MRI FOR RODENT TBI MODELS

S.T. Fricke

Georgetown University Med. Ctr., Washington , DC

Introduction: Physiological support and immobilization are required during MRI. The information content of images can include methods for identifying tissue quality and physicio-chemical parameters. Combined images, from the various imaging protocol, provide information that spans the realms of anatomical chemical and functional information. Longitudinal studies are possible using an animal as its own control.   Demonstrating the validity of an imaging technique requires the exact sectioning of tissue. It is now possible to perform such comparisons in a precise mechanical fashion.   The implications of this technology are discussed.

Methods: Magnetic Resonance Imaging is preformed at 7 tesla using customized animal management systems (ASI Instruments, Warren , MI ).   These systems include a full array of physiological monitoring and support.   The importance of the system is two fold: animal alignment in the imaging field and physiological support inside the imaging apparatus. The same experiments are preformed over 96 hours, removing and replacing the animal four separate times. Brain is excised, placed into brain tissue matrix (ASI Instruments, Warren , MI ) and sectioned.   Matrix and MRI stereotax are indexed to each other, same section is identified between sections and MRI.   Some sections are used as "slice culture", some are sent to histology and others to laser capture microdissection (LCM) for future RNA analysis.   After slice culture progression and manipulation slices are imaged.

Results: Images of apparent diffusion lesion size were mapped to lesions identified by perfusion imaging techniques. Diffusion/perfusion mismatch becomes obvious, thus indicating the region of potentially salvageable tissue.   When high-resolution images of a rodent brain are taken certainty of voxel placement for localized spectroscopy is possible.   Spectra from site of lesion and spectra from contralateral side of brain can be compared.

Discussion:   Identification of exact brain tissue regions between devices and techniques opens new doors in localized medicine. Equipment that take experiments from implant/insult to non-invasive, in-vivo monitoring of lesion progression --and the effects of treatment-- help better understand brain trauma and treatment. Midline shift can be noted and followed during inflammation and regression of lesion site, this may have implications in the use of contralateral data in TBI.   Such equipment can be used on multiple different imaging platforms to obtain even greater information content.