Parthiban Arumugam

Multisoftware Reproducibility Study of Stress and Rest Myocardial Blood Flow Assessed with 3D Dynamic PET/CT and a 1-Tissue-Compartment Model of 82Rb Kinetics

Routine quantification of myocardial blood flow (MBF) requires robust and reproducible processing of dynamic image series. The goal of this study was to evaluate the reproducibility of 3 highly automated software programs commonly used for absolute MBF and flow reserve (stress/rest MBF) assessment with 82Rb PET imaging. Methods: Dynamic rest and stress 82Rb PET scans were selected in 30 sequential patient studies performed at 3 separate institutions using 3 different 3-dimensional PET/CT scanners. All 90 scans were processed with 3 different MBF quantification programs, using the same 1-tissue-compartment model. Global (left ventricle) and regional (left anterior descending, left circumflex, and right coronary arteries) MBF and flow reserve were compared among programs using correlation and Bland–Altman analyses. Results: All scans were processed successfully by the 3 programs, with minimal operator interactions. Global and regional correlations of MBF and flow reserve all had an R2 of at least 0.92. There was no significant difference in flow values at rest (P = 0.68), stress (P = 0.14), or reserve (P = 0.35) among the 3 programs. Bland–Altman coefficients of reproducibility (1.96 × SD) averaged 0.26 for MBF and 0.29 for flow reserve differences among programs. Average pairwise differences were all less than 10%, indicating good reproducibility for MBF quantification. Global and regional SD from the line of perfect agreement averaged 0.15 and 0.17 mL/min/g, respectively, for MBF, compared with 0.22 and 0.26, respectively, for flow reserve. Conclusion: The 1-tissue-compartment model of 82Rb tracer kinetics is a reproducible method for quantification of MBF and flow reserve with 3-dimensional PET/CT imaging.

Early diagnosis of cardiac implantable electronic device generator pocket infection using 18F-FDG-PET/CT.

Aims To examine the utility of 18F-fluorodeoxyglucose positron emission tomography/computed tomography (18F-FDG PET/CT) in the early diagnosis of cardiac implantable electronic device (CIED) generator pocket infection. Methods and results A total of 86 patients with CIEDs were evaluated with 18F-FDG PET/CT imaging: 46 with suspected generator pocket infection and 40 without any history of infection. 18F-FDG activity in the region of the generator pocket was expressed as a semi-quantitative ratio (SQR)—defined as the maximum count rate around the CIED divided by the mean count rate between normal right and left lung parenchyma. All patients underwent standard clinical management, independent of the PET/CT result. Patients with suspected generator pocket infection that required CIED extraction (n = 32) had significantly higher 18F-FDG activity compared with those that did not (n = 14), and compared with controls (n = 40) [SQR: 4.80 (3.18–7.05) vs. 1.40 (0.88–1.73) vs. 1.10 (0.98–1.40), respectively; P < 0.001]. On receiver operator characteristic analysis, SQR had a high diagnostic accuracy (area under curve = 0.98) for the early identification of patients with confirmed infection (i.e. those ultimately needing extraction)—with an optimal SQR cut-off value of >2.0 (sensitivity = 97%; specificity = 98%). Conclusion This study highlights the potential benefits of evaluating patients with suspected CIED generator pocket infection using 18F-FDG PET/CT. In this study, 18F-FDG PET/CT had a high diagnostic accuracy in the early diagnosis of CIED generator pocket infection, even where initial clinical signs were underwhelming.

Assessment of a protocol for routine simultaneous myocardial blood flow measurement and standard myocardial perfusion imaging with rubidium-82 on a high count rate positron emission tomography system.

ObjectivesHigh count rate positron emission tomography (PET) systems offer the potential for accurate myocardial blood flow (MBF) quantification during first-pass dynamic imaging in conjunction with standard rubidium-82 (Rb-82) PET myocardial perfusion imaging (MPI). We investigate the feasibility of this using a Siemens Biograph mCT. Materials and methodsCurrent routine clinical PET MPI is performed with 1480 MBq (40 mCi) Rb-82. Dynamic first-pass images from 217 consecutive patients were reviewed for evidence of detector saturation, indicating that count rate limits had been exceeded. Phantom acquisitions in the presence of high count rates were performed to assess the effect of detector saturation on quantitative accuracy. ResultsAccurate MBF quantification and perfusion imaging using current protocols was successful in 85% of clinical cases. Detector block saturation was observed in 15% of cases, and phantom acquisitions indicate that saturation may have an adverse effect on quantitative accuracy. Visualization of transit or pooling of Rb-82 in the vessels in the axilla was the most consistent feature when saturation occurred. Reduction of administered activity to 1110 MBq (30 mCi) and subsequent evaluation of 159 patients ensured successful MBF quantification while maintaining good diagnostic quality perfusion imaging in 99% of cases. ConclusionMBF quantification and good-quality standard perfusion imaging can be performed on a high count rate PET system using a single-acquisition protocol. The administered activity requires optimization and we recommend 1110 MBq for PET MPI with a Biograph mCT.

Reduced-count myocardial perfusion SPECT with resolution recovery.

AimThe aim of this study was to determine whether resolution recovery (RR) iterative reconstruction algorithms can consistently produce diagnostic quality myocardial perfusion SPECT images for the patient population routinely scanned in this department. Reduced-count data were compared with full-count data without RR according to our established protocol. The desired outcome would be to implement the software to allow a reduction in the administered activity for routine myocardial SPECT. MethodsHalf-count SPECT data were derived from full-count datasets for 53 stress and rest routine myocardial SPECT scans on a GE Infinia camera. Full-count data were reconstructed using standard non-RR ordered subset expectation maximization reconstruction, whereas half-count data were reconstructed using Evolution RR software. Myocardial functional values, image quality and report outcomes of the full-count and half-count reports were compared. Sequential full-time and half-time myocardial SPECT acquisitions were performed for 15 stress and rest studies on a Siemens c.cam dedicated cardiac camera. Half-count data were reconstructed using Siemens Flash 3D RR. ResultsNo degradation in image quality was found when comparing full-count and half-count studies from the Infinia. Ten percent of the half-count studies from the c.cam were considered slightly worse than full-count data. Statistically significant differences in some full-count versus half-count functional values were found but the actual mean differences were not considered clinically significant. No difference was found for 44 out of 53 full-count versus half-count reports, a minor difference for seven out of 53 and a significant difference in two cases. ConclusionRR was found to produce diagnostic image quality for nearly all scans, but it was felt that a reduction of 50% from our standard protocol was too great. A proposed reduction of 33% administered activity was considered acceptable to produce consistently adequate diagnostic images for both manufacturers.

Metal artefact reduction algorithms prevent false positive results when assessing patients for cardiac implantable electronic device infection

Software-based metal artefact reduction (MAR) techniques are available to reduce artefacts from cardiac implantable electronic devices (CIED) in the CT data. The impact of disabling MAR techniques on quantification of 18F-FDG uptake around the CIED has not been examined. We consider the importance of enabling MAR in patients with suspected CIED infection to prevent inaccuracies in quantification of tissue tracer uptake on the attenuation-corrected PET images.

Myocardial perfusion scintigraphy using rubidium-82 positron emission tomography

INTRODUCTION Myocardial perfusion scintigraphy (MPS) is an established non-invasive technique for the diagnosis and management of patients with suspected or known coronary artery disease. Because of the wealth of prognostic data, MPS single photon emission computed tomography (SPECT) is the most commonly used functional test to detect inducible ischaemia. However, the increasing availability of positron emission tomography (PET) scanners for oncology along with the introduction of the generator-produced PET tracer rubidium-82 (⁸²Rb) has helped the growth of MPS PET. SOURCES OF DATA Relevant review articles, primary literature and clinical guidelines identified through medical literature search engines. AREAS OF AGREEMENT PET offers advantages over SPECT, including increased patient throughput because of rapid scanning protocols, reduced radiation exposure to patients and the ability to quantify tracer distribution accurately and hence measure myocardial perfusion in millilitre per gram per minute and hence myocardial perfusion reserve (MPR). AREAS OF CONTROVERSY Although PET has advantages over SPECT, there are no large-scale prognostic or cost-effectiveness data to support it use as the primary MPS technique. GROWING POINTS A wider use of absolute measurements of perfusion has the potential to improve diagnostic accuracy and to add prognostic value over relative assessment of myocardial perfusion. AREAS TIMELY FOR DEVELOPING RESEARCH Assessment of absolute myocardial perfusion may provide insight into the effects of traditional risk factors on perfusion reserve and the impact of risk factor modifications on progression of coronary artery disease.

Radionuclide Imaging of Cardiovascular Infection

Owing to expanding clinical indications, cardiac implantable electronic devices (CIEDs) are being increasingly used. Despite improved surgical techniques and the use of prophylactic antimicrobial therapy, the rate of CIED-related infection is also increasing. Infection is a potentially serious complication, with clinical manifestations ranging from surgical site infection and local symptoms in the region of the generator pocket to fulminant endocarditis. The utility of radionuclide imaging as a stand-alone noninvasive diagnostic imaging test in patients with suspected endocarditis has been less frequently examined. This article summarizes the recent advances in radionuclide imaging for evaluation of patients with suspected cardiovascular infections.

Prognostic value of demographic factors, pre-test probability scoring, exercise test diagnosis, and inability to exercise in patients with recent onset suspected cardiac chest pain

Aims: To assess the prognostic value of an inconclusive exercise test or inability to exercise in patients with recent onset suspected cardiac chest pain and to determine the independent predictors of events in these patients. Methods: This was an observational follow-up study of patients presenting to a rapid access chest pain clinic with a history of recent-onset suspected cardiac chest pain as referred by the family practitioner. The main outcome measure was a composite endpoint of death and acute coronary syndrome hospital admission. Results: The study cohort consisted of 1851 patients in whom a total of 147 events were recorded during a mean follow-up period of 4.1 ± 1.1 years. Those with events were significantly older (65.1 ± 12.5 years versus 56.4 ± 13.2 years, p < 0.001), had higher mean pre-test probability of coronary artery disease (CAD), and had higher prevalence of diabetes (18.4% vs. 13.6%, p < 0.001), hypertension (55.8% vs. 38.7%, p < 0.001), and smoking (36.7% vs. 25.4%, p = 0.03) than those without events. These patients were also more likely to have a positive exercise electrocardiogram (ECG) (15.6% vs. 8.6%, p < 0.001) or not have a diagnostic exercise test because of an inconclusive result or inability to exercise (60.5% vs. 28.6%, p < 0.001). Cox multivariate regression analysis showed that age (hazard ratio, HR 1.03, p < 0.001), pre-test probability of CAD (HR 1.08, p = 0.04), positive exercise ECG (HR 2.94, p < 0.001), and an inconclusive test or inability to exercise (HR 3.45, p < 0.001) were independent predictors of events. Conclusions: In patients with recent onset suspected cardiac chest pain, not having a diagnostic exercise ECG because of an inconclusive test or inability to exercise is an independent predictor of events and has similar prognostic implications to a positive exercise ECG. In addition, pre-test probability estimation at baseline is a robust indicator of clinical outcome. Future models of care need to incorporate early and increased access to non-exercise cardiac imaging techniques in order to meet the needs of this high-risk subgroup of patients.

Incidental detection of apical hypertrophic cardiomyopathy by myocardial perfusion imaging

BackgroundEchocardiography plays a central role in the diagnosis of hypertrophic cardiomyopathy (HCM). However, apical involvement of HCM may be missed because of foreshortening and inadequate clinical suspicion. These patients may be referred for single-photon emission computed tomography imaging. MethodsWe present three cases of HCM predominantly involving the cardiac apex, whose diagnosis was first suspected on myocardial perfusion imaging. These patients were referred for chest pain syndromes to exclude significant coronary artery disease. All were undiagnosed on initial routine transthoracic echocardiography, and none were specifically suspected by the referring clinicians. All cases underwent an adenosine stress rest technetium-99m tetrofosmin myocardial perfusion protocol, and were subsequently referred for transpulmonary contrast echocardiography. ResultsSingle-photon emission computed tomography imaging revealed increased tracer uptake in all cases, most marked in the apical myocardium. Inferior wall ischaemia was detected in one case, consistent with a coronary stenosis seen at angiography. Apical hypokinesia was noted in two patients on gated studies. Contrast echocardiography confirmed the diagnosis of HCM with apical involvement in all cases. ConclusionEchocardiography is the first-line imaging technique for the diagnosis of HCM, but apical involvement may be missed unless a contrast study is performed. The presence of increased apical tracer uptake on perfusion imaging should alert the referring physician to the possibility of apical HCM, irrespective of earlier echocardiographic findings.

Iodine-123 metaiodobenzylguanidine scintigraphy for the assessment of cardiac sympathetic innervation and the relationship with cardiac autonomic function in healthy adults using standardized methods.

Background Global iodine-123 metaiodobenzylguanidine (123I-MIBG) uptake is predictive of cardiovascular events and mortality in patients with heart failure. Normal variations in global and regional uptake, however, are not well defined and few studies have addressed the functional relevance of 123I-MIBG uptake and distribution in healthy individuals. Materials and methods We performed 123I-MIBG scintigraphy and cardiac autonomic function testing using the standardized methodology in 15 healthy individuals (mean age 54.6±5.3 years, male : female 10 : 5) with no evidence of previous myocardial infarction or ischaemic heart disease. Results Early heart to mediastinum ratio (HMR) was 1.67±0.13, late HMR was 1.73±0.16 and washout rate was 19.09±7.63% (4.20–31.30). Regional analysis showed reduced tracer uptake at the apex, base and inferior wall in all individuals. Early and late HMR correlated negatively with RFa (r=−0.603; P=0.05 and r=−0.644; P=0.033) and expiration and inspiration ratio (r=−0.616; P=0.043 and r=−0.676; P=0.022) and positively with LFa/RFa (r=0.711; P=0.014 and r=0.784; P=0.004). Washout rate correlated only with RFa (r=0.642; P=0.033). Conclusion Healthy adults show a heterogeneous pattern of cardiac innervation with reduced regional uptake of 123I-MIBG. Furthermore, HMR correlates with indices of cardiac sympathetic function, suggesting that it might not only be a useful prognostic marker but may also provide insight into the functional integrity of the cardiac autonomic nervous system.