Abstract
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Purpose: We aimed to assess normal reference values for quantified myocardial blood flow (MBF) on a hybrid PET/coronary-CT scanner and to test their diagnostic performance in patients with suspected coronary artery disease (CAD). Materials and Methods: Patients underwent sequential cardiac 82Rb-PET/CT (Siemens Biograph mCT) with stress/rest (Adenosine or Regadenoson) and integrated CT-based coronary angiography (CCTA). Patients were classified as normal (no stenosis on CCTA), with non-obstructive stenosis (<50% stenosis on CCTA) and with CAD (≥50% stenosis on CCTA). Stress MBF (sMBF), rest MBF (rMBF) and myocardial flow reserve (MFR) were calculated both globally and in each vascular territory by Syngo MBF (Siemens). On static PET images, ischemia was visually assessed and defined as SDS≥2, severe ischemia was defined as SDS≥7. Mann-Whitney-U test was used for comparison of non-parametric data across groups, ROC-analysis was performed to determine the diagnostic accuracy in identifying ischemia.Flow values are given in ml/g/min as mean±SD.
Results: Of overall 357 patients included, 153 patients were classified as normal, 99 as with non-significant stenosis and 105 as with CAD. Global sMBF and MFR were significantly higher in normal patients than in patients with CAD (3.61±0.71 vs. 3.04±0.77, p<0.0001; 3.08±0.84 vs. 2.68±0.79, p=0.0001), but were not significantly different compared to patients with non-obstructive stenosis (3.61±0.71 vs. 3.43±0.69, p=0.052; 3.08±0.84 vs. 2.99±0.82, p=0.45). rMBF in normal patients was not significantly different compared to patients with non-obstructive stenosis (1.27±0.40 vs. 1.24±0.36, p=0.70) and CAD (1.27±0.40 vs. 1.21±0.35, p=0.26). Global sMBF yielded superior accuracy in identifying myocardial ischemia using SDS≥2 over MFR (AUC 0.74 vs. 0.62, p=0.003) and in identifying severe ischemia using SDS≥7 (AUC 0.88 vs. 0.78, p=0.012). The superiority held true also over corrected MFR, wherein rMBF was corrected against rate-pressure product. Optimal threshold for global sMBF to detect myocardial ischemia was 3.5 ml/g/min (sensitivity 87.5%, specificity 48.7%, positive predictive value [PPV] 22%, negative predictive value [NPV] 96%).
Conclusions: Normal sMBF, rMBF and MFR values are provided for 82Rb-PET based on normal CCTA. To detect patients with ischemia, global sMBF provided higher diagnostic accuracy than MFR. Using sMBF-threshold of 3.5 ml/mg/min on 82Rb-PET/CT yielded similar NPV (96%) as CCTA to rule out CAD. Hence, resting scan could be omitted in patients with sMBF values above reference.
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