Biomedical subjects

R R Edelman

Publications and source records attributed to R R Edelman.

At least 199 records · Page 11Linked to original sources

PubMed1991

Ultrafast imaging using gradient echoes.

Ultrafast magnetic resonance (MR) imaging techniques can reduce scan times to less than 1 s. The rapid acquisition minimizes motion artifacts that have plagued MR studies of the heart and abdomen, and facilitates dynamic studies to observe physiological function. We first discuss fast gradient-echo methods, including various spoiled and steady-state gradient-echo techniques. Ultrafast methods are then considered, with the focus on turbo-fast low-angle shot (FLASH) (also known as snapshot or subsecond FLASH) imaging. Although turbo-FLASH is a subset of gradient echo methods, there are several distinguishing features. For instance, with T1- or T2-weighted turbo-FLASH, the magnetization never reaches a steady state, so that the phase encode order becomes an important imaging parameter. Furthermore, image contrast is obtained by adjusting the magnetization preparation module, which is independent of the data acquisition module that follows. The signal behavior and strategies for contrast optimization are discussed. Potential clinical applications, including perfusion imaging, cardiac cine, breath-hold abdominal imaging, angiography, diffusion imaging, and three-dimensional studies, are explored.

Fourier Analysis↗

PubMed1991

[MR angiography of the abdominal veins].

On the basis of the time-of-flight effect in 18 normal volunteers and 119 patients with different diseases of the abdominal veins (inferior vena cava, porto-splenic system, renal/hepatic/iliac veins) magnetic resonance (MR) angiograms were compared with the DSA, CT and US results. The MR technique included a series of 2D gradient-echo (Flash) images in which the patients held their breath and projection angiograms (PA) (MIP algorithm). PA of the inferior vena cava and renal veins had a sensitivity of 90% and a specificity of 88.8%. The results demonstrate that in all cases diseases of the large veins could be detected using all the MR information available. It is suggested that this method is so far not satisfactory in the evaluation of small vessels and slow intravascular flow conditions.

Abdomen↗

PubMed1990

[Magnetic resonance angiography. Work in progress].

Rapid progress has been made in the development and clinical application of magnetic resonance (MR) techniques for creating angiogram-like images of blood vessels. Combinations of techniques such as gradient-echo pulse sequences and flow compensation (bright blood imaging) or presaturation (black blood imaging) permit the signal intensities of moving spins to be altered, so as to generate contrast between flowing blood and stationary tissues. Postprocessing of the images allows the creation of projection angiograms, which show the vasculature in a large slice of the body. Preliminary studies suggest a variety of potential clinical applications, including intracranial arteriovenous malformations and aneurysms, carotid artery disease, portal hypertension, renal artery stenosis, peripheral arterial disease and venous thrombosis. At present, MR angiography is not directly competitive with conventional contrast angiography because of lower spatial resolution and loss of signal from flow turbulence and from slow flow. Nonetheless, it is proving to be a useful clinical tool for the investigation of vascular pathology involving the head and body.

Angiography↗

PubMed1990

Fast imaging.

Gradient-echo pulse sequences are a valuable adjunct to the standard spin-echo sequences used for MR imaging of the brain and spine. Gradient-echo techniques enhance the signal of flowing fluids and increase the conspicuity of vascular lesions. They also increase the sensitivity of MR for chronic hemorrhage and calcification. Finally, steady-state techniques produce a myelographic effect to help evaluate degenerative diseases of the spine.

Arterial Occlusive Diseases↗

PubMed1990

Abdominal aorta and renal artery stenosis: evaluation with MR angiography.

A blinded, prospective study with magnetic resonance (MR) angiography was performed to study patients who had undergone abdominal aortography. In 55 renal arteries among 25 patients, MR angiography had a sensitivity of 100% for detecting renal artery stenosis of 50% or greater and a specificity of 92%. With MR angiography, the degree of renal artery stenosis was overgraded in four of 55 renal arteries: Mild stenosis was overgraded as moderate stenosis in two arteries and as a severe stenosis in one, and a moderate stenosis was overgraded as a severe stenosis in one. The number of renal arteries was correctly determined in all cases. The renal arteries could be well evaluated only in the proximal third of the vessel, precluding detection of more distal stenoses. Atherosclerotic plaque uniformly appeared dark on gradient-echo images and was easily differentiated from bright, flowing blood in the aortic lumen. MR angiography enabled correct grading of the presence of atherosclerotic plaque and stenoses of the abdominal aorta in 22 of 25 patients (88%). The authors conclude that MR angiography has the potential to be a useful screening technique for patients with suspected renal artery stenosis and disorders of the abdominal aorta, but further clinical studies are warranted.

Angiography↗

PubMed1990

First-pass cardiac perfusion: evaluation with ultrafast MR imaging.

The authors studied cardiac perfusion by administering gadolinium diethylenetriaminepentaacetic acid (DTPA) in conjunction with an ultrafast imaging technique that produces strongly T1-weighted images. The method consisted of a 180 degrees inversion pulse, followed by a gradient-echo acquisition with a very short repetition time (less than 4 msec). Each image was acquired throughout a small fraction of the cardiac cycle. The method was applied in an isolated perfused rat heart model (acquisition time = 116 msec) and in human subjects without known cardiac disease (acquisition time = 125 msec). Fast, high-resolution images (128 X 128 matrix) were created by combining sequentially acquired small matrixes. After bolus administration of Gd-DTPA in the perfused rat heart model, contrast was pronounced between the nonperfused myocardium and perfused normal myocardium. First-pass wash-in and washout phases of the contrast material were observed in the perfused rat heart model and in human subjects. Results demonstrated the clinical feasibility of first-pass perfusion studies of the heart. The studies can be performed on a conventional whole-body imaging system with standard hardware.

Animals↗

PubMed1990

Cerebral blood flow: assessment with dynamic contrast-enhanced T2*-weighted MR imaging at 1.5 T.

The authors assessed regional cerebral blood flow dynamics with magnetic resonance (MR) imaging enhanced with gadolinium diethylenetriaminepentaacetic acid (DTPA). After bolus administration of Gd-DTPA, rapid T2*-weighted gradient-echo images were acquired. Image acquisition time ranged from 2 to 3 seconds. The signal intensity (SI) of brain tissue and blood vessels markedly decreased during the first pass of contrast agent through the brain due to the local field inhomogeneity caused by the concentrated paramagnetic contrast agent. The method was used in 18 subjects with no cerebrovascular disease and 32 patients with stroke, vascular stenosis, arteriovenous malformation, and cerebral neoplasm. Comparison with intracranial angiography was performed in three patients and with single-photon emission computed tomography of blood flow in four. The change in T2* relaxation rate was approximately linearly related to the dose of contrast agent. The SI change increased as the echo time was lengthened. Regions in cerebral infarcts, metastases, and arteriovenous malformations showed different enhancement patterns than those of edema around a lesion and of normal brain tissue. Abnormal circulation times in patients with vascular stenoses were demonstrated. The method provides information about cerebral blood flow dynamics not available from conventional MR imaging and MR angiography.

Adolescent↗

PubMed1990

Extracranial carotid arteries: evaluation with "black blood" MR angiography.

The authors evaluated the accuracy of "black blood" magnetic resonance (MR) angiography for depicting disease involving the extracranial carotid arteries. Two- and three-dimensional flow-compensated gradient-echo sequences were employed to create "bright blood" images. A thin-section spin-echo sequence with flow presaturation allowed the creation of black blood images. Projection angiograms were made from bright and black blood images with application of a maximum- or minimum-intensity projection algorithm, respectively. These methods were used in 13 healthy volunteers and 17 patients, and a prospective blinded comparison of MR angiography and conventional angiography was performed. Normal carotid arteries were well shown with both bright and black blood methods; in patients, both methods were sensitive for detecting carotid disease. However, bright blood angiography exaggerated the severity of carotid lesions in 13 of 33 arteries, mostly in severe disease; this problem was not encountered with black blood angiography. The authors conclude that bright blood angiography is a sensitive method for screening carotid disease; when a significant abnormality is found, black blood angiography should be performed for more precise delineation of the lesion.

Adult↗

PubMed1990

Segmented turboFLASH: method for breath-hold MR imaging of the liver with flexible contrast.

A method called segmented turboFLASH imaging allows high-resolution, multisection, short-inversion-time (TI) inversion-recovery (STIR), T1- or T2-weighted magnetic resonance (MR) studies of the liver to be completed within a breath-hold interval. The method was applied in a phantom and in 19 patients with hepatic lesions. Sequence comparisons were performed among segmented turboFLASH, single-shot turboFLASH, T1-weighted gradient-echo with ultrashort echo time, and T2-weighted spin-echo (SE) techniques. Signal from fat and liver could be nulled with the segmented turboFLASH method, with TIs of 10 and 300 msec, respectively; signal from these tissues could not be eliminated with the single-shot approach. Signal-difference-to-noise ratios and contrast for the best segmented sequences were comparable with those of the best T2-weighted SE and T1-weighted gradient-echo techniques. It is concluded that it is feasible to obtain breath-hold images with arbitrary tissue contrast by means of segmented turboFLASH imaging. The method may prove helpful for the detection and characterization of hepatic lesions and will likely have applications to other anatomic regions such as the chest and pelvis.

Adenoma, Bile Duct↗

PubMed1990

Magnetic resonance imaging of flow dynamics in the circle of Willis.

Magnetic resonance angiography was applied to the study of blood flow dynamics in the circle of Willis in nine patients with cerebrovascular disease and two normal volunteers. In conjunction with two-dimensional or three-dimensional gradient-echo acquisitions, selective presaturation of individual vessels was used to determine the direction of blood flow and the origin of the vascular supply. Presaturation causes signal loss within the territory supplied by the presaturated artery, without affecting vessels not crossing the presaturation slab. The results were correlated with those from transcranial Doppler sonography and conventional angiography. Magnetic resonance angiography was able to demonstrate the direction of blood flow, the presence or absence of collateral blood flow, and the blood supply to the pericallosal arteries, as well as the presence of a fetal posterior circulation. Magnetic resonance angiography is a noninvasive means for imaging the blood supply of the major intracranial arteries.

Adult↗

PubMed1990

Flow quantification in the superior sagittal sinus using magnetic resonance.

To date, the intracerebral veins and venous sinuses have not been amenable to noninvasive study. We describe a magnetic resonance (MR) technique using "bolus tracking" for rapid imaging and measurement of cerebral venous flow. We specifically applied the technique to the superior sagittal sinus, but it can be used for evaluation of other cerebral venous structures. In 10 healthy subjects and 21 patients referred for MR brain studies, mean flow was 420 ml/min. There was a significant inverse correlation between blood flow and age. There were dynamic changes in cerebral blood flow (CBF) during hyperventilation and hypercapnia. Since the cerebral cortex drains almost exclusively to the superior sagittal sinus, these flow measurements represent an index of global CBF. MR flow quantification provides a new means for assessing dynamic changes in CBF, and may prove useful for monitoring the effects of various disease processes and pharmaceutical agents on CBF.

Adolescent↗

PubMed1990

MR angiography.

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Angiography↗

PubMed1990

Bright pleural effusion and ascites on gradient-echo MR images: a potential source of confusion in vascular MR studies.

Motion of fluids other than blood can cause flow-related signal enhancement on MR images, including MR angiograms. In order to study this problem, the appearance of ascites (20 patients) and pleural effusions (five patients) was assessed on MR images made during suspended respiration with flow-compensated gradient-echo sequences as well as T1- and T2-weighted sequences. Signal intensities of vessels, fluid collections, and muscle were measured and vessel/muscle and vessel/fluid contrast were calculated. Fluid motion was measured with a bolus tracking technique that tags a selected volume of fluid with an RF presaturation. Fluid collections had a bright signal in four of five patients with pleural effusion and in 15 of 20 patients with ascites. The average contrast ratio between bright components of the fluid collections and vessels was only 0.03 +/- 0.09. Bright fluid collections were seen on MR angiograms and could obscure blood vessels. Bolus tracking measurements of ascites revealed multidirectional flow, suggesting that its bright signal is related to motion that continues during suspended respiration. Fluid collections appeared dark on T1-weighted images in all patients, indicating that a short T1 relaxation time was not a cause of the high signal intensity. The results indicate that, despite breath-holding, ascites and pleural effusions can show bright signal intensity on gradient-echo images. Awareness of this phenomenon will avoid confusion between moving fluid collections and flowing blood and identify a source of image degradation on both gradient-echo and T2-weighted spin-echo MR acquisitions.

Ascites↗

PubMed1989

Quantification of blood flow with dynamic MR imaging and presaturation bolus tracking.

A technique is described for rapid imaging of blood flow and dynamic measurement of its velocity. The method is a combination of bolus tracking and low-flip-angle gradient-echo cine angiography. This method provides precise determination of velocity with high temporal resolution in a single measurement. Unlike what occurs in phase imaging techniques, flow is displayed directly, eliminating potential errors that result from non-flow-related sources of phase shifts. Manipulation of raw data sets is avoided. Results obtained from a flow phantom, healthy volunteers, and a patient with an aortic aneurysm demonstrate the capability of the technique to track flow at low and high velocities and to differentiate flowing blood from thrombus. Because of its conceptual simplicity, rapidity, and lack of susceptibility to extraneous phase shifts, this technique may prove ideal for in vivo flow measurement and evaluation of flow patterns.

Aorta, Abdominal↗

PubMed1989

Projection arteriography and venography: initial clinical results with MR.

Motion currently limits the applications of magnetic resonance (MR) angiography in certain regions of the body. To overcome this problem, a series of breath-hold, two-dimensional, flow-compensated gradient-echo images were acquired. These images were then processed by means of the maximum intensity projection algorithm to produce projection angiograms. The method was evaluated in 10 healthy subjects and in 12 patients and validated by comparing conventional angiograms, contrast material-enhanced computed tomographic scans, and duplex sonograms with MR projection arteriograms and venograms of the chest, abdomen, and pelvis. The aorta and pulmonary arteries and their branches were demonstrated, as was detailed anatomy of the hepatic and portal venous systems and inferior vena cava. Renal arteries and veins could be studied in both native and transplanted kidneys. The method permits determination of flow direction and differentiation of arteries and veins and is superior to three-dimensional acquisition techniques for imaging slow blood flow. Initial results suggest that the method may have clinical applications for a variety of vascular disorders.

Arteries↗

PubMed1989

Intracerebral arteriovenous malformations: evaluation with selective MR angiography and venography.

Magnetic resonance (MR) angiography and spin-echo methods were used to evaluate intracerebral arteriovenous malformations (AVMs) in 10 patients. Spin-echo images obtained with flow presaturation demonstrated the nidus of the AVM in all cases, but it was difficult to determine feeding vessels. These vessels were directly visualized with three-dimensional MR angiography; their presence could be indirectly determined by means of selective presaturation of individual vessels, which resulted in a marked decrease in signal within the portion of the AVM supplied by that vessel. Vascular supplies from the internal carotid artery and anterior, middle, or posterior cerebral arteries were detected in all cases, but in three large malformations it was not possible to demonstrate small feeding vessels. MR angiograms were also helpful for further defining the nidus. The combination of MR angiographic and spin-echo methods provides information useful for therapeutic planning not provided by either technique alone.

Adult↗

PubMed1989

MR angiography and dynamic flow evaluation of the portal venous system.

We studied the value of MR angiographic techniques in imaging the portal venous system. Projection angiograms were created by postprocessing a series of two-dimensional, flow-compensated gradient-echo images. Flow velocity was determined by a bolus-tracking method with radiofrequency tagging and multiple data readout periods. Each image was acquired during a breath-hold. MR angiography was applied to six normal subjects and four patients with abnormal hemodynamics in the portal venous system. Flow velocity determined by MR was correlated with the results of duplex sonography. The main portal vein and intrahepatic branches were shown in all cases. Portosystemic collaterals were identified in all patients with portal hypertension. In normal subjects, peak flow velocities (17.9 +/- 2.8 cm/sec) on MR correlated well with values determined by duplex sonography (17.5 +/- 2.2 cm/sec) (r = .846, p less than .04). Reversed portal blood flow was shown in two patients. One patient with portal vein thrombosis had no evidence of flow by MR angiography. Our results indicate that MR angiography can provide a three-dimensional display of normal and abnormal vascular anatomy as well as functional information in the portal venous system.

Blood Flow Velocity↗

PubMed1989

Dynamic MR imaging of the liver with Gd-DTPA: initial clinical results.

Gd-DTPA was evaluated as a hepatic contrast agent for MR imaging. Twenty-six consecutive patients referred for suspected masses in the liver were studied at 1.5 T. Fourteen patients had hepatic metastases and one patient each had cholangiocarcinoma and multicentric hepatocellular carcinoma. Four patients had cavernous hemangiomas and the remainder had other benign lesions. Diagnoses were proved by biopsy, sonography, or radionuclide scintigraphy in 23 cases and by autopsy in one case. Precontrast scans were obtained by using standard pulse sequences. In addition, breath-hold scans were obtained before and after bolus administration of 0.1 mmol/kg Gd-DTPA by using a multislice T1-weighted gradient-echo pulse sequence with an ultrashort echo time. Mean lesion-liver signal difference/noise increased by 50% (p less than .01) in the immediate postcontrast phase. In two of 26 cases, multiple additional lesions as small as 3 mm were detected after contrast administration that were not seen before contrast administration. In no case was lesion-liver contrast worsened on scans obtained immediately after administration of contrast material. However, on delayed scans, detection of lesions worsened in some cases because of equilibration of contrast material between liver and lesion. These initial clinical results suggest that enhancement with Gd-DTPA is a practical method for improving lesion-liver contrast and has the potential to improve the accuracy of MR imaging in the liver. However, optimized fast imaging techniques are required for best results.

Contrast Media↗