Biomedical subjects

C L Dumoulin

Publications and source records attributed to C L Dumoulin.

At least 19 recordsLinked to original sources

PubMed1992

Secondary flow in the human common carotid artery imaged by MR angiography.

The blood flow in arteries affects both the biology of the vessels and the development of atherosclerosis. The flow is three-dimensional, unsteady, and difficult to measure or to model computationally. We have used phase-shift-based magnetic resonance angiography to image and measure the flow in the common carotid arteries of a healthy human subject. There was curvature of the vessels and thin-slice dynamic flow imaging showed evidence of the presence of secondary motions. Flexing the cervical spine straightened the vessels and reduced the asymmetry of the flow.

Adult↗

PubMed1991

Clinical evaluation of stenosis of the carotid bifurcation with magnetic resonance angiographic techniques.

We evaluated the images of 60 carotid artery bifurcations in 31 patients suspected to have carotid artery disease who underwent invasive carotid angiography and combined two-dimensional, phase-sensitive and a gradient-echo magnetic resonance angiography. The phase scans consisted of seven serial projections that were obtained at 20 degrees intervals (11.0 minutes) around the carotid bifurcation; the gradient-echo (GRASS) scans were composed of 11 axial images (2.4 minutes) acquired through the bifurcation. The two magnetic resonance angiographic techniques yielded complementary pieces of information and were used together to compare magnetic resonance angiography with invasive angiography. Comparison of magnetic resonance and invasive angiograms of the 60 carotid arteries shows that the sensitivity (86%) and specificity (92%) of the magnetic resonance angiographic techniques we used to diagnose clinically significant carotid stenosis approach but do not reach those of invasive angiography.

Aged↗

PubMed1991

Volume rendering and connectivity algorithms for MR angiography.

Several display algorithms for three-dimensional angiographic data are evaluated. The mathematical analysis assumes additive Gaussian noise to predict the background distribution function for maximum intensity projection, sum projection, and connectivity display methods. In the maximum intensity projection method the mean noise level increases with the number of voxels in the ray, while in the sum projection the noise distribution width increases with the projection thickness, but the mean level remains constant. Comparisons of maximum intensity projection, sum projection, and connectivity algorithms applied to an MR angiogram of the circle of Willis are made. Measurements of the noise distribution are in agreement with the analysis. Algorithms combining connectivity with maximum intensity and sum projection are also evaluated. In these methods, a projection image is created using only the voxels marked by connectivity, typically with a 6% threshold of the data. Fine vessels are resolved and background noise is reduced in agreement with the analysis.

Algorithms↗

PubMed1991

Quantitative measurement of blood flow using cylindrically localized Fourier velocity encoding.

A procedure for the quantitative measurement of blood velocity was developed and evaluated in the portal vein, aorta, and vena cava of healthy volunteers. This procedure utilizes Fourier velocity encoding and can be performed with or without cardiac gating. The accuracy of velocity measurements is determined by the accuracy of the gradient subsystem. Flow measurements derived from the velocity measurement are further limited in their accuracy by the luminal cross-section measurement. Spatial localization is accomplished with an excitation pulse having a cylindrical rather than slab geometry. Data are acquired in the presence of a readout gradient to provide resolution along the cylindrical axis.

Aorta↗

PubMed1991

Evaluation of the carotid artery bifurcation: comparison of magnetic resonance angiography and digital subtraction arch aortography.

Thirty-four carotid artery bifurcations were examined using both magnetic resonance angiography (MRA) and digital subtraction arch aortography to determine their accuracy when compared to selective carotid angiography. The sensitivity of MRA was 73% and its specificity was 91% when compared with selective carotid angiography. The sensitivity of arch aortography was 27% and its specificity was 100%.

Aged↗

PubMed1991

Magnetic resonance angiography of abdominal vessels: early experience using the three-dimensional phase-contrast technique.

Based on three-dimensional acquisition of three sequences sensitive to one flow-direction, abdominal magnetic resonance phase-contrast angiography (MRA) was performed in 13 volunteers and 20 patients. The subjects received no antiperistaltic medication and were allowed to breath normally during the three acquisition periods of 11 minutes. The frequency of demonstration of the normal aorta, superior mesenteric and right and left renal arteries was 100%/100%/91%/100%, and of the inferior vena cava, splenic, superior mesenteric and portal veins was 92%/67%/92%/100%, respectively, whereas other abdominal vessels were seen less constantly. In renal artery stenosis or occlusion, MRA detected eight out of nine pathological arteries, missed only a minimal stenosis and was never false positive. In all 10 cases of portal hypertension, MRA demonstrated the venous collaterals detected by conventional angiography and in six cases showed more collaterals, particularly paravertebral vessels. A Budd-Chiari syndrome was investigated as well. If the accuracy of MRA can be proved in larger studies, it may become an important diagnostic tool in evaluating abdominal vascular pathology, such as renal artery stenosis or portal hypertension.

Abdomen↗

PubMed1990

Peripheral vascular and abdominal applications of MR flow imaging techniques.

Many MR flow imaging techniques that have been successfully applied in the carotid arteries and intracranial circulation have been tested in the peripheral and abdominal vasculature. The results have been variable. The lack of success can be attributed to different imaging requirements as well as different patterns of blood flow. These requirements include a large field of view, sensitivity to a wide range of blood flow velocities and complex flow directions, and suppression of overlapping vascular structures and stationary tissue. We have designed strategies using phase contrast MR angiography (MRA) for imaging the arteries and veins of the lower extremity and the abdominal vasculature in normal subjects. This strategy takes advantage of the pulsatile flow pattern present in normal arteries. Overlapping blood flow and stationary tissue were suppressed by a combination of spatial presaturation, optimization of the amplitude and duration of the velocity sensitive gradients, and postprocessing techniques.

Blood Flow Velocity↗

PubMed1990

Three-dimensional phase-contrast MR angiography in the head and neck: preliminary report.

Morbidity and possible mortality associated with contrast angiography lead to its cautious use. A noninvasive method for screening and further delineating known abnormalities would be welcomed. This article reviews the initial results and application of MR imaging to vascular imaging in the head and neck. By using the three-dimensional phase-sensitive method of Dumoulin, Souza, and collaborators, we acquired MR angiograms in 37 min and portrayed blood flow in all the major arteries and veins. Feeding arteries and draining veins of arteriovenous malformations were well delineated; aneurysms as small as 3-4 mm were shown, and obstructed cerebral vessels and the patency of a highly stenotic internal carotid artery were demonstrated. MR angiography of the head or neck offers great promise as a noninvasive means of studying vascular abnormalities.

Adolescent↗

PubMed1990

Three-dimensional phase-contrast MR angiography in the head and neck: preliminary report.

Adolescent↗

PubMed1989

Three-dimensional phase contrast angiography.

Bipolar flow-encoding gradients can be used in a three-dimensional magnetic resonance imaging procedure to provide a noninvasive measure of in vivo blood flow. The resulting volume angiogram is a three-dimensional data matrix which can be retrospectively analyzed and displayed in a variety of ways. This angiographic technique provides good suppression of signals arising from stationary tissue, thereby permitting the visualization of small vessels having relatively slow flow. This suppression is obtained by modulating the amplitude of the flow-encoding gradient pulse to either cancel the stationary tissue signal or displace it relative to the flow signal in the volume image.

Angiography↗

PubMed1989

Three-dimensional time-of-flight magnetic resonance angiography using spin saturation.

A three-dimensional Fourier transform magnetic resonance imaging technique is presented. This procedure can be used to selectively detect flowing material such as blood in arteries and veins. Since flow is detected in a manner in which velocity-induced phase shifts are compensated, signal loss arising from complex flow and turbulence is minimized. The flow image is sensitive to all velocity components of flow. Applications of this technique are limited, however, to relatively straight vessels having appreciable flow. Examples of application of this technique to healthy and diseased carotid arteries are shown.

Angiography↗

PubMed1989

MR angiography with two-dimensional acquisition and three-dimensional display. Work in progress.

Magnetic resonance arteriograms of healthy volunteers and selected patients were produced with a new spoiled gradient-echo pulse sequence based on time-of-flight phenomena. The procedure involves sequential acquisition of many contiguous, thin (1.5-mm) axial two-dimensional sections. These volume data are then submitted to a raytracing projection program, which retrospectively yields multiple arbitrary projection angles rotating through any plane. Venous structures are suppressed with a presaturation slab superior to the current section. The slab location is advanced in concert with advancement of each new section location. The acquisition time varies from 6 to 13 minutes, depending on the number of sections acquired for three-dimensional display. This method obviates the subtraction of image data sets to suppress signals from stationary spins, is more sensitive to slow blood flow than three-dimensional methods of acquisition, and shows special promise for the study of extracranial vascular disease.

Adult↗

PubMed1988

Time-resolved magnetic resonance angiography.

A time-resolved phase contrast magnetic resonance angiography technique is described. This technique provides a series of angiograms obtained at different phases of the cardiac cycle. Such a series of angiograms can be used to evaluate blood flow dynamics. For example, turbulent flow in the regions of vessel bifurcations is easily demonstrated and followed during systole and diastole. Retrograde flow can also be observed. Dynamic angiography can be particularly useful in distinguishing transient image features, such as signal voids due to turbulent flow, from static features arising from vessel morphology.

Angiography↗

PubMed1987

Multiecho magnetic resonance angiography.

Several pulse sequences which generate projected MR angiograms are presented. These pulse sequences exploit multiple-gradient refocused echoes to obtain several independent angiograms, which can be combined or separately analyzed to provide more information than an individual angiogram. For example, a series of angiograms, each with a different projection axis, can be obtained in the time required to obtain a single angiogram using a single-echo method. If the view angle of each echo is the same, then the acquired angiograms can be added to enhance the signal-to-noise ratio. Another pulse sequence simultaneously obtains two or more angiograms, sensitive to orthogonal flow components of the overall blood flow. These angiograms are then added to give an angiogram which is sensitive to flow in all directions.

Angiography↗

PubMed1987

Lipid and water suppression by selective 1H homonuclear polarization transfer.

A pulse sequence is presented which uses Polarization Transfer by a Selective Homonuclear Technique (POTSHOT) to retain all resonances, in phase, from a selected coupled spin system while suppressing all other peaks, from both coupled and noncoupled spins. This technique, which is a selective form of Homonuclear Polarization Transfer (HPT), has been used in a 1.5-T whole-body system to generate edited 1H lactate spectra from lactate/oil phantoms and from excised dog hearts.

Animals↗

PubMed1987

Rapid scan magnetic resonance angiography.

The change in phase of transverse spin magnetization induced by macroscopic spin motion in the direction of an applied magnetic field gradient is used to generate projection angiograms. The method can provide a quantitative measure of laminar and pulsatile flow. Cardiac synchronization is not required provided that data are acquired at many points in the cardiac cycle. The use of short TR and a large number of excitations provides better suppression of stationary tissue and patient motion artifacts than is possible with cardiac gated studies. In addition to improvements in image quality, a substantial shortening of scan time is obtained.

Angiography↗

PubMed1987

3D reconstruction of the brain from magnetic resonance images using a connectivity algorithm.

We present high resolution three dimensional (3D) connectivity, surface construction and display algorithms that detect, extract, and display the surface of a brain from contiguous magnetic resonance (MR) images. The algorithms identify the external brain surface and create a 3D image, showing the fissures and surface convolutions of the cerebral hemispheres, cerebellum, and brain stem. Images produced by these algorithms also show the morphology of other soft tissue boundaries such as the cerebral ventricular system and the skin of the patient. For the purposes of 3D reconstruction, our experiments show that T1 weighted images give better contrast between the surface of the brain and the cerebral spinal fluid than T2 weighted images. 3D reconstruction of MR data provides a non-invasive procedure for examination of the brain surface and other anatomical features.

Adult↗

PubMed1986

Suppression of water and other noncoupled spins by homonuclear polarization transfer in magnetic resonance imaging.

The water component of an NMR image is suppressed by selectively detecting only those protons which are coupled to other protons. Selectivity is obtained by polarization transfer between the coupled spins. Since spin-spin coupling is independent of magnetic field strength, the suppression obtainable by polarization transfer is independent of chemical shift. Consequently, this technique does not require extremely homogeneous magnetic fields for the separation of water and lipid signals. In addition, water suppression by this technique is independent of T1 and T2. Suppression of the water signal intensity has been observed experimentally to be as high as a factor of 100. Suppression is limited only by instrumental imperfections.

Body Water↗