Adenosine-induced splenic switch-off on [¹⁵O]H₂O PET perfusion for the assessment of vascular vasodilatation

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 [¹⁵O]H₂O.

Thirty patients underwent [¹⁵O]H₂O 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].

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.

SSO can be quantified from [¹⁵O]H₂O 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 [¹⁵O]H₂O.