Diagnostic Value of ¹³N-Ammonia Myocardial Perfusion PET: Added Value of Myocardial Flow Reserve

Abstract

The ability to obtain quantitative values of flow and myocardial flow reserve (MFR) has been perceived as an important advantage of PET over conventional nuclear myocardial perfusion imaging (MPI). We evaluated the added diagnostic value of MFR over MPI alone as assessed with 13 N-ammonia and PET/CT to predict angiographic coronary artery disease (CAD). Methods: Seventy-three patients underwent 1-d adenosine stress-rest 13 N-ammonia PET/CT MPI, and MFR was calculated. The added value of MFR as an adjunct to MPI for predicting CAD (luminal narrowing $ 50%) was evaluated using invasive coronary angiography as a standard of reference. Results: Per patient, the sensitivity, specificity, positive predictive value, negative predictive value, and accuracy of MPI for detecting significant CAD were 79%, 80%, 91%, 59%, and 79%, respectively. Adding a cutoff of less than 2.0 for global MFR to MPI findings improved the values to 96% (P , 0.005), 80%, 93%, 89% (P , 0.005), and 92% (P , 0.005), respectively. Conclusion: The quantification of MFR in 13 N-ammonia PET/CT MPI provides a substantial added diagnostic value for detection of CAD. Particularly in patients with normal MPI results, quantification of MFR helps to unmask clinically significant CAD.Key Words: myocardial flow reserve; 13 N-ammonia; positron emission tomography; diagnostic value; myocardial perfusion imaging Nucl Med 2012; 53:1230 53: -1234 53: DOI: 10.2967 The PET technique confers advantages over SPECT related to improved image resolution and intrinsic attenuation correction (1). In addition, in myocardial perfusion imaging (MPI) PET offers quantitative assessment of myocardial blood flow (MBF) at rest and pharmacologic stress allowing calculation of myocardial flow reserve (MFR) (2). The latter is an index to evaluate blood circulation from the epicardial coronary arteries down to the microcirculation (3), which therefore provides functional information far beyond the epicardial section of the coronary vascular tree. Relative MPI such as SPECT (or PET without quantitative measurement) relies on induction of flow heterogeneities by hyperemic stress, which may sometimes underestimate the extent of coronary artery disease (CAD), as only the most severely underperfused territory may be evidenced (4). By contrast, absolute flow and MFR may reveal the true extent of CAD even at an early stage of subclinical atherosclerotic CAD. This possibility is supported by recent results documenting an added prognostic value for MFR over PET MPI alone with either 13 N-ammonia (5) or 82 Rb (6,7). Interestingly, MFR remained predictive throughout a 10-y follow-up period (5). Although many studies have revealed a reversed correlation of increasing coronary artery lesion narrowing with decreasing hyperemic flow and MFR in the respective myocardial territory (8-10), its diagnostic added value over MPI PET has not been assessed systematically. JWe evaluated the hypothesis that patients with decreased MFR (,2.0) would have a higher probability of CAD and that, thus, MFR would co...

Myocardial Blood Flow and Flow Reserve in Proximal and Mid-to-Distal Lesions of Left Anterior Descending Artery Measured By N-13 Ammonia PET/CT

“…However, the exact effects of hemodynamic change in multi-vessel disease on findings of MPI are yet to be completely known and should be studied in the future. The MBF heterogeneity might affect the regional MFR we investigated as concerned by some reports [10,28]. In this study the regional MFR was generally lower in pLAD stenosis throughout the LAD territory compared with mdLAD stenosis with two exceptions (segments 2 and 17), indicating its diagnostic implication in CAD.…”

Clinical Quantification of Myocardial Blood Flow Using PET: Joint Position Paper of the SNMMI Cardiovascular Council and the ASNC

“…Stress-first or stress-only imaging is feasible, but it is not routine practice with quantitative PET. Although several studies have suggested that peak hyperemic MBF is superior to MFR, [45][46][47] most studies have concluded that MFR is more powerful for risk stratification, [48][49][50][51][52][53] perhaps because of decreased variability compared with peak hyperemic MBF. 54 Whether postischemic stunning affects resting MBF with stressfirst imaging has not been well studied.…”

Absolute myocardial blood flow quantification with SPECT/CT: Is it possible?

“…2 This is compensated for to some extent by a higher retention and less flow-dependent nature of this tracer, as compared to Tl-201. 2 The Tc-99m MIBI extraction fraction is also much lower than the extraction fraction of PET tracers such as N-13 ammonia. 12,13 Nevertheless, when the extraction fraction of Tc99m MIBI (Fig.…”

“…They have been shown to provide clinically useful information beyond that provided by the assessment of relative perfusion defects in a variety of ways. These variables can potentially identify multivessel coronary artery disease (CAD) and predict the extent of disease more accurately than relative quantification or visual analysis of myocardial perfusion imaging (MPI), 1,2 which are the clinical standards today. The ability to quantify absolute MBF with stress MPI may permit improved identification of patients in whom the relative regional distribution of tracer may appear normal because of a balanced reduction of blood flow.…”