Biomedical subjects

D Saloner

Publications and source records attributed to D Saloner.

41 records · Page 3Linked to original sources

PubMedDate not supplied

High resolution cine MRI of vessel distension.

OBJECTIVE: We have evaluated the ability of high resolution cine MRI to quantify vessel distension. MATERIALS AND METHODS: Gradient echo imaging was used to acquire high resolution, cardiac-triggered imaging of the ascending aorta in normal volunteers to measure changes in the cross-sectional area of the lumen over the cardiac cycle. The effects of temporal resolution, spatial resolution, and the radiofrequency flip angle on the measurements were investigated. RESULTS: High spatial resolution improved the ability to detect changes in the luminal area. High temporal resolution allowed better tracking of maximal vessel distension. A small flip angle reduced the saturation of slow flow observed in imaging acquired using a large flip angle. CONCLUSION: Our study has demonstrated that high spatial resolution and high temporal resolution can substantially improve the measurement of vessel distension. We have overcome problems of intravoxel dephasing and spin saturation by using high spatial resolution, a short echo time with flow compensation, and a small flip angle.

Blood Vessels↗

PubMedDate not supplied

Velocity imaging by rapid cycle tagging.

The unique abilities of magnetic resonance imaging (MRI) to provide detailed images of blood flow in the body, and without resorting to the injection of contrast agents, has provided the stimulus for the keen interest in this subject. In this paper we discuss a technique aimed at providing quantitative information on the distribution of velocity of blood flow across the lumen of a vessel. The technique is designed to reduce the signal from stationary material allowing for a much more accurate determination of the signal from moving material. A particular feature is that the physical phenomenon sensitized is time-of-flight displacements or "fresh spin inflow," and the technique does not rely upon phase-sensitive modulations. Further this technique produces a steady-state spatial distribution of magnetization, and hence a signal, which reflects both the time at which material enters the selected slice and how long the material remains in the slice. In this way, a single image will provide the information necessary to extract information on the velocities of interest.

Blood Flow Velocity↗

PubMedDate not supplied

Artifacts associated with MR neuroangiography.

Neurovascular MR angiography (MRA) is rapidly gaining greater clinical acceptance. To provide functional information, novel techniques of acquisition, information processing, and display are used, generating a new set of artifacts. The purpose of this paper is to outline the causes, provide examples, and note clinical problems associated with MRA artifacts by grouping them into six common types: 1) poor visualization of small vessels, 2) overestimation of stenosis, 3) view-to-view variations, 4) false positives, 5) false negatives, and 6) vessel overlap. This in turn will lead to four generalized solutions: 1) optimize acquisition parameters, 2) edit volume boundaries before performing maximum intensity projection reconstructions, 3) refer to the individual source images, and 4) use alternative image processing. By organizing and simplifying both clinical problems and solutions into major categories, a greater understanding of the current clinical indications and the overall goals of MRA can be achieved.

Angiography↗

PubMedDate not supplied

Assessment of carotid artery stenosis by MR angiography: comparison with x-ray angiography and color-coded Doppler ultrasound.

PURPOSE: To compare magnetic resonance angiography (MRA) with duplex Doppler ultrasound (US) and x-ray angiography (XRA) in the evaluation of the carotid bifurcation. METHODS: The carotid arteries of 61 patients were studied using MRA, US, or XRA; 31 of the patients underwent all three examinations. MRA included both 2D and 3D time-of-flight sequences. Internal and external carotid artery origins were graded normal, mild, moderate, severe, or critical stenosis, or complete occlusion by each of the three studies. RESULTS: Spearman rank correlations of both internal and external carotid artery grades were 0.85 (MRA and XRA), 0.69 (MRA and US), and 0.73 (XRA and US). For internal carotid artery origins only, the correlations were 0.94 (MRA and XRA), 0.85 (MRA and US), and 0.82 (XRA and US). Of discrepancies in internal carotid artery interpretation greater than one grade, seven resulted from US error, three from MRA error, and one from XRA error. A 2-cm partially thrombosed aneurysm detected by US and MRA was missed by XRA. Of 16 possible ulcers on XRA, 11 were noted by MRA, none by US. CONCLUSIONS: MRA and XRA are similar in assessment of carotid bifurcation stenosis. MRA, like US, permits direct visualization of plaque. This preliminary study suggests that MRA may be used to clarify equivocal findings of US, or replace XRA in presurgical planning.

Aged↗

PubMedDate not supplied

Dural sinus occlusion: evaluation with phase-sensitive gradient-echo MR imaging.

The purpose of this study was to evaluate the usefulness of limited-flip-angle, phase-sensitive velocity imaging with gradient-recalled-echo (VIGRE) MR when combined with spin-echo MR in the diagnosis of dural sinus thrombosis. The VIGRE sequence consists of a rapid single-slice acquisition, 50/15/2 (TR/TE/excitations), and 30 degrees flip angle. At each slice position, a total of four images were reconstructed; these consisted of one magnitude image and three images sensitive to proton motion in each orthogonal direction. The flow direction and flow velocity (cm/sec) were obtained from each of the phase images, and results were correlated with data obtained from a phantom experiment. In normal controls, dural sinus velocities ranged from a mean of 9.9 to 14.4 cm/sec for the transverse and superior sagittal sinuses, respectively. Three patients with proved dural sinus occlusion were studied with spin-echo images at 1.5 T. Three-dimensional time-of-flight MR angiography was also performed in one patient. The presence of dural sinus occlusion was determined by the lack of flow void on the spin-echo images, the absence of phase shift on the VIGRE study, and the presence of retrograde flow on the phase image in the sinus proximal to the occluded segment. Time-of-flight angiography overestimated the extent of the thrombosis caused by spin saturation. Follow-up VIGRE studies detected the formation of collateral flow in one patient and recanalization with the establishment of normal antegrade sinus flow in the other. We conclude that phase-sensitive MR imaging is helpful in establishing the diagnosis and extent of dural sinus occlusion.(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗