Section 1. Optical properties: attenuation coefficient
Conventional optical coherence tomography (OCT) imaging presents images of the intensity of backscattered light from biological samples. Detection of disease relies upon the user identifying the pathological structures in the OCT images, based on intrinsic optical contrast of the tissue. Often, this contrast is insufficient for reliable and repeatable detection of this pathology by qualitative analysis of OCT images.
We have developed a method of processing 3D-OCT data to quantitatively measure the optical properties of biological tissue, specifically the total attenuation coefficient µt. It has been show that the attenuation coefficient changes for different tissue types, and importantly for diseased and pathological tissue. By extracting the local attenuation coefficients from 3D-OCT volumes, we can measure the ranges of attenuation coefficients of different tissue types. We have also generated quantitative parametric OCT images of the local attenuation coefficients, which improve differentiation of tissue types and identification of pathology, when compared to standard OCT backscatter images alone.
Assuming a single-scattering model of light propagation in tissue, in which light contributing to the OCT signal experiences only a single back-scattering event, the reflectance R(z) of light detected from a homogeneous tissue is determined from the exponential decay of irradiance versus depth z, in accordance with the Beer-Lambert law.
The attenuation coefficient µt [mm-1] describes this decay and is a result of scattering and absorption. The contribution of tissue absorption is very low at the near infrared wavelengths used in OCT and can be considered negligible in comparison to scattering. The OCT system introduces modulations to the biological sample reflectance, and this first needs to be corrected for and removed from the detected OCT signal before the attenuation coefficient can be calculated. After correction, the localised attenuation coefficient can be extracted from the OCT reflectance profiles at different lateral positions containing different tissue types, as shown in the below Figure 1, and we then also generate a parametric map of µt (x,y) [mm-1]. The resulting parametric maps are correlated with corresponding histology to determine the range of values of and demonstrate that quantitative parametric OCT images provide improved differentiation of attenuation coefficient for different tissue types, and also improve contrast and identification of these different tissue types and pathology in subsequent results, compared to standard OCT backscatter images alone.
Section 2. Microvasculature imaging quick links
1) Key applications
2) Key researchers:
- Christobel Saunders
- Peter Robbins
- Matthew Edmond
- Benjamin A. Wood
- Steven L. Jacques
- Tea Shavlakadze
- Miranda D. Grounds
- Fiona M. Wood
- Robert A. McLaughlin, Loretta Scolaro, Peter Robbins, Christobel Saunders, Steven L. Jacques, David D. Sampson, “Parametric imaging of cancer with optical coherence tomography”, Journal of Biomedical Optics, 15(4), 046029 (2010).
- Loretta Scolaro, Robert A. McLaughlin, Blake R. Klyen, Benjamin A. Wood, Peter D. Robbins, C Christobel M. Saunders, Steven L. Jacques, and David D. Sampson, “Parametric imaging of the local attenuation coefficient in human axillary lymph nodes assessed using optical coherence tomography”, Biomedical Optics Express, 3(2), pp. 366-379 (2012).
- Blake R. Klyen, Loretta Scolaro, Tea Shavlakadze, Miranda D. Grounds, and David D. Sampson, “Optical coherence tomography can assess skeletal muscle tissue from mouse models of muscular dystrophy by parametric imaging of the attenuation coefficient”, Biomedical Optics Express, 5(4), pp. 1217–1232 (2014).
- Peijun Gong, Robert A. McLaughlin, Yih Miin Liew, Peter R. T. Munro, Fiona M. Wood, and David D. Sampson, “Assessment of human burn scars with optical coherence tomography by imaging the attenuation coefficient of tissue after vascular masking”, Journal of Biomedical Optics, 19(2), 021111 (2014).