Panoramic Imaging
of the Isolated Rabbit Heart

Fluorescence imaging
of transmembrane potentials is used to observe cardiac activation during fibrillation and defibrillation. Studies of large-scale wavefront dynamics require visualization of the entire epicardial surface. The use of a single camera limits the observer to one view of the heart, and results in the distortion of image information. This problem may be overcome with the use of mirrors or multiple cameras, but requires reconciliation of several overlapping perspective projections into a continuous 3D representation of the cardiac surface.

An isolated rabbit heart was stained with the voltage-sensitive fluorescent dye di-4-ANEPPS. A high speed calibrated CCD camera was used to obtain three simultaneous sequences of images of epifluorescent activity: a frontal view and two posterior mirror reflections. In order to remove motion artifacts, cardiac contraction was decoupled using D600. Endocardial electrodes were placed in the right atrium and left ventricular apex.

A series of frontal snapshots were taken at incremental angles around the heart. These images were segmented to obtain the heart silhouette and used to form a volume model using the method of occluding contours. The surface of the resulting model was approximated by a triangular mesh using a marching cubes algorithm. In order to interpret the epifluorescent activity data in a three-dimensional context, the gray-scale fluorescence intensity images were texture mapped onto the geometric model.

A calibration target was used to determine the transformation matrices between the object and its mirror reflection, treating the reflection as a virtual version of the same object. This procedure provided a solution to the mirror reflection-to-surface correspondence. A radiometric correction algorithm was used to blend the textures across the regions of overlap.

The procedure described above was applied to 64 x 128 synthetic images of a patterned ball, images of a scale model of a rabbit heart, and to fibrillation sequences obtained from isolated rabbit hearts. The test ball validated the accuracy of the procedure, indicated by the correspondence of the pattern from the three individual views. Since fiducial markers could not be placed on the living organ itself, the scale model demonstrated the measurement of accuracy on a non-symmetric rigid object.


This technique allowed viewing of the action potential wavefronts in a realistic three-dimensional environment. Since each vertex on the mesh surface corresponds to a pixel from the fluorescent image, various measurements can be performed for each vertex, and displayed in pseudocolor.

For example, action potential duration, which is altered between normal heart activity and fibrillation, can be represented. Spiral wave phase singularities can also be represented three-dimensionally. We can also create 3D movies of whole-heart wavefront behavior.

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By combining 3D geometry of the heart and the wavefront information obtained from panoramic imaging techniques, this system permits measurement of epicardial electrodynamics over a geometrically realistic representation of the actual heart being studied. This method will aid in understanding fibrillation wavefront behavior.

Mark Bray
mark.bray@vanderbilt.edu