Mohan U. Sivananthan

Modified Look-Locker inversion recovery (MOLLI) for high-resolution T1 mapping of the heart.

A novel pulse sequence scheme is presented that allows the measurement and mapping of myocardial T1 in vivo on a 1.5 Tesla MR system within a single breath‐hold. Two major modifications of conventional Look‐Locker (LL) imaging are introduced: 1) selective data acquisition, and 2) merging of data from multiple LL experiments into one data set. Each modified LL inversion recovery (MOLLI) study consisted of three successive LL inversion recovery (IR) experiments with different inversion times. We acquired images in late diastole using a single‐shot steady‐state free‐precession (SSFP) technique, combined with sensitivity encoding to achieve a data acquisition window of <200 ms duration. We calculated T1 using signal intensities from regions of interest and pixel by pixel. T1 accuracy at different heart rates derived from simulated ECG signals was tested in phantoms. T1 estimates showed small systematic error for T1 values from 191 to 1196 ms. In vivo T1 mapping was performed in two healthy volunteers and in one patient with acute myocardial infarction before and after administration of Gd‐DTPA. T1 values for myocardium and noncardiac structures were in good agreement with values available from the literature. The region of infarction was clearly visualized. MOLLI provides high‐resolution T1 maps of human myocardium in native and post‐contrast situations within a single breath‐hold. Magn Reson Med 52:141–146, 2004.

Normal human left and right ventricular dimensions for MRI as assessed by turbo gradient echo and steady‐state free precession imaging sequences

To establish normal ranges of left ventricular (LV) and right ventricular (RV) dimensions as determined by the current pulse sequences in cardiac magnetic resonance imaging (MRI).

Myocardial T1 mapping: Application to patients with acute and chronic myocardial infarction

T1 maps obtained with modified Look‐Locker inversion recovery (MOLLI) can be used to measure myocardial T1. We aimed to evaluate the potential of MOLLI T1 mapping for the assessment of acute and chronic myocardial infarction (MI). A total of 24 patients with a first MI underwent MRI within 8 days and after 6 months. T1 mapping was performed at baseline and at selected intervals between 2–20 min following administration of gadopentetate dimeglumine (Gd‐DTPA). Delayed‐enhancement (DE) imaging served as the reference standard for delineation of the infarct zone. On T1 maps the myocardial T1 relaxation time was assessed in hyperenhanced areas, hypoenhanced infarct cores, and remote myocardium. The planimetric size of myocardial areas with standardized T1 threshold values was measured. Acute and chronic MI exhibited different T1 changes. Precontrast threshold T1 maps detected segmental abnormalities caused by acute MI with 96% sensitivity and 91% specificity. Agreement between measurements of infarct size from T1 mapping and DE imaging was higher in chronic than in acute infarcts. Precontrast T1 maps enable the detection of acute MI. Acute and chronic MI show different patterns of T1 changes. Standardized T1 thresholds provide the potential to dichotomously identify areas of infarction. Magn Reson Med 58:34–40, 2007.

Steady-state free precession magnetic resonance imaging of the heart: comparison with segmented k-space gradient-echo imaging.

Steady‐state free precession imaging is a promising technique for cardiac magnetic resonance imaging (MRI), as it provides improved blood/myocardial contrast in shorter acquisition times compared with conventional gradient‐echo acquisition. The better contrast could improve observer agreement and automatic detection of cardiac contours for volumetric assessment of the ventricles, but measurements might differ from those obtained using conventional methods. We compared volumetric measurements, observer variabilities, and automatic contour detection between a steady‐state free precession imaging sequence (BFFE = balanced fast field echo) and segmented k‐space gradient‐echo acquisition (TFE = turbo field echo) in 41 subjects. With BFFE, significantly higher end‐diastolic and end‐systolic volumes and lower wall thickness, ventricular mass, ejection fraction, and wall motion were observed (P < 0.0001), while interobserver variabilities were lower and automatic contour detection of endocardial contours was more successful. We conclude that the improved image quality of BFFE reduces the observer‐dependence of volumetric measurements of the left ventricle (LV) but results in significantly different values in comparison to TFE measurements. J. Magn. Reson. Imaging 2001;14:230–236.

Comparison of right ventricular volume measurements between axial and short axis orientation using steady-state free precession magnetic resonance imaging.

To compare right ventricular (RV) volume measurements and their reproducibility between axial and short axis orientation acquisition techniques.

Assessment of ventricular function and mass by cardiac magnetic resonance imaging.

Cardiac magnetic resonance imaging is currently the technique of choice for precise measurements of ventricular volumes, function and left ventricular (LV) mass. The technique is 3D and hence independent of geometrical assumptions; this, along with its excellent definition of endocardial and epicardial borders, makes it highly accurate and reproducible. Cardiac magnetic resonance (CMR) is particularly useful in research, as it is highly sensitive to small changes in ejection fraction and mass, and only a small number of subjects are required for a study. The excellent reproducibility makes temporal follow-up of any individual patient in the clinical setting a realistic possibility. This review examines the merits of CMR and describes the techniques used.

Role of MRI in clinical cardiology

Rapid progress has been made in cardiac MRI (CMRI) over the past decade, which has firmly established it as a reliable and clinically important technique for assessment of cardiac structure, function, perfusion, and myocardial viability. Its versatility and accuracy is unmatched by any other individual imaging modality. CMRI is non-invasive and has high spatial resolution and avoids use of potentially nephrotoxic contrast agent or radiation. It has been extensively studied against other established non-invasive imaging modalities and has been shown to be superior in many scenarios, particularly with respect to assessment of cardiac and great vessel morphology and left ventricular function. Furthermore, its clinical use continues to expand with increasing experience and proliferation of CMRI centres. As worldwide prevalence of cardiovascular disease continues to rise, CMRI provides opportunity for improved and cost-effective non-invasive assessment. Continued progress in CMRI technology promises to further widen its clinical application in coronary imaging, myocardial perfusion, comprehensive assessment of valves, and plaque characterisation.

Role of Cardiac Magnetic Resonance Imaging in the Assessment of Myocardial Viability

Dysfunctional myocardium that remains viable has the potential for contractile recovery after reperfusion.1 Dysfunctional but viable myocardium has been broadly divided into 2 closely linked pathophysiological states, myocardial hibernation and stunning. Stunned myocardium is the result of an ischemic insult leading to contractile dysfunction despite adequate reperfusion. Hibernating myocardium describes downregulation of myocyte metabolism as a result of prolonged reduction in perfusion, or, in some cases, repetitive episodes of myocardial stunning.2 The exact nature of structural changes in hibernating myocardium remains controversial.3 However, a spectrum of histological alterations has been noted, ranging from cellular dedifferentiation (fetal phenotype) to cellular degeneration (with more extensive fibrosis) with loss of contractile and cytoskeletal proteins. Worsening histological perturbations correlate with increasing duration of chronically low perfusion. Thus, accurate and early detection of viable myocardium has become an increasingly important guide to prognosis and therapy. Until recently, scintigraphic techniques and stress echocardiography were the mainstay of diagnosis.4,5 The focus of the present article is on the rapidly emerging clinical role of cardiovascular MRI (CMR) in the detection of viable myocardium. In patients with chronic ischemic left ventricular dysfunction, improvements in ejection fraction and exercise capacity after revascularization have been well documented.6–10 The prognostic importance of detecting myocardial viability hinges on 2 major considerations. First, medically treated viable myocardium is a harbinger of further nonfatal ischemic events and higher overall mortality. In patients with significant viable myocardium, the annual mortality rate is more than 4-fold greater in those treated medically compared with those patients who have had successful revascularization.11 Second, discrimination between viable and nonviable dysfunctional myocardium allows patients to avoid the risks associated with revascularization when they are unlikely to benefit. Although limited by the lack of large randomized studies, a recent meta-analysis indicated that the annual mortality rate …

Relationship Between Central Sympathetic Drive and Magnetic Resonance Imaging–Determined Left Ventricular Mass in Essential Hypertension

Background— Sympathetic activation has been implicated in the development of left ventricular hypertrophy (LVH). However, the relationship between sympathetic activation and LV mass (LVM) has not been clearly defined across a range of arterial pressure measurements. The present study was planned to determine that relationship, using cardiac magnetic resonance imaging to accurately quantify LVM, in hypertensive patients with and without LVH and in normal subjects. Methods and Results— Twenty-four patients with uncomplicated and untreated essential hypertension (LVH[−]) were compared with 25 patients with essential hypertension and left ventricular hypertrophy (LVH[+]) and 24 normal control subjects. Resting muscle sympathetic nerve activity was quantified as multiunit bursts and single units. Cardiac magnetic resonance imaging–determined LVM was indexed to body surface area (LVM index); in the LVH[−] group, LVM index was 67±2.1 g/m2, a value between those of the LVH[+] (91±3.4 g/m2) and normal control (57±2.2 g/m2) groups, respectively. The sympathetic activity in the LVH[−] group (53±1.3 bursts per 100 cardiac beats and 63±1.6 impulses per 100 cardiac beats) was between (at least P<0.001) those of the LVH[+] (66±1.7 bursts per 100 cardiac beats and 77±2.2 impulses per 100 cardiac beats) and normal control (39±3.0 bursts per 100 cardiac beats and 45±3.4 impulses per 100 cardiac beats) groups. Significant positive correlation existed between sympathetic activity and LVM index in the LVH[−] and LVH[+] groups (at least r=0.76, P<0.0001) but not in the normal control group. However, no consistent relationship existed between arterial blood pressure and sympathetic activity or LVM index. Conclusions— These findings further support the hypothesis that central sympathetic activation is associated with the development of LVH in human hypertension.

Heart-Type Fatty Acid-Binding Protein Predicts Long-Term Mortality and Re-Infarction in Consecutive Patients With Suspected Acute Coronary Syndrome Who Are Troponin-Negative

OBJECTIVES The purpose of this study was to establish the prognostic value of measuring heart fatty acid-binding protein (H-FABP) in patients with suspected acute coronary syndrome (ACS) (in particular, low- to intermediate-risk patients), in addition to troponin measured with the latest third-generation troponin assay. BACKGROUND We have previously shown that H-FABP is a useful prognostic marker in patients with proven ACS. METHODS Patients (n = 1,080) consecutively admitted to the hospital with suspected ACS were recruited over 46 weeks. Siemens Advia Ultra-TnI (Siemens Healthcare Diagnostics, Newbury, United Kingdom) and Randox Evidence H-FABP (Randox Laboratories, Ltd., Co., Antrim, United Kingdom) were analyzed on samples collected 12 to 24 h from symptom onset. After exclusion of patients with ST-segment elevation and new left bundle branch block, 955 patients were included in the analysis. RESULTS The primary outcome measure of death or readmission with myocardial infarction after a minimum follow-up period of 12 months (median 18 months) occurred in 96 of 955 patients (10.1%). The H-FABP concentration was an independent predictor of death or myocardial infarction, after multivariate adjustment. Patients with H-FABP concentrations >6.48 microg/l had significantly increased risk of adverse events (adjusted hazard ratio: 2.62, 95% confidence interval: 1.30 to 5.28, p = 0.007). Among troponin-negative patients (which constituted 79.2% of the cohort), the aforementioned cutoff of 6.48 microg/l identified patients at very high risk for adverse outcomes independent of patient age and serum creatinine. CONCLUSIONS We have demonstrated that the prognostic value of elevated H-FABP is additive to troponin in low- and intermediate-risk patients with suspected ACS. Other studies suggest that our observations reflect the value of H-FABP as a marker of myocardial ischemia, even in the absence of frank necrosis.