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Biomedical subjects

L Axel

Publications and source records attributed to L Axel.

At least 55 records · Page 3Linked to original sources
PubMed1994

Intramural myocardial shortening in hypertensive left ventricular hypertrophy with normal pump function.

BACKGROUND: In hypertensive left ventricular hypertrophy (LVH), intrinsic myocardial systolic function may be normal or depressed. Magnetic resonance tagging can depict intramural myocardial shortening in vivo. METHODS AND RESULTS: Tagged left ventricular magnetic resonance images were obtained in 30 hypertensive subjects with LVH (mean LV mass index, 142 +/- 41 g/m) and normal ejection fraction (mean, 64 +/- 9%) using spatial modulation of magnetization. In 26 subjects, circumferential myocardial shortening (%S) was compared with results obtained in 10 normal subjects at endocardium, midwall, and epicardium on up to 4 short-axis slices each. Similarly, in 10 subjects, midwall long-axis shortening at basal, midventricular, and apical sites was compared with results obtained in 12 normal volunteers. Circumferential %S was reduced in hypertensive subjects. Mean shortening was 29 +/- 6% at the endocardium in hypertensive subjects versus 44 +/- 6% in normal subjects (P = .0001); 20 +/- 6% at the midwall versus 30 +/- 6% (P = .0001); and 13 +/- 5% at the epicardium versus 21 +/- 5% (P = .0002). However, the transmural gradient in percent shortening from endocardium to epicardium in hypertensive subjects paralleled that in normal subjects. The normal base-to-apex gradient in circumferential %S was absent in LVH. In contrast to normal subjects, circumferential %S showed regional heterogeneity in hypertensive subjects, being maximal in the lateral wall and least in the inferior wall. Longitudinal shortening was also uniformly depressed in hypertensive subjects: 10 +/- 9% at the base versus 21 +/- 6% in normal subjects (P = .0001); 14 +/- 8% at the midventricle versus 18 +/- 3% (P = .03); and 14 +/- 8% at the apex versus 18 +/- 4% (P = .04). CONCLUSIONS: In hypertensive LVH with normal pump function, intramural circumferential and longitudinal myocardial shortening are depressed.

Female↗
PubMed1994

Two-dimensional left ventricular deformation during systole using magnetic resonance imaging with spatial modulation of magnetization.

BACKGROUND: Myocardial tissue tagging with the use of magnetic resonance imaging allows noninvasive regional analysis of heart wall motion and deformation. However, any evaluation of the effect of disease or treatment requires a baseline reference of normal values and variation. We studied the two-dimensional motion of material points imaged within the left ventricular wall using spatial modulation of magnetization (SPAMM) in 12 normal human volunteers. METHODS AND RESULTS: Five parallel short-axis and five parallel long-axis slices were acquired at five times during systole. SPAMM tags were generated at end diastole using a 7-mm grid. Intersection point data were analyzed for displacement, rotation, and torsion, and triangles of points were analyzed for local rotation and principal strains. Short-axis displacement was the least in the septum for all longitudinal levels (P < .001). Torsion about the long axis was uniform circumferentially because of the motion of the centroids used to reference the rotation. In the long-axis images, the base displaced longitudinally toward the apex, with the posterior wall moving farther than the anterior wall (13.4 +/- 2.2 versus 9.7 +/- 1.8 mm, P < .001) in this direction. The largest principal strain (maximum lengthening) was approximately radially oriented in both views. In the short-axis images, the minimum principal strain (maximum shortening) increased in magnitude toward the apex (P < .001) with little circumferential variation, except at midventricle, where the anterior wall showed greater contraction than the posterior wall (-0.21 +/- 0.03 versus -0.19 +/- 0.02, P < .02). CONCLUSIONS: Consistent regional variations in deformation are seen in the normal human heart. Displacement and maximum shortening strains are well characterized with two-dimensional magnetic resonance tagging; however, higher-resolution images will be required to study transmural variations.

Adult↗
PubMed1994

Regional heterogeneity of function in hypertrophic cardiomyopathy.

BACKGROUND: In patients with hypertrophic cardiomyopathy (HCM), left ventricular ejection performance may be normal while segmental myocardial function is distinctly abnormal. The advent of magnetic resonance tissue tagging has allowed the noninvasive evaluation of intramyocardial segmental shortening in vivo in a topographic and temporal manner. METHODS AND RESULTS: Ten patients with HCM documented by echocardiography and 10 healthy volunteers were studied with magnetic resonance tissue tagging by spatial modulation of magnetization. Percent circumferential myocardial shortening (%S) was compared at endocardium, midwall, and epicardial levels at four regions around the left ventricular short axis and from four short axis slices from apex to base at four or five time intervals during systole. In 8 patients and 8 control subjects, longitudinal shortening was evaluated within the septum and the lateral free wall at three levels from apex to base. Circumferential %S was less in HCM patients than in control subjects in the septal (13 +/- 5% versus 24 +/- 6%, P = .0002), inferior (13 +/- 5% versus 21 +/- 4%, P = .001), and anterior (17 +/- 5% versus 21 +/- 3%, P < .03) regions but not in the lateral region. Circumferential end-systolic %S was reduced in patients with HCM compared with control subjects at all levels from apex to base. The normal transmural gradient in circumferential end-systolic shortening was preserved with greatest %S at the endocardium. Most of the total cumulative circumferential shortening occurred earlier in systole in patients compared with control subjects, especially within the septum. Longitudinal end-systolic %S was depressed throughout the septum in patients compared with control subjects, most markedly at the base, but was normal in the lateral free wall. CONCLUSIONS: Circumferential myocardial segment shortening is depressed in HCM in the septum, inferior, and anterior regions and at all levels from apex to base, and much of the total cumulative shortening occurs early in systole. Longitudinal shortening is reduced in the basal septum in HCM. The heterogeneity of regional function in these patients may reflect the regional variation in the myocardial disarray and fibrosis that is characteristic of this disorder.

Adolescent↗
PubMed1994

Three-dimensional left ventricular deformation in hypertrophic cardiomyopathy.

BACKGROUND: In hypertrophic cardiomyopathy, ejection fraction is normal or increased, and force-length relations are reduced. However, three-dimensional (3D) motion and deformation in vivo have not been assessed in this condition. We have reconstructed the 3D motion of the left ventricle (LV) during systole in 7 patients with hypertrophic cardiomyopathy (HCM) and 12 normal volunteers by use of magnetic resonance tagging. METHODS AND RESULTS: Transmural tagging stripes were automatically tracked to subpixel resolution with an active contour model. A 3D finite-element model was used to interpolate displacement information between short- and long-axis slices and register data on a regional basis. Displacement and strain data were averaged into septal, posterior, lateral, and anterior regions at basal, midventricular, and apical levels. Radial motion (toward the central long axis) decreased slightly in patients with HCM, whereas longitudinal displacement (parallel to the long axis) of the base toward the apex was markedly reduced: 7.5 +/- 2.5mm (SD) versus 12.5 +/- 2.0 mm, P < .001. Circumferential and longitudinal shortening were both reduced in the septum (P < .01 at all levels). The principal strain associated with 3D maximal contraction was slightly depressed in many regions, significantly in the basal septum (-0.18 +/- 0.05 versus -0.22 +/- 0.02, P < .05) and anterior (-0.20 +/- 0.05 versus -0.23 +/- 0.02, P < .05) walls. In contrast, LV torsion (twist of the apex about the long axis relative to the base) was greater in HCM patients (19.9 +/- 2.4 degrees versus 14.6 +/- 2.7 degrees, P < .01). CONCLUSIONS: HCM patients had reduced 3D myocardial shortening on a regional basis; however, LV torsion was increased.

Adolescent↗
PubMed1993

Validation of tagging with MR imaging to estimate material deformation.

Myocardial tagging with magnetic resonance imaging is useful for non-invasive estimation of in vivo heart wall deformation. To validate the method of strain estimation and quantify the error of deformation estimates, a deformable silicone gel phantom in the shape of a cylindrical anulus was built and imaged. Four observers digitized the displacement of magnetic tags in two deformation modes: axial shear, caused by a 45 degrees rotation of the inner cylinder, and azimuthal shear, caused by a 13.5-mm longitudinal translation of the inner cylinder. In axial shear, good agreement was found between the angular displacement of stripes painted on the gel and an analytic solution. Displacement of magnetic tags also agreed with that solution. Interobserver and observer-model errors in deformation estimates were quantified for homogeneous and nonhomogeneous strain analysis. In homogeneous strain analysis, errors in point localization produced relatively large errors, which were reduced in nonhomogeneous strain analysis. Both estimates were unbiased across the range of deformations.

Artifacts↗
PubMed1993

Regional differences in function within noninfarcted myocardium during left ventricular remodeling.

BACKGROUND: The mechanisms of ventricular enlargement and dysfunction during postinfarct remodeling remain largely unknown. Although global left ventricular architectural changes after myocardial infarction are well documented, differences in function between adjacent and remote noninfarcted myocardium during left ventricular remodeling have not been investigated. These functional differences may relate to regional differences in wall stress during contraction and may contribute to chamber enlargement and global dysfunction after infarction. METHODS AND RESULTS: Anteroapical infarcts were produced in seven sheep by ligation of the mid left anterior descending coronary artery and second diagonal branch at thoracotomy. Magnetic resonance short-axis and long-axis images tagged by spatial modulation of magnetization were obtained before and 1 week, 8 weeks, and 6 months after infarction. Left ventricular volumes, mass, ejection fraction, and lengths of infarcted and noninfarcted segments were measured. Circumferential and longitudinal shortening in the subendocardium and subepicardium, wall thickness, and histopathology were assessed in infarcted segments and regions adjacent to and remote from the infarct border. We found that a difference in circumferential and longitudinal segmental shortening between adjacent and remote noninfarcted myocardium present at 1 week persisted up to 6 months after myocardial infarction. However, partial improvement of function in adjacent regions occurred during infarct healing between 1 and 8 weeks after infarction. Left ventricular volume increased up to 6 months after infarction, out of proportion to the concomitant eccentric hypertrophy, whereas the ejection fraction fell. Left ventricular dilatation late in the remodeling process was secondary to lengthening of noninfarcted segments, which were free of significant fibrosis. CONCLUSIONS: Left ventricular dilatation and eccentric hypertrophy during remodeling are associated with persistent differences in segmental function between adjacent and remote noninfarcted regions. These functional differences may reflect increased wall stress in adjacent noninfarcted regions and contribute to the global dilatation and dysfunction characteristic of left ventricular remodeling after infarction.

Animals↗
PubMed1992

Fully three-dimensional reconstruction from data collected on concentric cubes in Fourier space: implementation and a sample application to MRI.

An algorithm is proposed for rapid and accurate reconstruction from data collected in Fourier space at points arranged on a grid of concentric cubes. The Fourier transform of the object to be reconstructed is decomposed into the sum of three functions by subdividing its domain into three non-overlapping mutually orthogonal double pyramids. Each of the three functions is zero-valued outside one of the double pyramids and has values inside that double pyramid which are the same as those of Fourier transform of the object to be reconstructed at the same points. Inverse Fourier transforms of these individual functions can be calculated using the chirp z-transform. The outputs of these inverse transforms for the three functions are estimates of their values at points of the same rectangular grid. The function to be reconstructed is estimated for this grid by adding together the three inverse transforms. The whole process has computational complexity of the same order as required for the 3D fast Fourier transform and so (for medically relevant sizes of the data set) it is faster than backprojection into the same size rectangular grid. The design of the algorithm ensures that no interpolations are needed, in contrast to methods involving backprojection with their unavoidable interpolations. As an application, a 3D data collection method for MRI has been designed which directly samples the Fourier transform of the object to be reconstructed on concentric cubes as needed for the algorithm.

Algorithms↗
PubMed1992

Efficient method for selecting cardiac magnetic resonance image locations.

Selecting locations for long- and short-axis cardiac magnetic resonance images (MRIs) conventionally requires two preliminary image sets, one to find the plane of the left ventricular (LV) axis and a second to find the axis within that plane. By specifying the LV axis from landmarks on the initial image set, it is possible to go directly to short-axis images without the second set of preliminary images, thus improving efficiency and shortening the duration of the examination.

Heart↗
PubMed1992

Regional heart wall motion: two-dimensional analysis and functional imaging with MR imaging.

Analysis of the transmural distribution or nonradial components of myocardial motion has previously been possible only with use of invasive techniques such as implantation of radiopaque markers. Magnetic tagging of the heart wall in conjunction with magnetic resonance imaging allows noninvasive regional analysis of within-wall motion, including its separation into components of rigid body motion and deformation. The results of this analysis can be displayed as functional images. This provides a new tool for the study of heart wall motion that should be of use for both basic physiologic and clinical research applications.

Computer Simulation↗
PubMed1992

Three-dimensional motion and deformation of the heart wall: estimation with spatial modulation of magnetization--a model-based approach.

A method for in vivo estimation of the three-dimensional (3D) motion and deformation of the heart from tagged magnetic resonance images of the myocardium is presented. The method is based on a 3D deformable model fitted to the motion of tagged points in two views (short and long axes), which results in a comprehensive kinematic model of the dynamic geometry of the left ventricle. The method was applied to data obtained in four healthy volunteers, and data were pooled according to position within the model. Analytic modeling demonstrated that the calculated strain field was relatively invariant to the type of smoothing constraint applied; the greatest error was in the circumferential-radial shear strain. Displacement, torsion, and strain extracted from the model agreed with previous results of two-dimensional MR imaging analyses and 3D studies involving the implantation of radiopaque beads in canine myocardium. The model-driven approach provides an accurate and flexible technique for noninvasive estimation of 3D in vivo deformation of the human heart.

Adult↗
PubMed1991

Evaluation of aortic regurgitation by cardiac cine magnetic resonance imaging: planar analysis and comparison to Doppler echocardiography.

Cine magnetic resonance imaging (MRI) displays cardiac flow in cine loop fashion on multiple tomographic sections. Since laminar flow is easily distinguished from turbulent flow, cine MRI may be uniquely suited to the study of valvular regurgitation: the entire cardiac volume can be sampled and the regurgitant jet at the valve plane can be depicted. We therefore assessed aortic regurgitation (AR) by cine MRI in 35 patients and 11 normal volunteers and compared results to pulsed (n = 32) or color flow Doppler (n = 14). The extent of the flow disturbance was estimated for both cine MRI and Doppler by indexing the size of the maximal, single plane regurgitant jet area (JA) to the left ventricular (LV) area. Cine MRI JA/LV ratio compared well with pulsed (r = 0.81) and color flow (r = 0.88) Doppler; classification as mild (less than 20%), moderate (20-40%), and severe (greater than 40%) AR by both methods was identical in 43 of 46 cases with no differences of more than one grade. Overall sensitivity and specificity of cine MRI, compared to Doppler, were 94 and 95%, respectively. Cine MRI also depicted the regurgitant jet at the valve plane in 11 patients. Thus planar analysis of cine MRI images in patients with AR provides a semiquantitative assessment of the AR flow disturbance which is similar to Doppler but, in addition, can image the entire cardiac volume and the regurgitant jet at the valve plane.

Adult↗
PubMed1991

Circumferential myocardial shortening in the normal human left ventricle. Assessment by magnetic resonance imaging using spatial modulation of magnetization.

BACKGROUND: Conventional cardiac imaging methods do not depict true segmental myocardial shortening, since they cannot determine segment length between fixed points in the myocardium. METHODS AND RESULTS: We used electrocardiographically gated magnetic resonance imaging with spatial modulation of magnetization to noninvasively "tag" the myocardium with dark stripes at uniform 7-mm intervals center to center at end diastole. We then determined end-systolic stripe separation and thereby calculated circumferential shortening. When end systole was not reached in the first image series, a second temporally overlapped series starting in late systole was used to determine late-systolic shortening. Septal, anterior, lateral, and inferior segments were assessed at endocardium, midwall, and epicardium on five midventricular short-axis sections each in 10 normal volunteers. A transmural gradient in circumferential shortening was observed, with the percentage of endocardial segment shortening consistently greater than epicardial segment shortening (epicardial, 22 +/- 5%; midwall, 30 +/- 6%; and endocardial, 44 +/- 6%; p less than 0.0001 by analysis of variance). Circumferential shortening varied from apex to base with slices closer to the base of the left ventricle showing less shortening at the midwall (28 +/- 9%) and endocardium (39 +/- 6%) than more apical slices at the midwall (34 +/- 13%) and endocardium (49 +/- 9%) (p less than 0.05 and p less than 0.01, respectively, by analysis of variance). CONCLUSIONS: Transmural and longitudinal heterogeneity of circumferential shortening is present in the normal human left ventricle. Magnetic resonance imaging with spatial modulation of magnetization is a powerful new tool for assessment of circumferential shortening and provides information unobtainable with conventional imaging methods.

Adult↗
PubMed1990

Evaluation of mitral regurgitation by cine magnetic resonance imaging.

We used cine magnetic resonance imaging (MRI) to assess mitral regurgitation (MR) in 40 patients with coronary and/or valvular disease and 10 normal subjects and compared results to pulsed (n = 30) or color flow Doppler mapping (n = 20). Mitral regurgitation produced a dynamic signal void in the left atrium in systole in 15 of 16 patients with MR by pulsed Doppler and in an additional 15 of 16 patients whose MR was demonstrated by color flow Doppler. There were no false positives (sensitivity 94%, specificity 100% for both). The ratio of single-plane, maximal jet area to left atrial area was used to grade MR severity with mild defined as less than 20%, moderate between 20 and 40% and severe greater than 40%. Cine MRI classification was identical to pulsed Doppler echocardiography in 26 of 30 patients and to color flow Doppler in 16 of 20 patients with no differences of greater than 1 grade. Cine MRI consistently depicted smaller flow disturbances than pulsed Doppler (slope = 0.65) or color flow Doppler (slope = 0.60). Nonetheless, the cine MRI area ratio correlated well with pulsed Doppler (r = 0.78) and with color flow Doppler (r = 0.74). Thus, planar analysis of cine MRI in patients with MR of varying severity gave results that were similar to Doppler echocardiography. At present, for routine clinical assessment of MR, the benefits of cine MRI may be limited to patients in whom transthoracic Doppler echocardiography is not adequate.

Adult↗
PubMed1990

Hydrogen ultrathin phase-encoded spectroscopy (HUPSPEC).

This paper describes a new clinical spectroscopy pulse program, hydrogen ultrathin phase-encoded spectroscopy. This sequence combines high spatial resolution with magnitude hydrogen spectroscopy. A linear volume is spatially frequency encoded with a conventional readout gradient and phase encoded spectrally by incrementing the timing of acquisition. The pulse sequence is implemented on a whole-body MRI scanner and supports several standard scanner options, including autoprescanning, offset of the center of field of view in the frequency-encoding direction, and oblique imaging. Some preliminary experimental experience is reported, demonstrating the possibility of observing the spectral linewidths of fat and water in marrow, and of observing the spectral linewidths of fat and water in marrow, and of observing multiline spectra. Combination of the technique with water suppression methods in a sequence called WASHUP is also discussed.

Adult↗
PubMed1990

Pulmonary vascular cine MR imaging: a noninvasive approach to dynamic imaging of the pulmonary circulation.

Cine gradient-recalled magnetic resonance (MR) imaging, which has flow sensitivity and high temporal resolution, may potentially yield both morphologic and dynamic flow-related information in the pulmonary vasculature. The authors used this modality to evaluate pulmonary vessels in 12 healthy subjects and in 14 patients with a variety of cardiopulmonary disorders. Normal pulmonary arteries and veins were characterized by distinctive signal intensity and diameter variations as well as motion of the vessels during the cardiac cycle. Patients with pulmonary arterial hypertension demonstrated loss of the normal pulsatile systolic increase and diastolic decline in velocity-related signal intensity and in diameter of the proximal pulmonary arteries. Disorders of pulmonary venous signal and diameter profiles during the cardiac cycle, which show a characteristic biphasic pattern in healthy subjects, were identified in five patients with mitral valvular disease. These initial results indicate that cine MR imaging techniques hold promise in the evaluation of pathophysiologic conditions in the pulmonary circulation.

Adult↗
PubMed1989

The correction of nonuniform signal intensity profiles in magnetic resonance imaging.

The increasing use of digital image data in Radiology has opened the door to the routine use of numerical image-enhancement techniques. Of course, numerical image processing cannot put information into the image which is not already there. However, if some means can be found to separate diagnostic image information from noise or artifact, the diagnostic information can be extracted with post-processing. The diagnostic quality of an exam may be enhanced by such numerical manipulations, even though technically, the information content of the digitized image is reduced.

Algorithms↗
PubMed1989

Use of Gd-DTPA and fast gradient-echo and spin-echo MR imaging to demonstrate renal function in the rabbit.

The paramagnetic magnetic resonance (MR) imaging contrast agent gadolinium diethylenetriaminepentaacetic acid (DTPA) is freely filtered at the glomerulus and is neither secreted nor reabsorbed by the renal tubules. Fast MR imaging techniques, either gradient-echo or spin-echo, can be used to document the passage of Gd-DTPA through the renal tubules, as reflected by alteration in the MR signal intensity within the different anatomic regions of the kidney. Gradient-echo (repetition time of 35 msec, echo time of 7 msec, flip angles of 10 degrees-100 degrees) and spin-echo (repetition time of 35 msec, echo time of 8 msec) pulse sequences were used to acquire 20 consecutive images, one every 12 seconds, of the rabbit kidney. Both pulse sequences depicted the time course of Gd-DTPA distribution through the kidney but with distinctly different patterns of MR signal change. These dynamic MR images provide an MR nephrogram that directly demonstrates renal morphology and indirectly reflects the functional status of the renal vasculature, renal perfusion, and tubular concentrating ability.

Animals↗