A Novel Integration of MR Imaging and Raman Spectroscopy of Mouse Aortas

Noninvasive magnetic resonance imaging (MRI) has the potential to detect the fibrous cap, lipid core, calcifications, and hematoma; however, most MRI studies of atherosclerosis in animals and humans have been limited to evaluation of vessel dimensions. The chemical composition of an atherosclerotic plaque may be the most critical determinant of the vulnerability to rupture; therefore, methods capable of determining plaque composition, such as Raman spectroscopy and microscopy, have great potential for identifying these vulnerable plaques. We are currently developing an integrated technique of noninvasive in vivo MRI combined with ex vivo MRI and Raman microscopy to evaluate the morphology and chemical composition of the aorta in APOE-KO and LDLR-KO mice. MRI studies are performed using a 9.4T MRI system. Cardiac gated in vivo MRI of anesthetized mice show heart and vasculature features with an in plane resolution of ~100m. We are also investigating improvement in visualization of atherosclerotic plaques using a novel contrast agent. For ex vivo MRI, the tissue is embedded in gelatin in a 10 mm NMR tube and placed in a 10 mm volume coil. The morphology of the aorta tissue sample is subsequently examined with a Raman confocal microscope. Raman spectra are acquired at each region with a laser power of ~25mW, 785 nm excitation and a 100X objective. Adventitial fat cells, arterial wall cells and foam cells or cells from the lesion areas have very characteristic and different spectroscopic features. Our preliminary data show that by combining ex vivo MRI and Raman spectroscopy we can examine the composition and morphology of the extremely thin mouse aortic tissue. The results of this project will be used to guide development of in vivo MRI and Raman studies of the influence of gender, diet, and aging on the progression of atherosclerosis in novel mouse models of human cardiac disease.