ASNC imaging guidelines for SPECT nuclear cardiology procedures: Stress, protocols, and tracers

False positive pharmacologic myocardial perfusion SPECT study in the setting of a left bundle branch block

We herein report a case of a false positive vasodilatory pharmacologic SPECT stress test in the setting of a left bundle branch block (LBBB). While this is more commonly seen with exercise stress testing, it can also occur with pharmacologic stress testing. In our SPECT exam, we illustrate the commonly mistaken septal/anteroseptal perfusion defects in those patients with a LBBB. PET stress testing may be more reliable for patients with LBBB.

Doppler Echocardiography Assessment of Coronary Microvascular Function in Patients With Angina and No Obstructive Coronary Artery Disease

Echocardiographic evaluation is an essential part of the diagnostic work-up in patients with known or suspected cardiovascular disease. Transthoracic Doppler echocardiography (TTDE) enables straightforward and reliable visualization of flow in the left anterior descending artery. In the absence of obstructive coronary artery disease, low TTDE-derived coronary flow velocity reserve (CFVR) is considered a marker of coronary microvascular dysfunction (CMD). TTDE CFVR is free from ionizing radiation and widely available, utilizing high-frequency transducers, pharmacologic vasodilator stress, and pulsed-wave Doppler quantification of diastolic peak flow velocities. European Society of Cardiology guidelines recommend TTDE CFVR evaluation only following preceding anatomic invasive or non-invasive coronary imaging excluding obstructive CAD. Accordingly, clinical use of TTDE CFVR is limited and CMD frequently goes undiagnosed. An evolving body of evidence underlines that low CFVR is an important and robust predictor of adverse prognosis and continuing symptoms in angina patients both with and without obstructive CAD. The majority of angina patients have no obstructive CAD, particularly among women. This has led to the suggestion that there may be a gender-specific female atherosclerotic phenotype with less epicardial obstruction, and a low CFVR signifying CMD instead. Nevertheless, available evidence indicates low CFVR is an equally important prognostic marker in both men and women. In this review, TTDE CFVR was evaluated regarding indication, practical and technical aspects, and interpretation of results. Association with symptoms and prognosis, comparison with alternative invasive and non-invasive imaging modalities, and possible interventions in angina patients with low CFVR were discussed, and key research questions were proposed.

Regadenoson-induced T-wave heterogeneity complements coronary stenosis detection by myocardial perfusion imaging in men and women

AIMS

We analysed whether incorporating electrocardiographic interlead T-wave heterogeneity (TWH) with myocardial perfusion imaging (MPI) during pharmacologic stress improves detection of flow-limiting lesions (FLL).

METHODS AND RESULTS

Medical records of all 103 patients at our institution who underwent stress testing with regadenoson (0.4 mg IV bolus) within 3 months of coronary angiography from September 2017 to March 2019 were studied. Cases (N = 59) had angiographically significant FLL (≥50% of left main or ≥70% of other epicardial coronary arteries ≥2 mm in diameter); controls (N = 44) were normal or had non-FLL. TWH, i.e., interlead splay of T waves, was assessed from precordial leads V4-6 by second central moment analysis. Maximum TWHV4-6 levels during regadenoson stress were 68% higher in cases than in controls (P < 0.0001). TWHV4-6 generated areas under the receiver-operating characteristic (ROC) curve of 0.79 in men (P < 0.0001) and 0.71 in women (P = 0.007). In men, the ROC-guided 54-µV TWHV4-6 cut-point for FLL produced adjusted odds of 7.3 [95% confidence interval (CI): 1.3-41.5, P = 0.03], 79% sensitivity, and 78% specificity. In women, the ROC-guided 35-µV TWHV4-6 cut-point produced adjusted odds of 4.5 (95% CI: 1.1-18.9, P = 0.04), 84% sensitivity, and 52% specificity. Adding TWHV4-6 to MPI determinations reduced false-positive results by 70%, more than doubled true-negative results, and improved adjusted odds ratio to 6.8 (95% CI: 2.2-21.4, P = 0.001) with specificity of 78% in men and 86% in women.

CONCLUSION

This observational study is the first to demonstrate the benefit of combining TWHV4-6 with MPI to enhance FLL detection during MPI with regadenoson in both men and women.

The additional prognostic value of myocardial perfusion SPECT in patients with known coronary artery disease with high exercise capacity

BACKGROUND

The prognostic value of myocardial perfusion imaging (MPI) in patients with known coronary artery disease (CAD) and high exercise capacity is still unknown. We sought to determine the MPI additional prognostic value over electrocardiography (ECG) stress testing alone in patients with known CAD who achieved ≥ 10 metabolic equivalents (METs).

METHODS AND RESULTS

We evaluated 926 patients with known CAD referred for MPI with exercise stress. Patients were followed for a mean of 32.4 ± 9.7 months for the occurrence of all-cause death or nonfatal myocardial infarction (MI). Those achieving ≥ 10 METs were younger, predominantly male, and had lower prevalence of cardiovascular risk factors. Patients reaching ≥ 10 METs had a lower annualized rate of hard events compared to their counterparts achieving < 10 METs (1.13%/year vs 3.95%/year, P < .001). Patients who achieved ≥ 10 METs with abnormal scans had a higher rate of hard events compared to those with normal scans (3.37%/year vs 0.57%/year, P = .023). Cardiac workload < 10 METs and an abnormal MPI scan were independent predictors of hard events.

CONCLUSIONS

MPI is able to stratify patients with known CAD achieving ≥ 10 METs for the occurrence of all-cause death and nonfatal MI, with incremental prognostic value over ECG stress test alone.

Asystole following Regadenoson administration: Review of literature, risk factors and management

Regadenoson, a selective A2A receptor agonist, is widely used for vasodilator stress myocardial perfusion imaging and has a superior adverse effect profile when compared with other agents. However, with widespread use, there have been several reported cases of Regadenoson induced bradyarrhythmias and even asystole in patients with no known conduction system disease. In this article, we report a case of asystole following Regadenoson administration, evaluate mechanisms and risk factors for Regadenoson induced bradyarrhythmias to better identify patients at risk. We also review the available treatment options and propose recommendations for limiting its risk.

Evaluating the role of left ventricle global longitudinal strain in myocardial perfusion defect assessment

Myocardial perfusion defect, assessed with single photon emission computed tomography (SPECT), is useful for patient management and risk stratification. Left ventricle Global Longitudinal Strain (LV GLS) has gained interest for observing subclinical LV dysfunction. We aimed to investigate the utility of LV GLS in evaluating myocardial perfusion defect. A retrospective study of all patients who underwent SPECT and LV GLS at Tel Aviv Sourasky medical center. Overall, 86 patients were included. LV GLS and SPECT correlated in the base and apex sections for infraction, and in the apex only for ischemia. Adjusted analysis showed a significant correlation between LV GLS of both the mid and apical section and infarction by SPECT, but no association with ischemia. No associations were found by arterial supply territory. A sub-analysis of patients without left bundle branch block (LBBB) strengthened the correlations, with a 58-70% higher chance of both fixed and reversible defects for every 1-unit decrease LV GLS in the mid and apical sections. LV GLS effectively evaluated the presence of infarction by SPECT in the mid and apical sections, particularly in patients without LBBB. Due to its high availability, LV GLS may have a role in evaluating myocardial perfusion defect.

40 Years Anniversary of Cardiac 123I-mIBG Imaging: State of the Heart

Purpose of Review

This narrative review reflects on the body of evidence on cardiac 123I-mIBG imaging that has accumulated since the introduction in the late 1970s and focusses on to what extent cardiac 123I-mIBG imaging has fulfilled its potential in cardiology especially.

Recent Findings

In contrast to the linear relationship between 123I-mIBG-derived parameters and overall prognosis in heart failure, there seems a “bell-shape” curve for 123I-mIBG-derived parameters and arrhythmic events. In addition, there is a potential clinical role for cardiac 123I-mIBG in optimizing patient selection for expensive devices (i.e., ICD and CRT). This needs of course to be established in future trials.

Summary

Cardiac 123I-mIBG imaging is, despite the numerous of studies, sometimes mistakenly seen as a nice to have technique rather than a must have imaging modality. Although cardiac 123I-mIBG imaging has grown and matured over the years, its full clinical potential has still not been tested to the maximum.

Assessment of LV diastolic dysfunction in myocardial perfusion imaging: a correlative study with transthoracic echocardiography

OBJECTIVE

Myocardial perfusion imaging (MPI) by gated single-photon emission computed tomography (SPECT) is a feasible method in the evaluation of left ventricular perfusion and function. The purpose of this study was to determine the threshold and grading of left ventricular (LV) diastolic dysfunction (LVDD) using gated SPECT MPI.

METHODS

A total of 149 patients were recruited in the study. All of the patients underwent a standard 2-day stress/rest gated MPI study and transthoracic echocardiography within 2 weeks. The reconstructed rest-only images were analyzed by Cedar-Sinai's quantitative gated SPECT and the LV diastolic parameters, including peak filling rate (PFR), time to PFR (TTPF) and secondary PFR (PFR2) to PFR ratio were provided and compared to echocardiographic data.

RESULTS

68 (45.6%) and 81 (54.4%) of patients were categorized in LVDD-absent and LVDD-present groups on the basis of LVDD evidence in echocardiography, respectively. receiver-operating-characteristic analysis for PFR and TTPF was performed, resulting in diagnostic sensitivities of 70 and 57% and specificities of 60 and 75% for PFR <2.6 end-diastolic volumes (EDV)/s and TTPF>160.5 ms, respectively. Applying our previously used thresholds of <1.70 EDV/s for PFR, >208 ms for TTPF and >1 for PFR2/PFR, sensitivities and specificities of 9.9 and 96.6%, 9.9 and 95.6% and 13.8 and 88% were resulted, respectively. Grading of LVDD on the basis of MPI-obtained diastolic parameters showed considerable overlapping data by interquartile range.

CONCLUSION

Gated SPECT MPI can be used as a highly specific means for detection of LV diastolic dysfunction when compared to echocardiography. However, grading of severity of diastolic heart failure appears to be impracticable.

Non-invasive Imaging in Patients With Chronic Total Occlusions of the Coronary Arteries-What Does the Interventionalist Need for Success?

Chronic total occlusion (CTO) of coronary arteries is a common finding in patients with known or suspected coronary artery disease (CAD). Although tremendous advances have been made in the interventional treatment of CTOs over the past decade, correct patient selection remains an important parameter for achieving optimal results. Non-invasive imaging can make a valuable contribution. Ischemia and viability, two major factors in this regard, can be displayed using echocardiography, single-photon emission tomography, positron emission tomography, computed tomography, and cardiac magnetic resonance imaging. Each has its own strengths and weaknesses. Although most have been studied in patients with CAD in general, there is an increasing number of studies with positive preselectional factors for patients with CTOs. The aim of this review is to provide a structured overview of the current state of pre-interventional imaging for CTOs.

Multimodality imaging of myocardial viability: an expert consensus document from the European Association of Cardiovascular Imaging (EACVI)

In clinical decision making, myocardial viability is defined as myocardium in acute or chronic coronary artery disease and other conditions with contractile dysfunction but maintained metabolic and electrical function, having the potential to improve dysfunction upon revascularization or other therapy. Several pathophysiological conditions may coexist to explain this phenomenon. Cardiac imaging may allow identification of myocardial viability through different principles, with the purpose of prediction of therapeutic response and selection for treatment. This expert consensus document reviews current insight into the underlying pathophysiology and available methods for assessing viability. In particular the document reviews contemporary viability imaging techniques, including stress echocardiography, single photon emission computed tomography, positron emission tomography, cardiovascular magnetic resonance, and computed tomography and provides clinical recommendations for how to standardize these methods in terms of acquisition and interpretation. Finally, it presents clinical scenarios where viability assessment is clinically useful.

Stress CMR in patients with obesity: insights from the Stress CMR Perfusion Imaging in the United States (SPINS) registry

AIMS

Non-invasive assessment and risk stratification of coronary artery disease in patients with large body habitus is challenging. We aim to examine whether body mass index (BMI) modifies the prognostic value and diagnostic utility of stress cardiac magnetic resonance imaging (CMR) in a multicentre registry.

METHODS AND RESULTS

The SPINS Registry enrolled consecutive intermediate-risk patients who presented with a clinical indication for stress CMR in the USA between 2008 and 2013. Baseline demographic data including BMI, CMR indices, and ratings of study quality were collected. Primary outcome was defined by a composite of cardiovascular death and non-fatal myocardial infarction. Of the 2345 patients with available BMI included in the SPINS cohort, 1177 (50%) met criteria for obesity (BMI ≥ 30) with 531 (23%) at or above Class 2 obesity (BMI ≥ 35). In all BMI categories, >95% of studies were of diagnostic quality for cine, perfusion, and late gadolinium enhancement (LGE) sequences. At a median follow-up of 5.4 years, those without ischaemia and LGE experienced a low annual rate of hard events (<1%), across all BMI strata. In patients with obesity, both ischaemia [hazard ratio (HR): 2.14; 95% confidence interval (CI): 1.30-3.50; P = 0.003] and LGE (HR: 3.09; 95% CI: 1.83-5.22; P < 0.001) maintained strong adjusted association with the primary outcome in a multivariable Cox regression model. Downstream referral rates to coronary angiography, revascularization, and cost of care spent on ischaemia testing did not significantly differ within the BMI categories.

CONCLUSION

In this large multicentre registry, elevated BMI did not negatively impact the diagnostic quality and the effectiveness of risk stratification of patients referred for stress CMR.

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.

Diastolic dyssynchrony assessment by gated myocardial perfusion-SPECT in subjects who underwent cardiac resynchronization therapy

BACKGROUND

Left ventricular diastolic dyssynchrony (LVDD) can be assessed by gated myocardial perfusion single-photon emission computed tomography (GMP-SPECT). LVDD is an area of interest in subjects who underwent cardiac resynchronization therapy (CRT). The aim of this post hoc analysis was to assess the role of LVDD in subjects with CRT who were followed up at 6-month period.

MATERIAL & METHODS

Left ventricular diastolic dyssynchrony was assessed by GMP-SPECT at baseline and after CRT procedure in 160 subjects from 10 different cardiological centers. CRT procedure was performed as per current guidelines. Outcomes were defined as improvement in ≥1 New York Heart Association (NYHA) class, left ventricular ejection fraction (LVEF) by 5%, and reduction in end-systolic volume (ESV) by 15% and 5% points in Minnesota Living with Heart Failure Questionnaire. LVDD was defined as diastolic phase standard deviation ≥40 ± 14°.

RESULTS

Improvement in NYHA functional class occurred in 105 (65.6%), LVEF in 74 (46.3%), decrease in ESV in 86 (53.8%), and Minnesota score in 85 (53.1%) cases. Baseline LV diastolic standard deviation was 53.53° ± 20.85 and at follow-up 40.44° ± 26.1283; (P < 0.001). LVDD was not associated with improvement in clinical outcomes at follow-up.

CONCLUSION

CRT improves both systolic and diastolic dyssynchrony values at 6-month follow-up. LVDD at baseline is correlated with cardiac functionality at follow-up, but not with overall favorable clinical outcomes.

Reducing radiation dose from myocardial perfusion imaging in subjects with complex congenital heart disease

INTRODUCTION

The prevalence of defects and effective radiation dose from various myocardial perfusion imaging (MPI) strategies in congenital heart disease (CHD) is unknown.

METHODS

We studied 75 subjects with complex CHD (ages 5 to 80 years) referred for MPI between 2002 and 2015. A rest and exercise or pharmacologic stress MPI was performed using 99mTechnetium sestamibi, 82rubidium or 13N-ammonia, and Sodium iodide SPECT (single-photon emission computed tomography), SPECT/CT or Cadmium zinc telluride (CZT) SPECT or PET (positron emission tomography)/CT scanners. Deidentified images were interpreted semi-quantitatively in three batches: stress only MPI, stress/rest MPI, and stress/rest MPI with taking into account a history of ventricular septal defect repair. Effective radiation dose was estimated for stress/rest MPI and predicted for 1-day stress-first (normal stress scans), and for 2-day stress/rest MPI (abnormal stress scans).

RESULTS

The median age was 18.6 years. The most common type of CHD was transposition of the great arteries (63%). Rest/stress MPI was abnormal in 43% of subjects and 25% of the abnormal scans demonstrated reversible defects. Of the subjects with abnormal MPI, 33% had significant underlying anatomic coronary artery obstruction. Estimated mean effective radiation dose ranged from 2.1 ± 0.6 mSv for 13N-ammonia PET/CT to 12.5 ± 0.9 mSv for SPECT/CT. Predicted effective radiation dose was significantly lower for stress-first MPI and for 2-day stress/rest protocols.

CONCLUSIONS

Due to the relatively high prevalence of abnormal stress MPI, tailored protocols with a stress-first MPI as well as the use of 2-day protocols and advanced imaging technologies including CZT SPECT, novel image reconstruction software, and PET MPI could substantially reduce radiation dose in complex CHD.

Efficiency of tetrofosmin versus sestamibi achieved through shorter injection-to-imaging times: A systematic review of the literature

Based on superior image quality, more accurate gated images, and lower radiation exposure to patients, Technetium-99m (Tc-99m) based tracers are preferred over Thallium-201 for SPECT myocardial perfusion imaging. The two Tc-99m tracers, sestamibi and tetrofosmin, have many similar characteristics but there are differences in blood and liver clearance rates, as well as the recommended time after injection for imaging to achieve optimal image quality. Because published peer-reviewed studies examining optimal times between injection and imaging are limited, it can be difficult to identify evidence-based opportunities to optimize imaging protocols. Using systematic literature review methods, this study was designed to identify and consolidate the available evidence on the use of sestamibi compared to tetrofosmin for variable injection to imaging times in regard to test efficiency, including test length and re-scan rates, and image quality, including overall quality and cardiac to extra-cardiac ratios. The composite of this data shows that earlier imaging with tetrofosmin is equivalent to later imaging with sestamibi when assessing subjective image quality or when quantifying heart-to-extra-cardiac ratios. Image quality and heart-to-extra-cardiac ratios comparing early versus later imaging with tetrofosmin were comparable if not equivalent to each other. The equivalency of the imaging quality occurs with 15 minutes (on average) earlier imaging compared to sestamibi and 30 minutes compared to standard time tetrofosmin. The subjective findings of equivalent image quality are also shown with objective measurements of heart-to-extra-cardiac ratios. In this review, the significantly shorter injection-to-acquisition times with tetrofosmin compared to sestamibi resulted in better efficiency and less waiting times for patients; in addition, significantly higher re-scan rates with sestamibi compared to tetrofosmin due to hepatic activity contributed to better throughput with tetrofosmin.

Safety and tolerability of regadenoson in comparison with adenosine stress cardiovascular magnetic resonance: Data from a multicentre prospective registry

To assess the feasibility and incidence of immediate complications of stress cardiovascular magnetic resonance (CMR) with regadenoson in comparison with adenosine in a large referral population. This is a large, multicenter, prospective registry of vasodilator stress-CMR in a referral population. We recorded the clinical and demographic data, quality of test, CMR findings, hemodynamic data, and complications. Between January 2016 and July 2019, 2908 patients underwent stress-CMR, 2253 with regadenoson and 655 with adenosine. 25.1% of patients had previously known coronary artery disease (CAD). In 305 patients regadenoson was used due to presence of chronic obstructive pulmonary disease (COPD) or asthma, while in 1948 subjects regadenoson was used as first-line vasodilator. Quality was optimal in 90.0%, suboptimal in 9.5%, and poor in 0.5%. Images were diagnostic in 98.9%. After stress with regadenoson, aminophylline 200 mg was administered intravenously in all patients. No patient died or had severe immediate complications with regadenoson as opposed to 2 severe bronchospasm with adenosine (p = 0.05). 11 patients (0.5%) had non-severe complications with regadenoson and five patients (0.8%) with adenosine (p = n.s.). Only two patients (0.088%) had non-severe bronchospasm after regadenoson administration. All complications were solved in the CMR unit, with no need for further specific care. Factors significantly associated with presence of complications were history of COPD or asthma and detection of inducible ischaemia. Patients had significantly more minor symptoms when adenosine was used (66.0% vs. 18.4%, p < 0.0001). Stress-CMR with regadenoson is feasible, providing diagnostic information in a referral population. Regadenoson had an excellent safety profile and better tolerability than adenosine, with no serious immediate complications and low incidence of non-severe complications. Only inducible ischaemia and previous history of COPD or asthma were associated with complications after regadenoson-CMR. The incidence of minor symptoms was low.

Prognostic Value of Diastolic Dysfunction Derived From D-SPECT in Coronary Artery Disease Patients With Normal Ejection Fraction

Diastolic dysfunction (DD) with normal systolic function has been elucidated to be associated with heart failure and worse prognosis. The recently introduced single photon emission computed tomography (SPECT) with dedicated cardiac cadmium-zinc-telluride (CZT) cameras (D-SPECT) is a novel method to quantitate left ventricular functional parameters. We aimed to evaluate the prognostic value of DD derived from D-SPECT in coronary artery disease (CAD) patients with normal ejection fraction. All CAD patients who underwent D-SPECT and invasive coronary angiography within 3 months were considered. DD was defined as peak filling rate (PFR) <2.1 end diastolic volume (EDV, ml)/s according to the D-SPECT results. Patients were divided into three groups: group 1 (n = 226)-normal PFR; group 2 (n = 67)-ischemia-related DD (abnormal stress PFR and normal rest PFR); and group 3 (n = 106)-rest DD (abnormal rest PFR). The primary clinical endpoint of the present study was a composite of heart failure events (HFE). A total of 399 consecutive CAD patients with normal systolic function undergoing stress D-SPECT were analyzed. The incidence rates of HFE among the three groups were 4.0, 7.5, and 11.3%, respectively. Cox regression analysis showed that the multivariate predictors of HFE were rest PFR, diabetes mellitus, obesity, and old age. DD derived from D-SPECT in CAD patients with normal ejection fraction is predictive of HFE.

Inhibition of the Hepatic Uptake of 99mTc-Tetrofosmin Using an Organic Cation Transporter Blocker

The accumulation of high levels of ^99mTc-tetrofosmin (^99mTc-TF) in the hepatobiliary system can lead to imaging artifacts and interference with diagnosis. The present study investigated the transport mechanisms of ^99mTc-TF and attempted to apply competitive inhibition using a specific inhibitor to reduce ^99mTc-TF hepatic accumulation. In this in vitro study, ^99mTc-TF was incubated in HEK293 cells expressing human organic anion transporting polypeptide 1B1 (OATP1B1), OATP1B3, OATP2B1, organic anion transporter 2 (OAT2), organic cation transporter 1 (OCT1), OCT2, and Na⁺-taurocholate cotransporting polypeptide with or without each specific inhibitor to evaluate the contribution of each transporter to ^99mTc-TF transportation. In vivo studies, dynamic planar imaging, and single photon emission computed tomography (SPECT) experiments with rats were performed to observe alterations to ^99mTc-TF pharmacokinetics using cimetidine (CMT) as an OCT1 inhibitor. Time-activity curves in the liver and heart were acquired from dynamic data, and the ^99mTc-TF uptake ratio was calculated from SPECT. From the in vitro study, ^99mTc-TF was found to be transported by OCT1 and OCT2. When CMT-preloaded rats and control rats were compared, the hepatic accumulation of the ^99mTc-TF was reduced, and the time to peak heart count shifted to an earlier stage. The hepatic accumulation of ^99mTc-TF was markedly suppressed, and the heart-to-liver ratio increased 1.6-fold. The pharmacokinetics of ^99mTc-TF were greatly changed by OCT1 inhibitor. Even in humans, the administration of OCT1 inhibitor before cardiac SPECT examination may reduce ^99mTc-TF hepatic accumulation and contribute to the suppression of artifacts and the improvement of SPECT image quality.

Machine learning predicts per-vessel early coronary revascularization after fast myocardial perfusion SPECT: results from multicentre REFINE SPECT registry

AIMS

To optimize per-vessel prediction of early coronary revascularization (ECR) within 90 days after fast single-photon emission computed tomography (SPECT) myocardial perfusion imaging (MPI) using machine learning (ML) and introduce a method for a patient-specific explanation of ML results in a clinical setting.

METHODS AND RESULTS

A total of 1980 patients with suspected coronary artery disease (CAD) underwent stress/rest 99mTc-sestamibi/tetrofosmin MPI with new-generation SPECT scanners were included. All patients had invasive coronary angiography within 6 months after SPECT MPI. ML utilized 18 clinical, 9 stress test, and 28 imaging variables to predict per-vessel and per-patient ECR with 10-fold cross-validation. Area under the receiver operator characteristics curve (AUC) of ML was compared with standard quantitative analysis [total perfusion deficit (TPD)] and expert interpretation. ECR was performed in 958 patients (48%). Per-vessel, the AUC of ECR prediction by ML (AUC 0.79, 95% confidence interval (CI) [0.77, 0.80]) was higher than by regional stress TPD (0.71, [0.70, 0.73]), combined-view stress TPD (AUC 0.71, 95% CI [0.69, 0.72]), or ischaemic TPD (AUC 0.72, 95% CI [0.71, 0.74]), all P < 0.001. Per-patient, the AUC of ECR prediction by ML (AUC 0.81, 95% CI [0.79, 0.83]) was higher than that of stress TPD, combined-view TPD, and ischaemic TPD, all P < 0.001. ML also outperformed nuclear cardiologists' expert interpretation of MPI for the prediction of early revascularization performance. A method to explain ML prediction for an individual patient was also developed.

CONCLUSION

In patients with suspected CAD, the prediction of ECR by ML outperformed automatic MPI quantitation by TPDs (per-vessel and per-patient) or nuclear cardiologists' expert interpretation (per-patient).

Visually estimated coronary artery calcium score improves SPECT-MPI risk stratification

Aims

Computed tomographic attenuation correction (CTAC) scans for single photon emission computed tomography myocardial perfusion imaging (SPECT-MPI) may reveal coronary artery calcification. The independent prognostic value of a visually estimated coronary artery calcium score (VECACS) from these low-dose, non-gated scans is not established.

Methods & Results

VECACS was evaluated in 4,720 patients undergoing SPECT-MPI with CTAC using a 4-point scale. Major adverse cardiac events (MACE) were defined as all-cause mortality, acute coronary syndrome, or revascularization > 90 days after SPECT-MPI. Independent associations with MACE were determined with multivariable Cox proportional hazards analyses adjusted for age, sex, past medical history, perfusion findings, and left ventricular ejection fraction. During a median follow up of 2.9 years (interquartile range 1.8 - 4.2), 494 (10.5%) patients experienced MACE. Compared to absent VECACS, patients with increased VECACS were more likely to experience MACE (all log-rank p < 0.001), and findings were similar when stratified by normal or abnormal perfusion. Multivariable analysis showed an increased MACE risk associated with VECACS categories of equivocal (adjusted hazard ratio [HR] 2.54, 95% CI 1.45-4.45, p = 0.001), present (adjusted HR 2.44, 95% CI 1.74-3.42, p < 0.001) and extensive (adjusted HR 3.47, 95% CI 2.41-5.00, p < 0.001) compared to absent. Addition of VECACS to the multivariable model improved risk classification (continuous net reclassification index 0.207, 95% CI 0.131 - 0.310).

Conclusion

VECACS was an independent predictor of MACE in this large SPECT-MPI patient cohort. VECACS from CTAC can be used to improve risk stratification with SPECT-MPI without additional radiation.

Prognostic value of regadenoson stress myocardial perfusion imaging in patients with left bundle branch block or ventricular paced rhythm

BACKGROUND

Vasodilator stress myocardial perfusion imaging (MPI) is the provocative test of choice in patients with left bundle branch block (LBBB) or ventricular paced (V-paced) rhythm. The prognostic value of regadenoson SPECT myocardial perfusion imaging (MPI) in these patients has not been studied.

METHODS AND RESULTS

We conducted a retrospective cohort study of 562 patients [mean age, 69 ± 11 years; men, 53.3%] with LBBB (50.7%) or V-paced rhythm (49.3%) who underwent regadenoson stress SPECT-MPI. There were 321 (57.1%) subjects with abnormal MPI and 192 (34.2%) with myocardial ischemia. During a mean follow-up of 2.5 ± 1.9 years, 39 (6.9%) patients had a major adverse cardiac event (MACE), defined as cardiac death or myocardial infarction. The annualized MACE rate in patients with normal MPI was 0.9% (LBBB, 0.8%; V-paced, 1.0%). There was a significant stepwise increase in MACE rates with increasing burdens of perfusion abnormality (P < 0.001) and myocardial ischemia (P = 0.001). Increased risk with abnormal MPI [adjusted hazard ratio, 4.26; P = 0.001] and myocardial ischemia [adjusted hazard ratio, 2.70; P = 0.003] was independent of and incremental to important clinical covariates. Abnormal MPI and myocardial ischemia predicted MACE similarly in both LBBB and V-paced subgroups (interaction P values > 0.05).

CONCLUSION

In patients with LBBB and V-paced rhythm, regadenoson stress SPECT-MPI provides independent and incremental prognostic value in predicting adverse cardiac events.

Radiation exposure after myocardial perfusion imaging with Cadmium-Zinc-Telluride camera versus conventional camera

BACKGROUND

Patient exposure to radiation during the management of coronary heart disease (CHD) can be reduced with more efficient technologies in nuclear medicine, such as the Cadmium-Zinc-Telluride (CZT) gamma-camera for myocardial perfusion imaging (MPI) studies. However, it has been suggested that CZT has lower specificity, which might lead to more downstream radiological procedures, particularly among obese individuals.

METHODS AND RESULTS

We evaluated 244 patients with suspected CHD who underwent CZT-SPECT and matched 1:1 according to sex, age, and body mass index (BMI) with those undergoing MPI study with the Anger gamma-camera (Anger-SPECT). The outcome was the total radiation exposure from the MPI study added to the radiation exposure from all subsequent cardiac examinations during a 90-day follow-up. The total radiation dose after 90 days was significantly lower in the CZT-SPECT group (6.4 ± 4.8 vs 9.5±4.9 mSv, P < .001). After adjusting for potential confounders, CZT-SPECT remained associated with lower total radiation dose, but it significantly attenuated among obese individuals (Beta coefficient - 3.73 ± 0.86 for BMI < 30 vs - 2.30 ± 0.92 for BMI ≥ 30 Kg/m2, P for interaction < 0.032).

CONCLUSIONS

CZT-SPECT was associated with lower total radiation doses compared to Anger-SPECT, albeit this benefit may be attenuated in obese individuals.

Diagnostic accuracy of SPECT and PET myocardial perfusion imaging in patients with left bundle branch block or ventricular-paced rhythm

BACKGROUND

The difference in diagnostic accuracy of coronary artery disease (CAD) between vasodilator SPECT and PET myocardial perfusion imaging (MPI) in patients with left bundle branch block (LBBB) or ventricular-paced rhythm (VPR) is unknown.

METHODS

We identified patients with LBBB or VPR who underwent either vasodilator SPECT or PET MPI and subsequent coronary angiography. LBBB/VPR-related septal and anteroseptal defects were defined as perfusion defects involving those regions in the absence of obstructive CAD in the left anterior descending artery or left main coronary artery.

RESULTS

Of the 55 patients who underwent coronary angiography, 38 (69%) underwent SPECT and 17 patients (31%) underwent PET. PET compared to SPECT demonstrated higher sensitivity (88% vs 60%), specificity (56% vs 14%), positive predictive value (64% vs 20%), negative predictive value (83% vs 50%), and overall superior diagnostic accuracy (AUC .72 (95% CI .50-.93) vs .37 (95% CI .20-.54), P = .01) to detect obstructive CAD. LBBB/VPR-related septal and anteroseptal defects were more common with SPECT compared to PET (septal: 72% vs 17%, P = .001; anteroseptal: 47% vs 8%, P = .02).

CONCLUSIONS

PET has higher diagnostic accuracy when compared to SPECT for the detection of obstructive CAD in patients with LBBB or VPR.

Ischemic Heart Disease: Noninvasive Imaging Techniques and Findings

Ischemic heart disease is a leading cause of death worldwide and comprises a large proportion of annual health care expenditure. Management of ischemic heart disease is now best guided by the physiologic significance of coronary artery stenosis. Invasive coronary angiography is the standard for diagnosing coronary artery stenosis. However, it is expensive and has risks including vascular access site complications and contrast material–induced nephropathy. Invasive coronary angiography requires fractional flow reserve (FFR) measurement to determine the physiologic significance of a coronary artery stenosis. Multiple noninvasive cardiac imaging modalities can also anatomically delineate or functionally assess for significant coronary artery stenosis, as well as detect the presence of myocardial infarction (MI). While coronary CT angiography can help assess the degree of anatomic stenosis, its inability to assess the physiologic significance of lesions limits its specificity. Physiologic significance of coronary artery stenosis can be determined by cardiac MR vasodilator or dobutamine stress imaging, CT stress perfusion imaging, FFR CT, PET myocardial perfusion imaging (MPI), SPECT MPI, and stress echocardiography. Clinically unrecognized MI, another clear indicator of physiologically significant coronary artery disease, is relatively common and is best evaluated with cardiac MRI. The authors illustrate the spectrum of imaging findings of ischemic heart disease (coronary artery disease, myocardial ischemia, and MI); highlight the advantages and disadvantages of the various noninvasive imaging methods used to assess ischemic heart disease, as illustrated by recent clinical trials; and summarize current indications and contraindications for noninvasive imaging techniques for detection of ischemic heart disease.

Online supplemental material is available for this article.

Published under a CC BY 4.0 license.

Usefulness of the Duke Activity Status Index to Select an Optimal Cardiovascular Exercise Stress Test Protocol

Exercise testing represents the preferred stress modality for individuals undergoing evaluation of suspected myocardial ischemia. Patients with limited functional status may be unable to achieve an adequate exercise stress, thus influencing the diagnostic sensitivity of the results. The Duke Activity Status Index (DASI) is a clinically applicable tool to estimate exercise capacity. The purpose of the current study was to assess the utility of the DASI to identify patients unable to achieve an adequate exercise stress result. Patients referred for exercise stress testing were administered the DASI pre-exercise. Baseline characteristics and exercise variables were evaluated including DASI-metabolic equivalents (DASI-METs), peak METs, exercise time (ET), and %-predicted maximal heart rate (%PMHR). Criteria for determining adequate exercise stress was defined as ≥85%PMHR or ≥ 5-METs at peak exercise. In 608 cardiovascular stress tests performed during the study period; 314 were exercise stress. The median DASI-METs (8.4 [interquartile range; 6.7 to 9.9]) was associated with estimated peak exercise METs (R=0.50, p <0.001), ET (R=0.29, p <0.001), and %PMHR (R=0.19, p = 0.003). DASI-METs were different between those with < or ≥85%PMHR (7.9 [6.6-9.0] vs. 8.9 [7.1-9.9], P=0.025) and those with < or ≥5-METs (5.8 [4.6 to 6.6] versus 8.9 [7.3-9.9], p <0.001). Receiver operating characteristic curve analysis identified a DASI-MET threshold of ≤/>7.4 to optimally predict adequate exercise stress (sensitivity=93%, specificity=71%). In conclusion, the DASI correlates with peak METs, ET, and %PMHR among patients referred for exercise testing and can be used to identify patients with an increased likelihood of an inadequate stress test result.

Implementation of a Myocardial Perfusion Imaging Risk Algorithm to Inform Appropriate Downstream Invasive Testing and Treatment

BACKGROUND

To risk stratify patients undergoing single-photon emission computed tomography myocardial perfusion imaging (SPECT-MPI) in accordance with appropriate use criteria for referral to coronary angiography, we developed a risk classification algorithm incorporating appropriate use criteria-defined risk features. We evaluated the association between this algorithm with downstream angiography, revascularization, and all-cause mortality.

METHODS

We studied consecutive patients who underwent SPECT-MPI from January 1, 2015, to December 31, 2017, and assigned a scan risk of low, intermediate, high, or indeterminate. With this stratification, we assessed referral for angiography and revascularization within 3 months of SPECT-MPI and intermediate-term mortality.

RESULTS

Among 12 799 patients, the mean age was 66 years, and a majority were men (56.8%). Most patients were low risk (83.6%) followed by intermediate (9.9%) and high risk (5.2%). Compared with low-risk patients, intermediate- and high-risk patients were more frequently referred for angiography (14.8% and 13.6% versus 2.0%; P<0.001) and revascularization (7.7% and 6.8% versus 0.7%; P<0.001). In 1008 propensity-matched patients, scan risk was independently associated with angiography after adjustment for ischemia, scar, or stress ejection fraction. At a mean follow-up of 2.3 years, mortality was higher with increased scan risk (high, 10.4%; intermediate, 7.1%; low, 4.1%; P<0.001). Compared with low scan risk, intermediate (hazard ratio, 1.37 [95% CI, 1.09-1.72]; P=0.008) and high scan risk (hazard ratio, 1.98 [95% CI, 1.53-2.56]; P<0.001) were associated with mortality in multivariable analysis. Similar findings were observed for those undergoing pharmacological and exercise SPECT-MPI with comparatively worse prognosis among pharmacological patients.

CONCLUSIONS

This appropriate use criteria-derived risk classification algorithm for SPECT-MPI guided referral for coronary angiography and revascularization and was significantly associated with mortality. This algorithm may serve as an important tool to reaffirm appropriate use criteria and direct management of patients with stable ischemic heart disease undergoing stress testing.

Dermal and cardiac autonomic fiber involvement in Parkinson's disease and multiple system atrophy

Pathological aggregates of alpha-synuclein in peripheral dermal nerve fibers can be detected in patients with idiopathic Parkinson's disease and multiple system atrophy. This study combines skin biopsy staining for p-alpha-synuclein depositions and radionuclide imaging of the heart with [¹²³I]-metaiodobenzylguanidine to explore peripheral denervation in both diseases. To this purpose, 42 patients with a clinical diagnosis of Parkinson's disease or multiple system atrophy were enrolled. All patients underwent a standardized clinical work-up including neurological evaluation, neurography, and blood samples. Skin biopsies were obtained from the distal and proximal leg, back, and neck for immunofluorescence double labeling with anti-p-alpha-synuclein and anti-PGP9.5. All patients underwent myocardial [¹²³I]-metaiodobenzylguanidine scintigraphy. Dermal p-alpha-synuclein was observed in 47.6% of Parkinson's disease patients and was mainly found in autonomic structures. 81.0% of multiple system atrophy patients had deposits with most of cases in somatosensory fibers. The [¹²³I]-metaiodobenzylguanidine heart-to-mediastinum ratio was lower in Parkinson's disease than in multiple system atrophy patients (1.94 ± 0.63 vs. 2.91 ± 0.96; p < 0.0001). Irrespective of the diagnosis, uptake was lower in patients with than without p-alpha-synuclein in autonomic structures (1.42 ± 0.51 vs. 2.74 ± 0.83; p < 0.0001). Rare cases of Parkinson's disease with p-alpha-synuclein in somatosensory fibers and multiple system atrophy patients with deposits in autonomic structures or both fiber types presented with clinically overlapping features. In conclusion, this study suggests that alpha-synuclein contributes to peripheral neurodegeneration and mediates the impairment of cardiac sympathetic neurons in patients with synucleinopathies. Furthermore, it indicates that Parkinson's disease and multiple system atrophy share pathophysiologic mechanisms of peripheral nervous system dysfunction with a clinical overlap.

PET/CT Myocardial Perfusion Imaging Acquisition and Processing: Ten Tips and Tricks to Help You Succeed

PURPOSE OF REVIEW

Positron emission tomography (PET) is a leading non-invasive modality for the diagnosis of coronary artery disease due to its diagnostic accuracy and high image quality. With the latest advances in PET systems, clinicians are able to assess for myocardial ischemia and myocardial blood flow while exposing patients to extremely low radiation doses. This review will focus on the basics of acquisition and processing of hybrid PET/CT systems from appropriate patient selection to common artifacts and pitfalls.

RECENT FINDINGS

The continued development of hybrid PET/CT technology is producing scanners with exquisite sensitivity capable of generating high-quality images while exposing patients to low radiation doses. List mode acquisition is an essential component in all modern PET/CT scanners allowing simultaneous dynamic and ECG-gated imaging without lengthening scan duration. Various PET radiotracers are currently being developed but rubidium-82 and 13N-ammonia remain the most commonly used perfusion radiotracers. The development of mini 13N-ammonia cyclotrons is a promising tool that should increase access to this radiotracer. Misregistration, attenuation from extra-cardiac activity, and patient motion are the most common causes of artifacts during perfusion imaging. Techniques to automatically realign images and correct respiratory or patient motion artifacts continue to evolve. Despite the continuous evolution of PET imaging techniques, basic knowledge of scan parameters, acquisition techniques, and post processing tools remains essential to ensure high-quality images are produced and artifacts are recognized and corrected. Future research should focus on optimizing scanners to allow for shorter scan protocols and lower radiation exposure as well as continue developing techniques to minimize and correct for motion and misregistration artifacts.

Severe myocardial ischemia in a patient with diabetes mellitus and left bundle branch block

We present the case of a 69-year-old woman with diabetes mellitus, left bundle branch block, and obesity who develops cardiogenic shock after undergoing myocardial perfusion imaging and diagnostic left heart catheterization, but prior to coronary revascularization. This case highlights the risk of cardiac decompensation awaiting surgery in patients with multivessel coronary artery disease. It also emphasizes the subtleties involved in imaging patients with diabetes mellitus and left bundle branch block, as well as the risk of developing complete heart block in the setting of ischemia with underlying conduction disease.

Value of intraventricular dyssynchrony assessment by gated-SPECT myocardial perfusion imaging in the management of heart failure patients undergoing cardiac resynchronization therapy (VISION-CRT)

BACKGROUND

Placing the left ventricular (LV) lead in a viable segment with the latest mechanical activation (vSOLA) may be associated with optimal cardiac resynchronization therapy (CRT) response. We assessed the role of gated SPECT myocardial perfusion imaging (gSPECT MPI) in predicting clinical outcomes at 6 months in patients submitted to CRT.

METHODS

Ten centers from 8 countries enrolled 195 consecutive patients. All underwent gSPECT MPI before and 6 months after CRT. The procedure was performed as per current guidelines, the operators being unaware of gSPECT MPI results. Regional LV dyssynchrony (Phase SD) and vSOLA were automatically determined using a 17 segment model. The lead was considered on-target if placed in vSOLA. The primary outcome was improvement in ≥1 of the following: ≥1 NYHA class, left ventricular ejection fraction (LVEF) by ≥5%, reduction in end-systolic volume by ≥15%, and ≥5 points in Minnesota Living With Heart Failure Questionnaire (MLHFQ).

RESULTS

Sixteen patients died before the follow-up gSPECT MPI. The primary outcome occurred in 152 out of 179 (84.9%) cases. Mean change in LV phase standard deviation (PSD) at 6 months was 10.5°. Baseline dyssynchrony was not associated with the primary outcome. However, change in LV PSD from baseline was associated with the primary outcome (OR 1.04, 95% CI 1.01-1.07, P = .007). Change in LV PSD had an AUC of 0.78 (0.66-0.90) for the primary outcome. Improvement in LV PSD of 4° resulted in the highest positive likelihood ratio of 7.4 for a favorable outcome. In 23% of the patients, the CRT lead was placed in the vSOLA, and in 42% in either this segment or in a segment within 10° of it. On-target lead placement was not significantly associated with the primary outcome (OR 1.53, 95% CI 0.71-3.28).

CONCLUSION

LV dyssynchrony improvement by gSPECT MPI, but not on-target lead placement, predicts clinical outcomes in patients undergoing CRT.

Optimal 99mTc activity ratio in the single-day stress-rest myocardial perfusion imaging protocol: A multi-SPECT phantom study

BACKGROUND

This investigation used image data generated by an anthropomorphic phantom to determine the minimal 99mTc rest-stress activity concentration ratio (R) able to minimize the ghosting effect in the single-day stress-first myocardial perfusion imaging, using different positions of the perfusion defect (PD), scanners and reconstruction protocols.

METHODS

A cardiac phantom with a simulated PD was imaged under different R using different gamma cameras and reconstruction algorithms. The residual activity from precedent stress administration was simulated by modeling effective half-times in each compartment of the phantom and assuming a delay of 3 hours between the stress and rest studies. The net contrast (NC) of the PD in the rest study was assessed for different R, PD positions and scanner/software combinations. The optimal R will be the one that minimize the NC in the rest images RESULTS: The activity concentration ratio R, the position of the PD and the scanner/software combinations were all main effects with a statistically significant impact on the NC, in decreasing order of relevance. The NC diminished significantly only for R values up to 2. No further improvement was observed for NC for R values above 2 and up to 3. NC was significantly higher in anteroseptal than in posterolateral positions of the PD and higher for solid-state cameras.

CONCLUSIONS

A rest-stress activity concentration ratio R of 2 in single-day stress-first myocardial perfusion imaging is enough to achieve the maximum net contrast in the PD. This ratio should be used to optimize patient's radiation exposure.

Absolute myocardial blood flows derived by dynamic CZT scan vs invasive fractional flow reserve: Correlation and accuracy

PURPOSE

To define the diagnostic power of absolute myocardial blood flow (MBF) evaluation on dynamic CZT imaging in intermediate risk patients in comparison with invasive coronary angiography (ICA) and fractional flow reserve (FFR).

METHODS

Twenty-three stable CAD patients underwent one-day dynamic rest-stress 99mTc-Sestamibi myocardial perfusion imaging by CZT camera. Stress and rest MBF values were calculated semi-automatically using a net retention model by Leppo. Coronary flow reserve (CFR) and flow difference (FD) [MBF stress - MBF rest] were also estimated. A total of 28 vessels were functionally quantified with FFR: 19 (68%) vessels with a stenosis ≥ 70% and 9 (32%) with < 70% stenotic lesions.

RESULTS

The mean global MBFs at rest and during stress were 0.36 (IQR 0.33-0.54) mL/min/g and 0.67 (IQR 0.55-0.81) mL/min/g, respectively, with an average CFR of 1.80 (IQR 1.35-2.24). Moderate correlations between stenosis severity and FFR (r = 0.45; P = .01), stress MBF (r = -0.46; P = .01) and FD (r = -0.37; P = .04) were detected. FFR abnormalities were best predicted by absolute stress MBF, CFR and FD with values of ≤ 0.54 mL/min/g (sensitivity 61.5%; specificity 93.3%), ≤ 1.48 (sensitivity 69.2%; specificity 93.3%) and ≤ 0.18 mL/min/g (sensitivity 69.2%; specificity 100%), respectively.

CONCLUSIONS

The values of stress MBF, CFR and FD obtained through dynamic CZT acquisitions compare well with invasive FFR. The clinical use of dynamic acquisition of myocardial perfusion imaging by CZT may help cardiologist in the detection of hemodynamically significant CAD.

Patient-specific SPECT imaging protocols to standardize image noise

BACKGROUND

In addition to acquired photon counts, image noise depends on the image reconstruction algorithm. This work develops patient-specific activity or acquisition time protocols to standardize the average noise in a reconstructed image for different patients, cameras, and reconstruction algorithms.

METHODS

Image noise was calculated for images from 43 patients acquired on both a conventional and a multiple-pinhole cardiac SPECT camera. Functions were found to relate image noise to radiotracer activity, scan time, and body mass and were validated by normalizing the image noise in a test set of 58 patients.

RESULTS

There was a 3.6-fold difference in photon sensitivity between the two cameras but a 16-fold difference in activity-scan time was necessary to match the noise levels. Image noise doubled from 45 to 128 kg for the conventional camera (12.8 minutes) and tripled for the multiple-pinhole camera (5 minutes) for 350 MBq (9.5 mCi) 99mTc-tetrofosmin. It was 16.3% and 6.1% respectively for an average sized patient.

CONCLUSIONS

A linear scaling of activity with respect to the patient weight normalizes image noise but the scaling factors depend on the choice of camera and image reconstruction parameters. Therefore, equivalent numbers of acquired photon counts are not sufficient to guarantee equivalent image noise.

Comparison of myocardial blood flow and flow reserve with dobutamine and dipyridamole stress using rubidium-82 positron emission tomography

BACKGROUND

The objective of this study was to compare the hyperemic myocardial blood flow (MBF) and myocardial flow reserve (MFR) obtained with dobutamine to those of dipyridamole in patients referred for myocardial perfusion imaging (MPI) using 82Rb positron emission tomography.

METHODS

One hundred and fifty-six patients who underwent a 82Rb PET MPI study with dobutamine stress were included. A matching cohort of patients who underwent a 82Rb PET MPI study with dipyridamole stress was created, accounting for sex, age, history of coronary artery disease (CAD), prior revascularization, CAD risk factors, body mass index, and MPI interpretation.

RESULTS

Global rest MBF (median [interquartile range] 0.84 [0.64-1.00] vs 0.69 [0.59-0.85]), stress MBF (2.36 [1.73-3.08] vs 1.66 [1.25-2.06]), MFR (2.75 [2.19-3.64] vs 2.29 [1.78-2.84]), and corrected MFR (2.85 [2.14-3.64] vs 2.20 [1.65-2.75]) were all significantly higher (P < 0.0001) in the dobutamine cohort compared to the dipyridamole cohort.

CONCLUSION

The results of this study suggest that dobutamine produces higher MBF compared to dipyridamole in a representative population referred to nuclear cardiology laboratories.

Diagnostic accuracy of stress-only myocardial perfusion SPECT improved by deep learning

PURPOSE

Deep convolutional neural networks (CNN) for single photon emission computed tomography (SPECT) myocardial perfusion imaging (MPI) has been used to improve the diagnostic accuracy of coronary artery disease (CAD). This study was to design and evaluate a deep learning (DL) approach to automatic diagnosis of myocardial perfusion abnormalities from stress-only MPI.

METHODS

The new DL approach developed for this study was compared to a conventional quantitative perfusion defect size (DS) method. A total of 37,243 patients (51.5% males) undergone stress ^99mTc-Tetrofosmin or ^99mTc-Sestamibi MPI were selected retrospectively from Yale New Haven Hospital. Patients were dichotomized as studies with normal (75.4%) or abnormal (24.6%) myocardial perfusion based on final diagnoses of clinical nuclear cardiologists. Stress myocardial perfusion defect size was calculated using Yale quantitative analytic software. A deep CNN was trained using the circumferential count profile maps derived from SPECT MPI and was evaluated for the diagnosis of perfusion abnormality with a 5-fold cross-validation approach. In each fold, 27,933, 1862 and 7448 patients were used as training, validation and testing datasets, respectively. The area under the receiver-operating characteristic curve (AUC) was calculated and analyzed for all patients as well as for the eight sub-groups classified based on patient genders, quantitative algorithms, radioactive tracers and SPECT cameras.

RESULTS

The AUC value resulted from the DL method was significantly higher than that from the DS method (0.872 ± 0.002 vs. 0.838 ± 0.003, p < 0.01). Across the eight sub-groups, the DL method provided more consistent AUC values in terms of smaller standard deviation and higher diagnostic accuracy and specificity, but slightly lower sensitivity than the DS method (AUC: 0.865 ± 0.010 vs. 0.838 ± 0.019, Accuracy: 82.7% ± 2.5% vs. 78.5% ± 3.6%, Specificity: 84.9% ± 3.7% vs. 77.5% ± 6.5%, Sensitivity: 74.4% ± 4.2% vs. 79.8% ± 5.8%).

CONCLUSIONS

The incorporation of deep learning for stress-only MPI has a considerable potential to improve the diagnostic accuracy and consistency in the detection of myocardial perfusion abnormalities.

Regadenoson Stress Testing: A Comprehensive Review With a Focused Update

Regadenoson is a pharmacological stress agent that has been widely used since its approval by the Food and Drug Administration (FDA) in 2008. For many years, dipyridamole and adenosine, which are non-selective adenosine receptor agonists, were more popular. However, these agents are less preferred now due to their undesirable adverse effects as compared to regadenoson. In the ADVANCE (ADenoscan Versus regAdenosoN Comparative Evaluation) phase 3 clinical trial, regadenoson demonstrated non-inferiority to adenosine for detecting reversible myocardial ischemia. This review summarizes the clinical utilities of regadenoson as the most widely used pharmacological stress agent. Moreover, the use of regadenoson has been documented in specific patient populations. Although regadenoson has established safety and efficacy in most patients with chronic diseases, there are equivocal results in the literature for other chronic diseases. It is warranted to highlight that the use of regadenoson has not been studied in patients of low socioeconomic class; it is a condition that carries a significant burden on the cardiovascular system.

Impact of early post-stress 99mTc sestamibi ECG-gated SPECT myocardial perfusion imaging on the detection of ischemic LV dyssynchrony: an early step in the stunning cascade

Transient alterations in ventricular conduction and synchronized cardiac performance have been reported in experimental models of myocardial ischemia. In post-stress ^99mTc-sestamibi-gated-SPECT myocardial perfusion imaging (MPI), the time elapsed between tracer injection and image acquisition could influence the detection of ischemic left ventricular mechanical dyssynchrony (LVMD). We aimed at evaluating whether early vs. delayed post-stress MPI improve ischemic LVMD detection using the phase analysis parameters standard deviation (SD) and histogram bandwidth (HB) and to assess the correlation between stress-induced changes in SD and HB and other functional parameters. We prospectively studied 32 control subjects (Group-1) and 60 ischemic patients (Group-2). Stress-induced changes were calculated as stress minus rest (Δ). LVMD was defined as post-stress increases of either SD or HB. Group-2 showed higher ΔSD and ΔHB in early than in delayed images: early ΔSD: 1.63 (- 0.37 to 4.83) vs. delayed ΔSD: - 0.39 (- 3.82 to 1.74); early ΔHB: 2.50 (- 4 to 12) vs. ΔHB delayed: - 4 (- 15.75 to 4), all p < 0.01. ΔSD and ΔHB correlated linearly with ΔLV-ejection-fraction (EF) and ΔLV-end systolic-volume (ESV) in early images, all p < 0.01. Early images detected LVMD in more patients than delayed scans (78% vs. 38%; p < 0.01) All patients with LVEF drop in early post-stress evaluation had LVMD. Early post-stress images improve ischemic LVMD detection. Ischemic LVEF and LVESV changes correlate with ΔSD and ΔHB.

Splenic switch-off as a predictor for coronary adenosine response: validation against 13N-ammonia during co-injection myocardial perfusion imaging on a hybrid PET/CMR scanner

BACKGROUND

Inadequate coronary adenosine response is a potential cause for false negative ischemia testing. Recently, the splenic switch-off (SSO) sign has been identified as a promising tool to ascertain the efficacy of adenosine during vasodilator stress cardiovascular magnetic resonance imaging (CMR). We assessed the value of SSO to predict adenosine response, defined as an increase in myocardial blood flow (MBF) during quantitative stress myocardial perfusion 13 N-ammonia positron emission tomography (PET).

METHODS

We prospectively enrolled 64 patients who underwent simultaneous CMR and PET myocardial perfusion imaging on a hybrid PET/CMR scanner with co-injection of gadolinium based contrast agent (GBCA) and 13N-ammonia during rest and adenosine-induced stress. A myocardial flow reserve (MFR) of  > 1.5 or ischemia as assessed by PET were defined as markers for adequate coronary adenosine response. The presence or absence of SSO was visually assessed. The stress-to-rest intensity ratio (SIR) was calculated as the ratio of stress over rest peak signal intensity for splenic tissue. Additionally, the spleen-to-myocardium ratio, defined as the relative change of spleen to myocardial signal, was calculated for stress (SMRstress) and rest.

RESULTS

Sixty-one (95%) patients were coronary adenosine responders, but SSO was absent in 18 (28%) patients. SIR and SMRstress were significantly lower in patients with SSO (SIR: 0.56 ± 0.13 vs. 0.93 ± 0.23; p < 0.001 and SMRstress: 1.09 ± 0.47 vs. 1.68 ± 0.62; p < 0.001). Mean hyperemic and rest MBF were 2.12 ± 0.68 ml/min/g and 0.78 ± 0.26 ml/min/g, respectively. MFR was significantly higher in patients with vs. patients without presence of SSO (3.07 ± 1.03 vs. 2.48 ± 0.96; p = 0.038), but there was only a weak inverse correlation between SMRstress and MFR (R = -0.378; p = 0.02) as well as between SIR and MFR (R = -0.356; p = 0.004).

CONCLUSIONS

The presence of SSO implies adequate coronary adenosine-induced MBF response. Its absence, however, is not a reliable indicator for failed adenosine-induced coronary vasodilatation.

Blood pressure variability in patients with angina and non-obstructive coronary artery disease

There is a real challenge in the management of ischemia with non-obstructive coronary artery disease. So, we need to study the mechanisms of persistent angina and non-obstructive coronary artery (ANOCA) patients. One of those possible mechanisms is blood pressure variability (BPV). We aimed to study the relation between BPV and angina in patients with non-obstructive coronary artery disease. Our study included 150 patients with chest pain and positive non-invasive stress test suggestive of myocardial ischemia and normal coronary angiography or non-obstructive coronary artery disease. We used an ambulatory blood pressure monitoring device. We found a positive correlation between BPV as measured by average real variability (ARV) as well as standard deviation (SD) parameters and the severity of anginal symptoms with P values for all parameters was 0.001 except day systolic SD P-value was 0.021. We performed a regression analysis for all statistically significant parameters. We found that 24H diastolic ARV, day diastolic ARV, night diastolic ARV, 24H diastolic SD, day diastolic SD, and night diastolic SD were independent predictors of the severity of angina with P-values (0.015, 0.007, 0.011, 0.037, 0.014, and 0.029), respectively. We concluded that short-term BPV represented by ARV and SD had a consistent association with angina in patients with non-obstructive coronary artery disease. The diastolic parameters of ARV and SD were independent predictors of the severity of angina with non-obstructive coronary artery disease.

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

OBJECTIVES

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

BACKGROUND

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

METHODS

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

RESULTS

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

CONCLUSIONS

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