Main Page/BPHS 4090/In-Vivo Spectrocopy
Required Components
- USB Ocean Optics spectrometer
- Collection fiber for spectrometer
- PC with spectrometer software and MS Excel (or equivalent spreadsheet) for data processing
- White reflectance reference target
- White LED illumination source
- Blood pressure compression cuff
- Excel calculation spreadsheets
- Stopwatch timer (can use windows clock for this)
- A usb stick or some way to take your data with you for analysis
Objective
To measure the in-vivo oxygenation state of haemoglobin, and calculate the change in oxygenation before, during, and after reactive hyperaemia by analyzing the colour content of light diffusely reflected off of the skin.
Introduction
Optical methods of skin analysis are ideal because they can be performed non-invasively, and in real-time. It is quite intriguing that so much information can be discovered from something as simple as launching some photons at an object and analyzing what comes back. In this lab, you will be exploring the use of light as a non-invasive measurement tool to determine the in-vivo oxygenation status of haemoglobin in your blood. These measurements will be made in a non-invasive sense, so as much as you may enjoy slicing up your lab partner to get at their blood, it ain’t gonna happen here! You will, on the other hand, have the opportunity to cut off the blood flow to one of your lab partner(s) limbs, though sadly, this will only be temporary. In this lab you will get familiar with the concept of light propagation in turbid (scattering) media, as well as gain experience with optical spectroscopy methods. High resolution spectral information can be analyzed to allow semi-quantitative and fully quantitative analysis of biological materials, and is a very powerful technique, useful for a variety of biophysical applications.
Determination of physiologically relevant parameters in a quick, reliable and repeatable fashion is of paramount importance in healthcare and biological research. The optical properties of human skin have been the subject of numerous investigations over the years, and two of the most relevant parameters to measure are the haemoglobin (Hb) oxygenation state and melanin content. Hb and melanin are the two major cutaneous chromophores within human skin, which means that their concentrations are essentially responsible for the colour of your skin.
 Figure 1 - Absorption spectrum typical for melanin.
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Upon exposure to ultraviolet (UV) light, melatinocytes increase their production of melanin within the skin, we know this process by its more common name, a suntan. The absorption spectrum of melanin is shown in figure 1, and is almost linear over the visible spectrum. It is best measured in the spectral rang above 600 nm, as it is the main source of light absorption in the skin at this wavelength and beyond.
