In order to estimate the spatial resolution of the gamma-Camera system in planar imaging, capillaries with inner diameter of 1.1mm filled with ^99mTc-solution and placed at 2mm distances from each other have been used. Planar images obtained by positioning the camera close to the capillary phantoms reveal a 1.5mm spatial system resolution. For the evaluation of the system sensitivity to activity variations, a special phantom filled with ^99mTc-solutions of relative activity ratios 1:2:3:4:5:6:7:8 has been used (Fig. 1). The spatial resolution has been estimated in tomographic mode as well (See paper Comp.Med.Imag. 27 (2003) 307 by G. Loudos et al. ).

Fig. 1: Measured Planar and Tomographic spatial resolution of the IASA gamma-Camera

The gamma-Camera system is equipped with homogeneous and pixelated CsI(Tl) and BGO scintillation crystals of various sizes. This picture shows a pixelated CsI(Tl) scintillation crystal (Diameter: 48mm, Thickness: 4mm) with 1mm pixel size and epoxy spacer (0.1 mm) suitable for the detection of the 140 keV gamma-rays emitted from 99mTc-sources.

A new algorithm for the correction of the spatial distortion in the planar images has been developed in our laboratory. This technique is based on 2-dimensional interpolation algorithms using a reference table with well predefined nominal coordinates which are selected during the calibration phase of the system for a given set of collimator and scintillation crystal. A typical result of this correction is shown in Fig. 2.

Fig. 2: Uncorrected (left) and corrected (right) projection image of the 4mm CsI(Tl) pixelated scintillation crystal irradiated with a 60Co source without collimator.

More details on the correction of the spatial distortion in planar images for pixelated crystals can be found in the ITBS 2007 talk (by D. Thanasas et al. ) and in the papers Jinst 4 P06012 and IEEE-MIC09 M05-208 (D. Thanasas et al. ).