REMOVAL OF SEPTAL PENETRATION EFFECTS IN IMAGES OBTAINED WITH HIGH PURITY I-123

Abstract

High purity I-123 labeled agents have been used for imaging the brain and myocardium. Medium energy collimators give poor depth resolution and decreased sensitivity; images obtained with low energy collimators are degraded by septal penetration of the high energy photons. Two sets of images of a phantom were collected in a DEC PDP 11/34A computer interfaced to a singled-headed Siemens RotaCamera. The first set was obtained with a symmetrical window set on the photopeak at 159 keV. The second set was a subtraction mask obtained by setting a second analyzer window above the photopeak at approximately 200 keV. After applying a 2D Fourier smoothing filter the mask was subtracted from the photopeak data set. Reconstructed images of a Jaszczak phantom demonstrated a 20 to 25% increase in contrast with the subtraction technique. Reconstructed images of an Iowa Heart Phantom revealed an increase of approximately 75% in the contrast of the “myocardium” relative to the central cavity. The improvement in contrast in both phantoms was essentially the same for both Parzen and Shepp and Logan reconstruction filters but was dependent on the type of collimator used. This technique appears to be useful for improving the contrast in SPECT imaging of high purity I-123.