High-resolution Ex-vivo Mr Angiography of the Murine Heart Using Langendorff Gd-dtpa Perfusion Technique

Methods: Hearts were excised from normal mice and from a genetically modified mouse model developed to study cardiac hypertrophy [3]. Animals were humanely killed by cervical dislocation, the aorta cannulated and retrogradely perfused at constant flow (~ 3ml/min) using a Langendorff perfusion system. A first solution containing 0.75mM CaCl2 was perfused to allow the hearts to contract and clear the blood it contained. Next, 10mM BDM (2,3-butane-dione monoxime), an inhibitor of myofibrillar ATPase was then perfused for 6min to stop the contraction. Finally, a formalin solution containing 0.2ml/100ml Gd-DTPA (Magnevist) was perfused for 15min to fix the sample. The hearts were kept immersed in formalin/Gd-DTPA until imaging. Individual isolated hearts were then placed in an Eppendorf tube containing formalin/Gd-DTPA for MR examination. Angiograms were obtained by post-processing MR data acquired using a 9.4T Bruker Avance spectrometer and a spoiled 3D gradient echo imaging sequence with TR/TE/φ=50/5.3/40°. The field of view (FOV) was 15mm and an imaging matrix of 256x256x256 was employed giving isotropic voxels with a size of 59μm. The raw data was acquired using 20 signal averages. Individual axial slices were processed using the Analyze (Biomedical Imaging Resource, Mayo Clinic) software package to remove regions of image hyper-intensity arising in voxels corresponding to both the ventricles and the solution surrounding the heart. The Analyze package was subsequently used to generate the angiograms shown in Figure 1.