GOAL: This GUI Interaction aims to examine (a) the impact of optical absorption and scattering on temporally-resolved and temporal frequency-domain reflectance signals; and (b) the impact of optical properties and measurement selection on the tissue region probed by the detected photons.

Bring up the Vts.Gui.Wpf GUI

I. Sensitivity of Time-Resolved Reflectance R(t) to Optical Properties

Let us begin by examining the effect of optical absorption on the detection of temporally resolved reflectance.  Note that you can use the Export as Image and Export Data buttons to save your plots.

1. Select the Forward Solver/Analysis Panel.
2. Click Clear All and return the Y Axis Spacing back to Linear.
3. Uncheck use spectral panel inputs.
4. In the Fwd Solver: drop down menu select "Scaled Monte Carlo - NURBS (g=0.8, n=1.4)".
5. In the Solution Domain select Time-Domain, R(ρ,t).
6. For the Independent Axis, choose t and set ρ = 10 mm.
7. In Detection Times choose Begin = 0 ns and End = 0.5 ns with Number = 101 time points (1 point every 5 ps).
8. In Optical Properties: enter μ_a = 0.01mm^-1, μ'_s = 1mm^-1.
9. Click the Plot Reflectance button.
10. Confirm that the Hold On checkbox is selected.
11. Fix μ'_s = 1mm^-1 and repeat the above for μ_a = 0.03, 0.1 and 0.3 mm^-1.

    Question: Note the difference in the magnitude and shape of these plots. What do you believe is responsible for this? Hint: It may helpful to view the results under both linear and log y-axis spacing.

    Now let us examine the effect of reduced scattering on the detection of temporally resolved reflectance. 

12. Click the Clear All button.
13. Start again with Optical Properties: μ_a = 0.01mm^-1, μ'_s = 1mm^-1.
14. Click the Plot Reflectance button.
15. Confirm that the Hold On checkbox is selected.
16. Fix μ_a = 0.01mm^-1 and repeat the above for μ'_s = 0.5 and 1.5 mm^-1.

Questions:

1. Note that no photons are detected before a finite time in the time-resolved reflectance signal. Can you independently calculate the minimal delay time?
2. Note that the peak reflectance values are different and not located at the same time point. Can you speculate as to the origin of these features? Hint: It may help to use both linear and log y-axis spacing.
3. You are designing a time-resolved optical imaging system to detect early formation of a fibrous tumor. What is the approximate time resolution and source detector separation necessary to differentiate normal breast with μ'_s=0.6 mm^-1 from a fibroid tumor with μ'_s=1.2 mm^-1 using such a system?

II. Optical Property Recovery using Temporally-Resolved Reflectance Measurements: Impact of Noise and Initial Guess

Let us now examine the effect of optical absorption on the recovery of optical properties using temporally resolved reflectance.  Note that you can use the Export as Image and Export Data buttons to save your plots.

1. Select the Inverse Solver Panel.
2. For Fwd Solver: select "Scaled Monte Carlo - NURBS (g=0.8, n=1.4)", for Inv Solver: select "Standard Diffusion (Analytic - Isotropic Point Source)".
3. In Solution Domain select "Time-Domain R(ρ,t)".
4. For the Independent Axis, choose t and set ρ = 10 mm.
5. In Detection Times choose Begin = 0 ns and End = 1.0 ns with Number = 51 time points (1 point every 20 ps).
6. Set Optimization Parameters to: μ_a and μ'_s.
7. Simulate measured data: set Forward Simulation Optical Properties: to: μ_a = 0.01 mm^-1, μ'_s = 1 mm^-1, g = 0.8 and n = 1.4 and 2% noise.
8. Confirm the Hold On checkbox is checked.
9. Click the Plot Measured Data button.
10. Set Initial Guess Optical Properties: to: μ_a = 0.02 mm^-1, μ'_s = 1.2 mm^-1, g = 0.8 and n = 1.4.
11. Click the Plot Initial Guess button.
12. Click the Run Inverse Solver button.

Questions:

1. To what optical property values did the inverse solver converge? (Scroll to the bottom of the page to see the output).
2. Why are the converged values not exactly the forward simulation optical properties?
3. Perform the same analysis with 0% noise added to the simulated measured data. How accurate are the converged properties now?
4. Perform the same analysis with initial guess μ_a = 0.05 mm^-1, μ'_s = 0.7 mm^-1, g = 0.8 and n=1.4. How accurate are the converged properties now?
5. How would you modify the Detection Times to improve the inverse solution? Run the inverse solution with this new time window and check your results.

III. Sensitivity of Temporal Frequency Domain Reflectance to Optical Properties

First let us examine the sensitivity of Temporal Frequency Domain Reflectance to optical absorption

1. Go to the Forward Solver/Analysis Panel
2. For Fwd Solver: select "Scaled Monte Carlo - NURBS (g=0.8, n=1.4)"
3. In Solution Domain select "Frequency Domain R(ρ,ft)".
4. For the Independent Axis, choose ft and set ρ = 15 mm.
5. In Temporal Frequencies choose Begin = 0 GHz and End = 2 GHz with Number = 101 frequency points (1 point every 20 MHz).
6. In Optical Properties: enter μ_a = 0.01mm^-1, μ'_s=1mm^-1, n=1.4.
7. Click the Plot Reflectance button.
8. The Plot Toggle radio buttons toggle the plot from real/imag, amplitude and phase plots. The phase is shown in units of degrees. Use the Normalization radio buttons to switch between plots that are non-normalized ("None") and peak-normalized ("Max").
9. Confirm the Hold On checkbox is checked.
10. Keep n fixed at 1.4, keep  μ'_s fixed at 1 mm^-1, and repeat Step 7 for μ_a = 0.02 mm^-1,  μ_a = 0.05 mm^-1 and 0.1 mm^-1

Questions:

1. How does changing the tissue absorption coefficient affect the amplitude of the temporal frequency domain reflectance?
2. How does changing the tissue absorption coefficient affect the relationship between reflectance amplitude and temporal frequency? (Hint: use the "Max" Normalization setting) (Hint #2: You may wish to expand the upper Temporal Frequency limit to 3 GHz or 4 GHz)
3. How does changing the tissue absorption coefficient affect the phase shift of the temporal domain reflectance?
4. How does changing the tissue absorption coefficient affect the relationship between reflectance phase and temporal frequency?
5. Which range of temporal frequencies is most sensitive to absorption changes for amplitude and phase?

Now let us examine the sensitivity of Temporal Frequency Domain Reflectance to optical scattering

1. Click the Clear All button.
2. Set μ_a back to 0.01 mm^-1, keep n=1.4, and ρ = 15 mm.  For thes fixed values of μ_a and n, plot the reflectance for μ'_s = 0.5 mm^-1,  μ'_s = 1 mm^-1, μ'_s = 1.5 mm^-1, and μ'_s = 2 mm^-1
   

Questions:

1. How does changing the tissue reduced scattering coefficient affect the amplitude of the temporal frequency domain reflectance?  How does this trend compare to what you observed from changing the absorption?
2. How does changing the tissue reduced scattering coefficient affect the relationship between reflectance amplitude and temporal frequency? (Hint: use the "Max" Normalization setting) How does this trend compare to what you observed from changing the absorption?
3. How does changing the reduced scattering coefficient affect the phase shift of the temporal domain reflectance?  How does this trend compare to what you observed from changing the absorption?
4. How does changing the tissue reduced scattering coefficient affect the relationship between reflectance phase and temporal frequency? How does this trend compare to what you observed from changing the absorption?
5. Which range of temporal frequencies is most sensitive to scattering changes for amplitude and phase? How does this trend compare to what you observed from changing the absorption?

IV.  Optical Property Recovery using FDPM Instrumentation

Go to Lab_G_FDPM folder on Desktop and click to open.  Follow instructions in file Lab_G_FDPM_student_manual.pdf