Evaluation of the cervical carotid bifurcation using MR angiography and cine MRI

MR angiography (MRA) can less invasively evaluate the carotid bifurcation without contrast material. Previous reports on MRA of carotid bifurcation revealed problems of overestimation and false-positive interpretation of stenosis. To clarify reasons causing overestimation and false-positive interpretation we investigated flow dynamics in the carotid bifurcation by cine MRI. Twenty-eight patients who were suspected to have stenosis of the internal carotid artery by MRA were studied. Images of the carotid bifurcation were obtained with 3-D phase contrast method by 0.5-T MR scanner. All patients were examined by IV-DSA or direct carotid angiography. Cine MRI of the carotid bifurcation was obtained with gradinet-echo sequence by 1.5-T MR scanner. Comparison of MRA and conventional angiography in evaluating degree of stenosis in the carotid bifurcation demonstrated that there were 57.1% agreement, 32.1% false-positive estimation and 10.7% overestimation. Cine MRI demonstration turbulent flow in the normal carotid bifurcation and also in the sclerotic bifurcation. Turbulence in the carotid bifurcation with severe sclerosis was greater than that in the normal carotid bifurcation. Turbulent flow could be seen extending distally to the stenotic site of the internal carotid artery. Turbulent flow in the carotid bifurcation, causing a decrease or loss in signal intensity of MRA according to the severity of the turbulence, must be a major contributing factor in false-positive estimation and overestimation of stenosis. (author)