GOAL: familiarize with wavelength dependent optical properties for tissue as well as the relevant length and time scales

Select "Spectral Panel". Note that "Tissue Types" lists various tissues. Each tissue is modeled consisting from individual chromophores (e.g. water, blood, fat, etc.), each of which having certain concentrations pertinent to a particular tissue. In this exercise we will study how absorption and scattering properties of tissues (as well as their constituting chromophores) vary with the wavelength of illuminating radiation.

I. Pure Spectra

Goal: This portion of the GUI Interaction is to provide an introduction to the functionality of the Spectral Panel.

1. Select "Custom" tissue type.
2. In Absorber Concentrations specify concentrations to 1 μM for Hb and 0 μM for the other optical absorbers.
3. Please enter "Hb" in "Plot Label" box.
4. Press "Plot μ_a" button at the bottom of the panel.
5. Plot provides μ_a as a function of wavelength, λ, for Hb ("pure" Hb spectrum).
6. Confirm that the output is consistent with results shown in lecture 1 for 600<λ<1000.
7. Confirm the "Hold On" button is checked (under the graphing area on the left).
8. Repeat the steps I.1-I.6 for HbO₂.
9. Press "Clear All" button under the graphing area.

II. Tissue spectra

Goal: It is known that the liver is a highly cellular and blood filled tissue, while skin, by contrast, has less cellular content and more extracellular matrix proteins. As you do this excercise examine whether the μ_a and μ_s' spectra are consistent with the known composition and morphological properties of these tissues. Comment on the similarities / differences in their spectra.

1. Select "Skin" tissue type.
2. Notice the default absorber concentrations.
3. Please enter "Skin" in "Plot Label" box.
4. Plot μ_a of skin versus wavelength.
5. Confirm that the "Hold On" box is checked.
6. Repeat the steps II.1-II.4 for tissue type "Liver".
7. Press "Clear All" button.
8. Plot μ_s' spectra on the same axis for these tissue types.
9. Record the minimum and the maximum values of μ_a and μ_s' for these two tissues (Hover your mouse over the plots to see the corresponding numeric value).
10. Estimate minimum and maximum of the ratio μ_s' / μ_a within the spectral range λ = 600-1000nm.
11. Spatial and temporal scales.

Using the data collected in II.9-II.10 and the definitions below estimate minimum/maximum values of l_s,l_abs,l ^* within the spectral range of λ = 600-1000nm. Assume g = 0.8.

Additional Questions:

1. You have designed a device that can detect changes in μ_a as small as 0.01 mm^-1 at λ = 600nm. Assuming that changes in your system are limited to changes in Hb concentration, what is the smallest Hb concentration change that you detect? Similarly for HbO₂?