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Leon Axel

Publications and source records attributed to Leon Axel.

17 recordsLinked to original sources
PubMed2006

Multislice, dual-imaging sequence for increasing the dynamic range of the contrast-enhanced blood signal and CNR of myocardial enhancement at 3T.

PURPOSE: To develop a multislice, first-pass perfusion imaging sequence for increasing the effective dynamic range of the contrast-enhanced blood signal and the contrast-to-noise ratio (CNR) of myocardial wall enhancement. MATERIALS AND METHODS: A hybrid echo-planar imaging (EPI) pulse sequence was modified to acquire data for both the arterial input function (AIF) and the myocardium, using two different saturation-recovery time delays (TDs) and spatial resolutions, after a single saturation pulse. Five healthy subjects were scanned at 3T in three short-axis levels of the heart per heartbeat during passage of a high-dose bolus of contrast agent. The T(1)-weighted signal-time curve of the blood was converted to AIF using empirical conversion tables derived from phantom experiments. RESULTS: In all subjects the calculated AIF was consistently less distorted and higher for the short-TD protocol than for the long-TD protocol (peak concentration: 5.0 +/- 1.0 mM vs. 3.0 +/- 0.6 mM; P < 0.01). A combination of EPI, long TD, high-dose bolus of contrast agent, and 3T imaging yielded relatively strong peak enhancement in the myocardium (CNR = 11.9 +/- 3.3). CONCLUSION: Our dual-imaging approach at 3T seems promising for acquiring both a relatively accurate AIF and a high CNR of myocardial wall enhancement in multiple slices per heartbeat.

Adult↗
PubMed2006

Advances in MRI tagging techniques for determining regional myocardial strain.

MRI of the heart with magnetization tagging provides a potentially useful new way to assess cardiac mechanical function, through revealing the local motion of otherwise indistinguishable portions of the heart wall. Although still an evolving area, tagged cardiac MRI is already able to provide novel quantitative information on cardiac function. Exploiting this potential requires developing tailored methods for both imaging and image analysis. In this article, we review some of the progress that has been made in developing imaging methods for tagged cardiac MRI.

Cardiovascular Diseases↗
PubMed2006

Theory-based signal calibration with single-point T1 measurements for first-pass quantitative perfusion MRI studies.

RATIONALE AND OBJECTIVES: The aim of the study is to develop a theory-based signal calibration approach to be used for the conversion of signal-time curves to absolute contrast concentration-time curves for first-pass contrast-enhanced quantitative myocardial perfusion studies. MATERIALS AND METHODS: A normalization procedure was used to obtain a theoretical relationship between image signal and T1 and perform rapid single-point T1 measurements. T1 measurements were compared with reference T1 measurements. The method also was used in preliminary in vivo contrast-enhanced first-pass perfusion studies, and its applicability for dual-delay-time acquisitions was shown. A theory-based error sensitivity analysis was used to characterize the robustness of the method. RESULTS: The normalization procedure was implemented with minimal noise enhancement and insensitivity to small misregistrations through postprocessing techniques. The rapid T1 measurements are in excellent agreement with the reference measurements (R = 0.99, slope = 1.05, bias = -5.96 milliseconds). For in vivo studies, it is possible to simultaneously calibrate the arterial input function and myocardial enhancement curves acquired with different effective trigger delays through appropriate use of the theory-based signal calibration model. With this method, errors of in vivo baseline T1 estimates are large, but the effect of these large errors on the accuracy of contrast agent concentration estimates is limited. CONCLUSION: This theory-based signal calibration approach can be used to perform rapid T1 mapping and provides flexibility for in vivo calibration of signal-time curves resulting from dual-delay-time first-pass contrast-enhanced acquisitions.

Calibration↗
PubMed2005

Three-dimensional systolic kinematics of the right ventricle.

The right ventricle (RV) of the heart is responsible for pumping blood to the lungs. Its kinematics are not as well understood as that of the left ventricle (LV) due to its thin wall and asymmetric geometry. In this study, the combination of tagged MRI and three-dimensional (3-D) image-processing techniques was used to reconstruct 3-D RV-LV motion and deformation. The reconstructed models were used to quantify the 3-D global and local deformation of the ventricles in a set of normal subjects. When compared with the LV, the RV exhibited a similar twisting pattern, a more longitudinal strain pattern, and a greater amount of displacement.

Adolescent↗
PubMed2005

B(0) and B(1)-insensitive uniform T(1)-weighting for quantitative, first-pass myocardial perfusion magnetic resonance imaging.

Myocardial perfusion can be estimated, in principle, from first-pass MR images by converting the T(1)-weighted signal-time curves to contrast agent concentration-time curves. Typically, T(1) weighting is achieved by saturating the magnetization with a nonselective radiofrequency (RF) pulse prior to the imaging sequence. The accuracy of the perfusion estimate derived from the single-point T(1)-weighted signal depends on the initial residual longitudinal magnetization (RLM) produced by the saturation pulse. In this study we demonstrate that single-shot, echo-planar imaging can be used to show initial RLM resulting from incomplete saturation due to static magnetic field and RF field inhomogeneities in the heart at 1.5 T. Three saturation pulses, single, composite simple, and composite B(1)-insensitive rotation (BIR-4) were evaluated in phantom and cardiac experiments. The RLM image was calculated by normalizing the saturated image by a proton-density-weighted image. Mean RLM produced by the three saturation pulses was significantly different in noncontrast cardiac imaging (RLM(single) = 0.108 +/- 0.078; RLM(composite) = 0.051 +/- 0.052; RLM(BIR-4) = 0.011 +/- 0.009; P < 0.001; n = 20). Using a BIR-4 pulse to perform saturation of magnetization seems promising for improving the effectiveness and uniformity of T(1) weighting for first-pass perfusion imaging.

Adult↗
PubMed2005

Magnetic resonance imaging in the management of pericardial disease.

The pericardium, although seldom the primary cause of systemic illness, can be involved in almost every type of disease. Pericardial involvement may be subtle and escape detection unless specifically sought, or it can overshadow features of the underlying systemic disease. Suspected pericardial disease is usually initially evaluated with echocardiography. However, magnetic resonance imaging can offer additional valuable information. In addition to the excellent resolution and unlimited imaging planes available for visualization of the entire pericardial sac, the wide field of view allows for evaluation of involvement of adjacent cardiac structures. Dynamic functional imaging and tissue characterization with and without contrast can further characterize disease and provide information regarding concomitant myocardial disease and effects on cardiac motion. The treatment of specific pericardial conditions ultimately depends on the underlying disease process. Magnetic resonance imaging can provide useful information to aid in diagnosis, management, and guidance of therapy for pericardial disease.

Journal Article↗
PubMed2005

Tagged magnetic resonance imaging of the heart: a survey.

Magnetic resonance imaging (MRI) of the heart with magnetization tagging provides a potentially useful new way to assess cardiac mechanical function, through revealing the local motion of otherwise indistinguishable portions of the heart wall. While still an evolving area, tagged cardiac MRI is already able to provide novel quantitative information on cardiac function. Exploiting this potential requires developing tailored methods for both imaging and image analysis. In this paper, we review some of the progress that has been made in developing such methods for tagged cardiac MRI, as well as some of the ways these methods have been applied to the study of cardiac function.

Heart Diseases↗
PubMed2005

Saphenous vein graft aneurysm masquerading as a right atrial mass.

We report a case of a large saphenous vein graft (SVG) aneurysm masquerading as a right atrial mass on transesophageal echocardiogram. Cardiac magnetic resonance angiography reliably made a diagnosis of SVG aneurysm extrinsically compressing right atrium. This case illustrates the importance of using combined imaging modalities for the diagnosis and management of cardiac masses.

Aged↗
PubMed2004

Papillary muscles do not attach directly to the solid heart wall.

BACKGROUND: The papillary muscles (PMs) play an important role in normal cardiac function, helping to prevent leakage through the AV valves during systole. The nature of their attachment to the heart wall can affect the understanding of their function. This attachment is conventionally portrayed as a direct connection of their bases to the solid portion of the heart wall. X-ray multidetector CT provides a new, noninvasive way to investigate this connection in vivo. METHODS AND RESULTS: With the use of x-ray multidetector CT with interactive 3D reconstruction, the bases of the PMs are seen to attach to the trabeculae carneae lining the ventricular wall rather than directly to the solid portion of the wall, as has been conventionally believed. This is true for both the left and right ventricular PMs. CONCLUSIONS: This new picture of the geometry of the attachment of the PMs to the heart wall may have important implications for the understanding of their function, including the nature of the transmission of the forces between the PMs and the heart wall.

Contrast Media↗
PubMed2004

Assessment of pericardial disease by magnetic resonance and computed tomography.

Pericardial disease and its consequences can be well shown with magnetic resonance imaging (MRI) and computed tomography (CT). Here I review the normal and pathologic anatomy and physiology of the pericardium, approaches to MRI and CT imaging of the pericardium, and some specific considerations in common conditions affecting the pericardium.

Heart Diseases↗
PubMed2004

Quantification of the curvature and shape of the interventricular septum.

The interventricular septum (IVS) occupies a unique position within the heart, lying between the left (LV) and right (RV) ventricular cavities. Changes in its normal geometry may signify not only abnormalities of the septal myocardium, but also abnormal pressure differences between the LV and RV. Flattening of the IVS has been noted with cross-sectional imaging in association with pulmonary hypertension, but the septal curvature and shape have not previously been measured in three dimensions. This paper describes a method to model the RV surface of the IVS from spatially registered cross-sectional images for measurements of curvature. A smoothing 2D spline surface is constructed through the RV septal surface at regular times during the cardiac cycle, and the principal curvatures, as well as the Gaussian and mean curvatures, shape index, and curvedness, are calculated. Vector and color surface maps and graphs of average curvature and shape indices are constructed. Consistent curvature patterns were observed in four normal subjects. This method of measuring septal geometry can provide potentially useful new information on the effects of RV disease. We examine the problem of describing septal motion, and describe a simple measure of septal curvature that may be of clinical value.

Adult↗
PubMed2004

Increasing the signal-to-noise ratio in DENSE MRI by combining displacement-encoded echoes.

A new technique was developed to increase the signal-to-noise ratio (SNR) in displacement encoding with stimulated echoes (DENSE) MRI. This signal-averaged DENSE (sav-DENSE) technique is based on the SNR advantage of extracting a pair of DENSE images with uncorrelated noise from the complex complementary spatial modulation of the magnetization image, and combining them during image reconstruction. Eleven healthy volunteers were imaged at three short-axis locations with the use of sav-DENSE, cine DENSE, and myocardial tagging pulse sequences. In this study, sav-DENSE increased the SNR by 15-34% as compared to cine DENSE. Circumferential strain values measured by sav-DENSE and myocardial tagging were strongly correlated (slope = 0.95, intercept = -0.02, R = 0.92) and within the 95% limits of agreement. The breath-hold sav-DENSE technique yielded relatively accurate and precise quantification of 2D intramyocardial function, with a 40.2-ms temporal resolution and a 3.5 x 3.5 mm2 spatial resolution.

Adult↗
PubMed2003

In vivo strain and stress estimation of the heart left and right ventricles from MRI images.

Mechanical properties of the myocardium have been investigated intensively in the last four decades. Many complex strain energy functions have been used to estimate the stress-strain relationship of myocardium because the heart muscle is an inhomogeneous, anisotropic, and nearly incompressible material, which undergoes large deformations. These functions can be effective for fitting in vitro experimental data from myocardial stretch testing. However, it is difficult to model in vivo myocardium using these strain energy functions. Moreover, such estimates have so far been carried out almost exclusively on the left ventricle, because of the relative thinness and complex geometry of the right ventricle. Previous work from our research group has successful estimated the motion and deformation of both the left and the right ventricles, using data from noninvasive tagged magnetic resonance imaging. In this paper, we present a novel statistical model to estimate the in vivo material properties and strain and stress distribution in both ventricles, using such data. Two normal hearts and two hearts with right-ventricular hypertrophy (RVH) were studied and noticeable differences were found between the strain and stress distributions for normal volunteers and RVH patients. Compared to the strain energy function approach, our model is more intuitively understandable.

Humans↗
PubMed2003

MR Imaging of arrhythmogenic right ventricular cardiomyopathy: morphologic findings and interobserver reliability.

BACKGROUND: Magnetic resonance (MR) imaging is frequently used to diagnose arrhythmogenic right ventricular cardiomyopathy/dysplasia (ARVC/D). However, the reliability of various MR imaging features for diagnosing ARVC/D is unknown. The purpose of this study was to determine which morphologic MR imaging features have the greatest interobserver reliability for diagnosing ARVC/D. METHODS: Forty-five sets of films of cardiac MR images were sent to 8 radiologists and 5 cardiologists with experience in this field. There were 7 cases of definite ARVC/D as defined by the Task Force criteria. Six cases were controls. The remaining 32 cases had MR imaging because of clinical suspicion of ARVC/D. Readers evaluated the images for the presence of (a) right ventricle (RV) enlargement, (b) RV abnormal morphology, (c) left ventricle enlargement, (d) presence of high T(1) signal (fat) in the myocardium, and (e) location of high T(1) signal (fat) on a Likert scale with formatted responses. RESULTS: Readers indicated that the Task Force ARVC/D cases had significantly more (chi(2) = 119.93, d.f. = 10, p < 0.0001) RV chamber size enlargement (58%) than either the suspected ARVC/D (12%) or no ARVC/D (14%) cases. When readers reported the RV chamber size as enlarged they were significantly more likely to report the case as ARVC/D present (chi(2)(= )33.98, d.f. = 1, p < 0.0001). When readers reported the morphology as abnormal they were more likely to diagnose the case as ARVC/D present (chi(2) = 78.4, d.f. = 1, p < 0.0001), and the Task Force ARVC/D (47%) cases received significantly more abnormal reports than either suspected ARVC/D (20%) or non-ARVC/D (15%) cases. There was no significant difference between patient groups in the reported presence of high signal intensity (fat) in the RV (chi(2) = 0.9, d.f. = 2, p > 0.05). CONCLUSIONS: Reviewers found that the size and shape of abnormalities in the RV are key MR imaging discriminates of ARVD. Subsequent protocol development and multicenter trials need to address these parameters. Essential steps in improving accuracy and reducing variability include a standardized acquisition protocol and standardized analysis with dynamic cine review of regional RV function and quantification of RV and left ventricle volumes.

Adult↗
PubMed2002

Biomechanical dynamics of the heart with MRI.

Magnetic resonance imaging (MRI) provides a noninvasive way to evaluate the biomechanical dynamics of the heart. MRI can provide spatially registered tomographic images of the heart in different phases of the cardiac cycle, which can be used to assess global cardiac function and regional endocardial surface motion. In addition, MRI can provide detailed information on the patterns of motion within the heart wall, permitting calculation of the evolution of regional strain and related motion variables within the wall. These show consistent patterns of spatial and temporal variation in normal subjects, which are affected by alterations of function due to disease. Although still an evolving technique, MRI shows promise as a new method for research and clinical evaluation of cardiac dynamics.

Heart↗
PubMed2002

Fast imaging of phosphocreatine in the normal human myocardium using a three-dimensional RARE pulse sequence at 4 Tesla.

PURPOSE: To investigate the use of a three-dimensional rapid acquisition with relaxation enhancement (RARE) pulse sequence for direct acquisition of phosphocreatine (PCr) images of the human myocardium. MATERIALS AND METHODS: A short elliptical birdcage radiofrequency (RF) body coil was constructed to produce a uniform flip angle throughout the chest cavity. In vivo images using a spectrally-selective RARE sequence with a spatial resolution of 1.2 cm x 1.2 cm x 2.5 cm (4 cm(3)) were acquired in nine minutes and 40 seconds. RESULTS: Scans of phantoms demonstrated excellent spectral selectivity. The signal-to-noise ratio in the myocardium ranged from 12.6 in the anterior wall to 5.3 in the mid septum. CONCLUSION: This study demonstrates that PCr data can be acquired using a three-dimensional RARE sequence with greater spatial and temporal resolution than spectroscopic techniques.

Humans↗