Agreement between quantitative Rubidium-82 and Oxygen-15 water PET myocardial perfusion imaging on absolute myocardial blood flow and myocardial flow reserve
Authors: Soeby J H , Rasmussen L D , Mortensen J , Tolbod L P , Winther S , Bottcher M 
Published: June 2024

Abstract

Background
In stable chest pain patients, Rubidium-82 (82Rb) is commonly used for myocardial perfusion imaging (MPI) and allows for quantification of myocardial blood flow (MBF) and myocardial flow reserve (MFR). With increasing implementation, an alternative is [15O]H2O PET MPI, which has optimal tracer kinetics. However, the level of agreement on MBF and MFR between 82Rb and [15O]H2O PET is sparsely elucidated.

Purpose
To examine the agreement between 82Rb and [15O]H2O PET in the measurement of MBF and MFR.

Methods
This is a prospective cohort study conducted at a single hospital. By protocol, consecutive patients referred for clinically indicated routine 82Rb PET MPI underwent additional and subsequent [15O]H2O PET MPI during the same outpatient visit. Quantitative measurements of MBF and MFR were obtained using Syngo.PET for 82Rb PET with correction for non-linear extraction (1) and Carimas CE for [15O]H2O PET. Quantitative MBF and MFR measures were compared using Bland-Altman analysis.

Results
Forty-five patients were included from February to March 2023 with a mean time between 82Rb stress procedure to [15O]H2O rest procedure of 25 minutes (SD 9 minutes). In total, 44 paired rest, 40 paired stress, and 39 paired rest and stress procedures were available for statistical analyses. A lower rate-pressure product (RPP) (mean difference -335 mmHg x bpm, 95% CI -625 to -46) was observed during the 82Rb procedure vs. the [15O]H2O procedure, while other hemodynamic parameters were similar. Rest MBF was normalised to a RPP of 8000 mmHg x bpm.
The mean global rest MBF was 1.1 (SD 0.3) ml/g/min as measured by 82Rb PET versus 0.8 (SD 0.2) ml/g/min by [15O]H2O PET, yielding a mean difference of 0.3 ml/g/min (95% CI 0.1-0.3) and 95% limits of agreement (LoA) of -0.2 to 0.8 ml/g/min (Figure 1A+B). The mean global stress MBF was 2.1 (SD 0.7) ml/g/min as measured by 82Rb PET versus 2.5 (SD 0.9) ml/g/min by [15O]H2O PET, yielding a mean difference of -0.3 ml/g/min (95% CI -0.5 to -0.1) and 95% LoA of -1.6 to 0.9 ml/g/min (Figure 1C+D). The mean global MFR was 1.9 (SD 0.6) as measured by 82Rb PET versus 3.1 (SD 0.9) by [15O]H2O PET, yielding a mean difference of -1.1, (95% CI -1.4 to -0.9).
The median ratio of global MFR measured by 82Rb PET versus [15O]H2O PET was 0.63 (95% CI 0.58-0.68), corresponding to a relative difference of 37% lower (95% CI 32-42) global MFR by 82Rb PET vs. [15O]H2O PET. The 95% LoA of the ratio of global MFR measured by 82Rb PET versus [15O]H2O PET was (0.38-1) corresponding to 95% LoA of the relative difference of 52% lower to 3% higher (Figure 2C+D).

Conclusion
Compared with [15O]H2O PET, 82Rb PET overestimates global MBF at rest, underestimates global MBF at stress, and underestimates global MBFR, despite correction for non-linear extraction. The tracers had wide limits of agreement on MBF and MFR. Caution should be taken in direct comparisons of MBF and MFR obtained by these two tracers.