Head to head comparison of N-13 ammonia and Rubidium-82 PET myocardial perfusion scans in subjects with no history of coronary artery disease (CAD)

Objectives To compare the qualitative interpretation of Rb-82 versus N-13 ammonia PET myocardial perfusion scans in subjects without documented CAD.

Methods 10 subjects (5 males and 5 female), age range: 40-49, participants in a prospective study designed to validate a software-based method to measure absolute myocardial blood flow, with no history of CAD were included in this study. Subjects had a negative exercise stress test (n=9) or a negative CT coronary angiogram (n=1) prior to PET scans. All subjects underwent Rb-82 and N-13 ammonia PET scans with dipyridamole stress. Both scans were interpreted by 3 physicians. Each segment in the polar map was assigned a severity score and a final overall interpretation was provided based on a 5-point scale (normal, probably normal, equivocal, probably abnormal, abnormal).

Results The mean stress summed score (SSS) for Rb-82 PET studies was 0.27 ± 0.97 and the mean stress difference score (SDS) was 0, compared to 2.53 ± 2.43 and 1.60 ± 1.90 for N-13 ammonia, respectively. These differences were statistically significant (p = 0.01 and p = 0.008, respectively). The SSS ratings for N-13 ammonia and Rb-82 PET were significantly different for two of the readers (p<0.001), with a trend towards significance for the third reader (p=0.16). There was complete agreement among 3 readers in 8/10 subjects with Rb-82 PET, compared to 2/10 for N-13 ammonia PET scans. The interpretation confidence was higher with Rb-82 with 4/30 reads reported as probably normal and the remaining 26 as normal, compared to 4 equivocal interpretations, 2 probably abnormal, 6 probably normal, 10 abnormal and 8 normal interpretations with N-13 ammonia. The majority of defects on N-13 ammonia PET scans were noted in the lateral/inferolateral wall.

Conclusions N-13 ammonia myocardial perfusion PET scans may show greater variability and a lower specificity than Rb-82 scans when assessed using conventional visual interpretation criteria.

Research Support Siemens Medical Solution