Multispectral photoacoustic (MPA) imaging is a promising tool for the diagnosis of atherosclerotic carotids. Excitation of different constituents of a plaque with different wavelengths of the light may provide morphological information to evaluate plaque vulnerability. Preclinical validation of in vivo photoacoustic (PA) imaging requires a comprehensive phantom study. In this study, the design of optically realistic vessel phantoms for photoacoustics was examined by characterizing their optical properties for different dye concentrations, and comparing those to PA measurements. Four different concentrations of Indian ink and molecular dye were added to a 15 wt% PVA and 1 wt% orgasol mixture. Next, the homogeneously mixed gels were subjected to five freeze -thaw cycles to increase the stiffness of vessel phantoms (r inner = 2.5mm, r outer = 4mm). For each cycle, the optical absorbance was measured between 400 nm 990 nm using a plate reader. Additionally, photoacoustic responses of each vessel phantom at 808 nm were tested with a novel, hand-held, integrated PA probe. Measurements show that the PA signal intensity increases with the optical absorber concentration (0.3 to 0.9) in close agreement with the absorbance measurements. The freeze -thaw process has no significant effect on PA intensity. However, the total attenuation of optical energy increases after each freeze-thaw cycle, which is primarily due to the increase in the scattering coefficient. In future work, the complexity of these phantoms will be increased to examine the feasibility of distinguishing different constituents with MPA imaging.
Study: Physical cardiac simulators are widely used in surgical training as well as in preclinical device testing. Their fidelity rapidly advances, but often lacks patient-specific cardiac responses. On the other hand, computational simulations of the complete cardiovascular system are being investigated for years but rarely come together in a physical lab model. This study will show our progress in implementing real-time responsive models in a physical cardiac biosimulator. Methods: In this work we implemented a ventricular contraction model combined with a baroreflex response in LifeTec Group's Cardiac BioSimulator. This BioSimulator generates flow through hearts obtained from abattoirs using a piston pump. We programmed the pump to mimic the heart's contraction, and to respond to real-time pre-and afterload changes. The contraction model describes the ventricular behavior based on experimental data of myocardial fibers. Next, we will perform experiments with a pump connected to the left ventricle mimicking LVAD functionality and demonstrate ventricular unloading responses. Results: Contraction behavior and baroreflex response were implemented successfully in the pump model, thus representing contractile functionality. Preliminary tests on a simple benchtop model already showed real-time response in PV-loops by adjusting afterload resistance. Recently we added baroreflex functionality that describes heart rate response. Next results will focus on LVAD support simulations on the Cardiac Biosimulator. Conclusion: By combining a state-of-the-art cardiac simulator with a model that describes physiological contraction behavior of the heart, we are one step closer to a realistic simulator that comprises both anatomy and real tissue feedback as well as the correct physiological response that could even be used to assess and train the effect of an intervention.
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