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

MR imaging of Crohn disease: use of perflubron as a gastrointestinal contrast agent.

This study was undertaken to evaluate the use of perflubron (perfluorooctylbromide) as an oral contrast agent for magnetic resonance (MR) imaging of patients with Crohn disease. MR examinations were performed before and after perflubron administration in 12 patients with documented Crohn disease. Glucagon was administered intramuscularly before the post-perflubron examinations. Each patient also underwent abdominal computed tomography within 48 hours of MR imaging. The imaging studies were analyzed for effectiveness of bowel marking with oral contrast agent, clarity bowel wall visualization, and presence of bowel wall thickening and extraluminal manifestations of Crohn disease such as abscess or fistula formation. Analysis of the imaging studies showed effective marking of the bowel with perflubron and improved bowel wall visualization on postcontrast MR images. Detection of bowel wall thickening and extraluminal complications of Crohn disease was not significantly improved on postcontrast MR images. The authors conclude that perflubron administration effectively marked the bowel and increased the clarity of bowel wall visualization but did not significantly increase the detection of abnormalities related to Crohn disease in the study population.

Adult↗

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

Thyroid cyst mistaken for carotid pseudoaneurysm by MR angiography. Case report.

A normal volunteer for magnetic resonance angiography of the carotid arteries had an abnormal examination that suggested a common carotid pseudoaneurysm. High resolution sonography identified a normal carotid artery immediately adjacent to a thyroid lesion, part of which was cystic and which mimicked carotid aneurysmal disease.

Adult↗