Figure 1.
General flow chart of wavelength selection method.
General flow chart illustrating the process for selecting and testing optimal wavelength sets and spectral bandpass in clinical data obtained from breast tumor specimens and in tissue phantoms.
Figure 2.
Dominant absorbers of breast tissue in the UV-visible spectrum.
Molar extinction coefficient of oxy- and deoxy- hemoglobin and β-carotene in the 400–600 nm range.
Table 1.
Extracted ex vivo breast tissue properties used for training set.
Figure 3.
Diagram of combined Monte Carlo reflectance model and genetic algorithm.
Diagram detailing the steps of selecting wavelengths for quantitative tissue spectroscopy using the genetic algorithm and inverse Monte Carlo model.
Table 2.
Average µa (450–600 nm) of liquid phantoms containing hemoglobin, crocin, and polystyrene microspheres.
Table 3.
Top solutions for each optimization with varied increments and total number of wavelengths.
Figure 4.
Average of extracted errors for tissue parameters with increasing number of wavelengths.
Average extracted % error of [THb], [βc], and <µs’> for 5, 6, 7, 8, and 12 total wavelengths selected from 450–600 nm in 1 and 10 nm increments.
Figure 5.
Effect of increasing spectral bandpass.
(a) Simulation of the effect increasing spectral bandpass on a diffuse reflectance spectrum representing 10 µM [THb], 5.5 µM [βc], and 3.11 avg <µs’>. (b) Average extracted errors of [THb], [βc], avg <µs’> with increasing spectral bandpass.
Table 4.
Summary of average extracted errors of parameters for various tissue types for the top 3 optimized solutions.
Table 5.
Summary of average extracted errors of the ratio of [THb]/<µs’> and [βc]/<µs’> for various tissue types for the top 3 optimized solutions.
Table 6.
Comparison of the percent difference between median adipose and malignant tissue and fibroglandular and malignant tissue to the percent change of extractions using the optimized wavelengths and evenly spaced wavelengths to the full 450–600 nm spectrum.
Figure 6.
Bland-Altman plots of MC extractions using various wavelength combinations.
Bland-Altman plots assessing the agreement of MC extractions of [THb], [βc], <µs’>, [THb]/<µs’>, and [βc]/<µs’> in adipose, fibroglandular, and malignant tissue types using the full spectrum versus the optimized reduced wavelength spectrum with 8 wavelengths (470, 480, 490, 500, 510, 560, 580, 600 nm) shown in black and the regularly spaced intervals (400, 420, 440, 470, 500, 530, 570, 600 nm) shown in red. The solid lines indicate the mean difference (bias) between the extractions; the dashed lines indicate the 95% limits of agreement.
Figure 7.
Example spectral images of negative and positive margins obtained with and without optimization.
Representative margin maps of [βc]/<µs’> for normal (A–C), ductal carcinoma in situ (E–G), and invasive ductal carcinoma (I–K) using the full 450–600 nm spectrum, the optimized 8 wavelengths, and the un-optimized evenly spaced 8 wavelengths. Corresponding correlation coefficients for the 61-wavelength spectra and the reduced 8-wavelength spectra are shown. Distribution of the extracted βc/µs’ are shown in (D), (H), and (L) for each case, along with the threshold values used in the predictive model to separate positive from negative margins.
Figure 8.
Comparison of Monte Carlo extractions of normal and cancerous tissue parameters.
Comparison of the MC extractions of [THb], [βc], <µs’>, [THb]/<µs’>, and [βc]/<µs’> in adipose, fibroglandular, and malignant tissue types using full spectrum versus the optimized reduced wavelength spectrum and evenly spaced spectrum with 8 wavelengths. Sample sizes are Normal (N) = 344, and Tumor (T) = 38.
Figure 9.
Multi-absorber phantom optical properties extracted with and without optimization.
Comparison of extraction accuracy for [Hb], [Cr], and <µs’> using the full 450–600 nm spectrum, the optimized wavelength solution, and the evenly spaced wavelengths selected empirically for a previously reported system.