Magnetic resonance imaging of a tissue/implanted device biointerface using in vivo microdialysis sampling.

Real-time in vivo images of magnetic resonance contrast agent diffusion from implanted microdialysis probes were obtained by magnetic resonance (MR) microscopy. A gadolinium-containing contrast agent (Gd-DTPA) was infused through microdialysis probes implanted into the subcutaneous space of male Sprague-Dawley rats. The infusion of Gd-DTPA alters the T1 relaxation time for water protons near the microdialysis probe, thus causing an increase in brightness around the probe. Steady state concentration profiles of Gd-DTPA around the microdialysis probe were attained within 10 min. The distance for the diffusion of Gd-DTPA away from the probe was calculated to be approximately 1400 microm on the basis of an image intensity analysis. A 5-cm field of view was used with a 256 x 256 matrix, giving a voxel volume of 0.190 mm3 (195 microm x 195 microm x 5,000 microm). These experiments demonstrate the ability of magnetic resonance microscopy to obtain real-time images of Gd-DTPA diffusion around implanted microdialysis probes. This noninvasive technique may be useful for determining how fibrous encapsulation during long-term implantation may affect localized mass transport at a biointerface.