Correcting spatial distortion and non-uniformity in planar images from γ-Camera systems

In this work a correction method for the spatial distortion and non-uniformity of planar images is presented. It is based on an event-by-event correction algorithm suitable for images obtained from small Field of View (FOV) γ-Camera systems which are equipped with a Position Sensitive PhotoMultiplier Tube (PSPMT). In our study, the γ-Camera system consists of a 3 inch PSPMT with a 16X+16Y crossed wire anode (Model R2486, HAMAMATSU), a 4mm pixelated CsI(Tl) crystal (pixel-width 1mm) and a parallel (hexagonal) hole collimator. The correction of the spatial distortion is based on lookup tables with the coordinates of well defined reference points which are selected during the calibration phase of the system. The reference points are the centres of predefined pixels, well distinguishable at the planar image using a small laboratory 60Co source without collimation. The applied algorithm incorporates 2D-interpolation techniques and has been developed on a full automated graphics environment making use of the HIGZ (High Level Interface to Graphics and Zebra) program libraries from CERN. Both correction methods for the spatial distortion and non-uniformity have been applied to planar images obtained from small capillary phantoms filled with water solution of 99mTc. The method is also extended to tomographic images and the observed SPECT improvement in resolution is discussed.