Instrumentation for magnetic resonance angiography

MR angiography in carotid stenosis: a comparison of three techniques

PURPOSE

To compare the accuracy of three different magnetic resonance angiography (MRA) techniques for studying steno-occlusive disease of carotid arteries.

METHODS

64 patients were evaluated with three MRA techniques- three-dimensional (3D) time-of-flight (TOF), two-dimensional (2D) TOF, and 3D Phase-Contrast (PC); the acquisition was in the axial plane, the volume included the carotid bifurcation. Digital subtraction angiography (DSA) was considered the 'gold standard'. The MRA images were reprojected with a maximum intensity pixel ray-tracing (MIP) algorithm. The three MRA techniques were blindly graded as normal, mildly stenotic (0-29%), moderately stenotic (30-49%), severely stenotic (70-99%), or occluded.

RESULTS

DSA provided 128 diagnostic judgments: 92 were negatives and 36 positives. 2D TOF was in agreement with angiography in 116 of 128 cases (90%), but overestimated the results in seven cases and underestimated in five cases. 3D TOF agreed with angiography in 125 of 128 cases (97%), with one overestimation and two under estimations. 3D PC was concordant in 116 of 128 cases (90%), overestimating in six cases, underestimating in six cases. The sensitivity, specificity and diagnostic accuracy for 2D TOF was, respectively 84%, 94%, and 92%, while for 3D TOF was 94%, 100%, and 98%, and for 3D PC 86%, 98%, and 95%. The comparison of the three different MRA techniques provided no statistically significant difference (Friedman test P < 0.05).

CONCLUSION

The high degree of diagnostic accuracy of MRA found in the study of the steno-occlusive disease of the carotid arteries confirms the high degree of reliability of this methodology carried out with the 3D TOF technique, compared to 2D TOF and 3D PC.

Surgical clip artefact mimicking arterial stenosis: a problem with magnetic resonance angiography

In three patients undergoing three-dimensional phase contrast magnetic resonance angiography (MRA) for evaluation of renal transplant arteries, a convincing stenosis was demonstrated that was not present on conventional angiograms. In each patient there was a stainless steel surgical clip in the soft tissues adjacent to the renal artery. Although the clip artefact was easily recognized on the acquired tomographic magnetic resonance slices, it was completely indistinguishable from a true stenosis on the final projection images. This may limit the use of MRA in post-surgical vascular evaluation unless review is made of the phase contrast images.