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 ~100μm and a short acquisition time of 6.5 seconds. A complementary metal-oxide-semiconductor x-ray detector with a 99μm pixel pitch and a compact x-ray tube with a focal spot size of 0.8mm were installed in the HRCTe. In order to maximize the performance of the x-ray tube and the detector, we introduced a low-magnification geometry. This resulted in an effective focal spot size of 0.14mm, ensuring the resolution performance of the pixel pitch at the iso-center of 81μm. The scan z-directional coverage was 50mm. 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 0.25mm detector (WCT) and a dental CT (DCT). The 5%MTF of the HRCT, WCT, and DCT were approximately 3.8, 1.9, and 1.5mm⁻¹. The SPF² at 2.0mm⁻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.