Mimicking brain tissues by doping scatterers into gelatin tissue phantoms and determination of chemical species responsible for NMPPAS

Abstract

It has been shown that non-resonant multiphoton photoacoustic spectroscopy (NMPPAS) has a great potential to be used as a high resolution surgical guidance technique during brain tumor surgery due to its ability of non-invasive or minimally invasive tumor differentiation. However, for experimental purposes associated with method validation, the use of real tissues is not always ideal because of issues such as availability, safety, storage, chemical doping, necessary control of size and shape, etc. To overcome these issues, tissue phantoms made from animal tissues and/or biochemical constituents, are often employed for such analyses. This work demonstrates the ability to develop and characterize gelatin based tissue phantoms with comparable optical and acoustic properties to real tissues by doping the phantoms with a scattering substance, 0.3 μm diameter Al₂O₃ particles. Using these phantoms, light scattering coefficients (μs) of 39 cm⁻¹ have been generated, which are comparable to real brain tissue, thus making them a great alternative to real tissue for validation studies. In addition, this work also investigates the non-fluorescent species NAD+ found in the tissues, to evaluate its potential for being detected by NMPPAS. NMPPAS spectra of NAD+ shows a very promising beginning to determine other chemical species such as flavins, collagen, tryptophan, etc responsible for NMPPAS spectral signatures, associated with tumorogenesis.