Stress-first Imaging Research Articles

Impact of Gd-153 scanning line source attenuation correction on downstream invasive testing

BackgroundAttenuation correction (AC) using hardware and software solutions has been shown to increase the specificity of SPECT MPI by decreasing false positive results and improving prognostic ability. Theoretically this should reduce downstream testing and unnecessary costs. We sought to assess the consequences of the use of Gd-153 scanning line source attenuation correction during SPECT myocardial perfusion imaging (MPI) on downstream invasive testing. MethodsAll patients who underwent a clinically indicated Tc-99m stress SPECT MPI study from 2013 to 2015 at five hospitals (2 with AC and 3 without) were retrospectively reviewed. Patient demographics, results of testing, subsequent coronary angiography within 3 months, and revascularization were recorded. The results of the MPI studies, downstream angiogram utilization, and results of angiography were compared and a propensity matched subgroup analysis was performed. ResultsA total of 9968 patients underwent SPECT MPI during the study time period (6106 performed with AC and 3862 without). Out of 3928 patients included in the propensity matched cohort, there was no difference in the proportion of abnormal MPI results between the two groups (31.5% vs 30.4%, P = 0.47), however, more patients underwent coronary angiography within 90 days in the AC group (10.6% vs 8.7%, P = 0.05). There was no significant difference in the proportion of patients with angiographically significant obstructive disease (53.4% vs 56.1%, P = 0.19), however, fewer patients in the AC group with obstructive coronary disease were revascularized (36.1% vs 46.8%, P = 0.04). The findings remained consistent after sub-group analysis in patients without known coronary disease. ConclusionThe use of scanning line source AC did not meaningfully influence the rate of abnormal MPI results or downstream invasive testing in this cohort. The clinical utility of scanning line source AC may be limited to facilitating stress-first imaging protocols.

Stress only myocardial perfusion imaging - comparison of hospitalized and outpatient patients

Abstract Funding Acknowledgements Type of funding sources: None. Background In selected patients, stress-only myocardial perfusion imaging (MPI) has been proposed as an alternative to rest-stress MPI to reduce radiation exposure and enhance laboratory efficiency. The use of attenuation correction improves the diagnostic accuracy of stress-only imaging. However, criteria for selecting appropriate patients for stress-first imaging protocol are not uniform. There is limited data about stress-only MPI in hospitalized patients. The purpose of this study was to compare the proportion of suitable hospitalized and outpatient patients with normal MPI on a routine two-day protocol for stress-only MPI. Methods In a retrospective longitudinal cohort study, stress scintigrams (with and without attenuation correction) of consecutive hospitalized and outpatient patients who underwent MPI at our department by a routine two-day protocol and had a normal MPI were visually and semi-quantitatively re-examined. Patients with summed stress score 0 or 1 were considered as candidates for stress-only MPI. We also obtained data on the patients" clinical characteristics and their treatment. Results We studied 178 patients (mean age 68.8 ± 13.4 years, 89 hospitalized, 89 outpatient patients, 55.6 % female). Hospitalized patients were significantly older than outpatient participants (72.4 ± 13.0 vs. 65 ± 12.9 years, p < 0.001) with no significant differences in risk factors and clinical characteristics. Proportion of inpatients and outpatients suitable for stress-only MPI with and without attenuation correction is shown on Figure 1. There was no significant difference in stress-only MPI with and without attenuation correction between hospitalized and outpatient patients (Figure 1). 9.1% of patients in whom stress only MPI was possible had known coronary artery disease, whereas it was present in 25.0% of patients in whom stress-only MPI was not possible (p = 0.004). By using attenuation correction stress-only MPI could be performed in 54% of patients without known coronary artery disease. There was no difference between hospitalized patients and outpatients (52% vs. 56%, p = 0.700). Absence of coronary artery disease turned out as the only independent prognostic factor for application of stress-only MPI (odds ratio 3.433, 95% confidence interval 1.44-8.17, p = 0.003). There was no influence of hospitalization on the application of stress-only MPI. Conclusions When we choose the right patients (especially those without a known coronary artery disease) and use modern cameras that enable attenuation correction, we can perform stress-only MPI in 50% of patients with a normal MPI result. The same approach can be used for outpatients and inpatients.

Worldwide Diagnostic Reference Levels for Single-Photon Emission Computed Tomography Myocardial Perfusion Imaging: Findings From INCAPS

ObjectivesThis study sought to establish worldwide and regional diagnostic reference levels (DRLs) and achievable administered activities (AAAs) for single-photon emission computed tomography (SPECT) myocardial perfusion imaging (MPI). BackgroundReference levels serve as radiation dose benchmarks to compare individual laboratories against aggregated data, helping to identify sites in greatest need of dose reduction interventions. DRLs for SPECT MPI have previously been derived from national or regional registries. To date there have been no multiregional reports of DRLs for SPECT MPI from a single standardized dataset. MethodsData were submitted voluntarily to the INCAPS (International Atomic Energy Agency Nuclear Cardiology Protocols Study), a cross-sectional, multinational registry of MPI protocols. A total of 7,103 studies were included. DRLs and AAAs were calculated by protocol for each world region and for aggregated worldwide data. ResultsThe aggregated worldwide DRLs for rest-stress or stress-rest studies employing technetium Tc 99m–labeled radiopharmaceuticals were 11.2 mCi (first dose) and 32.0 mCi (second dose) for 1-day protocols, and 23.0 mCi (first dose) and 24.0 mCi (second dose) for multiday protocols. Corresponding AAAs were 10.1 mCi (first dose) and 28.0 mCi (second dose) for 1-day protocols, and 17.8 mCi (first dose) and 18.7 mCi (second dose) for multiday protocols. For stress-only technetium Tc 99m studies, the worldwide DRL and AAA were 18.0 mCi and 12.5 mCi, respectively. Stress-first imaging was used in 26% to 92% of regional studies except in North America where it was used in just 7% of cases. Significant differences in DRLs and AAAs were observed between regions. ConclusionsThis study reports reference levels for SPECT MPI for each major world region from one of the largest international registries of clinical MPI studies. Regional DRLs may be useful in establishing or revising guidelines or simply comparing individual laboratory protocols to regional trends. Organizations should continue to focus on establishing standardized reporting methods to improve the validity and comparability of regional DRLs.

SPECT myocardial perfusion imaging in liver transplantation candidates

BackgroundThe optimal cardiovascular evaluation prior to liver transplantation remains controversial and includes stress echocardiography, stress MPI, cardiac CTA, and coronary angiography. This study summarizes our experience of the past decade using SPECT MPI in patients with end-stage liver disease, including patient characteristics, stress testing protocols, test results, the need for repeat testing, and downstream testing. MethodsAll patients who underwent a clinically indicated stress SPECT MPI study as part of their pre-liver transplant evaluation from 2004 to 2014 were reviewed from the Nuclear Cardiology database. Results of perfusion imaging, repeat testing, subsequent angiography, and need for revascularization were reviewed. ResultsA total of 2500 patients were referred for SPECT MPI, of those 111 had known CAD and 271 underwent more than one MPI study. Compared to other patients undergoing stress MPI, pre-liver transplant patients were younger, had fewer cardiac risk factors and lower prevalence of prior cardiac history, and used pharmacologic stress more often. During the study decade, patient age increased, prevalence of hypertension increased and smoking decreased, prevalence of known CAD increased, and the number of abnormal studies decreased. Abnormal perfusion results were present in 7.8% of pre-liver transplant patients compared to 34.3% of all other patients. In a multivariate model, age and lower ejection fraction were associated with an abnormal MPI result. Of the 64 patients who underwent subsequent invasive or non-invasive coronary angiography after an abnormal MPI, obstructive CAD was diagnosed in 25 patients (1.0%), non-obstructive CAD was diagnosed in 23 patients (0.9%), and normal coronaries found in 16 patients (0.6%); a total of 18 (0.7%) of these underwent coronary revascularization. The average time to repeat testing was 27.2 ± 17.9 months. In a multivariate model, younger age and exercise stress were associated with repeat testing. In only 17 patients out of 271 with a normal initial perfusion, the repeat study became abnormal. The use of stress-first imaging was successful in 80% of patients with a reduction in Tc-99m dose from 39.1 to 18.3 mCi. ConclusionAbnormal SPECT MPI results in candidates for liver transplantation are infrequent compared to non-liver transplant patients and the incidence of obstructive CAD on subsequent angiography even less. Repeat testing in those on the transplant waiting list after initial normal test results appears to be of limited value. Stress-first protocols may be considered for the majority of these patients to reduce testing time and radiation exposure.

Triage of patients for attenuation-corrected stress-first Tc-99m SPECT MPI using a simplified clinical pre-test scoring model

BackgroundStress-only Tc-99m SPECT MPI saves time and reduces radiation exposure while a normal study has a benign prognosis. However, no guidelines exist as to which patients should undergo stress-first MPI. The purpose of this study was to validate a previously published pre-test prediction scoring model and refine the stress-first triage process further if possible. MethodsWe retrospectively reviewed all patients who underwent an attenuation-corrected Tc-99m SPECT MPI over a 39-month period. Based on 17-segment model semi-quantitative scoring, a successful stress-first MPI was defined as a summed stress attenuation-corrected score ≤ 1. Based on results from multivariate analysis, the previously published prediction score (comprised eight clinical and demographic variables) was compared to triage based on coronary artery disease (CAD) status alone and with the addition of other highly associated variables. Logistic regression and Chi-squared analyses were used to determine the magnitude of variable effect and to compare model results. ResultsA total of 2,277 patients were included, and the prediction score successfully stratified patients into low-risk (91.1% successful stress-first), intermediate-risk (79.4%), and high-risk (50.7%) groups. Comparing the use of the prediction score to the use of a history of CAD as the only triage factor, 69.0% of patients would be accurately triaged using the prediction score with a cutoff of 7 (maximized sensitivity and specificity), while 78.6% were correctly triaged with CAD status alone (P < .0001). The addition of variables highly associated with a successful stress-first protocol (congestive heart failure [OR 3.4] and an abnormal resting ECG [OR 2.1]) to CAD status further enhanced triage accuracy to 81% (P < .0001). ConclusionsWhile the previously described prediction score effectively identifies patients who can successfully undergo stress-first MPI, it is cumbersome. Triaging based solely on CAD status and with the addition of other key variables is practical and provides improved predictive accuracy for successful stress-first MPI. Utilizing this simplified pre-test scoring model may allow for wider adoption of stress-first imaging protocols which have clear advantages over traditional rest–stress protocols.

Abstract 188: Implementation of Choosing Wisely Recommendations for Stress-First Nuclear Myocardial Perfusion Imaging

Introduction: Current guidelines for myocardial perfusion imaging (MPI) encourage facilities to adopt patient-centered risk mitigation strategies such as individualized radiotracer dosing and stress-first imaging. Reducing radiation exposure is also a key recommendation of multiple societies participating in the Choosing Wisely campaign. The stated goal is for over 50% of studies to be performed with &lt;9 millisieverts (mSv) of radiation exposure. We hypothesized that adoption of a stress-first/stress-only imaging protocol would substantially reduce the median radiation dose administered in our nuclear lab. Methods: We switched the standard imaging protocol at the Malcom Randall VA Medical Center nuclear cardiology laboratory from rest-stress to stress-rest. To achieve this, a physician was required to review the stress images at the time they were obtained to determine if further imaging was indicated. Estimated effective radiation doses (in mSv) were calculated based on the radiotracer activity administered (in millicuries) used industry standards techniques. We compared 2 cohorts of patients: rest-stress studies consecutively done between 7/17/17 and 11/12/17 and stress-first studies consecutively done between 11/13/17 and 5/17/17. As a balancing measure, we compared the rate of normal studies between the cohorts. A normal MPI was defined as no evidence of ischemia or infarction with a preserved ejection fraction. Results: In the stress-first cohort, the median dose was 2.8 millisieverts (mSv) compared with 14.1 mSv in the rest-stress cohort (80.1% reduction, p&lt;0.0001). During the observed period, we estimate that 4,780 mSv of effective dose were avoided. In the rest-stress cohort, 424 studies were performed. In the stress-first cohort, 716 tests were performed, 423 stress only studies (59.1%) and 293 stress-rest studies (40.1%). The rate of normal studies in the stress-first cohort was not different from the rest-stress cohort (stress-first: 73.5%, (526/716) versus rest-stress: 71.7%, p=0.54, odds ratio 0.92, 95% CI 0.69-1.21) In the rest-stress cohort, 3 patients (1.0%) underwent coronary angiography and 2 patients (0.7%) underwent percutaneous coronary intervention (PCI). In the stress-first cohort 8 patients (1.1%) underwent coronary angiography and 2 patient (0.3%) underwent percutaneous coronary intervention (PCI). Conclusion: By switching from a rest-stress to a stress-first imaging protocol, we reduced the median radiation dose in our lab by 80%. We observed no change in the proportion of normal tests, suggesting no potential for harm with this strategy.

Multicenter evaluation of stress-first myocardial perfusion image triage by nuclear technologists and automated quantification

BackgroundA stress-first myocardial perfusion imaging (MPI) protocol saves time, is cost effective, and decreases radiation exposure. A limitation of this protocol is the requirement for physician review of the stress images to determine the need for rest images. This hurdle could be eliminated if an experienced technologist and/or automated computer quantification could make this determination. MethodsImages from consecutive patients who were undergoing a stress-first MPI with attenuation correction at two tertiary care medical centers were prospectively reviewed independently by a technologist and cardiologist blinded to clinical and stress test data. Their decision on the need for rest imaging along with automated computer quantification of perfusion results was compared with the clinical reference standard of an assessment of perfusion images by a board-certified nuclear cardiologist that included clinical and stress test data. ResultsA total of 250 patients (mean age 61 years and 55% female) who underwent a stress-first MPI were studied. According to the clinical reference standard, 42 (16.8%) and 208 (83.2%) stress-first images were interpreted as “needing” and “not needing” rest images, respectively. The technologists correctly classified 229 (91.6%) stress-first images as either “needing” (n = 28) or “not needing” (n = 201) rest images. Their sensitivity, specificity, positive predictive value (PPV), and negative predictive value (NPV) were 66.7%, 96.6%, 80.0%, and 93.5%, respectively. An automated stress TPD score ≥1.2 was associated with optimal sensitivity and specificity and correctly classified 179 (71.6%) stress-first images as either “needing” (n = 31) or “not needing” (n = 148) rest images. Its sensitivity, specificity, PPV, and NPV were 73.8%, 71.2%, 34.1%, and 93.1%, respectively. In a model whereby the computer or technologist could correct for the other’s incorrect classification, 242 (96.8%) stress-first images were correctly classified. The composite sensitivity, specificity, PPV, and NPV were 83.3%, 99.5%, 97.2%, and 96.7%, respectively. ConclusionTechnologists and automated quantification software had a high degree of agreement with the clinical reference standard for determining the need for rest images in a stress-first imaging protocol. Utilizing an experienced technologist and automated systems to screen stress-first images could expand the use of stress-first MPI to sites where the cardiologist is not immediately available for interpretation.

Myocardial perfusion scintigraphy dosimetry: optimal use of SPECT and SPECT/CT technologies in stress-first imaging protocol

PurposeOver the past decade, nuclear medicine experts have been seeking to minimize patient exposure to radiation in myocardial perfusion scintigraphy (MPS). This review describes the latest technological innovations in MPS, particularly with regard to dose reduction.MethodsWe searched in PubMed for original clinical papers in English, published after 2008, using the following research criteria: (dose) and ((reduction) or (reducing)) and ((myocardial) or (cardiac) or (heart)) and ((nuclear medicine) or (nuclear imaging) or (radionuclide) or (scintigraphy) or (SPET) or (SPECT)). Thereafter, recent reviews on the topic were considered and other relevant clinical papers were added to the results.ResultsOf 202 non-duplicate articles, 17 were included. To these, another eight papers cited in recent reviews were added. By optimizing the features of software, i.e., through algorithms for iterative reconstruction with resolution recovery (IRRs), and hardware, i.e., scanners and collimators, and by preferring, unless otherwise indicated, the use of stress-first imaging protocols, it has become possible to reduce the effective dose by at least 50% in stress/rest protocols, and by up to 89% in patients undergoing a diagnostic stress-only study with new technology. With today’s SPECT/CT systems, the use of a stress-first protocol can conveniently be performed, resulting in an overall dose reduction of about 35% if two-thirds of stress-first examinations were considered definitively normal.ConclusionUsing innovative gamma cameras, collimators and software, as well as, unless otherwise indicated, stress-first imaging protocols, it has become possible to reduce significantly the effective dose in a high percentage of patients, even when X-ray CT scanning is performed for attenuation correction.

Sequential SPECT/CT imaging starting with stress SPECT in patients with left bundle branch block suspected for coronary artery disease.

To investigate the impact of left bundle branch block (LBBB) on sequential single photon emission computed tomography (SPECT)/ CT imaging starting with stress-first SPECT. Consecutive symptomatic low- to intermediate-risk patients without a history of coronary artery disease (CAD) referred for SPECT/CT were included from an observational registry. If stress SPECT was abnormal, additional rest SPECT and, if feasible, coronary CT angiography (CCTA) were acquired. Of the 5,018 patients, 218 (4.3 %) demonstrated LBBB. Patients with LBBB were slightly older than patients without LBBB (65±12 vs. 61±11 years, p<0.001). Stress SPECT was more frequently abnormal in patients with LBBB (82 % vs. 46 %, p<0.001). After reviewing stress and rest images, SPECT was normal in 43 % of the patients with LBBB, compared to 77 % of the patients without LBBB (p<0.001). Sixty-four of the 124 patients with LBBB and abnormal stress-rest SPECT underwent CCTA (52 %), which could exclude obstructive CAD in 46 of the patients (72 %). Sequential SPECT/CT imaging starting with stress SPECT is not the optimal imaging protocol in patients with LBBB, as the majority of these patients have potentially false-positive stress SPECT. First-line testing using CCTA may be more appropriate in low- to intermediate-risk patients with LBBB. • Stress-first SPECT imaging is attractive if many patients demonstrate normal stress perfusion. • The majority of left bundle branch block patients have abnormal stress-first SPECT. • Coronary CT excluded obstructive CAD in many LBBB patients with abnormal SPECT. • Stress-first SPECT imaging is not the optimal imaging protocol in LBBB patients. • In LBBB patients imaging with initial coronary CT may be more appropriate.

A model for the prediction of a successful stress-first Tc-99m SPECT MPI

BackgroundStress-only Tc-99m MPI saves time, radiation exposure, and a normal study has a benign prognosis. However, a stress-first protocol is relatively labor intensive requiring pre-test screening for suitability and early post-stress image review to determine the need for rest imaging. The purpose of this study was to develop a simple clinical score used prior to a patient’s myocardial perfusion imaging (MPI) study to determine if they should undergo a stress-first protocol. MethodsWe reviewed all patients who underwent Tc-99m SPECT MPI over a 27-month period and divided them into derivation and validation cohorts. Patients were categorized as having a successful stress-first protocol based on a summed stress score ≤1, with or without attenuation correction. We generated a multivariable model from the derivation cohort to identify demographic and clinical correlates of successful stress-first imaging. Two validation cohorts using a CZT and a conventional SPECT camera were then used to test the performance of the model. ResultsThe derivation cohort included 1,996 patients and the validation cohort consisted of 1,005 CZT SPECT patients and 2,430 conventional SPECT patients. The following variables were associated with unsuccessful (i.e., abnormal) stress-first imaging: age >65 years (1 point), diabetes (2 points), typical chest pain (2 points), congestive heart failure (3 points), abnormal ECG (4 points), male gender (4 points), and documented CAD (5 points). Emergency Department location (−2 points) was negatively associated with an unsuccessful protocol. An increasing score showed a strong association with an unsuccessful stress-first protocol in both the derivation and the validation cohorts (P < .0001) and dividing the cohorts into low (<5), intermediate (≥5 and <10), and high (≥10) risk scores accurately stratified patients based on their frequencies of unsuccessful stress-first imaging. ROC curve analysis showed excellent prediction in both the derivation and the validation cohorts with an area under the curve of 0.82 and 0.75-0.83, respectively. ConclusionsThis pre-test scoring tool accurately identifies patients who can successfully undergo a stress-first imaging protocol without the need for rest imaging and may allow for wider adoption of stress-first imaging protocols.