SPECT imaging using single isotope corrections

Abstract

Commonly, Gamma Camera utilizes the signals from Photomultiplier Tubes (PMT) to determine the absorption point of incident gamma photons. These positions require a linearity correction to overcome the distortions introduced by the PMTs themselves. Following linearity, a uniformity correction is applied to correct the residual non-linearity and crystal intrinsic non-uniformity. The linearity and uniformity corrections are energy dependent and thus calibrations at several energies, using various isotopes, are usually performed. The corrections used in imaging utilize the calibration carried out at the closest energy. The linearity and uniformity calibrations procedures are frequently repeated at sites (i.e., in the case of changing of a PMT). Commonly, separate linearity and uniformity maps are created for each isotope. Difficulty results since the map creations themselves are long procedures that require having each of the isotopes on site. The current work presents a method to simplify the linearity and uniformity calibration procedure by performing the calibrations for a single isotope only. The linearity and uniformity corrections for all energies are based on the “single” isotope calibration and pre-acquired relative difference data. In case of the linearity correction the pre-acquired data are generic for the detector design, whereas for the case of the uniformity correction the pre-acquired data include acquisition of uniformity maps for several isotopes per system during manufacturing. In this study we demonstrate that a single isotope calibration is sufficient to achieve good image quality for various isotopes. Mechanisms of introducing non-linearity and non-uniformity, such as PMTs replacements are simulated. Single linearity and uniformity maps are created and images, acquired with different isotopes, corrected using the suggested concept, are evaluated. The image quality achieved for the various isotopes is similar to the image quality obtained using specific isotope calibrations.