Abstract:

Electrocardiographic imaging (ECGI) strongly relies on a priori assumptions and additional information to overcome ill-posedness. The major challenge of obtaining good reconstructions consists in finding ways to add information that effectively restricts the solution space without violating properties of the sought solution. In this work, we attempt to address this problem by constructing a spatio-temporal basis of body surface potentials (BSP) from simulations of many focal excitations. Measured BSPs are projected onto this basis and reconstructions are expressed as linear combinations of corresponding transmembrane voltage (TMV) basis vectors. The novel method was applied to simulations of 100 atrial ectopic foci with three different conduction velocities. Three signal-to-noise ratios (SNR) and bases of six different temporal lengths were considered. Reconstruction quality was evaluated using the spatial correlation coefficient of TMVs as well as estimated local activation times (LAT). The focus localization error was assessed by computing the geodesic distance between true and reconstructed foci. Compared with an optimally parameterized Tikhonov-Greensite method, the BSP basis reconstruction increased the mean TMV correlation by up to 22, 24, and 32% for an SNR of 40, 20, and 0 dB, respectively. Mean LAT correlation could be improved by up to 5, 7, and 19% for the three SNRs. For 0 dB, the average localization error could be halved from 15.8 to 7.9 mm. For the largest basis length, the localization error was always below 34 mm. In conclusion, the new method improved reconstructions of atrial ectopic activity especially for low SNRs. Localization of ectopic foci turned out to be more robust and more accurate. Preliminary experiments indicate that the basis generalizes to some extent from the training data and may even be applied for reconstruction of non-ectopic activity.

Abstract:

Contemporary surgical microscope systems have excellent optical properties but some desirable features re- main unavailable. The number of co-observers is currently re- stricted, by spatial and optical limitations, to only two. More- over, ergonomics poses are a problem: Current microscope systems impede free movement and sometimes demand that surgeons take uncomfortable postures over long periods of time. To rectify these issues, some companies developed surgi- cal microscope systems based on a streaming approach. These systems remove some of the limitations. Multi-observer po- sitions, for example, are not independent from each other, for example. In order to overcome the aforementioned limitations, we are currently developing an approach for the next genera- tion of surgical microscope: Namely the fully digital surgi- cal microscope, where the current observation system is re- placed with a camera array, allowing real-time 3D reconstruc- tion of surgical scenes and, consequently, the rendering of al- most unlimited views for multiple observers. These digital mi- croscopes could make the perspective through the microscope unnecessary allowing the surgeon to move freely and work in more comfortable postures. The requirements on the camera array in such a system have to be determined. For this purpose, we propose of estimation the minimal number of cameras and their positions needed for the 3D reconstruction of microsurgi- cal scenes. The method of estimation is based on the require- ments for the 3D reconstruction. Within the MATLAB simu- lation environment, we have developed a 3D model of a mi- crosurgical scene, used for the determination of the number of required cameras. In a next step a small, compact and cost- ef cient s ystem w ith f ew o pto-mechanical c omponents could be manufactured.