This blog post is an excerpt of a white paper written by Tobias Funk of Triple Ring Technologies.

To read the full article written by Triple Ring click here. To learn more about Zemax OpticStudio capabilities, request a free trial.

Design and optimization of biophotonic devices require modelling of light propagation in both the tissue and instrument. Monte Carlo simulations are typically used to model the propagation in tissue [1], while geometric ray tracing software such as Zemax OpticStudio is used to model the propagation in the instrument. 

Typically, these modelling tools are used separately and therefore many of the key benefits of modelling, such as accurate photon budgets, off-angle light effects, device-tissue alignment effects, and device performance over a range of conditions, are missed. Further, many Monte Carlo simulation engines cannot model realistic source distributions and geometries. To address these challenges, Triple Ring Technologies has developed a versatile GPU-accelerated Monte Carlo simulation platform (MCI) that is integrated with OpticStudio via its application programming interface (ZOS-API) to enable complete source tissue detector optical modelling. Triple Rings’ approach is presented and illustrated with two case studies that demonstrate the benefits of an integrated solution.

The field of tissue optics necessitates coping with high optical scattering, whereas traditional optical methods deal with ballistic photons. Information gathered by light propagation through diffuse media can be extremely useful. For example, the use of tissue optics is best known in health and wellness applications such as medical-grade pulse oximeters and consumer electronic devices for heart rate and fitness (e.g., Fitbit, Apple watch). 

There is a wealth of applications in the medical setting that improve quality of care such as fluorescence-guided surgery, diffuse optical imaging, and optical biopsy, among others. Due to the complex nature of photon transport in tissue, the evaluation and design of instrumentation based on tissue optics require robust simulation capability. 

Although Monte Carlo methods provide accurate representations of light scattering through tissue, a very large number of photons need to be propagated to overcome Poisson noise in the simulation. In addition, tissue optics applications have a highly multidimensional design space. Variables such as skin layer thickness, melanin concentration, hydration, and blood volume require multiple simulations to be run for a given instrument configuration; every permutation of properties generally requires its run, as the interplay between different factors can be highly nonlinear. This leads to long simulation times slowing down the instrument optimization process. To address this issue, Triple Ring Technologies (TRT) has developed Monte Carlo Integrated (MCI), a specialized GPU accelerated program optimized for high-speed simulations in diffuse media. Many elements of an optical system, such as light engines, excitation optics, and detection optics are more readily simulated using traditional geometric ray tracing methods. Optical design, such as that done with Zemax OpticStudio, is performed using numerical ray tracing in which optical elements interact with rays one by one either sequentially or non-sequentially. Models include elements such as lenses, prisms, and mirrors, along with source and detection elements. In these simulations, ray events are not dominated by volumetric scattering and can be accurately modelled with many fewer rays than are required to model light propagation through biological tissue.

Microscopes, camera systems, and other lens-based imaging devices are ideal candidates for design optimization with this approach. These simulations are ideally suited to design optical instrumentation which does not interact with a tissue layer; while OpticStudio can accurately model such interactions, the customized simulations required for modelling propagation through tissue are often computationally intensive.

When designing a tissue-optics-based instrument, the simulation of both the optical elements used in the device and the tissue in which the signal will propagate is necessary. It is critical to consider the entire photon chain, which includes the tissue/instrument interface. Triple Ring Technologies has formed a method to combine specialized tissue simulation models with Zemax OpticStudio, to offer the best of both worlds. Triple Ring illustrate their approach with two case studies: a pulse oximetry sensor and a device to perform fluorescence-guided surgery.

To read the full article written by Triple Ring click here.
To learn more about Zemax OpticStudio capabilities, request a free trial.

About Triple Ring
Triple Ring Technologies Triple Ring is a co-development company headquartered in Silicon Valley, with offices in Boston, Toronto, and Copenhagen. We stand side-by-side with innovators and entrepreneurs to solve hard problems, launch breakthrough products, and create new businesses. ISO 13485 certified, we provide expertise in optical, electrical, mechanical, and complete system design of products for medical, consumer and industrial markets. For more information about Triple Ring, contact: Tobias Funk tfunk@tripleringtech.com 1-(510)-592-3000x113.

Author:  
Tobias Funk
Triple Ring Technologies

References:
. S. L. Jacques, “Optical properties of biological tissues: a review,” Physics in Medicine and Biology, 58(11), R37–R61 (2013). 2.