Magnetic resonance volume flow and jet velocity mapping in aortic coarctation

Royal Brompton National Heart and Lung Hospital, National Heart and Lung Institute, London, England, United Kingdom.

OBJECTIVES. Nuclear magnetic resonance (MRI) velocity mapping was used to characterize flow waveforms and to measure volume flow in the ascending and descending thoracic aorta in patients with aortic coarctation and in healthy volunteers. We present the method and discuss the relation between these measurements and aortic narrowing assessed by MRI. Finally, we compare coarctation jet velocity measured by MRI velocity mapping with that obtained from continuous wave Doppler echocardiography. BACKGROUND. The development of a noninvasive imaging method for morphologic visualization of aortic coarctation and for measurement of its impact on blood flow is highly desirable in the preoperative and postoperative management of patients. METHODS. Magnetic resonance imaging phase-shift velocity mapping was used to measure ascending and descending aortic volume flow in 39 patients with aortic coarctation and in 12 healthy volunteers. Magnetic resonance imaging was also used for anatomic and peak jet velocity measurements. The latter were compared with those available from continuous wave Doppler study in 40% of the patients. RESULTS. Whereas ascending aortic volume flow measurement did not show significant differences between the patient and healthy control groups, volume flow curves in the descending aorta did show significant differences between the two groups. Peak volume flow (mean +/- SD) was 10.6 +/- 5.3 liters/min in patients and 19.6 +/- 4.7 liters/min in control subjects (p < 0.001). Time-averaged flow was 2.5 +/- 0.9 liters/min in patients and 3.9 +/- 1.1 liters/min in control subjects (p < 0.05). The descending/ascending aorta flow ratio was 0.47 +/- 0.19 in patients and 0.64 +/- 0.08 in control subjects (p < 0.05). These variables correlate well with the degree of aortic narrowing. Peak coarctation jet velocity measured by MRI velocity mapping is comparable to that obtained from continuous wave Doppler study (r = 0.95). CONCLUSIONS. We established normal ranges for volume flow in the descending aorta and demonstrated abnormalities in patients with aortic coarctation. These abnormalities are likely to be related to resistance to flow imposed by the coarctation and could represent an additional index for monitoring patients before and after intervention.

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