共查询到20条相似文献,搜索用时 78 毫秒
1.
M. Stuber M. A. Spiegel S. E. Fischer M. B. Scheidegger P. G. Danias E. M. Pedersen P. Boesiger 《Magma (New York, N.Y.)》1999,9(1-2):85-91
Myocardial tagging has shown to be a useful magnetic resonance modality for the assessment and quantification of local myocardial
function. Many myocardial tagging techniques suffer from a rapid fading of the tags, restricting their application mainly
to systolic phases of the cardiac cycle. However, left ventricular diastolic dysfunction has been increasingly appreciated
as a major cause of heart failure. Subtraction based slice-following CSPAMM myocardial tagging has shown to overcome limitations
such as fading of the tags. Remaining impediments, to this technique, however, are extensive scanning times (∼10 min), the
requirement of repeated breath-holds using a coached breathing pattern, and the enhanced sensitivity of artifacts related
to poor patient compliance or inconsistent depths of end-expiratory breath-holds. We therefore propose a combination of slice-following
CSPAMM myocardial tagging with a segmented EPI imaging sequence. Together with an optimized RF excitation scheme, this enables
to acquire as many as 20 systolic and diastolic grid-tagged images per cardiac cycle with a high tagging contrast during a
short period of sustained respiration. 相似文献
2.
Left ventricular quantification with breath-hold MR imaging: comparison with echocardiography 总被引:5,自引:0,他引:5
Jan G. Bogaert Hilde T. Bosmans Frank E. Rademakers Erwin P. Bellon Marie-Christine Herregods Johny A. Verschakelen Frans Van de Werf Guy J. Marchal 《Magma (New York, N.Y.)》1995,3(1):5-12
To evaluate the reproducibility of measurements of left ventricular (LV) dimensions, function, and myocardial mass, segmentedk-space gradient-recalled-echo (GRE) magnetic resonance (MR) imaging was performed on two occasions on 12 healthy volunteers.
To compare the MR data, all volunteers underwent a two-dimensional echocardiography with determination of LV dimensions and
function. The left ventricle was imaged during breath-hold by consecutive, contiguous short-axis views at end-diastole and
end-systole. An average of eight short-axis views was needed to encompass the whole left ventricle. This fast MR sequence
limited the total acquisition time to 12 min. LV volumes and masses were calculated after manual delineation of epicardial
and endocardial surfaces by two observers in a blinded fashion.
Interstudy variability varied between 4.1% and 10.3% for LV end-diastolic volume and end-systolic volume, respectively. Differences
in interobserver variability were smaller and varied between 3.6% and 7.3% for LV ejection fraction and end-diastolic volume,
respectively. Intraobserver variabilities ranged between 2.0% and 7.0% for LV ejection fraction and end-systolic volume, respectively.
These variability percentages agree very well with other studies in literature using other MR sequences. No significant differences
in LV dimensions or function were found between MR imaging and echocardiography. In conclusion, this MR sequence allows fast
and reproducible LV quantification. 相似文献
3.
This work reports a low-cost and versatile electronic device designed to trigger NMR acquisitions from the cardiac cycle of an isolated perfused heart, or to perform electrical stimulation of the heart. The triggering is synchronised with the pressure curve of the perfused heart. The cardiac pacing is achieved from pulses of the NMR system, or by an internal pulse generator, in order to be operated separately from the NMR instrument. 相似文献
4.
Plein S Smith WH Ridgway JP Kassner A Beacock DJ Bloomer TN Sivananthan MU 《Magma (New York, N.Y.)》2001,13(2):101-108
This study investigates the use of real-time acquisition in cardiac magnetic resonance imaging (MRI) for measurements of left
ventricular dimensions in comparison with conventional gradient echo acquisition. Thirty-one subjects with a variety of left
ventricular morphologies to represent a typical clinical population were studied. Short-axis data sets of the left ventricle
(LV) were acquired using a conventional turbo-gradient echo and an ultrafast hybrid gradient echo/echo planar sequence with
acquisition in real-time. End-diastolic volume (EDV), end-systolic volume (ESV), ejection fraction (EF) and left ventricular
mass (LV mass) were measured. The agreement between the two acquisitions and interobserver, intraobserver and interstudy variabilities
were determined. The bias between the two methods was 5.86 ml for EDV, 0.23 ml for ESV and 0.94% for EF. LV mass measurements
were significantly lower with the real-time method (mean bias 14.38 g). This is likely to be the result of lower spatial resolution
and chemical shift artefacts with the real-time method. Interobserver, intraobserver and interstudy variabilities were low
for all parameters. In conclusion, real time acquisition in MRI can provide accurate and reproducible measurements of LV dimensions
in subjects with normal as well as abnormal LV morphologies, but LV mass measurements were lower than with conventional gradient
echo imaging.
Presented in abstract form at the International Society of Magnetic Resonance in Medicine meeting in Denver, Colorado in April
2000. 相似文献
5.
To qualitatively assess the accuracy of automated cardiovascular magnetic resonance planning procedures devised from scout
acquisitions in free-breathing and breath-holding modes, to quantitatively evaluate the accuracy of the derived left ventricular
volumes, mass and function and compare these parameters with the ones obtained from the manually planned acquisitions. Ten
healthy volunteers underwent cardiovascular MR (CMR) acquisitions for ventricular function assessment. Short-axis data sets
of the left ventricle (LV) were manually planned and generated twice in an automatic fashion. Automated planning parameters
were derived from gated scout acquisitions in free-breathing and breath-holding modes. End-diastolic volume (EDV), end-systolic
volume (ESV), ejection fraction (EF), and left ventricular mass (LVM) were measured. The agreement between the manual and
automatic planning methods, as well as the variability of the aforementioned measurements were assessed. The differences between
two automated planning methods were also compared. The mean differences between the manual and automated CMR planning derived
from gated scouts in free-breathing mode were 8.05 ml (EDV), 1.84 ml (ESV), 0.69% (EF), and 4.72 g (LVM). The comparison between
manual and automated CMR planning derived from gated scouts in breath-holding mode yielded the following differences: 4.22
ml (EDV), 0.34 ml (ESV), 0.3% (EF), and –0.72 mg (LVM). The variability coefficients were 3.72 and 3.66 (EDV), 5.6 and 8.19
(ESV), 3.46 and 4.31 (EF), 6.49 and 5.20 (LVM) for the automated CMR planning methods derived from scouts in free-breathing
and breath-holding modes, respectively. Automated CMR planning methods can provide accurate measurements of LV dimensions
in normal subjects, and therefore may be utilized in the clinical environment to provide a cost-effective solution for functional
assessment of the human cardiovascular system. 相似文献
6.
We report on the development of an algorithm to improve the registration of serial 3D MR breast images using combined global
translation and rotation with locally varying parameters as geometric transformations. Several phantom and volunteer data
sets were acquired and registered using mutual information as a similarity measure of the matching process. After applying
a global translation by using a rigid matcher, optimum horizontal and vertical rotation angles were determined. In case of
the phantom measurements, angle optimization was performed for each slice of the 3D data set of the phantom, which was deliberately
shifted and rotated around different axes. In case of registration of volunteer data, optimum rotation parameters were calculated
for preselected equidistant slices of the data set to speed up the calculation time. For slices located between and outside
these support slices, the rotation angles were calculated by linear interpolation and extrapolation of the slope of the regression
determined by the optimized angles of the support slices. The algorithm improves the registration of serial 3D MR data sets
and represents a compromise between a rigid and an elastic 3D matching procedure. 相似文献
7.
OBJECTIVE: Self-gating (SG) is a method to record cardiac movement during MR imaging. It uses information from an additional short, non-spatially encoded data acquisition. This usually lengthens TE and increases the sensitivity to flow artifacts. A new flow compensation scheme optimized for self-gating sequences is introduced that has very little or no time penalty over self-gating sequences without flow compensation. MATERIALS AND METHODS: Three variants of a self-gated 2D spoiled gradient echo or fast low angle shot (FLASH) sequence were implemented: without (noFC), with a conventional, serial (cFC), and with a new, time-efficient flow compensation (sFC). In experiments on volunteers and small animals, the sequence variants were compared with regard to the SG signal and the flow artifacts in the images. RESULTS: Both cFC and sFC reduce flow artifacts in cardiac images. The SG signal of the sFC is more sensitive to physiological motion, so that a cardiac trigger can be extracted more precisely as in cFC. In a typical setting for small animal imaging, sFC technique reduces the echo/repetition time over cFC by about 23%/14%. CONCLUSION: The time-efficient sFC technique provides flow-compensated images with cardiac triggering in both volunteers and small animals. 相似文献
8.
6. Conclusions Due to its high temporal and spatial resolution, the described MR technique is able to face the requirements of the small
sized, fast beating mouse heart, resulting in time-resolved visualization of the cardiac morphology and function in great
detail. This allows for accurate and reproducible quantification of LV performance including wall motion and contraction-relaxation
dynamics. Hence, MRI offers the non-invasive investigation of physiological and pathophysiological changes of cardiac function
over time, both under acute and chronic myocardial stress.
Applied in models of cardiac failure, the MR method should aid understanding the mechanisms of LV remodeling after myocardial
infarction and LV hypertrophy due to pressure overload in gene-targeted mouse models. 相似文献
9.
Norbert M. Wilke Andrey Zenovich Olaf Muehling Michael Jerosch-Herold 《Magma (New York, N.Y.)》2000,11(1):61-64
4. Summary Employment of cardiac MRI techniques (cine MRI, wall thickening analysis, quantitative MRFPP, MR tissue tagging) allowed non-invasive
localization and assessment of early and late changes in myocardial function and perfusion produced by these new approaches
of myocardial revascularization. With its precision in assessment of myocardial perfusion and collateral-dependent territories,
cardiac MRI techniques may be of excellent use for the evaluation of effects on myocardial function and perfusion as well
as longitudinal outcomes in clinical trials with TMLR and angiogenesis therapies in patients with CAD. As growth factor therapies
approach phase III clinical trials, such vital questions as the most effective delivery system, dosages and techniques used
for treatment-monitoring parameters remain unanswered. In addition, better definitions of patient selection criteria for TMLR
and angiogenesis therapies for both short- and long-term maximum benefits are needed at this time. Large-scale clinical trials
with cardiac MRI techniques are needed to reliably assess functional and perfusion reserves of the myocardium pre and post
TMLR and angiogenesis therapies. MR-based outcome parameters may aid in answering questions pertinent to the new revascularization
treatments. 相似文献
10.
Magnetic resonance imaging of the pituitary gland in patients with secondary hypogonadism due to transfusional hemochromatosis 总被引:1,自引:0,他引:1
Gianvincenzo Sparacia Massimo Midiri Paolo D'Angelo Roberto Lagalla 《Magma (New York, N.Y.)》1999,8(2):87-90
To identify pituitary iron overload in patients with transfusional hemochromatosis causing secondary hypogonadism, we prospectively
evaluated signal intensity abnormalities of the anterior lobe of the pituitary gland of 18 patients affected by transfusion-dependent
thalassemia major and secondary hypogonadism. Magnetic resonance (MR) imaging is useful to assess pituitary iron overload
in patients with transfusional hemochromatosis and secondary hypogonadism by detection of a significant decreased signal intensity
of the anterior lobe of the pituitary gland on GRE T2*-weighted images. The decreased signal intensity of the anterior lobe of the pituitary gland on GRE T2*-weighted images was correlated to increasing serum ferritin level (r=−0.84,r
2=−0.70,P<0.001). Indeed, the lower the signal intensity of the pituitary gland the greater the serum ferritin level. However an exact
quantification of pituitary iron overload by correlation with serum ferritin level is not allowed. No correlation was found
between MR imaging results and hormonal status; however, the detection of pituitary iron overload on GRE T2*-weighted images is consistent with the hypothesis of hypogonadotrophic pituitary insufficiency due to iron-induced cellular
damage. 相似文献
11.
Desmond H. Y. Tse Christopher J. Wiggins Dimo Ivanov Daniel Brenner Jens Hoffmann Christian Mirkes Gunamony Shajan Klaus Scheffler Kâmil Uludağ Benedikt A. Poser 《Magma (New York, N.Y.)》2016,29(3):333-345
Objectives
To overcome the challenges of B0 and RF excitation inhomogeneity at ultra-high field MRI, a workflow for volumetric B0 and flip-angle homogenisation was implemented on a human 9.4 T scanner.Materials and methods
Imaging was performed with a 9.4 T human MR scanner (Siemens Medical Solutions, Erlangen, Germany) using a 16-channel parallel transmission system. B0- and B1-mapping were done using a dual-echo GRE and transmit phase-encoded DREAM, respectively. B0 shims and a small-tip-angle-approximation kT-points pulse were calculated with an off-line routine and applied to acquire T1- and T 2 * -weighted images with MPRAGE and 3D EPI, respectively.Results
Over six in vivo acquisitions, the B0-distribution in a region-of-interest defined by a brain mask was reduced down to a full-width-half-maximum of 0.10 ± 0.01 ppm (39 ± 2 Hz). Utilising the kT-points pulses, the normalised RMSE of the excitation was decreased from CP-mode’s 30.5 ± 0.9 to 9.2 ± 0.7 % with all B 1 + voids eliminated. The SNR inhomogeneities and contrast variations in the T1- and T 2 * -weighted volumetric images were greatly reduced which led to successful tissue segmentation of the T1-weighted image.Conclusion
A 15-minute B0- and flip-angle homogenisation workflow, including the B0- and B1-map acquisitions, was successfully implemented and enabled us to reduce intensity and contrast variations as well as echo-planar image distortions in 9.4 T images.12.
Michael K. Stehling Nicolaus G. Holzknecht Gerhard Laub Dieter Böhm Alexander von Smekal Maximilian Reiser 《Magma (New York, N.Y.)》1996,4(3-4):231-240
Purpose: To implement and evaluate two robust methods for T1-and T2-weighted snapshot imaging of the heart with data acquisition within a single heart beat and suppression of blood signal.
Methods: Both Tl-and T2-weighted diastolic images of the heart can be obtained with half Fourier single-shot turbo spin echo (HASTE) and turbo fast low-angle shot (turboFLASH) sequences, respectively, in less than 350 ms. Signal from flowing blood in the ventricles and large vessels can be suppressed by a preceding inversion recovery preparing pulse pair (PRESTO). Fifteen volunteers and five patients have been evaluated quantitatively for signal-to-noise ratio (SNR) contrast-to-noise ratio (CNR) and flow void and qualitatively for image quality, artifacts, and black-blood effect.
Results: Both PRESTO-HASTE and PRESTO-turboFLASH achieved consistently good image quality and blood signal suppression. In contrast to gradient-echo (GRE) echo-planar imaging techniques, (EPI) HASTE and turboFLASH are much less sensitive to local susceptibility differences in the thorax, resulting in a more robust imaging technique without the need for time-consuming system tuning. Compared to standard spin-echo sequences with cardiac triggering, HASTE and turboFLASH have significantly shorter image acquisition times and are not vulnerable to respiratory motion artifacts.
Conclusion: PRESTO-HASTE and PRESTO-turboFLASH constitute suitable methods for fast and high-quality cardiac magnetic resonance imaging (MRI). 相似文献
13.
Frank Wiesmann Jan Ruff Charlotte Dienesch Andrea Leupold Eberhard Rommel Axel Haase Stefan Neubauer 《Magma (New York, N.Y.)》2000,11(1):10-15
9. Conclusion Due to its high temporal and spatial resolution, magnetic resonance imaging meets the requirements for accurate and robust
in vivo visualization of the murine cardiovascular system. As an intrinsically three-dimensional imaging technique, it allows
for quantification of LV volumes without relying on geometric models. Therefore, MRI is uniquely suited for the investigation
of morphologic and functional changes in models of heart failure.
The potential application of MRI in the mouse comprises visualization of cardiovascular anatomy and pathology in newborn and
adult mice, detection of LV geometric and functional changes both acutely and chronically, visualization of cardiac microstructures
such as cardiac valves and coronary arteries, and characterization and quantification of arteriosclerotic plaques in major
murine arteries. Furthermore, MR spectroscopy applied to the mouse heart can give important information on in vivo myocardial
metabolism. Thus, we feel confident that high resolution MRI may substantially contribute to the understanding of the basic
mechanisms of a variety of cardiovascular diseases. 相似文献
14.
Dietrich O Herlihy A Dannels WR Fiebach J Heiland S Hajnal JV Sartor K 《Magma (New York, N.Y.)》2001,12(1):23-31
Introduction Diffusion-weighted MR imaging (DWI) of the spine requires robust imaging methods, that are insensitive to susceptibility effects
caused by the transition from bone to soft tissue and motion artifacts due to breathing, swallowing, and cardiac motion. The
purpose of this study was to develop a robust imaging method suitable for DWI of the spine.
Methods and subjects A radialk-space spin echo sequence has been implemented, which is sell-navigating because each acquisition line passes through the
origin ofk-space. Influence of cardiac motion and associated flow of cerebrospinal fluid is minimized by cardiac gating with a finger
photoplethysmograph. The sequence has been tested on a 1.5T system. Diffusion-weighted images of six normal volunteers were
acquired in the sagittal plane with 4b values between 50 and 500 s mm−2. Because of the symmetries of the cord, diffusion measurements in the head-foot (HF) or left-right (LR) directions were sufficient
to measure the dominant effects of anisotropy.
Results The apparent diffusion coefficients (ADCs) measured, respectively, in the LR and HF directions were (0.699 ± 0.050) × 10−3 and (1.805 ± 0.086) × 10−3 mm2 s−1 in the spinal cord. (1.588 ± 0.082) × 10−3 and (1.528 ± 0.052) × 10−3 mm2 s−1 in the intervertebral disks, and (0.346 ± 0.047) × 10−3 and (0.306 ± 0.035) × 10−3 mm2 s−1 in the vertebrae of the cervicothoraeic spine.
Conclusion Diffusion-weighted spin echo sequences with radial trajectories ink-space provide a means of achieving robust, high quality diffusion-weighted imaging and measuring ADCs in the spine. The application
of the diffusion-weighting gradients in different directions allows diffusion anisotropy to be measured. 相似文献
15.
Fractal dimension in the analysis of medical images 总被引:7,自引:0,他引:7
Fortin C.S. Kumaresan R. Ohley W.J. Hoefer S. 《IEEE engineering in medicine and biology magazine》1992,11(2):65-71
The analysis of cardiac magnetic resonance (MR) images and X-rays of bone is considered. Each image type is approached using a different form of fractal parameterization. For the MR images, the goal of the study is segmentation, and to this end small regions of the image are assigned a local value of fractal dimension. For the bone X-rays, rather than segmentation, the large-scale structure is parameterized by its fractal dimension. In both cases, the use of fractals leads to the classification of the parameters of interest. When applied to segmentation, this analysis yields boundary discrimination unavailable through previous methods. For the X-rays, texture changes are quantified and correlated with physical changes in the subject. In both cases, the parameterizations are robust with regard to noise present in the images, as well as to variable contrast and brightness 相似文献
16.
The concept and the implementation of a parallelized and spin-based simulator for magnetic resonance (MR) imaging is presented.
The dynamics of magnetization are modeled using the Bloch equation covering arbitrary radiofrequency (RF) pulses, gradients,
main-field inhomogeneity, and relaxation. A temporal decomposition of a given sequence is introduced, leaning to basic sequence
elements called atoms. A concept of spatial sampling of the object by spins is proposed, in the course of which Shannon's
sampling theorem must be respected. In biomedical MR imaging, spins can be modeled as noninteracting entities, permitting
an efficient parallelization of the simulation. The simulator ParSpin was implemented on a heterogeneous, interconnected cluster
of workstations based on existing message passing libraries. The communication overhead has been kept moderately small. The
aggregate computing performance of many processors enables the research into very complex problems (e.g., three-dimensional
or steady-state MR experiments requiring up to 106 spins). Additionally, ParSpin allows a comprehensive visualization for educational purposes. 相似文献
17.
Hidenori Takauji Shun'Ichi Kaneko Takayuki Tanaka 《Electrical Engineering in Japan》2006,156(4):22-32
This paper aims to propose a new scheme for robust tagging for landmark definition in unknown circumstance using some qualitative evaluations based on orientation code representation and matching, which has been proposed for robust image registration even in the presence of changes in illumination and occlusion. The necessary characteristics for effective tags include richness, similarity, and uniqueness, and are considered in order to design an algorithm for tag detection. These qualitative considerations can be utilized to design a simple and robust algorithm for tag definitions in combination with the robust image registration algorithm. © 2006 Wiley Periodicals, Inc. Electr Eng Jpn, 156(4): 22–32, 2006; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/eej.20351 相似文献
18.
Magnetization transfer contrast is a tool to obtain additional information on tissue using standard whole-body magnetic resonance (MR) units without any hardware extension. Short hard pulse sequences with a total duration of about 1 ms can provide selective saturation of protons with very short relaxation timesT
2 of 1–10 µs. Comparatively high amplitude of the radio-frequency field is advantageous; on the other hand, this amplitude is limited for whole-body units. The presented approach to achieve adapted hard pulse sequences is mainly based on maximum RF amplitudes corresponding with pulse angles per millisecond of 360 °, or 720°. The pulse sequences must not influence the magnetization of free protons with longer relaxation timesT
2>10 ms in a frequency range that depends on the circumstances of the application. This frequency range has to be markedly broader for imaging techniques than for localized spectroscopy. The number of pulses, the pulse durations and pulse angles, and the interpulse delays were systematically varied. The time intervals between repetitions of the hard pulse sequences in order to obtain stronger magnetization transfer contrast were also optimized experimentally for human skeletal muscle and brain.Additional reprints of this chapter may be obtained from the Reprints Department, Chapman & Hall, One Penn Plaza, New York, NY 10119. 相似文献
19.
T. Delzescaux F. Frouin A. De Cesare S. Philipp-Foliguet R. Zeboudj M. Janier A. Todd-Pokropek A. Herment 《Magma (New York, N.Y.)》2001,13(1):28-39
With the advent of ultra-fast MR I, it is now possible to assess non-invasively regional myocardial perfusion with multislice
coverage and sub-second temporal resolution. First-pass contrast enhanced studies are acquired with ECG-triggering and breath
holding. Nevertheless, some respiratory induced movements still remain. Myocardial perfusion can be assessed locally byparametric
imaging methods such as Factor Analysis of Medical Image Sequences (FAMIS), provided that residual motion can be corrected.
An a posteriori registration method implemented in the image domain is proposed. It is based on an adaptive registration model
of the heart combining three elementary shapes (left ventricle, right ventricle and pericardium). The registration procedure
is performed on a potential map derived from the distance map. To evaluate the quality of the registration procedure a superimposition
score between the registration model and the contour automatically extracted in the sequence is proposed. Rigid transformation
hypotheses and registration analysis provide an efficient and automatic method which allows the rejection of outlier images,
such as; outof synchronisation images, out of plane acquisitions. When compared to a manual registration method, this approach reduces processing
time and requires a minimal intervention from the operator. The proposed method performs registration with a subpixel accuracy.
It has been successfully applied to simulated images and clinical data. It should facilitate the use of MR first-pass perfusion
studies in clinical practice. 相似文献
20.
Claire Baldy Pierre Croisille Philippe Douek Didier Revel Michel Amiel 《Magma (New York, N.Y.)》1994,2(1):13-20
The calculation of the left ventricular (LV) function requires the endocardial and epicardial contours of the cavity to be accurately defined beforehand. This identification is generally achieved by manual tracing of the LV borders. Such manual methods are tedious and time-consuming, limiting their clinical usefulness for cardiac quantitative analysis. The purpose of this study was to evaluate an efficient method for drawing the LV borders from magnetic resonance (MR) images. This technique, based on the use of cubic B-spline curves to modelize the shape of the cavity, allows an interactive and real-time remodeling of the contours. The variability and the accuracy of this contour tracing tool have been evaluated on standard cine-MR images obtained in 10 healthy volunteers in a short-axis view. Theendocardial and epicardial areas and themean local error between the contours were compared through interobserver and intraobserver analyses. A good correlation was observed between the enclosed areas in both studies (r>0.98 for endocardium,r=0.99 for epicardium). The mean local error between the contours was less than 2.8% for the endocardial borders and less than 1.4% for the epicardial borders. This method has a high degree of flexibility for the interactive trace and deformation of contours. Although further validation is needed, this method may prove useful in clinical application to permit the measurement of LV function from MR imaging.Address for correspondence: Departement de Radiologie, Hôpital Cardiovasculaire et Pneumologique, BP Lyon Montchat, 69394 Lyon Cedex 03, France. Additional reprints of this chapter may be obtained from the Reprints Department, Chapman & Hall, One Penn Plaza, New York, NY 10119. 相似文献