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D Saloner

Publications and source records attributed to D Saloner.

At least 37 records · Page 2Linked to original sources
PubMed1994

High speed bolus tagging: time resolved velocity quantification of pulsatile flow in a single breath hold.

We have implemented a high speed method for cardiac-triggered blood velocity quantification within a single breath hold on a conventional MR system. The method, based on bolus tagging, was tested using a pulsatile flow phantom and evaluated in vivo. The image acquisition time was reduced by a factor of N by acquiring N phase encode lines per bolus tag application. The clarity of the flow tag was found to vary with how k-space was covered during data collection. The technique was optimized and multiple bolus tag images were obtained throughout the cardiac cycle within a single breathold.

Aorta, Thoracic↗
PubMed1994

Measurement of internal carotid artery stenosis from source MR angiograms.

PURPOSE: To determine whether interpretation of internal carotid artery (ICA) stenosis from source partitions is more accurate than interpretation from maximum-intensity projections (MIPs) from three-dimensional (3D) time-of-flight (TOF) magnetic resonance (MR) angiography. MATERIALS AND METHODS: The percentage of diameter ICA stenosis was measured on source images and MIPs from sagittal (n = 150) and transverse (n = 140) 3D TOF MR angiography. Measurements were compared with those from conventional angiography. RESULTS: Sensitivity and specificity for distinguishing 70%-99% stenosis were 96% and 78%, respectively, for sagittal MIPs, 88% and 90% for sagittal source images, 92% and 86% for transverse MIPs, and 92% and 95% for transverse source images. Areas under the receiver operating characteristic curves statistically significantly increased (P < .05) with interpretation from source images. Complete loss of intravascular signal was not encountered on source partitions except within a greater than 85% stenosis. CONCLUSION: Interpretation of source partitions rather than MIPs reduces the tendency for overestimation of stenosis with MR angiography and improves the specificity for discriminating 70%-99% stenosis.

Aged↗
PubMed1992

Evaluation of myocardial perfusion abnormalities with gadolinium-enhanced snapshot MR imaging in humans. Work in progress.

To determine whether myocardial perfusion abnormalities could be detected in patients with coronary artery disease by means of contrast material-enhanced magnetic resonance (MR) images, a snapshot imaging technique was used in six patients with coronary artery disease and four healthy subjects in conjunction with pharmacologic stress (dipyridamole infusion) and bolus injection of gadopentetate dimeglumine. MR images from all patients and healthy subjects were quantitatively analyzed to define spatial changes in signal intensity after administration of dipyridamole and gadopentetate dimeglumine. The resultant findings were compared with findings on thallium-201 scintigrams obtained after administration of dipyridamole and on coronary arteriograms in all patients. Nine myocardial regions supplied by stenosed arteries showed diminished levels of signal intensity after infusion of the contrast agent compared with those of normally perfused regions. These findings were in agreement with those obtained with T1-201 scintigraphy (in eight of nine regions) and arteriography. Thus, contrast-enhanced high-speed MR imaging with use of dipyridamole enabled detection of regional perfusion abnormalities in humans.

Adult↗
PubMed1992

Magnetic resonance angiography of the carotid artery combining two- and three-dimensional acquisitions.

To assess the agreement between magnetic resonance angiography and conventional angiography in the evaluation of carotid stenosis, 61 carotid arteries of 40 patients were studied by combined two- and three-dimensional magnetic resonance angiography and conventional angiography. Stenosis of the internal carotid artery was categorized as mild, moderate, severe, critical, or complete occlusion. In 42 arteries, the degree of stenosis according to magnetic resonance angiography correlated exactly to that found by conventional angiography. In the remaining 19 carotid arteries, the magnetic resonance angiographic measurement of stenosis differed from the conventional angiographic measurement by only one size category. The Spearman rank correlation coefficient was 0.95 (p < 0.001). This study showed that by combining information from two- and three-dimensional magnetic resonance angiographic studies and making use of the advantages of each method, magnetic resonance angiography was comparable to conventional angiography in determining carotid stenosis. Magnetic resonance angiography tended to demonstrate a higher level of stenosis when there was a discrepancy. These data demonstrate that magnetic resonance angiography is a steadily improving technology. Although additional studies need to be done, it seems clear that magnetic resonance angiography will be an imaging modality comparable in accuracy to conventional angiography.

Aged↗
PubMed1991

Color Doppler artifact from metallic carotid clamp.

The presence of mirror artifacts in color Doppler has been noted by others. In that report, the artifact arose from scattering at the smooth vessel wall and appeared as signal outside the lumen of the vessel, but with no change in flow direction. As experience increases, recognition of the artifacts of color Doppler will lead to a better understanding and more precise evaluation. This case shows that a band of metal around the carotid artery causes registration errors in color-coded Doppler, and perhaps other metal foreign bodies in the soft tissues have similar potential. The specific appearance of the artifact will depend sensitively on the geometrical configuration of the metal body itself and on its orientation relative to the surrounding anatomy and the ultrasound probe. Appropriate placement of the transducer will reduce such artifact.

Artifacts↗
PubMed1991

Noninvasive evaluation of cerebral ischemia. Trends for the 1990s.

A number of diagnostic tools have been developed over the past decade that facilitate the noninvasive evaluation of cerebral ischemia. From duplex Doppler ultrasound to xenon computed tomography and magnetic resonance angiography, a greater trend toward combining both anatomic and function information is anticipated. The methodology, limitations, and current clinical applications of these three diverse techniques, with emphasis on xenon computed tomography and magnetic resonance angiography, are discussed. Both xenon computed tomography and magnetic resonance angiography can be performed on current systems with minimal hardware and software modifications. As a result, standard anatomic and structural imaging can be supplemented with diverse information such as quantitative brain perfusion without and with flow challenging as well as flow mapping and velocity imaging, which approximates conventional x-ray angiography.

Brain↗
PubMed1990

Flow velocity quantitation using inversion tagging.

A method for quantitating flow velocities is presented. The technique tags multiple boli of magnetization in transit across a thick selection slab using rf inversion pulses. Results in phantoms and in vivo demonstrate that the method is robust and can provide velocity determinations in tortuous vessels.

Blood Flow Velocity↗
PubMed1990

Dedicated coil for carotid MR angiography.

A magnetic resonance imaging coil was developed to improve contrast in direct coronal and sagittal time-of-flight carotid angiograms. The sensitive volume of the coil extends from the carotid origins to the siphons. Angiographic contrast can be optimized for an arterial segment of interest by repositioning the coil to minimize presaturation of blood before it enters the segment.

Carotid Arteries↗
PubMed1989

Current applications of magnetic resonance vascular imaging.

A wide variety of MRI techniques is available for vascular imaging, each exploiting a different property of flowing blood to achieve contrast. These include spin-echo, which has been used for the diagnosis of aortic dissection and of great vessel anomalies, as well as for the evaluation of pulmonary flow in patients with pulmonary hypertension and pulmonary embolism. Spin echo excels in detecting infection and hematoma in the tissues around grafts and vessels. Phase display imaging has proven useful in differentiating signal of slow flow from that of intravascular thrombus. Imaging of peripheral vessels can be achieved with gradient refocused sequences, which provide bright intravascular signal over a wide range of flow velocities. These sequences may be combined with subtraction strategies to eliminate the signal from stationary tissues in order to generate an angiographic image. The advent of three-dimensional MR angiographic imaging techniques provides an effective way to display peripheral vessels. Early experience implies that MR angiography will play an important role in vascular imaging in the future, provided that the signal loss from turbulent flow can be minimized.

Arterial Occlusive Diseases↗
PubMedDate not supplied

Application of a connected-voxel algorithm to MR angiographic data.

A connected-voxel algorithm (CVA) that improves the contrast and conspicuity of blood vessels in maximum-intensity-projection (MIP) magnetic resonance (MR) angiography is described. Images from a variety of anatomic regions in healthy volunteers were calculated with either an MIP procedure alone or with data that had first been processed with the CVA. A low-signal-intensity threshold is first applied to separate groups of voxels associated with different vessels from one another and to eliminate the contribution from low-intensity stationary material. The remaining voxels are grouped by a connectivity criterion into discrete "objects." Vessels are represented by extended objects, and small objects are discarded. The CVA, therefore, reduces the full three-dimensional data set into a small number of discrete objects. It is a powerful technique that can be used to remove signal from vessels overlying the vessel of interest, to separate objects representing arterial flow from those representing venous flow, to eliminate flow artifact from projection images, and to more completely retain signal within the vascular lumen. This technique has been successfully demonstrated with MR angiography in healthy volunteers.

Algorithms↗
PubMedDate not supplied

MR angiography with a cardiac-phase--specific acquisition window.

A method for cardiac-phase-specific magnetic resonance (MR) angiography is presented. An electronics module permits incrementing of phase-encoding gradients and storage of incoming data only during a chosen portion of the cardiac cycle. Suppression of stationary material is maintained by delivering radio-frequency pulses at constant TR throughout the cycle. Imaging of a pulsatile flow phantom demonstrates that acquiring data only during systole substantially increases the signal intensity of flowing material. In addition, phase-encoding ghost artifacts are eliminated from the neighborhood of the vessel. Image acquisition time is minimized by acquiring only the low-frequency phase-encoding lines in the cardiac-phase-specific mode. In healthy volunteers, greatly improved MR angiograms of the lower extremities are obtained. Fat saturation and magnetization transfer further enhance vessel/background contrast. Acquiring data only during systole ensures rapid inflow for all phase-encoding lines, permitting a near-longitudinal section orientation without in-plane saturation. This substantially reduces total acquisition time relative to axial acquisition.

Blood Vessels↗
PubMedDate not supplied

Cardiac-gated MR angiography of pulsatile flow: k-space strategies.

Signal strength in time-of-flight magnetic resonance (MR) angiography of pulsatile flow is modulated by the time-varying intraluminal magnetization strength. The specific appearance of MR angiographic images therefore depends on the relationship of different phase-encoding steps to the pulsatile flow waveform. Cardiac-phase gating can be applied with phase-encoding reordering to acquire different regions of k-space during the desired phases of the cardiac cycle. The authors have developed a simulation program for evaluating the merits of different encoding strategies for pulsatile flow. The model was validated with phantom studies. High signal intensity relative to that in conventional MR angiographic studies can be attained with strategies that impose relatively small penalties in total acquisition time.

Artifacts↗
PubMedDate not supplied

Instrumentation for magnetic resonance angiography.

Magnetic resonance angiography (MRA) places high demands on instrumentation capabilities. Magnetic gradient strength capabilities, main magnetic field strength and homogeneity, and eddy current compensation all play a role in determining the quality of the flow studies. In addition, radiofrequency coil design and use is governed by the specific vascular territories of interest. Once the instrumentational and pulse sequence considerations have been optimized, the postprocessing and display of the acquired three-dimensional data sets is of key importance. Great strides have been made in addressing instrumentation needs for MRA, but further improvements are anticipated.

Algorithms↗
PubMedDate not supplied

Intensity dependence of flow signal in slice selective velocity measurements.

The quantitative determination of flow velocities using inflow-outflow techniques require slice selective excitation pulses. The intensity-velocity relationship for such methods is shown to be such that flow velocities estimated using techniques which rely on an absolute calibration of the measured intensity are sensitive to the details of the slice profile of the excited material. This can cause errors when the estimation of flow velocities is made from the image intensity. A method which provides a measure of the flow velocities and which relies only on relative variations in intensity is examined and shown to be insensitive to details of the slice profile.

Blood Flow Velocity↗
PubMedDate not supplied

A numerical study of magnetic resonance images of pulsatile flow in a two dimensional carotid bifurcation: a numerical study of MR images.

A numerical method to simulate magnetic resonance angiographic images is proposed. The new method greatly simplifies the calculation of the average phase in a voxel, the bottleneck of previous simulations, and reduces the computation time by more than a factor of 5. Both the Navier-Stokes and the Bloch equations are solved on the same mesh to obtain the distributions of the modulus and phase of the magnetization. The data in the frequency domain are reordered according to the gating strategy to generate the final images. Pulsatile flow through a 2D normal carotid bifurcation is considered as a test case. Images for magnetic resonance angiography with an uncompensated gradient waveform, a velocity-compensated gradient waveform and an uncompensated short-TE gradient waveform are compared. Systolic gating images are shown to have degraded image quality. Images acquired with diastolic-gating have little variation in magnetization strength throughout the pulsatile cycle and provide a better representation of the vessel lumen.

Algorithms↗
PubMedDate not supplied

MR flow imaging in projection through a stationary surround.

A magnetic resonance imaging technique is discussed which, by cyclic inversion of the longitudinal magnetization, produces boli of moving material with alternating sign of the magnetization. At periodic spacings along the flow direction, the signal strength from magnetization of positive sign is equal to that of negative sign. This results in a minimum in the intensity distribution. A banded intensity structure results reflecting the distribution of flow velocities across the imaged vessel. The inversion of the longitudinal magnetization causes an inherent suppression of the signal from stationary material allowing the collection of flow images in projection through a stationary surround without the need for image subtraction.

Blood Flow Velocity↗