Ta Pham

A multiwavelength, high bandwidth frequency-domain photon migration 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 in optically turbid media using a network analyzer, an avalanche photodiode detector and four amplitude-modulated diode lasers. The frequency-dependence of PDW phase and amplitude is measured and compared to analytically derived model functions in order to calculate absorption, μ, and reduced scattering, μ, parameters. The wavelength-dependence of absorption is used to determine tissue haemoglobin concentration, oxygen saturation and water concentration. We present preliminary results of non-invasive FDPM measurements obtained from normal and turnout-containing human breast tissue. Our data clearly demonstrate that physiological changes caused by the presence of small palpable lesions can be detected using a handheld FDPM probe.

Frequency-domain photon migration is a widely used technique for measuring the optical properties of turbid samples. Typically, FDPM data analysis is performed with models based on a photon diffusion equation; however, analytical solutions are difficult to obtain for many realistic geometries. Here, we describe the use of models based instead on representative samples and multivariate calibration. FDPM data at seven wavelengths and multiple modulation frequencies were gathered from turbid samples containing mixtures of three absorbing dyes. Values for μa and μs′ were extracted from the FDPM data in different ways, first with the diffusion theory and then with the chemometric technique of partial least squares. Dye concentrations were determined from the FDPM data by three methods, first by least-squares fits to the diffusion results and then by two chemometric approaches. The accuracy of the chemometric predictions was comparable or superior for all three dyes. Our results indicate that chemometrics can recover optical properties and dye concentrations from the frequency-dependent behavior of photon density waves, without the need for diffusion-based models. Future applications to more complicated geometries, lower-scattering samples, and simpler FDPM instrumentation are discussed. © 2000 Optical Society of America.

The objective of this study was to determine the optimal parameters for endometrial destruction by photodynamic therapy using tin ethyl etiopurpurin as a photosensitizer in the rat model. Different application routes and different time intervals after drug administration were compared when the uterine horn was illuminated with a fixed laser light dose of 375 J/cm2. Then PDT was performed 1.5 h after IV injection of 2 mg/kg SnET2 using decreasing light doses. Destruction of all endometrial glands was observed when the uterine horn was illuminated 1.5 h after IV drug administration. In contrast, weaker PDT effects were observed when light activation was delayed for 24 h following systemic or topical drug application even if the light dose was increased by a factor of 30. Endometrial fluorescence did not prove to be an effective method to predict optimal timing for photodynamic therapy, which was probably due to its binding to serum proteins. For photodynamic treatment of endometrial glands in the rat, IV administration 1.5 h before illumination was most efficient.

The basic principles of a non-contact, near-infrared technique for the mapping of layered tissues are discussed theoretically and verified experimentally. The propagation properties of diffuse photon-density waves in tissues depend on the optical properties of the tissue. When a layered medium is irradiated by amplitude modulated light, the difference in optical properties between the layers is evident in the phase and amplitude of the diffuse reflection coefficient, which is a result of the interference of the partial waves propagating in the different layers. Thus, diffuse photon- density waves are applicable to the analysis of the structure of layered tissue. The probing depth is determined by the modulation frequency of the incident light. For modulation frequencies between several hundred megahertz and a few gigahertz, this allows us to analyze the properties of muscle tissue of up to 4-8 mm below the surface. Experimental results based on chicken breast muscle are given. As an example, the technique might be of use for evaluating the depth of necrosis and the blood volume fraction in deep burns.