[Magnetic resonance angiography of the arteries supplying the brain]

MR flow quantification using RACE: clinical application to the carotid arteries

Real time MR flow quantification was performed with real time acquisition and evaluation of motion (RACE) in a rigid phantom under steady flow conditions and in the common carotid arteries of 43 subjects aged 24-78 years. Hemodynamic information included the intraluminal velocity distribution during the complete cardiac cycle, the distensibility of the arterial wall, and age-dependent changes of the flow curves. Systolic peak velocities of 51 +/- 33 cm/s and time-averaged volume flow rates of 4.3 +/- 2.0 ml/s were measured in healthy subjects. Flow rates below 3.0 ml/s and the observation of abnormal flow patterns indicated stenoses greater than 70% in the region of the bifurcation (sensitivity: 83.3%; specificity: 93.7%; accuracy: 71.4%). Improvements may be achieved from a combination with MR angiography, providing both functional and morphologic vascular information noninvasively within one observer-independent examination. MR imaging, therefore, has a strong potential for the diagnosis of critical stenoses in symptomatic patients.

Magnetic resonance angiography in vertebrobasilar ischemia. Preliminary experience

Forty-five patients were evaluated for vertebrobasilar ischemic disease by magnetic resonance imaging and magnetic resonance angiography (MRA). Ten also underwent intraarterial digital subtraction angiography. All were sorted into three groups based on results of the MRA and their clinical presentation. In the first group, vertebrobasilar ischemic disease could be reasonably excluded. In the second, such disease was nearly certain. In the third group, the vertebrobasilar system could not readily be assessed by the MRA alone and often required further studies. In 8 of 10 patients a strong correlation was found between MRA and intraarterial digital subtraction angiography. MRA provided valuable information for assessing vertebrobasilar disease and, in many instances, eliminated the need for invasive angiography.

MRA review

Magnetic resonance (MR) angiography is a rapidly evolving field in MR imaging, the main goal of which is a noninvasive tool for visualizing blood vessels. The acquisition of continuous images of the blood vessels, comparable to the conventional DSA images, as well as the functional evaluation of blood-flow velocities and flow patterns are the subject of continuing developments. The basic principles of the various techniques and their clinical applications are reviewed and the practical limitations in specific anatomic regions discussed. The review concludes with a survey of future developments.

MR imaging of poststenotic flow phenomena: experimental studies

Poststenotic flow patterns were analyzed in a flow phantom with a 1.5-T magnetic resonance (MR) imager, with use of different MR imaging and MR angiographic pulse sequences. Spin-echo, fast field-echo, two-dimensional inflow (multiple single-section technique), and flow-adjusted-gradient sequences were applied. For the spin-echo sequences, modulus and phase images were reconstructed from each data set. The length of the region of poststenotic changes in signal amplitude and phase measured at a constant flow rate increased with stenosis grade. Likewise, the length of the region of poststenotic changes measured at a constant stenosis grade increased with flow rate. Moreover, the results depended on the alignment of the flow direction with the readout gradient. Comparison of modulus and phase images allowed discrimination of turbulent and nonturbulent flow, which yields additional information on stenosis grade in clinical MR angiography.