3D Imaging Technology

3D Options

Optical imaging utilizing voltage-sensitive dyes has become a powerful tool for the analysis of cardiac excitation. Until recently, it has been primarily used for fluorescence surface recordings, where only the subsurface layers beneath the epicardial surface were shown to contribute to the optical signal. However, the myocardial wall can be up to 1 cm thick and imaging of the heart electrical activity throughout the thickness of the ventricular muscle would greatly add to the understanding of the mechanisms underlying cardiac arrhythmias.

Our research focuses on the development of novel algorithms for the three-dimensional reconstruction of cardiac electrical activity from optical signals. We have developed hybrid electrical-optical models for the synthesis of optical signals emanating from typical activation patterns in the myocardial wall (forward problem). These hybrid models have provided better insights in the genesis and interpretation of optical signals and also provided the basis for the solution of the inverse problem: reconstruct 3-D activity from 2-D images. We are currently applying techniques from diffusive optical tomography involving matrix inversion and regularization. We have also developed a novel multiplicative algorithm based on biaxial laser scanning. These methods have been validated computationally and are currently being tested in vitro.

3D Imaging Technology
Figure 1. 3-D reconstruction of cardiac electrical activity in isolated porcine RV wall. The slab was paced at 400 ms BCL on the epicardium and was stained with the NIR voltage-sensitive dye JPW-5034. The epicardium was scanned with a 50 mW diode laser (685nm) in 196 points and optical signals were recorded from the endocardium (biaxial scanning). Reconstruction was achieved by using our multiplicative tomography algorithm. The picture shows the activation front 6 ms after stimulation.

Optical Clearing

Mapping the myocardial fiber organization is important for assessing the electrical and mechanical properties of normal and diseased hearts. Current methods to determine the fiber organization have several limitations: histological sectioning mechanically distorts the tissue and is labor-intensive, while diffusion tensor imaging has low spatial resolution and requires expensive MRI scanners. Here, we utilized optical clearing, a fluorescent dye, and confocal microscopy to create 3D reconstructions of the myocardial fiber organization of guinea pig and mouse hearts. We have optimized the staining and clearing procedure to allow for the nondestructive imaging of whole hearts with a thickness up to 3.5 mm. Myocardial fibers could clearly be identified at all depths in all preparations.

Mouse heart
Figure 2. Mouse heart before and after optical clearing. A: Mouse heart in air, before dehydration and clearing. B: The same heart, after dehydration and clearing with 1:2 (v/v) benzyl alcohol: benzyl benzoate (BABB). C: The same heart, dehydrated, cleared and placed in a cuvette filled with BABB. A ruler was placed behind the cuvette to demonstrate the heart's transparency in BABB. Scale bar = 3 mm.