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

BACKGROUND

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

METHODS

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

CONCLUSIONS

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

How to achieve patient-centered testing: role of the protocol nurse

INTRODUCTION

Patient-centered cardiac testing is predicated on choosing the right test for the right patient. We studied the effects of changing from script-driven scheduling to nurse-driven protocoling of stress tests.

METHODS AND RESULTS

A protocol nurse reviewed records before scheduling and communicated with patients and ordering providers if needed. We found that instituting nurse protocolling of all non-imaging (ETT) and nuclear (MPI) stress tests (N = 3071) resulted in protocol changes in 37% of our patients, and reduced the proportion of tests that could not be performed as scheduled by 56% and cancelations by 71% (P < 0.001 for each). These changes were sustained over two successive 6-month periods following a baseline observation period of 6 months. For MPI, the most frequent nurse interventions were re-protocoling as stress-first MPI (12% of tests), changing test location for clinical reasons (13%), changing stress modality (7%), and care coordination (5%).

CONCLUSIONS

Changing from script-driven scheduling to protocol nursing contributed measurably to patient-centered testing.

Minimal rest activity for SPECT myocardial perfusion imaging in a one-day stress-first protocol

PURPOSE

Guidelines propose different rest-stress activity ratios (RSAR) for one-day stress-first SPECT myocardial perfusion imaging (MPI), but evidence is limited. Our aim was to determine and validate the minimal RSAR resulting in the same diagnostic outcome in one-day stress-first SPECT MPI.

METHODS

Forty-seven patients referred for rest after stress CZT-SPECT/CT MPI were prospectively included. Rest acquisitions were performed 3 h after stress. In addition to the stress and rest acquisitions, the first 22 patients underwent an additional acquisition prior to the rest injection to determine the remaining stress activity. Next, we simulated six RSARs varying from 1.0 to 3.5 in both patients and a phantom and compared the images to those using the reference RSAR of 4.0. Differences in summed difference score (SDS) >2 or ischemic defect interpretation were considered to significantly influence diagnostic outcome. After deriving the minimal RSAR, it was validated in 25 additional patients by comparing it to a RSAR of 4.0.

RESULTS

After 3 h only 26% of the stress activity was still present in the myocardium. SDS differences >2 were found in one (4%) patient using RSAR of 3.5, 2.5 and 2.0, in three (12%) using 1.5 and in five (20%) using SRAR of 1.0. These results were consistent with the phantom study showing SDS differences >2 for RSARs ≤1.5 and with the visual interpretation which showed an increased number of deviating scans for RSAR 1.0. Validating the RSAR of 2.0 resulted in a different SDS in one patient (SDS of 30 versus 11). Moreover, two scans were interpreted as ischemic instead of normal when using RSAR 2.0 and in two other scans the opposite was the case.

CONCLUSIONS

A RSAR of 2.0 in one-day stress-first MPI SPECT seems sufficient to obtain accurate diagnostic outcomes and is therefore recommended to reduce radiation exposure.

Detrimental effects of nitroglycerin use during regadenoson vasodilator stress testing: A cautionary tale

Vasodilator agents such as adenosine and regadenoson are commonly used pharmacologic stressors to assess for ischemia in patients undergoing myocardial perfusion studies. The recommended reversal agent for this mode of stress is aminophylline, although nitroglycerin is commonly administered as an attempt to reverse the symptoms or electrocardiographic (EKG) changes during the stress test. We demonstrate through two cases that incorrect administration of nitroglycerin can induce hypotension and worsen coronary steal, whereas appropriate administration of aminophylline can reverse the effects of pharmacologic vasodilators. While nitroglycerin is often used in patients with organic angina, it has the potential to worsen ischemia in the setting of pharmacologic vasodilator administration. These cases underscore the importance of administering the correct reversal agent for pharmacologic stress tests.

Prognosis of stress-only SPECT myocardial perfusion imaging with prone imaging

BACKGROUND

Stress-only single-photon emission computed tomography myocardial perfusion imaging (SO SPECT MPI) is associated with similarly benign prognosis as stress-rest SPECT MPI. However, previous studies have used attenuation correction rather than prone imaging to increase the rate of SO studies.

OBJECTIVES

To assess the prognosis of SO SPECT MPI performed with prone imaging.

METHODS

We performed a retrospective cohort analysis of all patients who underwent a Tc-99m gated SPECT MPI over a 58-month period.

RESULTS

Two thousand four hundred and sixty five patients were followed up. Of them, 1114 (45.2%) patients had a SO supine test, 388 (15.7%) underwent a SO supine and prone test, and the remaining 963 (39.1%) patients underwent a full stress-rest SPECT MPI. There was a similar annual mortality rate between the SO supine/prone group (1.3%), the SO supine (1.5%), and the stress-rest (1.5%) group (P = 0.47). Patients in the stress-rest group were significantly more likely to suffer from myocardial infarction (MI) as compared to the other two groups with an annual rate of 0.7% as compared to 0.4% (P = 0.049).

CONCLUSIONS

Normal supine-prone SO SPECT MPI is associated with a similarly benign prognosis as stress-rest SPECT MPI. The adjunction of prone imaging to the stress supine significantly increases the rate of SO SPECT MPI.

The radiation dose to overweighted patients undergoing myocardial perfusion SPECT can be significantly reduced: validation of a linear weight-adjusted activity administration protocol

BACKGROUND

Large body size can cause a higher proportion of emitted photons being attenuated within the patient. Therefore, clinical myocardial perfusion SPECT (MPS) protocols often include unproportionally higher radioisotope activity to obese patients. The aim was to evaluate if a linear weight-adjusted low-dose protocol can be applied to obese patients and thereby decrease radiation exposure.

METHODS AND RESULT

Two hundred patients (>110 kg, BMI 18-41, [n = 69], ≤ 110 kg, BMI 31-58, [n = 131]) underwent 99mTc-tetrofosmin stress examination on a Cadmium Zinc Telluride or a conventional gamma camera using new generations of reconstruction algorithm (Resolution Recovery). Patients <110 kg were administered 2.5 MBq/kg, patients between 110 and 120 kg received 430 MBq and patients >120 kg received 570 MBq according to clinical routine. Patients >110 kg had 130% total number of counts in the images compared to patients <110 kg. Recalculating the counts to correspond to an administered activity of 2.5 MBq/kg resulted in similar number of counts across the groups. Image analyses in a subgroup with images corresponding to high activity and 2.5 MBq/kg showed no difference in image quality or ischemia quantification.

CONCLUSION

Linear low-dose weight-adjusted protocol of 2.5 MBq/kg in MPS can be applied over a large weight span without loss of counts or image quality, resulting in a significant reduction in radiation exposure to obese patients.

Multimodality molecular imaging in cardiac regenerative therapy

Stem cell therapy holds great promise for the repair and regeneration of damaged myocardium. Disappointing results from recent large-scale randomized trials using adult stem cells, however, have led some to question the efficacy of this new therapeutic. Because most clinical stem cell trials have not incorporated molecular imaging to track cell fate, it may be premature to abandon this approach. Herein, we will review how multimodality imaging can be incorporated into cardiac regenerative therapy to facilitate the translation of stem cell therapy.

Downstream resource utilization following SPECT: Impact of age and gender

BACKGROUND

Previous studies have identified a downstream referral age and gender bias for invasive coronary anatomy evaluation after single-photon emission computed tomography myocardial perfusion imaging (SPECT MPI). The present study evaluates if such bias still persists despite advancements in SPECT MPI and angiography. We hypothesized that women and patients ≥80 years old are less likely to undergo invasive coronary angiography after adjusting for clinical and scan variables.

METHODS

Patients (n = 3824) who referred to a nuclear cardiology laboratory at a tertiary medical center were retrospectively identified. Regression analysis tested age (<55; 55-69; 70-79; ≥80 years) and gender as predictors of diagnostic angiogram at 90 days post-SPECT after adjustment for known CAD, CAD risk equivalent, SSS, SDS, and LVEF.

RESULTS

Younger patients were more likely to undergo an angiogram as compared to octogenarians (77% more likely if <55 years old, 69% if 55-69 years old, and 52% if 70-79 years old). No effect was found for gender.

CONCLUSIONS

Older patients were less likely to be referred for angiogram as compared to their younger counterparts. Further study is needed to determine which factors guide this decision-making process in older adults and the influence of these factors on the referral bias.

A quick glance at selected topics in this issue

A quick glance at selected topics in this issue" aims to highlight selected articles and provide a quick review to the readers.

Cardiovascular PET/MR: We need evidence, not hype

Recent introduction of hybrid positron emission tomography/magnetic resonance (PET/MR) scanners has created excitement regarding potential applications in cardiovascular medicine. This has led to a number of optimistic assessments of its potential value in the nuclear cardiology literature, although most published data are still at the feasibility or pre-clinical level. Such excitement is understandable and provides "fuel" for generation of the necessary clinical validation studies, which will be required. Given the current scrutiny from payers and government agencies to reduce the costs of cardiac imaging, the responsibility for showing additive benefit lies on the shoulders of those advocating for new, more expensive technologies. In the case of PET/MR, this will be a major challenge, given the high costs of the hybrid procedure and the need for potentially harmful ionizing radiation compared to a cardiac magnetic resonance (CMR)-only approach. The aim of this editorial is to provide a critical appraisal of the current evidence base for clinical use of PET/MR in cardiology.

A quick glance at selected topics in this issue

"A quick glance at selected topics in this issue" aims to highlight contents of the journal and provide a quick review to the readers.

Molecular imaging of atherosclerosis with integrated PET imaging

Atherosclerotic diseases account for nearly half of all deaths and are leading causes of adult disability. Our understanding of how atherosclerosis leads to cardiovascular disease events has evolved: from a concept of progressive luminal narrowing, to that of sudden rupture and thrombosis of biologically active atheroma. In concert with this conceptual shift, contemporary imaging techniques now allow imaging of biological processes that associate with plaque instability: active calcification and plaque inflammation. This review focuses on opportunities provided by positron emission tomography/computed tomography, to identify these high-risk biological features of atherosclerosis.

Evaluation of general-purpose collimators against high-resolution collimators with resolution recovery with a view to reducing radiation dose in myocardial perfusion SPECT: A preliminary phantom study

BACKGROUND

There is a growing focus on reducing radiation dose to patients undergoing myocardial perfusion imaging. This preliminary phantom study aims to evaluate the use of general-purpose collimators with resolution recovery (RR) to allow a reduction in patient radiation dose.

METHODS

Images of a cardiac torso phantom with inferior and anterior wall defects were acquired on a GE Infinia and Siemens Symbia T6 using both high-resolution and general-purpose collimators. Imaging time, a surrogate for administered activity, was reduced between 35% and 40% with general-purpose collimators to match the counts acquired with high-resolution collimators. Images were reconstructed with RR with and without attenuation correction. Two pixel sizes were also investigated. Defect contrast was measured.

RESULTS

Defect contrast on general-purpose images was superior or comparable to the high-resolution collimators on both systems despite the reduced imaging time. Infinia general-purpose images required a smaller pixel size to be used to maintain defect contrast, while Symbia T6 general-purpose images did not require a change in pixel size to that used for standard myocardial perfusion SPECT.

CONCLUSION

This study suggests that general-purpose collimators with RR offer a potential for substantial dose reductions while providing similar or better image quality to images acquired using high-resolution collimators.

Visual identification of coronary calcifications on attenuation correction CT improves diagnostic accuracy of SPECT/CT myocardial perfusion imaging

BACKGROUND

Coronary artery calcium (CAC) is a powerful CAD risk marker when assessed by dedicated calcium scoring CT scan. We assessed diagnostic implications of CAC visible on attenuation correction CT scans (CTAC) from SPECT/CT myocardial perfusion imaging (MPI).

METHODS

Visual presence or absence of CAC was assessed on CTAC in 1047 consecutive patients undergoing SPECT/CT MPI. Accuracy of MPI was assessed in patients undergoing invasive coronary angiography (ICA) within 1 year (n = 109). Outcomes were identified by retrospective chart review.

RESULTS

Prevalence of true positive SPECT/CT MPI studies was greater among patients with CAC on CTAC (70% vs 16%; p < .001); prevalence of false positive studies was greater among those without (68% vs 15%; p < .001). PPV of MPI was 0.82 in patients with CAC, but only 0.19 in those without. Within median follow-up of 27.7 months, patients with CAC had higher all-cause mortality (6% vs 0.4%; p < .001), more late revascularizations (8% vs 0.4%; p < .001), and more MI (5% vs 0.2%; p < .001). Hazard ratio for all-cause mortality, MI, or late revascularization was 22.7 (p < .001) for patients with CAC vs those without.

CONCLUSIONS

Visual assessment of CAC on CTAC should be performed during SPECT/CT MPI because it affects diagnostic certainty and may improve risk stratification.

Incidental detection of bronchial carcinoid on Tc-99m sestamibi SPECT/CT myocardial perfusion scintigraphy

Technetium-99m sestamibi MPS is a commonly employed imaging study for myocardial perfusion; however, incidental extracardiac sestamibi uptake requires further evaluation, and the tracer uptake in the thorax/mediastinum may be pathological. The authors present a case of significant extra-cardiac uptake seen on stress MPS images helping in the incidental detection of bronchial carcinoid.

"Same-Patient Processing" for multiple cardiac SPECT studies. 1. Improving LV segmentation accuracy

OBJECTIVES

This paper describes a novel approach (same-patient processing, or SPP) aimed at improving left ventricular segmentation accuracy in patients with multiple SPECT studies, and evaluates its performance compared to conventional processing in a large population of 962 patients undergoing rest and stress electrocardiography-gated SPECT MPI, for a total of 5,772 image datasets (6 per patient).

METHODS

Each dataset was independently processed using a standard algorithm, and a shape quality control score (SQC) was produced for every segmentation. Datasets with a SQC score higher than a specific threshold, suggesting algorithmic failure, were automatically reprocessed with the SPP-modified algorithm, which incorporates knowledge of the segmentation mask location in the other datasets belonging to the same patient. Experienced operators blinded as to whether datasets had been processed based on the standard or SPP approach assessed segmentation success/failure for each dataset.

RESULTS

The SPP approach reduced segmentation failures from 219/5772 (3.8%) to 42/5772 (0.7%) overall, with particular improvements in attenuation corrected (AC) datasets with high extra-cardiac activity (from 100/962 (10.4%) to 12/962 (1.4%) for rest AC, and from 41/962 (4.3%) to 9/962 (0.9%) for stress AC). The number of patients who had at least one of their 6 datasets affected by segmentation failure decreased from 141/962 (14.7%) to 14/962 (1.7%) using the SPP approach.

CONCLUSION

Whenever multiple image datasets for the same patient exist and need to be processed, it is possible to deal with the images as a group rather than individually. The same-patient processing approach can be implemented automatically, and may substantially reduce the need for manual reprocessing due to cardiac segmentation failure.

Budget impact of applying appropriateness criteria for myocardial perfusion scintigraphy: The perspective of a developing country

Myocardial perfusion imaging is widely used for the risk stratification of coronary artery disease. In view of its cost, besides radiation issues, judicious evaluation of the appropriateness of its indications is essential to prevent an unnecessary economic burden on the health system. We evaluated, at a tertiary-care, public Brazilian hospital, the appropriateness of myocardial perfusion scintigraphy indications, and estimated the budget impact of applying appropriateness criteria. An observational, cross-sectional study of 190 patients with suspected or known coronary artery disease referred for myocardial perfusion imaging was conducted. The appropriateness of myocardial perfusion imaging indications was evaluated with the Appropriate Use Criteria for Cardiac Radionuclide Imaging published in 2009. Budget impact analysis was performed with a deterministic model. The prevalence of appropriate requests was 78%; of inappropriate indications, 12%; and of uncertain indications, 10%. Budget impact analysis showed that the use of appropriateness criteria, applied to the population referred to myocardial perfusion scintigraphy within 1 year, could generate savings of $ 64,252.04 dollars. The 12% inappropriate requests for myocardial perfusion scintigraphy at a tertiary-care hospital suggest that a reappraisal of MPI indications is needed. Budget impact analysis estimated resource savings of 18.6% with the establishment of appropriateness criteria for MPI.

Differential risk reclassification improvement by exercise testing and myocardial perfusion imaging in patients with suspected and known coronary artery disease

OBJECTIVE

The objective of this study is to compare the incremental prognostic and net risk reclassification value of exercise testing alone vs exercise myocardial perfusion imaging (MPI) for estimating the risk of death in patients with suspected and known coronary artery disease (CAD).

METHODS

6702 patients with suspected CAD and 2008 with known CAD had treadmill exercise MPI and were followed for 2.5 ± 0.9 years for the occurrence of all-cause death. The estimation of risk of death and net reclassification improvement (NRI) were examined in three models. Model 1: clinical variables; Model 2: model 1+Duke Treadmill Score; and Model 3: model 2+ MPI variables. Risk estimates were categorized as <1%, 1-3%, and >3% risk of death per year.

RESULTS

In patients with suspected CAD, the global Chi-square for predicting risk of death increased significantly for Model 2 compared to Model 1 (74.78 vs 63.86 to (P = .001). However, adding MPI variables in Model 3 did not further improve predictive value (Chi-square 79.38, P = .10). In patients with suspected CAD risk, reclassification improved significantly in Model 2 over Model 1 (NRI = 0.12, 95% CI 0.02 to 0.22, P = .019), but not in Model 3 (NRI = 0.0009, 95% CI -0.072 to 0.070; P = .98). In contrast, in patients with known CAD Model 2 did not yield significant improvements for predicting risk and risk reclassification compared to Model 1. However, global Chi-square of Model 3 was significantly higher than that of Model 2 (30.03 vs 6.56, P < .0001) with associated significant reclassification improvement (NRI = 0.26 95% CI 0.067 to 0.46. P = .0084).

CONCLUSION

Risk reclassification by diagnostic testing is importantly influenced by baseline characteristics of patient cohorts. In patients with suspected CAD, NRI is predominately achieved by exercise variables, whereas in patients with known CAD, greatest NRI is obtained by MPI variables.

Long-term prognostic value of stress myocardial perfusion imaging and coronary computed tomography angiography: A meta-analysis

BACKGROUND

We conducted a meta-analysis to compare the long-term prognostic value of stress single-photon emission computed tomography myocardial perfusion imaging (MPI) and coronary computed tomography angiography (CCTA) for adverse cardiovascular events in subjects with suspected or known coronary artery disease.

METHODS AND RESULTS

We searched PubMed, Cochrane, Web of Science, and Scopus database between January 2000 and December 2014 for stress MPI and CCTA studies that followed up ≥ 100 subjects for ≥ 2.5 years and provided the unadjusted and/or adjusted hazard ratio (HR) at Cox regression analysis. Summary risk estimates for abnormal perfusion at MPI or ≥ 50% coronary stenosis at CCTA were derived in random effect regression analysis, and causes of heterogeneity were determined in meta-regression analysis. We identified 21 eligible articles (10 MPI and 11 CCTA) including 25,258 participants (13,484 in MPI and 11,774 in CCTA studies) with suspected or known coronary artery disease. Among the included publications, 8 MPI and 8 CCTA studies reported the HR for the occurrence of hard events (death and nonfatal myocardial infarction). The pooled HR was comparable for MPI and CCTA studies. The HR for the occurrence of a combined endpoint including revascularization as event was reported in 4 MPI and 6 CCTA studies. The pooled HR was higher for CCTA compared to MPI (P < .05) also when only MPI and CCTA studies with limited representation of prior CAD were considered.

CONCLUSIONS

The long-term prognostic value of MPI and CCTA for the occurrence of hard events is similar. However, the association between event-free survival and CCTA is higher than MPI when coronary revascularization is included in the endpoint.

Clinical applications of radionuclide imaging in the evaluation and management of patients with congenital heart disease

Non-invasive testing of children with congenital heart disease (CHD) began in the 1950s with the introduction of radionuclide studies to assess shunt fractions, pulmonary blood flow, and ventricular contractile function. Echocardiography and cardiac magnetic resonance imaging have since replaced radionuclide imaging in many of these roles. Concurrently, percutaneous and surgical repairs of complex CHD evolved, creating new roles for radionuclide imaging. In this paper on applications of radionuclide imaging in CHD, we review the multiple mechanisms for myocardial ischemia in CHD. We critically compare optimal radionuclide imaging techniques to other imaging modalities for assessing ischemia in CHD. We present the current role of nuclear imaging for assessing viability and pulmonary blood flow. We highlight the value added by advances in dedicated cardiac SPECT scanners, novel reconstruction software, and cardiac PET in performing low-dose radionuclide imaging in CHD. Finally, we discuss the emerging clinical indications for radionuclide imaging in CHD including coronary flow reserve assessment and evaluation of cardiovascular prosthesis and device infections.