Four dimensional bolus tagging imaging of pulsatile flow.

Inversion bolus tagging MR methods were used to provide a graphic depiction of the axial velocity in three spatial dimensions for pulsatile flow through complex geometries. Visualization of the flow field was readily apparent, and a train of tagged boli were depicted providing an immediate overview of the displacement of flowing fluid over the entire pulsatile cycle. Tagging efficiency obtained using adiabatic inversion pulses was improved compared to that with a windowed sinc pulse.

Calculation of the magnetization distribution for fluid flow in curved vessels.

The signal intensity in magnetic resonance angiography (MRA) images reflects both morphological and flow-related features of vascular anatomy. A thorough understanding of MRA, therefore, demands a careful analysis of flow-related effects. Computational fluid dynamics (CFD) methods are very powerful in determining flow patterns in 3D tortuous vessels for both steady and unsteady flow.

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.

MR imaging of flow through tortuous vessels: a numerical simulation.

A novel computer simulation technique is presented that allows the calculation of images from Magnetic Resonance Angiography (MRA) studies of blood flow in realistic curving and branching two-dimensional vessel geometries. Fluid dynamic calculations provide flow streamlines through curved or branching vessels. MR simulations generate images for specific MR pulse sequence parameters.

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.

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.