[Peripheral spin exchange nuclear spin resonance angiography: Studies of the effect of blood flow on contrast]

Sequential two-dimensional (2-D) inflow MR-angiography (SDSMRA) utilizes the bloodflow-induced changes in the MR-signal for intraluminal vessel contrast. To assess the effect of the peripheral arterial flowpulse on the average intraluminal MR-signalintensity (MIMRSI) seven healthy subjects, mean age 31 +/- 4 years, were studied using color Doppler flow mapping and SDSMRA. In each subject the regional MIMRSI was measured in 21 vascular segments and correlated with the regional flowpulse in a simple regression model. MIMRSI ranged from 915 +/- 299 in the right profunda femoris to 1378 +/- 283 in the distal abdominal aorta: distally, the trifurcation it was, with the exception of the posterior tibial artery in three subjects (MIMRSI = 545 +/- 64), not measurable. The regional differences in the peripheral flowpulse were without statistically measurable effect on MIMRSI. MIMRSI was best correlated to the systolic forward flow in 14, to the backward flow in 3, and to the mean forward flow in 1 vascular segment, respectively. The mean correlation coefficient (r) was 0.56, ranging from r = 0.11 in the right popliteal artery to r = 0.93 in the right superficial femoral artery. In the distal abdominal aorta no positive correlation between the blood flow and MIMRSI was determined. The regional differences in the peripheral arterial flow-pulse have no significant effect on MIMRSI in healthy men. MIMRSI correlates best with the systolic forward flow. However, on the average, 44% of the MIMRSI appear to be related to flow-independent yet unidentified factors. Optimal design of SDSMRA pulse sequences will require a better characterization of flow-dependent and flow-independent MIMRSI parameter.