Differentiation of heart failure related to dilated cardiomyopathy and coronary artery disease using gadolinium-enhanced cardiovascular magnetic resonance.

BACKGROUND: Heart failure treatment depends partly on the underlying cause of the disease. We evaluated cardiovascular magnetic resonance (CMR) for the problem of differentiating dilated cardiomyopathy (DCM) from left ventricular (LV) dysfunction caused by coronary artery disease (CAD). METHODS AND RESULTS: Late gadolinium enhancement with CMR was performed in 90 patients with heart failure and LV systolic dysfunction (63 patients with DCM and unobstructed coronary arteries and 27 with significant CAD at angiography). We also studied 15 control subjects with no coronary risk factors and/or unobstructed coronary arteries. None (0%) of the control subjects had myocardial gadolinium enhancement; however, all patients (100%) with LV dysfunction and CAD had enhancement, which was subendocardial or transmural. In patients with DCM, there were 3 findings: no enhancement (59%); myocardial enhancement indistinguishable from the patients with CAD (13%); and patchy or longitudinal striae of midwall enhancement clearly different from the distribution in patients with CAD (28%). CONCLUSIONS: Gadolinium CMR is a powerful technique to distinguish DCM from LV dysfunction related to CAD and yields new insights in DCM. These data suggest that using the coronary angiogram as the arbiter for the presence of LV dysfunction caused by CAD could have lead to an incorrect assignment of DCM cause in 13% of patients, possibly because of coronary recanalization after infarction. The midwall myocardial enhancement in patients with DCM is similar to the fibrosis found at autopsy; it has not previously been visualized in vivo and warrants further investigation. CMR may become a useful alternative to routine coronary angiography in the diagnostic workup of DCM.

Estimation of left ventricular mass and infarct size from nitrogen-13-ammonia PET images based on pathological examination of explanted human hearts.

The purpose of this study was to develop a technique to quantify left ventricular mass and infarct size in chronic ischemic heart disease from PET images based on correlation with pathological examination of explanted human hearts. Fourteen hearts from patients with cardiomyopathy who had 13N-ammonia scans prior to orthoptic heart transplantation were studied. Accurate estimation of the relative infarct size was possible in patients with a well-delineated, nearly transmural infarct (r = 0.93, y = 1.1x - 0.7, n = 11). Both absolute and relative infarct mass measurements on PET images correlated well with pathological measurements. We identified a population of patients with patchy interstitial or subendocardial scarring with globally reduced perfusion, for which the infarct size could not be estimated using the criteria derived for the patients with well-delineated infarcts.

Alterations in pulmonary artery flow patterns and shear stress determined with three-dimensional phase-contrast magnetic resonance imaging in Fontan patients.

OBJECTIVE: This study compares in vivo pulmonary blood flow patterns and shear stresses in patients with either the direct atrium-pulmonary artery connection or the bicaval tunnel connection of the Fontan procedure to those in normal volunteers. Comparisons were made with the use of three-dimensional phase contrast magnetic resonance imaging. METHODS: Three-dimensional velocities, flows, and pulmonary artery cross-sectional areas were measured in both pulmonary arteries of each subject. Axial, circumferential, and radial shear stresses were calculated with the use of velocities and estimates of viscosity. RESULTS: The axial velocities were not significantly different between subject groups. However, the flows and cross-sectional areas were higher in the normal group than in the two patient groups in both pulmonary arteries. The group with the bicaval connection had circular swirling in the cross section of both pulmonary arteries, causing higher shear stresses than in the controls. The disorder caused by the connection of the atrium to the pulmonary artery caused an increase in some shear stresses over the controls, but not higher than those found in the group having a bicaval tunnel. CONCLUSIONS: We found that pulmonary flow was equally reduced compared with normal flow in both patient groups. This reduction in flow can be attributed in part to the reduced size of the pulmonary arteries in both patient groups without change in axial velocity. We also found higher shear stress acting on the wall of the vessels in the patients having a bicaval tunnel, which may alter endothelial function and affect the longevity of the repair.

Quantitative imaging of renal blood flow and function.

Noninvasive renal blood flow quantitation has been historically difficult, although radionuclide imaging methods for measuring related parameters of renal function such as glomerular filtration rate and effective renal plasma flow have been successful. Radionuclide methods have long played an important role in the evaluation of renal function, but recent advances in other modalities such as positron emission tomography (PET), computed tomography (CT), and magnetic resonance imaging (MRI) have the potential to provide information not available with nuclear medicine techniques. The high spatial resolution provided by these modalities, coupled with dynamic imaging of contrast agents or radioactive tracers, potentially could allow detailed clinical evaluation of regional renal function and blood flow. A specialized MR technique, diffusion-weighted imaging, also shows promise for providing information not otherwise available concerning the renal microcirculation. This report provides a brief review of the available clinical techniques for the evaluation of renal blood flow and function as well as new methods under investigation.

Magnetic resonance perfusion/diffusion imaging of the excised dog kidney.

RATIONALE AND OBJECTIVES: The authors developed a model of tissue capillary beds applicable to perfusion/diffusion imaging with magnetic resonance imaging (MRI). The model consists of a formalin-fixed excised dog kidney attached to a variable speed pump. With this system, it is possible to perfuse the kidney at selected rates. METHODS: Using the intravoxel incoherent motion model (IVIM), the apparent diffusion coefficient (ADC), diffusion coefficient (D), and perfusion fraction (f) were computed for a region of interest (ROI) in the renal cortex and in the medulla of seven kidneys, one of which was injected with a vasodilator before fixation. ADC and D values were computed for both cortex and medulla. These values were normalized to zero flow and plotted against renal perfusion. The perfusion fraction f was expressed in percent and was not normalized to zero flow. RESULTS: Normalized ADC and f were correlated with tissue perfusion rates using the Spearman rank-sum test (n = 18, rs greater than 0.5, P less than or equal to .02 for the standard preparation in both cortex and medulla), whereas normalized D (rs much less than 0.5) was uncorrelated for both preparations in cortex and medulla. CONCLUSIONS: The isolated perfused dog kidney is a useful model of tissue capillary beds for perfusion imaging technique development. The perfusion/diffusion-related parameters ADC and f increase as flow increases in the tissues, whereas D does not.

Magnetic resonance angiography techniques.

After a radio frequency pulse, the decay of the magnetic resonance (MR) signal is described by two relaxation processes, T1 and T2. T1 describes the rate at which the magnetization realigns itself along the external magnetic field direction (ML), and T2 describes the rate of decay of the magnetization component along the transverse axis (MT). Magnetic resonance angiography (MRA) sequences have been developed that encode flow as changes in the apparent T1 or T2 of the moving blood relative to stationary tissues. MRA sequences typically use either time-of-flight (TOF) techniques to encode T1 or phase-contrast techniques to encode T2. TOF techniques encode flow as an apparent T1 shortening through the wash-in of fully relaxed blood from outside the image volume. The shorter T1 produces an enhancement of vascular structures relative to stationary tissues. TOF methods may use either sequential two-dimensional, three-dimensional, or multi-slab three-dimensional imaging sequences to produce a three-dimensional MRA data set. Phase-contrast methods use additional magnetic field gradients to encode flow as shifts in the phase of MT. Both TOF and phase-contrast methods use maximum intensity projection (MIP) images displayed in a cine format to aid in the visualization of three-dimensional vascular structures.

MRI complements standard assessment of right ventricular function after lung transplantation.

BACKGROUND: Changes in right ventricular mass and ejection fraction after single-lung transplantation for pulmonary hypertension are poorly understood. METHODS: To complement functional data provided by echocardiography, radionuclide ventriculography, and right heart catheterization, magnetic resonance imaging was used to assess right ventricular function in 5 single-lung transplant recipients with preoperative pulmonary hypertension and right ventricular dysfunction (right ventricular ejection fraction, 0.21 +/- 0.09). The right and left ventricular mass, ejection fraction, and mass ratio (left ventricular mass/right ventricular mass) were calculated from the magnetic resonance images. RESULTS: The mean pulmonary artery pressure fell from 72 +/- 18 to 21 +/- 8 mm Hg after transplantation. At 3 months after transplantation both the left ventricular and right ventricular ejection fractions approached normal values, as shown by both radionuclide ventriculography and magnetic resonance imaging, but the right ventricular mass remained abnormally high with slightly low mass ratios. By 1 year both the left ventricular and right ventricular masses had regressed to normal with near-normal mass ratios. CONCLUSIONS: Right ventricular performance returns to nearly normal early after transplantation, but the right ventricular mass regresses over a more prolonged time. Cine magnetic resonance imaging provides a noninvasive means of assessing changes in right ventricular function and mass after lung transplantation.

Noninvasive modalities. Cardiac MR imaging.

As outlined in this article, the strength of MR imaging is that it can provide flow, function, and in some cases metabolic data in a single examination, independent of patient body habitus. Future prospects for real-time imaging and in vivo mapping of fiber orientation promise further advances in our understanding of the structure-function relationship in diastole. Many of the MR imaging methods that have been developed for cardiovascular imaging are now mature and available on state-of-the-art scanners. Although MR imaging can provide detailed characterization of diastolic function, there is a paucity of clinical results which could lead to use guidelines. When more clinicians have access and become familiar with MR imaging, and the type of information that it can provide, clinical trials will be needed to establish the role of MR imaging for evaluation of diastolic function. In the meantime, MR imaging remains an excellent research tool for this application and will help yield further insights into the pathophysiology of diastolic dysfunction.

Application of linear optimization techniques to MRI phase contrast blood flow measurements.

The goal of this study was to use linear optimization techniques as a systematic method of cine phase contrast pulse sequence design and to apply this technique to the measurement of blood flow in vivo. The optimized waveforms were validated in a constant flow phantom with average velocities ranging from 5 to 50 cm/s. The same optimized sequence was also run in a segmented k-space variation with five phase encoding lines per segment. The magnetic resonance (MR) derived velocity measurements were accurate over the entire range of velocities tested (p < .05) in both cases. The same optimized pulse sequence was applied to the measurement of flow in main pulmonary artery of five normal volunteers and compared with stroke volumes and cardiac outputs calculated from right ventricular volume measurements. These measurements showed a mean difference between the MR phase contrast calculated stroke volume and the volumetric stroke volume measurement of 9.8 +/- 11.6%. The mean difference between the calculated phase contrast cardiac output and the volumetric cardiac output was 4.4 +/- 10%. These results imply that optimization techniques are an efficient method for designing cine phase contrast pulse sequences.

The plain chest radiograph and clinical management of pulmonary edema in pregnancy.

OBJECTIVE: To evaluate the reproducibility of radiographic quantification of pulmonary edema on the supine plain chest radiograph and to correlate the radiographic appearance of edema with the clinical assessment and treatment of pulmonary edema. STUDY DESIGN: Retrospective, blind, descriptive study of 24 women with singleton pregnancies in the last trimester selected because of a clinical question of pulmonary edema. RESULTS: Interobserver variability between radiologists resulted in an average weighted kappa of .71 in grading edema on a 0-3 scale where 0 = no edema and 3 = alveolar flooding. The vascular pedicle (a measure of central circulating volume) was larger among patients who received furosemide (63.4 mm) than those who did not (57.0 mm) (P = .01). The vascular pedicle was also larger among patients receiving tocolytics or steroids (62.8 mm) than those who did not (56.0 mm) (P = .01). The radiographic edema score tended to be lower in patients who received tocolytics and steroids (P = .05). The other correlations were not significant. CONCLUSION: Radiographic assessment of pulmonary edema shows fair to good reproducibility, but the clinical correlations are modest. A wider understanding of the wealth of physiologic information available on the plain chest radiograph may prove invaluable in understanding the clinical course and treatment of these patients.

TAGASIST: a post-processing and analysis tools package for tagged Magnetic Resonance Imaging.

The Magnetic Resonance Imaging technique myocardial tagging allows the tracking and measurement of local parameters of heart wall motion. Tagging provides detailed information about regional cardiac function never before available with non-invasive techniques. The growth of this technique has been limited in part by the availability of post-processing tools. We introduce the TAGged cine AnalySIS Tools package (TAGASIST) for the processing of images from this technique. TAGASIST includes a graphical user interface for image segmentation, kinematic analysis, plotting of regional averages as well as multiple subjects (or patient populations) simultaneously, statistical analysis, and a database of all studies processed.

MR coronary angiography: 2001 update.

Cardiovascular magnetic resonance (CMR) has developed multiple techniques that have made it possible to overcome the substantial difficulties in imaging coronary arteries. Tortuous small coronary arteries are imaged in 3D-volume data sets. Cardiac motion is reduced by diastolic gating with ultra-fast sequences. Respiration is suppressed by breath-holding or respiratory gating. Signal-to-noise can be increased with contrast agents. In clinical trials CMR has been successfully used to assess coronary artery stenoses, coronary artery bypass grafts, and anomalous coronary arteries. Recent developments in steady state imaging, volume selective imaging with tracking, parallel imaging techniques, vessel wall imaging, and intravascular contrast agents may soon enable CMR of the coronary arteries to become an effective and widespread clinical tool.

Evaluation of an image-based tracking workflow using a passive marker and resonant micro-coil fiducials for automatic image plane alignment in interventional MRI.

In this paper, an original workflow is presented for MR image plane alignment based on tracking in real-time MR images. A test device consisting of two resonant micro-coils and a passive marker is proposed for detection using image-based algorithms. Micro-coils allow for automated initialization of the object detection in dedicated low flip angle projection images; then the passive marker is tracked in clinical real-time MR images, with alternation between two oblique orthogonal image planes along the test device axis; in case the passive marker is lost in real-time images, the workflow is reinitialized. The proposed workflow was designed to minimize dedicated acquisition time to a single dedicated acquisition in the ideal case (no reinitialization required). First experiments have shown promising results for test-device tracking precision, with a mean position error of 0.79 mm and a mean orientation error of 0.24°.

The range of normal values of cardiovascular structures in infants, children, and adolescents measured by magnetic resonance imaging.

Magnetic resonance imaging (MRI) is a powerful diagnostic technique and research tool for assessment of congenital heart disease due to its ability to accurately assess anatomy, function, and flow in any orientation in the thorax. However, little data exist on normative reference values for cardiac structures, except in small study populations, and even fewer data exist for pediatric populations. In this review, MRI acquisition and analysis methods for assessment of aortic size, pulmonary artery size, and right and left ventricular function, volume, and mass are presented along with reference data obtained in pediatric populations by MRI. Where MRI data are not available, reference data obtained by echocardiography or angiography are included.

[Determining heart muscle perfusion by magnetic resonance tomography progressing to clinical application]. / Bestimmung der Herzmuskelperfusion mittels Magnetresonanztomographie auf dem Weg zur klinischen Anwendung.

Magnetic resonance imaging detects the flow of contrast-enhanced blood and even allows the quantitative assessment of myocardial perfusion. The clinical application of this method is being held back by the difficulties in image evaluation and the limitation of standard techniques to the acquisition of a single slice per heart beat cycle. Recent developments in scanner hardware as well as in image acquisition techniques open up the possibility of assessing myocardial perfusion over the entire heart with a spatial resolution in the range of 2 mm. As an example of such a new scanning strategy, a segmented gradient-echo recalled echo planar imaging sequence with preceding saturation is discussed and results in a patient with an infarction are presented. The clinical use of perfusion assessment covering the entire heart for the diagnosis of coronary artery disease is enhanced by the flexibility of magnetic resonance imaging for the assessment of functional cardiac parameters.

Contrast-enhanced coronary MRA.

Coronary angiography with magnetic resonance imaging (MRI) has long been a goal for bringing cardiac MRI into clinical use for diagnosis of coronary artery disease. In this paper, the fundamental problems of respiratory and cardiac motion, signal-to-noise ratio, and contrast-to-noise ratio are discussed in reference to implications for coronary imaging strategies. Various methods that have been proposed to improve signal-to-noise and contrast-to-noise ratios in MR coronary imaging are presented with an emphasis on the role of T1-shortening contrast agents, both extracellular and intravascular. Although much progress has been made in recent years in techniques for imaging the coronary arteries, ultimate clinical success remains unproved. Success will depend on synergistic developments in MR acquisition techniques, respiratory compensation methods, post-processing techniques, and contrast agents to develop a workable solution for reliable coronary imaging across a wide range of patients. J. Magn. Reson. Imaging 1999;10:703-708.