Feasibility of noninvasive quantitative measurements of intrarenal R(2) ' in humans using an asymmetric spin echo...

The purpose of this study was to demonstrate the feasibility of an asymmetric spin echo (ASE) single-shot echo planar imaging (EPI) sequence for the noninvasive quantitative measurement of intrarenal R(2) ' in humans within 20 s. The reproducibility of R(2) ' measurements with the ASE-EPI sequence was assessed in nine healthy young subjects in repeated studies conducted over three consecutive days. Moreover, we also evaluated whether the ASE-EPI sequence-measured R(2) ' reflected the intrarenal oxygenation changes induced by furosemide in another group of normal human subjects (n = 10). Different flow attenuation gradients (b = 0, 40 and 80 s/mm(2) ) were utilized to examine the impact of the intravascular signal contribution on the estimation of intrarenal R(2) '. In the absence of flow dephasing gradients (b = 0 s/mm(2) ), the computed coefficient of variation (CV) of R(2) ' was 21.31 ± 4.52%, and the estimated R(2) ' value decreased slightly, but not statistically significantly (p > 0.05), after the administration of furosemide in the medullary region. However, CV of R(2) ' was much smaller in the presence of flow dephasing gradients (9.68 ± 3.58% with b = 40 s/mm(2) and 10.50 ± 3.62% with b = 80 s/mm(2) ). Moreover, a significant reduction in R(2) ' in the renal medulla was obtained (p < 0.05 for both b = 40 s/mm(2) and b = 80 s/mm(2) ) after the administration of furosemide, reflecting an increase in oxygen tension in the medullary region. In addition, R(2) ' measurements did not differ between the b = 40 s/mm(2) and b = 80 s/mm(2) scans, suggesting that small diffusion gradients were sufficient to minimize the intravascular signal contribution. In summary, we have demonstrated that renal R(2) ' can be obtained rapidly using an ASE-EPI sequence. The measurement was highly reproducible and reflected the expected intrarenal oxygenation changes induced by furosemide.