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

OBJECTIVES

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

METHODS

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

RESULTS

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

CONCLUSION

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

Relationship between impaired myocardial blood flow by positron emission tomography and low-attenuation plaque burden and pericoronary adipose tissue attenuation from coronary computed tomography: From the prospective PACIFIC trial

BACKGROUND

Positron emission tomography (PET) is the clinical gold standard for quantifying myocardial blood flow (MBF). Pericoronary adipose tissue (PCAT) attenuation may detect vascular inflammation indirectly. We examined the relationship between MBF by PET and plaque burden and PCAT on coronary CT angiography (CCTA).

METHODS

This post hoc analysis of the PACIFIC trial included 208 patients with suspected coronary artery disease (CAD) who underwent [15O]H2O PET and CCTA. Low-attenuation plaque (LAP, < 30HU), non-calcified plaque (NCP), and PCAT attenuation were measured by CCTA.

RESULTS

In 582 vessels, 211 (36.3%) had impaired per-vessel hyperemic MBF (≤ 2.30 mL/min/g). In multivariable analysis, LAP burden was independently and consistently associated with impaired hyperemic MBF (P = 0.016); over NCP burden (P = 0.997). Addition of LAP burden improved predictive performance for impaired hyperemic MBF from a model with CAD severity and calcified plaque burden (P < 0.001). There was no correlation between PCAT attenuation and hyperemic MBF (r = - 0.11), and PCAT attenuation was not associated with impaired hyperemic MBF in univariable or multivariable analysis of all vessels (P > 0.1).

CONCLUSION

In patients with stable CAD, LAP burden was independently associated with impaired hyperemic MBF and a stronger predictor of impaired hyperemic MBF than NCP burden. There was no association between PCAT attenuation and hyperemic MBF.

A retrospective evaluation of Bayesian-penalized likelihood reconstruction for [15O]H2O myocardial perfusion imaging

BACKGROUND

New Block-Sequential-Regularized-Expectation-Maximization (BSREM) image reconstruction technique has been introduced for clinical use mainly for oncologic use. Accurate and quantitative image reconstruction is essential in myocardial perfusion imaging with positron emission tomography (PET) as it utilizes absolute quantitation of myocardial blood flow (MBF). The aim of the study was to evaluate BSREM reconstruction for quantitation in patients with suspected coronary artery disease (CAD).

METHODS AND RESULTS

We analyzed cardiac [15O]H2O PET studies of 177 patients evaluated for CAD. Differences between BSREM and Ordered-Subset-Expectation-Maximization with Time-Of-Flight (TOF) and Point-Spread-Function (PSF) modeling (OSEM-TOF-PSF) in terms of MBF, perfusable tissue fraction, and vascular volume fraction were measured. Classification of ischemia was assessed between the algorithms. OSEM-TOF-PSF and BSREM provided similar global stress MBF in patients with ischemia (1.84 ± 0.21 g⋅ml-1⋅min-1 vs 1.86 ± 0.21 g⋅ml-1⋅min-1) and no ischemia (3.26 ± 0.34 g⋅ml-1⋅min-1 vs 3.28 ± 0.34 g⋅ml-1⋅min-1). Global resting MBF was also similar (0.97 ± 0.12 g⋅ml-1⋅min-1 and 1.12 ± 0.06 g⋅ml-1⋅min-1). The largest mean relative difference in MBF values was 7%. Presence of myocardial ischemia was classified concordantly in 99% of patients using OSEM-TOF-PSF and BSREM reconstructions CONCLUSION: OSEM-TOF-PSF and BSREM image reconstructions produce similar MBF values and diagnosis of myocardial ischemia in patients undergoing [15O]H2O PET due to suspected obstructive coronary artery disease.

Quantitative Assessment of Myocardial Ischemia With Positron Emission Tomography

Recent advances in positron emission tomography (PET) technology and reconstruction techniques have now made quantitative assessment using cardiac PET readily available in most cardiac PET imaging centers. Multiple PET myocardial perfusion imaging (MPI) radiopharmaceuticals are available for quantitative examination of myocardial ischemia, with each having distinct convenience and accuracy profile. Important properties of these radiopharmaceuticals ( 15 O-water, 13 N-ammonia, 82 Rb, 11 C-acetate, and 18 F-flurpiridaz) including radionuclide half-life, mean positron range in tissue, and the relationship between kinetic parameters and myocardial blood flow (MBF) are presented. Absolute quantification of MBF requires PET MPI to be performed with protocols that allow the generation of dynamic multiframes of reconstructed data. Using a tissue compartment model, the rate constant that governs the rate of PET MPI radiopharmaceutical extraction from the blood plasma to myocardial tissue is calculated. Then, this rate constant ( K1 ) is converted to MBF using an established extraction formula for each radiopharmaceutical. As most of the modern PET scanners acquire the data only in list mode, techniques of processing the list-mode data into dynamic multiframes are also reviewed. Finally, the impact of modern PET technologies such as PET/CT, PET/MR, total-body PET, machine learning/deep learning on comprehensive and quantitative assessment of myocardial ischemia is briefly described in this review.

CT Coronary Angiography and Dynamic CT Myocardial Perfusion for Detection of Cardiac Allograft Vasculopathy

BACKGROUND

Cardiac allograft vasculopathy (CAV) is a major obstacle limiting long-term graft survival. Effective noninvasive surveillance modalities reflecting both coronary artery and microvascular components of CAV are needed.

OBJECTIVES

The authors evaluated the diagnostic performance of dynamic computed tomography-myocardial perfusion imaging (CT-MPI) and coronary computed tomography angiography (CCTA) for CAV.

METHODS

A total of 63 heart transplantation patients underwent combined CT-MPI and CCTA plus invasive coronary angiography (ICA) with intravascular ultrasonography (IVUS) between December 2018 and October 2021. The median interval between CT-MPI and heart transplantation was 4.3 years. Peak myocardial blood flow (MBF) of the whole myocardium (MBF_global) and minimum MBF (MBF_min) among the 16 segments according to the American Heart Association model, except the left ventricular apex, were calculated from CT-MPI. CCTA was assessed qualitatively, and the degree of coronary artery stenosis was recorded. CAV was diagnosed based on both ICA (ISHLT criteria) and IVUS. Patients were followed up for a median time of 2.3 years after CT-MPI and a median time of 5.7 years after transplantation.

RESULTS

Among the 63 recipients, 35 (55.6%) had diagnoses of CAV. The median MBF_global and MBF_min were significantly lower in patients with CAV (128.7 vs 150.4 mL/100 mL/min; P = 0.014; and 96.9 vs 122.8 mL/100 mL/min; P < 0.001, respectively). The combined use of coronary artery stenosis on CCTA and MBF_min showed the highest diagnostic performance with an area under the curve of 0.886 (sensitivity: 74.3%, specificity: 96.4%, positive predictive value: 96.3%, and negative predictive value: 75.0%).

CONCLUSIONS

The combination of CT-MPI and CCTA demonstrated excellent diagnostic performance for the detection of CAV. One-stop evaluation of the coronary artery and microvascular components involved in CAV using combined CCTA and CT-MPI may be a potent noninvasive screening method for early detection of CAV.

Adenosine vs. regadenoson for stress induction in dynamic CT perfusion scan of the myocardium: A single‑center retrospective comparison

Cardiac computed tomography (CT) angiography offers several approaches to determine the hemodynamic severity of coronary artery obstruction. Dynamic myocardial perfusion is based on serial CT imaging of contrast flow into the myocardium and calculation of absolute myocardial perfusion rates. East-Slovak Institute of Cardiovascular Diseases has been the first center in Slovakia intensively using this modern technique to increase the quality level of non-invasive diagnosis of symptomatic patients with a low to moderate pre-test probability of ischemic heart disease. The present study included 46 patients with a mean age of 64 years (33 men and 13 women). Prior to the CT study, myocardial stress was pharmacologically (adenosine, n=15 and regadenoson, n=31) induced by vasodilatation of the coronary arteries. Hemodynamic parameters (myocardial blood flow) were evaluated in all patients following successful CT perfusion without complications, allergic reaction or other severe side effects. The present study revealed that regadenoson increased the heart rate following infusion with a higher magnitude compared with adenosine. Moreover, the effect of regadenoson was independent of patient's body mass index and was associated with a lower incidence of mild adverse effects. The present study provided further clinical evidence for a more wider use of regadenoson over adenosine.

Prognostic Significance of Myocardial Blood Flow Quantification for Major Adverse Cardiac Events: A Systematic Review and Meta-analysis

Chronic coronary syndromes involve reduced myocardial blood flow (MBF). MBF is a reliable predictor of outcomes, independent of the presence of significant stenosis. Whether MBF can predict major adverse cardiac events (MACE) during long-term follow-up is unknown. PubMed, Embase, Cochrane, CNKI, and WANFANG were searched for papers published up to January 2021. The exposure was the incremental unit of stress MBF (mL/g/min) or low MBF versus high MBF. The imaging examinations included positron emission tomography/computed tomography and coronary magnetic resonance. The study outcome was the occurrence of MACE during follow-up, summarized as time-to-event hazard ratios (HRs) and 95% confidence intervals (CIs). Six studies (300 MACEs in 2326 patients) were included. Four studies presented stress MBF data by unit increments. The pooled HR showed that an increase in stress MBF by 1 mL/g/min is a protective factor for MACE (HR = 0.32; 95% CI, 0.18-0.57; I2 = 62.9%, Pheterogeneity = 0.044). Two studies reported stress MBF as low/high. The results showed that a high-stress MBF was protective against MACEs (HR = 0.43; 95% CI, 0.24-0.78; I2 = 39.5%, Pheterogeneity = 0.199). Quantification of stress MBF using positron emission tomography/computed tomography and coronary magnetic resonance might have incremental predictive value for future MACEs in a population at intermediate to high cardiovascular risk. The results will require validation in large prospective randomized controlled trials.

Anthropomorphic cardiac phantom for dynamic SPECT

BACKGROUND

As myocardial blood flow measurement (MBF) in SPECT systems became recently available, significant effort has been devoted to its validation. For that purpose, we have developed a cardiac phantom that is able to mimic physiological radiotracer variation in the left ventricle cavity and in the myocardium, while performing beating-like motion. The new phantom is integrated inside a standard anthropomorphic torso allowing a realistic tissue attenuation and gamma-ray scattering METHODS AND RESULTS: A mechanical cardiac phantom was integrated in a commercially available anthropomorphic torso. Using a GE Discovery 530c SPECT, measurements were performed. It was found that gamma-ray attenuation effects are significant and limit the MBF measurements to global/three-vessel resolution. Dynamic SPECT experiments were performed to validate MBF accuracy and showed mean relative error of 14%. Finally, the effect of varying radiotracer dose on the accuracy of dynamic SPECT was studied CONCLUSIONS: A dynamic cardiac phantom has been developed and successfully integrated in a standard SPECT torso. A good agreement was found between SPECT-reported MBF values and the expected results. Despite increased noise-to-signal ratio when radiotracer doses were reduced, MBF uncertainty did not increase significantly down to very low doses, thanks to the temporal integration of the activity during the measurement.

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.

Enhanced myocardial blood flow in ischemic cardiomyopathy by a slow-release synthetic prostacyclin agonist combined with coronary artery bypass grafting: The first human study in a Phase I/IIa clinical trial

Background

YS-1402, which is a polymerized form of the synthetic prostacyclin agonist ONO-1301, has been proven in several preclinical studies to induce therapeutic effects for patients with ischemic cardiomyopathy (ICM). In this human study, we assessed the safety, tolerability, and efficacy of YS-1402, combined with coronary artery bypass grafting (CABG), for ICM.

Methods

Twenty-four patients with ICM whose left ventricular ejection fraction was <40% with an indication for CABG were double-blindly assigned to four groups: placebo, 10-mg YS-1402, 30-mg YS-1402, and 100-mg YS-1402. YS-1402 or placebo medications were administered on the surface of the left ventricle at the time of the CABG. Pre- and postoperative cardiac function and myocardial blood flow were assessed for 6 months postoperatively, along with a safety assessment.

Results

No severe adverse events were related to YS-1402. The maximum blood concentration of ONO-1301 was less than that of the no observable adverse effect level. Significantly increased myocardial blood flow (MBF) and cardiac function were observed in the YS-1402 group 26 weeks postoperatively, although no improvement in MBF occurred in the placebo group.

Conclusion

This Phase I/IIa parallel group-controlled, dose-escalation study of YS-1402 combined with CABG for ICM demonstrated the safety, tolerability, and potential efficacy of YS-1402.

PET for Detection and Reporting Coronary Microvascular Dysfunction: A JACC: Cardiovascular Imaging Expert Panel Statement

Angina pectoris and dyspnea in patients with normal or nonobstructive coronary vessels remains a diagnostic challenge. Invasive coronary angiography may identify up to 60% of patients with nonobstructive coronary artery disease (CAD), of whom nearly two-thirds may, in fact, have coronary microvascular dysfunction (CMD) that may account for their symptoms. Positron emission tomography (PET) determined absolute quantitative myocardial blood flow (MBF) at rest and during hyperemic vasodilation with subsequent derivation of myocardial flow reserve (MFR) affords the noninvasive detection and delineation of CMD. Individualized or intensified medical therapies with nitrates, calcium-channel blockers, statins, angiotensin-converting enzyme inhibitors, angiotensin II type 1-receptor blockers, beta-blockers, ivabradine, or ranolazine may improve symptoms, quality of life, and outcome in these patients. Standardized diagnosis and reporting criteria for ischemic symptoms caused by CMD are critical for optimized and individualized treatment decisions in such patients. In this respect, it was proposed by the cardiovascular council leadership of the Society of Nuclear Medicine and Molecular Imaging to convene thoughtful leaders from around the world to serve as an independent expert panel to develop standardized diagnosis, nomenclature and nosology, and cardiac PET reporting criteria for CMD. This consensus document aims to provide an overview of the pathophysiology and clinical evidence of CMD, its invasive and noninvasive assessment, standardization of PET-determined MBFs and MFR into "classical" (predominantly related to hyperemic MBFs) and "endogen" (predominantly related to resting MBF) normal coronary microvascular function or CMD that may be critical for diagnosis of microvascular angina, subsequent patient care, and outcome of clinical CMD trials.

Negative Predictive Value and Prognostic Associations of Rb-82 PET/CT with Myocardial Blood Flow in CAV

BACKGROUND

Invasive coronary angiography (ICA) is the traditional screening modality for cardiac allograft vasculopathy (CAV). Positron emission tomography/computed tomography (PET/CT) scan with myocardial blood flow (MBF) quantification has emerged as a potential noninvasive alternative.

OBJECTIVES

The aim of the study was to validate the diagnostic and prognostic value of a previously published algorithm for diagnosing CAV via PET/CT scans with MBF in a larger population. The study also sought to assess the downstream use of ICA when using PET/CT scanning as a screening modality.

METHODS

Patients with heart transplantation without prior revascularization who underwent PET/CT scans with MBF were identified retrospectively. The accuracy of the algorithm was assessed in patients who underwent PET/CT scanning within 1 year of ICA. The prognostic value was assessed via a composite outcome of heart failure hospitalization, myocardial infarction, retransplantation, and all-cause mortality.

RESULTS

A total of 88 patients for the diagnostic portion and 401 patients for the prognostic portion were included. PET CAV 0 had high negative predictive value for moderate to severe CAV (97%) and PET CAV 2/3 had a high positive predictive value for moderate to severe CAV (68%) by ICA. The cohort was followed for a median of 1.2 (IQR: 1.0-1.8) years with 46 patients having an adverse event. The annualized event rates were 6.9%, 9.3%, and 30.8% for PET CAV 0, 1, and 2/3, respectively (P < 0.001).

CONCLUSIONS

An algorithm using PET/CT scanning with MBF demonstrates high a negative predictive value for CAV. PET CAV 2/3 is associated with a higher risk of adverse events and need for revascularization. PET/CT scanning with MBF is a reasonable alternative to ICA for screening for CAV.

Cardiovascular Magnetic Resonance Parametric Mapping Techniques for the Assessment of Chronic Coronary Syndromes

The term chronic coronary syndromes encompasses a variety of clinical presentations of coronary artery disease (CAD), ranging from stable angina due to epicardial coronary artery disease to microvascular coronary dysfunction. Cardiac magnetic resonance (CMR) imaging has an established role in the diagnosis, prognostication and treatment planning of patients with CAD. Recent advances in parametric mapping CMR techniques have added value in the assessment of patients with chronic coronary syndromes, even without the need for gadolinium contrast administration. Furthermore, quantitative perfusion CMR techniques have enabled the non-invasive assessment of myocardial blood flow and myocardial perfusion reserve and can reliably identify multivessel coronary artery disease and microvascular dysfunction. This review summarizes the clinical applications and the prognostic value of the novel CMR parametric mapping techniques in the setting of chronic coronary syndromes and discusses their strengths, pitfalls and future directions.

Impact of Temporal Resolution and Methods for Correction on Cardiac Magnetic Resonance Perfusion Quantification

BACKGROUND

Acquisition of magnetic resonance first-pass perfusion images is synchronized to the patient's heart rate (HR) and governs the temporal resolution. This is inherently linked to the process of myocardial blood flow (MBF) quantification and impacts MBF accuracy but to an unclear extent.

PURPOSE

To assess the impact of temporal resolution on quantitative perfusion and compare approaches for accounting for its variability.

STUDY TYPE

Prospective phantom and retrospective clinical study.

POPULATION AND PHANTOM

Simulations, a cardiac perfusion phantom, and 30 patients with (16, 53%) or without (14, 47%) coronary artery disease.

FIELD STRENGTH/SEQUENCE

3.0 T/2D saturation recovery spoiled gradient echo sequence.

ASSESSMENT

Dynamic perfusion data were simulated for a range of reference MBF (1 mL/g/min-5 mL/g/min) and HR (30 bpm-150 bpm). Perfusion imaging was performed in patients and a phantom for different temporal resolutions. MBF and myocardial perfusion reserve (MPR) were quantified without correction for temporal resolution or following correction by either MBF scaling based on the sampling interval or data interpolation prior to quantification. Simulated data were quantified using Fermi deconvolution, truncated singular value decomposition, and one-compartment modeling, whereas phantom and clinical data were quantified using Fermi deconvolution alone.

STATISTICAL TESTS

Shapiro-Wilk tests for normality, percentage error (PE) for measuring MBF accuracy in simulations, and one-way repeated measures analysis of variance with Bonferroni correction to compare clinical MBF and MPR. Statistical significance set at P < 0.05.

RESULTS

For Fermi deconvolution and an example simulated 1 mL/g/min, the MBF PE without correction for temporal resolution was between 55.4% and -62.7% across 30-150 bpm. PE was between -22.2% and -6.8% following MBF scaling and between -14.2% and -14.2% following data interpolation across the same HR. An interpolated HR of 240 bpm reduced PE to ≤10%. Clinical rest and stress MBF and MPR were significantly different between analyses.

DATA CONCLUSION

Accurate perfusion quantification needs to account for the variability of temporal resolution, with data interpolation prior to quantification reducing MBF variability across different resolutions.

LEVEL OF EVIDENCE

3 TECHNICAL EFFICACY STAGE: 1.

Phenotype-based management of coronary microvascular dysfunction

40-70% of patients undergoing invasive coronary angiography with signs and symptoms of ischemia are found to have no obstructive coronary artery disease (INOCA). When this heterogeneous group undergo coronary function testing, approximately two-thirds have demonstrable coronary microvascular dysfunction (CMD), which is independently associated with adverse prognosis. There are four distinct phenotypes, or subgroups, each with unique pathophysiological mechanisms and responses to therapies. The clinical phenotypes are microvascular angina, vasospastic angina, mixed (microvascular and vasospastic), and non-cardiac symptoms (reclassification as non-INOCA). The Coronary Vasomotor Disorders International Study Group (COVADIS) have proposed standardized criteria for diagnosis. There is growing awareness of these conditions among clinicians and within guidelines. Testing for CMD can be done using invasive or non-invasive modalities. The CorMicA study advocates the concept of 'functional angiography' to guide stratified medical therapy. Therapies broadly fall into two categories: those that modulate cardiovascular risk and those to alleviate angina. Management should be tailored to the individual, with periodic reassessment for efficacy. Phenotype-based management is a worthy endeavor for both patients and clinicians, aligning with the concept of 'precision medicine' to improve prognosis, symptom burden, and quality of life. Here, we present a contemporary approach to the phenotype-based management of patients with INOCA.

18F-flurpiridaz positron emission tomography segmental and territory myocardial blood flow metrics: incremental value beyond perfusion for coronary artery disease categorization

AIMS

We determined the feasibility and diagnostic performance of segmental 18F-flurpiridaz myocardial blood flow (MBF) measurement by positron emission tomography (PET) compared with the standard territory method, and assessed whether flow metrics provide incremental diagnostic value beyond relative perfusion quantitation (PQ).

METHODS AND RESULTS

All evaluable pharmacological stress patients from the Phase III trial of 18F-flurpiridaz were included (n = 245) and blinded flow metrics obtained. For each coronary territory, the segmental flow metric was defined as the lowest 17-segment stress MBF (SMBF), myocardial flow reserve (MFR), or relative flow reserve (RFR) value. Diagnostic performances of segmental and territory MBF metrics were compared by receiver operating characteristic (ROC) areas under the curve (AUC). A multiple logistic model was used to evaluate whether flow metrics provided incremental diagnostic value beyond PQ alone. The diagnostic performances of segmental flow metrics were higher than their territory counterparts; SMBF AUC = 0.761 vs. 0.737; MFR AUC = 0.699 vs. 0.676; and RFR AUC = 0.716 vs. 0.635, respectively (P < 0.001 for all). Similar results were obtained for per-vessel coronary artery disease (CAD) ≥70% stenosis categorization and per-patient analyses. Combinatorial analyses revealed that only SMBF significantly improved the diagnostic performance of PQ in CAD ≥50% stenoses, with PQ AUC = 0.730, PQ + segmental SMBF AUC = 0.782 (P < 0.01), and PQ + territory SMBF AUC = 0.771 (P < 0.05). No flow metric improved diagnostic performance when combined with PQ in CAD ≥70% stenoses.

CONCLUSION

Assessment of segmental MBF metrics with 18F-flurpiridaz is feasible and improves flow-based epicardial CAD detection. When combined with PQ, only SMBF provides additive diagnostic performance in moderate CAD.

Invasive evaluation of coronary microvascular dysfunction

Coronary microvascular dysfunction (CMD) is a prevalent cause of ischemic heart disease and is associated with poorer quality of life and worse patient outcomes. Both functional and structural abnormalities of the microcirculation can generate ischemia in the absence of epicardial stenosis or worsen concomitant obstructive coronary artery disease (CAD). The invasive assessment of CMD allows for the evaluation of the entirety of the coronary vascular tree, from the large epicardial vessels to the microcirculation, and enables the study of vasomotor function through vasoreactivity testing. The standard evaluation of CMD includes vasomotor assessment with acetylcholine, as well as flow- and resistance-derived indices calculated with either thermodilution or Doppler guidewires. Tailored treatment based upon the information gathered from the invasive evaluation of CMD has been demonstrated to reduce the burden of angina; therefore, a thorough understanding of these procedures is warranted with the aim of improving the quality of life of the patient. This review summarizes the most widespread approaches for the invasive evaluation of CMD, with a focus on patients with ischemia and non-obstructive CAD.

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.

Coronary circulatory function with increasing obesity: A complex U-turn

AIMS

The aim of this investigation was to explore and characterize alterations in coronary circulatory function in function of increasing body weight with medically controlled cardiovascular risk factors and, thus, "metabolically" unhealthy obesity.

MATERIALS AND METHODS

We prospectively enrolled 106 patients with suspected CAD but with normal stress-rest myocardial perfusion on ¹³ N-ammonia PET/CT and with medically controlled or no cardiovascular risk factors. ¹³ N-ammonia PET/CT concurrently determined myocardial blood flow (MBF) during pharmacologically induced hyperaemia and at rest. Based on body mass index (BMI), patients were grouped into normal weight (BMI: 20.0-24.9 kg/m² , n = 22), overweight (BMI: 25.0-29.9 kg/m² , n = 27), obese (BMI: 30.0-39.9 kg/m² , n = 31), and morbidly obese (BMI ≥ 40kg/m² , n = 26).

RESULTS

Resting MBF was comparable among groups (1.09 ± 0.18 vs. 1.00 ± 0.15 vs. 0.96 ± 0.18 vs.. 1.06 ± 0.31 ml/g/min; p = .279 by ANOVA). Compared to normal weight individuals, the hyperaemic MBF progressively decreased in in overweight and obese groups, respectively (2.54 ± 0.48 vs. 2.02 ± 0.27 and 1.75 ± 0.39 ml/g/min; p < .0001), while it increased again in the group of morbidly obese individuals comparable to normal weight (2.44 ± 0.41 vs. 2.54 ± 0.48 ml/g/min, p = .192). The BMI of the study population correlated with the hyperaemic MBF in a quadratic or U-turn fashion (r = .34, SEE = 0.46; p ≤ .002).

CONCLUSIONS

The U-turn of hyperaemic MBF from obesity to morbid obesity is likely to reflect contrasting effects of abdominal versus subcutaneous adipose tissue on coronary circulatory function indicative of two different disease entities, but needing further investigations.

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.

Effect of PET-CT misalignment on the quantitative accuracy of cardiac 15O-water PET

BACKGROUND

Quantification of myocardial blood flow (MBF) with PET requires accurate attenuation correction, which is performed using a separate CT. Misalignment between PET and CT scans has been reported to be a common problem. The purpose of the present study was to assess the effect of PET CT misalignment on the quantitative accuracy of cardiac 15O-water PET.

METHODS

Ten clinical patients referred for evaluation of ischemia and assessment of MBF with 15O-water were included in the study. Eleven different misalignments between PET and CT were induced in 6 different directions with 10 and 20 mm amplitudes: caudal (+Z), cranial (- Z), lateral (±X), anterior (+Y), and anterior combined with cranial (+ Y and - Z). Blood flow was quantified from rates of washout (MBF) and uptake (transmural MBF, MBFt) for the whole left ventricle and the three coronary territories. The results from all misalignments were compared to the original scan without misalignment.

RESULTS

MBF was only minorly affected by misalignments, but larger effects were seen in MBFt. On the global level, average absolute deviation across all misalignments for MBF was 1.7% ± 1.4% and for MBFt 5.4% ± 3.2 Largest deviation for MBF was - 4.8% ± 5.8% (LCX, X + 20) and for MBFt - 19.3% ± 9.6% (LCX, X + 20). In general, larger effects were seen in LAD and LCX compared to in RCA.

CONCLUSION

The quantitative accuracy of MBF from 15O-water PET, based on the washout of the tracer, is only to a minor extent affected by misalignment between PET and CT.

Comparison of left ventricle mechanical dyssynchrony parameters in ischemic and non-ischemic patients using 13N-NH3 PET/CT

BACKGROUND-AIM

The relationship between perfusion pattern and stress-induced changes in Left Ventricular Mechanical Dyssynchrony (LVMD) has been previously described with controversial results using stress-rest perfusion imaging studies. The aim of this study was to assess the relationship between perfusion pattern and stress-induced changes in LVMD usingo regadenoson/rest13N-NH3 PET/CT.

METHODS

There were 74 patients who underwent stress-rest 13N-NH PET/CT from January 2014 to October 2018 excluding patients with left bundle branch block, ventricular pacing and myocardial necrosis. The patients were divided into those with reversible perfusion defects at stress (Ischemic group, n = 18) and patients without reversible perfusion defects (non-ischemic group, n = 56). The LVMD parameters included: phase standard deviation (PSD) and phase histogram bandwidth (PHB), after stress and at rest. The ΔPSD (post-stressPSD-restPSD) and ΔPHB (post-stressPHB-restPHB) were calculated to measure stress-induced changes in LVMD.

RESULTS

There were no significant differences in LVMD parameters between post-stress and at rest in both groups. The PSD post-stress, ΔPSD and PHB post-stress were significantly higher in the ischemic group.

CONCLUSIONS

Using a vasodilator as a stress, the PSD and PHB post-stress and ΔPSD were significantly higher in the ischemic patients than the non-ischemic group, while there were no significant differences in each cohort between stress and rest indices.

Optimal saturation recovery time for minimizing the underestimation of arterial input function in quantitative cardiac perfusion MRI

Purpose

The purpose of this study was to determine an optimal saturation‐recovery time (TS) for minimizing the underestimation of arterial input function (AIF) in quantitative cardiac perfusion MRI without multiple gadolinium injections per subject.

Methods

We scanned 18 subjects (mean age = 59 ± 14 years, 9/9 males/females) to acquire resting perfusion data and 1 additional subject (age = 38 years, male) to obtain stress‐rest perfusion data using a 5‐fold accelerated pulse sequence with radial k‐space sampling and applied k‐space weighted image contrast (KWIC) filters on the same k‐space data to retrospectively reconstruct five AIF images with effective TS ranging from 10 to 21.2 ms (2.8 ms steps). Undersampled images were reconstructed using a compressed sensing framework with temporal‐total‐variation and temporal‐principal‐component as 2 orthogonal sparsifying transforms. The image processing steps included, same motion correction across five different AIF images, signal normalization by the proton‐density‐weighted‐image, signal‐to‐T₁ conversion using a Bloch equation, T₁‐to‐gadolinium‐concentration conversion assuming fast water exchange, T₂* correction to the AIF, and gadolinium‐concentration to myocardial blood flow (MBF) conversion based on a Fermi model.

Results

Among five TS values, the shortest TS (10 ms) produced significantly (P < 0.05) higher peak AIF and lower resting MBF (13.73 mM, 0.73 mL g⁻¹ min⁻¹) than 12.8 ms (11.24 mM, 0.89 mL g⁻¹ min⁻¹), 15.6 ms (9.56 mM, 1.05 mL g⁻¹ min⁻¹), 18.4 ms (8.55 mM, 1.17 mL g⁻¹ min⁻¹), and 21.2 ms (7.95 mM, 1.27 mL g⁻¹ min⁻¹). Similarly, shorter TS reduced underestimation of AIF (or overestimation of MBF) for both during stress and at rest, but this effect was canceled in myocardial‐perfusion‐reserve (MPR).

Conclusion

This study demonstrates that TS of 10 ms reduces the underestimation of AIF and, hence, the overestimation of MBF compared with longer TS values (12.8‐21.2 ms).