Relationship between the optimum cut off frequency for Butterworth filter and lung-heart ratio in 99mTc myocardial SPECT

Background: We investigated whether the lungheart ratio parameter (LHR) can be used to identify the optimum cut off frequency for Butterworth filter in 99mTc myocardial SPECT imaging. Materials and Methods: This study involved a cardiac phantom system consisting of cardiac insert in which 1.10 cm cold defect was inserted into its myocardium wall and filled with 4.0 μCi/ml (0.148 MBq/ml) 99mTc concentration. The cardiac insert was then put into a cylindrical tank which filled with six different 99mTc concentrations as background. Thus, six target background concentrations ratios (T/B) were carried out. The LHR was determined for every SPECT raw image obtained corresponding to each T/B. Then, 130 different combinations of filter parameters from Butterworth filter were utilized to reconstruct each SPECT raw image. The determination of count in myocardium, background, and defect regions of interest (ROI) were performed for every reconstructed image. All the count values were then used to calculate contrast, signal-to-noise ratio (SNR), and defect size. Each criterion was graded (1 to 100) and then summed together to obtain total grade. The optimum cut off frequency for each LHR was determined from the total grade. The relation between optimum cut off frequency for Butterworth filter and LHR was established using linear regression. Results: There were good relationship between the optimum Butterworth cut off frequency and LHR (R2 = 0.864, p < 0.01). The optimal cut off frequency correspond to the change in LHR can be expressed by the equation: Optimum cut off frequency = 0.715*LHR + 0.227. Conclusion: This study suggests that the optimum cut off frequency for Butterworth filter should be determined by referring to LHR in each patient study. Iran. J. Radiat. Res., 2010 8 (1): 17-24