Rapid measurement of Gd-DTPA extraction fraction in a dialysis system using echo-planar imaging.
Gd-DTPA (Magnevist, Berlex, Wayne, NJ) extraction fractions (EF) have been measured for three dialysis filter types using an echo-planar imaging (EPI) Look-Locker T1 measurement technique under conditions of fast and slow flow. The mean EF measured in Fresenius (Bad Homburg, Germany) F3, F6, and F8 dialysis filters were 0.015 +/- 0.005, 0.053 +/- 0.004, and 0.084 +/- 0.003, respectively, under conditions of fast flow which provided complete refreshment of spins in the intervals between read-out pulse samples of the T1 relaxation recovery. Data acquisition and post-processing techniques were developed to extend the accuracy of the LL technique to systems with slow flow which did not provide complete refreshment of spins between samples of the T1 recovery. A multi-shot EPI LL interleaved acquisition of relaxation recovery space (IRRS) provided T1 measurement accuracy comparable to the refreshed system, +/- 10, but at the expense of increased scan times (factor of 2 or 3). Discarding the first few non-equilibrium relaxation recovery samples from the T1 fit allowed accurate T1 estimation (+/- 10) with a single-shot EPI LL method under conditions of slow flow. These EPI LL EF measurement methods may provide useful techniques for evaluating renal function in vivo.