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Results for “Echo-Planar Imaging”

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At least 19 recordsLinked to original sources
PubMed1992

Real-time dynamics of an extravascular magnetic resonance contrast medium in acutely infarcted myocardium using inversion recovery and gradient-recalled echo-planar imaging.

RATIONALE AND OBJECTIVES: The purposes of this study are to evaluate the first-pass profile of gadolinium-BOPTA/Dimeg (Gd-BOPTA/Dimeg) during its transit through hearts subjected to acute myocardial infarction, and to delineate these infarcted regions by the use of ultrafast magnetic resonance imaging (MRI). METHODS: Regional ischemia was induced in anesthetized rats by occluding the left coronary artery. Imaging parameters for single shot EPI included TE, 10 mseconds; AT, 33 mseconds; and 64 x 64-pixel matrix. Consecutive images were obtained every 1 to 2 seconds over a 30-second period. After approximately two images, Gd-BOPTA/Dimeg was injected intravenously (0.05 and 0.25 mmol/kg). RESULTS: Gd-BOPTA/Dimeg (0.05 mmol/kg), with inversion recovery EPI, produced a substantial increase in signal intensity of right and then left ventricular blood. Normally perfused myocardium also was enhanced, but not the acutely infarcted region. Clear delineation of the infarcted region as negatively enhanced "cold spots" persisted for at least 20 seconds. Gd-BOPTA/Dimeg (0.25 mmol/kg) with standard gradient-recalled EPI produced a different profile of signal intensity changes. Signal intensities of ventricular blood and normal myocardium were greatly reduced, leaving the infarcted zone as a positively enhanced "hot spot." Delineation of the infarcted region persisted for 6 to 8 seconds. The infarcted zone detected with MRI corresponded to that observed at autopsy. CONCLUSIONS: Regions of acute myocardial infarction can be detected as negatively enhanced "cold spots" or positively enhanced "hot spots" by studying the first-pass dynamics of Gd-BOPTA/Dimeg through hearts with regional ischemia by use of single shot EPI.

Animals↗
PubMedDate not supplied

Magnetic resonance imaging of brain function.

New techniques for imaging of brain function are described, which utilize magnetic resonance imaging. Echo-planar imaging (EPI), the preferred method, is introduced and technical issues are discussed. Two recent approaches for measurement of blood flow are explained: contrast agent bolus tracking and black blood perfusion. An intrinsic contrast technique, which utilizes the paramagnetism of deoxyhemoglobin, is presented. Results from experiments on functional imaging of the human brain are shown, and the specific advantages of MRI for this purpose are discussed.

Animals↗
PubMed1992

Brain parenchyma motion: measurement with cine echo-planar MR imaging.

With echo-planar magnetic resonance (MR) imaging, the authors measured the intrinsic pulsatile motion of brain parenchyma. Phase-sensitive, electrocardiography-gated, two-dimensional cine images were acquired throughout the cardiac cycle by using a spin-echo, blipped echo-planar MR pulse sequence. Transverse and coronal planes were obtained in 14 healthy volunteers. Corrections were made for gross head motion. Brain motion consisted of a rapid displacement in systole, with a slow diastolic recovery. The motion occurred chiefly in the cephalocaudal and lateral directions; the anteroposterior motions were relatively small. Cephalocaudal velocities increase with proximity to the foramen magnum. The lateral motion is mainly a compressive motion of the thalami. Brain parenchymal velocities were as high as 2 mm/sec caudally in the brain stem and 1.5 mm/sec medially in the thalami. Net parenchymal excursions were at most 0.5 mm. Phase-based echo-planar velocity measurements agreed well with echo-planar Fourier velocity zeugmatography measurements and were consistent with reported values. Velocity mapping with echo-planar imaging offers a rapid and flexible method of assessing the pulsation velocities of the human brain.

Adult↗
PubMed1992

Proton (fat/water) chemical shift imaging in medical magnetic resonance imaging. Current status.

Fat/water CSI has recently been transformed from an experimental method to a routine clinical MRI approach, particularly for evaluating paramagnetic contrast enhancement in fat-rich regions and as a piggyback method for decreasing MRI artifacts, such as in MR angiographic and echo-planar imaging. The full and appropriate use of CSI in medical MRI requires consideration of the factors and strategies outlined in this review. As the commercial implementation of fat/water CSI continues, we can expect further applications in clinical and experimental studies. For example, in imaging areas where MRI has been of limited efficacy, such as pancreas imaging, skin microimaging and vascular imaging, there are indications that these CSI methods may have practical importance. It seems reasonable to project that for high chemically specific detail, medical fat/water CSI will ultimately be supplanted by SI methods, and certainly by localized spectroscopy. The power of the fat/water CSI method remains its extremely high anatomic resolution, which cannot be achieved by current spectroscopy or SI methods. The fat/water CSI methods provide a means for clinically relevant MRI with more accurate and chemically specific information. Expansion of these methods into three-dimensional and fast imaging formats is already taking place at or near the commercial level. For example, the feasibility of combining echo-planar imaging and CSI methods has already been demonstrated. Methods based on the phase-contrast techniques, such as susceptibility mapping and interferometry, are additional implementations that can provide detailed and more specific information in a high anatomic detail format.

Adipose Tissue↗
PubMed1992

Dynamic mapping of the human visual cortex by high-speed magnetic resonance imaging.

We report the use of high-speed magnetic resonance imaging to follow the changes in image intensity in the human visual cortex during stimulation by a flashing checkerboard stimulus. Measurements were made in a 2.1-T, 1-m-diameter magnet, part of a Bruker Biospec spectrometer that we had programmed to do echo-planar imaging. A 15-cm-diameter surface coil was used to transmit and receive signals. Images were acquired during periods of stimulation from 2 s to 180 s. Images were acquired in 65.5 ms in a 10-mm slice with in-plane voxel size of 6 x 3 mm. Repetition time (TR) was generally 2 s, although for the long flashing periods, TR = 8 s was used. Voxels were located onto an inversion recovery image taken with 2 x 2 mm in-plane resolution. Image intensity increased after onset of the stimulus. The mean change in signal relative to the prestimulation level (delta S/S) was 9.7% (SD = 2.8%, n = 20) with an echo time of 70 ms. Irrespective of the period of stimulation, the increase in magnetic resonance signal intensity was delayed relative to the stimulus. The mean delay measured from the start of stimulation for each protocol was as follows: 2-s stimulation, delay = 3.5 s (SD = 0.5 s, n = 10) (the delay exceeds stimulus duration); 20- to 24-s stimulation, delay = 5 s (SD = 2 s, n = 20).

Brain Mapping↗
PubMed1992

Multiplanar gradient recalled images of the knee: comparison of different flip angles and echo times.

To determine the most appropriate combination of echo time (TE) and flip angle in gradient echo images of the knee, the authors used different TEs (10, 20 and 30 msec) and flip angles (10, 30, 50, 70, 90, 120 and 150 degrees) to perform a systematic study of MRI on 10 volunteer knees. Contrast-to-noise ratios of cartilage-fat, fluid-cartilage, fluid-fat and fluid-ligament were calculated and compared. Images with a 30-degree flip angle combined with 20 msec of TE were found to have the best contrast-to-noise ratios in both objective data analysis and subjective observation. Hyaline cartilage of the knee was hyperintense and was well delineated on this pulse sequence, appearing distinct in contrast to the intra-articular fluid. It is concluded that this T2-weighted gradient echo pulse sequence is an alternative to conventional spin echo T2-weighted imaging of the knee.

Echo-Planar Imaging↗
PubMedDate not supplied

MR-guided focused ultrasound surgery.

Magnetic resonance guided focused ultrasound surgery provides a minimally invasive controlled method for selectively destroying deep-lying tissue. A thermal analysis of focused ultrasound provides an estimate of the time-dependent temperature distribution and thermal dose required for ultrasound surgery. The temperature distribution is estimated by accumulating heat sources, considering the effects of thermal conductivity, heat content, and perfusion. In this study, both gel phantoms and excised in vitro bovine muscle specimens were imaged in a 1.5 T MR system while heated with a 5 cm diameter, 10 cm focal length, 1.1 MHz transducer. During sonication, the thermal effects were observed with T1-weighted pulse sequences. Below a critical temperature, the heat zone appeared as a dark spot that moved with the focal spot. Above a critical thermal dose, the in vitro tissue was irreversibly altered and the focal lesion was observed on both the MR image and the specimen slice.

Absorption↗
PubMed1992

Measurement of blood flow and perfusion in the cardiovascular system.

Complete evaluation of cardiovascular disease by a single imaging technique requires measurement of bulk flow in blood vessels and estimation of relative or ideally absolute perfusion at the tissue level. Magnetic resonance (MR) measurement of blood flow in arteries and veins has been done using the velocity-encoded phase cine gradient echo technique. This technique has been applied with cine MR to measure normal and pathologically high velocities. Measurement of relative perfusion in the myocardium has used the intravenous injection of T1 relaxation enhancing and magnetic susceptibility MR contrast media with rapid image acquisition using echoplanar imaging. MR images (MRIs) acquired during steady-state distribution or during the first passage of these contrast media have depicted ischemic myocardial regions.

Animals↗
PubMed1992

[MRI of the wrist joint].

Due to the development of new surface coils and the use of thin slices, MRI has become an essential diagnostic tool in wrist pathology. After several technical considerations, the authors describe the normal MRI appearance of the various anatomical structures of the wrist, particularly the triangular fibrocartilaginous complex of the wrist and the elements of the carpal tunnel. They review the principal indications for MRI: chronic diseases such as carpal tunnel syndrome and traumatic ligamentous and cartilaginous lesions. The bone marrow lesions detected in the presence of occult fractures and osteonecrosis of the lunate or scaphoid are then briefly considered. The diagnostic criteria of median nerve compression (carpal tunnel syndrome) include morphological and signal changes in the nerve, abnormal palmar convexity of the flexor retinaculum and signs of tenosynovitis of the intracarpal flexor tendons. However, in practice, MRI is only useful when there is disagreement between the clinical and EMG findings and in postoperative recurrences, in which case it may reveal insufficient section of the retinaculum or the presence of exuberant postoperative fibrosis responsible for persistent nerve compression. Traumatic tears of the triangular fibrocartilage are characterised by a linear high signal intensity image (on T1 and T2 weighted sequences), usually situated in the periphery of the articular disk. Degenerative lesions tend to be central, within the disk and are frequently observed after the age of 40 years.

Carpal Bones↗
PubMed1992

Fast spiral coronary artery imaging.

A flow-independent method for imaging the coronary arteries within a breath-hold on a standard whole-body MR imager was developed. The technique is based on interleaved spiral k-space scanning and forms a cardiac-gated image in 20 heartbeats. The spiral readouts have good flow properties and generate minimal flow artifacts. The oblique slices are positioned so that the arteries are in the plane and so that the chamber blood does not obscure the arteries. Fat suppression by a spectral-spatial pulse improves the visualization of the arteries.

Adipose Tissue↗
PubMed1992

[Nasal and sinusal polyposis. Semiology and values of magnetic resonance imaging].

Twelve patients with nasal polyposis were examined with magnetic resonance imaging (MRI) prior to surgical ethmoidectomies (20 ethmoidectomies). MRI signal was analyzed in correlation with surgical findings in order to define the semiology of nasal and sinuses polyps. One of the most important point of this semiology is based on the analysis of sequences after administration of gadolinium. MRI seems an interesting method for analysing the extension of nasal polyposis and could be useful for ENT surgeons before an endoscopic nasal surgery.

Adolescent↗
PubMed1992

Magnetic resonance imaging: applications of novel methods in studies of porous media.

NMR imaging is finding broad applications in nonbiological areas including the study of fluid flow and fluid ingress in porous media. The porous media include at the one end mineral rocks and various building materials through various solid plastic materials to foodstuffs at the other end of the spectrum. The fluids within these various media range from crude oil and water mixtures, and water itself, to a range of organic solvents in plastic materials. This paper is concerned with the flow and ingress of water through Bentheimer sandstone and Ninian reservoir specimens, and also in solid nylon blocks.

Echo-Planar Imaging↗
PubMed1992

Intracerebral lesion contrast with spin-echo and fast spin-echo pulse sequences.

Fast spin-echo (FSE) magnetic resonance (MR) imaging was compared with conventional, peripherally gated T2-weighted spin-echo (SE) imaging in the detection of high- and low-signal-intensity lesions in the central nervous system. Lesion detectability was determined with percentage of contrast measurements and contrast-to-noise ratios with two different measurements for noise. All three measures of lesion detectability were similar. FSE and SE sequences were quantitatively equivalent in the detection of high-signal-intensity lesions. The SE sequence, however, was superior to the FSE sequence in the detection of small, low-signal-intensity lesions in the central nervous system caused by magnetic susceptibility effects.

Adolescent↗
PubMed1992

Perfusion/diffusion quantitation with magnetic resonance imaging.

Quantitation of perfusion and diffusion in tissues using magnetic resonance imaging (MRI) techniques is an active area of research in many laboratories. Several different approaches have been taken to address the problem of determining microcirculatory flow or perfusion in the body with MRI. Methods have been developed that depend on pulse sequence designs to sensitize the acquisitions to proton movement that is part of physiologic perfusion. Other methods that are being studied take a different approach by using injected MR contrast agents coupled with high temporal resolution acquisitions to produce time-density curves that can be related to perfusion in the tissues of interest. Yet other approaches use blood as the tracer itself to provide a means of determining perfusion. All of these techniques and others provide quantitative information related to microcirculatory flow in tissues.

Animals↗
PubMed1992

[Contribution of gradient-echo MRI in the study of subacromial pathology: correlation between surgery and arthrography].

30 asymptomatic volunteer subjects and more than 400 patients with suspected rotator cuff lesions were examined by MRI at 0.5 T using T2*-PD weighted gradient echo (T2-GEI) sequences. Its superiority over T2 spin echo imaging was established in previous studies. The results were compared to those of surgery in 87 cases and arthrography in 233 cases (associated with CT arthrography in 70 cases). In the operated patients, T2-GEI and arthrography correctly diagnosed 49 complete ruptures (CR). T2-GEI was found to be superior to arthrography for defining the real extent of the rupture, the degree of tendon retraction and the local muscular trophicity, essential information to define the therapeutic indications. In contrast, among 22 lesions of the long biceps tendon, correctly demonstrated by arthrography or CT arthrography, 5 intracapsular lesions were not detected by MRI. MRI was able to detect 8 lesions of the anterior labrum associated with a CR not demonstrated by arthrography. Lastly, among the 18 cases of partial inferior rupture (PIR), 6 partial superficial ruptures and 14 cases of inflammatory changes, correctly diagnosed by MRI, only 8 PIR were also demonstrated by arthrography. For the non-operated patients investigated by the two modalities (146 cases), T2-GEI and arthrography were concordant in 43 cases. In contrast, 103 intact cuffs on arthrography showed features on T2-GEI compatible with tendinopathy without rupture, bursitis and degenerative changes. In the absence of very fine surgical or histological correlations for these small lesions, it is impossible, at the present time, to determine the real sensitivity and specificity of MRI.

Arthrography↗
PubMedDate not supplied

Why fat is bright in RARE and fast spin-echo imaging.

Fast spin-echo (FSE) sequences are becoming popular for T2-weighted clinical imaging because they result in a severalfold reduction in imaging time and because they provide conventional spin-echo contrast for most tissues. Fat, however, has been observed to have anomalously high signal intensity on FSE images. The present study shows that the brighter fat results from the multiple 180 degrees refocusing pulses, which eliminate diffusion-mediated susceptibility dephasing and suppress J-coupling modulation of the echo train.

Adipose Tissue↗
PubMed1992

Cardiopulmonary vascular imaging.

Magnetic resonance angiography (MRA) effectively maximizes the flow sensitivity of MR imaging (MRI) to display the body's vasculature. Although MRA has proven quite effective in imaging the intracranial and extracranial vessels, cardiopulmonary MRA faces several additional inherent challenges. Cardiorespiratory motion, vessel pulsatility, and irregular flow patterns all degrade image quality and necessitate appropriate compensation schemes. Although preliminary cardiopulmonary MRA methods appear promising, near instantaneous scan times may be necessary to fully maximize the potential of this technique. Multislice spin-echo and gradient-echo techniques have also proven effective. These methods may compensate for cardiac motion through either ECG-gating or referencing, and may maximize the signal characteristics from the intrinsic slow blood flow of the pulmonary vasculature. Phase velocity mapping techniques, which have proven capable of quantifying blood flow in the body, appear equally promising in preliminary studies in evaluating the cardiopulmonary vascular system. Because of the nature of blood flow dynamics in the cardiopulmonary vascular system, spin-echo (SE), gradient refocussed echo (GRE), and possibly phase mapping technique appear well suited for evaluating these regions.

Artifacts↗
PubMed1992

Real-time observation of transient focal ischemia and hyperemia in cat brain.

Gradient-recalled echo-planar (T2*-weighted) imaging was used to noninvasively monitor regional blood oxygenation state changes in real time during transient episodes of focal ischemia in cat brain. Varying ischemic intervals (12 s to 30 min) were caused by middle cerebral artery occlusion. A rapid signal drop was noted upon occlusion, due to deoxygenation of static blood in the ischemic tissues. Upon successful reperfusion, the signal intensity recovered immediately and increased above (overshot) the baseline level before slowly returning to normal. The "overshoot" response was strongly dependent on the duration of the ischemic interval and is thought to reflect reactive hyperemia.

Animals↗