Regional mouse heart deformation analysis via Computer Aided Speckle Interferometry: A feasibility study
With heart disease a leading cause of death in the United States, there is a distinct need for the development of methods to identify potential precursors. The goal of this research was to acquire displacement measurements from a beating mouse heart using speckle interferometry, and assess the overall feasibility of the process. Such a method could provide valuable information on alternations of wall mechanics between the normal and pathological states in the heart. Other investigators have previously used larger animals such as pigs, but mice were used here primarily due to the availability of various genetically modified models, as well as the ease of compiling larger sample sizes. ^ Excised hearts, beating spontaneously under sinus rhythm, were instrumented in two different custom setups. The first, a "working heart" system which was more physiologically accurate, allowed pressure and volume data to be synchronized with the beating heart images. However, imaging artifacts were more prominent with this setup, so a second, less involved Langendorff setup, was the principal system used. This was mainly an aortic head pressure perfusing the coronaries, allowing the ventricle to beat freely. Pressure/volume data wasn't acquired for this setup, but imaging was significantly better. Processing of the images was done via Matlab®. Computer Aided Speckle Interferometry (CASI) was the primary method of tracking, which involved performing two-dimensional cross-correlations from image to image. Strains were then calculated with help from surface fits to displacement data. Validation was performed with speckled latex linearly stretched in one direction on an Instron machine. The latex was imaged and the data was run through the algorithm. The machine's software provided displacement and strain values, which when compared to the computed values, matched up very well. ^ Results from normal mouse hearts suggest that speckle interferometry can provide high density displacement information similar to that acquired from larger hearts. While the method is effective, there are still some specific challenges that need to be overcome in order to improve the robustness of this methodology. Specifically, it is challenging to get a large number of speckles directly on the region of interest. This area is very small, especially since it needs to be orthogonal to the camera. Small displacement differences in the cardiac cycles and perceived quantization errors add up as gross displacement artifacts, confounding further calculations. ^ Despite the few hindrances, the overall method works well by accurately tracking displacements. Strain calculations in heart and validation videos followed expected trends. The CASI method is a viable option for tracking mouse heart deformation. It is by no means perfect, but with further improvement could definitely become a low-cost, almost fully-automated, reproducible technique for attaining valuable heart testing information.^
Engineering, Biomedical|Engineering, Electronics and Electrical
Richard Daniel Hartnett,
"Regional mouse heart deformation analysis via Computer Aided Speckle Interferometry: A feasibility study"
Dissertations and Master's Theses (Campus Access).