Non-invasive monitoring of changes in rabbit hearts with aging using MR microscocpy
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KeywordsRadial Diffusivity Rabbit Heart Stripe Pattern Purkinje Fiber Compensatory Hypertrophy
Loss of myocytes followed by compensatory hypertrophy of the remaining cells and interstitial fibrosis are common hallmarks observed in aging hearts [1, 2]. The cardiac conduction system is also subject to alterations with aging, resulting in reduced thresholds to diseases . Biopsy is an accurate and informative means to delineate the age-related changes. However, it is destructive and requires intensive labor, often with severe complications for 3D reconstruction. The aim of this study was to investigate non-invasively morphological changes in aging heart using MR microscopy.
Materials and method
Isolated heart preparation
Hearts (n = 5) of New Zealand White male rabbits (2-5 kg) were isolated and fixed in situ according to the approved animal protocol. Young hearts (n = 2) were 6 month ~ 1 year old. Old hearts were 3 ~ 4 years old.
MR experiments were performed on a 17.6 T / 89 mm vertical wide-bore magnet (Bruker Instruments, Billerica, MA). Three dimensional MR microscopy data were collected using a fast gradient pulse sequence, achieving a voxel resolution of 35 x 35 x 82 μm3. High angular resolution diffusion microscopy (HARDM) using 21 directions was performed with a standard PGSE sequence, achieving an in-plane resolution of 60 μm2 with a slice thickness of 600 μm. The b-value was 1000 s/mm2.
Volume rendering of the 3D MR data sets was performed using ImageJ (ver. 1.31, http://rsbweb.nih.gov/ij/). The tensor processing of HARDM data sets was conducted using fanDTasia™ (©2008, http://www.cise.ufl.edu/~abarmpou/ ) and MATLAB (Mathsoft, Cambridge, MA).
Magnetic resonance microscopy was performed using 17.6 T magnet at Advanced Magnetic Resonance Imaging and Spectroscopy center and the McKnight Brain Institute. Funding for this work was provided by the NIH (1R01EB012874), the NSF through the National High Magnetic Field Laboratory, and seed grants (JRF) from the McKnight Brain Institute and the Department of Radiology, UF.
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