Estimation of effective scatterer size and number density in near-infrared tomography
Light scattering from tissue originates from the fluctuations in intra-cellular and extra-cellular components, so it is possible that macroscopic scattering spectroscopy could be used to quantify sub-microscopic structures.
Both electron microscopy (EM) and optical phase contrast microscopy were used to study the origin of scattering from tissue. EM studies indicate that lipid-bound particle sizes appear to be distributed as a monotonic exponential function, with sub-micron structures dominating the distribution. Given assumptions about the index of refraction change, the shape of the scattering spectrum in the near infrared as measured through bulk tissue is consistent with what would be predicted by Mie theory with these particle size histograms.
The relative scattering intensity of breast tissue sections (including 10 normal & 23 abnormal) were studied by phase contrast microscopy. Results show that stroma has higher scattering than epithelium tissue, and fat has the lowest values; tumor epithelium has lower scattering than the normal epithelium; stroma associated with tumor has lower scattering than the normal stroma.
Mie theory estimation scattering spectra, was used to estimate effective particle size values, and this was applied retrospectively to normal whole breast spectra accumulated in ongoing clinical exams. The effective sizes ranged between 20 and 1400 nm, which are consistent with subcellular organelles and collagen matrix fibrils discussed previously. This estimation method was also applied to images from cancer regions, with results indicating that the effective scatterer sizes of region of interest (ROI) are pretty close to that of the background for both the cancer patients and benign patients; for the effective number density, there is a big difference between the ROI and background for the cancer patients, while for the benign patients, the value of ROI are relatively close to that of the background. Ongoing MRI-guided NIR studies indicated that the fibroglandular tissue had smaller effective scatterer size and larger effective number density than the adipose tissue.
The studies in this thesis provide an interpretive approach to estimate average morphological scatter parameters of bulk tissue, through interpretation of diffuse scattering as coming from effective Mie scatterers.