Development and evaluation of an ultra-high-resolution cone-beam computed tomography system for hand and foot.

Objective: To develop an experimental ultra-high-resolution cone-beam computed tomography (UHRCBCT) system for imaging the human hand and foot and to evaluate its spatial resolution, image noise, radiation dose, and feasibility through phantom and volunteer studies.

Materials and methods: The UHRCBCT system was built based on a 0.5-mm focal spot X-ray tube and a 0.099-mm pixel CMOS detector. A low magnification geometry (magnification: 1.22) was applied to reduce geometry blurring. Images were reconstructed with a voxel size of 0.10 × 0.10 × 0.10 mm³. Radiation dose was quantified by measuring the CT dose index (CTDI) corresponding to the scanning method. Spatial resolution and image noise were quantitatively evaluated using a 0.1-mm copper wire and a water phantom, respectively, in comparison with those of a high-resolution multi-slice CT system (HRMSCT, detector size: 0.25 mm at isocenter) for the matched radiation dose. Scans were also performed on a foot phantom using UHRCBCT and HRMSCT and on carpal bones of healthy volunteers using UHRCBCT under ethical approval.

Results: The effective dose estimated from CTDI was 0.024 mSv using a conversion factor of 0.0005 mSv/(mGy cm), which was within the lowest category for healthy volunteers in ICRP publication 103. The 5%MTF-based spatial resolution was 0.10 mm, significantly smaller than 0.23 mm achieved by HRMSCT. Image noise was approximately twice as high in UHRCBCT; however, trabecular bone structures and joint spaces were more distinctly visualized in both phantom and volunteer images.

Conclusion: UHRCBCT achieved a high resolution of 0.10-mm in imaging trabecular hand and foot bones with an acceptable radiation dose, indicating potential for clinical application in orthopedic diagnosis.