Splenic switch-off in [15O]H2O-PET myocardial perfusion imaging using parametric blood flow images.

BACKGROUND:Evaluation of sufficient adenosine response constitutes a significant challenge in myocardial perfusion imaging (MPI). Splenic switch-off in MPI studies denotes visually (qualitatively) reduced splenic radiotracer signal during adenosine stress and is considered indicative of sufficient cardiac vasodilation. In this study, we examined semi-quantitative and quantitative approaches to splenic switch-off assessment using [15O]H2O-PET with either summed activity images or calculated parametric splenic blood flow images. METHODS:Cohort 1: 90 clinical patients undergoing [15O]H2O MPI in whom adenosine response was considered clinically adequate were identified to characterize the corresponding splenic switch-off. Spleen stress/rest-ratio (SSR-ratio) was calculated as spleen stress signal intensity/spleen rest signal intensity on both summed activity and parametric blood flow images. COHORT 2: 25 patients with repeat MPI due to suspected insufficient adenosine response were identified to observe if splenic switch-off on initial MPI could predict the outcome of the repeat MPI. COHORT 3: 54 patients who were considered adenosine responders on MPI and who had a CAG follow-up within 3 months after MPI served as a separate validation group. RESULTS:Splenic switch-off was present in most patients with clinically sufficient adenosine response (Cohort 1) illustrated by both visual (74.4-86.7%), semi-quantitative (summed activity images) (85.6%) and quantitative (parametric blood flow images) (92.2%) evaluation which corresponds to the distribution in patients with sufficient adenosine response and follow-up CAG (Cohort 3) In patients suspected of insufficient adenosine response on the initial MPI (Cohort 2), the repeat MPI only yielded different MBF results if the initial SSR-ratio was > 0.90 on splenic parametric blood flow images. CONCLUSION:Quantitative splenic switch-off assessment on parametric blood flow images was superior to the semi-quantitative splenic switch-off approach. Patients with suspected insufficient initial adenosine response and SSR-ratio > 0.90 can benefit from a repeat MPI. Thus, integration of quantitative splenic switch-off using parametric blood flow images in evaluation of adenosine response may support future clinical decision-making.