QUANTIFICATION OF COLLATERAL BLOOD-FLOW IN COARCTATION OF THE AORTA BY VELOCITY-ENCODED CINE MAGNETIC-RESONANCE-IMAGING

Background Knowledge about the volume of collateral flow provides insi ght into the severity of coarctation of the aorta and may be critical in planning the operative approach. There is currently no method for t he quantification of collateral flow in coarctation of the aorta. In t his study, we applied velocity encoded cine magnetic resonance imaging (VENC-MR) to establish the flow pattern and volume of collateral flow in the descending thoracic aorta in normal subjects and patients with coarctation, introducing a new possibility to quantify the severity o f the coarctation by determining the amount of collateral flow. Method s and Results VENC-MR was used to measure flow in the proximal and dis tal descending thoracic aorta in 10 normal subjects. In 23 patients wi th coarctation, flow was measured near the coarctation site and above the diaphragm. Patients were divided into a group with moderate to sev ere coarctation and a group with mild coarctation on the basis of clin ical gradient between upper and lower extremities and the estimation o f the gradient across the coarctation by Doppler echocardiography. The gradient across the coarctation and the degree of anatomic narrowing were also assessed by MR imaging. In normal volunteers, VENC-MR showed a 7+/-6% decrease in total flow, from proximal to distal aorta. The i nterobserver reproducibility was 3.9% to 4.9% (mean, 4.4%). In patient s with moderate to severe coarctation, VENC-MR demonstrated an 83+/-50 % increase in total flow from proximal to distal aorta, yielding a sig nificant change compared with normal subjects (P<.01). Patients with m ild coarctation showed a normal flow pattern and no significant change in total flow. There was a significant relation between the amount of flow increase in the distal aorta and the reduction in luminal diamet er at the coarctation site (r=.94) as well as the clinical gradient (r =.84). Conclusions This study shows the normal flow pattern in the des cending thoracic aorta and its reversal in coarctation due to collater al flow. Thus, VENC-MR can measure collateral how in coarctation and s erves as a unique method for providing this important measurement of t he severity of coarctation of the aorta.