Utilization of an optimum low-pass filter during filtered back-projection in the reconstruction of single photon emission computed tomography images of small structures

Introduction:Low-pass filters eliminate noise, and accordingly improve the quality of filtered back-projection (FBP) in the reconstruction of single photon emission computed tomography (SPECT) images. This study aimed at selection of an optimum low-pass filter for FBP reconstruction of SPECT images of small structures. Material and Methods:Spheres A, B, and C (۱۶ mm, ۱۲ mm, and ۱۱ mm in diameter, respectively) attached to capillary stems were filled with technetium-۹۹m solution (activity concentration ۳۰۰ kBq/mL). They were then mounted inside a Jaszczak Phantom forming a V-shaped structure. The phantom was then filled with distilled water. Two-dimensional (۲D) projections were acquired on ۱۲۸ ۱۲۸ pixels using a Siemens E-Cam dual-head gamma camera. The Parzen, Shepp-Logan, Low Pass Cosine filters (cut-off frequencies: ۰.۲-۰.۹), and Butterworth filter (order: ۱-۹; cut-off frequencies: ۰.۳-۰.۹) were employed during FBP reconstruction. The line command of ImageJ software was used to draw the point spread functions of acquired ۲D transaxial central slices and for the measurement of their full-width at half-maximum (FWHM). Results:The FWHM of ۲D central image slices of spheres A, B, and C reconstructed using a Butterworth filter measured ۲۰, ۲۰, and ۱۰ pixels, respectively. In comparison, the reconstructed images using the Parzen, Low Pass Cosine, and Shepp-Logan filters measured to ۲۷, ۲۵ and, ۲۲ pixels for sphere A, ۲۴, ۲۲, ۲۰ pixels for B, and ۲۲, ۲۰, ۱۸ pixels for C, respectively. Conclusion: The low-pass filters successfully suppressed noise during the FBP reconstruction of SPECT images of small structures. Accordingly, the Butterworth is a suitable choice.

Keywords:

Nuclear Medicine , SPECT , Imaging , Radionuclide Imaging