Approaching Cardiac Development in Three Dimensions by Magnetic Resonance Microscopy
Cardiac neural crest (CNC) ablation in embryonic chicks leads to conotruncal anomalies of the heart as a result of altered cardiac looping. Altered looping results from failure of the myocardium from the secondary heart field to be added to the outflow tract. Various imaging techniques have been applied to visualize embryonic heart development. However, morphological abnormalities frequently cannot clearly be identified or appreciated in 2 dimensions, particularly those involving misorientation of cardiovascular structures and changes of myocardial volume. We present here 3-dimensional (3D) reconstructions of the embryonic chick heart at looping stages in sham-operated and CNC-ablated embryos acquired by magnetic resonance microscopy (MRM) using a new dual-contrast method for specimen preparation that combines perfusion fixation and immersion in fixative with a macro-molecular gadolinium-based contrast agent. In contrast to previous techniques, this method provides imaging not only of the cardiac chambers and vessel lumens but also of internal and external cardiac structures, such as the ventricular wall, myocardial trabeculations, cardiac jelly, and endocardial cushions. Furthermore, it allows morphovolumetric analysis of hearts at different stages. There is an excellent correlation between images obtained from MRM and those obtained by routine histology (Figure 1). 3D MRM can represent anatomic information ranging from sectional images along arbitrary anatomic planes to volumetric reconstructions of the heart (Figure 2 and Movies I through IV). A great advantage of 3D reconstructions is that rotation of the image around any axis is possible without the limitations associated with interpretation based on a single plane, as shown in Figure 3 and in Movies V and VI. MRM was performed on a 9.4-T magnet using custom-designed radiofrequency coils (Helmholz pair and solenoid coils), resulting in image resolutions of 25- and 31-μm3 isotropic voxels for 2 stages of chick embryos (stage 22 [day 4] and stage 28 [day 5.5 to 6]). The 3D imaging data were postprocessed with ImageJ (NIH). The movies were created in VoxelView (Vital Images) and Matlab (The MathWorks), and the 3D images and slices in Slicer Dicer (PIXOTEC, LLC).
This work was supported by National Institute of Health grants HL36059, HD17063, and HD39946 to Dr Kirby and P41-05959 to Dr Johnson, the German Heart Foundation, German Research Council (Dr Yelbuz), and the American Heart Association, Georgia Affiliate, Postdoctoral fellowship to Dr Yelbuz.
↵*Both authors contributed equally to this work.
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The editor of Images in Cardiovascular Medicine is Hugh A. McAllister, Jr, MD, Chief, Department of Pathology, St Luke’s Episcopal Hospital and Texas Heart Institute, and Clinical Professor of Pathology, University of Texas Medical School and Baylor College of Medicine.
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