Original ArticleImpact of point spread function modeling and time-of-flight on myocardial blood flow and myocardial flow reserve measurements for rubidium-82 cardiac PET
Introduction
The benefits of myocardial perfusion imaging with rubidium-82 (Rb-82) and positron emission tomography (PET) compared with single photon emission tomography (SPECT) have been widely reported.1,2 A key advantage of Rb-82 cardiac PET is the ability to measure myocardial blood flow (MBF) at rest and stress and, consequently, calculate myocardial flow reserve (MFR)3 with high repeatability and reproducibility across operators and multi-vendor software.4, 5, 6 MFR has particular value in the detection of multi-vessel or balanced three-vessel coronary artery disease (CAD)7 and in predicting outcome in patients assessed for ischaemia.8 However, like attenuation-corrected SPECT cardiac imaging, Rb-82 cardiac PET is prone to artifacts due to mis-registration,9 which have been shown to produce errors in MFR measurements.10 Time-of-flight (TOF) PET has been shown to potentially offer increased resilience to mis-registration artifacts.11,12 Furthermore, advanced PET reconstructions with point spread function (PSF) modeling and TOF have been shown, in many studies, to offer considerable benefits in FDG oncology studies.13, 14, 15 By contrast, the number of studies that have investigated the impact of these reconstructions on Rb-82 cardiac PET is far smaller.16, 17, 18 These studies do show some benefits but the complete impact on all aspects, including kinetic analysis, of Rb-82 cardiac PET has yet to be determined. This is relevant because it has been shown, in dynamic brain imaging, that reconstructions with PSF modeling have a significant impact on the image-derived blood input function (BIF).19 The BIF is a key factor in the determination of MBF and changes influence the measurement20 and hence the calculation of MFR. With the assumption that PSF modeling and TOF reconstructions should offer advantages in Rb-82 cardiac PET, in terms of image quality, the rationale of this study was to determine the impact of these algorithms on MBF and MFR measurements in Rb-82 cardiac PET.
Section snippets
Patient study group
Forty consecutive patients referred for assessment of CAD with Rb-82 cardiac PET were retrospectively selected for inclusion in this study. All data were fully anonymised before analysis. After inspection of dynamic data, three patients were excluded: one for poor myocardial segmentation in the MBF processing software and two for excessive movement during the stress acquisition. The remaining 37 patients consisted of 26 males (mean [range] age: 63.1 year [35–90]; mean [range] weight: 83.4 kg
BIF area under curve
Figure 1(A) shows the BIF TAC for a single patient at rest and stress. It can be seen from the plot that the structure of the TACs are very similar for rest and stress. Performing the Mann-Whitney test on the BIF AUC for rest against stress data in either reconstruction showed no significant difference between the two data sets. As such, BIF AUC data were analyzed as a single group irrespective of whether they were from the rest or stress acquisitions. The plot of the average ratio of
Discussion
We believe that this is only the second study to investigate the use of advanced PET reconstructions with PSF modeling and TOF in Rb-82 cardiac PET and the first to evaluate their impact on MBF and MFR for dynamic data. The work has shown that MFR measurements appear to be robust for the two reconstruction algorithms. However, we noted a considerable variability in the relative changes seen for MBF between the two reconstructions (Fig. 5(A) and 5(B)). In addition, substantial increases in MBF,
Conclusion
This preliminary study has indicated that myocardial flow reserve measurements from dynamic rubidium-82 dynamic PET appear to be robust when generated by standard or advanced PET reconstruction algorithms with PSF modeling and TOF. Differences in MBF values were seen, possibly due to reductions in partial volume effects, which warrant further investigation, supported by additional anatomical imaging such as contrast-enhanced CT or cardiac MR. Potential improvements in the robustness of the
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