Local and superficial near-infrared ͑NIR͒ optical-property characterization of turbid biological tissues can be achieved by measurement of spatially resolved diffuse reflectance at small source-detector separations ͑Ͻ1.4 mm͒. However, in these conditions the inverse problem, i.e., calculation of localized absorption and the reduced scattering coefficients, is necessarily sensitive to the scattering phase function. This effect can be minimized if a new parameter of the phase function ␥, which depends on the first and the second moments of the phase function, is known. If ␥ is unknown, an estimation of this parameter can be obtained by the measurement, but the uncertainty of the absorption coefficient is increased. A spatially resolved reflectance probe employing multiple detector fibers ͑0.3-1.4 mm from the source͒ is described. Monte Carlo simulations are used to determine ␥, the reduced scattering and absorption coefficients from reflectance data. Probe performance is assessed by measurements on phantoms, the optical properties of which were measured by other techniques ͓frequency domain photon migration ͑FDPM͒ and spatially resolved transmittance͔. Our results show that changes in the absorption coefficient, the reduced scattering coefficient, and ␥ can be measured to within Ϯ0.005 mm Ϫ1, Ϯ0.05 mm Ϫ1 , and Ϯ0.2, respectively. In vivo measurements performed intraoperatively on a human skull and brain are reported for four NIR wavelengths ͑674, 811, 849, 956 nm͒ when the spatially resolved probe and FDPM are used. The spatially resolved probe shows optimum measurement sensitivity in the measurement volume immediately beneath the probe ͑typically 1 mm 3 in tissues͒, whereas FDPM typically samples larger regions of tissues. Optical-property values for human skull, white matter, scar tissue, optic nerve, and tumors are reported that show distinct absorption and scattering differences between structures and a dependence on the phase-function parameter ␥.

SUMMARYA 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-dependence of PDW phase and amplitude is measured and compared to analytically derived model functions in order to calculate absorption, µ a , and reduced scattering, µ 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.

The polymerase chain reaction (PCR) technique offers a promising alternative to tissue culture for the rapid and sensitive detection of cytomegalovirus (CMV) infection. However, high levels of background amplification detected in samples containing water but no DNA make interpretation of borderline positive samples extremely difficult and reduce the sensitivity of the assay. The signal from amplification of water or positive samples can be eliminated by DNase treatment, but not by filtration through anisotropic membrane, autoclaving, or ultraviolet irradiation. A lag time of 10 to 12 cycles is observed before the reactions with water will show product formation by liquid hybridization detection. The use of nested PCR eliminates the background and, in serial dilutions of a positive sample, shows a 500- to 1000-fold increase in sensitivity by liquid hybridization detection. We suggest that the background signal is arising from small fragments of DNA, which may be produced by autoclaving viral culture material. Such fragments would escape filtration, and overlapping fragments of DNA can prime one another to form complete mosaic sequences that will then amplify. Nested PCR, appropriately controlled for the number of cycles at each step, should successfully overcome such false positives caused by fragmented DNA, no matter if the contamination occurs at the collection site, in processing, or at the facility performing the test.