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 echoplanar 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 postprocessing 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.