Internal validation of myocardial flow reserve PET imaging using stress/rest myocardial activity ratios with Rb-82 and N-13-ammonia

Abstract

Background: Myocardial flow reserve (MFR) measurement provides incremental diagnostic and prognostic information. The objective of the current study was to investigate the application of a simplified model for the estimation of MFR using only the stress/rest myocardial activity ratio (MAR) in patients undergoing rest-stress cardiac PET MPI.

Methods and results: Rest and dipyridamole stress dynamic PET imaging was performed in consecutive patients using ⁸²Rb or ¹³NH₃ (n = 250 each). Reference standard MFR was quantified using a standard one-tissue compartment model. Stress/rest myocardial activity ratio (MAR) was calculated using the LV-mean activity from 2 to 6 minutes post-injection. Simplified estimates of MFR (MFR_EST) were then calculated using an inverse power function. For ¹³NH₃, there was good correlation between MFR and MFR_EST values (R = 0.63), with similar results for ⁸²Rb (R = 0.73). There was no bias in the MFR_EST values with either tracer. The overall diagnostic performance of MFR_EST for detection of MFR < 2 was good with ROC area under the curve (AUC) = 83.2 ± 1.2% for ¹³NH₃ and AUC = 90.4 ± 0.7% for ⁸²Rb.

Conclusion: MFR was estimated with good accuracy using ⁸²Rb and ¹³NH₃ with a simplified method that relies only on stress/rest activity ratios. This novel approach does not require dynamic imaging or tracer kinetic modeling. It may be useful for routine quality assurance of PET MFR measurements, or in scanners where full dynamic imaging and tracer kinetic modeling is not feasible for technical or logistical reasons.

Keywords: Cardiac PET; Flow quantification; Flow reserve.