Quantification Of Myocardial Blood Flow Research Articles

Automatic motion correction for myocardial blood flow estimation improves diagnostic performance for coronary artery disease in 18F-flurpiridaz PET-MPI

BackgroundMotion correction (MC) is critical for accurate quantification of myocardial blood flow (MBF) and flow reserve (MFR) from 18F-flurpiridaz PET myocardial perfusion imaging (MPI). However, manual correction is time consuming and introduces inter-observer variability. We aimed to validate an automatic MC algorithm for 18F-flurpiridaz PET-MPI in terms of diagnostic performance for predicting coronary artery disease (CAD). MethodsIn total, 231 patients who underwent invasive coronary angiography and rest/pharmacologic stress 18F-flurpiridaz PET-MPI from phase III Flurpiridaz trial (NCT01347710) were enrolled. For manual MC, two operators (Reader 1 and Reader 2) shifted each frame's images in three directions. The automatic MC algorithm, initially developed for 82Rb-chloride PET-MPI, was optimized for 18F-flurpiridaz. Diagnostic performance was compared using minimal segmental MBF/MFR with and without MC to predict CAD ≥70% stenosis by angiography. ResultsManual MC took 10 minutes per case (both stress and rest) on average, while automatic MC required <17 seconds. The area under the receiver operating characteristic curves (AUCs) for significant CAD using minimal segmental MBF were comparable between automatic and manual MC (AUC=0.877 automatic, AUC=0.888 Reader 1 and AUC=0.892 Reader 2; all p>0.05). AUCs of minimal segmental MBF with manual and automatic MC were significantly higher than without MC (p<0.05 for both). Similar findings were observed with minimal segmental MFR. ConclusionsAutomatic MC can be performed rapidly, with diagnostic performance for predicting obstructive CAD comparable to manual MC. This method could be utilized for analysis of MBF/MFR in patients undergoing 18F-flurpiridaz PET-MPI.

Quantitative perfusion by cardiac magnetic resonance analysis reveals compromised myocardial perfusion in patients with angina with non-obstructive coronary artery disease

Abstract Introduction Stress perfusion cardiac magnetic resonance (CMR) visually detects myocardial ischemia through first-pass contrast-enhanced imaging by identifying perfusion defects. However, in generalized myocardial diseases like angina with non-obstructed coronary arteries (ANOCA), visual assessment becomes challenging due to diffuse sub-endocardial perfusion defects, or the findings may even falsely appear normal. Fully automated quantitative perfusion (QP), allowing absolute quantification of myocardial blood flow (MBF) and deriving myocardial perfusion reserve (MPR), might increase diagnostic accuracy in ANOCA patients. Therefore, the purpose of this study is to test the use of QP in detecting ANOCA diagnosed by the invasive golden standard. Methods This study is a cross-sectional cohort study assessing the use of fully automated QP CMR in patients with ANOCA compared with age- and sex-matched healthy controls. All participants underwent adenosine stress perfusion CMR, including visual assessment and quantification of MBF and MPR. Furthermore, all ANOCA patients underwent intracoronary function testing (ICFT) to idenity vasospasm and/or coronary microvascular dysfunction. Results This study included 24 ANOCA patients (83% women, 56.8±8.9 years) and 25 healthy controls (80% women, 56.2±7.2 years). Visual perfusion assessment showed no group differences in terms of perfusion defects (p=0.536). However, in QP, ANOCA patients had higher relative MBF than healthy controls (0.83±0.15 vs 0.74±0.17, p=0.046), while global perfusion was significantly lower during stress (2.43±0.72 vs 2.99±0.65 ml/g/min, p=0.006). Moreover, ANOCA patients had significantly lower MPR than healthy controls (2.24 ±0.79 vs 2.68 ±0.64, respectively p=0.036), with a higher prevalence of an impared MPR (50% vs. 20%, p=0.027). MPR was not significantly different between the various ANOCA entities as stratified during ICFT (p=0.766). Conclusions ANOCA patients displayed significantly reduced MPR, indicating impaired perfusion. The prevalence of diminished MPR was higher in the ANOCA group compared to the healthy controls, constrasting with no differences in visual assessment. These results are promising and underscores the possibilities of the use of QP in detecting vasomotor dysfunction non-invasively in ANOCA patients.Quantitative Perfusion by CMR results

Prognostic value of quantitative anatomical and functional measures of coronary artery disease in diabetic and non-diabetic patients

Abstract Background Diabetes is associated with increased risk of coronary artery disease (CAD). However, the relative prognostic importance of anatomical and functional findings of CAD in the presence vs. absence of diabetes is incompletely understood. Technological advances have made quantitative analysis of coronary artery plaques and stenosis feasible by coronary computed tomography angiography (CTA). In turn, positron emission tomography (PET) enables absolute quantification of myocardial blood flow (MBF). Purpose To study long-term prognostic value of quantified severity of coronary atherosclerosis and myocardial perfusion in non-diabetic vs. diabetic patients with suspected CAD. Methods From two academic medical centres, we identified symptomatic patients with suspected CAD who had undergone coronary CTA and [15O]H2O PET myocardial perfusion imaging during adenosine stress. Based on artificial intelligence -guided quantitative analysis of coronary CTA scans, the anatomical severity of CAD was measured as the presence of obstructive CAD (≥50% diameter stenosis) and percent atheroma volume (PAV; higher vs. lower than median). The functional severity of CAD was measured as the presence of regional myocardial ischemia (≥2 adjacent segments with stress MBF &amp;lt;2.3 ml/g/min) and global stress MBF (&amp;lt;2.2 ml/g/min vs. ≥ 2.2 ml/g/min) by PET. Annual rates of adverse events (AER) including all-cause mortality, myocardial infarction (MI), and unstable angina pectoris (UAP) were evaluated. Results Among 1311 patients, 251 (19%) had diabetes. Patients with diabetes had more frequently obstructive CAD (55% vs. 43%, p&amp;lt;0.001) and regional myocardial ischemia (51% vs. 43%, p=0.015), higher plaque burden by PAV (12% vs. 7%, p&amp;lt;0.001), and lower global stress MBF (2.78 ml/g/min vs. 3.05 ml/g/min, p&amp;lt;0.001). During median follow-up of 7.1 years, 171 (13.0%) patients experienced AE (85 deaths, 56 MIs, and 30 UAPs). Patients with diabetes had higher AER than non-diabetic patients (3.1% vs. 1.6%, p&amp;lt;0.001). The presence of obstructive stenosis was associated with increased AER in non-diabetic (2.6% vs. 1.0%, p&amp;lt;0.001) and diabetic patients (4.2% vs. 1.9%, p&amp;lt;0.001). High plaque burden by PAV was associated with increased AER in non-diabetic (2.8% vs. 0.7%, p&amp;lt;0.001) and diabetic patients (3.9% vs. 1.7%, p&amp;lt;0.001). The presence of regional myocardial ischemia was associated with increased AER in non-diabetic (2.5% vs. 1.1%, p&amp;lt;0.001), but not in diabetic patients (3.4% vs. 2.7%, p=0.238). Low global stress MBF was associated with increased AER in non-diabetic (2.9% vs. 1.3%, p&amp;lt;0.001), but not among diabetic patients (3.2% vs. 3.0%, p=0.286). Conclusions Diabetes was associated with more advanced CAD. Quantified severity of anatomical findings predicted long-term adverse outcome in non-diabetic and diabetic patients. In contrast, functional imaging risk stratified non-diabetic patients, whereas diabetic patients had impaired long-term outcome irrespective of perfusion findings.

Relationship between microvascular status and diagnostic performance of stress dynamic CT perfusion imaging.

This study aimed to investigate the relationship between microvascular status in the non-ischemic myocardium and the diagnostic performance of stress dynamic CT perfusion imaging (CTP) in detecting hemodynamically significant stenosis. This study included 157 patients who underwent coronary computed tomography angiography (CTA), CTP, and invasive coronary angiography (ICA), including fractional flow reserve (FFR). Hemodynamically significant stenosis was defined by FFR and ICA. A relative myocardial blood flow (MBF) for each myocardial segment was normalized to the highest MBF (remote MBF) among 16 segments. The receiver operating characteristic curve analysis for detecting hemodynamically significant stenosis at the vessel level indicated that patients with lower, intermediate, and higher remote MBF had areas under the curve (AUC) of 0.66, 0.70, and 0.80, respectively, for absolute MBF and AUCs of 0.63, 0.70, and 0.83, respectively, for relative MBF. The optimal cut-off values for absolute MBF were proportional to the levels of remote MBFs, while the ones for relative MBF were more consistent across lower to higher remote MBFs. For the patients with high remote MBF, the relative MBF demonstrated a sensitivity of 69%, specificity of 88%, and accuracy of 85% in detecting hemodynamically significant stenosis. The microvascular status in the non-ischemic myocardium influenced the diagnostic performance of dynamic CTP and threshold values of absolute MBFs, suggesting the potential preference for relative MBF over absolute MBF in clinical settings. Dynamic CTP's quantification of MBF offers the benefit of indicating reliability in ischemia detection relative to microvascular status. Question The relationship between microvascular status and diagnostic performance of dynamic CTP imaging has not been fully investigated. Findings The diagnostic performance of dynamic CTP and threshold values of absolute MBF were impacted by microvascular status. Clinical relevance The differences in diagnostic accuracy of dynamic CTP related to varying remote MBF values necessitate a personalized evaluation of myocardial perfusion in dynamic CTP images.

Association Between Coronary Microvascular Dysfunction and Exercise Capacity in Dilated Cardiomyopathy.

Aerobic exercise capacity is an independent predictor of mortality in dilated cardiomyopathy (DCM), but the central mechanisms contributing to exercise intolerance in DCM are unknown. Characterize coronary microvascular function in DCM and determine if cardiovascular magnetic resonance (CMR) measures are associated with aerobic exercise capacity. Prospective case-control comparison of adults with DCM and matched controls. Adenosine-stress perfusion CMR to assess cardiac structure, function and automated inline myocardial blood flow quantification, and cardiopulmonary exercise testing (CPET) to determine peak VO2, were performed. Pre-specified multivariable linear regression, including key clinical and cardiac variables, was undertaken to identify independent associations with peak VO2. Sixty-six patients with DCM (mean age 61 years, 71% male) were propensity-matched to 66 controls (mean age 59 years, 71% male) based on age, sex, body mass index and diabetes. DCM patients had markedly lower peak VO2 (19.8±5.5 versus 25.2±7.3mL/kg/min; P<0.001). The DCM group had greater left ventricular (LV) volumes, lower systolic function, and had more fibrosis compared to controls. In the DCM group, there was similar rest but lower stress myocardial blood flow (1.53±0.49 versus 2.01±0.60mL/g/min; P<0.001) and lower MPR (2.69±0.84 versus 3.15±0.84; P=0.002). Multivariable linear regression demonstrated that LV ejection fraction, extracellular volume fraction and MPR, were independently associated with percentage predicted peak VO2 in DCM (R2=0.531, P<0.001). In comparison to controls, DCM patients have lower stress myocardial blood flow and MPR. In DCM, MPR, LV ejection fraction and fibrosis are independently associated with aerobic exercise capacity.

Current Role of Myocardial Blood Flow Quantification with PET/CT in the Management of Coronary Artery Disease

Current Role of Myocardial Blood Flow Quantification with PET/CT in the Management of Coronary Artery Disease

Quantification of myocardial blood flow using dynamic myocardial perfusion computed tomography

Quantification of myocardial blood flow using dynamic myocardial perfusion computed tomography

TAI-GAN: A Temporally and Anatomically Informed Generative Adversarial Network for early-to-late frame conversion in dynamic cardiac PET inter-frame motion correction

Inter-frame motion in dynamic cardiac positron emission tomography (PET) using rubidium-82 (82Rb) myocardial perfusion imaging impacts myocardial blood flow (MBF) quantification and the diagnosis accuracy of coronary artery diseases. However, the high cross-frame distribution variation due to rapid tracer kinetics poses a considerable challenge for inter-frame motion correction, especially for early frames where intensity-based image registration techniques often fail. To address this issue, we propose a novel method called Temporally and Anatomically Informed Generative Adversarial Network (TAI-GAN) that utilizes an all-to-one mapping to convert early frames into those with tracer distribution similar to the last reference frame. The TAI-GAN consists of a feature-wise linear modulation layer that encodes channel-wise parameters generated from temporal information and rough cardiac segmentation masks with local shifts that serve as anatomical information. Our proposed method was evaluated on a clinical 82Rb PET dataset, and the results show that our TAI-GAN can produce converted early frames with high image quality, comparable to the real reference frames. After TAI-GAN conversion, the motion estimation accuracy and subsequent myocardial blood flow (MBF) quantification with both conventional and deep learning-based motion correction methods were improved compared to using the original frames. The code is available at https://github.com/gxq1998/TAI-GAN.

Arterial Input Function (AIF) Correction Using AIF Plus Tissue Inputs with a Bi-LSTM Network.

Background: The arterial input function (AIF) is vital for myocardial blood flow quantification in cardiac MRI to indicate the input time-concentration curve of a contrast agent. Inaccurate AIFs can significantly affect perfusion quantification. Purpose: When only saturated and biased AIFs are measured, this work investigates multiple ways of leveraging tissue curve information, including using AIF + tissue curves as inputs and optimizing the loss function for deep neural network training. Methods: Simulated data were generated using a 12-parameter AIF mathematical model for the AIF. Tissue curves were created from true AIFs combined with compartment-model parameters from a random distribution. Using Bloch simulations, a dictionary was constructed for a saturation-recovery 3D radial stack-of-stars sequence, accounting for deviations such as flip angle, T2* effects, and residual longitudinal magnetization after the saturation. A preliminary simulation study established the optimal tissue curve number using a bidirectional long short-term memory (Bi-LSTM) network with just AIF loss. Further optimization of the loss function involves comparing just AIF loss, AIF with compartment-model-based parameter loss, and AIF with compartment-model tissue loss. The optimized network was examined with both simulation and hybrid data, which included in vivo 3D stack-of-star datasets for testing. The AIF peak value accuracy and ktrans results were assessed. Results: Increasing the number of tissue curves can be beneficial when added tissue curves can provide extra information. Using just the AIF loss outperforms the other two proposed losses, including adding either a compartment-model-based tissue loss or a compartment-model parameter loss to the AIF loss. With the simulated data, the Bi-LSTM network reduced the AIF peak error from -23.6 ± 24.4% of the AIF using the dictionary method to 0.2 ± 7.2% (AIF input only) and 0.3 ± 2.5% (AIF + ten tissue curve inputs) of the network AIF. The corresponding ktrans error was reduced from -13.5 ± 8.8% to -0.6 ± 6.6% and 0.3 ± 2.1%. With the hybrid data (simulated data for training; in vivo data for testing), the AIF peak error was 15.0 ± 5.3% and the corresponding ktrans error was 20.7 ± 11.6% for the AIF using the dictionary method. The hybrid data revealed that using the AIF + tissue inputs reduced errors, with peak error (1.3 ± 11.1%) and ktrans error (-2.4 ± 6.7%). Conclusions: Integrating tissue curves with AIF curves into network inputs improves the precision of AI-driven AIF corrections. This result was seen both with simulated data and with applying the network trained only on simulated data to a limited in vivo test dataset.

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

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

Myocardial blood flow quantification with SPECT

IntroductionThe addition of absolute myocardial blood flow (MBF) data improves the diagnostic and prognostic accuracy of relative perfusion imaging with nuclear medicine. Cardiac-specific gamma cameras allow measurement of MBF with SPECT. MethodsThis paper reviews the evidence supporting the use of SPECT to measure myocardial blood flow (MBF). Studies have evaluated SPECT MBF in large animal models and compared it in humans with invasive angiographic measurements and against the clinical standard of PET MBF. The repeatability of SPECT MBF has been determined in both single-site and multi-center trials. ResultsSPECT MBF has excellent correlation with microspheres in an animal model, with the number of stenoses and fractional flow reserve, and with PET-derived MBF. The inter-user coefficient of variability is ∼20% while the COV of test-retest MBF is ∼30%. SPECT MBF improves the sensitivity and specificity of the detection of multi-vessel disease over relative perfusion imaging and provides incremental value in predicting adverse cardiac events. ConclusionSPECT MBF is a promising technique for providing clinically valuable information in the assessment of coronary artery disease.

PET-determined myocardial perfusion and flow in coronary artery disease characterization

Positron emission tomography (PET) myocardial perfusion imaging in conjunction with tracer-kinetic modeling enables the concurrent assessment of myocardial perfusion and regional myocardial blood flow (MBF) of the left ventricle in absolute terms in milliliters per gram per minute (mL/g/min). The non-invasive quantification of MBF during pharmacologically induced hyperemia, at rest, and corresponding myocardial flow reserve (MFR) opens a new avenue for the identification and characterization of classical or endogen type of coronary microvascular dysfunction (CMD) as functional substrate for microvascular angina in patients with non-obstructive coronary artery disease (CAD) and/or no CAD at all. Further, PET-MBF quantification expands the scope of conventional myocardial perfusion imaging from the identification of advanced, and flow-limiting, epicardial CAD to early stages of atherosclerosis and/or CMD. Adding MBF assessment to myocardial perfusion may also reliably unravel diffuse ischemia owing to significant left main stenosis and/or multivessel CAD, commonly confirmed by peak stress transient ischemic cavity dilation of the left ventricle during maximal vasomotor stress compared to rest on gated PET images. Owing to high spatial and contrast resolution in conjunction with photon-attenuation free myocardial perfusion PET images, PET is preferentially used for CAD detection in advanced obesity and women with pronounced breast habitus. With increasing clinical use of cardiac PET perfusion and MBF assessment, individualized, and image-guided cardiovascular treatment decisions in CAD patients is likely to ensue, while its translation into improved cardiovascular outcome remains to be investigated.

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

BackgroundIt is clinically needed to explore a more efficient imaging protocol for single photon emission computed tomography (SPECT) myocardial blood flow (MBF) quantitation derived from cadmium zinc telluride (CZT) SPECT camera for the routine clinical utilization. MethodsOne hundred and twenty patients with matched clinical characteristics and angiographic findings who completed one-day rest/stress SPECT imaging with either the intermittently sequential imaging (ISI) protocol (two dynamic and two electrocardiography (ECG)-gated scans) or the continuous rapid imaging (CRI) protocol (two dynamic/ECG-gated scans) were included. MBF quantitation adopted residual activity correction (RAC) to correct for rest residual activity (RRA) in the stress dynamic SPECT scan for the detection of flow-limited coronary artery disease. ResultsThe CRI protocol reduced about 6.2 times shorter than the ISI protocol (25.5 min vs 157.6 min), but slightly higher than the RRA (26.7% ± 3.6% vs 22.3% ± 4.9%). With RAC, both protocols demonstrated close stress MBF (2.18 ± 1.13 vs 2.05 ± 1.10, P > 0.05) and myocardial flow reserve (MFR) (2.42 ± 1.05 vs 2.48 ± 1.11, P > 0.05) to deliver comparable diagnostic performance (sensitivity = 82.1%–92.3%, specificity = 81.2%–91.2%). Myocardial perfusion and left ventricular function overall showed no significant difference (all P > 0.26). ConclusionOne-day rest/stress SPECT with the CRI protocol and rest RAC is feasible to warrant the diagnostic performance of MBF quantitation with a shortened examination time and enhanced patient comfort. Further evaluation on the impact of extracardiac activity to regional MBF and perfusion pattern is required. Additional evaluation is needed in a patient population that is typical of those referred for SPECT MPI, including those with known or suspected coronary microvascular disease.

Comparison of Myocardial Blood Flow Quantification Models for Double ECG Gating Arterial Spin Labeling MRI: Reproducibility Assessment.

Arterial spin labeling (ASL) allows non-invasive quantification of myocardial blood flow (MBF). Double-ECG gating (DG) ASL is more robust to heart rate variability than single-ECG gating (SG), but its reproducibility requires further investigation. Moreover, the existence of multiple quantification models hinders its application. Frequency-offset-corrected-inversion (FOCI) pulses provide sharper edge profiles than hyperbolic-secant (HS), which could benefit myocardial ASL. To assess the performance of MBF quantification models for DG compared to SG ASL, to evaluate their reproducibility and to compare the effects of HS and FOCI pulses. Prospective. Sixteen subjects (27 ± 8 years). 1.5 T/DG and SG flow-sensitive alternating inversion recovery ASL. Three models for DG MBF quantification were compared using Monte Carlo simulations and in vivo experiments. Two models used a fitting approach (one using only a single label and control image pair per fit, the other using all available image pairs), while the third model used a T1 correction approach. Slice profile simulations were conducted for HS and FOCI pulses with varying B0 and B1. Temporal signal-to-noise ratio (tSNR) was computed for different acquisition/quantification strategies and inversion pulses. The number of images that minimized MBF error was investigated in the model with highest tSNR. Intra and intersession reproducibility were assessed in 10 subjects. Within-subject coefficient of variation, analysis of variance. P-value <0.05 was considered significant. MBF was not different across acquisition/quantification strategies (P = 0.27) nor pulses (P = 0.9). DG MBF quantification models exhibited significantly higher tSNR and superior reproducibility, particularly for the fitting model using multiple images (tSNR was 3.46 ± 2.18 in vivo and 3.32 ± 1.16 in simulations, respectively; wsCV = 16%). Reducing the number of ASL pairs to 13/15 did not increase MBF error (minimum = 0.22 mL/g/min). Reproducibility of MBF was better for DG than SG acquisitions, especially when employing a fitting model. 2 TECHNICAL EFFICACY: Stage 1.

Rationale and design of the RAPID-WATER-FLOW trial: Radiolabeled perfusion to identify coronary artery disease using water to evaluate responses of myocardial FLOW

ObjectivesThe objective of this study was to determine the diagnostic performance of 15O-water positron emission tomography (PET) myocardial perfusion imaging to detect coronary artery disease (CAD) using the truth-standard of invasive coronary angiography (ICA) with fractional flow reserve (FFR) or instantaneous wave-Free Ratio (iFR) or coronary computed tomography angiogram (CCTA). Background15O-water has a very high first-pass extraction that allows accurate quantification of myocardial blood flow and detection of flow-limiting CAD. However, the need for an on-site cyclotron and lack of automated production at the point of care and relatively complex image analysis protocol has limited its clinical use to date. MethodsThe RAPID WATER FLOW study is an open-label, multicenter, prospective investigation of the accuracy of 15O-water PET to detect obstructive angiographic and physiologically significant stenosis in patients with suspected CAD. The study will include the use of an automated system for producing, dosing, and injecting 15O-water and enrolling approximately 215 individuals with suspected CAD at approximately 10 study sites in North America and Europe. The primary endpoint of the study is the diagnostic sensitivity and specificity of the 15O-water PET study using the truth-standard of ICA with FFR or iFR to determine flow-limiting stenosis, or CCTA to rule out CAD and incorporating a quantitative analytic platform developed for the 15O-water PET acquisitions. Sensitivity and specificity are to be considered positive if the lower bound of the 95% confidence interval is superior to the threshold of 60% for both, consistent with prior registration studies.Subgroup analyses include assessments of diagnostic sensitivity, specificity, and accuracy in female, obese, and diabetic individuals, as well as in those with multivessel disease. All enrolled individuals will be followed for adverse and serious adverse events for up to 32 hours after the index PET scan.The study will have >90% power (one-sided test, α = 0.025) to test the hypothesis that sensitivity and specificity of 15O-water PET are both >60%. ConclusionsThe RAPID WATER FLOW study is a prospective, multicenter study to determine the diagnostic sensitivity and specificity of 15O-water PET as compared to ICA with FFR/iFR or CCTA. This study will introduce several novel aspects to imaging registration studies, including a more relevant truth standard incorporating invasive physiologic indexes, coronary CTA to qualify normal individuals for eligibility, and a more quantitative approach to image analysis than has been done in prior pivotal studies. Clinical trial registration informationClinical-Trials.gov (#NCT05134012).

Cardiac PET Myocardial Blood Flow Quantification Assessment of Early Cardiac Allograft Vasculopathy

BackgroundPositron emission tomography (PET) has demonstrated utility for diagnostic and prognostic assessment of cardiac allograft vasculopathy (CAV) but has not been evaluated in the first year after transplant. ObjectivesThe authors sought to evaluate CAV at 1 year by PET myocardial blood flow (MBF) quantification. MethodsAdults at 2 institutions enrolled between January 2018 and March 2021 underwent prospective 3-month (baseline) and 12-month (follow-up) post-transplant PET, endomyocardial biopsy, and intravascular ultrasound examination. Epicardial CAV was assessed by intravascular ultrasound percent intimal volume (PIV) and microvascular CAV by endomyocardial biopsy. ResultsA total of 136 PET studies from 74 patients were analyzed. At 12 months, median PIV increased 5.6% (95% CI: 3.6%-7.1%) with no change in microvascular CAV incidence (baseline: 31% vs follow-up: 38%; P = 0.406) and persistent microvascular disease in 13% of patients. Median capillary density increased 30 capillaries/mm2 (95% CI: −6 to 79 capillaries/mm2). PET myocardial flow reserve (2.5 ± 0.7 vs 2.9 ± 0.8; P = 0.001) and stress MBF (2.7 ± 0.6 vs 2.9 ± 0.6; P = 0.008) increased, and coronary vascular resistance (CVR) (49 ± 13 vs 47 ± 11; P = 0.214) was unchanged. At 12 months, PET and PIV had modest correlation (stress MBF: r = −0.35; CVR: r = 0.33), with lower stress MBF and higher CVR across increasing PIV tertiles (all P < 0.05). Receiver-operating characteristic curves for CAV defined by upper-tertile PIV showed areas under the curve of 0.74 for stress MBF and 0.73 for CVR. ConclusionsThe 1-year post-transplant PET MBF is associated with epicardial CAV, supporting potential use for early noninvasive CAV assessment. (Early Post Transplant Cardiac Allograft Vasculopahty [ECAV]; NCT03217786)

Influence of different time framings, reconstruction algorithms and post-processing methods on the quantification of myocardial blood flow from 13 N-NH3 PET images.

The aim was to investigate to what extent the quantification of myocardial blood flow (MBF) from dynamic 13 N-NH3 positron emission tomography(PET) images is affected by time frame schemes, time-of-flight (ToF), reconstruction algorithms, blood pool volume of interest (VOI) locations and compartment models in patients with suspected chronic coronary syndrome. A standard MBF value was determined from 25 patients' rest/stress 13 N-NH3 PET/CT images reconstructed with ordered subset expectation maximization (OSEM), 5 s time frame for the first frames without ToF, subsequently analyzed using a basal VOI and the deGrado compartment model. MBFs calculated using 2or 10 s for the first frames, ToF, block-sequential regularized expectation maximization (BSREM), apical or large VOI, Hutchins or Krivokapich compartment models were compared to MBFstandard in Bland-Altman plots (bias ± SD). Good agreement in global rest/stress MBF (mL/min/g) was found when changing the time frame scheme or reconstruction algorithm (MBFstandard vs. MBF2s : -0.02 ± 0.06; MBF10s : 0.01 ± 0.07; MBFBSREM : 0.01 ± 0.07), while a lower level of agreement was found when altering the other factors (MBFstandard vs.MBFToF : -0.07 ± 0.10; MBFapical VOI : -0.27 ± 0.25; MBFlarge VOI : -0.11 ± 0.10; MBFHutchins : -0.08 ± 0.10; MBFKrivokapich : -0.47 ± 0.50). Quantification of MBF from 13 N-NH3 PET images is more affected by choice of compartment models, ToF and blood pool VOIs than by different time frame schemes and reconstruction algorithms.

Dynamic CZT-SPECT: Characterizing the Lower Values of Myocardial Blood Flow and Reserve.

CZT-SPECT myocardial perfusion enables quantification of myocardial blood flow (MBF). Normal values and thresholds have been accurately defined in PET but remain unclear in SPECT. The aim of this study was to report normal MBF and myocardial flow reserve values in very low-risk patients referred for coronary artery disease screening with dynamic SPECT, in comparison with patients experiencing coronary artery disease. Eighty-four patients (31 male) were analyzed. The mean 10 years risk of fatal cardiovascular events score was 2.7% ± 1.4%. The mean global stress MBF and myocardial flow reserve were 1.6 ± 0.6 mL/min/g and 2.7 ± 0.7.

Improved reproducibility for myocardial ASL: Impact of physiological and acquisition parameters.

To investigate and mitigate the influence of physiological and acquisition-related parameters on myocardial blood flow (MBF) measurements obtained with myocardial Arterial Spin Labeling (myoASL). A Flow-sensitive Alternating Inversion Recovery (FAIR) myoASL sequence with bSSFP and spoiled GRE (spGRE) readout is investigated for MBF quantification. Bloch-equation simulations and phantom experiments were performed to evaluate how variations in acquisition flip angle (FA), acquisition matrix size (AMS), heart rate (HR) and blood relaxation time ( ) affect quantification of myoASL-MBF. In vivo myoASL-images were acquired in nine healthy subjects. A corrected MBF quantification approach was proposed based on subject-specific values and, for spGRE imaging, subtracting an additional saturation-prepared baseline from the original baseline signal. Simulated and phantom experiments showed a strong dependence on AMS and FA ( >0.73), which was eliminated in simulations and alleviated in phantom experiments using the proposed saturation-baseline correction in spGRE. Only a very mild HR dependence ( >0.59) was observed which was reduced when calculating MBF with individual . For corrected spGRE, in vivo mean global spGRE-MBF ranged from 0.54 to 2.59mL/g/min and was in agreement with previously reported values. Compared to uncorrected spGRE, the intra-subject variability within a measurement (0.60mL/g/min), between measurements (0.45mL/g/min), as well as the inter-subject variability (1.29mL/g/min) were improved by up to 40% and were comparable with conventional bSSFP. Our results show that physiological and acquisition-related factors can lead to spurious changes in myoASL-MBF if not accounted for. Using individual and a saturation-baseline can reduce these variations in spGRE and improve reproducibility of FAIR-myoASL against acquisition parameters.

New Non-Invasive Imaging Technologies in Cardiac Transplant Follow-Up: Acquired Evidence and Future Options.

Heart transplantation (HT) is the established treatment for end-stage heart failure, significantly enhancing patients' survival and quality of life. To ensure optimal outcomes, the routine monitoring of HT recipients is paramount. While existing guidelines offer guidance on a blend of invasive and non-invasive imaging techniques, certain aspects such as the timing of echocardiographic assessments and the role of echocardiography or cardiac magnetic resonance (CMR) as alternatives to serial endomyocardial biopsies (EMBs) for rejection monitoring are not specifically outlined in the guidelines. Furthermore, invasive coronary angiography (ICA) is still recommended as the gold-standard procedure, usually performed one year after surgery and every two years thereafter. This review focuses on recent advancements in non-invasive and contrast-saving imaging techniques that have been investigated for HT patients. The aim of the manuscript is to identify imaging modalities that may potentially replace or reduce the need for invasive procedures such as ICA and EMB, considering their respective advantages and disadvantages. We emphasize the transformative potential of non-invasive techniques in elevating patient care. Advanced echocardiography techniques, including strain imaging and tissue Doppler imaging, offer enhanced insights into cardiac function, while CMR, through its multi-parametric mapping techniques, such as T1 and T2 mapping, allows for the non-invasive assessment of inflammation and tissue characterization. Cardiac computed tomography (CCT), particularly with its ability to evaluate coronary artery disease and assess graft vasculopathy, emerges as an integral tool in the follow-up of HT patients. Recent studies have highlighted the potential of nuclear myocardial perfusion imaging, including myocardial blood flow quantification, as a non-invasive method for diagnosing and prognosticating CAV. These advanced imaging approaches hold promise in mitigating the need for invasive procedures like ICA and EMB when evaluating the benefits and limitations of each modality.