Analysis of the intrinsic spatial resolution for the Stockholm University Karolinska Hospital cylindrical SPECT camera

The experimental results of measurements of the intrinsic spatial resolution of the Stockholm University Karolinska Hospital Cylindrical SPECT camera are presented. The camera is built up around a monolithic 12.5 mm thick NaI(Tl) crystal. It has 72 hexagonal 60 mm PM tubes mounted directly on the light guide. Each PM-signal is acquired and treated individually. Calibration data was taken using a 1 mm collimated Tc-99m point source successively positioned at points forming rectangular grids. Assessments of event positions were performed by centroid (Anger), and Maximum Likelihood (ML) methods. A statistical comparison of the results by the two methods was performed over two grids; one 12 mm square with 1 mm spacing of the grid points, and another 36 mm square with 6 mm between grid points. Both grids were centred over one PM-tube. The centroid data was properly re-mapped by an inverse distortion field operation. The ML estimator was based on the underlying multinomial statistics for 7-tuples as light collecting units. Polynomial and spline interpolation between calibration points was evaluated and compared for the ML method. The measured resolution (FWHM) obtained was 3.41 +/- 0.23 mm and 3.58 +/- 0.20 mm in the X and Y directions, respectively, when corrected for the 1 mm aperture of the source.