A challenge for high-speed and high-resolution CT for extremities with clinical feasibility

Existing micro-CT systems can visualize the trabecular bone microstructure; however, its application is limited because of the small scan field of view and the long scan time for clinical use. We developed a high-resolution CT for human extremities (HRCTe) with clinical feasibility, which can achieve a spatial resolution of similar to 100 mu m and a short acquisition time of 6.5 seconds. A complementary metal-oxide-semiconductor X-ray detector with a 99-mu m pixel pitch and a compact X-ray tube with a focal spot size of 0.8 mm were installed in the HRCTe. In order to maximize the performance of the Xray tube and the detector, we introduced a low-magnification geometry. This resulted in an effective focal spot size of 0.14 mm, ensuring the resolution performance of the pixel pitch at the iso-center of 81 mu m. The scan z-directional coverage was 50 mm. For the technical assessment, modulation transfer function (MTF) and noise power spectrum (NPS) were measured using a wire phantom and a water phantom, respectively. A squared system performance function (SPF2) was calculated as MTF2/NPS. These results were compared with those measured using a high-resolution mode of a whole-body CT with a 0.25-mm detector (WCT) and a dental CT (DCT). The 5%MTF of the HRCT, WCT, and DCT were approximately 3.8, 1.9, and 1.5 mm(-1). The SPF2 at 2.0 mm(-1) of the developed CT was 260% higher than that of WCT. The trabecular bones in an anthropomorphic foot phantom were visualized much clearer with HRCTe than with both WCT and DCT.