Frequency-domain photon migration measurements of normal and malignant tissue optical properties in a human subject.

A 1-GHz multifrequency, multiwavelength frequency-domain photon migration instrument is used to measure quantitatively the optical absorption (mu(a)) and effective optical scattering (mu(s) ?) of normal and malignant tissues in a human subject. Large ellipsoidal (~10-cm major axis, ~6-cm minor axes) subcutaneous malignant lesions were compared with adjacent normal sites in the abdomen and back. Absorption coefficients recorded at 674, 811, 849, and 956 nm were used to calculate tissue hemoglobin concentration (oxyhemoglobin, deoxyhemoglobin, and total), water concentration, hemoglobin oxygen saturation, and blood volume fraction in vivo. Our results show that the normal and the malignant tissues measured in the patient have clearly resolvable optical and physiological property differences that may be broadly useful in identifying and characterizing tumors

<title>Quantitative diffusive wave spectroscopy in tissues</title>

High frequency, intensity-modulated light waves are attenuated and phase-shifted by the absorption and scattering properties of highly scattering media, such as tissue. The simultaneous measurement of the average light intensity, modulation amplitude, and phase-shift at a fixed distance from a sinusoidally modulated light source, permits a quantitative determination of the absolute values of the absorption and scattering coefficients from a frequency-domain scan. Our studies have established the range of modulation frequencies that give the highest sensitivity to changes of the optical parameters in model systems. We have measured the optical absorption spectra of dyes suspended in highly scattering media. These spectra match those found in non-scattering media. This frequency-domain approach provides a simple method to perform quantitative spectroscopy in highly scattering media

Noninvasive measurements of breast tissue optical properties using frequencydomain photon migration

A multiwavelength, high bandwidth (1 GHz) frequency-domain photon migration (FDPM) instrument has been developed for quantitative, non-invasive measurements of tissue optical and physiological properties. The instrument produces 300 kHz to 1 GHz photon density waves (PDWs) in optically turbid media using a network analyser, an avalanche photodiode detector and four amplitude-modulated diode lasers (674 nm, 811 nm, 849 nm, and 956 nm). The frequency of PDW phase and amplitude is measured and compared to analytically derived model functions in order to calculate absorption, mu a, and reduced scattering, mu s, parameters. The wavelength-dependence of absorption is used to determine tissue haemoglobin concentration (total, oxy- and deoxy- forms), oxygen saturation and water concentration. We present preliminary results of non-invasive FDPM measurements obtained from normal and tumour-containing human breast tissue. Our data clearly demonstrate that physiological changes caused by the presence of small (about 1 cm diameter) palpable lesions can be detected using a handheld FDPM probe

Gigahertz photon density waves in a turbid medium: Theory and experiments

The predictions of the frequency-domain standard diffusion equation (SDE) model for light propagation in an infinite turbid medium diverge from the more complete [Formula Presented] approximation to the linear Boltzmann transport equation at intensity modulation frequencies greater than several hundred MHz. The [Formula Presented] approximation is based on keeping only the terms l=0 and l=1 in the expansion of the angular photon density in spherical harmonics, and the nomenclature [Formula Presented] approximation is used since the spherical harmonics of order l=1 can be written in terms of the first order Legendre polynomial, which is traditionally represented by the symbol [Formula Presented]. Frequency-domain data acquired in a quasi-infinite turbid medium at modulation frequencies ranging from 0.38 to 3.2 GHz using a superheterodyning microwave detection system were analyzed using expressions derived from both the [Formula Presented] aproximation equation and the SDE. This analysis shows that the [Formula Presented] approximation provides a more accurate description of the data over this range of modulation frequencies. Some researchers have claimed that the [Formula Presented] approximation predicts that a light pulse should propagate with an average speed of c/ √3 in a thick turbid medium. However, an examination of the Green’s function that we obtained from the frequency-domain [Formula Presented] approximation model indicates that a photon density wave phase velocity of c/ √3 is only asymptotically approached in a regime where the light intensity modulation frequency aproaches infinity. The Fourier transform of this frequency-domain result shows that in the time domain, the [Formula Presented] approximation predicts that only the leading edge of the pulse (i.e., the photons arriving at the detector at the earliest time) approaches a speed of c/√3. © 1996 The American Physical Society