Author: Hyo-Min Cho, Changwoo Lee 👨🔬
Affiliation: Korea Research Institute of Standards and Science 🌍
Purpose: We develop sphere phantoms to assess spatial resolution of computed tomography (CT) systems and validate its usability using table-top X-ray experiment systems.
Methods: We manufactured sphere phantoms having LEGO brick shape using computer numerical control (CNC) machining, and Teflon balls were individually inserted into the sphere phantoms. Each sphere phantom can be easily combined using a stud-and-tube coupling system. For usability test for CT systems, experimental data acquisition was performed on the table-top X-ray system, which include an X-ray source (RAD-14, VAREX, USA) and a flat-panel detector (VIVIX-D 1717G, VIEWORKS, South Korea). The source to iso-center distance and the detector to iso-center distance are 850 mm and 200 mm, respectively. The X-ray source was operated with 70 kVp, and the detector pixel size was 0.280 × 0.280 mm2 with a 2 × 2 binning mode. We reconstructed a sphere phantom using the FDK algorithm at the iso-center, and the reconstruction volume images of the developed sphere phantom were used to measure the spatial resolution. We extracted the edge spread function from the reconstructed sphere image. Then, the MTF can be calculated by taking the modulus of the Fourier transform of the derivative of the edge spread function.
Results: The measured MTF from the experimental data show well agreement with the ideal MTF (i.e., simulated MTF). To evaluate the estimation performance quantitatively, the full-width at half maximum (FWHM) are measured from the measured MTF and ideal MTF. The FWHM of measured MTF and ideal MTF were 0.151 and 0.154, respectively, demonstrating the effectiveness of the developed sphere phantom for measuring the spatial resolution.
Conclusion: In this work, we developed sphere phantoms for quantitative evaluation of CT systems resolution. Based on the results of this work, the developed phantom can be adapted to evaluate the resolution performance of CT systems.