Measurement of Gd‐DTPA dialysis clearance rates by using a look‐locker imaging technique

The exponential clearance rate constant, (k), and filtration fraction (FF) have been measured for dialysis of Gadoliniumdiethylenetriaminepentaacetic acid (Gd‐DTPA) (Magnevist, Berlex, Wayne, NJ) solutions by using a Look‐Locker imaging technique under conditions of flow. The measured values of k for the Baxter CA‐50, CA‐110, and CA‐210 filters were 0.0037 ± 0.0003, 0.0057 ± 0.0017, and 0.0092 ± 0.0018 min−1, respectively, for dialysis of 4.0 liters of aqueous Gd‐DTPA solutions. The measured values of FF for the Baxter CA‐110 and CA‐210 filters were 0.060 ± 0.013 and 0.089 ± 0.015, respectively, for dialysis of aqueous Gd‐DTPA at 350 ml/min. The k and FF measurements agree with values that use inversion recovery (IR) on static samples obtained by drawing aliquots of solution during the course of dialysis. This in vitro experiment suggests that accurate in vivo measurements of filtration fraction and glomerular filtration rate (GFR) may be possible.