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Biomedical subjects

R R Edelman

Publications and source records attributed to R R Edelman.

At least 253 records · Page 14Linked to original sources
PubMedDate not supplied

Breath-hold R2* mapping with a multiple gradient-recalled echo sequence: application to the evaluation of intrarenal oxygenation.

Blood oxygenation level dependent (BOLD) MRI is sensitive to changes in regional oxygen supply versus demand and is therefore potentially useful in evaluating susceptibility to ischemic injury. Recently, we have demonstrated the use of BOLD MRI to evaluate intrarenal oxygenation using single shot echo-planar imaging (EPI). Here, we present an alternate implementation of BOLD MRI sequence, using multiple gradient echoes, that does not require any specialized hardware.

Echo-Planar Imaging↗
PubMedDate not supplied

Three-dimensional low dose gadolinium-enhanced peripheral MR venography.

Our initial experience with low dose contrast-enhanced (LCE) peripheral MR venography (MRV) is presented. Five subjects were studied using three-dimensional (3D) fast imaging with a steady-state precession (FISP) sequence. A dose of 60 ml of gadopentetate dimeglumine diluted 1:20 was used. A tourniquet was applied during lower extremity MR venography. The venous anatomy was well depicted with the 3D LCE technique in all subjects. Compared to the two-dimensional (2D) time-of-flight (TOF) technique, acquisition time of 3D LCE MRV was much shorter, images looked sharper, and more veins could be seen. It is not affected by in-plane saturation and can be performed repeatedly because of the low dose of contrast. This technique holds promise for the detection of venous thrombosis and other disorders.

Adult↗
PubMedDate not supplied

A phantom for diffusion-weighted imaging of acute stroke.

A tissue phantom for diffusion-weighted imaging was developed, basing its contrast between two compartments on different apparent diffusion coefficients, without contrast due to T2 relaxation and proton density. These contrast properties of the phantom simulate the situation found in normal gray matter and areas of acute ischemia. A possible application of the phantom was demonstrated for the investigation of the accuracy of volume measurements based on diffusion-weighted images.

Acute Disease↗
PubMedDate not supplied

Basic principles of magnetic resonance angiography.

The flow of blood through magnetic field gradients and radiofrequency fields produces signal changes that can be used to distinguish blood vessels from surrounding stationary tissue. The field of magnetic resonance (MR) angiography attempts to overcome this limitation by creating images that depict blood vessels in a projective format similar to a conventional invasive angiogram, but without the need for ionizing radiation or a contrast agent. This article reviews basic concepts involved in MR angiography, including signal changes from time-of-flight and phase effects, maximum intensity projection algorithm for postprocessing of two-dimensional (2D) and three-dimensional (3D) image sets, and methods for flow quantification. Potential problems with MR angiography are considered, as well as means to overcome them.

Algorithms↗
PubMedDate not supplied

Magnetic resonance angiography of the abdominal aorta.

Magnetic resonance angiography (MRA) of the abdominal aorta was performed in 36 patients using the "bright-blood" technique on the basis of a series of flow-compensated breath-hold 2 D-GE pulse sequences. Diverse diseases included complete occlusion, stenosis, atherosclerotic or dissecting aneurysm and renal artery stenosis. Coronal and axial projection angiograms [maximum intensity projection (MIP) algorithm] and individual GE images were compared with DSA and contrast-enhanced computed tomography (CT). Our data showed a good correlation of MR and digital subtraction arteriography (DSA) or CT resp. in all cases, when both rotating MIP angiograms and individual GE images were analyzed. Thus, MR is suggested to be a useful noninvasive diagnostic method for the abdominal aorta, particularly in preoperative staging of aneurysms, aortic occlusive disease, and stenosis of the proximal main renal artery. Drawbacks of the method are a signal loss in slow or turbulent flow conditions, and unsatisfactory spatial resolution in small vessels.

Adult↗
PubMedDate not supplied

Ovarian fibroma: findings by contrast-enhanced MRI.

Ovarian fibromas are solid neoplasms that are difficult to differentiate radiologically from uterine leiomyomas. In this report, we describe the contrast-enhanced magnetic resonance imaging features of a 13-cm-diameter solid pelvic mass that allowed us to make the prospective diagnosis of ovarian fibroma.

Adult↗
PubMedDate not supplied

Contrast in rapid MR imaging: T1- and T2-weighted imaging.

Partial saturation (PS) is an imaging technique that is useful in applications that require rapid image acquisitions (imaging time less than 1 min). Image contrast in PS imaging, as in other magnetic resonance methods, depends on the often conflicting effects of differences in proton density, T1, and T2. Previous analyses of pulse sequence optimization to maximize image contrast have assumed 90 degrees pulses and examined the effects of varying repetition times (TR) and echo times (TE). In this paper we present theoretical calculations and images made with a 0.6 T imager to show that the radiofrequency pulse tip angle alpha, and not the pulse sequence timing parameters, is the most important parameter for producing image contrast. For large tip angles (alpha greater than or equal to 60 degrees), contrast is primarily determined by differences in T1, but for small tip angles (alpha approximately equal to 25 degrees), contrast is primarily due to differences in T2. The T2-weighted images can be produced as quickly as T1-weighted images by using a small pulse angle and a long TE; it is not necessary to use a long TR to reduce the effects of T1 differences. Optimum pulse angles are calculated, and the potential advantages and disadvantages of T2-weighted and T1-weighted PS imaging are discussed.

Humans↗
PubMedDate not supplied

MR imaging of superior sulcus carcinoma.

Magnetic resonance (MR) imaging was performed in 10 patients with biopsy proven superior sulcus carcinomas to determine the extent of local tumor invasion. Chest wall invasion or extension into the base of the neck was demonstrated in five patients. This finding was facilitated by the contrast between the bright signal intensity of tumor and the low signal intensity of muscle on T2-weighted images. In three patients, MR clearly depicted direct invasion of the mediastinum. This finding was facilitated on the MR image because of inherent contrast between the mediastinal fat and tumor. Coronal and sagittal images showed the relationship of tumor to the subclavian artery and brachial plexus in all cases. Encasement of the artery was confirmed in two cases and brachial plexus involvement in three. However, MR failed to detect evidence of rib destruction in five patients in whom rib involvement was confirmed by other studies. Magnetic resonance appears to be a useful imaging modality in determining the extent of local disease and, therefore, the selection of patients for surgical resection. Multiplanar imaging and contrast between tumor and muscle and tumor and fat allow assessment of invasion of the mediastinum and base of the neck, subclavian artery, and brachial plexus.

Adult↗
PubMedDate not supplied

CT and MRI of mycotic aneurysms of the abdominal aorta.

In two of three patients with mycotic aneurysms of the abdominal aorta, diagnosis was delayed, with a fatal outcome in one patient. A combination of studies, such as indium white blood cell scanning, and anatomical imaging modalities, such as CT and MRI, may be necessary to arrive at the correct diagnosis.

Aged↗
PubMedDate not supplied

Clinical correlations of diffusion and perfusion lesion volumes in acute ischemic stroke.

The aim of this study was to describe the clinico-radiological correlations of magnetic resonance (MR) perfusion and diffusion-weighted imaging (DWI) abnormalities in ischemic stroke. Eighteen patients had undergone MR imaging and clinical evaluation within 24 h of symptom onset and at or after 7 days. During the first 24 h the volume of perfusion abnormality (measured on the relative mean transit time map) was larger than the DWI lesion in 12/18 patients. In 6/18 patients the DWI lesion volume was larger. Acutely (<24 h) all lesion volumes showed a significant correlation with acute clinical severity measured by the National Institutes of Health Stroke Scale score. The correlations of the hypoperfusion volume (rho = 0.86, p = 0.0001) and the volume 'tissue at risk' (larger than the DWI and perfusion lesion volumes, rho = 0.86, p = 0. 0001) with acute clinical severity were slightly higher than for the DWI lesion volume (rho = 0.76, p = 0.0001). The difference between the volume of tissue at risk (acutely) and the infarct on follow-up T(2)-weighted imaging correlated significantly with change in clinical severity from acute to chronic time points (rho = 0.72, p = 0.001). Such clinico-radiological relationships may support the use of DWI and perfusion MR in decisions concerning the administration and evaluation of stroke therapies.

Acute Disease↗
PubMedDate not supplied

Diffusion-weighted magnetic resonance imaging in Alzheimer's disease.

Diffusion-weighted imaging (DWI) is a powerful new magnetic resonance imaging technique for evaluating tissue pathophysiology in vivo. We performed DWI in three orthogonal spatial directions in 10 patients with mild to moderate Alzheimer's disease (AD) and 11 control subjects. Average apparent diffusion coefficients (ADCavg) were calculated for gray matter regions, and anisotropy indexes were calculated for white matter regions. Global measures of atrophy and white matter hyperintensities (WMH) were obtained on T2-weighted images to control for their potential confounding effects on ADCavg and anisotropy. The measures of atrophy and WMH differed between the groups and were used as covariates in the subsequent statistical analyses. Patients with AD demonstrated diminished anisotropy in the posterior white matter (p < 0.0001) and increased ADCavg in the hippocampus (p < 0.05) when compared to the control group. Diffusion measures did not correlate with the severity of dementia. DWI provides a unique, quantitative parameter that may be sensitive to the pathophysiological and/or microstructural abnormalities that occur in AD.

Aged↗
PubMedDate not supplied

Echo-planar functional MR imaging of epilepsy with concurrent EEG monitoring.

BACKGROUND AND PURPOSE: The role of functional MR (fMR) imaging in the evaluation of patients with epilepsy has not been systematically studied. Our purpose was to identify the fMR correlates of interictal epileptiform discharges. METHODS: Twenty patients with epilepsy and frequent interictal discharges were studied with concurrent EEG monitoring on a 1.5-T echo-planar magnet to acquire blood-oxygenation-level-dependent (BOLD) images in the baseline (OFF) and immediate post-discharge (ON) states. Analysis was performed using subtraction of average ON and OFF data (method I); cross-correlation analysis between the ON and OFF states (method II); and individual spike analysis (ISA), with which signal intensity in the individual ON states was statistically analyzed using a weighted comparison with the mean and variance of the OFF states (method III). Agreement of fMR activation with EEG localization was determined. RESULTS: Eighteen of 20 patients had interictal discharges during the monitoring period. Method I yielded visually detectable sites of BOLD signal differences in only one patient. Method II resulted in two patients with sites of BOLD activation. Method III, ISA, resulted in regions of increased BOLD signal corresponding to the EEG focus in nine of 10 patients. CONCLUSION: fMR studies can often reveal sites of increased BOLD signal that correspond to sites of interictal EEG discharge activity. Because of variable intensity changes associated with discharge activity, ISA resulted in increased sensitivity.

Adult↗
PubMedDate not supplied

MR angiography of the extracranial carotid arteries using a two-slab oblique 3-D acquisition.

PURPOSE: To describe an oblique, two-slab 3-D acquisition technique for MR angiography of the extracranial carotid arteries, an approach chosen to minimize saturation effects when the body coil is used as transmitter, as is often the situation when a dedicated neck coil is used as receiver. SUBJECTS: Five healthy subjects and 17 patients in whom carotid artery disease was suspected underwent MR angiography using the above technique. RESULTS: Flow contrast was much better than in direct sagittal acquisition. Comparisons between multislab transverse 3-D acquisition and the oblique approach showed that a greater length of the carotid arteries was depicted and scan time was less for oblique acquisitions. CONCLUSIONS: Use of oblique imaging is a simple and effective solution to the problem of coil-related saturation effects.

Adult↗
PubMedDate not supplied

[Nuclear magnetic resonance tomography of the liver with Turbo FLASH].

A Turbo FLASH sequence consisting of an initial non-selective 180 degree inversion pulse followed by an ultrafast FLASH sequence with very short repetition and echo times (TR = 7 ms, TE = 4 ms) was used to study 20 patients with focal liver lesions. The results were compared to T1-weighted gradient-echo (108/5/80 for TR/TE/flip angle) and T2-weighted spin-echo sequences (TR/TE/excitations = 2500 ms/40 ms, 90 ms, 140 ms/2). Liver-spleen contrast of the fast scans was superior to T1- and T2-weighted images for TI = 300 ms (0.59 +/- 0.12 vs 0.33 +/- 0.07 and 0.42 +/- 0.14 respectively). Liver-lesion contrast of the fast scans for TI = 300-700 ms was superior to the T1-weighted gradient echo sequence (0.49 +/- 0.21 vs 0.23 +/- 0.09), equal to the T2-weighted spin echo sequence for TE = 90 ms (0.54 +/- 0.17) but inferior to the 140 ms echo (0.63 +/- 0.18). On Turbo FLASH scans, there were no flow or motion artifacts and lesions borders and structures were better delineated than on the spin-echo images. Imaging time for the whole liver is less than a minute.

Adenoma, Bile Duct↗
PubMedDate not supplied

MR of hemorrhage: a new approach.

Using a modification of the partial saturation (PS) pulse sequence, we developed an MR method that permits the acquisition of highly T1- and T2-weighted images of the head and body in as little as 10 sec. The PS images, which were acquired at 0.6 T in a series of six patients with acute and subacute hemorrhage, showed a striking reduction in the signal intensity of hemorrhagic lesions. This effect, which is related to bulk magnetic susceptibility variations, was either minimal or absent on conventional T1- and T2-weighted spin-echo (SE) images. Our results suggest that high-field systems are not needed in order to image acute and subacute hemorrhage.

Brain Diseases↗