Preliminary Protocol for Measuring the Reproducibility and Accuracy of Flow values on Digital PET/CT Systems in [15O]H2O Myocardial Perfusion Imaging Using a Flow Phantom

Background: Several factors may decrease the accuracy of quantitative PET myocardial perfusion imaging (MPI). It is therefore essential to ensure that myocardial blood flow (MBF) values are reproducible and accurate, and to design systematic protocols for assessing this. Until now, no systematic phantom protocols have been available to assess the technical factors affecting measurement accuracy and reproducibility in MPI. Materials and Methods: We implemented a standard measurement protocol, which applies a flow phantom in order to compare image-derived flow values with respect to a ground truth flow value with [15O]H2O MPI performed on both a Discovery MI (DMI-20, GE Healthcare) and a Biograph Vision 600 (Vision-600, Siemens Healthineers) system. Both systems have automatic [15O]H2O radio water generators (Hidex Oy) individually installed, allowing us to also study the differences occurring due to two different bolus delivery systems. To investigate the technical factors contributing to the modelled flow values, we extracted the [15O]H2O bolus profiles, the flow values from the kinetic modeling (Qin and Qout), and finally calculated their differences between test-retest measurements on both systems. Results: The input time activity curves (TAC) showed dependency on the bolus injection curves. The measurements performed on the DMI-20 system produced Qin and Qout values equal to each other as well as to the reference flow value across all test-retest measurements. Also, all DMI-20 repeatability differences were below 15 %. The measurements performed on the Vision-600 system showed more variation between Qin and Qout values across test-retest measurements and exceeded the 15 % difference in half (6/12) of the measurements. Conclusions: This preliminary study proposes a protocol for measuring the accuracy and reproducibility of flow between different injector and PET systems. Our results suggest that flow values can be reproduced on DMI-20 or Vision-600 systems and with two different injector systems, with less than 15 % error. The most significant factor contributing to the variation was the injected bolus, which directly affects the phantom input TAC. In order to extend the protocol to a multi-center setting, a standardized and repeatable bolus injection protocol needs to be designed.