Test-retest repeatability and software reproducibility of myocardial flow measurements using rest/adenosine stress Rubidium-82 PET/CT with and without motion correction in healthy young volunteers

Preliminary protocol for measuring the reproducibility and accuracy of flow values on digital PET/CT systems in [15O]H2O myocardial perfusion imaging using a flow phantom

BACKGROUND

Several factors may decrease the accuracy of quantitative PET myocardial perfusion imaging (MPI). It is therefore essential to ensure that myocardial blood flow (MBF) values are reproducible and accurate, and to design systematic protocols to achieve this. Until now, no systematic phantom protocols have been available to assess the technical factors affecting measurement accuracy and reproducibility in MPI.

MATERIALS AND METHODS

We implemented a standard measurement protocol, which applies a flow phantom in order to compare image-derived flow values with respect to a ground truth flow value with [15O]H2O MPI performed on both a Discovery MI (DMI-20, GE Healthcare) and a Biograph Vision 600 (Vision-600, Siemens Healthineers) system. Both systems have automatic [15O]H2O radio water generators (Hidex Oy) individually installed, allowing us to also study the differences occurring due to two different bolus delivery systems. To investigate the technical factors contributing to the modelled flow values, we extracted the [15O]H2O bolus profiles, the flow values from the kinetic modeling (Qin and Qout), and finally calculated their differences between test-retest measurements on both systems.

RESULTS

The measurements performed on the DMI-20 system produced Qin and Qout values corresponging to each other as well as to the reference flow value across all test-retest measurements. The repeatability differences on DMI-20 were 2.1% ± 2.6% and 3.3% ± 4.1% for Qin and Qout, respectively. On Vision-600 they were 10% ± 8.4% and 11% ± 10% for Qin and Qout, respectively. The measurements performed on the Vision-600 system showed more variation between Qin and Qout values across test-retest measurements and exceeded 15% difference in 7/24 of the measurements.

CONCLUSIONS

A preliminary protocol for measuring the accuracy and reproducibility of flow values in [15O]H2O MPI between digital PET/CT systems was assessed. The test-retest reproducibility falls below 15% in majority of the measurements conducted between two individual injector systems and two digital PET/CT systems. This study highlights the importance of implementing a standardized bolus injection and delivery protocol and importance of assessing technical factors affecting flow value reproducibility, which should be carefully investigated in a multi-center setting.

Pulmonary blood volume assessment from a standard cardiac rubidium-82 imaging protocol: impact of adenosine-induced hyperemia

BACKGROUND

This study aimed to assess the feasibility of estimating the pulmonary blood volume noninvasively using standard Rubidium-82 myocardial perfusion imaging (MPI) and characterize the changes during adenosine-induced hyperemia.

METHODS

This study comprised 33 healthy volunteers (15 female, median age = 23 years), of which 25 underwent serial rest/adenosine stress Rubidium-82 MPI sessions. Mean bolus transit times (MBTT) were obtained by calculating the time delay from the Rubidium-82 bolus arrival in the pulmonary trunk to the arrival in the left myocardial atrium. Using the MBTT, in combination with stroke volume (SV) and heart rate (HR), we estimated pulmonary blood volume (PBV = (SV × HR) × MBTT). We report the empirically measured MBTT, HR, SV, and PBV, all stratified by sex [male (M) vs female (F)] as mean (SD). In addition, we report grouped repeatability measures using the within-subject repeatability coefficient.

RESULTS

Mean bolus transit times was shortened during adenosine stressing with sex-specific differences [(seconds); Rest: Female (F) = 12.4 (1.5), Male (M) = 14.8 (2.8); stress: F = 8.8 (1.7), M = 11.2 (3.0), all P ≤ 0.01]. HR and SV increased during stress MPI, with a concomitant increase in the PBV [mL]; Rest: F = 544 (98), M = 926 (105); Stress: F = 914 (182), M = 1458 (338), all P < 0.001. The following test-retest repeatability measures were observed for MBTT (Rest = 17.2%, Stress = 17.9%), HR (Rest = 9.1%, Stress = 7.5%), SV (Rest = 8.9%, Stress = 5.6%), and for PBV measures (Rest = 20.7%, Stress = 19.5%) CONCLUSION: Pulmonary blood volume can be extracted by cardiac rubidium-82 MPI with excellent test-retest reliability, both at rest and during adenosine-induced hyperemia.

Myocardial creep and cardiorespiratory motion correction improves diagnostic accuracy of Rubidium-82 cardiac positron emission tomography

AIM

To evaluate the feasibility of retrospectively detecting and correcting periodical (cardiac and respiratory motion) and non-periodical shifts of the myocardial position (myocardial creep) using only the acquired Rubidium-82 positron emission tomography raw (listmode) data.

METHODS

This study comprised 25 healthy participants (median age = 23 years) who underwent repeat rest/adenosine stress Rubidium-82 myocardial perfusion imaging (MPI) and 53 patients (median age = 64 years) considered for revascularization who underwent a single MPI session. All subjects were evaluated for myocardial creep during MPI by assessing the myocardial position every 200 ms. A proposed motion correction protocol, including corrections for cardiorespiratory and creep motion (3xMC), was compared to a guideline-recommended protocol (StandardRecon). For the volunteers, we report test-retest repeatability using standard error of measurements (SEM). For the patient cohort, we evaluated the area under the receiver operating curve (AUC) for both stress and ischemic total perfusion deficits (sTPD and iTPD, respectively) using myocardial ischemia defined as fractional flow reserve values < 0.8 in the relevant coronary segment as the gold standard.

RESULTS

Test-retest repeatability was significantly improved following corrections for myocardial creep (SEM; sTPD: StandardRecon = 2.2, 3xMC = 1.8; iTPD: StandardRecon = 1.6, 3xMC = 1.2). AUC analysis of the ROC curves revealed significant improvements for iTPD measurements following 3xMC [sTPD: StandardRecon = 0.88, 3xMC = 0.92 (P = .21); iTPD: StandardRecon = 0.88, 3xMC = 0.95 (P = .039)].

CONCLUSION

3xMC has the potential to improve the diagnostic accuracy of myocardial MPI obtained from positron emission tomography. Therefore, its use should be considered both in clinical routine and large-scale multicenter studies.

Assessment of resting myocardial blood flow in regions of known transmural scar to confirm accuracy and precision of 3D cardiac positron emission tomography

BACKGROUND

Composite invasive and non-invasive data consistently demonstrate that resting myocardial blood flow (rMBF) in regions of known transmural myocardial scar (TMS) converge on a value of ~ 0.30 mL/min/g or lower. This value has been confirmed using the 3 most common myocardial perfusion agents (13N, 15O-H2O and 82Rb) incorporating various kinetic models on older 2D positron emission tomography (PET) systems. Thus, rMBF in regions of TMS can serve as a reference "truth" to evaluate low-end accuracy of various PET systems and software packages (SWPs). Using 82Rb on a contemporary 3D-PET-CT system, we sought to determine whether currently available SWP can accurately and precisely measure rMBF in regions of known TMS.

RESULTS

Median rMBF (in mL/min/g) and COV in regions of TMS were 0.71 [IQR 0.52-1.02] and 0.16 with 4DM; 0.41 [0.34-0.54] and 0.10 with 4DM-FVD; 0.66 [0.51-0.85] and 0.11 with Cedars; 0.51 [0.43-0.61] and 0.08 with Emory-Votaw; 0.37 [0.30-0.42], 0.07 with Emory-Ottawa, and 0.26 [0.23-0.32], COV 0.07 with HeartSee.

CONCLUSIONS

SWPs varied widely in low end accuracy based on measurement of rMBF in regions of known TMS. 3D PET using 82Rb and HeartSee software accurately (0.26 mL/min/g, consistent with established values) and precisely (COV = 0.07) quantified rMBF in regions of TMS. The Emory-Ottawa software yielded the next-best accuracy (0.37 mL/min/g), though rMBF was higher than established gold-standard values in ~ 5% of the resting scans. 4DM, 4DM-FDV, Cedars and Emory-Votaw SWP consistently resulted values higher than the established gold standard (0.71, 0.41, 0.66, 0.51 mL/min/g, respectively), with higher interscan variability (0.16, 0.11, 0.11, and 0.09, respectively).

TRIAL REGISTRATION

clinicaltrial.gov, NCT05286593, Registered December 28, 2021, https://clinicaltrials.gov/ct2/show/NCT05286593 .

Performance of 8- vs 16 ECG-gated reconstructions in assessing myocardial function using Rubidium-82 myocardial perfusion imaging: Findings in a young, healthy population

BACKGROUND

Current imaging guidelines recommend using at least 16 ECG gates when performing MUGA and cardiac SPECT to assess left ventricular ejection fraction (LVEF). However, for Rubidium-82 (82Rb) PET, 8 ECG-gated reconstructions have been a mainstay. This study investigated the implications of quantitative assessments when employing 16 gate, instead of 8 gate, reconstructions for 82Rb myocardial perfusion imaging (MPI).

METHODS

The study comprised 25 healthy volunteers (median age 23 years) who underwent repeat MPI sessions employing 82Rb PET/CT. We report LVEF, its reserve (stress LVEF - rest LVEF), and their repeatability measures (RMS method) obtained for 8- and 16 ECG-gated reconstructions.

RESULTS

Similar LVEF and LVEF reserve estimates were found for the 8- and 16-gated reconstructions ([%] LVEF (8/16 gates): rest = 61 ± 6/64 ± 6, stress = 68 ± 7/71 ± 6, LVEF reserve (8/16 gates): 8 ± 3/6 ± 4, and all P ≥ 0.13). Similar test-retest repeatability measures were observed for rest and stress LVEF and their reserves [LVEF (8/16 gates); Rest = 4.5/4.6 (P = 0.81), Stress = 3.5/3.2 (P = 0.33), LVEF reserve = 46.7/49.3 (P = 0.13)].

CONCLUSION

In healthy subjects, 8 and 16 ECG gates can be used interchangeably if only volumetric assessments are desired. However, if filling and emptying rates are of interest, a minimum of 16 ECG gates should be employed.

Automated dynamic motion correction improves repeatability and reproducibility of myocardial blood flow quantification with rubidium-82 PET imaging

BACKGROUND

Patient motion reduces the accuracy of PET myocardial blood flow (MBF) measurements. This study evaluated the effect of automatic motion correction on test-retest repeatability and inter-observer variability in a clinically relevant population.

METHODS

Patients with known or suspected CAD underwent repeat rest 82Rb PET scans within minutes as part of their scheduled rest-stress perfusion study. Two trained observers evaluated the presence of heart motion in each scan. Global LV and per-vessel MBF were computed from the dynamic rest images before and after automatic motion correction. Test-retest and inter-observer variability were assessed using intra-class correlation and Bland-Altman analysis.

RESULTS

140 pairs of test-retest scans were included, with visual motion noted in 18%. Motion correction decreased the global MBF values by 3.5% (0.80 ± 0.24 vs 0.82 ± 0.25 mL⋅min-1⋅g-1; P < 0.001) suggesting that the blood input function was underestimated in cases with patient motion. Test-retest repeatability of global MBF improved by 9.7% (0.25 vs 0.28 mL⋅min-1⋅g-1; P < 0.001) and inter-observer repeatability was improved by 7.1% (0.073 vs 0.079 mL⋅min-1⋅g-1; P = 0.012). There was a marked impact on both test-retest repeatability as well as inter-observer repeatability in the LCX territory, with improvements of 16.5% (0.30 vs 0.36 mL⋅min-1⋅g-1; P < 0.0000) and 18.4% (0.13 vs 0.16 mL⋅min-1⋅g-1; P < 0.001), respectively.

CONCLUSION

Automatic motion correction improved test-retest repeatability and reduced differences between observers.

Optimization of the left ventricle ejection fraction estimate obtained during cardiac adenosine stress 82Rubidium-PET scanning: impact of different reconstruction protocols

BACKGROUND

Left ventricular ejection fraction (LVEF) estimation using adenosine stress myocardial perfusion imaging (MPI) can be challenging. The short half-life of adenosine and the guideline-recommended adenosine infusion stop during Rubidium-82 acquisition protocol may affect the accuracy and repeatability of the LVEF measures.

METHODS

This study comprised 25 healthy volunteers (median age 23 years) who underwent repeat myocardial perfusion imaging (MPI) sessions employing Rubidium-82 PET/CT. A guideline-recommended reconstruction protocol was used for both rest and adenosine stress MPI (150-360 s post-radiotracer injection, standardrecon). For the stress MPI protocol, two additional reconstruction protocols were considered; one was employing 60 seconds data (150-210 seconds, shortfixed) and the other a dynamic frame window based on the bolus arrival of Rubidium-82 in the heart until 210 seconds (x-210 seconds, shortindividual). We report rest and stress LVEF, the LVEF reserve, and the LVEF reserve repeatability.

RESULTS

Differences in the LVEF assessments were observed between the guideline recommended and alternative reconstruction protocol (LVEF stress MPI: standardrecon = 68 ± 7%, shortfixed = 71 ± 7% (P = .08), shortindividual = 72 ± 7% (P = .04)), and the LVEF reserve was reduced for the guideline-recommended protocol (standardrecon = 7.8 ± 3.5, shortfixed = 10.1 ± 3.7, shortindividual = 10.5 ± 3.6, all P < .001). The best repeatability measures were obtained for the shortindividual protocol (repeatability: standardrecon = 45.3%, shortfixed = 41.2%, shortindividual = 31.7%).

CONCLUSION

We recommend using the shortindividual reconstruction protocol for improved LVEF repeatability and reserve assessment. Alternatively, in centers with limited technical support we recommend the use of the shortfixed protocol.

Myocardial perfusion reserve in patients with chronic hepatitis C before and after direct-acting antiviral treatment-a pilot study

INTRODUCTION

Patients with chronic hepatitis C (CHC) have an increased risk of atherosclerotic cardiovascular disease which may be due to inflammation and endothelial dysfunction caused by the chronic infection. In this prospective pilot study, we assessed, for the first time among patients with CHC the myocardial perfusion reserve (MPR) by Rubidium-82 (⁸² Rb) positron emission tomography (PET)/computed tomography (CT) before and after direct-acting antiviral (DAA) treatment and compared them with biomarkers of systemic inflammation and endothelial dysfunction.

METHODS

We included 10 patients with CHC who received 8 or 12 weeks of DAA treatment. To obtain the MPR, a cardiac ⁸² Rb PET/CT scan at rest and adenosine-induced stress was performed at baseline and between 12 and 24 weeks post DAA treatment. Additionally, markers of endothelial dysfunction and inflammation were measured at baseline and 12 weeks after DAA treatment.

RESULTS

All 10 patients achieved cure and the median age was 50 (range: 40-62 years). The median MPR before treatment was 3.1 (range: 2.3-4.8) compared to 2.9 (range: 2.2-4.1) after DAA treatment p = 0.63. Also, cure after DAA treatment was not associated with an overall significant decrease in markers of endothelial dysfunction and inflammation.

DISCUSSION

Cure after DAA treatment in patients with CHC did not improve coronary microvascular function nor did it lead to a decrease in soluble markers of cardiovascular risk in the given time frame where the patients were followed. It should be noted, that MPR before DAA treatment was in the normal range. Considering the small sample size and short follow-up time, further studies are warranted to determine if viral clearance has an effect on coronary microvascular function and endothelial dysfunction.

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

BACKGROUND

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

METHODS

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

RESULTS

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

CONCLUSIONS

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

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

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

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.

Coronary Microvascular Dysfunction: A Practical Approach to Diagnosis and Management

PURPOSE OF REVIEW

The purpose of this review is to provide an overview of diagnostic and treatment considerations in patients with coronary microvascular dysfunction (CMD) in the absence of obstructive coronary artery disease (CAD).

RECENT FINDINGS

The prevalence of obstructive CAD in unselected patient populations referred for evaluation of angina is less than 10%. A significant proportion of patients with angina and no obstructive CAD have CMD, a condition associated with impaired cardiovascular prognosis. Non-invasive and invasive evaluation of coronary microvascular function is feasible and widely available, yet CMD is underdiagnosed and undertreated. A patient-tailored treatment approach guided by coronary microvascular testing shows promising results for patient-reported outcomes of symptom burden and quality of life. Coronary microvascular testing should be considered in angina patients with no obstructive CAD, before other causes of chest pain are explored. A patient-tailored treatment approach guided by a complete evaluation of epicardial anatomy and macro-and microvascular function may help optimize treatment strategy and prevent unnecessary medical interventions. More research is needed to establish the long-term effect of patient-tailored therapies on risk reduction in CMD.

Gender differences and caffeine impact in adenosine-induced hyperemia

Background: Caffeine consumption before adenosine stress myocardial perfusion imaging (MPI) is known to affect the hemodynamic response and, thus, reduce the stress myocardial blood flow (MBF) and myocardial flow reserve (MFR) assessments. However, it is not clear if any gender-specific differences in the hemodynamic response following caffeine consumption exist. This study aimed to evaluate if such differences exist and, if so, their impact on MBF and MFR assessments. Methods: This study comprised 40 healthy volunteers (19 women). All volunteers underwent four serial rest/stress MPI sessions employing Rubidium-82; two sessions were acquired without controlled caffeine consumption, and two sessions following oral ingestion of either 100mg and 300mg caffeine or 200mg and 400mg caffeine. For the caffeine imaging sessions, caffeine was ingested orally 1hr before the MPI scan. Results: Increase in plasma caffeine concentration (PCC) (mg/l) following consumption of caffeine was larger in women (MPI session without caffeine vs. MPI session with caffeine: women = 0.3±0.2 vs. 5.4±5.1, men = 0.1±0.2 vs. 2.7±2.6, both p<0.001). Caffeine consumption led to reduced stress MBF and MFR assessments for men while no changes were reported for women (women (PCC<1mg/l vs PCC≥1mg/l): stress MBF = 3.3±0.6 vs. 3.0±0.8 ml/g/min, P = 0.07; MFR = 3.7±0.6 vs. 3.5±1.0, P = 0.35; Men (PCC<1mg/l vs PCC≥1mg/l): stress MBF= 2.7±0.7 vs. 2.1±1.0 ml/g/min, P = 0.005, MFR = 3.8±1.0 vs. 3.1±1.4, P = 0.018). Significant differences in the stress MBF were observed for the two genders (both p≤0.001), while similar MFR were reported (both p≥0.12). Conclusion: Associations between increases in PCC and reductions in stress MBF and MFR were observed for men, while women did not have the same hemodynamic response. Stress MBF was affected at lower plasma caffeine concentrations in men than women.

Transthoracic Assessment of Coronary Flow Velocity Reserve: A Practical Approach to Diagnostic Testing in Patients with Angina and No Obstructive Coronary Artery Disease

More than half of the patients with symptoms suggestive of myocardial ischemia presenting at invasive angiography have no obstructive coronary artery disease (CAD). A large proportion of these patients have ischemia caused by coronary microvascular dysfunction, a condition associated with adverse cardiovascular prognosis. Measurement of coronary flow velocity reserve by transthoracic Doppler echocardiography is a feasible and reproducible method for the evaluation of coronary microvascular function. This review provides a practical overview of the method in a clinical setting of angina and noobstructive CAD, including technical details and prognostic significance.

Multiparametric Cardiac 18F-FDG PET in Humans: Kinetic Model Selection and Identifiability Analysis

Cardiac ¹⁸F-FDG PET has been used in clinics to assess myocardial glucose metabolism. Its ability for imaging myocardial glucose transport, however, has rarely been exploited in clinics. Using the dynamic FDG-PET scans of ten patients with coronary artery disease, we investigate in this paper appropriate dynamic scan and kinetic modeling protocols for efficient quantification of myocardial glucose transport. Three kinetic models and the effect of scan duration were evaluated by using statistical fit quality, assessing the impact on kinetic quantification, and analyzing the practical identifiability. The results show that the kinetic model selection depends on the scan duration. The reversible two-tissue model was needed for a one-hour dynamic scan. The irreversible two-tissue model was optimal for a scan duration of around 10-15 minutes. If the scan duration was shortened to 2-3 minutes, a one-tissue model was the most appropriate. For global quantification of myocardial glucose transport, we demonstrated that an early dynamic scan with a duration of 10-15 minutes and irreversible kinetic modeling was comparable to the full one-hour scan with reversible kinetic modeling. Myocardial glucose transport quantification provides an additional physiological parameter on top of the existing assessment of glucose metabolism and has the potential to enable single tracer multiparametric imaging in the myocardium.