Comparison between N13NH3-PET and 99mTc-Tetrofosmin-CZT SPECT in the evaluation of absolute myocardial blood flow and flow reserve

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.

The Influence of Kinetic Models and Attenuation Correction on Cadmium-Zinc-Telluride Single-Photon Emission Computed Tomography (CZT SPECT)-Derived Myocardial Blood Flow and Reserve: Correlation with Invasive Angiography Data

(1) Background: The objective of this study was to determine the optimal post-processing model for dynamic cadmium-zinc-telluride single-photon emission computed tomography (CZT-SPECT). (2) Methods: A total of 235 patients who underwent diagnostic invasive coronary angiography within three months of the SPECT and those who had coronary computed tomography angiography (CCTA) before SPECT (within 3 months) were enrolled in this study. Each SPECT study was processed to obtain global and regional stress myocardial blood flow (sMBF), rest-MBF (rMBF), myocardial flow reserve (MFR) and flow difference (FD) estimates obtained with 1-tissue-compartment (1TCM) and net retention (NR) modes, both with and without attenuation correction. (3) Results: The use of AC led to significantly higher sMBF, rMBF and DF values obtained by 1TCM compared those values derived by 1TCM with NAC; the lowest values of stress MBF and rest MBF were obtained by 1TCM_NAC. The resting flow, MFR and DF were significantly (p < 0.005) higher in the AC model than in NAC. All quantitative variables were significantly (p < 0.05) higher in NR_NAC than in the 1TC_NAC model. Finally, sMBF, rMBF and FD showed significantly (p < 0.05) higher values by using 1TMC_AC compared to NR_AC. (4) Conclusions: We suggested that 1-compartment and net retention models correctly reflect coronary microcirculation and can be used for clinical practice for evaluating quantitative myocardial perfusion by dynamic SPECT. Attenuation correction is an important step in post-processing dynamic SPECT data, which increases the consistency and diagnostic accuracy of models.

Prognostic value of myocardial flow reserve measured with CZT cardiac-dedicated SPECT low-dose dynamic myocardial perfusion imaging in patients with INOCA

BACKGROUND

Clinical use of dynamic myocardial perfusion imaging (D-MPI) of cadmium-zinc-telluride (CZT) cardiac-dedicated SPECT is growing, showing a higher application value than conventional SPECT. The prognostic value of ischemia in patients with non-obstructive coronary arteries (INOCA) remains an important challenge for investigation. The primary objective of this study was to investigate the prognostic value of myocardial flow reserve (MFR) measured with low-dose D-MPI of CZT cardiac-dedicated SPECT in the assessment of patients with INOCA.

METHODS

Consecutive screening of patients with INOCA and obstructive coronary artery disease (OCAD) who had coronary angiography (CAG) data was performed within three months before or after D-MPI imaging. The patients who met the inclusion criteria were retrospectively analyzed and follow-up by telephone was performed. The enrolled patients were then divided into the INOCA and OCAD groups. INOCA was defined as signs and/or symptoms of myocardial ischemia but with < 50% epicardial stenosis. OCAD was defined as obstructive stenosis (≥ 50% stenosis) of epicardial coronary arteries or their major branches on the CAG. Medical treatments, Seattle Angina Questionnaire (SAQ) scores, and major adverse cardiac events (MACEs) were studied. The Kaplan-Meier survival curve, Log-rank test, and univariable COX regression analysis were used to evaluate the prognosis of patients and associated predictors, with P < 0.05 being considered statistically significant.

RESULTS

A total of 303 patients (159 males and 144 females) were enrolled for the final analysis after excluding 24 patients who were lost to follow-up. The mean age of the included cases was 61.94 ± 8.59 years, of which 203 (67.0%) cases were OCAD and 100 (33.0%) cases were INOCA, respectively. The median follow-up was 16 months (14-21 months). Kaplan-Meier survival curves showed that the incidence of MACE was similar in the INOCA and OCAD groups (log-rank P = 0.2645), while those with reduced MFR showed a higher incidence of MACE than those with normal MFR (log-rank P = 0.0019). The subgroup analysis in the OCAD group revealed that 105 patients with reduced MFR had a higher incidence of MACE than those with normal MFR (log-rank P = 0.0226). The subgroup analysis in the INOCA group showed that 37 patients with reduced MFR had a higher incidence of MACE than those with normal MFR in the INOCA group (log-rank P = 0.0186). Univariable Cox regression analysis showed for every 1 unit increase in MFR, the risk of MACE for INOCA was reduced by 66.1% and that for OCAD by 64.2%. For each 1 mL·g-1·min-1 increase in LV-sMBF, the risk of MACE was reduced by 72.4% in INOCA patients and 63.6% in OCAD patients.

CONCLUSIONS

MFR measured with low-dose D-MPI CZT SPECT provides incremental prognostic value in patients with INOCA. Patients with reduced MFR show an increased risk of MACE, increased symptom burdens, and impaired quality of life. INOCA patients with reduced MFR experienced higher rate of MACE than OCAD patients with normal MFR.

SPECT myocardial blood flow quantitation for the detection of angiographic stenoses with cardiac-dedicated CZT SPECT

PURPOSE

CZT SPECT with the enhanced imaging characteristic facilitates SPECT myocardial blood flow (MBF) quantitation moving toward a clinical utility to uncover myocardial ischemia. The purpose of this study was to investigate the diagnostic performance of stress MBF, myocardial flow reserve (MFR) and myocardial flow capacity (MFC) derived from CZT SPECT in the detection of coronary artery disease (CAD).

METHODS

One-hundred and eighty patients underwent two-day rest/adenosine-stress scans for SPECT MBF quantitation. All dynamic SPECT images were reconstructed and corrected with necessary corrections. The one-tissue two-compartment kinetic model was utilized to fit kinetic parameters (K1, k2 and FBV) by numeric optimization and converted to MBF from K1. Rest MBF, stress MBF and MFR in left ventricle and coronary territories were calculated from flow polar maps. MFC was assessed by extents of moderately and severely abnormal flow statuses using an integrated flow diagram. Per-patient and per-vessel analyses were performed to determine cutoff values for the detection of angiographically obstructive and flow-limited CAD.

RESULTS

Using the threshold of ≥ 50% stenosis, 149 patients (82.78%) were classified to have obstructive lesions in 355 vessels (65.74%). Using the threshold of ≥ 70% stenosis, 113 patients (62.78%) were classified to have flow-limited lesions in 282 vessels (52.22%). On per-patient analysis, the optimal cutoff values of stress MBF and MFR to detect ≥ 50% stenosis were (1.44 ml/min/g, 1.96) and (1.34 ml/min/g and 1.75) to detect ≥ 70% stenosis. The optimal cutoff values for severely and combined moderately severely abnormal MFC extents were (2.3-2.5%, 23.1%) and (7.5%, 29.4%), respectively. The overall sensitivity of MFC (0.84-0.86, 0.86-0.90) to detect ≥ 50% and ≥ 70% lesions surpassed those of stress MBF (0.78. 0.78) and MFR (0.80, 0.75) (all p < 0.05) with similar specificity (MFC = 0.84-0.90, 0.87-0.91; stress MBF = 0.87, 0.91; MFR = 0.84, 0.89) (all p≥ 0.05).

CONCLUSION

The non-invasive SPECT MBF quantitation using CZT SPECT is a reliable method to detect angiographically obstructive and flow-limited CAD. Myocardial flow capacity can outperform with higher diagnostic sensitivity than stress MBF or MFR alone.

Multicenter Evaluation of the Feasibility of Clinical Implementation of SPECT Myocardial Blood Flow Measurement: Intersite Variability and Imaging Time

BACKGROUND

Single-center studies have shown that single photon emission computed tomography myocardial blood flow (MBF) measurement is accurate compared with MBF measured with microspheres in a porcine model, positron emission tomography, and angiography. Clinical implementation requires consistency across multiple sites. The study goal is to determine the intersite processing repeatability of single photon emission computed tomography MBF and the additional camera time required.

METHODS

Five sites (Canada, Italy, Japan, Germany, and Singapore) each acquired 25 to 35 MBF studies at rest and with pharmacological stress using technetium-99m-tetrofosmin on a pinhole-collimated cadmium-zinc-telluride-based cardiac single photon emission computed tomography camera with standardized list-mode imaging and processing protocols. Patients had intermediate to high pretest probability of coronary artery disease. MBF was measured locally and at a core laboratory using commercially available software. The time a room was occupied for an MBF study was compared with that for a standard rest/stress myocardial perfusion study.

RESULTS

With motion correction, the overall correlation in MBF between core laboratory and local site was 0.93 (range, 0.87-0.97) at rest, 0.90 (range, 0.84-0.96) at stress, and 0.84 (range, 0.70-0.92) for myocardial flow reserve. The local-to-core difference in global MBF (bias-MBF) was 5.4% (-3.8% to 14.8%; median [interquartile range]) at rest and 5.4% (-6.2% to 19.4%) at stress. Between the 5 sites, bias-MBF ranged from -1.6% to 11.0% at rest and from -1.9% to 16.3% at stress; the interquartile range in bias-MBF was between 9.3% (4.8%-14.0%) and 22.3% (-10.3% to 12.0%) at rest and between 17.0% (-11.3% to 5.6%) and 33.3% (-10.4% to 22.9%) at stress and was not significantly different between most sites. Both bias and interquartile range were like previously reported interobserver variability and less than the SD of the test-retest difference of 30%. The overall difference in myocardial flow reserve was 1.52% (-10.6% to 11.3%). There were no significant differences between with and without motion correction. The average additional acquisition time varied between sites from 44 to 79 minutes.

CONCLUSIONS

The average bias-MBF and bias-MFR values were small with standard deviations substantially less than the test-retest variability. This demonstrates that MBF can be measured consistently across multiple sites and further supports that this technique can be reliably implemented.

REGISTRATION

URL: https://www.

CLINICALTRIALS

gov; Unique identifier: NCT03427749.

Measuring myocardial blood flow using dynamic myocardial perfusion SPECT: artifacts and pitfalls

Dynamic acquisition allows absolute quantification of myocardial perfusion and flow reserve, offering an alternative to overcome the potential limits of relative quantification, especially in patients with balanced multivessel coronary artery disease. SPECT myocardial perfusion is widely available, at lower cost than PET. Dynamic cardiac SPECT is now feasible and has the potential to be the next step of comprehensive perfusion imaging. In order to help nuclear cardiologists potentially interested in using dynamic perfusion SPECT, we sought to review the different steps of acquisition, processing, and reporting of dynamic SPECT studies in order to enlighten the potentially critical pitfalls and artifacts. Both patient-related and technical artifacts are discussed. Key parameters of the acquisition include pharmacological stress, radiopharmaceuticals, and injection device. When it comes to image processing, attention must be paid to image-derived input function, patient motion, and extra-cardiac activity. This review also mentions compartment models, cameras, and attenuation correction. Finally, published data enlighten some facets of dynamic cardiac SPECT while several issues remain. Harmonizing acquisition and quality control procedures will likely improve its performance and clinical strength.

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.

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.

Prognostic value of combined coronary angiography-derived IMR and myocardial perfusion imaging by CZT SPECT in INOCA

BACKGROUND

A significant proportion of ischemia with non-obstructive coronary artery disease (INOCA) demonstrate coronary microvascular dysfunction (CMD), a condition associated with abnormal myocardial perfusion imaging (MPI) and adverse outcomes. Coronary angiography-derived index of microvascular resistance (caIMR) is a novel non-invasive technique to assess CMD. We aimed to investigate the prognostic value of combined caIMR and MPI by CZT SPECT in INOCA patients.

METHODS

Consecutive 151 patients with chest pain and < 50% coronary stenosis who underwent coronary angiography and MPI within 3 months were enrolled. caIMR was calculated by computational pressure-flow dynamics. CMD was defined as caIMR ≥ 25. The endpoint was major adverse cardiac events (MACE: cardiovascular death, nonfatal myocardial infarction, revascularization, angina-related rehospitalization, heart failure, and stroke).

RESULTS

Of all INOCA patients, CMD was present in 93 (61.6%) patients. The prevalence of abnormal MPI was significantly higher in CMD compared with non-CMD patients (40.9% vs 13.8%, P < .001). CMD showed a higher risk of MACE than non-CMD patients. Patients with both CMD and abnormal MPI had the worst prognosis, followed by patients with CMD and normal MPI (log-rank P < .001). Cox regression analysis identified CMD (HR 3.121, 95%CI 1.221-7.974, P = .017) and MPI (HR 2.704, 95%CI 1.030-7.099, P = .043) as predictive of MACE. The prognostic value of INOCA patients enhanced significantly by adding CMD and MPI to the model with clinical risk factors (AUC = 0.777 vs 0.686, P = .030).

CONCLUSION

caIMR-derived CMD is associated with increased risk of MACE among INOCA patients. Patients with abnormalities on both caIMR and MPI had the worse outcomes.

Left ventricular function and volumes from gated [13N]-ammonia positron emission tomography myocardial perfusion imaging: A prospective head-to-head comparison against CMR using a hybrid PET/MR device

BACKGROUND

Positron emission tomography (PET) myocardial perfusion imaging (MPI) can be used to evaluate left ventricular (LV) volumes and function. We performed a head-to-head comparison of LV function and volumes obtained simultaneously using [13N]-ammonia-PET and cardiac magnetic resonance (CMR), with the latter serving as the reference standard.

METHODS AND RESULTS

In this prospective study, 51 patients underwent [13N]-ammonia-PET MPI and CMR using a hybrid PET/MR device. Left ventricular end-systolic volumes (LVESV), end-diastolic volumes (LVEDV), stroke volumes (LVSV), ejection fractions (LVEF), and segmental wall motion were analyzed for both methods and were compared using correlational and Bland-Altman (BA) analysis; segmental wall motion was compared using ANOVA. The agreement between [13N]-ammonia-PET and CMR for LVEF was good, with minimal bias (- .6%) and narrow BA limits of agreement (- 7.9% to 6.8%), but [13N]-ammonia-PET systematically underestimated LV volumes, with high bias in LVESV (- 11.2 ml), LVEDV (- 28.9 ml), and LVSV (- 17.5 ml). Mean segmental wall motion in [13N]-ammonia-PET differed significantly among the corresponding normokinetic (6.6 ± 2 mm), hypokinetic (5.1 ± 2 mm), and akinetic (3.3 ± 2 mm) segments in CMR (P < .01).

CONCLUSION

LVEF and LV wall motion can be accurately assessed using [13N]-ammonia-PET MPI, although LV volumes are significantly underestimated compared to CMR.

The Role of Imaging in Preventive Cardiology in Women

PURPOSE OF REVIEW

The prevalence of CVD in women is increasing and is due to the increased prevalence of CV risk factors. Traditional CV risk assessment tools for prevention have failed to accurately determine CVD risk in women. CAC has shown to more precisely determine CV risk and is a better predictor of CV outcomes. Coronary CTA provides an opportunity to determine the presence of CAD and initiate prevention in women presenting with angina. Identifying women with INOCA due to CMD with use of cPET or cMRI with MBFR is vital in managing these patients. This review article outlines the role of imaging in preventive cardiology for women and will include the latest evidence supporting the use of these imaging tests for this purpose.

RECENT FINDINGS

CV mortality is higher in women who have more extensive CAC burden. Women have a greater prevalence of INOCA which is associated with higher MACE. INOCA is due to CMD in most cases which is associated with traditional CVD risk factors. Over half of these women are untreated or undertreated. Recent study showed that stratified medical therapy, tailored to the specific INOCA endotype, is feasible and improves angina in women. Coronary CTA is useful in the setting of women presenting with acute chest pain to identify CAD and initiate preventive therapy. CAC confers greater relative risk for CV mortality in women versus (vs.) men. cMRI or cPET is useful to assess MBFR to diagnose CMD and is another useful imaging tool in women for CV prevention.

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.

Improved precision of SPECT myocardial blood flow using a net tracer retention model

BACKGROUND

Noninvasive quantification of absolute myocardial blood flow (MBF) and myocardial flow reserve (MFR) provides incremental benefit to relative myocardial perfusion imaging (MPI) to diagnose and manage heart disease. MBF can be measured with single-photon emission computed tomography (SPECT) but the uncertainty in the measured values is high. Standardization and optimization of protocols for SPECT MBF measurements will improve the consistency of this technique. One element of the processing protocol is the choice of kinetic model used to analyze the dynamic image series.

PURPOSE

This study evaluates if a net tracer retention model (RET) will provide a better fit to the acquired data and greater test-retest precision than a one-compartment model (1CM) for SPECT MBF, with (+MC) and without (-MC) manual motion correction.

METHODS

Data from previously acquired rest-stress MBF studies (31 SPECT-PET and 30 SPECT-SPECT) were reprocessed ± MC. Rate constants (K1) were extracted using 1CM and RET, +/-MC, and compared pairwise with standard PET MBF measurements using cross-validation to obtain calibration parameters for converting SPECT rate constants to MBF and to assess the goodness-of-fit of the calibration curves. Precision (coefficient of variation of test re-test relative differences, COV) of flow measurements was computed for 1CM and RET ± MC using data from the repeated SPECT MBF studies.

RESULTS

Both the RET model and MC improved the goodness-of-fit of the SPECT MBF calibration curves to PET. All models produced minimal bias compared with PET (mean bias < 0.6%). The SPECT-SPECT MBF COV significantly improved from 34% (1CM+MC) to 28% (RET+MC, P = 0.008).

CONCLUSION

The RET+MC model provides a better calibration of SPECT to PET and blood flow measurements with better precision than the 1CM, without loss of accuracy.

Myocardial Perfusion and Coronary Physiology Assessment of Microvascular Dysfunction in Patients Undergoing Transcatheter Aortic Valve Implantation-Rationale and Design

The prevalence of coronary artery disease (CAD) in patients with severe aortic stenosis (AS) is 30-68%. Nevertheless, there is still not enough evidence to use invasive assessment of lesion severity, because the hemodynamic milieu of AS may impact the fractional flow reserve (FFR) and non-hyperemic indices. Therefore, the aim of the study is two-fold. First, to measure acute and long-term changes of FFR, index of microvascular resistance (IMR), and coronary flow reserve (CFR) in patients undergoing TAVI procedure. Second, to compare the diagnostic accuracy of intracoronary indices with myocardial perfusion measured by cadmium-zinc-telluride single-photon emission tomography (CZT-SPECT) and find cut-off values defining significant stenosis. We plan to enroll 40 patients eligible for TAVI with intermediate stenosis (30-70%) in the left anterior descending (LAD) coronary artery. In each patient FFR, CFR, and IMR will be measured in addition to myocardial blood flow calculated by CZT-SPECT before and either immediately after TAVI (acute cohort) or in 6 months (late cohort) after the procedure. FFR, CFR, and IMR will be matched with the results of myocardial perfusion measured by CZT-SPECT in the area of LAD. As a result, cut-off values of FFR, CFR, and IMR defining the decreased blood flow will be found.

The current status of CZT SPECT myocardial blood flow and reserve assessment: Tips and tricks

Cardiac PET-derived measurements of myocardial blood flow (MBF) and myocardial flow reserve (MFR) are proven robust indexes of the severity of coronary artery disease (CAD). They facilitate the diagnosis of diffuse epicardial and microvascular disease and are also of prognostic significance. However, low availability and high cost have limited their wide clinical implementation. Over the last 15 years, cadmium zinc telluride (CZT)-based detectors have been implemented into SPECT imaging devices. Myocardial perfusion scintigraphy can be performed faster and with less radiation exposure as compared with standard gamma cameras. Rapid dynamic SPECT studies with higher count rates can be performed. This technological breakthrough has renewed the interest in SPECT MBF assessment in patients with CAD. Currently, two cardiac-centered CZT gamma cameras are available commercially-Discovery NM530c and D-SPECT. They differ in parameters such as collimator design, number of detectors, sensitivity, spatial resolution and image reconstruction. A number of publications have focused on the feasibility of dynamic CZT SPECT and on the correlation with cardiac PET and invasive coronary angiography measurements of fractional flow reserve. Current study reviews the present status of MBF and MFR assessment with CZT SPECT. It also aims to provide an overview of specific issues related to acquisition, processing and interpretation of quantitative studies in patients with 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.

A study protocol for an observational cohort investigating cardiac transthyretin amyloidosis flow reserve before and after Tafamidis treatment: The AMYTRE study

Introduction

Anginal symptoms and signs of ischemia have been reported in some patients with cardiac transthyretin amyloidosis (ATTR) without obstructive epicardial coronary artery disease (CAD). Few studies found that coronary microvascular dysfunction was highly prevalent in subjects with cardiac amyloidosis, even in the absence of epicardial CAD. The purpose of this study is to confirm the coronary microvascular dysfunction, and to go further with evaluation of the effect of Tafamidis on microvascular dysfunction after 24 months of treatment.

Methods and analysis

This study is a multicentric, prospective, observational cohort study. Adult patients with confirmed ATTR cardiomyopathy seen in the nuclear medicine departments of three large referral centers and treated with Tafamidis will be included. At baseline, patients will have a clinical and echocardiography evaluation. They will undergo a dynamic rest/stress cardiac scintigraphy with flow and reserve measurements before and 24 months after Tafamidis introduction. The primary outcome of this study will be the variation of stress and rest myocardial blood flow and flow reserve between baseline and 24 months after treatment. The effect of Tafamidis will be assessed by an intention to treat analysis.

Ethics and dissemination

The study has received the following approvals: Orleans Hospital Research Committee (CHRO-2021-05) and Sud-Mediterranée IV Regional Ethics Committee (21 06 02). Results will be made available to physicians, the funders, and other researchers.

Clinical trial registration

[https://clinicaltrials.gov/ct2/show/NCT05103943], identifier [NCT05103943].

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.

Definition and epidemiology of coronary microvascular disease

Ischemic heart disease remains one of the leading causes of death and disability worldwide. However, most patients referred for a noninvasive computed tomography coronary angiogram (CTA) or invasive coronary angiogram for the investigation of angina do not have obstructive coronary artery disease (CAD). Approximately two in five referred patients have coronary microvascular disease (CMD) as a primary diagnosis and, in addition, CMD also associates with CAD and myocardial disease (dual pathology). CMD underpins excess morbidity, impaired quality of life, significant health resource utilization, and adverse cardiovascular events. However, CMD often passes undiagnosed and the onward management of these patients is uncertain and heterogeneous. International standardized diagnostic criteria allow for the accurate diagnosis of CMD, ensuring an often overlooked patient population can be diagnosed and stratified for targeted medical therapy. Key to this is assessing coronary microvascular function-including coronary flow reserve, coronary microvascular resistance, and coronary microvascular spasm. This can be done by invasive methods (intracoronary temperature-pressure wire, intracoronary Doppler flow-pressure wire, intracoronary provocation testing) and non-invasive methods [positron emission tomography (PET), cardiac magnetic resonance imaging (CMR), transthoracic Doppler echocardiography (TTDE), cardiac computed tomography (CT)]. Coronary CTA is insensitive for CMD. Functional coronary angiography represents the combination of CAD imaging and invasive diagnostic procedures.

The diagnostic value of SPECT CZT quantitative myocardial blood flow in high-risk patients

BACKGROUND

The objective of this study was to evaluate the accuracy of global MBF and MFR quantitation performed by myocardial perfusion scintigraphy (MPS) for the detection of multivessel coronary artery disease (CAD).

METHODS

52 CAD patients underwent CZT MPS, with the evaluation of MBF and MFR, followed by invasive coronary angiography (ICA). According to MPS and ICA results, all patients were divided into three groups: (1) non-obstructive CAD and normal MPS scan (control group) (n = 7), (2) one vessel disease (1VD) (n = 16), (3) multivessel disease (MVD) (n = 29).

RESULTS

Global absolute MBF and MFR were significantly reduced in MVD patients as compared to those with 1VD [0.93 (IQR 0.76; 1.39) vs 1.94 (1.37; 2.21) mL·min-1·g-1, P = .00012] and [1.4 (IQR 1.02; 1.85) vs 2.3 (1.8; 2.67), P = . 0 004], respectively. The Syntax score correlated with global stress MBF (ρ = - 0.64; P < .0001) and MFR (ρ = - 0.53; P = .0003). ROC analysis showed higher sensitivity and specificity for stress MBF and MFR compared with semiquantitative MPS stress evaluation. Multivariate regression analysis showed that only stress MBF [OR (95% CI) 0.59 (0.42-0.82); P < .0003] was an independent predictor of MVD.

CONCLUSIONS

Quantitative myocardial blood flow values assessed with the use of CZT camera may identify high-risk patients, such as those with multivessel disease.

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.

Quantitative Assessment Using the Compartment Model for Detecting Regional Coronary Artery Disease by Dynamic Myocardial Perfusion Single-Photon Emission Computed Tomography

BACKGROUND

This study aimed to quantitatively evaluate myocardial perfusion single-photon emission computed tomography (SPECT) using an original analysis tool in the compartment model for detecting regional significant coronary artery disease (CAD).Methods and Results:This study analyzed 41 patients (median age, 76 years) with suspected or known CAD who underwent both dynamic SPECT using ^{99 m}Tc-tetrofosmin and invasive coronary angiography. The quantitative analysis was performed using a single-tissue compartment model to evaluate the diagnostic performance of the myocardial flow reserve (MFR) for regional significant CAD, excluding infarcted territories. In the regional analysis, 114 vessels were assessed, of which 31 were diagnosed as significant coronary lesions (≥70% stenosis and/or fraction flow reserve ≤0.8). The MFR of regional significant CAD was significantly lower than that of non-significant CAD (1.11 [0.97-1.31] vs. 1.74 [1.30-2.27]; P<0.001). In the receiver operating characteristic curve analysis, the MFR displayed an area under the curve (AUC) of 0.81. While analyzing each coronary artery territory, the diagnostic performance of the MFR value in the left anterior descending (LAD) artery territory was found to be significantly higher than that found in qualitative assessment (AUC: 0.84 vs. 0.61).

CONCLUSIONS

A quantitative analysis of dynamic SPECT data facilitated detecting regional CAD. For the LAD artery, the MFR displayed a higher diagnostic performance than the qualitative assessment of conventional myocardial perfusion SPECT.

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.

Changing Paradigms in the Diagnosis of Ischemic Heart Disease by Multimodality Imaging

Coronary artery disease (CAD) represents the most common cardiovascular disease, with high morbidity and mortality. Historically patients with chest pain of suspected coronary origin have been assessed with functional tests, capable to detect haemodynamic consequences of coronary obstructions through depiction of electrocardiographic changes, myocardial perfusion defects or regional wall motion abnormalities under stress condition. Stress echocardiography (SE), single-photon emission computed tomography (SPECT), positron emission tomography (PET) and cardiovascular magnetic resonance (CMR) represent the functional techniques currently available, and technical developments contributed to increased diagnostic performance of these techniques. More recently, cardiac computed tomography angiography (cCTA) has been developed as a non-invasive anatomical test for a direct visualisation of coronary vessels and detailed description of atherosclerotic burden. Cardiovascular imaging techniques have dramatically enhanced our knowledge regarding physiological aspects and myocardial implications of CAD. Recently, after the publication of important trials, international guidelines recognised these changes, updating indications and level of recommendations. This review aims to summarise current standards with main novelties and specific limitations, and a diagnostic algorithm for up-to-date clinical management is also proposed.

FT4/FT3 ratio: A novel biomarker predicts coronary microvascular dysfunction (CMD) in euthyroid INOCA patients

BACKGROUND

Ischemia and no obstructive coronary artery disease (INOCA) patients who presented coronary microvascular dysfunction (CMD) demonstrate a poor prognosis, yet the risk factors for CMD remain unclear. Subtle changes in thyroid hormone levels within the normal range, especially the free thyroxine (FT4)/free triiodothyronine (FT3) ratio, have been shown to regulate the cardiovascular system. This prospective study investigated the correlation between FT4/FT3 ratio and CMD in euthyroid patients with INOCA.

METHODS

This prospective study (www.chictr.org.cn/, ChiCTR2000037112) recruited patients with myocardial ischemia symptoms who underwent both coronary angiography (CAG) and myocardial perfusion imaging (MPI) with dynamic single-photon emission computed tomography (D-SPECT). INOCA was defined as coronary stenosis< 50% and CMD was defined as coronary flow reserve (CFR)<2.5. All patients were excluded from abnormal thyroid function and thyroid disease history.

RESULTS

Among 71 INOCA patients (15 [21.1%] CMD), FT4 and FT4/FT3 ratio in CMD group were significantly higher and both showed significantly moderate correlation with CFR (r=-0.25, p=0.03; r=-0.34, p=0.003, respectively). The ROC curve revealed that FT4/FT3 ratio had the highest efficacy for predicting CMD with an optimized cutoff value>3.39 (AUC 0.78, p<0.001, sensitivity, 80.0%; specificity, 71.4%). Multivariate logistic regression showed that FT4/FT3 ratio was an independent predictor of CMD (OR 7.62, 95% CI 1.12-51.89, p=0.038, P for trend=0.006).

CONCLUSION

In euthyroid INOCA patients, increased FT4/FT3 ratio levels are associated with the occurrence of CMD, presenting a novel biomarker for improving the risk stratification.

Impact of attenuation correction for CZT-SPECT measurement of myocardial blood flow

OBJECTIVES

Most of cardiac dedicated CZT-SPECT systems are not equipped with CT, whereas PET systems are. We evaluated the impact of AC correction on CZT-SPECT myocardial blood flow (MBF) and myocardial flow reserve (MFR) measurements.

METHODS

104 patients were included. SPECT data were acquired on cadmium zinc telluride (CZT)-based pinhole cardiac camera in listmode using a stress (250 ± 17 MBq)/rest (511 ± 23 MBq) 1-day Tc-99m-tetrofosmin protocol. Low-dose CT was acquired on another SPECT/CT camera in the same position. All analysis was performed using Corridor4DM.

RESULTS

Stress and rest MBF were significantly lower when AC was applied (P < 0.001). For regional and global MFR, there was no significant difference between AC and NAC measurements (P > 0.25 at least). Mean global LV MFR was 2.43 ± 0.87 and 2.33 ± 0.89, respectively, for NAC and AC measurements. Using a threshold of 2, 86 patients (83%) remained classified as normal and abnormal regarding global LV MFR whether AC was applied or not. Mean difference between NAC and AC values for the 18 other patients was 0.3.

CONCLUSION

AC correction does not significantly affect MFR measurement both in regional and global LV analyses.

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

BACKGROUND

We measured myocardial blood flow (MBF) and perfusion reserve (MPR) by dynamic CZT-SPECT and 82Rb-PET in patients with suspected or known coronary artery disease (CAD) and compared the accuracy of the two methods in predicting obstructive CAD.

METHODS

Twenty-five patients with available coronary angiography data underwent 99mTc-sestamibi CZT-SPECT and 82Rb-PET cardiac imaging. Stress and rest MBF and MPR were calculated by both methods and compared. Diagnostic accuracies of CZT-SPECT and PET were also assessed using a receiver-operator-characteristic curve.

RESULTS

CZT-SPECT yielded similar baseline MBF, but higher hyperemic MBF and MPR values compared to PET. There was a modest correlation between the two methods for MPR (r = 0.56, P < .01). MPR by CZT-SPECT showed a good ability in identify a reduced MPR by PET, with an area under the curve of 0.85. A MPR cut-off of 2.5 was identified by CZT-SPECT for detection of abnormal MPR by PET, with a sensitivity, specificity and accuracy of 86%, 73% and 80%. The area under the curve for the identification of obstructive CAD by regional MPR were 0.83 for CZT-SPECT and 0.84 for PET (P = .90). At CZT-SPECT, a regional MPR of 2.1 provided the best trade-off between sensitivity and specificity for identifying obstructive CAD. Diagnostic accuracy of CZT-SPECT and PET using respective cut-off values was comparable (P = .62).

CONCLUSION

Hyperemic MBF and MPR values obtained by CZT-SPECT are higher than those measured by 82Rb-PET imaging, with a moderate correlation between the two methods. CZT-SPECT shows good diagnostic accuracy for the identification of obstructive CAD. These findings may encourage the use of this new technique to a better risk stratification and patient management.

Measuring SPECT myocardial blood flow at the University of Ottawa Heart Institute

The introduction of new cardiac SPECT cameras has made it practical to do dynamic SPECT imaging and opened the door to performing myocardial blood flow (MBF) imaging with SPECT. In this paper, we describe in detail our approach to dynamic SPECT MBF imaging using a multi-pinhole cardiac SPECT camera and commercially available kinetic analysis software. We use a 1-day rest/stress protocol with 370 MBq injected at rest and 1,000 MBq at stress with a 1- to 2-hour interval between rest and stress imaging. The tracer is injected mechanically over 30 seconds using a syringe pump. Projection data are acquired in listmode for a duration of 11 minutes and then reframed into a dynamic series. Each image is reconstructed independently using vendor-supplied software. The dynamic images are corrected for residual activity and manually corrected for motion using rigid-body translation. The uptake rate constant, K1, is calculated using a 1-tissue-compartment kinetic model and converted to MBF using a previously determined extraction fraction correction.

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.

Diagnostic efficiency of quantification of myocardial blood flow and coronary flow reserve with CZT dynamic SPECT imaging for patients with suspected coronary artery disease: a comparative study with traditional semi-quantitative evaluation

Background

Myocardial blood flow (MBF) quantitation with cadmium-zinc-telluride (CZT) dynamic single-photon emission computed tomography (SPECT) is being increasingly investigated toward clinical utilization.

Methods

In this prospective study, forty-nine patients with suspected or known coronary artery disease (CAD) underwent a rest/adenosine triphosphate (ATP) stress dynamic and routine gated myocardial perfusion imaging (MPI) by CZT SPECT and then received coronary angiography (CAG). Quantitative diagnosis from the dynamic SPECT and a flow diagram was automatically obtained by the dedicated software and compared with the result of semi-quantitative analysis with gated MPI using the angiographic stenosis as the reference standard.

Results

When stenosis ≥50% was considered at the participant level, the sensitivity (SN), specificity (SP), positive predictive value (PPV), negative predictive value (NPV) and accuracy (AC) of the quantitative diagnosis were higher than semi-quantitative method as (84.4% vs. 65.6%, 88.2% vs. 70.6%, 93.1% vs. 80.8%, 75.0% vs. 52.2%, 85.7% vs. 67.3%) (all P<0.05). The receiver operating characteristic (ROC) curve analysis generated the optimal critical value as 1.86 and 1.61 mL/min/g for stress MBF (sMBF) and MFR, respectively. The diagnosis performance of the quantitative diagnosis was higher than semi-quantitative method as (78.9% vs. 68.4%, 63.3% vs. 60.0%, 57.7% vs. 52.0%, 82.6% vs. 75.0%, 69.4% vs. 63.3%) for the criteria of ≥75% stenosis on CAG (all P<0.05) with optimal critical values as 1.71 and 1.15 mL/min/g. There was no significant difference between sMBF and MFR.

Conclusions

The diagnostic efficiency by using the quantitative method of CZT dynamic SPECT imaging is superior to traditional semi-quantitative gated MPI for the diagnosis of CAD, which improved the diagnostic specificity and accuracy when the critical was stenosis ≥50%.