Indian Journal of Nuclear Medicine

Noise reduction is one of the important tasks in clinical SPECT imaging. One has to be judicious in the selection of filters and its parameters for reducing noise, as there may be some common frequencies in the noise and real image data. Various digital filters (for reducing noise) have been proposed. The manufacturers normally supply default filter parameters to the user which may not be relevant in different clinical situations. We conducted a phantom study to standardize the filterparameters and compared them with those suggested by the vendor. The images of SPECT performance phantom filled with ^99mTc (222 MBq) were acquired in 128 x 128 matrix using high-resolution parallel hole collimators on Varicam Dual Head Gamma Camera. The images were reconstructed using filtered back-projection technique with attenuation correction applied as per Chang's method (attenuation coefficient = 0.125). A Ramp filter; sixteen different Hanning filter, thirteen different Metzfilter, and nine different Butterworth filter parameters were applied during imagereconstruction. Four different Nuclear Medicine physicians evaluated theimages togive a score of true positive (TP). Metz-6 (cut-off = 75, power = 30, FWHM = 57) filter provided best image quality of the phantom. Our result did not exactly match with default one. We therefore, suggest that the filter parameters must bestandardized before being put to clinical use.