Consequences of scattering for spectral imaging of turbid biologic tissue

Abstract

Spectral imaging permits two-dimensional mapping of the backscattering properties of biological systems. Such mapping requires broadband illumination of the entire area of interest. However, imaging of turbid biological media under these conditions often involves mean photon path lengths that exceed the pixel size. Using a numerical Monte Carlo model, we have studied the effects of photon scattering in a hemoglobin-bearing model system. We find that photon migration and the resulting wavelength-dependent optical coupling between pixels can complicate the analysis of imaging spectroscopy data. In fact, the wavelength dependence of photon trajectories also alters the distribution of photon exit angles at the tissue surface. We therefore find that the finite optical field of view of an imaging spectrometer can affect the measured spectra in the absence of chromatic aberrations.

Fast Three-Dimensional Fluorescence Imaging of Activity in Neural Populations by Objective-Coupled Planar Illumination Microscopy

“…and D.T., unpublished data). Furthermore, since the distortion and scattering of light by tissue is reduced at longer wavelengths (Arnoldussen et al, 2000;Kim and Keller, 2003), functional imaging could benefit greatly by development of near-infrared calcium-sensitive dyes. Even without such advances, planar illumination will permit high-speed, cellular-resolution imaging of neural activity for in vitro preparations such as the retina or hippocampal slices, for the apical dendrites of cortical neurons in vivo, and for many in vivo invertebrate preparations.…”

Optical properties of human skin, subcutaneous and mucous tissues in the wavelength range from 400 to 2000 nm

“…The development of optical methods in modern medicine in the areas of diagnostics, therapy and surgery has stimulated the investigation of optical properties of various biological tissues, since the efficacy of laser treatment depends on the photon propagation and fluence rate distribution within irradiated tissues. Examples of diagnostic use are the monitoring of blood oxygenation and tissue metabolism [1,2], laser Doppler flowmetry [3], pulse oximetry [4], detection of cancer by fluorescence [5,6] and spectrophotometric methods [7,8] and various techniques recently suggested for optical imaging [9][10][11].…”

Optical Imaging and Measurement of Angiogenesis

“…In some anatomical locations, such as various regions of the gastrointestinal tract, it may be possible to directly image superficial microvessels; however, in most situations microvascular function will need to be inferred from bulk tissue measurements. Accurate determination of values such as hemoglobin saturation and total hemoglobin concentration from bulk tissue measurements will probably require a model of light propagation in tissue to account for tissue scattering effects which can result in wavelength-dependent crosstalk between adjacent pixels due to differences in the pathlength and exit angles of photons emanating from neighboring tissue regions [112]. Some researchers have employed tissue light propagation model-based processing of reflectance spectral imaging data, which range from relatively simple to detailed and complex for different tissues such as colon and skin [113][114][115].…”