Validation of optimal cut-off frequency using a Butterworth filter in single photon emission computed tomography reconstruction for the target organ: Spatial domain and frequency domain

摘要

In single photon emission computed tomography (SPECT) images, we evaluated cut-off frequency using two methods: spatial domain method (normalized mean square error: NMSE) and frequency domain method (radius direction distribution function in the power spectrum: Pr (n)) and we calculated the optimal cut-off frequency of the Butterworth filter according to the nuclide and collimator used, and the target organ. The optimized cut-off frequencies (Fc) were determined for nuclides of 99m-Tc, 123-I, 201-Tl, and LEHR and LEGP collimators, and compared. The Pr (n) was used to evaluate the SPECT images for frequency domain analysis, and the NMSE method was used for the assessment of images in spatial domain. In the brain phantom for both of these methods of analysis, the optimal Fc varies depending on the nuclide and collimator. Fc in use for 99m-Tc is 0.802 [cycles/cm] with LEHR and 0.656 [cycles/cm] with LEGP. However, those in use for 123-I are 0.656 [cycles/cm] with LEHR. In the myocardial phantom, the appropriate Fc are 0.516 [cycles/cm] with LEHR, and 0.469 [cycles/cm] with LEGP in use of 99m-Tc. We concluded that the cut-off frequency of the Butterworth filter should be changed in reconstructing SPECT images according to the collimator, nuclide and target organs.