Speckle arises as a natural consequence of the limited spatial-frequency bandwidth of the interference signals measured in optical coherence tomography (OCT). In images of highly scattering biological tissues, speckle has a dual role as a source of noise and as a carrier of information about tissue microstructure. The first half of this paper provides an overview of the origin, statistical properties, and classification of speckle in OCT. The concepts of signal-carrying and signal-degrading speckle are defined in terms of the phase and amplitude disturbances of the sample beam. In the remaining half of the paper, four speckle-reduction methods-polarization diversity, spatial compounding, frequency compounding, and digital signal processing-are discussed and the potential effectiveness of each method is analyzed briefly with the aid of examples. Finally, remaining problems that merit further research are suggested. © 1999 Society of Photo-Optical Instrumentation Engineers.

https://www.spiedigitallibrary.org/journals/Journal-of-Biomedical-Optics/volume-4/issue-01/0000/Speckle-in-optical-coherence-tomography/10.1117/1.429925.pdf

Speckle in Optical Coherence Tomography

We have studied the optical properties of mammalian cell suspensions to provide a mechanistic basis for interpreting the optical properties of tissues in vivo. Measurements of the wavelength dependence of the reduced scattering coefficient and measurements of the phase function demonstrated that there is a distribution of scatterer sizes. The volumes of the scatterers are equivalent to those of spheres with diameters in the range between ~0.4 and 2.0 mum. Measurements of isolated organelles indicate that mitochondria and other similarly sized organelles are responsible for scattering at large angles, whereas nuclei are responsible for small-angle scattering. Therefore optical diagnostics are expected to be sensitive to organelle morphology but not directly to the size and shape of the cells.

Mechanisms of light scattering from biological cells relevant to noninvasive optical-tissue diagnostics

https://www.edwinvanderpol.com/publications/manuscripts/van_der_pol_2014_JTH_Vesicle_size_distribution.pdf

Particle size distribution of exosomes and microvesicles determined by transmission electron microscopy, flow cytometry, nanoparticle tracking analysis, and resistive pulse sensing.

Digital holography is an emerging field of new paradigm in general imaging applications. We present a review of a subset of the research and development activities in digital holography, with emphasis on microscopy techniques and applications. First, the basic results from the general theory of holography, based on the scalar diffraction theory, are summarized, and a general description of the digital holographic microscopy process is given, including quantitative phase microscopy. Several numerical diffraction methods are described and compared, and a number of representative configurations used in digital holography are described, including off-axis Fresnel, Fourier, image plane, in-line, Gabor, and phase-shifting digital holographies. Then we survey numerical techniques that give rise to unique capabilities of digital holography, including suppression of dc and twin image terms, pixel resolution control, optical phase unwrapping, aberration compensation, and others. A survey is also given of representative application areas, including biomedical microscopy, particle field holography, micrometrology, and holographic tomography, as well as some of the special techniques, such as holography of total internal reflection, optical scanning holography, digital interference holography, and heterodyne holography. The review is intended for students and new researchers interested in developing new techniques and exploring new applications of digital holography.

/pdf/principles-and-techniques-of-digital-holographic-microscopy-56tmwltigo.pdf

Principles and techniques of digital holographic microscopy

We have developed a digital holographic microscope (DHM), in a transmission mode, adapted to the quantitative study of cellular dynamics. Living cells in culture are optically probed by measuring the phase shift they produce on the transmitted wave front. The high temporal stability of the phase signal, equivalent to lambda/1800, and the low acquisition time (~20micros) enable to monitor cellular dynamics processes. An experimental procedure allowing to calculate both the integral refractive index and the cellular thickness (morphometry) from the measured phase shift is presented. Specifically, the method has been applied to study the dynamics of neurons in culture during a hypotonic stress. Such stress produces a paradoxical decrease of the phase which can be entirely resolved by applying the methodological approach described in this article; indeed the method allows to determine independently the thickness and the integral refractive index of cells.

/pdf/measurement-of-the-integral-refractive-index-and-dynamic-44yc3rfw21.pdf

Measurement of the integral refractive index and dynamic cell morphometry of living cells with digital holographic microscopy

With a phase microscope the phase shift of cells from type L 929 fibroblast and mitochondria from liver cells was measured. Compared to the total phase shift caused by the cell relative to vacuum (approximately 1400 nm) the single phase shift of the mitochondria (approximately 180 nm) is small. Only the nucleus and the membrane of the cell give a visibly different phase shift relative to the mean value of the cell. The Fraunhofer diffraction of the measured phase object is calculated. With a simplified scattering theory, i.e. Rayleigh - Gans scattering, different phase objects are investigated and their differential cross section is discussed.

https://iopscience.iop.org/article/10.1088/0031-9155/41/3/002/pdf

The spatial variation of the refractive index in biological cells

Determination of the specific heat capacity of healthy and tumorous human tissue

Successful laserinduced tumor therapy requires the knowledge of optical properties of tissue as well as of the thermal ones (specific heat capacity, thermal conductivity, thermal diffusivity). Therefore, a comprehensive review of one of those values, the specific heat capacity c p , of different human and animal tissues is given measured calorimetrically by us or collected from the literature. A Differential Scanning Calorimeter was used to determine the in vitro specific heat capacities of various healthy and tumorous human tissues. The influence of freezing in liquid nitrogen and of thermal coagulation on the specific heat capacity was investigated.

Specific heat capacities of human and animal tissues

The thermophysical properties heat conductivity λ, thermal conductivity α. specific heat capacity c p , and the density ρ as well as the rtermal resistance λc p ρ of various human and animal (canine, pig, rabbit) tissues were collected from the literature. Heat conductivity, heat capacity and density are strongly influenced by the water content of the tissue. Furthermore, heat and thermal conductivity depending on the status of the tissue (in vivo reap. in vitro). Thus, the effective heat capacities of in vivo tissues are up to three times higher than the in vitro ones. A short description of important measuring methods for the heat (steady state method) reap. the thermal conductivity (thermal pulse decay method) is given. The uncertainly of these methods are discussed. A Differential Scanning Calorimeter was used to determine the in vitro specific heat capacities of healthy and tumorous human tissues. The influence of freezing in liquid nitrogen and of thermal coagulation on the heat capacity is investigated.

Review of thermal properties of biological tissues

The distribution of light scattered by finger joints is studied in the near-IR region. It is shown that variations in the optical parameters of the tissue (scattering coefficient {mu}{sub s}, absorption coefficient {mu}{sub a}, and anisotropy factor g) depend on the presence of the rheumatoid arthritis (RA). At the first stage, the distribution of scattered light was measured in diaphanoscopic experiments. The convolution of a Gaussian error function with the scattering phase function proved to be a good approximation of the data obtained. Then, a new method was developed for the reconstruction of distribution of optical parameters in the finger cross section. Model tests of the quality of this reconstruction method show good results. (laser biology and medicine)

Olaf Minet

Papers

The spatial variation of the refractive index in biological cells

Determination of the specific heat capacity of healthy and tumorous human tissue

Specific heat capacities of human and animal tissues

Review of thermal properties of biological tissues

Light scattering study of rheumatoid arthritis