title: MRI characterization of agarose gel micro-droplets at acute time-points within the rabbit lumbar muscle.
abstract: Agarose gel micro-droplets supplemented with provisional matrix proteins have been shown to enhance encapsulated cell survival for cell therapy applications. This study evaluated micro-droplet T(1) and T(2) relaxation on a 1.5 T clinical MRI scanner to guide the optimization of encapsulated cell delivery to intermediate-sized animals. Preliminary in vitro experiments using encapsulated human blood-derived endothelial progenitor cells (EPCs) documented a negligible impact of EPC encapsulation on agarose micro-droplet T(1) and T(2) relaxation, even following transient immersion in 2.3 mm Gd-DTPA. Furthermore, Gd-DTPA immersion did not adversely impact encapsulated cell viability. These results allowed for efficient pre-clinical methodological development using direct injections into the rabbit lumbar region of agarose droplets without cells (n=6). At time-points to 6 h, in vivo injection sites displayed elevated T(2) and T(1) (1.8%: DeltaT(2)=53+/-28%, DeltaT(1)=50+/-25%, n=13; 2.5%: DeltaT(2)=41+/-10%, DeltaT(1)=41+/-26%, n=11). Rapid imaging sequences displayed high conspicuity at sites of Gd-DTPA-immersed capsule injection, which persisted for less than 4 h. Therefore, basic differences of micro-droplet T(1) and T(2) when compared to tissue provide a platform for acute tracking of encapsulated cell fate. Transient Gd-DTPA encapsulation accentuates T(1) differences.
authors.affiliation: Department of Cardiology, St Michael's Hospital, University of Toronto, Toronto, ON, Canada. warren.foltz@sw.ca
authors.forename: Warren D
authors.initials: WD
authors.lastname: Foltz
authors.forename: Mark L
authors.initials: ML
authors.lastname: Ormiston
authors.forename: Duncan J
authors.initials: DJ
authors.lastname: Stewart
authors.forename: David W
authors.initials: DW
authors.lastname: Courtman
authors.forename: Alexander J
authors.initials: AJ
authors.lastname: Dick
mesh_terms: D000818:Animals; D018929:Cell Culture Techniques / Q000295:instrumentation / Q000379:methods*; D002470:Cell Survival; D019786:Gadolinium DTPA / Q000737:chemistry; D005782:Gels / Q000737:chemistry; D007089:Image Enhancement / Q000379:methods*; D008159:Lumbar Vertebrae; D008279:Magnetic Resonance Imaging; D045164:Mesenchymal Stem Cell Transplantation / Q000295:instrumentation / Q000379:methods*; D059630:Mesenchymal Stem Cells / Q000166:cytology*; D044085:Microfluidics / Q000295:instrumentation / Q000379:methods*; D018482:Muscle, Skeletal / Q000166:cytology*; D011817:Rabbits; D012685:Sepharose / Q000737:chemistry*
chemical_list: D005782:Gels; D012685:Sepharose; D019786:Gadolinium DTPA