Spatiotemporal Quantification of Local Drug Delivery Using MRI

Controlled release formulations for local, in vivo drug delivery are of growing interest to device manufacturers, research scientists, and clinicians; however, most research characterizing controlled release formulations occurs in vitro because the spatial and temporal distribution of drug delivery is difficult to measure in vivo. In this work, in vivo magnetic resonance imaging (MRI) of local drug delivery was performed to visualize and quantify the time resolved distribution of MRI contrast agents. Three-dimensional T (1) maps (generated from T (1)-weighted images with varied T (R)) were processed using noise-reducing filtering. A segmented region of contrast, from a thresholded image, was converted to concentration maps using the equation 1/T (1) = 1/T (1,0) + R (1) C, where T (1,0) and T (1) are the precontrast and postcontrast T (1) map values, respectively. In this technique, a uniform estimated value for T (1,0) was used. Error estimations were performed for each step. The practical usefulness of this method was assessed using comparisons between devices located in different locations both with and without contrast. The method using a uniform T (1,0), requiring no registration of pre- and postcontrast image volumes, was compared to a method using either affine or deformation registrations.