Single Photon Emission Computed Tomography (SPECT) Myocardial Perfusion Imaging Guidelines: Instrumentation, Acquisition, Processing, and Interpretation

Temporal trends in the contribution of modifiable cardiovascular risk factors to cardiovascular and all-cause mortality in patients undergoing myocardial perfusion imaging in a large city in Brazil

BACKGROUND

Most cardiovascular (CV) events stem from modifiable risk factors, but it remains uncertain whether their impact on mortality has decreased in recent years as a result of treatment, particularly in low- and middle-income countries. We evaluated the temporal trends in the population attributable fraction (PAF) of modifiable risk factors to CV mortality in patients undergoing myocardial perfusion imaging (MPI) for suspected coronary artery disease in a large city in Brazil.

METHODS

The cohort comprised 25,127 patients without established CV disease undergoing MPI in a referral center in Curitiba, Brazil, from 2010 to 2018. Baseline demographic, clinical and risk factors were prospectively collected. Modifiable risk factors encompassed hypertension, dyslipidemia, diabetes mellitus, sedentary lifestyle, obesity, and smoking. The primary outcome was CV death occurring up to 4 years of follow-up. The PAF of each risk factor was calculated for each triennium using multivariable Cox proportional regression models, adjusting for age, sex and family history of premature coronary disease.

RESULTS

Over 9 years, there were 1438 deaths, 444 due to CV causes. In the first triennium, sedentary lifestyle exhibited the highest PAF (49%) for CV death, followed by hypertension (17%), diabetes mellitus (8%) and smoking habit (6%). The PAF for all risk factors combined remained relatively stable thorough the triennia (2010-2012: 57% vs 2013-2015: 64% vs 2016-2018: 47%, p = NS).

CONCLUSION

In this large cohort of patients referred to MPI, the PAF of modifiable CV risk factors did not diminish in the last decade, with sedentary lifestyle having the largest contribution for CV mortality.

CONDENSED ABSTRACT

This study examinated temporal trends in the impact of modifiable cardiovascular (CV) risk factors on CV and overall mortality in a cohort of 25,127 patients undergoing myocardial perfusion imaging from 2010 to 2018. Sedentary behavior consistently had the greatest impact on both CV and overall mortality, followed by hypertension and diabetes. Smoking had a lesser effect, while obesity showed no independent association with the outcomes. The contributions of these modifiable CV risk factors remained stable over the study period, suggesting that interventions promoting physical activity may be essential in mitigating the burden of CV disease.

Correlates of markers of dyssynchrony in patients with STEMI and multivessel disease: an analysis from the IAEA SPECT STEMI trial

BACKGROUND

In this substudy of the Value of Gated-SPECT MPI for Ischemia- Guided PCI of non-culprit vessels in STEMI Patients with Multi vessel Disease after primary PCI trial after primary PCI we aim to assess if infarct size affects conventional measures of dyssynchrony at rest. Additionally, we explore if there is an independent correlation of stress-inducible ischemia with dyssynchrony at rest.

METHODS

The 48 patients with imaging at randomization were analyzed. Gated-single-photon emission computed tomography (SPECT) MPI with vasodilator stress and technetium-99m-labeled tracers was performed. The phase histogram bandwidth (HBW), phase SD, and entropy were obtained with the QGS software. Correlation between dyssynchrony at rest and infarct size and inducible ischemia was performed using the Spearman test.

RESULTS

According to normal database limits dyssynchrony parameters at rest were abnormal for men. In women only HBW was abnormal. Correlation between the summed rest score with dyssynchrony was significant only for entropy ( P  = 0.035). No correlation was observed for dyssynchrony and stress-induced ischemia.

CONCLUSION

Entropy, as a measure of dyssynchrony, has potential in the assessment of patients with STEMI and multivessel disease after primary PCI. Smaller residual myocardial scars in PCI-reperfused patients with STEMI may contribute to the lack of correlation between dyssynchrony at rest and infarct size and stress-induced ischemia, respectively.

Assessing the diagnostic value of left ventricular synchrony indices derived from phase analysis by D-SPECT in identifying obstructive coronary artery disease

This study aimed to assess the diagnostic efficacy of left ventricular synchrony (LVS) for detecting coronary artery disease (CAD). We explored whether the LVS index derived from phase analysis of D-SPECT provides superior diagnostic value compared to conventional perfusion analysis in identifying obstructive CAD. Patients with suspected or confirmed CAD underwent drug-stress/rest gated D-SPECT myocardial perfusion imaging (MPI) and coronary angiography (CAG). A 50% stenosis was set as the threshold for obstructive CAD. 110 participants were enrolled in this analysis. There were significant differences in phase standard deviation (PSD), phase histogram bandwidth (PHB) and entropy among the four groups. Patients without cardiac disease and those with mild-moderate stenosis exhibited no noticeable contraction asynchrony. However, LVS indices demonstrated a gradual increase with the progression of coronary stenosis when compared to NC (P < 0.001). Obstructive CAD was identified in 43 out of 110 participants (39%). Optimal cutoff values for diagnosing obstructive CAD during stress were determined as 7.6° for PSD, 24° for PHB, and 37% for entropy, respectively. Notably, PSD, PHB, and entropy indices exhibited higher sensitivity compared to MPI. The integration of the stress-induced LVS indices into routine MPI analysis resulted in a significantly greater area under the curve (AUC), leading to improved diagnostic performance and enhanced differential capacity. Stress-induced LVS indices increase with the severity of coronary artery stenosis by D-SPECT phase analysis. Further, the indices-derived phase analysis exhibits superior sensitivity and discriminatory ability compared to MPI in detecting obstructive CAD.

Interpretation of SPECT wall motion with deep learning

OBJECTIVES

We sought to develop a novel deep learning (DL) workflow to interpret single-photon emission computed tomography (SPECT) wall motion.

BACKGROUND

Wall motion assessment with SPECT is limited by image temporal and spatial resolution. Visual interpretation of wall motion can be subjective and prone to error. Artificial intelligence (AI) may improve accuracy of wall motion assessment.

METHODS

A total of 1038 patients undergoing rest electrocardiogram (ECG)-gated SPECT and echocardiography were included. Using echocardiography as truth, a DL-model (DL-model 1) was trained to predict the probability of abnormal wall motion. Of the 1038 patients, 317 were used to train a DL-model (DL-model 2) to assess regional wall motion. A 10-fold cross-validation was adopted. Diagnostic performance of DL was compared with human readers and quantitative parameters.

RESULTS

The area under the receiver operating characteristic curve (AUC) and accuracy (ACC) of DL model (AUC: .82 [95% CI: .79-.85]; ACC: .88) were higher than human (AUC: .77 [95% CI: .73-.81]; ACC: .82; P < .001) and quantitative parameter (AUC: .74 [95% CI: .66-.81]; ACC: .78; P < .05). The net reclassification index (NRI) was 7.7%. The AUC and accuracy of DL model for per-segment and per-vessel territory diagnosis were also higher than human reader. The DL model generated results within 30 seconds with operable guided user interface (GUI) and therefore could provide preliminary interpretation.

CONCLUSIONS

DL can be used to improve interpretation of rest SPECT wall motion as compared with current human readers and quantitative parameter diagnosis.

The Effect of Heat Exposure on Myocardial Blood Flow and Cardiovascular Function

BACKGROUND

Heat extremes are associated with greater risk for cardiovascular death. The pathophysiologic mechanisms mediating this association are unknown.

OBJECTIVE

To quantify the myocardial blood flow (MBF) requirements of heat exposure.

DESIGN

Experimental study. (ClinicalTrials.gov: NCT04549974).

SETTING

Laboratory-based.

PARTICIPANTS

61 participants, comprising 20 healthy young adults (mean age, 28 years), 21 healthy older adults (mean age, 67 years), and 20 older adults with coronary artery disease (CAD) (mean age, 70 years).

INTERVENTION

Participants were heated until their core temperature increased 1.5 °C; MBF was measured before heat exposure and at every increase of 0.5 °C in core temperature.

MEASUREMENTS

The primary outcome was MBF measured by positron emission tomography-computed tomography. Secondary outcomes included heart rate, blood pressure, and body weight change.

RESULTS

At a core temperature increase of 1.5 °C, MBF increased in healthy young adults (change, 0.8 mL/min/g [95% CI, 0.5 to 1.0 mL/min/g]), healthy older adults (change, 0.7 mL/min/g [CI, 0.5 to 0.9 mL/min/g]), and older adults with CAD (change, 0.6 mL/min/g [CI, 0.3 to 0.8 mL/min/g]). This represented a 2.08-fold (CI, 1.75- to 2.41-fold), 1.79-fold (CI, 1.59- to 1.98-fold), and 1.64-fold (CI, 1.41- to 1.87-fold) change, respectively, from preexposure values. Imaging evidence of asymptomatic heat-induced myocardial ischemia was seen in 7 adults with CAD (35%) in post hoc analyses.

LIMITATIONS

In this laboratory-based study, heating was limited to about 100 minutes and participants were restricted in movement and fluid intake. Participants refrained from strenuous exercise and smoking; stopped alcohol and caffeine intake; and withheld β-blockers, calcium-channel blockers, and nitroglycerin before heating.

CONCLUSION

Heat exposure that increases core temperature by 1.5 °C nearly doubles MBF. Changes in MBF did not differ by age or presence of CAD, but some older adults with CAD may experience asymptomatic myocardial ischemia.

PRIMARY FUNDING SOURCE

Canadian Institutes of Health Research.

Impact of cardiac size on diagnostic performance of single-photon emission computed tomography myocardial perfusion imaging: insights from the REgistry of Fast Myocardial Perfusion Imaging with NExt generation single-photon emission computed tomography

AIMS

Variation in diagnostic performance of single-photon emission computed tomography (SPECT) myocardial perfusion imaging (MPI) has been observed, yet the impact of cardiac size has not been well characterized. We assessed whether low left ventricular volume influences SPECT MPI's ability to detect obstructive coronary artery disease (CAD) and its interaction with age and sex.

METHODS AND RESULTS

A total of 2066 patients without known CAD (67% male, 64.7 ± 11.2 years) across nine institutions underwent SPECT MPI with solid-state scanners followed by coronary angiography as part of the REgistry of Fast Myocardial Perfusion Imaging with NExt Generation SPECT. Area under receiver-operating characteristic curve (AUC) analyses evaluated the performance of quantitative and visual assessments according to cardiac size [end-diastolic volume (EDV); <20th vs. ≥20th population or sex-specific percentiles], age (<75 vs. ≥75 years), and sex. Significantly decreased performance was observed in patients with low EDV compared with those without (AUC: population 0.72 vs. 0.78, P = 0.03; sex-specific 0.72 vs. 0.79, P = 0.01) and elderly patients compared with younger patients (AUC 0.72 vs. 0.78, P = 0.03), whereas males and females demonstrated similar AUC (0.77 vs. 0.76, P = 0.67). The reduction in accuracy attributed to lower volumes was primarily observed in males (sex-specific threshold: EDV 0.69 vs. 0.79, P = 0.01). Accordingly, a significant decrease in AUC, sensitivity, specificity, and negative predictive value for quantitative and visual assessments was noted in patients with at least two characteristics of low EDV, elderly age, or male sex.

CONCLUSION

Detection of CAD with SPECT MPI is negatively impacted by small cardiac size, most notably in elderly and male patients.

Machine learning predictions of the adverse events of different treatments in patients with ischemic left ventricular systolic dysfunction

This study aimed to develop several new machine learning models based on hibernating myocardium to predict the major adverse cardiac events(MACE) of ischemic left ventricular systolic dysfunction(LVSD) patients receiving either percutaneous coronary intervention(PCI) or optimal medical therapy(OMT). This study included 329 LVSD patients, who were randomly assigned to the training or validation cohort. Least absolute shrinkage and selection operator(LASSO) regression was used to identify variables associated with MACE. Subsequently, various machine learning models were established. Model performance was compared using receiver operating characteristic(ROC) curves, the Brier score(BS), and the concordance index(C-index). A total of 329 LVSD patients were retrospectively enrolled between January 2016 and December 2021. Utilizing LASSO regression analysis, five factors were selected. Based on these factors, RSF, GBM, XGBoost, Cox, and DeepSurv models were constructed. In the development and validation cohorts, the C-indices were 0.888 vs. 0.955 (RSF). The RSF model (0.991 vs. 0.982 vs. 0.980) had the highest area under the ROC curve (AUC) compared with the other models. The BS (0.077 vs. 0.095vs. 0.077) of RSF model were less than 0.25 at 12, 18, and 24 months. This study developed a novel predictive model based on RSF to predict MACE in LVSD patients who underwent either PCI or OMT.

Myocardial blood flow quantification with SPECT

INTRODUCTION

The addition of absolute myocardial blood flow (MBF) data improves the diagnostic and prognostic accuracy of relative perfusion imaging with nuclear medicine. Cardiac-specific gamma cameras allow measurement of MBF with SPECT.

METHODS

This paper reviews the evidence supporting the use of SPECT to measure myocardial blood flow (MBF). Studies have evaluated SPECT MBF in large animal models and compared it in humans with invasive angiographic measurements and against the clinical standard of PET MBF. The repeatability of SPECT MBF has been determined in both single-site and multi-center trials.

RESULTS

SPECT MBF has excellent correlation with microspheres in an animal model, with the number of stenoses and fractional flow reserve, and with PET-derived MBF. The inter-user coefficient of variability is ∼20% while the COV of test-retest MBF is ∼30%. SPECT MBF improves the sensitivity and specificity of the detection of multi-vessel disease over relative perfusion imaging and provides incremental value in predicting adverse cardiac events.

CONCLUSION

SPECT MBF is a promising technique for providing clinically valuable information in the assessment of coronary artery disease.

Advances in Clinical Care with Contemporary Cardiac SPECT

State of the art of cardiac SPECT imaging continues to advance. Contemporary clinical applications of cardiac SPECT are reviewed and illustrated. Beyond traditional stress and rest myocardial perfusion imaging, the role of digital SPECT technology, ultra low dose imaging with efficient stress first / stress only if normal imaging, deep learning algorithms relative to coronary angiography and SPECT CT, sourceless emission attenuation correction, myocardial blood flow and blood flow reserve to assess ischemic jeopardy, culprit ischemic territories, and cardiac allograft vasculopathy, advanced methods of SPECT detection of amyloid cardiomyopathy, resting MPI to define pre-operative regional scar prior to operative ablation, parametric radionuclide ventriculography to quantify dyssynchrony and benefit of biventricular pacing, assessment of treatment response of RV and LV function in patients with pulmonary hypertension, dual isotope MIBG imaging to assess cardiac risk, and the value proposition of real world effectiveness of SPECT cardiac imaging are illustrated.

How to assess nonresponsiveness to vasodilator stress

Myocardial perfusion imaging (MPI) is a powerful tool for the functional assessment of ischemia in patients with suspected or known coronary artery disease (CAD). Given that the diagnostic accuracy and prognostic value of MPI and post-test management are highly dependent on achieving an adequate stress vasodilatory response, it is critical to identify those who may not have adequately responded to vasodilator pharmacological stress agents such as adenosine, dipyridamole, and regadenoson. Caffeine, a potent inhibitor of the adenosine receptor, is a compound that can affect vasodilatory hemodynamics, result in false negative studies, and potentially alter management in cases of inaccurate test results. Vasodilator non-responsiveness can be suspected by examining hemodynamics, quantitative positron emission tomography (PET) metrics such as myocardial flow reserve (MFR), and splenic response to stress. Quantitative MFR values of 1-1.2 should raise suspicion for nonresponsiveness in the setting of normal perfusion, along with the absence of a splenic switch off. Newer metrics, such as splenic response ratio, can be used to aid in the identification of potential nonresponders to pharmacologic vasodilators.

Effects of Ivabradine on Myocardial Perfusion in Chronic Angina: A Prospective, Preliminary, Open-Label, Single-Arm Study

INTRODUCTION

Ivabradine reduces heart rate (HR), episodes of angina, and nitrate consumption, and increases exercise capacity in patients with chronic angina (CA). In this exploratory study, myocardial perfusion scintigraphy (MPS) was used to evaluate changes in the percentage of myocardial ischemia after ivabradine therapy in patients with CA.

METHODS

This prospective, open-label, single-arm study included patients with CA receiving maximum tolerated doses of beta blockers, who had a resting HR ≥ 70 bpm and had experienced ischemia according to MPS during an exercise test at baseline. Participants received ivabradine 5 mg twice daily (titrated according to HR) concomitant with beta blockers. A second MPS was performed after 3 months, without interruption of treatment with beta blockers or ivabradine. The primary outcome was change in the percentage of myocardial ischemia from baseline to 3 months. Time to ischemia during the exercise test, the proportion of patients presenting angina during the exercise test, and health status, assessed using the seven-item Seattle Angina Questionnaire-7 (SAQ-7), were also evaluated.

RESULTS

Twenty patients (3 females) with a mean (± standard deviation [SD]) age of 62.2 ± 6.5 years were included in the study, of whom 55% had diabetes, 70% had previous myocardial revascularization, and 45% had previous myocardial infarction. The percentage of patients with myocardial ischemia significantly decreased from baseline to 3 months after initiation of treatment with ivabradine (- 2.9%; 95% confidence interval [CI] - 0.3 to - 5.5; p = 0.031). Mean time to appearance of ischemia increased from 403 ± 176 s at baseline to 466 ± 136 s at 3 months after initiation of ivabradine (Δ62 s; 95% CI 18-106 s; p = 0.008), and the proportion of patients experiencing angina during the exercise test decreased from 40% at baseline to 5% also at 3 months (p = 0.016). Mean resting HR decreased from 76 ± 7 bpm at baseline to 55 ± 8 bpm at 3 months (p < 0.001). The mean SAQ-7 summary score improved from 69 ± 21 at baseline to 83 ± 12 at 3 months (p = 0.001). No serious adverse effects were reported.

CONCLUSION

Ivabradine added to beta blockers was associated with a reduction in detectable myocardial ischemia by MPS in patients with CA. Infographic available for this article.

TRIAL REGISTRATION

The trial has been retrospectively registered with the Brazilian Registry of Clinical Trials (REBEC) under the following number RBR-5fysqrh (date of registration: 30 November 2023).

Radiomics Nomogram Derived from Gated Myocardial Perfusion SPECT for Identifying Ischemic Cardiomyopathy

Personalized management involving heart failure (HF) etiology is crucial for better prognoses. We aim to evaluate the utility of a radiomics nomogram based on gated myocardial perfusion imaging (GMPI) in distinguishing ischemic from non-ischemic origins of HF. A total of 172 heart failure patients with reduced left ventricular ejection fraction (HFrEF) who underwent GMPI scan were divided into training (n = 122) and validation sets (n = 50) based on chronological order of scans. Radiomics features were extracted from the resting GMPI. Four machine learning algorithms were used to construct radiomics models, and the model with the best performances were selected to calculate the Radscore. A radiomics nomogram was constructed based on the Radscore and independent clinical factors. Finally, the model performance was validated using operating characteristic curves, calibration curve, decision curve analysis, integrated discrimination improvement values (IDI), and the net reclassification index (NRI). Three optimal radiomics features were used to build a radiomics model. Total perfusion deficit (TPD) was identified as the independent factors of conventional GMPI metrics for building the GMPI model. In the validation set, the radiomics nomogram integrating the Radscore, age, systolic blood pressure, and TPD significantly outperformed the GMPI model in distinguishing ischemic cardiomyopathy (ICM) from non-ischemic cardiomyopathy (NICM) (AUC 0.853 vs. 0.707, p = 0.038). IDI analysis indicated that the nomogram improved diagnostic accuracy by 28.3% compared to the GMPI model in the validation set. By combining radiomics signatures with clinical indicators, we developed a GMPI-based radiomics nomogram that helps to identify the ischemic etiology of HFrEF.

Self-supervised deep representation learning of a foundation transformer model enabling efficient ECG-based assessment of cardiac and coronary function with limited labels

Background: Although deep learning methods have shown great promise for identification of structural and functional cardiac abnormalities using electrocardiographic data, these methods are data hungry, posing a challenge for critically important tasks where ground truth labels are relatively scarce. Impaired coronary microvascular and vasomotor function is difficult to identify with standard clinical methods of cardiovascular testing such as coronary angiography and noninvasive single photon emission tomography (SPECT) myocardial perfusion imaging (MPI). Gold standard data from positron emission tomography (PET) are gaining emphasis in clinical guidelines but are expensive and only available in relatively limited centers. We hypothesized that signals embedded within resting and stress electrocardiograms (ECGs) identify individuals with microvascular and vasomotor dysfunction. Methods: We developed and pretrained a self-supervised foundation vision transformer model using a large database of unlabeled ECG waveforms (N=800,035). We then fine-tuned the foundation model for two clinical tasks: the difficult problem of identifying patients with impaired myocardial flow reserve (AI-MFR), and the relatively easier problem of detecting impaired LVEF (AI-LVEF). A second ECG database was labeled with task-specific annotations derived from quantitative PET MPI (N=4167). Diagnostic accuracy of AI predictions was tested in a holdout set of patients undergoing PET MPI (N=1031). Prognostic evaluation was performed in the PET holdout cohort, as well as independent cohorts of patients undergoing pharmacologic or exercise stress SPECT MPI (N=6635). Results: The diagnostic accuracy of AI-MFR with SSL pretraining increased significantly compared to de novo supervised training (AUROC, sensitivity, specificity: 0.758, 70.1%, 69.4% vs. 0.632, 66.1%, 57.3%, p < 0.0001). SSL pretraining also produced a smaller increase in AI-LVEF accuracy (AUROC, sensitivity, specificity: 0.946, 89.4%, 85.9% vs. 0.918, 87.6%, 82.5%, p < 0.02). Abnormal AI-MFR was found to be significantly associated with mortality risk in all three test cohorts (Hazard Ratio (HR) 2.61 [95% CI 1.83, 3.71], p < 0.0001, PET cohort; HR 2.30 [2.03, 2.61], p < 0.0001, pharmacologic stress SPECT cohort; HR 3.76 [2.36, 5.99], p < 0.0001, exercise stress SPECT cohort). Conclusion: SSL pretraining of a vision transformer foundation model enabled identification of signals predictive of impaired MFR, a hallmark of microvascular and vasomotor dysfunction, and impaired LV function in resting and stress ECG waveforms. These signals are powerful predictors of prognosis in patients undergoing routine noninvasive stress testing and could enable more efficient diagnosis and management of these common conditions.

Prognostic Value of Stress Myocardial Perfusion Imaging Across the Spectrum of Cardiovascular Risk

BACKGROUND

Single-photon emission computed tomography (SPECT) myocardial perfusion imaging (MPI) is widely used to identify ischemia. There is limited research to evaluate if there is a risk threshold below which SPECT-MPI may not add significant prognostic value.

METHODS

Between January 1, 2012, and December 31, 2018, individuals who underwent SPECT-MPI were stratified into 4 risk groups. The primary outcome was acute myocardial infarction (MI) or death. Multivariable Cox proportional hazards regression analysis was used to calculated hazard ratios (HRs) with 95% confidence intervals (CIs).

RESULTS

Among 48,845 patients (52.3% male, median age 67 years), 8.5% were low risk, 4.8% borderline risk, 18.1% intermediate risk, and 68.6% high risk based on the American College of Cardiology pooled cohort equation. Ischemia was more commonly detected in the high-risk cohort (19.4% in high-risk vs 6.5% in low-risk). SPECT-MPI testing was associated with a significantly increased use of preventive medications such as statin therapy, regardless of stress test results. At a median follow-up of 4.2 years, there was no significant association between ischemia and death or MI in the low-risk cohort (adjusted HR, 1.91; 95% CI, 0.94-3.92) or the borderline-risk cohort (adjusted HR, 1.58; 95% CI, 0.79-3.15). Ischemia was associated with a higher risk of death or MI in the intermediate-risk (adjusted HR, 1.57; 95% CI, 1.24-1.99) and high-risk groups (adjusted HR, 1.54; 95% CI, 1.44-1.64).

CONCLUSIONS

SPECT-MPI was less useful for risk stratification among low-risk patients because of their low event rates regardless of test results.

Adjacent object distorts the organ-of-interest in filtered back-projection tomographic image reconstruction: 'ramp filter' or 'reconstruction' artifact revisited

OBJECTIVE

To simulate the artifact caused by an adjacent object on organ-of-interest during filtered back-projection (FBP) tomographic reconstruction (the so-called "ramp filter" artifact) and to demonstrate the extent to which an organ-of-interest is influenced by such adjacent hot spot or attenuating object.

METHODS AND MATERIALS

Two simulations are conducted with two simplified phantoms: "hot spot" and "cardiac." First one is used to visualize effect of hot spot on its periphery. Second one is used to evaluate effect of nearby object (liver) on left ventricle (LV) as organ-of-interest. To generate sinograms, forward projection process is done with and without modeling radiation attenuation. FBP using windowed ramp filter is done. All slices are analyzed by plotting intensity profiles.

RESULTS

In tomographic slices, there is a hypo-intense halo around presumed edge of object when compared to background intensity, more noticeable in phantoms with less blurring. Even with ramp filter applied, no halo is visible in FBP without attenuation for cardiac phantom. In contrast, in slices with considering attenuation, zones with different levels of count suppression on both sides of object are visualized instead. The most prominent one is between liver and LV in simulation with higher-attenuating object and higher activity.

CONCLUSION

A single hot spot with sufficient amount of blurring does not distort its surroundings. Hot spots and attenuating objects near organ-of-interest, however, distort myocardial perfusion imaging. Artifactual defects are thus only created when attenuation is modeled during FBP, producing zones of count suppression between organ-of-interest and nearby object or hot spot.

10-year experience of utilizing a stress-first SPECT myocardial perfusion imaging

BACKGROUND

Despite its potential benefits, the utilization of stress-only protocol in clinical practice has been limited. We report utilizing stress-first single-photon emission computed tomography (SPECT) myocardial perfusion imaging (MPI).

METHODS

We assessed 12,472 patients who were referred for SPECT-MPI between 2013 and 2020. The temporal changes in frequency of stress-only imaging were assessed according to risk factors, mode of stress, prior coronary artery disease (CAD) history, left ventricular function, and symptom status. The clinical endpoint was all-cause mortality.

RESULTS

In our lab, stress/rest SPECT-MPI in place of rest/stress SPECT-MPI was first introduced in November 2011 and was performed more commonly than rest/stress imaging after 2013. Stress-only SPECT-MPI scanning has been performed in 30-34% of our SPECT-MPI studies since 2013 (i.e.. 31.7% in 2013 and 33.6% in 2020). During the study period, we routinely used two-position imaging (additional prone or upright imaging) to reduce attenuation and motion artifact and introduced SPECT/CT scanner in 2018. The rate of stress-only study remained consistent before and after implementing the SPECT/CT scanner. The frequency of stress-only imaging was 43% among patients without a history of prior CAD and 19% among those with a prior CAD history. Among patients undergoing treadmill exercise, the frequency of stress-only imaging was 48%, while 32% among patients undergoing pharmacologic stress test. In multivariate Cox analysis, there was no significant difference in mortality risk between stress-only and stress/rest protocols in patients with normal SPECT-MPI results (p = 0.271).

CONCLUSION

Implementation of a stress-first imaging protocol has consistently resulted in safe cancellation of 30% of rest SPECT-MPI studies.

Phase I, first-in-human study of XTR004, a novel 18F-labeled tracer for myocardial perfusion PET: Biodistribution, radiation dosimetry, pharmacokinetics, and safety after a single injection at rest

OBJECTIVES

This study assessed the imaging characteristics, pharmacokinetics and safety of XTR004, a novel 18F-labeled Positron Emission Tomography (PET) myocardial perfusion imaging tracer, after a single injection at rest in humans.

METHODS

Eleven healthy subjects (eight men and three women) received intravenous XTR004 (239-290 megabecquerel [MBq]). Safety profiles were monitored on the dosing day and three follow-up visits. Multiple whole-body PET scans were conducted over 4.7 h to evaluate biodistribution and radiation dosimetry. Blood and urine samples collected for 7.25 h were metabolically corrected to characterize pharmacokinetics.

RESULTS

In the first 0-12 min PET images of ten subjects, liver (26.81 ± 4.01), kidney (11.43 ± 2.49), lung (6.75 ± 1.76), myocardium (4.72 ± 0.67) and spleen (3.1 ± 0.84) exhibited the highest percentage of the injected dose (%ID). Myocardial uptake of XTR004 in the myocardium initially reached 4.72 %ID and 7.06 g/mL, and negligibly changed within an hour (Δ: 7.20%, 5.95%). The metabolically corrected plasma peaked at 2.5 min (0.0013896 %ID/g) and halved at 45.2 min. Whole-body effective dose was 0.0165 millisievert (mSv)/MBq. Cumulative urine excretion was 8.18%. Treatment-related adverse events occurred in seven out of eleven subjects (63.6%), but no severe adverse event was reported.

CONCLUSIONS

XTR004 demonstrated a favorable safety profile, rapid, high, and stable myocardial uptake and excellent potential for PET myocardial perfusion imaging (MPI). Further exploration of XTR004 PET MPI for detecting myocardial ischemia is warranted.

Nuclear Cardiology in the Era of Precision Medicine: Tailoring Treatment to the Individual Patient

Nuclear cardiology, employing advanced imaging technologies like positron emission tomography (PET) and single photon emission computed tomography (SPECT), is instrumental in diagnosing, risk stratifying, and managing heart diseases. Concurrently, precision medicine advocates for treatments tailored to each patient's genetic, environmental, and lifestyle specificities, promising a revolution in personalized cardiovascular care. This review explores the synergy between nuclear cardiology and precision medicine, highlighting advancements, potential enhancements in patient outcomes, and the challenges and opportunities of this integration. We examined the evolution of nuclear cardiology technologies, including PET and SPECT, and their role in cardiovascular diagnostics. We also delved into the principles of precision medicine, focusing on genetic and molecular profiling, data analytics, and individualized treatment strategies. The integration of these domains aims to optimize diagnostic accuracy, therapeutic interventions, and prognostic evaluations in cardiovascular care. Advancements in molecular imaging and the application of artificial intelligence in nuclear cardiology have significantly improved the precision of diagnostics and treatment plans. The adoption of precision medicine principles in nuclear cardiology enables the customization of patient care, leveraging genetic information and biomarkers for enhanced therapeutic outcomes. However, challenges such as data integration, accessibility, cost, and the need for specialized expertise persist. The confluence of nuclear cardiology and precision medicine offers a promising pathway toward revolutionizing cardiovascular healthcare, providing more accurate, effective, and personalized patient care. Addressing existing challenges and fostering interdisciplinary collaboration is crucial for realizing the full potential of this integration in improving patient outcomes.

Recent progress on polySarcosine as an alternative to PEGylation: Synthesis and biomedical applications

Biotherapeutic PEGylation to prolong action of medications has gained popularity over the last decades. Various hydrophilic natural polymers have been developed to tackle the drawbacks of PEGylation, such as its accelerated blood clearance and non-biodegradability. Polypeptoides, such as polysarcosine (pSar), have been explored as hydrophilic substitutes for PEG. pSar has PEG-like physicochemical characteristics such as water solubility and no reported cytotoxicity and immunogenicity. This review discusses pSar derivatives, synthesis, characterization approaches, biomedical applications, in addition to the challenges and future perspectives of pSar based biomaterials as an alternative to PEG.

Cardiovascular Imaging in Women

Multimodality cardiovascular imaging is a cornerstone diagnostic tool in the diagnosis, risk stratification, and management of cardiovascular diseases, whether those involving the coronary tree, myocardial, or pericardial diseases in general and particularly in women. This manuscript aims to shed some light and summarize the very features of cardiovascular disease in women, explore their unique characteristics and discuss the role of cardiovascular imaging in ischemic heart disease and cardiomyopathies. The role of four imaging modalities will be discussed including nuclear medicine, echocardiography, noninvasive coronary angiography, and cardiac magnetic resonance.

Deep learning approach using SPECT-to-PET translation for attenuation correction in CT-less myocardial perfusion SPECT imaging

OBJECTIVE

Deep learning approaches have attracted attention for improving the scoring accuracy in computed tomography-less single photon emission computed tomography (SPECT). In this study, we proposed a novel deep learning approach referring to positron emission tomography (PET). The aims of this study were to analyze the agreement of representative voxel values and perfusion scores of SPECT-to-PET translation model-generated SPECT (SPECTSPT) against PET in 17 segments according to the American Heart Association (AHA).

METHODS

This retrospective study evaluated the patient-to-patient stress, resting SPECT, and PET datasets of 71 patients. The SPECTSPT generation model was trained (stress: 979 image pairs, rest: 987 image pairs) and validated (stress: 421 image pairs, rest: 425 image pairs) using 31 cases of SPECT and PET image pairs using an image-to-image translation network. Forty of 71 cases of left ventricular base-to-apex short-axis images were translated to SPECTSPT in the stress and resting state (stress: 1830 images, rest: 1856 images). Representative voxel values of SPECT and SPECTSPT in the 17 AHA segments against PET were compared. The stress, resting, and difference scores of 40 cases of SPECT and SPECTSPT were also compared in each of the 17 segments.

RESULTS

For AHA 17-segment-wise analysis, stressed SPECT but not SPECTSPT voxel values showed significant error from PET at basal anterior regions (segments #1, #6), and at mid inferoseptal regions (segments #8, #9, and #10). SPECT, but not SPECTSPT, voxel values at resting state showed significant error at basal anterior regions (segments #1, #2, and #6), and at mid inferior regions (segments #8, #9, and #11). Significant SPECT overscoring was observed against PET in basal-to-apical inferior regions (segments #4, #10, and #15) during stress. No significant overscoring was observed in SPECTSPT at stress, and only moderate over and underscoring in the basal inferior region (segment #4) was found in the resting and difference states.

CONCLUSIONS

Our PET-supervised deep learning model is a new approach to correct well-known inferior wall attenuation in SPECT myocardial perfusion imaging. As standalone SPECT systems are used worldwide, the SPECTSPT generation model may be applied as a low-cost and practical clinical tool that provides powerful auxiliary information for the diagnosis of myocardial blood flow.

Spherization indices measured by resting SPECT improve risk stratification in patients with ischemia with non-obstructive coronary artery disease (INOCA)

BACKGROUND

The prevalence of ischemia with non-obstructive coronary artery disease (INOCA) is substantial, but its risk stratification has been suboptimal. Resting SPECT myocardial perfusion imaging (MPI) could provide useful heart information including spherical indices. We aimed to evaluate the prognostic value of spherical indices in individuals with INOCA.

RESULTS

During a median follow-up of 47.2 ± 20.8 months, 49 (17.2%) patients experienced major adverse cardiac events (MACE). Compared to those without MACE, those with MACE had a higher shape index (SI) (0.60 ± 0.07 vs. 0.58 ± 0.06; P = 0.028) and a lower E2 (eccentricity index calculated by the QPS) (0.81 ± 0.05 vs. 0.83 ± 0.04; P = 0.019). MACE event-free survival analysis revealed significant differences in the SI and E2 among all patients (all log-rank P < 0.01). Multivariate Cox analysis showed abnormal SI (HR: 2.73, 95% CI 1.44-5.18, P = 0.002) and E2 (HR: 1.94, 95% CI 1.08-3.48, P = 0.026) were both independent predictors for MACE when they were put into the same model, respectively. The incorporation of the SI into the baseline model demonstrated a significant improvement in the predictive accuracy for MACEs (P = 0.026), whereas E2 did not exhibit a similar improvement (P > 0.05).

CONCLUSION

For patients with INOCA, spherical indices (especially the SI) were associated with long-term MACE, which could be a preferable indicator for risk stratification and prognostic prediction.

Decomposition Technique for Bio-Transmittance Imaging Based on Attenuation Coefficient Matrix Inverse

Human body tissue disease diagnosis will become more accurate if transmittance images, such as X-ray images, are separated according to each constituent tissue. This research proposes a new image decomposition technique based on the matrix inverse method for biological tissue images. The fundamental idea of this research is based on the fact that when k different monochromatic lights penetrate a biological tissue, they will experience different attenuation coefficients. Furthermore, the same happens when monochromatic light penetrates k different biological tissues, as they will also experience different attenuation coefficients. The various attenuation coefficients are arranged into a unique k×k-dimensional square matrix. k-many images taken by k-many different monochromatic lights are then merged into an image vector entity; further, a matrix inverse operation is performed on the merged image, producing N-many tissue thickness images of the constituent tissues. This research demonstrates that the proposed method effectively decomposes images of biological objects into separate images, each showing the thickness distributions of different constituent tissues. In the future, this proposed new technique is expected to contribute to supporting medical imaging analysis.

A computational approach for analysis of intratumoral heterogeneity and standardized uptake value in PET/CT images1

BACKGROUND

By providing both functional and anatomical information from a single scan, digital imaging technologies like PET/CT and PET/MRI hybrids are gaining popularity in medical imaging industry. In clinical practice, the median value (SUVmed) receives less attention owing to disagreements surrounding what defines a lesion, but the SUVmax value, which is a semi-quantitative statistic used to analyse PET and PET/CT images, is commonly used to evaluate lesions.

OBJECTIVE

This study aims to build an image processing technique with the purpose of automatically detecting and isolating lesions in PET/CT images, as well as measuring and assessing the SUVmed.

METHODS

The pictures are separated into their respective lesions using mathematical morphology and the crescent region, which are both part of the image processing method. In this research, a total of 18 different pictures of lesions were evaluated.

RESULTS

The findings of the study reveal that the threshold is satisfied by both the SUVmax and the SUVmed for most of the lesion types. However, in six instances, the SUVmax and SUVmed values are found to be in different courts.

CONCLUSION

The new information revealed by this study needs to be further investigated to determine if it has any practical value in diagnosing and monitoring lesions. However, results of this study suggest that SUVmed should receive more attention in the evaluation of lesions in PET and CT images.

Unveiling New Strategies Facilitating the Implementation of Artificial Intelligence in Neuroimaging for the Early Detection of Alzheimer's Disease

Alzheimer's disease (AD) is a chronic neurodegenerative disorder with a global impact. The past few decades have witnessed significant strides in comprehending the underlying pathophysiological mechanisms and developing diagnostic methodologies for AD, such as neuroimaging approaches. Neuroimaging techniques, including positron emission tomography and magnetic resonance imaging, have revolutionized the field by providing valuable insights into the structural and functional alterations in the brains of individuals with AD. These imaging modalities enable the detection of early biomarkers such as amyloid-β plaques and tau protein tangles, facilitating early and precise diagnosis. Furthermore, the emerging technologies encompassing blood-based biomarkers and neurochemical profiling exhibit promising results in the identification of specific molecular signatures for AD. The integration of machine learning algorithms and artificial intelligence has enhanced the predictive capacity of these diagnostic tools when analyzing complex datasets. In this review article, we will highlight not only some of the most used diagnostic imaging approaches in neurodegeneration research but focus much more on new tools like artificial intelligence, emphasizing their application in the realm of AD. These advancements hold immense potential for early detection and intervention, thereby paving the way for personalized therapeutic strategies and ultimately augmenting the quality of life for individuals affected by AD.

Role of CT attenuation correction gated SPECT MPI in prediction of pulmonary hypertension

OBJECTIVE

To elucidate the value of gated SPECT-MPI using CT attenuation correction (AC) for prediction of pulmonary hypertension (PHT) in coronary patients by estimation of reliability of non-contrast CT in measurement of main pulmonary artery diameter (MPAd) as well as by assessment of potential predictive role of gated parameters as beneficial accessory findings.

BACKGROUND

Contrast-enhanced CT is known as an accurate tool for assessment of MPAd to predict PHT. [1] The low-dose non-contrast CT which is used for AC in MPI study, however, has an unclear value in precise vascular diameter measurement; it is also uncertain whether gated parameters could help to predict PHT.

METHODS AND PATIENTS

A total of 207 patients, who had a transthoracic echocardiography and MPI with an interval of maximum one month, underwent this retrospective study. PHT was defined as a RVSP ≥36 mmHg by echocardiography; peak tricuspid regurgitation velocity (PTRV) was also calculated to use as a criterion for PHT. Of all subjects, 120 had RVSP ≥ 36 and 87 showed RVSP < 36; there also were 191 and 16 patients with PTRV ≤ 3.4 m/s and >3.4 m/s, respectively. Comparison was made unconnectedly between each group regarding the echocardiography results with the MPI parameters, with and without CT-AC, including MPAd derived from CT as well as RV/LV uptake ratio, shape index and septal wall motion and thickening scores to define the best indicators of PHT.

RESULTS

There was a significant association between established benchmark of PHT in echocardiography (RVSP), with MPAd derived from non-contrast CT as well as with LV shape index from gated study and RV/LV uptake ratio acquired from non-AC SPECT-MPI. Also, stress and rest RV/LV uptake ratio, MPAd, LV end-systolic and LV end-diastolic shape indexes are significantly higher in patients with RVSP ≥ 36 mmHg compare to patients with RVSP < 36 mmHg.

CONCLUSIONS

Gated-SPECT-MPI using CT-AC can predict PHT by reliable estimation of MPAd as well as by defining RV/LV uptake ratio and shape index, providing an added clinical value for this invaluable modality in cardiac patients.

Current status and perspectives of nuclear cardiology

Nuclear cardiology has long been used to identify myocardial ischemia for appropriate treatment strategies for stable coronary artery disease (CAD). After the Ischemia Trial, it is time to reevaluate the significance of ischemia assessment. Functional imaging continues to play pivotal role in detecting microcirculatory disturbances. PET provides a clear image of blood flow distribution and is useful for the quantitative evaluation of myocardial flow reserve (MFR), which plays an important role in predicting treatment strategies and improving prognosis in CAD. Heart failure has become a major area of focus in cardiovascular medicine. Radionuclide imaging has been widely applied in this field. FDG PET is useful in identifying cardiac sarcoidosis and active inflammation. Clinical values of I-123 MIBG and BMIPP SPECT have been reported worldwide from Japan. Additionally, clinical experiences of Tc-99m pyrophosphate imaging have recently gained attention for assessing cardiac amyloidosis. Cardiac PET/CT and PET/MR imaging permit combined assessment of metabolic/functional/structural analyses of various cardiac diseases. While other non-invasive imaging modalities have rapidly been developed, the roles of radionuclide imaging remain to be valuable for early and accurate diagnosis and patient management in most cases of chronic CAD and various cardiovascular diseases.

Optimizing stress-only myocardial perfusion imaging: a clinical prediction model to improve patient selection

BACKGROUND

Stress-only single photon emission computed tomography myocardial perfusion imaging (MPI) offers numerous advantages in terms of improved workflow, cost and radiation reduction but is currently not widely utilized due to challenges in selecting appropriate patients for this technique.

METHODS

Data from 5959 individuals were used to derive (N = 4018) and validate (N = 1941) a binomial logistic regression model to predict normal stress MPI studies (stress total perfusion deficit  < 4%, ejection fraction ≥ 50%). Model performance was analyzed using receiver operator characteristic curves. A simplified point-scoring system was developed and its impact on imaging workflow was assessed.

RESULTS

Significant predictors of abnormal vs. normal stress MPI included male sex, age > 65 years, cardiomyopathy, congestive heart failure, myocardial infarction, angina, and pharmacological stress. The final model and simplified scoring system were associated with areas under the curve of 0.81 (95% CI 0.79-0.83) and 0.80 (95% CI 0.79-0.82) in the validation group, respectively. Use of the scoring system was estimated to result in a decrease of 56.5% in the number of non-contributory imaging studies acquired with minimal patient rescheduling.

CONCLUSION

A prediction tool derived from simple clinical information can identify candidates for stress-only MPI studies with a beneficial impact on departmental workflow.

A new perspective on an old method: gated SPECT imaging for left ventricular contractile function assessment

The ejection fraction (LVEF) is a commonly used marker of left ventricular function. However, because it is strongly influenced by loading conditions, it can be inaccurate in representing cardiac contractility. We therefore evaluated a gated SPECT based tool to simultaneously assess preload, afterload, and contractility. Using gated SPECT-determined ventricular volumes and arterial tension measurements, we calculated ventricular and arterial elastance (Ev and Ea), as well as end-diastolic volumes, which are surrogates for contractility, afterload, and preload, respectively. We applied this protocol to 1462 consecutive patients and assessed the ventricular function in patients with and without myocardial infarction. The median LVEF was 68% (IQR 62-74%). Patients with infarction exhibited decreased contractility (ventricular elastance of 3 mmHg/ml vs. 6 mmHg/ml), compensated by an increase of preload (end-diastolic volume of 100 ml vs. 78 ml) and a decrease in afterload (arterial elastance of 1.8 mmHg/ml vs. 2.2 ml/mmHg). These interactions yielded a preserved ejection fraction in both groups. Gated SPECT-measured volumes were consistent with values reported in the literature. In addition, the combination of nuclear imaging and arterial tension measurement accounted for not only the ejection fraction but also the loading context, providing a more accurate representation of cardiac contractility.

Exponential dosing to standardize myocardial perfusion image quality with rubidium-82 PET

BACKGROUND

82Rb PET is commonly performed using the same injected activity in all patients, resulting in lower image quality in larger patients. This study compared 82Rb dosing with exponential vs proportional functions of body weight on the standardization of myocardial perfusion image (MPI) quality.

METHODS

Two sequential cohorts of N = 60 patients were matched by patient weight. Rest and dipyridamole stress 82Rb PET was performed using 0.1 MBq·kg-2 exponential and 9 MBq·kg-1 proportional dosing. MPI scans were compared qualitatively with visual image quality scoring (IQS) and quantitatively using the myocardium-to-blood contrast-to-noise ratio (CNR) and blood background signal-to-noise ratio (SNR) as a function of body weight.

RESULTS

Average (min-max) patient body weight was 81 ± 18 kg (46-137 kg). Proportional dosing resulted in decreasing CNR, SNR, and visual IQS with increasing body weight (P < 0.05). Exponential dosing eliminated the weight-dependent decreases in these image quality metrics that were observed in the proportional dosing group.

CONCLUSION

82Rb PET dosing as an exponential (squared) function of body weight produced consistent stress perfusion image quality over a wide range of patient weights. Dramatically lower doses can be used in lighter patients, with the equivalent population dose shifted toward the heavier patients to standardize diagnostic image quality.

4D display of CT LV endocardial and epicardial models morphed from PET Rb-82 perfusion studies accurately quantifies segmental myocardial thickening

BACKGROUND

MPI-derived LV wall thickening assessments for diagnostic purposes has been part of clinical guidelines for two decades. It relies on visual evaluation of tomographic slices or regional quantification displayed in 2D polar maps. 4D displays have not entered clinical usage nor have they been validated on their potential to provide equivalent information. The purpose of this work was to validate a 4D realistic display recently designed to quantitatively represent the thickening information from gated MPI into CT-morphed endocardial and epicardial moving surfaces.

METHODS

Forty patients who underwent 82Rb PET were selected based on LV perfusion quantification. CTA templates of heart anatomy were selected to represent the LV anatomy. Generic CT-derived LV endocardial and epicardial surfaces were modified to represent the end diastolic (ED) phase according to PET-derived ED LV dimensions and wall thickness. These CT myocardial surfaces were then morphed by means of thin plate spline (TPS) techniques, according to the gated PET slices count changes (WThPET) and LV wall motion (WMoPET). A geometric thickening (GeoTh) equivalent to LV WThPET was defined on epicardial and endocardial CT surfaces over the cardiac cycle and the two measures compared. WThPET and GeoTh correlations were performed on a case-by-case basis, by segment and by pooling all 17 segments. Pearson's correlation coefficients (PCC) were calculated to assess the equivalence of the two measures.

RESULTS

Two cohorts of patients (normal and abnormal) were identified based on SSS. R coefficients were as follows: for all pooled segments PCCstress and PCCrest were respectively 0.91 and 0.89 (normal), and 0.9 and 0.91 (abnormal); when individual 17 segments were considered mean PCCstress = 0.92 [0.81-0.98] and mean PCCrest = 0.93 [0.83-0.98] for the abnormal perfusion group; mean PCCstress = 0.89 [0.78-0.97] and mean PCCrest = 0.89 [0.77-0.97] for the normal. When individual studies were considered, R was always > .70 with the exception of five abnormal studies. Inter-user analysis was also conducted.

CONCLUSIONS

Our novel technique for the visualization of LV wall thickening by means of 4D CT endocardial and epicardial surface models accurately replicated 82Rb slice thickening results showing promise for its usage for diagnostic purposes.

Patient-level explainable machine learning to predict major adverse cardiovascular events from SPECT MPI and CCTA imaging

BACKGROUND

Machine learning (ML) has shown promise in improving the risk prediction in non-invasive cardiovascular imaging, including SPECT MPI and coronary CT angiography. However, most algorithms used remain black boxes to clinicians in how they compute their predictions. Furthermore, objective consideration of the multitude of available clinical data, along with the visual and quantitative assessments from CCTA and SPECT, are critical for optimal patient risk stratification. We aim to provide an explainable ML approach to predict MACE using clinical, CCTA, and SPECT data.

METHODS

Consecutive patients who underwent clinically indicated CCTA and SPECT myocardial imaging for suspected CAD were included and followed up for MACEs. A MACE was defined as a composite outcome that included all-cause mortality, myocardial infarction, or late revascularization. We employed an Automated Machine Learning (AutoML) approach to predict MACE using clinical, CCTA, and SPECT data. Various mainstream models with different sets of hyperparameters have been explored, and critical predictors of risk are obtained using explainable techniques on the global and patient levels. Ten-fold cross-validation was used in training and evaluating the AutoML model.

RESULTS

A total of 956 patients were included (mean age 61.1 ±14.2 years, 54% men, 89% hypertension, 81% diabetes, 84% dyslipidemia). Obstructive CAD on CCTA and ischemia on SPECT were observed in 14% of patients, and 11% experienced MACE. ML prediction's sensitivity, specificity, and accuracy in predicting a MACE were 69.61%, 99.77%, and 96.54%, respectively. The top 10 global predictive features included 8 CCTA attributes (segment involvement score, number of vessels with severe plaque ≥70, ≥50% stenosis in the left marginal coronary artery, calcified plaque, ≥50% stenosis in the left circumflex coronary artery, plaque type in the left marginal coronary artery, stenosis degree in the second obtuse marginal of the left circumflex artery, and stenosis category in the marginals of the left circumflex artery) and 2 clinical features (past medical history of MI or left bundle branch block, being an ever smoker).

CONCLUSION

ML can accurately predict risk of developing a MACE in patients suspected of CAD undergoing SPECT MPI and CCTA. ML feature-ranking can also show, at a sample- as well as at a patient-level, which features are key in making such a prediction.

Association Between Symptoms of Chronic Psychological Distress and Myocardial Ischemia Induced by Mental Stress in Patients With Coronary Artery Disease

Background Mental stress-induced myocardial ischemia is a frequent phenomenon in patients with coronary artery disease and is associated with a greater risk of future cardiovascular events. The association between chronic symptoms of psychological distress and mental stress-induced ischemia is not clear. Methods and Results We used a composite score of psychological distress derived from symptoms of depression, posttraumatic stress disorder, anxiety, anger, and perceived general stress. Participants underwent myocardial perfusion imaging with both mental (public speaking task) and conventional (exercise or pharmacological) stress testing. Overall, 142 (15.9%) patients experienced mental stress-induced myocardial ischemia. After adjusting for demographic factors, medical history, and medication use, patients in the highest tertile of psychological distress score had 35% higher odds of having mental stress-induced ischemia compared to those in the lowest tertile (odds ratio [OR], 1.35 [95% CI, 1.06-2.22]). Stratified analyses showed that the association between psychological distress score and mental stress-induced myocardial ischemia was significantly associated only within the subgroup of patients with a prior myocardial infraction, with patients with a prior myocardial infarction in the highest tertile having a 93% higher odds of developing myocardial ischemia with mental stress (95% CI, 1.07-3.60). There was no significant association between psychological distress and conventional stress-induced ischemia (OR, 1.19 [95% CI, 0.87-1.63]). Conclusions Among patients with a history of myocardial infarction, a higher level of psychosocial distress is associated with mental stress-induced myocardial ischemia but not with ischemia induced by a conventional stress test.

ACC/AHA/ASE/ASNC/ASPC/HFSA/HRS/SCAI/SCCT/SCMR/STS 2023 Multimodality Appropriate Use Criteria for the Detection and Risk Assessment of Chronic Coronary Disease

The American College of Cardiology (ACC) Foundation, along with key specialty and subspecialty societies, conducted an appropriate use review of stress testing and anatomic diagnostic procedures for risk assessment and evaluation of known or suspected chronic coronary disease (CCD), formerly referred to as stable ischemic heart disease (SIHD). This document reflects an updating of the prior Appropriate Use Criteria (AUC) published for radionuclide imaging, stress echocardiography (echo), calcium scoring, coronary computed tomography angiography (CCTA), stress cardiac magnetic resonance (CMR), and invasive coronary angiography for SIHD. This is in keeping with the commitment to revise and refine the AUC on a frequent basis. As with the prior version of this document, rating of test modalities is provided side-by-side for a given clinical scenario. These ratings are explicitly not considered competitive rankings due to the limited availability of comparative evidence, patient variability, and the range of capabilities available in any given local setting1-4.This version of the AUC for CCD is a focused update of the prior version of the AUC for SIHD4. Key changes beyond the updated ratings based on new evidence include the following: 1. Clinical scenarios related to preoperative testing were removed and will be incorporated into another AUC document under development. 2. Some clinical scenarios and tables were removed in an effort to simplify the selection of clinical scenarios. Additionally, the flowchart of tables has been reorganized, and all clinical scenario tables can now be reached by answering a limited number of clinical questions about the patient, starting with the patient's symptom status. 3. Several clinical scenarios have been revised to incorporate changes in other documents such as pretest probability assessment, atherosclerotic cardiovascular disease (ASCVD) risk assessment, syncope, and others. ASCVD risk factors that are not accounted for in contemporary risk calculators have been added as modifiers to certain clinical scenarios. The 64 clinical scenarios rated in this document are limited to the detection and risk assessment of CCD and were drawn from common applications or anticipated uses, as well as from current clinical practice guidelines.5 These clinical scenarios do not specifically address patients having acute chest pain episodes. They may, however, be applicable in the inpatient setting if the patient is not having an acute coronary syndrome and warrants evaluation for CCD.Using standardized methodology, clinical scenarios were developed to describe common patient encounters in clinical practice focused on common applications and anticipated uses of testing for CCD. Where appropriate, the scenarios were developed on the basis of the most current ACC/American Heart Association guidelines. A separate, independent rating panel scored the clinical scenarios in this document on a scale of 1 to 9, following a modified Delphi process consistent with the recently updated AUC development methodology. Scores of 7 to 9 indicate that a modality is considered appropriate for the clinical scenario presented, midrange scores of 4 to 6 indicate that a modality may be appropriate for the clinical scenario, and scores of 1 to 3 indicate that a modality is rarely appropriate.

Cardiovascular Imaging in Contemporary Cardio-Oncology: A Scientific Statement From the American Heart Association

Advances in cancer therapeutics have led to dramatic improvements in survival, now inclusive of nearly 20 million patients and rising. However, cardiovascular toxicities associated with specific cancer therapeutics adversely affect the outcomes of patients with cancer. Advances in cardiovascular imaging have solidified the critical role for robust methods for detecting, monitoring, and prognosticating cardiac risk among patients with cancer. However, decentralized evaluations have led to a lack of consensus on the optimal uses of imaging in contemporary cancer treatment (eg, immunotherapy, targeted, or biological therapy) settings. Similarly, available isolated preclinical and clinical studies have provided incomplete insights into the effectiveness of multiple modalities for cardiovascular imaging in cancer care. The aims of this scientific statement are to define the current state of evidence for cardiovascular imaging in the cancer treatment and survivorship settings and to propose novel methodological approaches to inform the optimal application of cardiovascular imaging in future clinical trials and registries. We also propose an evidence-based integrated approach to the use of cardiovascular imaging in routine clinical settings. This scientific statement summarizes and clarifies available evidence while providing guidance on the optimal uses of multimodality cardiovascular imaging in the era of emerging anticancer therapies.

Lung-to-heart ratio analysis using virtual planar images obtained from myocardial perfusion SPECT data: A phantom and clinical studies

BACKGROUNDS

The lung-to-heart ratio (L/H ratio) in myocardial perfusion scintigraphy (MPS) is a useful marker that complements the sensitivity of ischemia detection. However, it requires planar imaging acquired following a separate protocol in addition to single-photon emission computed tomography (SPECT). We developed a novel method for constructing virtual planar image (VPI) from SPECT data.

METHODS

Myocardial phantoms using Tl-201 were built with different amounts of radioactivity in the lungs. SPECT data and conventional planar images of these phantoms were collected with an Anger-type gamma camera. VPIs were constructed by adding all coronal images reconstructed from SPECT data. The clinical utility of VPIs obtained from 52 patients who underwent MPS with Tc-99m sestamibi was evaluated.

RESULTS

The radioactivity linearity of VPIs was satisfactory, with a correlation coefficient of r ≥ .99 between the measured amounts of radioactivity and image counts. The L/H ratios obtained from VPI analysis were strongly correlated with those of conventional planar images with a correlation coefficient of r ≥ .99 in the phantom study and r = .929 in clinical application.

CONCLUSION

The accuracy of VPI-based L/H ratio analysis was comparable to that of conventional planar image-based analysis. VPIs could be used as an alternative method of obtaining planar images in clinical settings.

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

BACKGROUND

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

METHODS

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

RESULTS

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

CONCLUSIONS

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

REGISTRATION

URL: https://www.

CLINICALTRIALS

gov; Unique identifier: NCT03427749.

Adjustment of acquisition arc in cardiac malposition during myocardial perfusion SPECT imaging: computer simulation based on deterministic modeling

OBJECTIVES

To simulate cardiac malpositions, leftward and rightward shift and dextrocardia, and also to compare distribution of activity of septal and lateral walls of left ventricle acquired in standard acquisition arc and after relevant adjustment.

METHODS

In this study, digital phantoms with cardiac malpositions are designed and procedure of acquisition of scan in standard arc (from right anterior oblique to left posterior oblique) and adjusted acquisition arc is simulated. The three situations of malposition including leftward and rightward shift and dextrocardia are considered. For all types, acquisition is conducted in standard and then adjusted arcs (from anterior to posterior and also from right to left for leftward and rightward shifts, respectively, and for dextrocardia, from left anterior oblique to right posterior oblique). All obtained projections are reconstructed using the algorithm of filtered back projection. During forward projection to obtain sinograms, radiation attenuation is also modeled by incorporation of a simplified transmission map to emission map. The resulting tomographic slices of the LV (septum, apex, and lateral wall) are presented visually and are compared by plotting intensity profiles of the walls. Finally, normalized error images are also computed. All the computations are performed in MATLAB software package.

RESULTS

In transverse slice, septum and lateral wall are attenuated progressively from apex, which is closer to the camera, to the base in similar fashion. In tomographic slices of standard acquisition arc, the septum shows remarkably higher activity compared to lateral wall. However, after adjustment, both seems equally intense and progressively being attenuated from apex to base, similar to that found in phantom with normally positioned heart. Likewise, for the phantom with rightward shift, when the scanning was done in standard arc, the septum is more intense than the lateral wall. And similarly, adjustment of the arc renders both walls equally intense. In dextrocardia, level of attenuation of basal parts of septum and lateral wall is higher in 360° arc compared to adjusted 180° arc.

CONCLUSION

Adjustment of acquisition arc exerts perceptible changes in distribution of activity over LV walls which are more compatible with normally positioned heart.

Machine learning-based diagnosis and risk classification of coronary artery disease using myocardial perfusion imaging SPECT: A radiomics study

This study aimed to investigate the diagnostic performance of machine learning-based radiomics analysis to diagnose coronary artery disease status and risk from rest/stress Myocardial Perfusion Imaging (MPI) single-photon emission computed tomography (SPECT). A total of 395 patients suspicious of coronary artery disease who underwent 2-day stress-rest protocol MPI SPECT were enrolled in this study. The left ventricle myocardium, excluding the cardiac cavity, was manually delineated on rest and stress images to define a volume of interest. Added to clinical features (age, sex, family history, diabetes status, smoking, and ejection fraction), a total of 118 radiomics features, were extracted from rest and stress MPI SPECT images to establish different feature sets, including Rest-, Stress-, Delta-, and Combined-radiomics (all together) feature sets. The data were randomly divided into 80% and 20% subsets for training and testing, respectively. The performance of classifiers built from combinations of three feature selections, and nine machine learning algorithms was evaluated for two different diagnostic tasks, including 1) normal/abnormal (no CAD vs. CAD) classification, and 2) low-risk/high-risk CAD classification. Different metrics, including the area under the ROC curve (AUC), accuracy (ACC), sensitivity (SEN), and specificity (SPE), were reported for models' evaluation. Overall, models built on the Stress feature set (compared to other feature sets), and models to diagnose the second task (compared to task 1 models) revealed better performance. The Stress-mRMR-KNN (feature set-feature selection-classifier) reached the highest performance for task 1 with AUC, ACC, SEN, and SPE equal to 0.61, 0.63, 0.64, and 0.6, respectively. The Stress-Boruta-GB model achieved the highest performance for task 2 with AUC, ACC, SEN, and SPE of 0.79, 0.76, 0.75, and 0.76, respectively. Diabetes status from the clinical feature family, and dependence count non-uniformity normalized, from the NGLDM family, which is representative of non-uniformity in the region of interest were the most frequently selected features from stress feature set for CAD risk classification. This study revealed promising results for CAD risk classification using machine learning models built on MPI SPECT radiomics. The proposed models are helpful to alleviate the labor-intensive MPI SPECT interpretation process regarding CAD status and can potentially expedite the diagnostic process.

Characterization of left ventricular diastolic parameters of gated-single-photon emission computed tomography myocardial perfusion imaging in patients with diabetes and normal myocardial perfusion and systolic function

BACKGROUND

Diabetic cardiomyopathy is defined as an independent entity with a specified pathological progression from diastolic dysfunction with preserved ejection fraction to overt heart failure. Myocardial perfusion imaging (MPI) with gated-single-photon emission computed tomography (G-SPECT) has been introduced as a feasible tool to evaluate left ventricular (LV) diastolic function. The aim of this study was to investigate the characteristics of diastolic parameters derived from G-SPECT MPI in diabetic patients compared to patients at very low risk of coronary artery disease (CAD) and with no other CAD risk factors.

METHODS

This cross-sectional study was performed on patients referred to the nuclear medicine department for G-SPECT MPI. Demographic and clinical data, as well as medical history, were extracted from a digital registry system including 4447 patients. Then, two matched groups of patients with only diabetes as cardiac risk factor ( n  = 126) and those without any identifiable CAD risk factors ( n  = 126) were selected. Diastolic parameters of MPI, including peak filling rate, time to peak filling rate, mean filling rate at the first third of diastole and second peak filling rate, were derived using quantitative software for eligible cases.

RESULTS

The mean age of the diabetic and nondiabetic groups was 57.1 ± 14.9 and 56.7 ± 10.6 years, respectively ( P  = 0.823). Comparison of quantitative SPECT MPI parameters between the two groups showed a statistically significant difference only in total perfusion deficit scores, whereas none of the functional parameters, including diastolic and dyssynchrony indices and the shape index, were significantly different. There were also no significant differences in diastolic function parameters between diabetes and nondiabetes patients in the age and gender subgroups.

CONCLUSION

Based on the G-SPECT MPI findings, there is a comparable prevalence of diastolic dysfunction in patients with only diabetes as a cardiovascular risk factor and low-risk patients with no cardiovascular risk factors in the setting of normal myocardial perfusion and systolic function.

Association of Right Ventricular Myocardial Blood Flow With Pulmonary Pressures and Outcome in Cardiac Amyloidosis

BACKGROUND

Cardiac amyloidosis (CA) is a restrictive and infiltrative cardiomyopathy, characterized by increased biventricular filling pressures and low output. Symptoms are predominantly of right heart origin. The role of right ventricular (RV) myocardial blood flow (MBF) in CA has not been studied.

OBJECTIVES

This study aimed to first associate RV MBF measured by using positron emission tomography (PET) with reference standards of RV pressures and then to explore its prognostic value in CA.

METHODS

Cardiac PET was performed at rest in 52 patients with CA and 9 healthy control subjects. MBF was quantified from the right and left ventricles by using 11C-acetate, 15O-water, or both (n = 25). RV pressure was measured invasively or by echocardiography. Associations between biventricular MBF toward symptoms, RV function, and outcome (death or acute heart failure) were studied in patients with CA.

RESULTS

MBF of the right ventricle (MBFRV) and the ratio of MBFRV and MBF of the left ventricle (MBFRV/LV) for the 2 tracers were significantly correlated (r > 0.92). MBFRV was directly correlated with RV systolic pressures with both tracers (P ≤ 0.005). MBFLV was inversely correlated with wall thickness (P < 0.0001). MBFRV/LV was significantly associated with N-terminal pro-B-type natriuretic peptide levels, NYHA functional class, RV pressures, and RV systolic function (all; P < 0.001). Twenty-six cardiac events (25 deaths) occurred during follow-up (median 44 months). MBFRV/LV higher than 56% was associated with a diagnosis of pulmonary hypertension (AUC: 0.96 [95% CI: 0.91-1.00]; P < 0.0001); and predicted outcome with HR: 9.0 (95% CI: 4.2-14.5), P < 0.0001).

CONCLUSIONS

Measurements of MBFRV using PET are feasible, as confirmed with 2 different tracers. Imbalance between RV and LV myocardial perfusion is associated with increased RV load and adverse events in cardiac amyloidosis.

Prognostic utility of 99mTc-MIBI single photon emission computerized tomography myocardial perfusion imaging in patients with ischemia and non-obstructive coronary artery disease

Objective

The aim of our study was to evaluate the prognostic value of gated SPECT MPI in non-obstructed coronary arteries (INOCA) patients, sought to stratify patients more accurately and thus derive more reliable prognostic information.

Materials and methods

In total, 167 patients with INOCA were enrolled. The patients were divided into two groups according to their SSS. Patients were followed-up regularly in terms of major adverse cardiovascular event (MACE), including cardiac death, nonfatal myocardial infarction, stroke, re-hospitalization with angina pectoris, and recurrent angina pectoris. Kaplan-Meier curves and Cox's proportional hazards models were used to analyze survival and identify predictive factors.

Results

Adverse cardiac events occurred in 33 cases (19.8%). The rate of MACE was higher in the summed stress score (SSS) ≥4 group than in the SSS 0-3 group (30.1% vs. 9.5%, respectively, P = 0.001) and MACE-free survival was lower (annual MACE-free rates of 87.5% vs. 96.2%, respectively, P = 0.003). Event-free survival was consistently higher in patients with normal arteries than in those with non-obstructive coronary artery disease (annual MACE-free rates of 96.1% and 88.4%, P = 0.035). When the SSS and the CAG results were combined, patients with normal coronary arteries (SSS 0-3) had the best prognosis and those with non-obstructive coronary artery stenosis (SSS ≥ 4) had the worst. However, the early prognosis of patients with non-obstructive coronary artery disease and SSS of 0-3 was comparable to that of patients with normal coronary arteries and SSS ≥ 4 (annual MACE-free rates of 100%, 94.6%, 93.1%, and 78.2%, respectively). Multivariate Cox's regression indicated that the SSS [hazard ratio (HR) = 1.126, 95% confidence interval (CI) 1.042-1.217, P = 0.003] and non-obstructive coronary artery disease (HR = 2.559, 95% CI 1.249-5.246, P = 0.01) were predictors of adverse cardiac events.

Conclusion

SPECT MPI data were prognostic for INOCA patients, thus identifying groups at high risk. The long-term predictive efficacy of such data exceeded that of CAG data. A combination of the two measures more accurately stratified INOCA patients in terms of risk.

Myocardial blood flow evaluation with dynamic cadmium-zinc-telluride single-photon emission computed tomography: Bright and dark sides

Myocardial blood flow (MBF) and myocardial perfusion reserve (MPR) assessment with non-invasive techniques represent an important tool to evaluate both coronary artery disease severity and extent. Currently, cardiac positron emission tomography-computed tomography (PET-CT) is the "gold standard" for the assessment of coronary function and provides accurate estimations of baseline and hyperemic MBF and MFR. Nevertheless, due to the high cost and complexity, PET-CT is not widely used in clinical practice. The introduction of cardiac-dedicated cadmium-zinc-telluride (CZT) cameras has renewed researchers' interest on MBF quantitation by single-photon emission computed tomography (SPECT). Indeed, many studies evaluated MPR and MBF measurements by dynamic CZT-SPECT in different cohorts of patients with suspected or overt coronary artery disease. As well, many others have compared the values obtained by CZT-SPECT to the ones by PET-CT, showing good correlations in detecting significant stenosis, although with different and non-standardized cut-off values. Nevertheless, the lack of standardized protocol for acquisition, reconstruction and elaboration makes more difficult to compare different studies and to further assess the real advantages of MBF quantitation by dynamic CZT-SPECT in clinical routine. Many are the issues involved in the bright and dark sides of dynamic CZT-SPECT. They include different type of CZT cameras, different execution protocols, different tracers with different myocardial extraction fraction and distribution, different software packages with different tools and algorithms, often requiring manual post-processing elaboration. This review article provides a clear summary of the state of the art on MBF and MPR evaluation by dynamic CZT-SPECT and outlines the major issues to solve to optimize this technique.

Association between CZT‑SPECT myocardial blood flow and coronary stenosis: A cross‑sectional study

The association between the quantitative and semi-quantitative parameters of myocardial blood flow obtained using cadmium-zinc-telluride single photon emission computed tomography (CZT-SPECT) and coronary stenosis remains unclear. Therefore, the objective of the present study was to evaluate the diagnostic value of two parameters obtained using CZT-SPECT in patients with suspected or known coronary artery disease. A total of 24 consecutive patients who underwent CZT-SPECT and coronary angiography within 3 months of each other were included in the study. To evaluate the predictive ability of the regional difference score (DS), coronary flow reserve (CFR), and the combination thereof for positive coronary stenosis at the vascular level, receiver operating characteristic (ROC) curves were plotted and the area under the curves (AUCs) were calculated. Comparisons of the reclassification ability for coronary stenosis between different parameters were assessed by calculating the net reclassification index (NRI) and the integrated discrimination improvement (IDI). The 24 participants (median age: 65 years; range: 46-79 years; 79.2% male) included in this study had a total of 72 major coronary arteries. When stenosis ≥50% was defined as the criteria for positive coronary stenosis, the AUCs and the 95% confidence interval (CI) for regional DS, CFR, and the combination of the two indices were 0.653 (CI, 0.541-0.766), 0.731 (CI, 0.610-0.852) and 0.757 (CI, 0.645-0.869), respectively. Compared with single DS, the combination of DS and CFR increased the predictive ability for positive stenosis, with an NRI of 0.197-1.060 (P<0.01) and an IDI of 0.0150-0.1391 (P<0.05). When stenosis ≥75% was considered as the criteria, the AUCs were 0.760 (CI, 0.614-0.906), 0.703 (CI, 0.550-0.855), and 0.811 (CI, 0.676-0.947), respectively. Compared with DS, CFR had an IDI of -0.3392 to -02860 (P<0.05) and the combination of DS and CFR also enhanced the predictive ability, with an NRI of 0.0313-1.0758 (P<0.01). In conclusion, both regional DS and CFR had diagnostic values for coronary stenosis, but the diagnostic abilities differed in distinguishing between different degrees of stenosis, and the efficiency was improved with a combination of DS and CFR.

SPECT at the speed of PET: a feasibility study of CZT-based whole-body SPECT/CT in the post 177Lu-DOTATATE and 177Lu-PSMA617 setting

PURPOSE

To evaluate the feasibility of using the StarGuide (General Electric Healthcare, Haifa, Israel), a new generation multi-detector cadmium-zinc-telluride (CZT)-based SPECT/CT, for whole-body imaging in the setting of post-therapy imaging of 177Lu-labeled radiopharmaceuticals.

METHODS

Thirty-one patients (34-89 years old; mean ± SD, 65.5 ± 12.1) who were treated with either 177Lu-DOTATATE (n=17) or 177Lu-PSMA617 (n=14) as part of standard of care were scanned post-therapy with the StarGuide; some were also scanned with the standard GE Discovery 670 Pro SPECT/CT. All patients had either 64Cu-DOTATATE or 18F-DCFPyL PET/CT prior to first cycle of therapy for eligibility check. The detection/targeting rate (lesion uptake greater than blood pool uptake) of large lesions meeting RECIST 1.1 size criteria on post-therapy StarGuide SPECT/CT was evaluated and compared to the standard design GE Discovery 670 Pro SPECT/CT (when available) and pre-therapy PET by two nuclear medicine physicians with consensus read.

RESULTS

This retrospective analysis identified a total of 50 post-therapy scans performed with the new imaging protocol from November 2021 to August 2022. The StarGuide system acquired vertex to mid-thighs post-therapy SPECT/CT scans with 4 bed positions, 3 min/bed and a total scan time of 12 min. In comparison, the standard GE Discovery 670 Pro SPECT/CT system typically acquires images in 2 bed positions covering the chest, abdomen, and pelvis with a total scan time of 32 min. The pre-therapy 64Cu-DOTATATE PET takes 20 min with 4 bed positions on GE Discovery MI PET/CT, and 18F-DCFPyL PET takes 8-10 min with 4-5 bed positions on GE Discovery MI PET/CT. This preliminary evaluation showed that the post-therapy scans acquired with faster scanning time using StarGuide system had comparable detection/targeting rate compared to the Discovery 670 Pro SPECT/CT system and detected large lesions defined by RECIST criteria on the pre-therapy PET scans.

CONCLUSION

Fast acquisition of whole-body post-therapy SPECT/CT is feasible with the new StarGuide system. Short scanning time improves the patients' clinical experience and compliance which may lead to increased adoption of post-therapy SPECT. This opens the possibility to offer imaged-based treatment response assessment and personalized dosimetry to patients referred for targeted radionuclide therapies.

High-sensitivity cardiac SPECT system design with collimator-less interspaced mosaic-patterned scintillators

Purpose

Single-photon emission computed tomography (SPECT) is an important tool for myocardial perfusion imaging (MPI). Mechanical collimators cause the resolution-sensitivity trade-off in the existing cardiac SPECT systems, which hinders fast cardiac scan capability. In this work, we propose a novel collimator-less cardiac SPECT system with interspaced mosaic-patterned scintillators, aiming to significantly improve sensitivity and reduce scan time without trading-off image resolution.

Methods

We propose to assemble a collimator-less cardiac SPECT with 7 mosaic-patterned detector modules forming a half-ring geometry. The detector module consists of 10 blocks, each of which is assembled with 768 sparsely distributed scintillators with a size of 1.68 mm × 1.68 mm × 20 mm, forming a mosaic pattern in the trans-axial direction. Each scintillator bar contains 5 GAGG(Ce) scintillators and 5 optical-guide elements, forming a mosaic pattern in the axial direction. In the Monte Carlo simulations, the in-plane resolution and axial resolution are evaluated using a hot-rod phantom and 5 disk phantoms, respectively. We simulate a cardiac phantom that is placed in a water-filled cylinder and evaluate the image performance with different data acquisition time. We perform image reconstruction with the expectation-maximization algorithm using system matrices derived from the simulation of a uniform cylindrical source filling the field-of-view (FOV). Besides, a 2-D prototype system is designed to demonstrate the feasibility of the collimator-less imaging concept.

Results

In the simulation system, the sensitivity is 16.31% ± 8.85% in a 180 mm (Φ) × 100  mm (L) FOV. The 6-mm rods in the hot rod phantom and the 5-mm disks in the disk phantom are clearly separable. Satisfactory MPI image quality is achieved in the cardiac phantom study with an acquisition time of 30 s. In prototype experiments, the point sources with an 8 mm center-to-center distance are clearly separable at different positions across the FOV.

Conclusion

The study reveals a promising approach to high-sensitivity SPECT imaging without a heavy-metal collimator. In cardiac imaging, this approach opens the way to a very fast cardiac scan with good resolution. Further works are ongoing to build a practical 3-D imaging system based on the existing design.

Value of PET ECG gating in a cross-validation study of cardiac function assessment by PET/MR imaging

BACKGROUND

This work investigated the impact of different cardiac gating methods on the assessment of cardiac function by FDG-PET in a cross-validation PET/MR study.

METHODS AND RESULTS

MR- and PET-based left ventricular end-diastolic, end-systolic volumes, and ejection fraction (EDV, ESV, and EF) were delineated in 30 patients with a PET/MR examination. Cardiac PET imaging was performed using three ECG gating methods: fixed number of gates per beat (STD), STD with a beat acceptance window (STD-BR), and fixed gate duration (FW). High MR-PET correlations were found in all the values. ESVs correlated better than EDVs and EFs: Pearson's r coefficient [0.92, 0.92, 0.92] in ESV vs [0.75, 0.81, 0.80] in EDV and [0.79, 0.91, 0.87] in EF, for each method [STD, STD-BR, FW]. Biases with respect to MRI for all the evaluated PET methods were less than 13% in EDV, 5% in ESV, and 14% in EF, but with wide limits of agreements, in the range (59-68)% in EDV, (65-70)% in ESV, and (49-71)% in EF. STD showed the strongest disagreement, while there were no marked differences between STD-BR and FW.

CONCLUSION

Based on these findings, PET- and MR-based cardiac function parameters were highly correlated but in substantial disagreement with variabilities introduced by the selected PET ECG gating method. The most significant differences were associated with the ECG gating method susceptible to highly irregular beats, while similar performance was observed in the methods using uniform adjustment of gates width per beat with the beat acceptance window, and fixed gate width along all the beats. Thus, strict quality controls of R peak detection are needed to minimize its impact on the function assessment.