Scatter correction by two-window method standardizes cardiac I-123 MIBG uptake in various gamma camera systems

Heart to mediastinum count ratio (H/M) has been commonly utilized as an indicator of myocardial I-123 MIBG uptake. However, normal ranges of H/M were markedly different among various gamma camera systems. The purpose of this study was to clarify whether scatter correction by two-window method standardizes H/M among various gamma camera systems. Scatter uncorrected and corrected MIBG imaging was acquired in phantom and human studies in combination with low energy high-resolution collimator (LEHR) and medium energy collimator (MEC). For scatter correction, energy window width of 159 keV±10% was applied to main window imaging and 193 keV±9.5% was applied to upper window imaging for scatter correction. In phantom study, a significant difference was observed in uncorrected H/M among three gamma camera systems using LEHR or MEC (2.09±0.06 vs. 2.58±0.03 in GCA7200 camera, 2.00±0.07 vs. 2.42±0.06 in DS7 camera and 2.16±0.04 vs. 2.67±0.07 in Vertex plus camera). However, there was no significant difference in corrected H/M among the three gamma camera systems, either with LEHR or MEC (2.70±0.07 vs. 2.69±0.07 in GCA7200 camera, 2.66±0.08 vs. 2.61±0.05 in DS7 camera and 2.66±0.05 vs. 2.61±0.05 in Vertex plus camera). In human study, uncorrected H/M in DS7 camera with LEHC was significantly lower than that in GCA7200 camera with MEC (1.60±0.37 vs. 1.85±0.54, N=14). In contrast, the difference was insignificant in corrected H/M (2.12±0.59 vs. 2.16±0.68). There was a very excellent correlation in corrected H/M between DS7 and GCA7200 cameras (r=0.991, p<0.001). This study demonstrated that scatter correction by the two-window method standardizes the H/M in MIBG scintigraphy either with LEHR or MEC. Scatter corrected H/M can be applied to measure a standardized parameter of MIBG uptake in human clinical studies using various gamma camera systems. (author)