SPONSORED: OPTICAL MODELLING


biological tissue is spatially heterogeneous; structures like blood vessels and hair follicles can alter the measurement from one point to another.’ As a result, the values from


the same tissue type can vary dramatically, as Calabro explained: ‘Simulations have to make modelling assumptions, not only because it’s impossible to fully characterise the structure of the tissue under the surface a priori, but also because including these small structures dramatically decreases the simulation efficiency. For those reasons, the models have to assume some level of structural homogeneity that is not 100 per cent physically accurate.’ Tissue simulations are also


characterised by a high number of scattering events, however a low proportion of rays is actually collected, making such simulations extremely computationally demanding. ‘A single simulation of one scattering value and one absorption value at a single wavelength can take days,’


Calabro explained. This is where Synopsys’


LightTools can help, providing biomedical optics researchers with a versatile and intuitive tool to design diagnostic methods and devices to measure tissue properties. ‘We have developed a built-in


utility that guides the user in building broadband optical property profiles (absorption, scattering, refractive index). It is pre-populated with data and values curated from the research literature. With that as a starting point, the user can modify individual components (such as blood volume or water fraction) as needed,’ Calabro explained. ‘So, even if optically measured data from a particular tissue type is unavailable, users can build a reasonable estimate based on physiologically-based assumptions. These variables can also be used as tolerancing or optimisation variables, with the utility automatically updating the optical properties in the model. These capabilities take tissue modelling beyond simply importing static


measured data, recognising the unique challenges that need to be addressed when simulating tissue.’


This provides the end- user with versatility and a comprehensive toolset, where the tools required to design and develop a device with accurate tissue simulation are combined. Calabro explained: ‘Whereas


programs used in academic research settings, such as MCML, primarily use text-based I/O, and are limited to simple geometries like rectangular blocks, LightTools has extensive options for complex geometries and user-friendly analysis tools, with no large text files to parse and analyse separately.’ What’s more, with integrated tools like optimisation and tolerancing, LightTools can properly account for the inherent variability of tissue- optical properties. This combination of usability


and versatility sets LightTools apart from other simulation and modelling tools for those


working in the bio-optics field. In a new technical paper,


Synopsys presents the most up-to-date compilation of research and data available in the literature regarding the optical properties of human tissue. It provides the optical, biological and measurement details required when modelling human tissue in LightTools. It also describes how this information has been incorporated into a new Human Tissue Utility. ‘While modelling of biological tissue has made tremendous advances in the past few decades, it continues to be a work in progress with many unknowns still to explore. It is our hope that tools such as the tissue material utility in LightTools help make tissue modelling more accessible to those who are not biomedical optics experts. As the field continues to grow, and research data is added to the literature, it is our intention to regularly update and incorporate new data into the utility,’ Calabro concluded. EO


New White Paper now online


Modelling biological tissues in LightTools


By Katherine Calabro, R&D engineer, Snopsys


VIEW FOR FREE*


www.electrooptics.com/white-papers


Electro Optics


*Registration required


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