WHAT IS DOSI?
Diffuse optical spectroscopic imaging (DOSI) performs quantitative absorption spectroscopy in thick tissues. Frequency Domain Photon Migration (FDPM) is an established technique for measuring tissue optical properties (i.e., absorption, and reduced scattering).[Pham, et al., 2000] The FDPM technique uses light sources modulated at tens to hundreds of MHz to measure both the amplitude and the phase shift of multiply-scattered light.[Fishkin and Gratton, 1993] Typically diffusion-based models are used to calculate absolute and scattering tissue optical properties from these phase and amplitude measurements. Within the near-infrared (NIR) spectral range (650-1000 nm) were FDPM is routinely employed, the tissue concentrations of oxygenated (ctO2Hb) and deoxygenated hemoglobins (ctHHb), water (ctH2O), and bulk lipid may be calculated from tissue absorption spectra. FDPM techniques can separate the effects of absorption from scattering using a single spatial location.[Fishkin, et al., 1996] Distinction of absorption from scattering is important because NIR light is strongly multiply scattered by tissues.[Wilson, et al., 1988] By combination of FDPM with standard steady-state spectral methods, complete coverage of the NIR spectral range can be achieved.[Cerussi, et al., 2006] Thus our DOS method combines the best of both worlds: the quantitative accuracy of FDPM along with the broadband spectral content of NIRS.
We also have started a new DOSI wiki page that goes into much more detail about DOSI. You can learn about the history of technology development, and learn more about how the system works and what it measures.
HOW DOES DOSI WORK?
Absorption spectroscopy is a very powerful tool for understanding the properties of molecules. It is commonly used in chemistry and biology to measure the concentrations and/or states of molecules in solution. For our purposes, we rely upon this interaction between light and matter to inform us about biological molecules. Below we have listed the most common absorbers known to exhibit significant near infrared (NIR, 600-1100 nm) spectral region.
NIR Tissue Absorption
Other NIR chromophores not listed:
Melanin, important in skin
Tissues, however, complicate absorption spectroscopy because tissues heavily scatter NIR photons. The picture below demonstrates this effect. On the left is a picture of a standard cuvette used in absorption spectroscopy, filled with a water-soluble blue dye. A red laser beam (He-Ne) easily passes through this sample (from the left). Changes in the intensity (or number of photons/area) are directly related to the concentration of the blue dye in the sample. On the right, we placed a highly-scattering solution (Intralipid, a venous fat emulsion) to mimic the effects of scattering in tissues. Instead of a nice pencil-beam passing through the sample, we observe a reddish diffusive hue through the sample. Recovering the concentration of the blue dye in the cuvette just got a lot harder.
WHAT RESEARCH IS GOING ON IN THE DOSI GROUP?
- Development of DOSI instruments (portable clinical and wearable systems)
- Engineering of new optical probes (minimally invasive and non invasive)
- Development of algorithms (data fitting, physiological models)
- 3D reconstruction of spectroscopic signatures
- Spectroscopic analysis methods
- Water binding in tissues
- Malignant-specific absorption biomarkers
- Angiogenesis and Vascular responsiveness
- Tissue composition
- Breast Cancer (detection, theraputic monitoring)
- Critical Care Medicine/Trauma
- Exercise physiology
- Neonatal critical care
- Sinus Imaging