Multiple Window Spatial Registration: Failure of the NEMA Standard to Adequately Quantitate Image Misregistration with Gallium-67

Abstract

Multiple window spatial registration (MWSR) characterizes positional deviations in a gamma camera as a function of gamma ray energy. Good MWSR is important for imaging with gallium-67 (⁶⁷Ga) and indium-111 (¹¹¹In). We evaluated the MWSR of three gamma cameras using ⁶⁷Ga. Measurements were made using the National Electrical Manufacturers Association (NEMA) technique. The MWSR accuracy was measured in multiple locations along the x and y axis of the gamma camera. For all three gamma cameras, the MWSR was within the manufacturer’s specification at locations corresponding to 75% of the useful field of view (UFOV). However at other locations, all cameras had misregistration errors outside the manufacturer’s specification. The magnitude of these misregistration errors was regional in nature and did not correlate with distance from the center of the field of view. These findings indicate that the current NEMA protocol for measurement of MWSR does not reflect the true degree of misregistration over the UFOV of gamma cameras.