Characterization of 3D PET systems for accurate quantification of myocardial blood flow

Three-dimensional (3D) mode imaging is the current standard for positron emission tomography-computed tomography (PET-CT) systems. Dynamic imaging for quantification of myocardial blood flow (MBF) with short-lived tracers, such as Rb-82- chloride (Rb-82), requires accuracy to be maintained over a wide range of isotope activities and scanner count-rates. We propose new performance standard measurements to characterize the dynamic range of PET systems for accurate quantitative imaging. Methods: 1100-3000 MBq of Rb-82 or N-13-ammonia was injected into the heart wall insert of an anthropomorphic torso phantom. A decaying isotope scan was performed over 5 half-lives on 9 different 3D PET-CT systems and 1 3D/twodimensional (2D) PET-only system. Dynamic images (28x15s) were reconstructed using iterative algorithms with all corrections enabled. Dynamic range was defined as the maximum activity in the myocardial wall with <10% bias, from which corresponding dead-time, count-rates and/or injected activity limits were established for each scanner. Scatter correction residual bias was estimated as the maximum cavity blood-tomyocardium activity ratio. Image quality was assessed via the coefficient of variation measuring non-uniformity of the left ventricle (LV) myocardium activity distribution. Results: Maximum recommended injected activity/body-weight, peak dead-time correction factor, count-rates and residual scatter bias for accurate cardiac MBF imaging were: 3-14 MBq/kg, 1.5-4.0, 22-64 Mcps singles and 4-14 Mcps prompt coincidence count-rates, and 2-10% on the investigated scanners. Non-uniformity of the myocardial activity distribution varied from 3-16%. Conclusion: Accurate dynamic imaging is possible on the 10 3D-PET systems if the maximum injected MBq/kg values are respected to limit peak dead-time losses during the bolus first-pass transit

Cardiovascular magnetic resonance of myocardial edema using a short inversion time inversion recovery (STIR) black-blood technique: Diagnostic accuracy of visual and semi-quantitative assessment

<p>Abstract</p> <p>Background</p> <p>The short inversion time inversion recovery (STIR) black-blood technique has been used to visualize myocardial edema, and thus to differentiate acute from chronic myocardial lesions. However, some cardiovascular magnetic resonance (CMR) groups have reported variable image quality, and hence the diagnostic value of STIR in routine clinical practice has been put into question. The aim of our study was to analyze image quality and diagnostic performance of STIR using a set of pulse sequence parameters dedicated to edema detection, and to discuss possible factors that influence image quality. We hypothesized that STIR imaging is an accurate and robust way of detecting myocardial edema in non-selected patients with acute myocardial infarction.</p> <p>Methods</p> <p>Forty-six consecutive patients with acute myocardial infarction underwent CMR (day 4.5, +/- 1.6) including STIR for the assessment of myocardial edema and late gadolinium enhancement (LGE) for quantification of myocardial necrosis. Thirty of these patients underwent a follow-up CMR at approximately six months (195 +/- 39 days). Both STIR and LGE images were evaluated separately on a segmental basis for image quality as well as for presence and extent of myocardial hyper-intensity, with both visual and semi-quantitative (threshold-based) analysis. LGE was used as a reference standard for localization and extent of myocardial necrosis (acute) or scar (chronic).</p> <p>Results</p> <p>Image quality of STIR images was rated as diagnostic in 99.5% of cases. At the acute stage, the sensitivity and specificity of STIR to detect infarcted segments on visual assessment was 95% and 78% respectively, and on semi-quantitative assessment was 99% and 83%, respectively. STIR differentiated acutely from chronically infarcted segments with a sensitivity of 95% by both methods and with a specificity of 99% by visual assessment and 97% by semi-quantitative assessment. The extent of hyper-intense areas on acute STIR images was 85% larger than those on LGE images, with a larger myocardial salvage index in reperfused than in non-reperfused infarcts (p = 0.035).</p> <p>Conclusions</p> <p>STIR with appropriate pulse sequence settings is accurate in detecting acute myocardial infarction (MI) and distinguishing acute from chronic MI with both visual and semi-quantitative analysis. Due to its unique technical characteristics, STIR should be regarded as an edema-weighted rather than a purely T2-weighted technique.</p

T2-weighted cardiovascular magnetic resonance in acute cardiac disease

Cardiovascular magnetic resonance (CMR) using T2-weighted sequences can visualize myocardial edema. When compared to previous protocols, newer pulse sequences with substantially improved image quality have increased its clinical utility. The assessment of myocardial edema provides useful incremental diagnostic and prognostic information in a variety of clinical settings associated with acute myocardial injury. In patients with acute chest pain, T2-weighted CMR is able to identify acute or recent myocardial ischemic injury and has been employed to distinguish acute coronary syndrome (ACS) from non-ACS as well as acute from chronic myocardial infarction

Review of journal of cardiovascular magnetic resonance 2010

There were 75 articles published in the Journal of Cardiovascular Magnetic Resonance (JCMR) in 2010, which is a 34% increase in the number of articles since 2009. The quality of the submissions continues to increase, and the editors were delighted with the recent announcement of the JCMR Impact Factor of 4.33 which showed a 90% increase since last year. Our acceptance rate is approximately 30%, but has been falling as the number of articles being submitted has been increasing. In accordance with Open-Access publishing, the JCMR articles go on-line as they are accepted with no collating of the articles into sections or special thematic issues. Last year for the first time, the Editors summarized the papers for the readership into broad areas of interest or theme, which we felt would be useful to practitioners of cardiovascular magnetic resonance (CMR) so that you could review areas of interest from the previous year in a single article in relation to each other and other recent JCMR articles [1]. This experiment proved very popular with a very high rate of downloading, and therefore we intend to continue this review annually. The papers are presented in themes and comparison is drawn with previously published JCMR papers to identify the continuity of thought and publication in the journal. We hope that you find the open-access system increases wider reading and citation of your papers, and that you will continue to send your quality manuscripts to JCMR for publication

Fast T2 gradient-spin-echo (T2-GraSE) mapping for myocardial edema quantification: first in vivo validation in a porcine model of ischemia/reperfusion

BACKGROUND: Several T2-mapping sequences have been recently proposed to quantify myocardial edema by providing T2 relaxation time values. However, no T2-mapping sequence has ever been validated against actual myocardial water content for edema detection. In addition, these T2-mapping sequences are either time-consuming or require specialized software for data acquisition and/or post-processing, factors impeding their routine clinical use. Our objective was to obtain in vivo validation of a sequence for fast and accurate myocardial T2-mapping (T2 gradient-spin-echo [GraSE]) that can be easily integrated in routine protocols. METHODS: The study population comprised 25 pigs. Closed-chest 40 min ischemia/reperfusion was performed in 20 pigs. Pigs were sacrificed at 120 min (n = 5), 24 h (n = 5), 4 days (n = 5) and 7 days (n = 5) after reperfusion, and heart tissue extracted for quantification of myocardial water content. For the evaluation of T2 relaxation time, cardiovascular magnetic resonance (CMR) scans, including T2 turbo-spin-echo (T2-TSE, reference standard) mapping and T2-GraSE mapping, were performed at baseline and at every follow-up until sacrifice. Five additional pigs were sacrificed after baseline CMR study and served as controls. RESULTS: Acquisition of T2-GraSE mapping was significantly (3-fold) faster than conventional T2-TSE mapping. Myocardial T2 relaxation measurements performed by T2-TSE and T2-GraSE mapping demonstrated an almost perfect correlation (R(2) = 0.99) and agreement with no systematic error between techniques. The two T2-mapping sequences showed similarly good correlations with myocardial water content: R(2) = 0.75 and R(2) = 0.73 for T2-TSE and T2-GraSE mapping, respectively. CONCLUSIONS: We present the first in vivo validation of T2-mapping to assess myocardial edema. Given its shorter acquisition time and no requirement for specific software for data acquisition or post-processing, fast T2-GraSE mapping of the myocardium offers an attractive alternative to current CMR sequences for T2 quantification

Is Hemorrhage in Acute Reperfused Myocardial Infarction a New Marker for the Severity of Tissue Injury?

Introduction: Reperfusion injury in myocardial infarction leads to microvascular obstruction, which can occur with or without gross reperfusion hemorrhage. The incidence and implications of reperfusion hemorrhage are not well investigated. A recently described in vivo imaging approach using T2*-weighted cardiovascular magnetic resonance can help investigate the pathophysiology of reperfusion hemorrhage in vivo. Hypothesis: We hypothesized that hemorrhage reflects a severer from of reperfusion injury and therefore occurs with larger infarct size and worse LV function as compared to reperfusion injury without hemorrhage. Methods: In 14 female mongrel dogs, myocardial infarction was induced by ligation of the left anterior descending coronary artery for 2–4 hours, followed by reperfusion. On day 3 ± 1, a cardiovascular magnetic resonance study was performed in vivo to (1) assess presence of microvascular obstruction, defining reperfusion injury (2) assess presence of reperfusion hemorrhage (3) quantify left ventricular end-diastolic volume, ejection fraction and cardiac output and (4) quantify infarct size with late enhancement. An independent-samples t-test was performed to compare these parameters in dogs with and without hemorrhage in reperfusion injury. Results: From 14 dogs, 9 had microvascular obstruction, and 4/9 had reperfusion hemorrhage in addition to microvascular obstruction. Dogs with hemorrhagic infarcts had significantly larger infarct size (26.1 ± 6.6 g vs. 5.5 ± 3.9 g, p \u3c 0.05), lower LV ejection fraction (28 ± 7% vs. 53 ± 12%, p \u3c 0.05), and lower cardiac output (1.9 ± 0.2 l/min vs. 2.8 ± 0.5 l/min, p \u3c 0.05). There were no differences in LV end-diastolic volume and LV mass. Discussion and conclusion: In this dog model of ischemia/reperfusion injury, gross hemorrhage was associated with significantly larger infarct size and worse LV functional parameters. This supports the hypothesis that hemorrhage may occur with advanced, severe ischemic tissue injury only