title: Spatiotemporal quantification of local drug delivery using MRI.
abstract: 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 T1 maps (generated from T1-weighted images with varied TR) were processed using noise-reducing filtering. A segmented region of contrast, from a thresholded image, was converted to concentration maps using the equation 1/T1=1/T1,0+R1C, where T1,0 and T1 are the precontrast and postcontrast T1 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 T1,0, requiring no registration of pre- and postcontrast image volumes, was compared to a method using either affine or deformation registrations.
authors.affiliation: Center for Interventional Biomaterials, School of Biological and Health Systems Engineering, Arizona State University, P.O. Box 879709, Tempe, AZ 85287, USA.
authors.forename: Morgan B
authors.initials: MB
authors.lastname: Giers
authors.forename: Alex C
authors.initials: AC
authors.lastname: McLaren
authors.forename: Jonathan D
authors.initials: JD
authors.lastname: Plasencia
authors.forename: David
authors.initials: D
authors.lastname: Frakes
authors.forename: Ryan
authors.initials: R
authors.lastname: McLemore
authors.forename: Michael R
authors.initials: MR
authors.lastname: Caplan
mesh_terms: D000818:Animals; D001843:Bone Cements; D002626:Chemistry, Pharmaceutical; D019295:Computational Biology; D003287:Contrast Media / Q000493:pharmacokinetics; D003692:Delayed-Action Preparations / Q000493:pharmacokinetics*; D016503:Drug Delivery Systems; D019786:Gadolinium DTPA / Q000493:pharmacokinetics; D006801:Humans; D021621:Imaging, Three-Dimensional; D008279:Magnetic Resonance Imaging / Q000379:methods* / Q000706:statistics & numerical data; D019904:Polymethyl Methacrylate; D019736:Prostheses and Implants; D011817:Rabbits
chemical_list: D001843:Bone Cements; D003287:Contrast Media; D003692:Delayed-Action Preparations; D019904:Polymethyl Methacrylate; D019786:Gadolinium DTPA