Adenosine-induced splenic switch-off on [(15)O]H(2)O PET perfusion for the assessment of vascular vasodilatation

BACKGROUND: Splenic switch-off (SSO) is a marker of adequate adenosine-induced vasodilatation on cardiac magnetic resonance perfusion imaging. We evaluate the feasibility of quantitative assessment of SSO in myocardial positron emission tomography (PET) perfusion imaging using [(15)O]H(2)O. METHODS: Thirty patients underwent [(15)O]H(2)O PET perfusion with adenosine stress. Time-activity curves, as averaged standardized uptake values (SUV(avg)), were extracted from dynamic PET for spleen and liver. Maximum SUV(avg), stress and rest spleen-to-liver ratio (SLR), and the splenic activity concentration ratio (SAR) were computed. Optimal cut-off values for SSO assessment were estimated from receiver operating characteristics (ROC) curve for maximum SUV(avg) and SLR. Also, differences between coronary artery disease, myocardial ischemia, beta-blockers, and diabetes were assessed. Data are presented as median [interquartile range]. RESULTS: In concordance with the SSO phenomenon, both the spleen maximum SUV(avg) and SLR were lower in adenosine stress when compared to rest perfusion (8.1 [6.5, 9.2] versus 16.4 [13.4, 19.0], p < 0.001) and (0.81 [0.63, 1.08] versus 1.86 [1.73, 2.06], p < 0.001), respectively. During adenosine stress, the SSO effect was most prominent 40–160 s after radiotracer injection. Cut-off values of 12.6 and 1.57 for maximum SUV(avg) and SLR, respectively, were found based on ROC analysis. No differences in SAR, SLR(Rest), or SLR(Stress) were observed in patients with coronary artery disease, myocardial ischemia, or diabetes. CONCLUSIONS: SSO can be quantified from [(15)O]H(2)O PET perfusion and used as a marker for adequate adenosine-induced vasodilatation response. In contrary to other PET perfusion tracers, adenosine-induced SSO is time dependent with [(15)O]H(2)O.