MAGNETIC-RESONANCE VOLUME FLOW AND JET VELOCITY MAPPING IN AORTIC COARCTATION

Objectives. Nuclear magnetic resonance (MRI) velocity mapping was used to characterize Bow waveforms and to measure volume flow in the ascen ding and descending thoracic aorta in patients with aortic coarctation and in healthy volunteers. We present the method and discuss the rela tion 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 echocardiograp hy. Background. The development of a noninvasive imaging method for mo rphologic visualization of aortic coarctation and for measurement of i ts impact on blood flow is highly desirable in the preoperative and po stoperative management of patients. Methods. Magnetic resonance imagin g phase shift velocity mapping was used to measure ascending and desce nding aortic volume flow in 39 patients with aortic coarctation and in 12 healthy volunteers. Magnetic resonance imaging was also used for a natomic and peak jet velocity measurements. The latter were compared w ith those available from continuous wave Doppler study in 40% of the p atients. Results. Whereas ascending aortic volume flow measurement did not show significant differences between tl;e patient and healthy con trol groups, volume how curves in the descending aorta did show signif icant differences between the two groups. Peak volume flow (mean +/- S D) 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 l iters/min in patients and 3.9 +/- 1.1 liters/min in control subjects ( p < 0.05). The descending/ ascending aorta how ratio was 0.47 +/- 0.19 in patients and 0.64 +/- 0.08 in control subjects (p < 0.05). These v ariables correlate well with the degree of aortic narrowing. Peak coar ctation jet velocity measured by MRI velocity mapping is comparable to that obtained from continuous wave Doppler study (r = 0.95). Conclusi ons. We established normal ranges for volume flow in the descending ao rta and demonstrated abnormalities in patients with aortic coarctation . These abnormalities are likely to be related to resistance to flow i mposed by the coarctation and could represent an additional index for monitoring patients before and after intervention.