Regadenoson pharmacologic rubidium-82 PET: a comparison of quantitative perfusion and function to dipyridamole

Clinical implications of compromised 82Rb PET data acquisition

BACKGROUND

We wished to document the prevalence and quantitative effects of compromised 82Rb PET data acquisitions on myocardial flow reserve (MFR).

METHODS AND RESULTS

Data were analyzed retrospectively for 246 rest and regadenoson-stress studies of 123 patients evaluated for known or suspected CAD. An automated injector delivered pre-determined activities of 82Rb. Automated quality assurance algorithms identified technical problems for 7% (9/123) of patients. Stress data exhibited 2 instances of scanner saturation, 1 blood peak detection, 1 blood peak width, 1 gradual patient motion, and 2 abrupt patient motion problems. Rest data showed 1 instance of blood peak width and 2 abrupt patient motion problems. MFR was lower for patients with technical problems flagged by the quality assurance algorithms than those without technical problems (1.5 ± 0.5 versus 2.1 ± 0.7, P = 0.01), even though rest and stress ejection fraction, asynchrony and relative myocardial perfusion measures were similar for these two groups (P > 0.05), suggesting that MFR accuracy was adversely affected by technical errors.

CONCLUSION

It is important to verify integrity of 82Rb data to ensure MFR computation quality.

Left ventricular ejection fraction, myocardial blood flow and hemodynamic variables in adenosine and regadenoson vasodilator 82-Rubidium PET

AIMS

In most Rubidium-(Rb)-positron emission tomography (PET) studies, dipyridamole was used as vasodilator. The aim was to evaluate vasodilator PET left ventricular ejection fraction (LVEF), myocardial blood flow (MBF), hemodynamics, and the influence of adenosine and regadenoson on these variables.

METHODS AND RESULTS

Consecutive patients (N = 2299) with prior coronary artery disease (CAD) or no prior CAD undergoing adenosine/regadenoson 82Rb-PET were studied and compared according to CAD status and normal/abnormal PET (summed stress score 0-3 vs. ≥4). Rest and stress LVEF differed significantly depending on CAD status and scan results. In patients with no prior CAD, rest/stress LVEF were 68% and 72%, in patients with prior CAD 60% and 63%. LVEF during stress increased 5 ± 6% in normal compared to 1 ± 8% in abnormal PET (P<0.001). Global rest myocardial blood flow(rMBF), stress MBF(sMBF) and myocardial flow reserve (sMBF/rMBF) were significantly higher in no prior CAD patients compared to prior CAD patients(1.3 ± 0.5, 3.3 ± 0.9, 2.6 ± 0.8 and 1.2 ± 0.4, 2.6 ± 0.8, 2.4 ± 0.8 ml/g/min, respectively, P<0.001) and in normal versus abnormal scans, irrespective of CAD status(no prior CAD: 1.4 ± 0.5, 3.5 ± 0.8, 2.8 ± 0.8 and 1.2 ± 0.8, 2.5 ± 0.8, 2.2 ± 0.7; prior CAD: 1.3 ± 0.4, 3.1 ± 0.8, 2.7 ± 0.8 and 1.1 ± 0.4, 2.3 ± 0.7, 2.2 ± 0.7 ml/g/min, respectively, P<0.001). LVEF and hemodynamic values were similar for adenosine and regadenoson stress. Stress LVEF ≥70% excluded relevant ischemia (≥10%) with a negative predictive value (NPV) of 94% (CI 92-95%).

CONCLUSIONS

Rest/stress LVEF, LVEF reserve and MBF values are lower in abnormal compared to normal scans. Adenosine and regadenoson seem to have similar effect on stress LVEF, MBF and hemodynamics. A stress LVEF ≥70% has a high NPV to exclude relevant ischemia.

Activity regimes for 82Rb cardiac PET: Effects on absolute MBF and MPI

BACKGROUND

Selection of optimal tracer activity for 82Rb PET is based on a trade-off between necessary count-statistics in the late static phase and detector saturation in the early blood-pool phase. Administered tracer activity recommended in prescribing information differs substantially from recommendations in current literature. The present study examines the effect on both absolute myocardial blood flow (MBF), myocardial flow reserve (MFR) and relative myocardial perfusion imaging (MPI) of reducing dose.

METHODS

Forty patients were scanned twice on a PMT-based PET/CT (GE D690): At recommended activity (1110 MBq) and at either 740 or 370 MBq. MBF, MFR, total perfusion deficit (TPD) and ejection fractions (EF) were quantified. Results were compared using linear regression and Bland-Altman plots.

RESULTS

Linear correlation between MBF at 1110 MBq at either reduced activity had an R2 > 0.98. A small bias (± 5%-9%) was observed with opposite signs for 1110/740 and 1110/370. Limits of agreement for MBF were larger for 1110/370. MFR had a lower linear correlation (R2 = 0.96), but wide limits of agreement especially for 1110/370. TPD and EF correlated well at 1110/740 (R2 = 0.96 and 0.99, respectively), but large scatter was observed for 1110/370.

CONCLUSION

Reduction of the tracer activity to 740 MBq, significantly reduced dead-time correction factors, while still producing reliable static and gated images. However, despite large dead-time at 1110 MBq, no systematic bias on absolute MBF was observed compared to reduced activities.

Quantitative myocardial perfusion response to adenosine and regadenoson in patients with suspected coronary artery disease

BACKGROUND

The aim of the present study was to compare the quantitative flow responses of regadenoson against adenosine using cardiac 15O-water PET imaging in patients with suspected or known coronary artery disease (CAD).

METHODS

Hyperemic myocardial blood flow (MBF) after adenosine and regadenoson was compared using correlation and Bland-Altman analysis in 21 patients who underwent rest and adenosine 15O-water PET scans followed by rest and regadenoson 15O-water PET scans.

RESULTS

Global mean (± SD) MBF values at rest and stress were 0.92 ± 0.27 and 2.68 ± 0.80 mL·g·min for the adenosine study and 0.95 ± 0.29 and 2.76 ± 0.79 mL·g·min for the regadenoson study (P = 0.55 and P = 0.49). The correlations between global and regional adenosine- and regadenoson-based stress MBF were strong (r = 0.80 and r = 0.77). The biases were small for both global and regional MBF comparisons (0.08 and 0.09 mL·min·g), but the limits of agreement were wide for stress MBF.

CONCLUSION

The correlation between regadenoson- and adenosine-induced hyperemic MBF was strong but the agreement was only moderate indicating that established cut-off values for 150-water PET should be used cautiously if using regadenoson as vasodilator.

Regadenoson versus dipyridamole: Evaluation of stress myocardial blood flow response on a CZT-SPECT camera

BACKGROUND

Regadenoson is a selective adenosine receptor agonist. It is currently unclear if the level of hyperemia differs between stress agents. We compared Myocardial Blood Flow (MBF) and Myocardial Flow Reserve (MFR) response on CZT-SPECT Myocardial Perfusion Imaging (MPI) to evaluate if dipyridamole and regadenoson could induce the same level of hyperemia.

METHODS

228 patients with dynamic CZT-SPECT MPI were retrospectively analyzed (66 patients stressed with regadenoson and 162 with dipyridamole) in terms of MBF and MFR. To rule out confounding factors, two groups of 41 patients were matched for clinical characteristics in a sub-analysis, excluding high cardiovascular risk patients.

RESULTS

Overall stress MBF was higher in regadenoson patients (1.71 ± 0.73 vs. 1.44 ± 0.55 mL·min-1·g-1 for regadenoson and dipyridamole, respectively, p < .05). However, when confounding factors were ruled out, stress MBF (1.57 ± 0.56 vs. 1.61 ± 0.62 mL·min-1·g-1 for dipyridamole and regadenoson, respectively, p = .88) and MFR (2.62 ± 0.77 vs. 2.46 ± 0.76 for dipyridamole and regadenoson, respectively, p = .40) were not different between regadenoson and dipyridamole.

CONCLUSIONS

Our results suggest that dipyridamole and regadenoson induce equivalent hyperemia in dynamic SPECT with similar stress MBF and MFR in comparable patients.

Impact of regadenoson-induced myocardial creep on dynamic Rubidium-82 PET myocardial blood flow quantification

BACKGROUND

Repositioning of the heart during myocardial perfusion imaging (MPI) using Rubidium-82 (Rb-82) PET may occur when using regadenoson. Our aim was to determine the prevalence and the effect of correcting for this myocardial creep on myocardial blood flow (MBF) quantification.

METHODS

We retrospectively included 119 consecutive patients who underwent dynamic rest- and regadenoson-induced stress MPI using Rb-82 PET. The presence of myocardial creep was visually assessed in the dynamic stress PET series by identifying differences between the automatically drawn myocardium contour and the activity. Uncorrected and corrected stress MBFs were compared for the three vascular territories (LAD, LCX, and RCA) and for the whole myocardium.

RESULTS

Myocardial creep was observed in 52% of the patients during stress. Mean MBF values decreased after correction in the RCA from 4.0 to 2.7 mL/min/g (P  < 0.001), in the whole myocardium from 2.7 to 2.6 mL/min/g (P  = 0.01), and increased in the LAD from 2.5 to 2.6 mL/min/g (P  = 0.03) and remained comparable in the LCX (P  = 0.3).

CONCLUSIONS

Myocardial creep is a frequent phenomenon when performing regadenoson-induced stress Rb-82 PET and has a significant impact on MBF values, especially in the RCA territory. As this may hamper diagnostic accuracy, myocardial creep correction seems necessary for reliable quantification.

Comparative Performances of Dipyridamole and Regadenoson to Detect Myocardial Ischemia using Cardiac Cadmium-Zinc-Telluride Single-Photon Emission Computerized Tomography

Objective:

We evaluated the relative performances of dipyridamole (Dip) and regadenoson (Reg) in a cohort of patients referred for coronary artery disease diagnosis or follow-up using myocardial perfusion imaging.

Materials and Methods:

We retrospectively included 515 consecutive patients referred for ^99mTc-sestamibi myocardial perfusion single-photon emission computerized tomography (SPECT) on a cadmium-zinc-telluride (CZT) camera after pharmacologic stress. About three quarters (n = 391, 76%) received Dip. Reg was administrated to patients with chronical respiratory disease or with body mass index (BMI) over 38 kg/m² (n = 124, 24%). Patients with an abnormal stress scan (92%) underwent a rest imaging on the same day. Qualitative interpretation of perfusion images was achieved using QPS software, and the ischemic area was assessed using the 17-segment model. In patients undergoing a stress-rest protocol, perfusion polar plots were postprocessed using automated in-house software to quantify the extension, intensity, and location of the reversible perfusion defect. Statistical comparison between groups was performed using univariate and multivariate analysis.

Results:

Qualitative analysis concluded to myocardial ischemia in 70% of the patients (69% in the Dip group, 76% in the Reg group, P = ns). In those patients, the number of involved segments (Dip 2.5 ± 1.6, Reg 2.7 ± 1.6, P = ns) and the proportion of patients with an ischemic area larger than two segments (Dip 30%, Reg 37%, P = ns) were comparable. Automated quantification of the reversible perfusion defect demonstrated similar defect extension, intensity, and severity in the two groups. Defect location was identical at the myocardial segment and vascular territory scales.

Conclusions:

Reg and Dip showed equal performances for ischemic burden characterization using myocardial CZT SPECT.

Minimal starting time of data reconstruction for qualitative myocardial perfusion rubidium-82 positron emission tomography imaging

OBJECTIVE

Qualitative positron emission tomography (PET) myocardial perfusion imaging (MPI) scans are reconstructed with a delay after an injection of rubidium-82 (Rb) to ensure blood pool clearance and sufficient left ventricle to myocardium contrast. Our aim was to derive the minimal starting time of data reconstruction (STDR) after an injection of Rb for which the diagnostic value and image quality remained unaffected.

MATERIALS AND METHODS

We retrospectively included 23 patients who underwent rest-stress Rb PET MPI using 740 MBq. Patients fulfilling one of the two criteria indicating a slow blood pool clearance (ejection fraction <50% and/or cardiac output <3 l/min) were included in a consecutive manner. PET images using five different STDRs (1:15-2:15 min) were reconstructed and compared with reference images (STDR of 2:30 min). Differences in the summed rest score greater than or equal to 3 and total perfusion deficit greater than 3% were considered to significantly influence the diagnostic value. In addition, image quality was scored by two experts as not interpretable, inferior, adequate, or excellent.

RESULTS

The summed rest score differed greater than or equal to 3 from the reference in seven or more patients (≥30%) using STDR less than or equal to 2:00 min (P<0.02). STDR less than or equal to 1:30 min resulted in six or more patients (≥26%) with a total perfusion deficit difference greater than 3% (P<0.03).In addition, STDR less than or equal to 2:00 min resulted in a lower image quality (P<0.002) and STDR less than or equal to 2:15 min resulted in greater than or equal to two scans with noninterpretable image quality.

CONCLUSION

STDR less than or equal to 2:15 min resulted in lower diagnostic value or insufficient image quality for qualitative PET MPI using 740 MBq Rb. An STDR of 2:30 min can be considered for clinical adoption.

Minimizing rubidium-82 tracer activity for relative PET myocardial perfusion imaging

OBJECTIVES

Recommended rubidium-82 activities for relative myocardial perfusion imaging (MPI) using present-generation PET scanners may be unnecessarily high. Our aim was to derive the minimum activity for a reliable relative PET MPI assessment.

MATERIALS AND METHODS

We analyzed 140 scans from 28 consecutive patients who underwent rest-stress MPI-PET (Ingenuity TF). Scans of 852, 682, 511, and 341 MBq were simulated from list-mode data and compared with a reference scan using 1023 MBq. Differences in the summed rest score, total perfusion deficit, and image quality were obtained between the reference and each of the simulated rest scans. Combined stress-rest scans obtained at a selected activity of 682 MBq were diagnostically interpreted by experts and outcome was compared with the reference scan interpretation.

RESULTS

Differences in summed rest score more than or equal to 3 were found using 682, 511, and 341 MBq in two (7%), four (14%), and five (18%) patients, respectively. Differences in total perfusion deficit more than 7% were only found at 341 MBq in one patient. Image quality deteriorated significantly only for the 341 MBq scans (P<0.001). Interpretation of stress-rest scans did not differ between 682 and 1023 MBq scans.

CONCLUSION

A significant reduction in administered Rb-82 activity is feasible in relative MPI. An activity of 682 MBq resulted in reliable diagnostic outcomes and image quality, and can therefore be considered for clinical adoption.

Accuracy of 82Rb PET/CT Myocardial Perfusion Imaging with Regadenoson Stress, Including 3-Year Clinical Outcomes

The purpose of this study was to determine the clinical accuracy of ⁸²Rb PET/CT myocardial perfusion imaging (MPI) when performed with regadenoson stress in a U.S. Department of Veterans Affairs (VA) population of patients. Methods: The initial cohort of 480 patients undergoing vasodilator PET MPI with regadenoson stress at our institution from September 2009 through July 2010 was closely tracked for short-term outcomes based on correlation with invasive coronary catheterization. Long-term outcomes were determined by major adverse cardiac event rates based on data extraction from the electronic medical record and grouped by summed stress score (SSS) for a 3-y period. Results: At the 3-y follow-up, there had been 31 patient deaths, 5 of which were heart-related. Twenty-four patients had documented myocardial infarctions. Event rates and cardiac death rates were highly predicted by the results of PET MPI. Seventy patients underwent invasive cardiac catheterization within 60 d of the PET MPI. Patients were increasingly likely to undergo catheterization as their SSS increased. Catheterization correlation demonstrated a sensitivity of 95%, a positive predictive value of 88.4% for significant coronary artery disease, and an overall accuracy of 86% for PET MPI with regadenoson stress when compared with invasive catheterization. Conclusion: PET MPI with regadenoson stress demonstrates high accuracy when correlated with invasive catheterization and clinical outcomes. The SSS was highly predictive of cardiac events and patient survival in a VA population over a 3-y period of clinical follow-up.

Clinical use of quantitative cardiac perfusion PET: rationale, modalities and possible indications. Position paper of the Cardiovascular Committee of the European Association of Nuclear Medicine (EANM)

Until recently, PET was regarded as a luxurious way of performing myocardial perfusion scintigraphy, with excellent image quality and diagnostic capabilities that hardly justified the additional cost and procedural effort. Quantitative perfusion PET was considered a major improvement over standard qualitative imaging, because it allows the measurement of parameters not otherwise available, but for many years its use was confined to academic and research settings. In recent years, however, several factors have contributed to the renewal of interest in quantitative perfusion PET, which has become a much more readily accessible technique due to progress in hardware and the availability of dedicated and user-friendly platforms and programs. In spite of this evolution and of the growing evidence that quantitative perfusion PET can play a role in the clinical setting, there are not yet clear indications for its clinical use. Therefore, the Cardiovascular Committee of the European Association of Nuclear Medicine, starting from the experience of its members, decided to examine the current literature on quantitative perfusion PET to (1) evaluate the rationale for its clinical use, (2) identify the main methodological requirements, (3) identify the remaining technical difficulties, (4) define the most reliable interpretation criteria, and finally (5) tentatively delineate currently acceptable and possibly appropriate clinical indications. The present position paper must be considered as a starting point aiming to promote a wider use of quantitative perfusion PET and to encourage the conception and execution of the studies needed to definitely establish its role in clinical practice.

Quantitative myocardial perfusion PET parametric imaging at the voxel-level

Quantitative myocardial perfusion (MP) PET has the potential to enhance detection of early stages of atherosclerosis or microvascular dysfunction, characterization of flow-limiting effects of coronary artery disease (CAD), and identification of balanced reduction of flow due to multivessel stenosis. We aim to enable quantitative MP-PET at the individual voxel level, which has the potential to allow enhanced visualization and quantification of myocardial blood flow (MBF) and flow reserve (MFR) as computed from uptake parametric images. This framework is especially challenging for the (82)Rb radiotracer. The short half-life enables fast serial imaging and high patient throughput; yet, the acquired dynamic PET images suffer from high noise-levels introducing large variability in uptake parametric images and, therefore, in the estimates of MBF and MFR. Robust estimation requires substantial post-smoothing of noisy data, degrading valuable functional information of physiological and pathological importance. We present a feasible and robust approach to generate parametric images at the voxel-level that substantially reduces noise without significant loss of spatial resolution. The proposed methodology, denoted physiological clustering, makes use of the functional similarity of voxels to penalize deviation of voxel kinetics from physiological partners. The results were validated using extensive simulations (with transmural and non-transmural perfusion defects) and clinical studies. Compared to post-smoothing, physiological clustering depicted enhanced quantitative noise versus bias performance as well as superior recovery of perfusion defects (as quantified by CNR) with minimal increase in bias. Overall, parametric images obtained from the proposed methodology were robust in the presence of high-noise levels as manifested in the voxel time-activity-curves.

Regadenoson versus dipyridamole hyperemia for cardiac PET imaging

OBJECTIVES

The goal of this study was to compare regadenoson and dipyridamole hyperemia for quantitative myocardial perfusion imaging.

BACKGROUND

Regadenoson is commonly used for stress perfusion imaging. However, no study in nuclear cardiology has employed a paired design to compare quantitative hyperemic flow from regadenoson to more traditional agents such as dipyridamole. Additionally, the timing of regadenoson bolus relative to tracer administration can be expected to affect quantitative flow.

METHODS

Subjects underwent 2 rest/stress cardiac positron emission tomography scans using an Rb-82 generator. Each scan employed dipyridamole and a second drug in random sequence, either regadenoson according to 5 timing sequences or repeated dipyridamole. A validated retention model quantified absolute flow and coronary flow reserve.

RESULTS

A total of 176 pairs compared regadenoson (126 pairs, split unevenly among 5 timing sequences) or repeated dipyridamole (50 pairs). The cohort largely had few symptoms, only risk factors, and nearly normal relative uptake images, with 8% typical angina or dyspnea, 20% manifest coronary artery disease, and a minimum quadrant average of 80% (interquartile range: 76% to 83%) on dipyridamole scans. Hyperemic flow varied among regadenoson timing sequences but showed consistently lower stress flow and coronary flow reserve compared with dipyridamole. A timing sequence most similar to the regadenoson package insert achieved about 80% of dipyridamole hyperemia, whereas further delaying radiotracer injection reached approximately 90% of dipyridamole hyperemia. Because of the small numbers of pairs for each regadenoson timing protocol and a paucity of moderate or large perfusion defects, we did not observe a difference in relative uptake.

CONCLUSIONS

With the standard timing protocol from the package insert, regadenoson achieved only 80% of dipyridamole hyperemia quantitatively imaged by cardiac positron emission tomography using Rb-82. A nonstandard protocol using a more delayed radionuclide injection after the regadenoson bolus improved its effect to 90% of dipyridamole hyperemia.

Detection of obstructive coronary artery disease using regadenoson stress and 82Rb PET/CT myocardial perfusion imaging

Our objective was to study the diagnostic performance of regadenoson (82)Rb myocardial perfusion PET imaging to detect obstructive coronary artery disease (CAD).

METHODS

We studied 134 patients (mean age, 63 ± 12 y; mean body mass index, 31 ± 9 kg/m(2)) without known CAD (96 with coronary angiography and 38 with low pretest likelihood of CAD). Stress left ventricular ejection fraction (LVEF) minus rest LVEF defined LVEF reserve. The Duke score was used to estimate the anatomic extent of jeopardized myocardium.

RESULTS

Regadenoson PET had a high sensitivity, 92% (95% confidence interval [CI], 83%-97%), in detecting obstructive CAD, with a normalcy rate of 97% (95% CI, 86%-99%), specificity of 77% (54/70 patients; 95% CI, 66%-86%), and area under the receiver-operator-characteristic curve of 0.847 (95% CI, 0.774-0.903; P < 0.001). Regadenoson PET demonstrated high sensitivity to detect CAD in patients with single-vessel CAD (89%; 95% CI, 70%-98%). The mean LVEF reserve was significantly higher in patients with normal myocardial perfusion imaging results (6.5% ± 5.4%) than in those with mild (4.3 ± 5.1, P = 0.03) and moderate to severe reversible defects (-0.2% ± 8.4%, P = 0.001). Also, mean LVEF reserve was significantly higher in patients with a low likelihood of CAD (7.2% ± 4.5%, P < 0.0001) and mild or moderate jeopardized myocardium than in those with significant jeopardized myocardium (score ≥ 6), -2.8% ± 8.3%.

CONCLUSION

Regadenoson (82)Rb myocardial perfusion imaging is accurate for the detection of obstructive CAD. LVEF reserve is high in patients without significant ischemia or significant angiographic jeopardized myocardium.