Cardiac Magnetic Resonance Imaging Techniques Research Articles

MRI assessment of cardiac tumours: part 1, multiparametric imaging protocols and spectrum of appearances of histologically benign lesions.

Cardiac magnetic resonance imaging (MRI) is the reference standard technique for assessment and characterization of a suspected cardiac tumour. It provides an unrestricted field of view, high temporal resolution and non-invasive tissue characterization based on multi-parametric assessment of the chemical micro-environment. MRI exploits differences in hydrogen proton density in conjunction with T1 and T2 relaxation properties of different tissues to help differentiation normal from abnormal and benign from malignant lesions. In this article we review specific cardiac MRI techniques, tumour protocol design and the appearance of the spectrum of histologically benign tumours.

T1 mapping: characterisation of myocardial interstitial space.

Myocardial fibrosis is always present in end-stage heart failure and is a major independent predictor of adverse cardiac outcome. Cardiac magnetic resonance (CMR) is an imaging method that permits a non-invasive assessment of the heart and has been established as the “gold standard” for the evaluation of cardiac anatomy and function, as well as for quantifying focal myocardial fibrosis in both ischaemic and non-ischaemic heart disease. However, cardiac pathologies characterised by diffuse myocardial fibrosis cannot be evaluated by late gadolinium enhancement (LGE) imaging, as there are no reference regions of normal myocardium. Recent improvements in CMR imaging techniques have enabled parametric mapping of relaxation properties (T1, T2 and T2*) clinically feasible within a single breath-hold. T1 mapping techniques performed both with and without contrast enable the quantification of diffuse myocardial fibrosis and myocardial infiltration. This article reviews current imaging techniques, emerging applications and the future potential and limitations of CMR for T1 mapping.Teaching points• Myocardial fibrosis is a common endpoint in a variety of cardiac diseases.• Myocardial fibrosis results in myocardial stiffness, heart failure, arrhythmia and sudden death.• T1-mapping CMR techniques enable the quantification of diffuse myocardial fibrosis.• Native T1 reflects myocardial disease involving the myocyte and interstitium.• The use of gadolinium allows measurement of the extracellular volume fraction, reflecting interstitial space.

T1 and T2 mapping: new perspectives in cardiac magnetic resonance imaging

Cardiac magnetic resonance (MR) imaging is currently considered the gold standard for characterizing changes in myocardial structure, in particular to assess myocardial edema and focal fibrosis. In spite of this potential capability, the traditional MR sequences usually employed for these purposes have significant limitations and provide only qualitative information. Recent developments in cardiac MR imaging techniques currently provide clinically-feasible mapping of T1 and T2 relaxation times, thus providing a quantitative assessment of the parameters of interest. Myocardial edema can be evaluated using T2 mapping techniques. These have shown a superior performance compared to the traditional T2-weighted and STIR sequences, both in acute inflammatory cardiomyopathies and in acute ischemic injury. T1 mapping techniques, performed both with and without contrast medium, enable to quantify diffuse myocardial fibrosis and to assess myocardial edema and infiltration. This article will review current methodologies for cardiac T1 and T2 parametric mapping and their potential and limitations in the assessment of myocardial damage.

Pre-clinical functional Magnetic Resonance Imaging part II: The heart

One third of all deaths worldwide in 2008 were caused by cardiovascular diseases (CVD), and the incidence of CVD related deaths rises ever more. Thus, improved imaging techniques and modalities are needed for the evaluation of cardiac morphology and function.Cardiac magnetic resonance imaging (CMRI) is a minimally invasive technique that is increasingly important due to its high spatial and temporal resolution, its high soft tissue contrast and its ability of functional and quantitative imaging. It is widely accepted as the gold standard of cardiac functional analysis.In the short period of small animal MRI, remarkable progress has been achieved concerning new, fast imaging schemes as well as purpose-built equipment. Dedicated small animal scanners allow for tapping the full potential of recently developed animal models of cardiac disease. In this paper, we review state-of-the-art cardiac magnetic resonance imaging techniques and applications in small animals at ultra-high fields (UHF).

Abstract 9803: Optimization and Comparison of Myocardial T1 Techniques at 3T in Patients With Aortic Stenosis

BACKGROUND: T1 mapping is an emerging cardiac magnetic resonance imaging technique to assess diffuse myocardial fibrosis. However, the optimal approach remains uncertain, especially at 3T. We sought to optimize and compare the most widely-used techniques. METHODS: T1 mapping was performed at 3T using the modified-look-locker-inversion sequence in 20 healthy volunteers and 20 patients with aortic stenosis (AS). Pre- and post-contrast myocardial T1, the partition coefficient (λ) and interstitial contrast volume of distribution (Vd) were assessed. After establishing the optimal time-point and myocardial region for analysis, we compared the reproducibility of these T1 measures and their ability to differentiate asymptomatic patients with AS from healthy volunteers. RESULTS: There was no segmental variation across the ventricle in any of the T1 measures evaluated. λ and Vd did not vary with time, while post-contrast T1 was relatively constant between 15-30min. Thus, mid-cavity myocardium at 20min was used for subsequent analyses. Vd displayed excellent intra-, inter-observer, and scan-rescan reproducibility (intra-class correlation coefficients (ICC) 1.00, 0.97 and 0.96 respectively), as did λ (ICC 0.99, 0.94, 0.93 respectively). Moreover, Vd and λ were both higher in patients with AS compared to controls (Vd 28.3±1.7 versus 26.0±1.6%, p <0.001; λ 0.46±0.03 versus 0.44±0.03, p =0.02) (Figure 1A). By comparison, scan-rescan reproducibilities for pre- and post-contrast myocardial T1 values were only modest (ICC 0.72 and 0.56) with no differences observed between cases and controls (both p>0.05) (Figure 1B). CONCLUSIONS: We recommend Vd and λ to assess diffuse myocardial fibrosis at 3T based upon their superior reproducibility and ability to identify disease states.

Newer Imaging Modalities in the Assessment of Heart Function in Single Ventricle Hearts

The limitations of geometry assumptions in 2-dimensional echocardiographic assessment of the single ventricle (SV) have been overcome by recent advances in 3-D echocardiography. Improved reproducibility for measuring ventricular volumes and ejection fraction using 3-D echocardiography makes it ideally suited for serial monitoring of SV systolic function and should be considered in routine echocardiography imaging protocols for SV. The moderate correlation of Doppler derived E/e' ratio with invasive ventricular end diastolic pressure in SV, suggests it might be useful in the assessment of SV diastolic function. Speckle tracking imaging is intensely studied and promises to be a simple and repeatable imaging tool for quantifying SV function. In contrast, the advances in cardiac magnetic resonance imaging techniques promise to offer insights into the pathogenesis of myocardial dysfunction in SV. Late gadolinium enhancement imaging is a robust tool in assessing macroscopic myocardial scarring and T1 mapping and stress perfusion imaging are newer modalities that might improve understanding of the mechanisms in progressive myocardial dysfunction in SV hearts.

Multiphase segmentation using an implicit dual shape prior: Application to detection of left ventricle in cardiac MRI

Cardiac magnetic resonance imaging (MRI) has been extensively used in the diagnosis of cardiovascular disease and its quantitative evaluation. Cardiac MRI techniques have been progressively improved, providing high-resolution anatomical and functional information. One of the key steps in the assessment of cardiovascular disease is the quantitative analysis of the left ventricle (LV) contractile function. Thus, the accurate delineation of LV boundary is of great interest to improve diagnostic performance. In this work, we present a novel segmentation algorithm of LV from cardiac MRI incorporating an implicit shape prior without any training phase using level sets in a variational framework. The segmentation of LV still remains a challenging problem due to its subtle boundary, occlusion, and inhomogeneity. In order to overcome such difficulties, a shape prior knowledge on the anatomical constraint of LV is integrated into a region-based segmentation framework. The shape prior is introduced based on the anatomical shape similarity between endocardium and epicardium. The shape of endocardium is assumed to be mutually similar under scaling to the shape of epicardium. An implicit shape representation using signed distance function is introduced and their discrepancy is measured in a probabilistic way. Our shape constraint is imposed by a mutual similarity of shapes without any training phase that requires a collection of shapes to learn their statistical properties. The performance of the proposed method has been demonstrated on fifteen clinical datasets, showing its potential as the basis in the clinical diagnosis of cardiovascular disease.

Defining late onset occult asymptomatic cardiotoxicity in childhood cancer survivors exposed to anthracycline therapy: a cardiac magnetic resonance imaging study

Background There are over 270,000 childhood cancer survivors in the US. Of these survivors, more than 50% have been treated with anthracyclines and are at risk of developing progressive cardiotoxicity. Novel cardiac magnetic resonance imaging (CMRI) techniques are now able to reliably detect diffuse myocardial fibrosis and changes in regional myocardial function. We hypothesized that these novel CMRI techniques will identify occult asymptomatic cardiotoxicity in a cohort of childhood cancer survivors with normal global systolic function. Methods Twenty seven long-term childhood cancer survivors between 11.8-28.8 years with a cumulative dose >240mg/ m2 (mean 363±89) and normal systolic function (SF>29%) were studied 2.4-24 years after exposure to anthracycline therapy. Patients underwent CMRI techniques to characterize changes in T1 relaxation time, left ventricular myocardial peak circumferential and longitudinal strain parameters and were analyzed using the 17-segment model. Extracellular volume (ECV) was measured in 13 subjects all of whom were late gadolinium enhancement (LGE) negative. We performed standard CMRI assessment and quantification of myocardial mass, end-systolic and end-diastolic volumes, ejection fraction, and end systolic fiber stress. Results Twenty seven of 60 planned subjects have been imaged. End systolic fiber stress was significantly increased with higher cumulative anthracycline dose (R2=0.18, p<0.03) and younger age at diagnosis (R2=0.20, p<0.02). Lower average circumferential strain magnitude (ecc) and regional changes in peak circumferential strain were seen in multiple segments despite n ormal values of global systolic function by echocardiography and CMRI (Figure1). T1 maps are depicted in Figure 1. The mean T1 values of the myocardium were not significantly different between patients and controls at 4 min (375±67ms vs.389±36, p<0.07) and 10 min (433±52 ms vs.435±36, p<0.39), but were significantly lower at 20 minutes (455±50ms vs. 487 ±44, p<0.003) (Figure 2). Low myocardial T1 at 20 minutes was significantly associated with increases in end systolic fiber stress (R2=0.7, p<0.002). Higher mean ECV was observed in patients with cumulative dose ≥400mg/m2 (0.27 vs. 0.21, p<0.05). Conclusions

A novel cardiac magnetic resonance imaging technique to evaluate left ventricular diastolic function in patients with hypertrophic cardiomyopathy

Background The temporal and spatial resolution of cardiac magnetic resonance (CMR) imaging allows precise tracking of the left ventricle (LV) atrioventricular junction (AVJ) throughout the cardiac cycle. Similar to tissue Doppler imaging in echocardiography, AVJ motion assessed by CMR reflects diastolic LV function. A prior study by our group demonstrated significant differences in the displacement and velocity of the AVJ during diastole in patients with heart failure with preserved ejection fraction compared to normal hearts. In the current study we hypothesized that diastolic left ventricular function defined by AVJ motion is abnormal in patients with hypertrophic cardiomyopathy (HCM), a group known to have altered LV relaxation properties. Methods We retrospectively identified 24 patients with known or suspected HCM and normal ejection fractions who underwent CMR as part of their clinical assessment and 14 normal control subjects. The longitudinal motion of the lateral and septal AVJs was tracked at 25 times through the cardiac cycle using the 4-chamber cine CMR view . The baseline position of the AVJ was defined at end diastole and its longitudinal displacement was measured relative to a reference line drawn between the LV apex and the midpoint of the mitral annnulus. The displacement of the AVJ in relation to its starting position at end diastole was normalized by LV length. Based on the resulting plots of AVJ position versus time in the cardiac cycle (see figure below) five motion variables were calculated: maximum longitudinal displacement (MD) of the AVJ, maximum velocity during early diastole (MVED), velocity at half-maximal displacement during early diastole (VHMDED), slope of the best fit line of displacement in diastasis (VDS), and the ratio of VDS/MVED. Data obtained in HCM patients were compared to normal control subjects using the Student t-test. Results Means and standard deviations were calculated for each of the AVJ motion variables (MD, VHMDED, MVED, VDS, VDS/MVED) for the septal (S) and lateral walls (LW) of HCM patients and normal control subjects. Lateral and septal AVJ data were directly compared to the corresponding walls in patients and controls. We found highly statistically significant differences in MD and the four CMR correlates of diastolic LV function (VHMDED, MVED, VDS, VDS/MVED) in patients with HCM compared to normal controls, as noted in the table below. Conclusions Novel CMR correlates of diastolic left ventricular function are markedly abnormal in patients with HCM. Measured at the AVJ, patients with HCM had significantly less maximal displacements, slower velocities during early diastolic filling, and higher velocities during diastasis compared to normal control subjects. The evaluation of AVJ motion by CMR may provide a new method to assess diastolic function.

Cardiac Magnetic Resonance Imaging and the Assessment of Ebstein Anomaly in Adults

No published studies have evaluated the role of cardiac magnetic resonance (CMR) imaging for the assessment of Ebstein anomaly. Our objective was to evaluate the right heart characteristics in adults with unrepaired Ebstein anomaly using contemporary CMR imaging techniques. Consecutive patients with unrepaired Ebstein anomaly and complete CMR studies from 2004 to 2009 were identified (n = 32). Volumetric measurements were obtained from the short-axis and axial views, including assessment of the functional right ventricular (RV) end-diastolic volume (EDV) and end-systolic volume. The volume of the atrialized portion of the right ventricle in end-diastole was calculated as the difference between the total RVEDV and the functional RVEDV. The reproducibility of the measurements in the axial and short-axis views was determined within and between observers. The median value derived from the short-axis and axial views was 136 ml/m(2) (range 59 to 347) and 136 ml/m(2) (range 63 to 342) for the functional RVEDV, 153 ml/m(2) (range 64 to 441) and 154 ml/m(2) (range 67 to 436) for the total RVEDV, 49% (range 32% to 46%) and 50% (range 40% to 64%) for the functional RV ejection fraction, respectively. The axial measurements demonstrated lower intraobserver and interobserver variability than the short-axis approach for all values, with the exception of the intraobserver functional RVEDV and interobserver total RVEDV for which the limits of agreement and variance were not significantly different between the 2 views. In conclusion, measurements of right heart size and systolic function in patients with Ebstein anomaly can be reliably achieved using CMR imaging. Axial imaging appeared to provide more reproducible data than that obtained from the short-axis views.

Optimizing Cardiac MR Imaging: Practical Remedies for Artifacts

With ongoing technical advances in magnetic resonance (MR) imaging, the clinical demand for cardiac MR evaluations has been increasing. Cardiac MR imaging techniques have evolved from traditional spin-echo sequences to breath-hold spoiled gradient-echo and balanced steady-state free precession sequences. The most recently developed techniques allow evaluation of myocardial function, perfusion, and viability; coronary angiography; flow quantification; and standard morphologic assessments. However, even with the most sophisticated acquisition techniques, artifacts commonly occur at cardiac MR imaging. Knowledge of the origin, imaging appearance, and significance of these artifacts is essential to avoid misinterpreting them as true lesions. Some artifacts are caused by simple errors in positioning of the patient, coil, or electrocardiographic leads; radiofrequency interference from nearby electronic equipment; or metallic objects within the magnetic field. Others are directly related to a specific MR imaging sequence or technique. Accelerated imaging techniques such as parallel imaging, which are used to shorten acquisition and breath-hold times in cardiac evaluations, are particularly vulnerable to artifacts. If an artifact severely degrades image quality, the acquisition should be repeated with appropriate adjustments to decrease or eliminate the problem.

Location of Q-wave myocardial infarction in the era of cardiac magnetic resonance imaging techniques: An update

Autonomic nervous system (ANS) is governed by complex interactions arising from feedback loops of nonlinear systems that operate over a wide range of temporal and spatial scales, enabling the organism to adapt to stress, metabolic changes and diseases. This study is aimed to assess multifractal and nonlinear characteristics of the ANS during ischemic events provoked by a prolonged percutaneous coronary intervention (PCI) procedure. Eighty-seven patients from the STAFF III database were used. Patients were classified into 2 groups: (1) with prior myocardial infarction (MI) and (2) without MI (noMI). R–R signals during three 3-min stages of the procedures were analyzed using multifractal and surrogate data techniques. Multifractal indices increased significantly from the pre-inflation stage to the post-deflation stage. These variations were more marked for the noMI group. Multifractal changes significantly correlated with both the decreased parasympathetic and the increased sympathetic modulations accounted by classical linear indices. Multifractal measures resulted to be a more powerful indicator than linear HRV indices in quantifying the ischemia-induced changes. Right coronary artery (RCA) occlusions provoke greater multifractal reactions throughout the PCI procedure. Our findings suggest reduced complex multifractal and nonlinear reactions of ANS activity in patients with prior MI in comparison to the noMI group, possibly due to degradation in the complexity of control mechanism of heart rate generation.

Location of Q-wave myocardial infarction in the era of cardiac magnetic resonance imaging techniques

gold standard technique that provides precise identification of infarcted myocardium in vivo. It is therefore appropriate to use CE-CMR verification of the accuracy of electrocardiographic (ECG) localization of infarction. The correlation between abnormal Qwaves in various ECG leads and the affected left ventricular (LV) walls has been documented in the literature. Therefore, it is necessary to develop a new terminology by considering the relationships between changes in particular leads and infarct location as documented by CE-CMR. In 2005, a consensus group sponsored by the International Society of Noninvasive Cardiology met in Barcelona to develop a document containing this new terminology, which had been published in Circulation. The left ventricle is generally divided into approximately equal halves: the anteroseptal zone perfused by the left anterior descending (LAD) coronary artery as well as its branches and the inferolateral zone perfused by either the right or the circumflex coronary arteries. Fig. 1 shows the correspondence between the 17 segments of the left ventricle and their supplying coronary arteries. Variation among individuals in coronary anatomy affects the relationship between coronary arteries and myocardial segments. Pathologic Q waves have been defined by classic criteria and by criteria (Selvester criteria) documented by computer application. Infarcts identified using both of these criteria sets have now been studied using the CE-CMR as a gold standard. Recently, Q-wavemyocardial infarction (MI) patterns, using the classic criteria that match better with the infarcted areas, have been defined, and the correlation of these ECG criteria with their corresponding infarction areas detected by CE-CMR has been reported to be high (86% overall concordance). Preliminary studies on the Selvester criteria of the infarcts in the anteroseptal half of the left ventricle have also documented a high correlation with CMR assessment.

Cardiac Magnetic Resonance Imaging and Transesophageal Echocardiography in Patients With Transcatheter Closure of Patent Foramen Ovale

We studied the value of cardiac magnetic resonance imaging (CMRI) before and after closure of patent foramen ovale (PFO) in patients with cryptogenic ischemic events. Cardiac magnetic resonance imaging is a powerful noninvasive tool for detailed assessment of cardiac anatomy and function. The relevance of CMRI compared with transesophageal echocardiography (TEE) in patients undergoing transcatheter PFO closure has not been evaluated so far. Contrast-enhanced CMRI and TEE were performed in 75 patients before and after PFO closure. Twelve months after PFO closure, both imaging techniques were repeated in 61 patients with contrast application. To determine provokable atrial right-to-left shunting in CMRI, we applied a contrast-enhanced perfusion imaging technique. Detection of atrial septal aneurysm (ASA) was achieved by means of a high-resolution cine imaging technique. Before PFO closure, ASA was seen with CMRI in 28 of 75 cases (37.3%), compared with 47 of 75 (62.7%) cases using TEE. There were a total of 211 CMRI studies with a corresponding TEE performed in 75 patients. No shunt was present in 107 of 211 studies with both techniques. Contrast-enhanced right-to-left shunting was detected by CMRI in 48 of 72 (66.6%) cases with moderate or severe shunts seen with TEE, but only in 6 of 32 (18.8%) studies with mild shunts with TEE. Anomalous venous returns were excluded in all patients. In two patients, coronary anomalies were seen. The present CMRI technique is inferior to TEE in detection of contrast-enhanced right-to-left shunting and identification of ASA.

A comparison of left ventricular mass between two-dimensional echocardiography, using fundamental and tissue harmonic imaging, and cardiac MRI in patients with hypertension

Purpose: To compare left ventricular mass (LVM) as measured by two-dimensional (2D) echocardiography using two different calculation methods: truncated ellipse (TE) and area length (AL), in both fundamental and tissue harmonic imaging frequencies, to LVM as measured by, the current gold standard, cardiac magnetic resonance imaging (MRI). Turbo gradient echo (TGE) pulse sequence was utilized for MRI. Materials and methods: Thirty-two subjects with history of hypertension were recruited. The images were acquired, contours were traced and the LVM was calculated for all four different echocardiography methods as well as for the cardiac MRI method. The intra-observer variabilities were calculated. The four different echocardiography methods were compared to cardiac MRI using the method described by Bland and Altman. Results: Twenty-five subjects had adequate paired data sets. The mean LVM as measured by cardiac MRI was 162±55 g and for the four different echocardiography methods were: fundamental AL 165±55 g, harmonic AL 168±53 g, fundamental TE 148±50 g, harmonic TE 149±45 g. The intra-observer variability for cardiac MRI method, expressed as bias ± 1 standard deviation of the difference (S.D.D.), was 2.3±9.2 g and for the four different echocardiography methods were: fundamental TE 0.4±26.8 g, fundamental AL 0.6±27.0 g, harmonic TE 6.7±21.8 g, harmonic AL 6.4±22.9 g. The mean LVM for the AL method was closest to the cardiac MRI technique, while TE underestimated LVM. The 95% limits of agreement were consistently wide for all the 2D echocardiography modalities when compared with the cardiac MRI technique. Conclusion: The intra-observer variability in measurements of 2D echocardiographic LVM, together with the wide limits of agreement when compared to the gold standard (cardiac MRI) are sufficiently large to make serial estimates of LVM, of single patients or small groups of subjects, by 2D echocardiography, unreliable.

Imaging myocardial strain

Measuring the local mechanical activity of the heart has lagged behind the measurement of electrical activity due to a lack of measurement tools. Myocardial wall motion abnormalities have been studied for years in the context of regional ischemia. Implanted beads and screws have been used to measure the mechanical activity of the heart in a few isolated regions. Over the past decade, precise and accurate methods for measuring local three-dimensional (3-D) myocardial motion with magnetic resonance imaging (MRI) have been developed using presaturation tagging patterns, velocity encoded phase maps, and displacement encoded phase maps. Concurrently, the quality of cardiac MRI images improved greatly with the use of customized receiver coils and the speed of acquisition has increased dramatically with the advent of undersampling techniques and new generations of MR machines with faster switching gradient coils. The use of these cardiac MRI techniques to produce an image of the local deformation of the heart in the form of a myocardial strain image is described. Using these images, the "mechanical activation" of the heart are defined, that is, the time of onset of contraction. A map of the mechanical activation over the heart is a direct analogy to an electrical activation map of the heart.

Clinical management of β-Thalassemia major

Management of patients with β-thalassemia is based on adequate, safe blood transfusions (free of transfusion-transmitted diseases) and prevention of iron overload. Iron overload causes multiple endocrinopathies, contributes to osteoporosis, and is the cause of cardiac disease. Cardiac disease, secondary to iron damage, causes death in developed countries as a result of noncompliance to deferoxamine from the third decade of life. In underdeveloped countries, cardiac death starts from 12 years of age, due to nonavailability of deferoxamine. With the emergence of the advanced cardiac magnetic resonance imaging technique, early diagnosis of heart iron will allow the currently available iron-chelating agents (oral and parenteral) to be used in an innovative way to improve the quality of life and improve survival of patients with β-thalassemia.

Clinical aspects of transfusional iron overload

Most of our knowledge of transfusional iron overload has been obtained from patients with β‐thalassemia major (TM). Iron overload causes multiple endocrinopathies presenting in the first decade of life with growth disturbance, followed by thyroid dysfunction. By the second decade of life, carbohydrate metabolism is disturbed in up to 25% of patients and failure of sexual development, even in well‐chelated patients, appears as the commonest endocrine complication. In the third and fourth decades of life, osteopenia and osteoporosis are the causes of morbidity in over 50% of well‐chelated and transfused TM patients. Cardiac disease, secondary to iron damage, causes death in developed countries as a result of noncompliance to desferrioxamine mesylate (DFX) from the third decade of life. In underdeveloped countries, cardiac death starts from 12 years of age, due to the nonavailability of the iron chelating agent DFX. With the emergence of the advanced cardiac magnetic resonance imaging technique, early diagnosis of heart iron will allow the use of parenteral and oral chelators in an innovative way to improve survival and the quality of life for TM patients.

Magnetic resonance microimaging for noninvasive quantification of myocardial function and mass in the mouse.

The purpose of this work was to develop high-resolution cardiac magnetic resonance imaging techniques for the in vivo mouse model for quantification of myocardial function and mass. Eight male mice were investigated on a 7-Tesla MRI scanner. High-quality images in multiple short axis slices (in-plane resolution 117 microm2, slice thickness 1 mm) were acquired with an ECG-gated cine sequence. Left ventricular end-diastolic and end-systolic volumes and mass were calculated from segmented slice volumes. There was precise agreement of left ventricular mass determined ex vivo and by MRI. Intraobserver (5%) and interobserver (5%) variability of in vivo MR measurements were low.

Magnetic resonance imaging of chronic myocardial infarcts in formalin-fixed human autopsy hearts.

In post-myocardial infarction patients, three-dimensional structure of the infarct as well as infarct size are likely to be important factors affecting mortality, cardiac function, and arrhythmias. Current morphological methods for determining three-dimensional infarct structure in autopsied hearts are inexact and time consuming. The cardiac magnetic resonance imaging techniques used in living patients have shown potential in determining infarct size and structure but have limited resolution for morphometric postmortem studies. The recent development of magnetic resonance microscopy raises the possibility that three-dimensional infarct structure can be quantified at microscopic levels in autopsied hearts. The purpose of this study was to determine the ability of magnetic resonance imaging at different spatial resolutions to differentiate infarcted from noninfarcted myocardium. Magnetic resonance imaging was performed at 2.0 T on cross sections taken from 10 autopsied hearts containing old myocardial infarcts. T1 was derived from six images with repetition times (TRs) for each image ranging from 100 to 3200 milliseconds. T2 was derived from multi-echo images with echo times (TEs) ranging from 10 to 60 milliseconds. Resolution was approximately 400 x 400 microns in 2-mm-thick slices. Sites of infarcted and noninfarcted tissue were identified from histological sections taken from each slice, and the T1 and T2 values of these sites were obtained. Microscopic images were acquired with voxels of 100 x 100 x 625 microns, representing tissue volumes more than 1000-fold smaller than conventional clinical images. In all cases, T1 of infarcted tissue (459 +/- 266 milliseconds, mean +/- SD) was greater than that of noninfarcted tissue (272 +/- 163 milliseconds). Also, in all cases, T2 of infarcted tissue (49 +/- 14 milliseconds) was greater than that of noninfarcted tissue (35 +/- 8 milliseconds). T1 and T2 values for infarcted tissue are significantly different from those of noninfarcted tissue (P < .001). Based on these findings, it should be possible to develop techniques to perform three-dimensional imaging and quantitation of infarcts with a resolution of 400 microns or less. When volumetric three-dimensional imaging was performed using a T1-weighted sequence, the resulting 256(3) arrays supported isotropic resolution at 400 microns (voxel volume, 0.064 mm3). Subsequent volume rendering using a compositing algorithm clearly shows the infarcted areas in three dimensions. The techniques demonstrate the potential for quantitative three-dimensional cardiac morphometry using magnetic resonance imaging.