A fast-Fourier-transform method of topography and interferometry is proposed. By computer processing of a noncontour type of fringe pattern, automatic discrimination is achieved between elevation and depression of the object or wave-front form, which has not been possible by the fringe-contour-generation techniques. The method has advantages over moire topography and conventional fringe-contour interferometry in both accuracy and sensitivity. Unlike fringe-scanning techniques, the method is easy to apply because it uses no moving components.

Fourier-transform method of fringe-pattern analysis for computer-based topography and interferometry

In vivo near-infrared fluorescence imaging

Author(s): Vogel, Alfred; Venugopalan, Vasan | Abstract: The mechanisms of pulsed laser ablation of biological tissues were studied. The transiently empty space created between the fiber tip and the tissue surface improved the optical transmission to the target and thus increased the ablation efficiency. It was found that the structure and morphology also affect the energy transport among tissue constituents.

/pdf/mechanisms-of-pulsed-laser-ablation-of-biological-tissues-58cltfa63z.pdf

Mechanisms of pulsed laser ablation of biological tissues.

When a molecule absorbs a photon of appropriate energy, a chain of photophysical events ensues, such as internal conversion or vibrational relaxation (loss of energy in the absence of light emission), fluorescence, intersystem crossing (from singlet state to a triplet state) and phosphorescence, as shown in the Jablonski diagram for organic molecules (Fig. 1). Each of the processes occurs with a certain probability, characterized by decay rate constants (k). It can be shown that the average length of time τ for the set of molecules to decay from one state to another is reciprocally proportional to the rate of decay: τ = 1/k. This average length of time is called the mean lifetime, or simply lifetime. It can also be shown that the lifetime of a photophysical process is the time required by a population of N electronically excited molecules to be reduced by a factor of e. Correspondingly, the fluorescence lifetime is the time required by a population of excited fluorophores to decrease exponentially to N/e via the loss of energy through fluorescence and other non-radiative processes. The lifetime of photophycal processes vary significantly from tens of femotoseconds for internal conversion1,2 to nanoseconds for fluorescence and microseconds or seconds for phosphorescence.1






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Figure 1


Jablonski diagram and a timescale of photophysical processes for organic molecules.

/pdf/fluorescence-lifetime-measurements-and-biological-imaging-xfalzh4w7e.pdf

Fluorescence Lifetime Measurements and Biological Imaging

Optical imaging of live animals has grown into an important tool in biomedical research as advances in photonic technology and reporter strategies have led to widespread exploration of biological processes in vivo. Although much attention has been paid to microscopy, macroscopic imaging has allowed small-animal imaging with larger fields of view (from several millimeters to several centimeters depending on implementation). Photographic methods have been the mainstay for fluorescence and bioluminescence macroscopy in whole animals, but emphasis is shifting to photonic methods that use tomographic principles to noninvasively image optical contrast at depths of several millimeters to centimeters with high sensitivity and sub-millimeter to millimeter resolution. Recent theoretical and instrumentation advances allow the use of large data sets and multiple projections and offer practical systems for quantitative, three-dimensional whole-body images. For photonic imaging to fully realize its potential, however, further progress will be needed in refining optical inversion methods and data acquisition techniques.

Looking and listening to light: the evolution of whole-body photonic imaging.

In this paper we present the absorption coefficient mu(a) and the isotropic scattering coefficient mu(s)(') for 22 human skin samples measured using a double integrating sphere apparatus in the wavelength range of 1000-2200 nm These in vitro results show that values for mua) follow 70% of the absorption coefficient of water and values for mu(s)(') range from 3 to 16 cm(-1) From the measured optical properties, it was found that a 2% Intralipid solution provides a suitable skin tissue phantom

https://www.spiedigitallibrary.org/journals/Journal-of-Biomedical-Optics/volume-6/issue-02/0000/Optical-properties-of-human-skin-in-the-near-infrared-wavelength/10.1117/1.1344191.pdf

Optical properties of human skin in the near infrared wavelength range of 1000 to 2200 nm.

Bioluminescent and fluorescent reporters are finding increased use in optical molecular imaging in small animals. In the work presented here, issues related to the sensitivity of in vivo detection are examined for standard reporters. A highsensitivity imaging system that can detect steady-state emission from both bioluminescent and fluorescent reporters is described. The instrument is absolutely calibrated so that animal images can be analyzed in physical units of radiance allowing more quantitative comparisons to be performed. Background emission from mouse tissue, called autoluminescence and autofluorescence, is measured and found to be an important limitation to detection sensitivity of reporters. Measurements of dual-labeled (bioluminescent/fluorescent) reporter systems, including PC-3M-luc/DsRed2-1 and HeLaluc/PKH26, are shown. The results indicate that although fluorescent signals are generally brighter than bioluminescent signals, the very low autoluminescent levels usually results in superior signal to background ratios for bioluminescent imaging, particularly compared with fluorescent imaging in the green to red part of the spectrum. Fluorescence detection sensitivity improves in the far-red to near-infrared, provided the animals are fed a low-chlorophyll diet to reduce autofluorescence in the intestinal region. The use of blue-shifted excitation filters is explored as a method to subtract out tissue autofluorescence and improve the sensitivity of fluorescent imaging. Mol Imaging (2004) 3, 9 – 23.

https://journals.sagepub.com/doi/pdf/10.1162/15353500200403196

Quantitative Comparison of the Sensitivity of Detection of Fluorescent and Bioluminescent Reporters in Animal Models

— We present near-infrared frequency-domain photon migration imaging for the lifetime sensitive detection and localization of exogenous fluorescent contrast agents within tissue-simulating phantoms and actual tissues. We employ intensity-modulated excitation light that is expanded and delivered to the surface of a tissue or tissue-simulating phantom. The intensity-modulated fluorescence generated from within the volume propagates to the surface and is collected using a gain-modulated image-intensified charge-coupled device camera. From the spatial values of modulation amplitude and phase of the detected fluorescent light, micromolar volumes of dieth-ylthiatricarbocyanine iodide (π= 1.17 ns) and indocyanine green (ICG) (π= 0.58 ns) embedded 1.0 cm deep in a tissue phantom are localized and discriminated on the basis of their lifetime differences. To demonstrate the utility of frequency-domain fluorescent measurements for imaging disease, we image the fluorescence emitted from the surface of in vivo and ex vivo canine mammary gland tissues containing lesions with preferential uptake of ICG. Pathology confirms the ability to detect spontaneous mammary tumors and regional lymph nodes amidst normal mammary tissue and fat as deep as 1.5 cm from the tissue surface.

Imaging of spontaneous canine mammary tumors using fluorescent contrast agents.

A new method is described for obtaining a 3-D reconstruction of a bioluminescent light source distribution inside a living animal subject, from multispectral images of the surface light emission acquired on charge-coupled device (CCD) camera. The method uses the 3-D surface topography of the animal, which is obtained from a structured light illumination technique. The forward model of photon transport is based on the diffusion approximation in homogeneous tissue with a local planar boundary approximation for each mesh element, allowing rapid calculation of the forward Green's function kernel. Absorption and scattering properties of tissue are measured a priori as input to the algorithm. By using multispectral images, 3-D reconstructions of luminescent sources can be derived from images acquired from only a single view. As a demonstration, the reconstruction technique is applied to determine the location and brightness of a source embedded in a homogeneous phantom subject in the shape of a mouse. The technique is then evaluated with real mouse models in which calibrated sources are implanted at known locations within living tissue. Finally, reconstructions are demonstrated in a PC3M-luc (prostate tumor line) metastatic tumor model in nude mice.

https://umanitoba.ca/faculties/health_sciences/medicine/units/cacs/sam/media/Xenogen_DLIT_2007.pdf

Three-dimensional reconstruction of in vivo bioluminescent sources based on multispectral imaging.

The use of near-infrared (NIR) measurements of photon migration has been recently demonstrated for the
detection of breast cancer in Europe. Yet the clinical success of this potential screening tool depends upon consistent detection of the disease at earlier stages than is currently possible with conventional x-ray mammography. In this paper, we present the optical property measurements of 115 histologically classified breast tissue specimens in order to determine whether consistent and significant optical contrast exists for detection of the disease. Our in vitro optical properties measured with a double integrating sphere technique show consistent changes (yet statistically insignificant) in effective scattering coefficients, ms8, with tissue classification of infiltrating carcinoma (n=48), ductal carcinoma in situ (n=5), mucinous carcinoma (n=3), normal fatty (n=23), and normal fibrous tissues (n=35). However, there is little change in the in vitro tissue absorption coefficient, ma , measured at 749, 789, and 836 nm. For normal and diseased tissue specimens extracted from the same patient, we found differences in optical properties, indicating optical contrast. Using a finite-element
prediction of light propagation, we evaluated this optical contrast for photon migration detection of ductal carcinoma in situ tissues using these optical properties measured in vitro.

https://www.spiedigitallibrary.org/journals/journal-of-biomedical-optics/volume-1/issue-3/0000/Optical-properties-of-normal-and-diseased-breast-tissues--prognosis/10.1117/12.239905.pdf

Tamara L. Troy

Papers

Optical properties of human skin in the near infrared wavelength range of 1000 to 2200 nm.

Quantitative Comparison of the Sensitivity of Detection of Fluorescent and Bioluminescent Reporters in Animal Models

Imaging of spontaneous canine mammary tumors using fluorescent contrast agents.

Three-dimensional reconstruction of in vivo bioluminescent sources based on multispectral imaging.

Optical properties of normal and diseased breast tissues: prognosis for optical mammography