Time-resolved fluorescence and photon migration studies in biomedical and model random media

Abstract

This review highlights time-resolved fluorescence kinetics and photon transport in tissues and other biomedical media with a special emphasis on ultrafast measurements of key optical parameters. Measurements of fluorescence decay lifetimes from human breast and atherosclerotic artery tissues in the uv and visible region are described after a brief description of fundamentals of fluorescence kinetics. A time-dependent diffusion model for photon migration and various ultrafast methods for time-resolved light scattering measurements to obtain key optical parameters of tissues and other model turbid media are presented. The usefulness of optical parameters as markers in optical diagnostics and imaging is considered. Time-gated measurements of ballistic and snake photons to obtain shadowgrams and an inverse numerical reconstruction of the interior map of a turbid medium from time-resolved data in the context of optical tomography are presented.

Diffuse optical mammotomography: state-of-the-art and prospects

“…It is also necessary to allow for the difference in refractive index between the normal tissues and malignant neoplasms, which should be taken into account in the tomographic reconstruction algorithms. Thus, e.g., the refractive index of normal breast tissue at the wavelength 800 nm amounts to 1.403, while in the case of malignant neoplasm it is 1.431 [10]. As to the functional parameters, from Table 2 it is seen that the ranges of characteristic values of haemoglobin oxygen saturation essentially overlap in healthy breast tissue and malignant tissue, namely, 49 -92% and 38 -81%.…”

“…The traditional approach to the estimation of f consists in the linearization of Eq. (6) by expanding it into the Taylor series [3,5,9,10,12,17] …”

“…The time-domain technique implies the irradiation of the tissue with ultrashort pulses having the duration 10 -9 -10 -11 s and the detection of broadened pulses of scattered radiation, the so-called temporal point spread functions (TPSFs). In the time-domain near IR spectroscopy the optical parameters are assessed by comparison of the measured TPSF with the pulse shape, calculated using the diffusion approximation to the radiative transport theory (the fitting method [10]). The frequency-domain and the time-domain techniques implement time-resolved irradiation mode, the fundamental base of which is the excitation of so-called diffuse waves of photon density in the strongly scattering medium [1-3, 15, 22, 25].…”

“…If, e.g., one neglects the third and the higher terms of the expansion, the system of linear algebraic equations (SLAE) follows    f f f . The reconstruction methods based on the singe inversion of the system (8) and using only single-step linearization of the operator equation (6) are known as linear or perturbation methods [3, 5, 9, 12, [10,51]. These calculations do not require considerable time expenditures only in particular cases of homogeneous scattering objects with simple geometries, when the known analytical solutions of the radiative transport equation can be applied [5,6,10,22,32,43,46,52,69,80,83,93,98,104,106,110,115,224,237].…”

Recent advances in the development of Raman spectroscopy for deep non‐invasive medical diagnosis

“…SORS utilises the diffuse component of light in analogy with techniques used in NIR absorption tomography [10][11][12] and fluorescence spectroscopy [13][14][15][16]. The concept was developed from earlier temporal-domain Raman counterparts [5,[17][18][19][20] which utilised time-correlated single-photon counting [17] or picosecond Raman Kerr gating (the latter developed originally for fluorescence rejection from Raman spectra [4,[21][22][23].…”