Quantification of myocardial perfusion reserve by CZT-SPECT: A head to head comparison with 82Rubidium PET imaging

Myocardial flow reserve derived from D-SPECT for evaluating non-culprit ischemic lesions in STEMI patients: comparison with quantitative flow ratio

OBJECTIVES

This study sought to elucidate the diagnostic performance and concordance between myocardial flow reserve (MFR) derived from dynamic single-photon emission computed tomography (D-SPECT) and quantitative flow ratio (QFR) in evaluating non-culprit ischemic lesions following ST-elevation myocardial infarction (STEMI). Additionally, the study investigated the integration of MFR with angiographic microvascular resistance (AMR) derived from coronary angiography to determine its utility in screening and stratifying non-culprit ischemic lesions.

BACKGROUND

The diagnostic performance and agreement between MFR and QFR in evaluating non-culprit ischemic lesions in STEMI patients with multivessel disease are unknown.

METHODS

This research encompassed a cohort of 106 STEMI patients with at least 1 intermediate non-culprit ischemic lesion, characterized by 40-80% diameter stenosis. After undergoing percutaneous coronary intervention, patients were evaluated using QFR and, approximately five days later, underwent D-SPECT to assess myocardial blood flow (MBF) and MFR. MFR was evaluated against QFR as a reference for diagnostic performance and agreement, including sensitivity analysis in vessels with normal microvascular function. Furthermore, MFR, combined with AMR, effectively screened and stratified non-culprit ischemic lesions. Non-culprit ischemic lesions were defined by QFR ≤ 0.80 and normal microvascular function by AMR < 255 mmHg*s/m.

RESULTS

Among non-culprit lesions, MFR predicted a QFR ≤ 0.80 with a sensitivity of 85%, specificity of 86%, and accuracy of 86%. The positive predictive value was 56%, and the negative predictive value was 96%. The MFR cut-off was 1.93, with an area under the receiver operating characteristic curve of 0.90 (95% CI: 0.84 to 0.94). MFR showed similar diagnostic performance in patients with normal microcirculation. Moreover, low MFR with normal AMR indicated non-culprit ischemic lesions caused solely by epicardial narrowing, while low MFR with abnormal AMR indicated ischemic lesions complicated by microvascular dysfunction.

CONCLUSION

MFR derived from D-SPECT exhibits good diagnostic performance and moderate agreement in identifying non-culprit ischemic lesions in patients with STEMI. Combining AMR with MFR effectively screens and stratifies non-culprit ischemic lesions.

TRIAL REGISTRATION

ChiCTR.org.cn. ChiCTR2200059934. Registered 13 May 2022.

Non-invasive and quantitative evaluation of myocardial PET imaging: Next step for advanced therapy

Myocardial positron emission tomography (PET) is superior in detecting ischemia in patients with left main or multivessel disease, conditions that are challenging to assess using single-photon emission computed tomography (SPECT). Additionally, quantitative measurements of myocardial blood flow and myocardial flow reserve (MFR) have been established as significant prognostic indicators for patients with ischemic heart disease. Moreover, 13N-ammonia PET offers high temporal and spatial resolution, enabling the assessment of both left and right ventricular strain, a quantitative marker of regional myocardial wall motion. Ongoing research aims to translate these advanced PET-based methodologies into SPECT imaging. Furthermore, MFR has proven valuable for diagnosing and predicting cardiac allograft vasculopathy in heart transplant recipients. More recently, it has also been utilized to evaluate the efficacy of cardiac regeneration therapy in individuals with severe heart failure and reduced cardiac function. This review presents existing evidence and highlights recent advancements in myocardial PET.

Emerging Applications of Positron Emission Tomography in Coronary Artery Disease

Coronary artery disease remains the leading cause of morbidity and mortality worldwide. With the changing clinical manifestation and novel therapeutical options, precise disease phenotyping becomes increasingly important at the point of care. In the management of coronary artery disease, myocardial perfusion imaging (MPI) remains the cornerstone of clinical practice. Although traditionally MPI has been primarily performed with single photon emission computed tomography (SPECT), nowadays, given the changing spectrum of the disease, greater precision and additional assessment of myocardial blood flow are desired. Due to the fundamental advantages of PET over SPECT, i.e., higher spatial resolution, accurate attenuation correction for each scan, and higher count rates, the sensitivity and specificity of PET MPI are higher than those of SPECT MPI and are estimated to be approximately 90-92% vs. 83-88% and 81-87% vs. 70-76%, respectively, according to meta-analysis data. Consequently, over the past decade, we have witnessed an increased uptake of positron emission tomography (PET) MPI. With the improved spatial resolution, the ability to quantify myocardial blood flow, and the potential to depict the burden of coronary atherosclerosis with low-dose computed tomography, PET/CT is uniquely positioned to facilitate a comprehensive non-invasive assessment of disease, providing an opportunity for precision medicine. The wealth of data obtained during a single imaging session can be challenging to integrate at the time of image analysis. There has therefore been an increasing interest in developing predefined thresholds or variables (scores) which combine the multidimensional data acquired with PET MPI. Beyond MPI, PET can also serve for the assessment of disease activity at the atherosclerotic plaque level, further refining our understanding of the biology of coronary artery disease and providing hope for enhanced prediction of myocardial infarctions. In this narrative review, we present the current applications of PET MPI in coronary artery disease and focus specifically on two areas that have recently garnered considerable interest-the integration of multiparametric PET MPI data and coronary plaque activity PET imaging.

Validation of advanced hybrid SPECT/CT system using dynamic anthropomorphic cardiac phantom

OBJECTIVE

Myocardial blood flow (MBF) assessment can provide incremental diagnostic and prognostic information and thus the validation of dynamic SPECT is of high importance. We recently developed a novel cardiac phantom for dynamic SPECT validation and compared its performance against the GE Discovery NM 530c. We now report its use for validation of a new hybrid SPECT/CT System featuring advanced cadmium zinc telluride (CZT) technology in a ring array detector design (StarGuide™, GE HealthCare).

METHODS

Our recently developed cardiac phantom with injected technetium-99m radiotracer was used to create physiological time activity curves (TACs) for the left ventricular (LV) cavity and the myocardium. The TACs allow the calculation of uptake rate (K1) and MBF. The StarGuide system was used to acquire and process the TACs, and these were compared to the TACs produced by the phantom and its mathematical model. Fifteen (15) experiments with different doses representing various MBF values were conducted, and a standard statistic tool was applied for significance.

RESULTS

The TACs produced by the StarGuide system had a significant correlation (p < 0.001) with the reference TACs generated by the phantom both for the LV (r = 0.94) and for the myocardium (r = 0.89). The calculated MBF difference between the system and the phantom was 0.14 ± 0.16 ml/min/g and the average relative absolute difference was 13.2 ± 8.1%. A coefficient of variance of ≤ 11% was observed for all MBF subranges. The regional uptake rate values were similar to the global one with a maximum difference of 5%.

CONCLUSIONS

Our newly developed dynamic cardiac phantom was used for validation of the dynamic hybrid SPECT/CT CZT-based system (StarGuide™, GE). The accuracy and precision of the system for assessing MBF values were high. The new StarGuide system can reliably perform dynamic SPECT acquisitions over a wide range of myocardial perfusion flow rates.

Myocardial blood flow quantification with SPECT

INTRODUCTION

The addition of absolute myocardial blood flow (MBF) data improves the diagnostic and prognostic accuracy of relative perfusion imaging with nuclear medicine. Cardiac-specific gamma cameras allow measurement of MBF with SPECT.

METHODS

This paper reviews the evidence supporting the use of SPECT to measure myocardial blood flow (MBF). Studies have evaluated SPECT MBF in large animal models and compared it in humans with invasive angiographic measurements and against the clinical standard of PET MBF. The repeatability of SPECT MBF has been determined in both single-site and multi-center trials.

RESULTS

SPECT MBF has excellent correlation with microspheres in an animal model, with the number of stenoses and fractional flow reserve, and with PET-derived MBF. The inter-user coefficient of variability is ∼20% while the COV of test-retest MBF is ∼30%. SPECT MBF improves the sensitivity and specificity of the detection of multi-vessel disease over relative perfusion imaging and provides incremental value in predicting adverse cardiac events.

CONCLUSION

SPECT MBF is a promising technique for providing clinically valuable information in the assessment of coronary artery disease.

Self-supervised deep representation learning of a foundation transformer model enabling efficient ECG-based assessment of cardiac and coronary function with limited labels

Background: Although deep learning methods have shown great promise for identification of structural and functional cardiac abnormalities using electrocardiographic data, these methods are data hungry, posing a challenge for critically important tasks where ground truth labels are relatively scarce. Impaired coronary microvascular and vasomotor function is difficult to identify with standard clinical methods of cardiovascular testing such as coronary angiography and noninvasive single photon emission tomography (SPECT) myocardial perfusion imaging (MPI). Gold standard data from positron emission tomography (PET) are gaining emphasis in clinical guidelines but are expensive and only available in relatively limited centers. We hypothesized that signals embedded within resting and stress electrocardiograms (ECGs) identify individuals with microvascular and vasomotor dysfunction. Methods: We developed and pretrained a self-supervised foundation vision transformer model using a large database of unlabeled ECG waveforms (N=800,035). We then fine-tuned the foundation model for two clinical tasks: the difficult problem of identifying patients with impaired myocardial flow reserve (AI-MFR), and the relatively easier problem of detecting impaired LVEF (AI-LVEF). A second ECG database was labeled with task-specific annotations derived from quantitative PET MPI (N=4167). Diagnostic accuracy of AI predictions was tested in a holdout set of patients undergoing PET MPI (N=1031). Prognostic evaluation was performed in the PET holdout cohort, as well as independent cohorts of patients undergoing pharmacologic or exercise stress SPECT MPI (N=6635). Results: The diagnostic accuracy of AI-MFR with SSL pretraining increased significantly compared to de novo supervised training (AUROC, sensitivity, specificity: 0.758, 70.1%, 69.4% vs. 0.632, 66.1%, 57.3%, p < 0.0001). SSL pretraining also produced a smaller increase in AI-LVEF accuracy (AUROC, sensitivity, specificity: 0.946, 89.4%, 85.9% vs. 0.918, 87.6%, 82.5%, p < 0.02). Abnormal AI-MFR was found to be significantly associated with mortality risk in all three test cohorts (Hazard Ratio (HR) 2.61 [95% CI 1.83, 3.71], p < 0.0001, PET cohort; HR 2.30 [2.03, 2.61], p < 0.0001, pharmacologic stress SPECT cohort; HR 3.76 [2.36, 5.99], p < 0.0001, exercise stress SPECT cohort). Conclusion: SSL pretraining of a vision transformer foundation model enabled identification of signals predictive of impaired MFR, a hallmark of microvascular and vasomotor dysfunction, and impaired LV function in resting and stress ECG waveforms. These signals are powerful predictors of prognosis in patients undergoing routine noninvasive stress testing and could enable more efficient diagnosis and management of these common conditions.

Feasibility of myocardial blood flow quantification to detect flow-limited coronary artery disease with a one-day rest/stress continuous rapid imaging protocol on cardiac-dedicated cadmium zinc telluride single photon emission computed tomography

BACKGROUND

It is clinically needed to explore a more efficient imaging protocol for single photon emission computed tomography (SPECT) myocardial blood flow (MBF) quantitation derived from cadmium zinc telluride (CZT) SPECT camera for the routine clinical utilization.

METHODS

One hundred and twenty patients with matched clinical characteristics and angiographic findings who completed one-day rest/stress SPECT imaging with either the intermittently sequential imaging (ISI) protocol (two dynamic and two electrocardiography (ECG)-gated scans) or the continuous rapid imaging (CRI) protocol (two dynamic/ECG-gated scans) were included. MBF quantitation adopted residual activity correction (RAC) to correct for rest residual activity (RRA) in the stress dynamic SPECT scan for the detection of flow-limited coronary artery disease.

RESULTS

The CRI protocol reduced about 6.2 times shorter than the ISI protocol (25.5 min vs 157.6 min), but slightly higher than the RRA (26.7% ± 3.6% vs 22.3% ± 4.9%). With RAC, both protocols demonstrated close stress MBF (2.18 ± 1.13 vs 2.05 ± 1.10, P > 0.05) and myocardial flow reserve (MFR) (2.42 ± 1.05 vs 2.48 ± 1.11, P > 0.05) to deliver comparable diagnostic performance (sensitivity = 82.1%-92.3%, specificity = 81.2%-91.2%). Myocardial perfusion and left ventricular function overall showed no significant difference (all P > 0.26).

CONCLUSION

One-day rest/stress SPECT with the CRI protocol and rest RAC is feasible to warrant the diagnostic performance of MBF quantitation with a shortened examination time and enhanced patient comfort. Further evaluation on the impact of extracardiac activity to regional MBF and perfusion pattern is required. Additional evaluation is needed in a patient population that is typical of those referred for SPECT MPI, including those with known or suspected coronary microvascular disease.

Impact of cardiac history and myocardial scar on increase of myocardial perfusion after revascularization

PURPOSE

We sought to assess the impact of coronary revascularization on myocardial perfusion and fractional flow reserve (FFR) in patients without a cardiac history, with prior myocardial infarction (MI) or non-MI percutaneous coronary intervention (PCI). Furthermore, we studied the impact of scar tissue.

METHODS

Symptomatic patients underwent [15O]H2O positron emission tomography (PET) and FFR before and after revascularization. Patients with prior CAD, defined as prior MI or PCI, underwent scar quantification by magnetic resonance imaging late gadolinium enhancement.

RESULTS

Among 137 patients (87% male, age 62.2 ± 9.5 years) 84 (61%) had a prior MI or PCI. The increase in FFR and hyperemic myocardial blood flow (hMBF) was less in patients with prior MI or non-MI PCI compared to those without a cardiac history (FFR: 0.23 ± 0.14 vs. 0.20 ± 0.12 vs. 0.31 ± 0.18, p = 0.02; hMBF: 0.54 ± 0.75 vs. 0.62 ± 0.97 vs. 0.91 ± 0.96 ml/min/g, p = 0.04). Post-revascularization FFR and hMBF were similar across patients without a cardiac history or with prior MI or non-MI PCI. An increase in FFR was strongly associated to hMBF increase in patients without a cardiac history or with prior MI/non-MI PCI (r = 0.60 and r = 0.60, p < 0.01 for both). Similar results were found for coronary flow reserve. In patients with prior MI scar was negatively correlated to hMBF increase and independently predictive of an attenuated CFR increase.

CONCLUSIONS

Post revascularization FFR and perfusion were similar among patients without a cardiac history, with prior MI or non-MI PCI. In patients with prior MI scar burden was associated to an attenuated perfusion increase.

Prognostic value of myocardial perfusion imaging by cadmium zinc telluride single-photon emission computed tomography in patients with suspected or known coronary artery disease: a systematic review and meta-analysis

BACKGROUND

Aim of this study was to define the prognostic value of stress myocardial perfusion imaging by cadmium zinc telluride (CZT) single-photon emission computed tomography (SPECT) for prediction of adverse cardiovascular events in patients with known or suspected coronary artery disease (CAD).

METHODS AND RESULTS

Studies published until November 2022 were identified by database search. We included studies using stress myocardial perfusion imaging by CZT-SPECT to evaluate subjects with known or suspected CAD and providing primary data of adverse cardiovascular events. Total of 12 studies were finally included recruiting 36,415 patients. Pooled hazard ratio (HR) for the occurrence of adverse events was 2.17 (95% confidence interval, CI, 1.78-2.65) and heterogeneity was 66.1% (P = 0.001). Five studies reported data on adjusted HR for the occurrence of adverse events. Pooled HR was 1.69 (95% CI, 1.44-1.98) and heterogeneity was 44.9% (P = 0.123). Seven studies reported data on unadjusted HR for the occurrence of adverse events. Pooled HR was 2.72 (95% CI, 2.00-3.70). Nine studies reported data useful to calculate separately the incidence rate of adverse events in patients with abnormal and normal myocardial perfusion. Pooled incidence rate ratio was 2.38 (95% CI, 1.39-4.06) and heterogeneity was 84.6% (P < 0.001). The funnel plot showed no evidence of asymmetry (P = 0.517). At meta-regression analysis, we found an association between HR for adverse events and presence of angina symptoms and family history of CAD.

CONCLUSIONS

Stress myocardial perfusion imaging by CZT-SPECT is a valuable noninvasive prognostic indicator for adverse cardiovascular events in patients with known or suspected CAD.

Regional CZT myocardial perfusion reserve for the detection of territories with simultaneously impaired CFR and IMR in patients without obstructive coronary artery disease: a pilot study

OBJECTIVES

To assess the diagnostic performances of CZT myocardial perfusion reserve (MPR) for the detection of territories with simultaneous impaired coronary flow reserve (CFR) and index of microcirculatory resistance (IMR) in patients without obstructive coronary artery disease.

METHODS

Patients were prospectively included before being referred for coronary angiography. All patients underwent CZT MPR before invasive coronary angiography (ICA) and coronary physiology assessment. Rest and dipyridamole-induced stress myocardial blood flow (MBF) and MPR were quantified using 99mTc-SestaMIBI and a CZT camera. Fractional flow reserve (FFR), Thermodilution CFR, and IMR were assessed during ICA.

RESULTS

Between December 2016 and July 2019, 36 patients were included. 25/36 patients presented no obstructive coronary artery disease. A complete functional assessment was performed in 32 arteries. No territory presented a significant ischemia on CZT myocardial perfusion imaging. A moderate yet significant correlation was observed between regional CZT MPR and CFR (r = 0.4, P = .03). Sensitivity, specificity, positive and negative predictive value, and accuracy of regional CZT MPR versus the composite invasive criterion (impaired CFR and IMR) were 87 [47% to 99%], 92% [73% to 99%], 78% [47% to 93%], 96% [78% to 99%], and 91% [75% to 98%], respectively. All territories with a regional CZT MPR ≤ 1.8 showed a CFR < 2. Regional CZT MPR values were significantly higher in arteries with CFR ≥ 2 and IMR < 25 (negative composite criterion, n = 14) than in those with CFR < 2 and IMR ≥ 25 (2.6 [2.1 to 3.6] versus 1.6 [1.2 to 1.8]), P < .01).

CONCLUSION

Regional CZT MPR presented excellent diagnostic performances for the detection of territories with simultaneously impaired CFR and IMR reflecting a very high cardiovascular risk in patients without obstructive coronary artery disease.

Role of nuclear cardiology in diagnosis and risk stratification of coronary microvascular disease

Coronary flow reserve (CFR) with positron emission tomography/computed tomography (PET/CT) has an important role in the diagnosis of coronary microvascular disease (CMD), aids risk stratification and may be useful in monitoring therapy. CMD contributes to symptoms and a worse prognosis in patients with coronary artery disease (CAD), nonischemic cardiomyopathies, and heart failure. CFR measurements may improve our understanding of the role of CMD in symptoms and prognosis in CAD and other cardiovascular diseases. The clinical presentation of CAD has changed. The prevalence of nonobstructive CAD has increased to about 50% of patients with angina undergoing angiography. Ischemia with nonobstructive arteries (INOCA) is recognized as an important cause of symptoms and has an adverse prognosis. Patients with INOCA may have ischemia due to CMD, epicardial vasospasm or diffuse nonobstructive CAD. Reduced CFR in patients with INOCA identifies a high-risk group that may benefit from management strategies specific for CMD. Although measurement of CFR by PET/CT has excellent accuracy and repeatability, use is limited by cost and availability. CFR measurement with single-photon emission tomography (SPECT) is feasible, validated, and would increase availability and use of CFR. Patients with CMD can be identified by reduced CFR and selected for specific therapies.

Radiomics for the detection of diffusely impaired myocardial perfusion: A proof-of-concept study using 13N-ammonia positron emission tomography

AIM

The current proof-of-concept study investigates the value of radiomic features from normal 13N-ammonia positron emission tomography (PET) myocardial retention images to identify patients with reduced global myocardial flow reserve (MFR).

METHODS

Data from 100 patients with normal retention 13N-ammonia PET scans were divided into two groups, according to global MFR (i.e., < 2 and ≥ 2), as derived from quantitative PET analysis. We extracted radiomic features from retention images at each of five different gray-level (GL) discretization (8, 16, 32, 64, and 128 bins). Outcome independent and dependent feature selection and subsequent univariate and multivariate analyses was performed to identify image features predicting reduced global MFR.

RESULTS

A total of 475 radiomic features were extracted per patient. Outcome independent and dependent feature selection resulted in a remainder of 35 features. Discretization at 16 bins (GL16) yielded the highest number of significant predictors of reduced MFR and was chosen for the final analysis. GLRLM_GLNU was the most robust parameter and at a cut-off of 948 yielded an accuracy, sensitivity, specificity, negative and positive predictive value of 67%, 74%, 58%, 64%, and 69%, respectively, to detect diffusely impaired myocardial perfusion.

CONCLUSION

A single radiomic feature (GLRLM_GLNU) extracted from visually normal 13N-ammonia PET retention images independently predicts reduced global MFR with moderate accuracy. This concept could potentially be applied to other myocardial perfusion imaging modalities based purely on relative distribution patterns to allow for better detection of diffuse disease.

Myocardial blood flow evaluation with dynamic cadmium-zinc-telluride single-photon emission computed tomography: Bright and dark sides

Myocardial blood flow (MBF) and myocardial perfusion reserve (MPR) assessment with non-invasive techniques represent an important tool to evaluate both coronary artery disease severity and extent. Currently, cardiac positron emission tomography-computed tomography (PET-CT) is the "gold standard" for the assessment of coronary function and provides accurate estimations of baseline and hyperemic MBF and MFR. Nevertheless, due to the high cost and complexity, PET-CT is not widely used in clinical practice. The introduction of cardiac-dedicated cadmium-zinc-telluride (CZT) cameras has renewed researchers' interest on MBF quantitation by single-photon emission computed tomography (SPECT). Indeed, many studies evaluated MPR and MBF measurements by dynamic CZT-SPECT in different cohorts of patients with suspected or overt coronary artery disease. As well, many others have compared the values obtained by CZT-SPECT to the ones by PET-CT, showing good correlations in detecting significant stenosis, although with different and non-standardized cut-off values. Nevertheless, the lack of standardized protocol for acquisition, reconstruction and elaboration makes more difficult to compare different studies and to further assess the real advantages of MBF quantitation by dynamic CZT-SPECT in clinical routine. Many are the issues involved in the bright and dark sides of dynamic CZT-SPECT. They include different type of CZT cameras, different execution protocols, different tracers with different myocardial extraction fraction and distribution, different software packages with different tools and algorithms, often requiring manual post-processing elaboration. This review article provides a clear summary of the state of the art on MBF and MPR evaluation by dynamic CZT-SPECT and outlines the major issues to solve to optimize this technique.

The prognostic value of CZT SPECT myocardial blood flow (MBF) quantification in patients with ischemia and no obstructive coronary artery disease (INOCA): a pilot study

BACKGROUND

Despite the demonstrated adverse outcome, it is difficult to early identify the risks for patients with ischemia and no obstructive coronary artery disease (INOCA). We aimed to explore the prognostic potential of CZT SPECT in INOCA patients.

METHODS

The study population consisted of a retrospective cohort of 118 INOCA patients, all of whom underwent CZT SPECT imaging and invasive coronary angiography (ICA). Dynamic data were reconstructed, and MBF was quantified using net retention model. Major adverse cardiovascular events (MACEs) were defined as cardiovascular death, nonfatal myocardial infarction, nonfatal stroke, heart failure, late coronary revascularization, or hospitalization for unstable angina.

RESULTS

During a median follow-up of 15 months (interquartile range (IQR) 11-20), 19 (16.1%) MACEs occurred; both stress myocardial blood flow (sMBF) ([Formula: see text]) and coronary flow reserve (CFR) ([Formula: see text]) were significantly lower in the MACE group. Optimal thresholds of sMBF<3.16 and CFR<2.52 were extracted from the ROC curves, and both impaired sMBF (HR: 15.08; 95% CI 2.95-77.07; [Formula: see text]) and CFR (HR: 6.51; 95% CI 1.43-29.65; [Formula: see text]) were identified as prognostic factors for MACEs. Only sMBF<3.16 (HR: 11.20; 95% CI 2.04-61.41; [Formula: see text]) remained a robust predictor when sMBF and CFR were integrated considered. Compared with CFR, sMBF provides better prognostic model discrimination and reclassification ability (C-index improvement = 0.06, [Formula: see text]; net reclassification improvement (NRI) = 0.19; integrated discrimination improvement (IDI) = 0.10).

CONCLUSION

The preliminary results demonstrated that quantitative analysis on CZT SPECT provides prognostic value for INOCA patients, which may allow the stratification for early prevention and intervention.

Review of cardiovascular imaging in the Journal of Nuclear Cardiology 2022: single photon emission computed tomography

In this review, we will summarize a selection of articles on single-photon emission computed tomography published in the Journal of Nuclear Cardiology in 2022. The aim of this review is to concisely recap major advancements in the field to provide the reader a glimpse of the research published in the journal over the last year. This review will place emphasis on myocardial perfusion imaging using single-photon emission computed tomography summarizing advances in the field including in prognosis, non-perfusion variables, attenuation compensation, machine learning and camera design. It will also review nuclear imaging advances in amyloidosis, left ventricular mechanical dyssynchrony, cardiac innervation, and lung perfusion. We encourage interested readers to go back to the original articles, and editorials, for a comprehensive read as necessary but hope that this yearly review will be helpful in reminding readers of articles they have seen and attracting their attentions to ones they have missed.

A preliminary study of dobutamine myocardial flow reserve on 99mTc-Sestamibi CZT-SPECT

BACKGROUND

With improved resolution and sensitivity, the cadmium zinc telluride (CZT) detector measures myocardial blood flow (MBF) and myocardial flow reserve (MFR) via single photon emission computed tomography (SPECT). Recently, many studies have used vasodilator stress to obtain quantitative indexes. However, dobutamine used as a pharmaceutical stress has been rarely used to quantify myocardial perfusion using CZT-SPECT. Our study retrospectively analyzed the blood flow performance of ^99mTc-Sestamibi (^99mTc -MIBI) CZT-SPECT comparing dobutamine to adenosine.

PURPOSE

The study aims to explore whether dobutamine stress can be used for the myocardial perfusion quantitative analysis via CZT-SPECT as well as compare dobutamine MBF and MFR to adenosine.

METHODS

It was a retrospective study. A total of 68 patients with suspected or known coronary artery disease (CAD) were consecutively enrolled in this study. Thirty-four patients underwent dobutamine stress ^99mTc-MIBI CZT-SPECT. Another thirty-four patients underwent adenosine stress ^99mTc-MIBI CZT-SPECT. Patient characteristics, myocardial perfusion imaging (MPI) results, gated-myocardial perfusion imaging (G-MPI) results and quantitative analysis of MBF and MFR were collected.

RESULTS

In dobutamine stress group, stress MBF was significantly higher than rest MBF (median [interquartile range], 1.63 [1.46-1.94] vs. 0.89 [0.73-1.06], P < 0.001). In adenosine stress group, similar results were observed (median [interquartile range], 2.01 [1.34-2.20] vs. 0.88 [0.75-1.01], P < 0.001). When comparing the dobutamine and adenosine stress group, global MFR showed significant differences (median [interquartile range], the dobutamine group: 1.88 [1.67-2.38] vs. the adenosine group: 2.19 [1.87-2.64], P = 0.037).

CONCLUSION

MBF and MFR can be measured using dobutamine ^99mTc -MIBI CZT-SPECT. In small sample single-center study, there was a difference in MFR produced by adenosine and dobutamine within the suspected or the known CAD population.

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 .

Radionuclide Tracers for Myocardial Perfusion Imaging and Blood Flow Quantification

Myocardial perfusion imaging by nuclear cardiology is widely validated for the diagnosis, risk stratification, and management of patients with suspected or known coronary artery disease. Numerous radiopharmaceuticals are available for single-photon emission computed tomography and PET modalities. Each tracer shows advantages and limitations that should be taken into account in performing an imaging examination. This review aimed to summarize the state-of-the-art radiotracers used for myocardial perfusion imaging and blood flow quantification, highlighting the new technologic advances and promising possible applications.

Advances in Single-Photon Emission Computed Tomography

The clinical presentation of coronary artery disease (CAD) has changed during the last 20 years with less ischemia on stress testing and more nonobstructive CAD on coronary angiography. Single-photon emission computed tomography (SPECT) myocardial perfusion imaging should include the measurement of myocardial flow reserve and assessment of coronary calcium for the diagnosis of nonobstructive CAD and coronary microvascular disease. SPECT/CT systems provide reliable attenuation correction for better specificity and low-dose CT for coronary calcium evaluation. SPECT MFR measurement is accurate, well validated, and repeatable.

Precision of Myocardial Blood Flow and Flow Reserve Measurement During CZT SPECT Perfusion Imaging Processing: Intra- and Interobserver Variability

The aim of this study was to evaluate the reproducibility of myocardial blood flow (MBF) and myocardial flow reserve (MFR) measurement in patients referred for dynamic SPECT. Methods: We retrospectively analyzed patients referred for myocardial perfusion imaging. SPECT data were acquired on a cadmium zinc telluride-based pinhole cardiac camera in list mode using a stress (251 ± 15 MBq)/rest (512 ± 26 MBq) 1-d ^99mTc-tetrofosmin protocol. Kinetic analyses were done with software using a 1-tissue-compartment model and converted to MBF using a previously determined extraction fraction correction. MFR was analyzed and compared globally and regionally. Motion detection was applied, but not attenuation correction. Results: In total, 124 patients (64 male, 60 female) were included, and SPECT acquisitions were twice reconstructed by the same nuclear medicine board-certified physician for 50 patients and by 2 different physicians for 74. Both intra- and interobserver measurements of global MFR had no significant bias (-0.01 [P = 0.94] and 0.01 [P = 0.67], respectively). However, rest MBF and stress MBF were significantly different in global left ventricular evaluation (P = 0.001 and P = 0.002, respectively) and in the anterior territory (P < 0.0001) on interuser analysis. The average coefficient of variation was 15%-30% of the mean stress MBF if the analysis was performed by the same physician or 2 different physicians and was around 20% of the mean MFR independently of the processing physician. Using the MFR threshold of 2, we noticed good intrauser agreement, whereas it was moderate when the users were different (κ = 0.75 [95% CI, 0.56-0.94] vs. 0.56 [95% CI, 0.36-0.75], respectively). Conclusion: Repeated measurements of global MFR by the same physician or 2 different physicians were similar, with an average coefficient of variation of 20%. Better reproducibility was achieved for intrauser MBF evaluation. Automation of processing is needed to improve reproducibility.

Regional myocardial perfusion imaging in predicting vessel-related outcome: interplay between the perfusion results and angiographic findings

BACKGROUND

Despite myocardial perfusion imaging (MPI) by cadmium-zinc-telluride (CZT) single-photon emission computed tomography (SPECT) camera is largely used in the diagnosis and risk stratification of patients with suspected or known coronary artery disease (CAD), no data are available on the prognostic value of a regional MPI evaluation. We evaluated the prognostic value of regional MPI by the CZT camera in predicting clinical outcomes at the vessel level in patients with available angiographic data.

METHODS AND RESULTS

Five hundred and forty-one subjects with suspected or known CAD referred to 99mTc-sestamibi gated CZT-SPECT cardiac imaging and with available angiographic data were studied. Both regional total perfusion deficit (TPD) and ischemic TPD (ITPD) were calculated separately for each vascular territory (left anterior descending, left circumflex, and right coronary artery). The outcome end points were cardiac death, target vessel-related myocardial infarction, or late coronary revascularization. The prevalence of CAD ≥ 50%, regional stress TPD, and regional ITPD was significantly higher in vessels with events as compared to those without (both P < 0.001). The receiver operating characteristics area under the curve for regional ITPD for the identification of vessel-related events was 0.81 (95% confidence interval 0.75-0.86). An ITPD value of 2.0% provided the best trade-off for identifying the vessel-related event. At multivariable analysis, both CAD ≥ 50% and ITPD ≥ 2.0% resulted in independent predictors of events.

CONCLUSIONS

Regional myocardial perfusion assessed by the CZT camera demonstrated good reliability in predicting vessel-related events in patients with suspected or known CAD.

Myocardial flow reserve estimation with contemporary CZT-SPECT and 99mTc-tracers lacks precision for routine clinical application

BACKGROUND

PET myocardial flow reserve (MFR) has established diagnostic and prognostic value. Technological advances have now enabled SPECT MFR quantification. We investigated whether SPECT MFR precision is sufficient for clinical categorization of patients.

METHODS

Validation studies vs invasive flow measurements and PET MFR were reviewed to determine global SPECT MFR thresholds. Studies vs PET and a SPECT MFR repeatability study were used to establish imprecision in SPECT MFR measurements as the standard deviation of the difference between SPECT and PET MFR, or test-retest SPECT MFR. Simulations were used to evaluate the impact of SPECT MFR imprecision on confidence of clinically relevant categorization.

RESULTS

Based on validation studies, the typical PET MFR categories were used for SPECT MFR classification (< 1.5, 1.5-2.0, > 2.0). Imprecision vs PET MFR ranged from 0.556 to 0.829, and test-retest imprecision was 0.781-0.878. Simulations showed correct classification of up to only 34% of patients when 1.5 ≤ true MFR ≤ 2.0. Categorization with high confidence (> 80%) was only achieved for extreme MFR values (< 1.0 or > 2.5), with correct classification in only 15% of patients in a typical lab with MFR of 1.8 ± 0.5.

CONCLUSIONS

Current SPECT-derived estimates of MFR lack precision and require further optimization for clinical risk stratification.

Myocardial blood flows and reserves on solid state camera: Correlations with coronary history and cardiovascular risk factors

OBJECTIVES

Study designed to test association between stress-induced myocardial blood flow (sMBF), resting MBF (rMBF), and MBF reserve (MFR) and coronary artery disease (CAD) in a population of CAD and non-coronary patients. Secondary objectives were to confront visual analysis and dynamic analysis and to explore potential association between MBF and several cardiovascular risk factors METHODS: A total of 155 patients who underwent dynamic myocardial perfusion imaging on a CZT camera were included. sMBF, rMBF, and MFR were evaluated, and cardiovascular risk was assessed.

RESULTS

Significantly lower total sMBF and MFR were observed in CAD patient vs non-CAD patient. In comparison with visual analysis, lower sMBF were found in pathologic territory, lower rMBF in necrotic territory and lower MFR in necrotic ones. A significant correlation between total sMBF, rMBF and diabetes was found.

CONCLUSION

sMBF and MFR as assessed on CZT gamma-cameras can be used to determine the coronary state. Low total sMBF might be an independent risk factor of coronaropathy. An inverse correlation was suggested between total sMBF and rMBF with diabetes.

Insights into Myocardial Perfusion PET Imaging: the Coronary Flow Capacity

Purpose of Review

The present work summarizes the clinical relevance of coronary flow capacity (CFC) with an eye on future perspectives.

Recent findings

CFC concept has been recently introduced providing a comprehensive framework for coronary physiology evaluation.

Summary

It has been widely demonstrated that coronary artery disease (CAD) is a complex disease with a multifactorial etiology resulting from different pathogenic mechanisms. Cardiac positron emission tomography (PET) currently represents the gold standard for CAD assessment, providing absolute myocardial perfusion data including coronary flow reserve (CFR), calculated as the ratio of hyperemic to rest absolute myocardial blood flows. CFC can be obtained from dynamic PET images by plotting the primary stress perfusion data and CFR values for each pixel on a graph of predefined exact ranges. The routine evaluation of this parameter may add diagnostic and prognostic value to clinical and conventional imaging data.

Myocardial Blood Flow and Flow Reserve in Patients With Acute Myocardial Infarction and Obstructive and Non-Obstructive Coronary Arteries: CZT SPECT Study

Background

To assess single-photon emission computed tomography cadmium-zinc-telluride (SPECT CZT)-derived myocardial blood flow (MBF) flow reserve (MFR) and flow difference (FD) in patients with acute myocardial infarction (AMI) and to compare this data with serum cardiac troponin and cardiac magnetic resonance (CMR) findings.

Methods

A total of 31 patients with AMI underwent invasive coronary angiography (ICA), serial high-sensitivity serum cardiac troponin I (cTnI) measurement, and CZT SPECT with visual and quantitative (MBF, MFR, and FD) perfusion parameters, and contrast-enhanced CMR. All patients with AMI were divided into two groups: (1) with non-obstructive coronary arteries (MINOCA), n = 10; (2) with obstructive coronary artery disease (MICAD), n = 21.

Results

The values of SSS and SRS were significantly (p < 0.01) higher whereas global stress MBF, MFR significantly lower in patients with MICAD as compared to MINOCA - 5.0 (3.0; 5.0) vs. 9.0 (5.0; 13.0); 2.0 (1.0; 3.0) vs. 6.0 (3.0; 11.0); 2.02 (1.71; 2.37) vs. 0.86 (0.72; 1.02) ml/min/g; and 2.61 (2.23; 3.14) vs. 1.67 (1.1; 1.9), respectively. Stress MBF correlated with cTnI at 24 h and day 4: ρ = -0.39; p = 0.03 and ρ = -0.47; p = 0.007, respectively. FD correlated with cTnI at 24 h and day 4: ρ = -0.39; p = 0.03 and ρ = -0.46; p = 0.009. CMR analysis showed that infarct size, MVO and myocardial edema in patients with MICAD were significantly (< 0.05) higher as compared to MINOCA: 19.4 (10.4; 29.7) vs. 1.8 (0.0; 6.9); 0.1 (0.0; 0.7) vs. 0.0 (0.0; 0.0) and 19.5 (12.0;30.0) vs. 3.0 (0.0; 12.0), respectively. According to vessel-based analysis of CMR data, acute myocardial injury (defined as late gadolinium enhancement and myocardial edema) was observed more frequently in patients with MICAD compared to MINOCA: 34(37%) vs. 5(5%) p = 0.005, respectively. The values of regional stress MBF, MFR and FD were significantly decreased in LV territories characterized by myocardial injury compared to those without: 0.98 (0.73; 1.79) vs. 1.33 (0.94; 2.08) p < 0.01, 1.64 (1.0; 2.36) vs. 2.0 (1.53; 2.89) p < 0.01 and 0.33 (0.05; 0.57) vs. 0.56 (0.36; 1.32) p> 0.01, respectively.

Conclusion

In patients with AMI, SPECT CZT-derived flow measures were associated with the high-sensitivity troponin I as well as the extent of edema, microvascular obstruction, and infarct size detected by CMR. On the regional level, quantitative SPECT CZT measures were significantly lower in vessel territories characterized by myocardial injury.

Low-dose dobutamine stress gated blood pool SPECT assessment of left ventricular contractile reserve in ischemic cardiomyopathy: a feasibility study

PURPOSE

The purpose of the present study was to evaluate the feasibility of gated blood pool single-photon emission computed tomography (GBPS) with low-dose dobutamine (LDD) stress test, performed on a single-photon emission computed tomography (SPECT) camera equipped with cadmium-zinc-telluride (CZT) solid-state detectors, in assessing of left ventricle (LV) contractile reserve in patients with ischemic cardiomyopathy (ICM).

METHODS

A total of 52 patients (age 59 ± 7.2 years, 47 men and 5 women) with ICM and a control group of 10 patients without obstructive coronary artery lesion underwent GBPS and transthoracic echocardiography (TTE) at rest and during LDD stress test (5, 10, 15 µg/kg/min). The duration of each GBPS step was 5 min. Stress-induced changes in LV ejection fraction (ΔLVEF), peak ejection rate, LV volumes, and mechanical dyssynchrony (phase histogram standard deviation, phase histogram bandwidth and entropy) obtained with GBPS were estimated.

RESULTS

All GBPS indices except end-diastolic volume showed significant dynamics during stress test in both groups. The majority of parameters in ICM patients showed significant changes at a dobutamine dose of 10 µg/kg/min as compared to the rest study. Seventeen percent of ICM patients, but none from the control group, showed a decrease in LVEF during stress, accompanied by a significant increase in entropy. The intra- and inter-observer reproducibility was excellent for both rest and stress studies. There was a moderate correlation (r = 0.5, p = 0.01) between GBPS and TTE, with a mean difference value of - 1.7 (95% confidence interval - 9.8; 6.4; p = 0.06) in ΔLVEF.

CONCLUSION

Low-dose dobutamine stress GBPS performed with high-efficiency CZT-SPECT cameras can be performed for evaluating stress-induced changes in LV contractility and dyssynchrony with lower acquisition time. A dobutamine dose of 10 µg/kg/min can potentially suffice to detect stress-induced changes in patients with ICM during GBPS.

TRIAL REGISTRATION

ClinicalTrials.gov identifier: NCT04508608 (August 7, 2020).

Accuracy and Reproducibility of Myocardial Blood Flow Quantification by Single Photon Emission Computed Tomography Imaging in Patients With Known or Suspected Coronary Artery Disease

BACKGROUND

Single photon emission computed tomography (SPECT) has limited ability to identify multivessel and microvascular coronary artery disease. Gamma cameras with cadmium zinc telluride detectors allow the quantification of absolute myocardial blood flow (MBF) and myocardial flow reserve (MFR). However, evidence of its accuracy is limited, and of its reproducibility is lacking. We aimed to validate ^99mTc-sestamibi SPECT MBF and MFR using standard and spline-fitted reconstruction algorithms compared with ¹³N-ammonia positron emission tomography in a cohort of patients with known or suspected coronary artery disease and to evaluate the reproducibility of this technique.

METHODS

Accuracy was assessed in 34 participants who underwent dynamic ^99mTc-sestamibi SPECT and ¹³N-ammonia positron emission tomography and reproducibility in 14 participants who underwent 2 ^99mTc-sestamibi SPECT studies, all within 2 weeks. A rest/pharmacological stress single-day SPECT protocol was performed. SPECT images were reconstructed using a standard ordered subset expectation maximization (OSEM) algorithm with (N=21) and without (N=30) application of spline fitting. SPECT MBF was quantified using a net retention kinetic model' and MFR was derived as the stress/rest MBF ratio.

RESULTS

SPECT global MBF with splines showed good correlation with ¹³N-ammonia positron emission tomography (r=0.81, P<0.001) and MFR estimates (r=0.74, P<0.001). Correlations were substantially weaker for standard reconstruction without splines (r=0.61, P<0.001 and r=0.34, P=0.07, for MBF and MFR, respectively). Reproducibility of global MBF estimates with splines in paired SPECT scans was good (r=0.77, P<0.001), while ordered subset expectation maximization without splines led to decreased MBF (r=0.68, P<0.001) and MFR correlations (r=0.33, P=0.3). There were no significant differences in MBF or MFR between the 2 reproducibility scans independently of the reconstruction algorithm (P>0.05 for all).

CONCLUSIONS

MBF and MFR quantification using ^99mTc-sestamibi cadmium zinc telluride SPECT with spatiotemporal spline fitting improved the correlation with ¹³N-ammonia positron emission tomography flow estimates and test/retest reproducibility. The use of splines may represent an important step toward the standardization of SPECT flow estimation.

First Validation of Myocardial Flow Reserve Derived from Dynamic 99mTc-Sestamibi CZT-SPECT Camera Compared with 13N-Ammonia PET

¹³N-ammonia positron emission tomography (NH₃-PET) can evaluate myocardial blood flow (MBF) at rest, stress, and myocardial flow reserve (MFR) as well as the ratio of MBF at stress to that at rest. MFR is useful in predicting the prognoses of patients with various heart diseases. Cadmium-zinc-telluride single photon emission computed tomography (CZT-SPECT) enables us to acquire dynamic images of radiotracer kinetics and measure original MBF and MFR using ^99mTc-sestamibi. This study aimed to investigate the utility of CZT-SPECT for quantitative assessment of MBF compared to NH₃-PET. We validated the correlation of MBF and MFR between CZT-SPECT and NH₃-PET. Fourteen patients using one-day rest/stress CZT-SPECT, D-SPECT followed by NH₃-PET within 1 month were enrolled and analyzed prospectively. The reproducibility of the MBF and MFR obtained with these two methods was examined using Spearman's correlation coefficient and Bland-Altman plot analysis. The diagnostic value of D-SPECT for abnormal MFR defined using NH₃-PET results as MFR < 2.0 was assessed using receiver-operating characteristic (ROC) analysis. The median duration between D-SPECT and NH₃-PET was 20 days. Although MBF was overestimated by D-SPECT compared to NH₃-PET at high value (mean difference, 0.43 [0.34-0.53]), MBF and MFR were correlated with the two modalities (MBF: r = 0.71, P < 0.0001, MFR: r = 0.60, P < 0.0001). The ROC curve analysis demonstrated a cutoff of 1.6 for detecting abnormal MFR with D-SPECT (sensitivity, 68%; specificity, 91%; AUC, 0.75). MBF and MFR obtained using D-SPECT and NH₃-PET had a good correlation, suggesting that the quantitative MFR evaluation by CZT-SPECT may help understand the trend of NH₃-PET MFR.

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.

Combining flow and reserve measurement during myocardial perfusion imaging: A new era for myocardial perfusion scintigraphy?

Myocardial flow reserve represents the ratio of myocardial blood flow between stress and rest, giving functional information about both macrocirculation and microcirculation; it has been reported extensively in positron emission tomography, with an increase in diagnostic performance, providing important prognostic information and being a powerful tool to guide therapy. Advances in single photon emission computed tomography, with the widespread availability of "cadmium zinc telluride" single photon emission computed tomography cameras, raise the question of myocardial flow reserve use in daily clinical practice. In this article, we review the pathophysiology of myocardial blood flow and myocardial flow reserve, and the initial data available from single photon emission computed tomography myocardial blood flow and myocardial flow reserve evaluation; we also discuss potential limitations to the wider implementation of flow evaluation in single photon emission computed tomography.

Assessment of the routine reporting of very low-dose exercise-first myocardial perfusion SPECT from a large-scale real-world cohort and correlation with the subsequent reporting of coronary stenosis at angiography

PURPOSE

Our study assesses the routine reporting of exercise ischemia using very low-dose exercise-first myocardial perfusion SPECT in a large number of patients and under real-life conditions, by evaluating correlations with the subsequent routine reporting of coronary stenosis by angiography and with factors that predict ischemia.

METHODS

Data from 13,126 routine exercise MPI reports, from 11,952 patients (31% women), using very low doses of sestamibi and a high-sensitivity cardiac CZT camera, were extracted to assess the reporting of significant MPI-ischemia (> 1 left ventricular segment), to determine the MPI normalcy rate in a group with < 5% pretest probability of coronary artery disease (CAD) (n = 378), and to assess the ability of MPI to predict a > 50% coronary stenosis in patients with available coronary angiography reports in the 3 months after the MPI (n = 713).

RESULTS

The median effective patient dose was 2.51 [IQR: 1.00-4.71] mSv. The normalcy rate was 98%, and the MPI-ischemia rate was independently predicted by a known CAD, the male gender, obesity, and a < 50% LV ejection fraction, ranging from 29.5% with all these risk factors represented to 1.5% when there were no risk factors. A > 50% coronary stenosis was significantly predicted by MPI-ischemia, less significantly for mild (odds ratio [95% confidence interval]: 1.61 [1.26-1.96]) than for moderate-to-severe MPI-ischemia (4.05 [3.53-4.57]) and was also impacted by having a known CAD (2.17 [1.83-2.51]), by a submaximal exercise test (1.48 [1.15-1.81]) and being ≥ 65 years of age (1.43 [1.11-1.76]).

CONCLUSION

Ischemia detected using a very low-dose exercise-first MPI protocol in a large-scale clinical cohort and under real-life routine conditions is a highly significant predictor for the subsequent reporting of coronary stenosis, although this prediction is enhanced by other variables. This weakly irradiating approach is amenable to being repeated at shorter time intervals, in target patient groups with a high probability of MPI-ischemia.

Planning the Follow-Up of Patients with Stable Chronic Coronary Artery Disease

Cardiovascular disease remains the leading cause of death among Europeans, Americans, and around the world. In addition, the prevalence of coronary artery disease (CAD) is increasing, with the highest number of hospital visits, hospital readmissions for patients with decompensated heart failure, and a high economic cost. It is, therefore, a priority to try to plan the follow-up of patients with stable chronic CAD (scCAD) in relation to the published data, experience, and new technology that we have today. Planning the follow-up of patients with scCAD goes beyond the information provided by clinical management guidelines. It requires understanding the importance of a cross-sectional and longitudinal analysis in the clinical history of scCAD, because it has an impact on the cost of healthcare in relation to mortality, economic factors, and the burden of medical consultations. Using the data provided in this work facilitates and standardizes the clinical follow-up of patients with scCAD, and following the marked line makes the work for the clinical physician much easier, by including most clinical possibilities and actions to consider. The follow-up intervals vary according to the clinical situation of each patient and can be highly variable. In addition, the ability to properly study patients with imaging techniques, to stratify at different levels of risk, helps plan the intervals during follow-up. Given the complexity of coronary artery disease and the diversity of clinical cases, more studies are required in the future focused on improving the planning of follow-up for patients with scCAD. The perspective and future direction are related to the valuable utility of integrated imaging techniques in clinical follow-up.

Research Progress of Imaging Methods for Detection of Microvascular Angina Pectoris in Diabetic Patients

Diabetes is a complex metabolic disease characterized by hyperglycemia. Its complications are various, often involving the heart, brain, kidney, and other essential organs. At present, the number of diabetic patients in the world is growing day by day. The cardiovascular disease caused by diabetes has dramatically affected the quality of life of diabetic patients. It is the leading cause of death of diabetic patients. Diabetic patients often suffer from microvascular angina pectoris without obstructive coronary artery disease. Still, there are typical ECG ischemia and angina pectoris, that is, chest pain and dyspnea under exercise. Unlike obstructive coronary diseases, nitrate does not affect chest pain caused by coronary microvascular angina in most cases. With the increasing emphasis on diabetic microvascular angina, the need for accurate diagnosis of the disease is also increasing. We can use SPECT, PET, CMR, MCE, and other methods to evaluate coronary microvascular function. SPECT is commonly used in clinical practice, and PET is considered the gold standard for non-invasive detection of myocardial blood flow. This article mainly introduces the research progress of these imaging methods in detecting microvascular angina in diabetic patients.

Myocardial Flow Reserve Measurement During CZT-SPECT Perfusion Imaging for Coronary Artery Disease Screening: Correlation With Clinical Findings and Invasive Coronary Angiography-The CFR-OR Study

Purpose: The aim of this study was to assess the results of cadmium zinc telluride (CZT)- single-photon emission computed tomography (SPECT) myocardial flow reserve (MFR) in coronary artery disease (CAD) screening regarding clinical risk and its correlation to invasive coronary angiography (ICA). Methods: A total of 137 patients (61 male and 76 female) referred for CAD screening myocardial perfusion imaging (MPI) between November 2018 and April 2020 were included in the CFR-OR prospective trial. The 10-year risk of cardiovascular death according to the European Society of Cardiology (SCORE) was calculated. SPECT 1-day 99mTc-tetrofosmin protocol was acquired on CZT cardiac-dedicated pinhole cameras. Low-dose thoracic CT was used for coronary calcium score (CCS) evaluation. ICA, when performed within 3 months, was also analyzed. Results: Mean SCORE and mean global MFR were, respectively, 4 ± 3.1% and 2.50 ± 0.74; 34 patients had impaired CFR (using a threshold of 2). There was a significant inverse correlation between MFR and SCORE (p = 0.006), gender (p = 0.019), and number of cardiovascular risk factors (p = 0.01). MFR was significantly reduced in patients with CCS above 1 (p = 0.01). No significant correlation was found between MFR and individual cardiovascular risk factors (dyslipidemia, hypertension, diabetes, or family history of CAD). A total of 23 patients underwent ICA. Global MFR SPECT sensitivity and specificity were 83.3 and 100 %, respectively, with an area under the curve of 0.94. Conclusion: Adding MFR to SPECT MPI for CAD screening on CZT camera may contribute to high-risk patient identification and enhance diagnostic performances. MFR could help physician decision to perform ICA.

Advances in translational imaging of the microcirculation

The past few decades have seen an explosion in the development and use of methods for imaging the human microcirculation during health and disease. The confluence of innovative imaging technologies, affordable computing power, and economies of scale have ushered in a new era of "translational" imaging that permit us to peer into blood vessels of various organs in the human body. These imaging techniques include near-infrared spectroscopy (NIRS), positron emission tomography (PET), and magnetic resonance imaging (MRI) that are sensitive to microvascular-derived signals, as well as computed tomography (CT), optical imaging, and ultrasound (US) imaging that are capable of directly acquiring images at, or close to microvascular spatial resolution. Collectively, these imaging modalities enable us to characterize the morphological and functional changes in a tissue's microcirculation that are known to accompany the initiation and progression of numerous pathologies. Although there have been significant advances for imaging the microcirculation in preclinical models, this review focuses on developments in the assessment of the microcirculation in patients with optical imaging, NIRS, PET, US, MRI, and CT, to name a few. The goal of this review is to serve as a springboard for exploring the burgeoning role of translational imaging technologies for interrogating the structural and functional status of the microcirculation in humans, and highlight the breadth of current clinical applications. Making the human microcirculation "visible" in vivo to clinicians and researchers alike will facilitate bench-to-bedside discoveries and enhance the diagnosis and management of disease.

Effects of the COVID-19 pandemic on myocardial perfusion imaging for ischemic heart disease

Purpose

We assessed the effects of the COVID-19 pandemic on myocardial perfusion imaging (MPI) for ischemic heart disease during the lockdown imposed by the Italian Government.

Methods

We retrospectively reviewed the number and the findings of stress single-photon emission computed tomography (SPECT)-MPI performed between February and May 2020 during the COVID-19 pandemic at the University of Napoli Federico II. The number and the findings of stress SPECT-MPI studies acquired in the corresponding months of the years 2017, 2018, and 2019 were also evaluated for direct comparison.

Results

The number of stress SPECT-MPI studies performed during the COVID-19 pandemic (n = 123) was significantly lower (P < 0.0001) compared with the mean yearly number of procedures performed in the corresponding months of the years 2017, 2018, and 2019 (n = 413). Yet, the percentage of abnormal stress SPECT-MPI studies was similar (P = 0.65) during the pandemic (36%) compared with the mean percentage value of the corresponding period of the years 2017, 2018, and 2019 (34%).

Conclusion

The number of stress SPECT-MPI studies was significantly reduced during the COVID-19 pandemic compared with the corresponding months of the previous 3 years. The lack of difference in the prevalence of abnormal SPECT-MPI studies between the two study periods strongly suggests that many patients with potentially abnormal imaging test have been missed during the pandemic.