Spatially Resolved Diffusive Reflectance Spectroscopy

MedView is an innovative technology company offering advanced, proprietary 3D spatially resolved diffusive reflectance spectroscopy systems using penetrating near infrared (NIR) light for medical/pharma, industrial and scientific applications. Our proprietary technology is the culmination of 8 years of R&D investment performed by one of the company founders during his studies at the University of Waterloo, ON, Canada.

One of these applications is to “see” inside human tissues for medical purposes. Most tissues are considered to be nearly transparent in the NIR range of the spectrum (700 – 1000 nm, see Figure 1) owing to the lack of strong absorbers. This enables deeper penetration of NIR light into tissue without damage.

Our technology exploits the propagation and distribution of light in an optically turbid medium such as human tissues (see Figure 2) to detect objects underneath. In this imaging modality (see Figure 3), a point light source penetrates into a scattering and absorbing medium. The radial decaying dependence of the photons which are diffusely reflected and exit the medium defines various optical properties of the sample. The diffuse reflectance from the surface is collected spatially using a contact probe consisting of a series of waveguides. In this imaging system, the light source is either continuous wave (CW) or picosecond pulsed wave (PW).

Our innovative technology is an excellent non-invasive platform to study different materials (gas, liquid, and solid) for industry and scientific applications and also for imaging biological tissues for medical diagnostic applications.

Fig.1: The electromagnetic spectrum.

Fig.1: The electromagnetic spectrum.

Fig.2: Light absorption spectra of a sample tissue.

Fig.2: Light absorption spectra of a sample tissue.

Fig.3: Different measurement modes: Countinous Wave, Pulesed Wave, and Intensity Modulated.

Fig.3: Different measurement modes: Countinous Wave, Pulesed Wave, and Intensity Modulated.

Brownian Random Walk in Diffusive Turbid Media

Euclid (fl. 300 BC), a Greek mathematician who is often referred to as the “Father of Geometry”, was first to realize that light in air seldom propagates in a straight path from a source to our eyes. In fact, particles of light emitted from a source experience multiple reflection, refraction, diffraction, absorption, and scattering from the air molecules they encounter along their path. In highly diffusive turbid media, light undergoes a large amount of scattering events while interacting with randomly positioned, highly disordered scatterers and leads to the seemingly random nature of motion. Thus, the diffusive transport is mostly independent of both the wave nature of light and the particular size and morphology of the scatterers.

The history of diffusion dates back to 1827 when Robert Brown discovered irregular motion of tiny particles (pollen) in water while looking at them through a microscope, but was not able to determine what caused this motion. Many decades later, Albert Einstein (1905) and Marian Smoluchowski (1906) independently brought the theoretical solution to “Brownian motion” and also indirectly confirmed the existence of atoms and molecules. Subsequently, Jean Perrin’s experimental study in 1908 of the Brownian motion of minute particles suspended in liquid verified the Einstein-Smoluchowski diffusion theory and thereby directly confirmed the atomic nature of matter.

Diffusion Theory

The transport of light that undergoes Brownian random walk at the microscopic level is described macroscopically using the diffusion equation. Although tracking individual light photons at each scattering event is very complicated as propagation evolves, the average motion of a cloud of light photons after many scattering events is easily traced.

For backscattering spectroscopy, one technique to detect objects inside turbid media is spatially resolved diffusive reflectance measurements. The depth of objects is probed by the photon-path-distribution function from one source to a series of detectors. Considering one source-to-detector separation and a homogenous turbid medium, photon path distribution has a “banana” shape which extends from the source to the detector. In a medium with weak absorption, the modal line of the “photon banana” (i.e., the curve that runs along the center of the banana with the highest probability of photon migration) is related to the source-to-detector separation, rsd, and reaches a maximum depth, zmax, according to the following relation: zmax∝rsd.


Medical Diagnostics & Imaging

  • Vein Detection (with 3D spatial location)
  • Epidural Space Detection
  • In-vivo Skin Lesion Imaging
  • Non-invasive Blood Glucose Monitoring

Industrial & Scientific Applications

  • Food Quality Inspection & Engineering
  • Material Microstructure and Chemical Composition
  • Pharmaceutical Manufacturing QA/QC
  • Multilayer Turbidity Measurement