A simple quantitative method for assessment of multiple window spatial registration

Full text: When acquiring images using multiple analyser windows, it is important that the image from each window registers in the same spatial location to prevent image degradation through loss of spatial resolution. The NEMA performance standard measurement for multiple window spatial registration (MWSR), while only requiring a simple jig, requires specialized analysis software that is not normally available. We have developed a test that uses a simple jig that provides a quantitative assessment of MWSR using software analysis tools that are available on most gamma camera systems. A 50 mm thick lead brick with a slot cut along its long axis and a 'V' groove in the top is used as a jib. A vial of activity laid in the top groove is collimated by the brick and produces a line source of activity. A 67Ga line source image, acquired using three analyser windows, and a 99Tcm line source image are collected using the jig for 5000 k counts each into a 1024 image matrix. Line profiles are drawn across both images and the full width at half maximum (FWHM) of each profile determined. Tools for performing this analysis are widely available on camera systems. The ratio of the 67Ca to 99Tcm FWHM values b used as a quantitative indication of the MWSR for the camera. An average ratio of 1.05 has been observed for a Toshiba 901A/HC gamma camera over a 2 year period. We have taken a ratio of 1.10 as an action threshold above which camera adjustment is required