Carotid arteries: evaluation with low-field-strength MR angiography

Magnetic resonance (MR) angiography of neck vessels was performed with a 0.2-T permanent magnet by using a two-dimensional, time-of-flight technique. Thirty-one patients were included in the study. The imaging parameters used included a repetition time of 60 msec, an echo time of 10 msec, a 90 degrees flip angle, and a 192 x 256 matrix; 40-50 sequential two-dimensional sections were acquired through the neck. Stenosis was graded on a scale of 1-5. Correlation of digital and MR angiography was made in the clinically nonrelevant cases (stenoses of grades 1 and 2), with overestimation to grade 3 in six cases. Two grade 3 stenoses were overestimated as grade 4. Severe stenoses were correctly characterized in all but one case, which was underestimated because of a segmental short extension of the stenotic lesion. Obstructions were found in two cases. Areas with a lack of signal were observed in four patients with severe stenosis and in two with tortuous arteries. Correct diagnosis, however, was achieved with analysis of the maximum intensity projection animation display. Low-field-strength MR angiography has the same clinical value as that performed with high field strengths.