Review: comparison of PET rubidium-82 with conventional SPECT myocardial perfusion imaging

PET Imaging of Metabolism, Perfusion, and Hypoxia: FDG and Beyond

ABSTRACT

Imaging glucose metabolism with [18F]fluorodeoxyglucose positron emission tomography has transformed the diagnostic and treatment algorithms of numerous malignancies in clinical practice. The cancer phenotype, though, extends beyond dysregulation of this single pathway. Reprogramming of other pathways of metabolism, as well as altered perfusion and hypoxia, also typifies malignancy. These features provide other opportunities for imaging that have been developed and advanced into humans. In this review, we discuss imaging metabolism, perfusion, and hypoxia in cancer, focusing on the underlying biology to provide context. We conclude by highlighting the ability to image multiple facets of biology to better characterize cancer and guide targeted treatment.

Cardiovascular positron emission tomography: established and emerging role in cardiovascular diseases

Cardiac positron emission tomography (PET) imaging has established themselves firmly as excellent and reliable functional imaging modalities in assessment of the spectrum of coronary artery disease. With the explosion of technology advances and the dream of flow quantification now a reality, the value of PET is now well realized. Cardiac PET has proved itself as precise imaging modality that provides functional imaging of the heart in addition to anatomical imaging. It has established itself as one of the best available techniques for evaluation of myocardial viability. Hybrid PET/computed tomography provides simultaneous integration of coronary anatomy and function with myocardial perfusion and metabolism, thereby improving characterization of the dysfunctional area and chronic coronary artery disease. The availability of quantitative myocardial blood flow evaluation with PET provides additional prognostic information and increases diagnostic accuracy in the management of patients with coronary artery disease. Hybrid imaging seems to hold immense potential in optimizing management of cardiovascular diseases and furthering clinical research.

Cost-effectiveness of 82-Rubidium PET myocardial perfusion imaging for the diagnosis of myocardial ischemia depending on the prevalence of coronary artery disease

BACKGROUND

82-Rubidium-Positron emission tomography myocardial perfusion imaging (Rb-PET-MPI) offers higher diagnostic performance for the detection of myocardial ischemia compared to Tc-SPECT-MPI. The aim of this economic evaluation was to perform a cost-effectiveness analysis of Rb-PET-MPI versus Tc-SPECT-MPI in patients with suspected myocardial ischemia according to pretest probabilities (PTP) of obstructive coronary artery disease based on the results of the RUBIS Trial.

METHODS

Costs and effectiveness were calculated for all patients over 1 year and an incremental analysis of differences in costs and effectiveness in terms of diagnostic accuracy was performed. The uncertainty of the results was estimated using bootstrap. The analysis was conducted from the perspective of the French health care system with a time horizon of 12 months.

RESULTS

The average cost of a Rb-PET-MPI-based strategy for the detection of myocardial ischemia was €219 lower than a SPECT-MPI-based strategy (€1192 (± 1834) vs €973 (± 1939), p < 0.01). The one-year incremental cost-effectiveness ratio was negative: - €2730 (money saved per additional accurate diagnosis) in patients presenting PTP > 15% for the Rb-PET-MPI vs. Tc-SPECT-MPI strategy. Analysis of the joint distribution of costs and outcomes found that the Rb-PET-MPI strategy had a 92% probability to be dominant (cost-saving and outcome-improving).

CONCLUSIONS

Rb-PET-MPI is cost-effective compared to Tc-SPECT-MPI for the detection of myocardial ischemia in patients with PTP > 15% of obstructive coronary artery disease.

TRIAL REGISTRATION

RUBIS Trial registration: NCT01679886, Registered 03 September 2012, https://clinicaltrials.gov/ct2/show/NCT01679886 .

A highly predictive cardiac positron emission tomography (PET) risk score for 90-day and one-year major adverse cardiac events and revascularization

BACKGROUND

With the increase in cardiac PET/CT availability and utilization, the development of a PET/CT-based major adverse cardiovascular events, including death, myocardial infarction (MI), and revascularization (MACE-Revasc) risk assessment score is needed. Here we develop a highly predictive PET/CT-based risk score for 90-day and one-year MACE-Revasc.

METHODS AND RESULTS

11,552 patients had a PET/CT from 2015 to 2017 and were studied for the training and development set. PET/CT from 2018 was used to validate the derived scores (n = 5049). Patients were on average 65 years old, half were male, and a quarter had a prior MI or revascularization. Baseline characteristics and PET/CT results were used to derive the MACE-Revasc risk models, resulting in models with 5 and 8 weighted factors. The PET/CT 90-day MACE-Revasc risk score trended toward outperforming ischemic burden alone [P = .07 with an area under the curve (AUC) 0.85 vs 0.83]. The PET/CT one-year MACE-Revasc score was better than the use of ischemic burden alone (P < .0001, AUC 0.80 vs 0.76). Both PET/CT MACE-Revasc risk scores outperformed risk prediction by cardiologists.

CONCLUSION

The derived PET/CT 90-day and one-year MACE-Revasc risk scores were highly predictive and outperformed ischemic burden and cardiologist assessment. These scores are easy to calculate, lending to straightforward clinical implementation and should be further tested for clinical usefulness.

Second-Line Myocardial Perfusion Imaging to Detect Obstructive Stenosis: Head-to-Head Comparison of CMR and PET

BACKGROUND

Guidelines recommend verification of myocardial ischemia by selective second-line myocardial perfusion imaging (MPI) following a coronary computed tomography angiography (CTA) with suspected obstructive coronary artery disease (CAD). Head-to-head data on the diagnostic performance of different MPI modalities in this setting are sparse.

OBJECTIVES

The authors sought to compare, head-to-head, the diagnostic performance of selective MPI by 3.0-T cardiac magnetic resonance (CMR) and ⁸²rubidium positron emission tomography (RbPET) in patients with suspected obstructive stenosis at coronary CTA using invasive coronary angiography (ICA) with fractional flow reserve (FFR) as reference.

METHODS

Consecutive patients (n = 1,732, mean age: 59.1 ± 9.5, 57.2% men) referred for coronary CTA with symptoms suggestive of obstructive CAD were included. Patients with suspected stenosis were referred for both CMR and RbPET and subsequently ICA. Obstructive CAD was defined as FFR ≤0.80 or >90% diameter stenosis by visual assessment.

RESULTS

In total, 445 patients had suspected stenosis on coronary CTA. Of these, 372 patients completed both CMR, RbPET and subsequent ICA with FFR. Hemodynamically obstructive CAD was identified in 164 of 372 (44.1%) patients. Sensitivities for CMR and RbPET were 59% (95% CI: 51%-67%) and 64% (95% CI: 56%-71%); P = 0.21, respectively, and specificities 84% (95% CI: 78%-89%) and 89% (95% CI: 84%-93%]); P = 0.08, respectively. Overall accuracy was higher for RbPET compared with CMR (73% vs 78%; P = 0.03).

CONCLUSIONS

In patients with suspected obstructive stenosis at coronary CTA, CMR, and RbPET show similar and moderate sensitivities but high specificities compared with ICA with FFR. This patient group represents a diagnostic challenge with frequent mismatch between advanced MPI tests and invasive measurements. (Danish Study of Non-Invasive Diagnostic Testing in Coronary Artery Disease 2 [Dan-NICAD 2]; NCT03481712).

Added value of coronary artery calcium score in the reporting of SPECT versus PET myocardial perfusion imaging

BACKGROUND

Knowledge of coronary artery calcium score (CACS) influences the interpretation of myocardial perfusion imaging (MPI) with SPECT; however, the impact on PET interpretation remains unclear. We compared the added value of CACS to reporting MPI using SPECT vs PET.

METHODS

We retrospectively included 412 patients. 206 patients who underwent Rb-82 PET were propensity-based matched to a cohort of 4018 patients who underwent cadmium-zinc-telluride SPECT MPI to obtain a comparable group of 206 SPECT patients. Next, we created four image sets: SPECT MPI-only, PET-only, SPECT + CACS, and PET + CACS. Two physicians interpreted the 824 images as normal, equivocal, or abnormal for ischemia or irreversible defects. Additionally, event rates were compared between PET and SPECT groups during 30-month follow-up.

RESULTS

PET yielded more scans interpreted as normal than SPECT (88% vs 80%, respectively, P = 0.015). Adding CACS to SPECT increased the percentage of normal scans to 86% (P = 0.014), whereas this effect was absent for PET (90%, P = 0.77). Annualized event rates for images interpreted as normal did not differ and varied between 0.7 and 2.0% (P > 0.084).

CONCLUSION

Adding CACS correctly increased the percentage of normal scans for SPECT MPI but not for PET, possibly limiting the effect of adding CACS to reporting PET.

Positron Emission Tomography in Coronary Heart Disease

With advances in scanner technology, postprocessing techniques, and the development of novel positron emission tomography (PET) tracers, the applications of PET for the study of coronary heart disease have been gaining momentum in the last few years. Depending on the tracer and acquisition protocol, cardiac PET can be used to evaluate the atherosclerotic lesion (plaque imaging) and to assess its potential consequences—ischemic versus nonischemic (perfusion imaging) and viable versus scarred (viability imaging) myocardium. The scope of this review is to summarize the role of PET in coronary heart disease.

New Insights in Early Detection of Anticancer Drug-Related Cardiotoxicity Using Perfusion and Metabolic Imaging

Cardio-oncology requires a good knowledge of the cardiotoxicity of anticancer drugs, their mechanisms, and their diagnosis for better management. Anthracyclines, anti-vascular endothelial growth factor (VEGF), alkylating agents, antimetabolites, anti-human epidermal growth factor receptor (HER), and receptor tyrosine kinase inhibitors (RTKi) are therapeutics whose cardiotoxicity involves several mechanisms at the cellular and subcellular levels. Current guidelines for anticancer drugs cardiotoxicity are essentially based on monitoring left ventricle ejection fraction (LVEF). However, knowledge of microvascular and metabolic dysfunction allows for better imaging assessment before overt LVEF impairment. Early detection of anticancer drug-related cardiotoxicity would therefore advance the prevention and patient care. In this review, we provide a comprehensive overview of the cardiotoxic effects of anticancer drugs and describe myocardial perfusion, metabolic, and mitochondrial function imaging approaches to detect them before over LVEF impairment.

Synthesis and evaluation of 99mTc-DOTA-ARA-290 as potential SPECT tracer for targeting cardiac ischemic region

Objectives

Myocardial infarction caused by ischemia of heart tissue is the main reason for death worldwide; therefore, early detection can reduce mortality and treatment costs. Erythropoietin (EPO) has protection effects on ischemic tissue due to nonhematopoietic peptide (pHBSP; ARA-290) which is derived from the B-subunit of EPO.

Materials and Methods

We designed and synthesized a modified DOTA-(Lys-Dabcyl⁶, Phe⁷)-ARA-290 using Fmoc solid-phase peptide synthesis strategies. To improve serum stability, Fmoc-Lys-(Dabcyl)-OH as lipophilic amino acid was synthesized along with Fmoc-Phe-OH which then were substituted with Arg⁶ and Ala⁷, respectively; they were then investigated for the ability to detect ischemic cardiac imaging. DOTA-(Lys-Dabcyl⁶,Phe⁷)-ARA-290 was labeled with technetium 99m, and its radiochemical purity (RCP), stability in the presence of human serum and, specific bind to hypoxic H9c2 cells were evaluated. In vivo studies for biodistribution and SPECT scintigraphy were checked in a normal and cardiac ischemia rat model.

Results

Radiolabeling purity was obtained more than 96% by ITLC, and in vitro stability of the radiopeptide up to 6 hr was 85%. The binding of ^99mTc-ARA-290 to hypoxic cells was remarkably higher than normoxic cells (3 times higher than normoxic cells at 1 hr). Biodistribution and SPECT imaging on the cardiac ischemic model showed that radiopeptide considerably accumulated in the ischemic region (cardiac ischemic-to-lung rate = 3.65 ID/g % at 0.5 hr).

Conclusion

The results of studies, in vitro and in vivo, indicated that 99mTc-DOTA-(Lys-Dabcyl6,Phe7)-ARA-290 could be an appropriate candidate for early diagnosis of cardiac ischemia.

Simultaneous assessment of coronary flow reserve and left ventricular function during vasodilator stress evaluated by 13N-ammonia hybrid PET/MRI

AIM

To explore changes in left ventricular (LV) function and the relationship of these changes with myocardial blood flow (MBF) evaluated by ¹³N-ammonia hybrid positron-emission tomography (PET)/magnetic resonance imaging (MRI) during vasodilator stress in patients with suspected coronary artery disease (CAD).

MATERIALS AND METHODS

Fifty-two consecutive patients with suspected CAD, who underwent ¹³N-ammonia PET/MRI, were enrolled. Vasodilator stress was induced by intravenous injection of adenosine. MBF and coronary flow reserve (CFR) were calculated from dynamic acquisition of ¹³N-ammonia PET. LV function was evaluated by MRI both at rest and during vasodilator stress. An abnormal perfusion on myocardial images was defined as a summed difference score of ≥4.

RESULTS

MRI showed that the LV end-diastolic volume, LV end-systolic volume, and LV ejection fraction (LVEF) remained unchanged during vasodilator stress in all patients (n=52) as well as in the patients with CFR of <2 (n=27), stress MBF of <1.3 ml/g/min (n=28), abnormal myocardial perfusion (n=30), and more than one diseased vessel (n=46). In only four patients, the LVEF measured by MRI decreased by >5% during vasodilator stress. In these four patients, CFR was lower (1.57 ± 0.12 versus 2.18 ± 0.86, p<0.01) and the number of diseased vessels was higher (2.75 ± 0.50 versus 1.48 ± 0.92, p<0.01) than in patients without post-stress LV dysfunction.

CONCLUSION

The LV volume and systolic function evaluated by cardiac MRI remained unchanged during vasodilator stress; however, LV dysfunction during vasodilator stress may occur in patients with severe CAD.

Worldwide Variation in the Use of Nuclear Cardiology Camera Technology, Reconstruction Software, and Imaging Protocols

OBJECTIVES

This study sought to describe worldwide variations in the use of myocardial perfusion imaging hardware, software, and imaging protocols and their impact on radiation effective dose (ED).

BACKGROUND

Concerns about long-term effects of ionizing radiation have prompted efforts to identify strategies for dose optimization in myocardial perfusion scintigraphy. Studies have increasingly shown opportunities for dose reduction using newer technologies and optimized protocols.

METHODS

Data were submitted voluntarily to the INCAPS (International Atomic Energy Agency Nuclear Cardiology Protocols Study) registry, a multinational, cross-sectional study comprising 7,911 imaging studies from 308 labs in 65 countries. The study compared regional use of camera technologies, advanced post-processing software, and protocol characteristics and analyzed the influence of each factor on ED.

RESULTS

Cadmium-zinc-telluride and positron emission tomography (PET) cameras were used in 10% (regional range 0% to 26%) and 6% (regional range 0% to 17%) of studies worldwide. Attenuation correction was used in 26% of cases (range 10% to 57%), and advanced post-processing software was used in 38% of cases (range 26% to 64%). Stress-first single-photon emission computed tomography (SPECT) imaging comprised nearly 20% of cases from all world regions, except North America, where it was used in just 7% of cases. Factors associated with lower ED and odds ratio for achieving radiation dose ≤9 mSv included use of cadmium-zinc-telluride, PET, advanced post-processing software, and stress- or rest-only imaging. Overall, 39% of all studies (97% PET and 35% SPECT) were ≤9 mSv, while just 6% of all studies (32% PET and 4% SPECT) achieved a dose ≤3 mSv.

CONCLUSIONS

Newer-technology cameras, advanced software, and stress-only protocols were associated with reduced ED, but worldwide adoption of these practices was generally low and varied significantly between regions. The implementation of dose-optimizing technologies and protocols offers an opportunity to reduce patient radiation exposure across all world regions.

Comparison of diagnostic accuracy of PET-derived myocardial blood flow parameters: A meta-analysis

BACKGROUND

Although absolute quantification of myocardial blood flow (MBF) by positron emission tomography provides additive diagnostic value to visual analysis of perfusion defect, diagnostic accuracy of different MBF parameters remain unclear.

METHODS

Clinical studies regarding the diagnostic accuracy of hyperemic MBF (hMBF), myocardial flow reserve (MFR) and/or relative flow reserve (RFR) were searched and systematically reviewed. On a per-vessel basis, pooled measures of the parameters' diagnostic performances were analyzed, regarding significant coronary stenosis defined by fractional flow reserve or diameter stenosis.

RESULTS

Ten studies (2,522 arteries from 1,099 patients) were finally included. Pooled sensitivity [95% confidence interval (CI)] was 0.853 (0.821-0.881) for hMBF, 0.755 (0.713-0.794) for MFR, and 0.636 (0.539-0.726) for RFR. Pooled specificity (95% CI) was 0.844 (0.827-0.860) for hMBF, 0.804 (0.784-0.824) for MFR, and 0.897 (0.860-0.926) for RFR. Pooled area under the curve ± standard error was 0.900 ± 0.020 for hMBF, 0.830 ± 0.026 for MFR, and 0.873 ± 0.048 for RFR.

CONCLUSIONS

hMBF showed the best sensitivity while RFR showed the best specificity in the diagnosis of significant coronary stenosis. MFR was less sensitive than hMBF and less specific than hMBF and RFR.

Technetium-99 m-PEGylated dendrimer-G2-(Dabcyle-Lys6,Phe7)-pHBSP: A novel Nano-Radiotracer for molecular and early detecting of cardiac ischemic region

In cardiac ischemic disorder, pyroglutamate helix B surface peptide (pHBSP) which derived from erythropoietin causes to increase cell stability. To improve the serum stability of pHBSP, two lipophilic amino acids Arg⁶, Ala⁷ were replaced with Fmoc-(Dabcyle)-Lys-OH and Fmoc-Phe-OH during the peptide synthesis. This peptide was subsequently conjugated to PEGylated dendrimer-G₂ and labeled with ^99mTcO₄^- to detect cardiac ischemic region. Radiochemical purity (RCP) of ^99mTc-PEGylated dendrimer-G₂-(Dabcyle-Lys⁶,Phe⁷)-pHBSP was evaluated by ITLC method. In addition, the radiopeptide was investigated for stability in human serum and binding affinity to hypoxic cells in myocardium H9c2 cell lines. Biodistribution and SPECT/CT scintigraphy were assessed in cardiac ischemic rats. Radiochemical yield indicated that the anionic dendrimer has a very high potential to complex formation with ^99mTcO^-₄ (RCP > 94%) which was stable in human serum with RCP 89% up to 6 h. The binding of ^99mTc- nanoconjugate to hypoxic cells was significantly more than normoxic cells (3-fold higher compared to normoxic cells at 1 h). In biodistribution studies, erythropoietin receptor-Beta common receptor (EPO-BcR)-positive uptake in the cardiac ischemic region was 3.62 ± 0.44% ID/g 30 min post injection. SPECT imaging showed a prominent uptake of ^99mTc-nanoconjugate in EPO-BcR expressing ischemic heart.

Rubidium-82 PET imaging is feasible in a rat myocardial infarction model

BACKGROUND

Small-animal myocardial infarct models are frequently used in the assessment of new cardioprotective strategies. A validated quantification of perfusion using a non-cyclotron-dependent PET tracer would be of importance in monitoring response to therapy. We tested whether myocardial PET perfusion imaging is feasible with Rubidium-82 (82Rb) in a small-animal scanner using a rat myocardial infarct model.

METHODS

18 Sprague-Dawley rats underwent permanent coronary artery ligation (infarct group), and 11 rats underwent ischemia-reperfusion (reperfusion group) procedure. 82Rb-PET and magnetic resonance imaging (MRI) were conducted before and after the intervention. Perfusion was compared to both left ventricle ejection fraction (LVEF) and infarct size assessed by MRI.

RESULTS

Follow-up global 82Rb-uptake correlated significantly with infarct size (infarct group: r = -0.81, P < 0.001 and reperfusion group: r = -0.61, P = 0.04). Only 82Rb-uptake in the infarct group correlated with LVEF. At follow-up, a higher segmental 82Rb-uptake in the infarct group was associated with better wall motion (β = 0.034, CI [0.028;0.039], P < 0.001, R2 = 0.30), and inversely associated with scar transmurality (β = -2.4 [-2.6; -2.2], P < 0.001, R2 = 0.59). The associations were similar for the reperfusion group.

CONCLUSION

82Rb-PET is feasible in small animal scanners despite the long positron range and enables fast and time-efficient myocardial perfusion imaging in rat models.

Identifying Subclinical Coronary Abnormalities and Silent Myocardial Ischemia After Arterial Switch Operation

The incidence of late coronary complications is reported around 8% after arterial switch operation (ASO) for d-transposition of the great arteries, but the affected patients are usually asymptomatic. Exercise stress test (EST) and myocardial perfusion imaging (MPI) are common non-invasive modalities to screen for silent myocardial ischemia, but their diagnostic reliability in children after ASO is unclear. We retrospectively reviewed asymptomatic patients following ASO with EST, MPI, and coronary imaging studies (CIS) and examined the reliability of each test in identifying abnormal coronary lesions responsible for myocardial ischemia. Thirty-seven asymptomatic patients (24 males; ages 12.7 ± 3.7 years) had EST, in which 27 and 33 patients also underwent MPI and CIS, respectively. Exercise capacity was comparable to the age- and sex-matched 37 controls. In seven patients with angiographically proven moderate to severe coronary abnormalities, only two patients had positive EST and/or MPI, and five patients were negative including one patient who later developed exercise-induced cardiac arrest due to severe proximal left coronary artery stenosis. Two patients with positive EST or MPI showed no corresponding coronary abnormalities by CIS. Occurrence of acquired late coronary abnormalities did not correlate with the original coronary anatomy or initial surgical procedures. There is no single reliable method to identify the risk of myocardial ischemia after ASO. Although CIS are regarded as a gold standard, multidisciplinary studies are essential to risk-stratify the potential life-threatening coronary lesions after ASO in children.

Quantification of PET Myocardial Blood Flow

PURPOSE OF REVIEW

The aim of this review is to provide an update on quantification of myocardial blood flow (MBF) with positron emission tomography (PET) imaging. Technical and clinical aspects of flow quantification with PET are reviewed.

RECENT FINDINGS

The diagnostic and prognostic values of myocardial flow quantification have been established in numerous studies and in various populations. MBF quantification has also shown itself to be particularly useful in the assessment of coronary microvascular dysfunction and in evaluation of cardiac allograft vasculopathy. Overall, myocardial flow reserve (MFR) and hyperemic MBF can lead to improved risk stratification by providing information complementary to that of other markers of disease severity, such as fractional flow reserve. Flow quantification enhances MPI's ability to detect both significant epicardial disease and microvascular dysfunction. With recent technological and methodological advances, flow quantification with PET is no longer restricted to cyclotron-equipped academic centers.

Hybrid cardiac imaging using PET/MRI: a joint position statement by the European Society of Cardiovascular Radiology (ESCR) and the European Association of Nuclear Medicine (EANM)

Positron emission tomography (PET) and magnetic resonance imaging (MRI) have both been used for decades in cardiovascular imaging. Since 2010, hybrid PET/MRI using sequential and integrated scanner platforms has been available, with hybrid cardiac PET/MR imaging protocols increasingly incorporated into clinical workflows. Given the range of complementary information provided by each method, the use of hybrid PET/MRI may be justified and beneficial in particular clinical settings for the evaluation of different disease entities. In the present joint position statement, we critically review the role and value of integrated PET/MRI in cardiovascular imaging, provide a technical overview of cardiac PET/MRI and practical advice related to the cardiac PET/MRI workflow, identify cardiovascular applications that can potentially benefit from hybrid PET/MRI, and describe the needs for future development and research. In order to encourage its wide dissemination, this article is freely accessible on the European Radiology and European Journal of Hybrid Imaging web sites.

KEY POINTS

• Studies and case-reports indicate that PET/MRI is a feasible and robust technology. • Promising fields of application include a variety of cardiac conditions. • Larger studies are required to demonstrate its incremental and cost-effective value. • The translation of novel radiopharmaceuticals and MR-sequences will provide exciting new opportunities.

Subacute cardiac rubidium-82 positron emission tomography (82Rb-PET) to assess myocardial area at risk, final infarct size, and myocardial salvage after STEMI

BACKGROUND

Determining infarct size and myocardial salvage in patients with ST-segment elevation myocardial infarction (STEMI) is important when assessing the efficacy of new reperfusion strategies. We investigated whether rest 82Rb-PET myocardial perfusion imaging can estimate area at risk, final infarct size, and myocardial salvage index when compared to cardiac SPECT and magnetic resonance (CMR).

METHODS

Twelve STEMI patients were injected with 99mTc-Sestamibi intravenously immediate prior to reperfusion. SPECT, 82Rb-PET, and CMR imaging were performed post-reperfusion and at a 3-month follow-up. An automated algorithm determined area at risk, final infarct size, and hence myocardial salvage index.

RESULTS

SPECT, CMR, and PET were performed 2.2 ± 0.5, 34 ± 8.5, and 32 ± 24.4 h after reperfusion, respectively. Mean (± SD) area at risk were 35.2 ± 16.6%, 34.7 ± 11.3%, and 28.1 ± 16.1% of the left ventricle (LV) in SPECT, CMR, and PET, respectively, P = 0.04 for difference. Mean final infarct size estimates were 12.3 ± 15.4%, 13.7 ± 10.4%, and 11.9 ± 14.6% of the LV in SPECT, CMR, and PET imaging, respectively, P = .72. Myocardial salvage indices were 0.64 ± 0.33 (SPECT), 0.65 ± 0.20 (CMR), and 0.63 ± 0.28 (PET), (P = .78).

CONCLUSIONS

82Rb-PET underestimates area at risk in patients with STEMI when compared to SPECT and CMR. However, our findings suggest that PET imaging seems feasible when assessing the clinical important parameters of final infarct size and myocardial salvage index, although with great variability, in a selected STEMI population with large infarcts. These findings should be confirmed in a larger population.

Implementation of a cardiac PET stress program: comparison of outcomes to the preceding SPECT era

BACKGROUND

Cardiac positron emission testing (PET) is more accurate than single photon emission computed tomography (SPECT) at identifying coronary artery disease (CAD); however, the 2 modalities have not been thoroughly compared in a real-world setting. We conducted a retrospective analysis of 60-day catheterization outcomes and 1-year major adverse cardiovascular events (MACE) after the transition from a SPECT- to a PET-based myocardial perfusion imaging (MPI) program.

METHODS

MPI patients at Intermountain Medical Center from January 2011-December 2012 (the SPECT era, n = 6,777) and January 2014-December 2015 (the PET era, n = 7,817) were studied. Outcomes studied were 60-day coronary angiography, high-grade obstructive CAD, left main/severe 3-vessel disease, revascularization, and 1-year MACE-revascularization (MACE-revasc; death, myocardial infarction [MI], or revascularization >60 days).

RESULTS

Patients were 64 ± 13 years old; 54% were male and 90% were of European descent; and 57% represented a screening population (no prior MI, revascularization, or CAD). During the PET era, compared with the SPECT era, a higher percentage of patients underwent coronary angiography (13.2% vs. 9.7%, P < 0.0001), had high-grade obstructive CAD (10.5% vs. 6.9%, P < 0.0001), had left main or severe 3-vessel disease (3.0% vs. 2.3%, P = 0.012), and had coronary revascularization (56.7% vs. 47.1%, P = 0.0001). Similar catheterization outcomes were seen when restricted to the screening population. There was no difference in 1-year MACE-revasc (PET [5.8%] vs. SPECT [5.3%], P = 0.31).

CONCLUSIONS

The PET-based MPI program resulted in improved identification of patients with high-grade obstructive CAD, as well as a larger percentage of revascularization, thus resulting in fewer patients undergoing coronary angiography without revascularization.

FUNDING

This observational study was funded using internal departmental funds.

Myocardial Perfusion Imaging Versus Computed Tomography Angiography-Derived Fractional Flow Reserve Testing in Stable Patients With Intermediate-Range Coronary Lesions: Influence on Downstream Diagnostic Workflows and Invasive Angiography Findings

Background

Data on the clinical utility of coronary computed tomography angiography–derived fractional flow reserve (FFR_CT) are sparse. In patients with intermediate (40–70%) coronary stenosis determined by coronary computed tomography angiography, we investigated the association of replacing standard myocardial perfusion imaging with FFR_CT testing with downstream utilization of invasive coronary angiography (ICA) and the diagnostic yield of ICA (rate of no obstructive disease, and rate of revascularization).

Methods and Results

This was a single‐center observational study of symptomatic patients with suspected coronary artery disease referred to coronary computed tomography angiography between 2013 and 2015. Patients were divided into 3 historical groups based on the adjunctive functional testing approach: myocardial perfusion imaging (n=1332) or FFR_CT “implementation” (n=800) or “clinical use” (n=1391). Propensity score matching was used to estimate the average period effect on outcomes. Patients in the FFR_CT clinical use group versus the myocardial perfusion imaging group were older and had higher pretest probability of obstructive disease. After adjusting for baseline risk characteristics, there was a reduction in downstream ICA utilization (absolute risk difference: −4.2; 95% CI, −6.9 to −1.6; P=0.002). In patients referred to ICA, findings of no obstructive coronary artery disease decreased (−12.8%; 95% CI, −22.2 to −3.4; P=0.008) and rate of coronary revascularization increased (14.1%; 95% CI, 3.3–24.9; P=0.01), as did availability of functional information for guidance of revascularization (27.8%; 95% CI, 11.3–44.4; P<0.001) after clinical adoption of FFR_CT.

Conclusions

Replacing adjunctive myocardial perfusion imaging with FFR_CT testing for functional assessment of intermediate stenosis determined by coronary computed tomography angiography in stable coronary artery disease was associated with less ICA utilization, and a higher ICA diagnostic yield. The findings in this observational study needs confirmation in prospective, randomized trials.

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.

Highly Sensitive Detection of Minimal Cardiac Ischemia using Positron Emission Tomography Imaging of Activated Platelets

A reliable method for the diagnosis of minimal cardiac ischemia would meet a strong demand for the sensitive diagnosis of coronary artery disease in cardiac stress testing and risk stratification in patients with chest pain but unremarkable ECGs and biomarkers. We hypothesized that platelets accumulate early on in ischemic myocardium and a newly developed technology of non-invasive molecular PET imaging of activated platelets can thus detect minimal degrees of myocardial ischemia. To induce different degrees of minimal cardiac ischemia, the left anterior descending artery (LAD) was ligated for 10, 20 or 60 min. Mice were injected with a newly generated scFv_{anti-GPIIb/IIIa}-⁶⁴CuMeCOSar radiotracer, composed of a single-chain antibody that only binds to activated integrin GPIIb/IIIa (α_IIbβ_III) and thus to activated platelets, and a sarcophagine cage MeCOSar complexing the long half-life PET tracer copper-64. A single PET/CT scan was performed. Evans Blue/TTC staining to detect necrosis as well as classical serological biomarkers like Troponin I and heart-type fatty acid-binding protein (H-FABP) were negative, whereas PET imaging of activated platelets was able to detect small degrees of ischemia. Taken together, molecular PET imaging of activated platelets represents a unique and highly sensitive method to detect minimal cardiac ischemia.

Prognostic value of extracardiac incidental findings on attenuation correction cardiac computed tomography

BACKGROUND

Attenuation corrected computed tomography (CTAC) is often performed to improve the specificity of single-photon emission tomography imaging. Extracardiac incidental findings are frequently observed. It is unclear whether these findings have any prognostic value.

METHODS

Consecutive patients (n = 1139) at a tertiary care center were retrospectively evaluated for incidental findings on CTAC. Clinically significant incidental findings were defined as findings warranting physician follow-up. Information regarding subsequent resource utilization was obtained by chart review. Cox proportional hazard model adjusted for demographic and clinical variables was used to evaluate association of these incidental findings with all-cause and cancer-specific mortality.

RESULTS

A total of 135 (12%) patients with incidental findings were identified, 83 of whom (68%) were newly diagnosed. Lung nodules were the most common finding, present in 92 (68%) patients. Over a median follow-up of 468 days, incidental findings were not significantly associated with increased risk of all-cause mortality (HR 1.34; 95% CI 0.77-2.33, P = 0.29) but was significantly associated with cancer-specific mortality (HR 3.21; 95% CI 1.26-8.14, P = 0.01). This association remained statistically significant when the analysis was limited to newly diagnosed incidental findings. Among patients with incidental findings, follow-up radiographic studies were conducted in 87%, and invasive procedures performed in 32%. Physician office-based follow-up of these findings occurred in 42% of patients and incidental finding-related hospitalization occurred in 14%.

CONCLUSIONS

This study shows that incidental findings are common and were associated with all-cause and cancer-specific mortality but only the later remained statistically significant after multivariable adjustment.

Fate of Organic Functionalities Conjugated to Theranostic Nanoparticles upon Their Activation

Neutron activation is widely applied for the preparation of radioactive isotopes to be used in imaging and/or therapy. The type of diagnostic/therapeutic agents varies from small chelates coordinating radioactive metal ions to complex nanoparticulate systems. Design of these agents often relies on conjugation of certain organic functionalities that determine their pharmacokinetics, biodistribution, targeting, and cell-penetrating abilities, or simply on tagging them with an optical label. The conjugation chemistry at the surface of nanoparticles and their final purification often require laborious procedures that become even more troublesome when radioactive materials are involved. This study represents a thorough investigation on the effects of neutron activation on the organic moieties of functionalized nanoparticles, with special focus on (166)Ho2O3 particles conjugated with PEG-fluorescein and PEG-polyarginine motives. Spectroscopic and thermogravimetric analyses demonstrate only a limited degradation of PEG-fluorescein upon irradiation of the particles up to 10 h using a thermal neutron flux of 5 × 10(16) m(-2) s(-1). Cell experiments show that the polyarginine-based mechanisms of membrane penetration remain unaltered after exposure of the functionalized particles to the mixed field of neutrons and gammas present during activation. This confirms that radiation damage on the PEG-polyarginines is minimal. Intrinsic radiations from (166)Ho do not seem to affect the integrity of conjugated organic material. These findings open up a new perspective to simplify the procedures for the preparation of functionalized metal-based nanosystems that need to be activated by neutron irradiation in order to be applied for diagnostic and/or therapeutic purposes.

Myocardial blood flow assessment with 82rubidium-PET imaging in patients with left bundle branch block

OBJECTIVES

Perfusion abnormalities are frequently seen in Single Photon Emission Computed Tomography (SPECT) when a left bundle branch block is present. A few studies have shown decreased coronary flow reserve in the left anterior descending territory, regardless of the presence of coronary artery disease.

OBJECTIVE

We sought to investigate rubidium-82 (82Rb) positron emission tomography imaging in the assessment of myocardial blood flow and coronary flow reserve in patients with left bundle branch block.

METHODS

Thirty-eight patients with left bundle branch block (GI), median age 63.5 years, 22 (58%) female, 12 with coronary artery disease (≥70%; GI-A) and 26 with no evidence of significant coronary artery disease (GI-B), underwent rest-dipyridamole stress 82Rb-positron emission tomography with absolute quantitative flow measurements using Cedars-Sinai software (mL/min/g). The relative myocardial perfusion and left ventricular ejection fraction were assessed in 17 segments. These parameters were compared with those obtained from 30 patients with normal 82Rb-positron emission tomography studies and without left bundle branch block (GII).

RESULTS

Stress myocardial blood flow and coronary flow reserve were significantly lower in GI than in GII (p<0.05). The comparison of coronary flow reserve between GI-A and GI-B showed that it was different from the global coronary flow reserve (p<0.05) and the stress flow was significantly lower in the anterior than in the septal wall for both groups. Perfusion abnormalities were more prevalent in GI-A (p=0.06) and the left ventricular ejection fraction was not different between GI-A and GI-B, whereas it was lower in GI than in GII (p<0.001).

CONCLUSION

The data confirm that patients with left bundle branch block had decreased myocardial blood flow and coronary flow reserve and coronary flow reserve assessed by 82Rb-positron emission tomography imaging may be useful in identifying coronary artery disease in patients with left bundle branch block.

Quantitative myocardial blood flow with Rubidium-82 PET: a clinical perspective

Positron emission tomography (PET) allows assessment of myocardial blood flow in absolute terms (ml/min/g). Quantification of myocardial blood flow (MBF) and myocardial flow reserve (MFR) extend the scope of conventional semi-quantitative myocardial perfusion imaging (MPI): e.g. in 1) identification of the extent of a multivessel coronary artery disease (CAD) burden, 2) patients with balanced 3-vessel CAD, 3) patients with subclinical CAD, and 4) patients with regional flow variance, despite of a high global MFR. A more accurate assessment of the ischemic burden in patients with intermediate pretest probability of CAD can support the clinical decision-making in treatment of CAD patients as a complementary tool to the invasive coronary angiography (CAG). Recently, several studies have proven Rubidium-82 ((82)Rb) PET's long-term prognostic value by a significant association between compromised global MFR and major adverse cardiovascular events (MACE), and together with new diagnostic possibilities from measuring the longitudinal myocardial perfusion gradient, cardiac (82)Rb PET faces a promising clinical future. This article reviews current evidence on quantitative (82)Rb PET's ability to diagnose and risk stratify CAD patients, while assessing the potential of the modality in clinical practice.

Multi-modality imaging for the assessment of myocardial perfusion with emphasis on stress perfusion CT and MR imaging

High-quality and non-invasive diagnostic tools for assessing myocardial ischemia are necessary for therapeutic decisions regarding coronary artery disease. Myocardial perfusion has been studied using myocardial contrast echo perfusion, single-photon emission computed tomography, positron emission tomography, cardiovascular magnetic resonance, and, more recently, computed tomography. The addition of coronary computed tomography angiography to myocardial perfusion imaging improves the specificity and overall diagnostic accuracy of detecting the hemodynamic significance of coronary artery stenosis. This study reviews the benefits, limitations, and imaging findings of various imaging modalities for assessing myocardial perfusion, with particular emphasis on stress perfusion computed tomography and cardiovascular magnetic resonance imaging.

A nuclear chocolate box: the periodic table of nuclear medicine

Radioisotopes of elements from all parts of the periodic table find both clinical and research applications in radionuclide molecular imaging and therapy (nuclear medicine). This article provides an overview of these applications in relation to both the radiological properties of the radionuclides and the chemical properties of the elements, indicating past successes, current applications and future opportunities and challenges for inorganic chemistry.

Non-invasive imaging for subclinical coronary atherosclerosis in patients with peripheral artery disease

Patients with peripheral artery disease are at high risk of coronary artery disease. An increasing number of studies show that a large proportion of patients with peripheral artery disease have significant coronary atherosclerosis, even in the absence of symptoms. Although the reported prevalence of subclinical coronary artery disease varies widely in patients with peripheral artery disease, it could include more than half of patients. No consensus exists to date on either the rationale for screening patients with peripheral artery disease for coronary atherosclerosis or the optimal algorithm and method for screening. An increasing number of imaging modalities are emerging that allow improved in vivo non-invasive characterization of atherosclerotic plaques. These novel imaging methods may lead to early detection of high-risk vulnerable plaques, enabling clinicians to improve risk stratification of patients with peripheral artery disease, and thus paving the way for individualized therapy.