Measurement of Gd-DTPA diffusion through PVA hydrogel using a novel magnetic resonance imaging method

Polyvinyl alcohol-cryogel (PVA-C) is a hydrogel that is an excellent tissue mimic. In order to characterize mass transfer in this material, as well as to demonstrate in principle the ability to noninvasively measure solute di ffusion in tissue, we measured the diffusion coefficient of the magnetic re sonance (MR) contrast agent gadolinium diethylene triaminopentaacetic acid (Gd-DTPA) through PVA-C using a clinical MR imager. The method involved fil ling thick-walled rectangular PVA-C "cups" with known concentrations of Gd- DTPA solutions. Then by using a fast inversion recovery spin echo MR imagin g protocol, a signal "null" contour was created in the MR image that corres ponded to a second, known concentration of Gd-DTPA. By collecting a series of MR images through the PVA-C wall as a function of time, the displacement of this second known isoconcentration contour could be tracked. Applicatio n of Fick's second law of diffusion yielded the diffusion coefficient. Seve n separate experiments were performed using various combinations of initial concentrations of Gd-DTPA within the PVA-C cups (3.2, 25.6, or 125 mM) and tracked isoconcentrations contours (0.096, 0.182, or 0.435 mM Gd-DTPA). Th e experimental results and the predictions of Fick's law were in excellent agreement. The diffusivity of Gd-DTPA through 10% PVA hydrogel was found to be (2.6 +/- 0.04) x 10(-10) m(2)/s (mean +/- s.e.m.). Separate permeabilit y studies showed that the diffusion coefficient of Gd-DTPA through this hyd rogel did not change with an applied pressure of up to 7.1 kPa. Accurate me asurements could be made within 30 min if suitable Gd-DTPA concentrations w ere selected. Due to the excellent repeatability and fast data acquisition time, this technique Is very promising for future in vivo studies of specie s transport in tissue. (C) 1999 John Wiley & Sons, Inc.