 and P6 = 3.8), corresponding to 95-138 µm resolutions. The smallest bars visually observed on the QRM pattern phantom image were 100 µm. The geometric accuracy was better than 0.1%. A highly linear (R2 > 0.999) relationship between measured and expected CT numbers for both the CT number accuracy and linearity sections of the phantom was observed with a voltage dependent slope. A cupping effect was observed on the uniform slices. This effect was clearly highlighted by the uniformity-to-noise ratio (P1 = 0.58, P2&3&4 = 0.75, P5 = 1.35 and P6 = 2.74) especially for the low-noise protocols P5 and P6. The best low contrast discrimination was observed for P2 and P5 protocols. In conclusion the eXplore CT 120 achieved a resolution in the range 95-138 µm. It was found to be linear and geometrically accurate. The major difference between the protocols was the noise level which limits the detectability of low contrasts.