Assessment of the size, position, and optical properties of breast tumors in vivo by noninvasive optical methods.

We present a method for the noninvasive determination of the size, position, and optical properties (absorption and reduced scattering coefficients) of tumors in the human breast. The tumor is first detected by frequency-domain optical mammography. It is then sized, located, and optically characterized by use of diffusion theory as amodel for the propagation of near-infrared light in breast tissue. Our method assumes that the tumor is a spherical inhomogeneity embedded in an otherwise homogeneous tissue. We report the results obtained on a 55-year-old patient with a papillary cancer in the right breast. We found that the tumor absorbs and scatters near-infrared light more strongly than the surrounding healthytissue. Our method has yielded a tumor diameter of 2.1 ? 0.2cm, which is comparable with the actual size of 1.6 cm, determined after surgery. From the tumor absorption coefficients at two wavelengths (690 and 825 nm), we calculated the total hemoglobin concentration (40 ? 10 muM) and saturation (71 ? 9%) of the tumor. These results can provide the clinical examiner with more detailed information about breast lesions detected by frequency-domain optical mammography, thereby enhancing its potential for specificity.

Contrast features of breast cancer in frequency-domain laser scanning mammography.

Frequency-domain optical mammography has been advocated to improve contrast and thus cancer detectability in breast transillumination. To the best of our knowledge, this report provides the first systematic clinical results of a frequency-domain laser scanning mammograph (FLM). The instrument provides monochromatic light at 690 and 810 nm, whose intensity is modulated at 110.0010 and 110.0008 MHz, respectively. The breast is scanned by stepwise positioning of source and detector, and amplitude and phase for both wavelengths are measured by a photomultiplier tube using heterodyne detection. Images are formed representing amplitude or phase data on linear gray scales. Furthermore, various algorithms carrying on more than one signal (amplitude ratio, phase difference, µa,µs',N) were essayed. Twenty visible cancers out of 25 cancers in the first 59 investigations were analyzed for their quantitative contrast with respect to the whole breast or to defined reference areas. Contrast definitions refer to the signal itself (definition 1), to the signal noise (definition 2), or were based on nonparametric comparison (definition 3). The amplitude signal provides better contrast than the phase signal. Ratio images between red and infrared amplitudes gave variable results; in some cases the tumor contrast was canceled. The algorithms to determine µa and µs' from amplitude and phase data did not significantly improve upon objective contrast. The N algorithm, using the phase signal to flatten the amplitude signal did significantly improve upon contrast according to contrast definitions 1 and 2, however, did not improve upon nonparametric contrast. Thus, with the current instrumentation, the phase signal is helpful to correct for the complex and variable geometry of the breast. However, an independent informational content for tumor differentiation could not be determined. The flat field algorithm did greatly enhance optical contrast in comparison with amplitude or amplitude ratio images. Further evaluation of FLM will have to be based on the N-algorithm images. © 1998 Society of Photo-Optical Instrumentation Engineers.

Frequency-domain techniques enhance optical mammography: initial clinical results.

We present a novel approach to optical mammography and initial clinical results. We have designed and developed a frequency-domain (110-MHz) optical scanner that performs a transillumination raster scan of the female breast in approximately 3 min. The probing light is a dual-wavelength (690 and 810 nm, 10-mW average power), 2-mm-diameter laser beam, and the detection optical fiber is 5 mm in diameter. The ac amplitude and phase data are processed with use of an algorithm that performs edge effect corrections, thereby enhancing image contrast. This contrast enhancement results in a greater tumor detectability compared with simple light intensity images. The optical mammograms are displayed on a computer screen in real time. We present x-ray and optical mammograms from two patients with breast tumors. Our initial clinical results show that the frequency-domain scanner, even at the present stage of development, has the potential to be a useful tool in mammography.

Frequency-domain optical mammography: edge effect corrections.

We have investigated the problem of edge effects in laser-beam transillumination scanning of the human breast. Edge effects arise from tissue thickness variability along the scanned area, and from lateral photon losses through the sides of the breast. Edge effects can be effectively corrected in frequency-domain measurements by employing a two-step procedure: (1) use of the phase information to calculate an effective tissue thickness for each pixel location; (2) application of the knowledge of tissue thickness to calculate an edge-corrected optical image from the ac signal image. The measurements were conducted with a light mammography apparatus (LIMA) designed for feasibility tests in the clinical environment. Operating in the frequency-domain (110 MHz), this instrument performs a transillumination optical scan at two wavelengths (685 and 825 nm). We applied the proposed two-step procedure to data from breast phantoms and from human breasts. The processed images provide higher contrast and detectability in optical mammography with respect to raw data breast images.

[FeS/FeS2], a redox system for the origin of life (some experiments on the pyrite-hypothesis).

The FeS/FeS, redox system, whose importance is stressed in recent theories on the origin of life, has been tested experimentally. In this paper it is demonstrated by thermodynamical calculations as well as by experiments, that cyclohexanone, which served as model compound, can be reduced by the aforementioned redox system. Reactions were carried out in methanol and DMF at 25 degrees C and at 100 degrees C. Besides products that were synthesised in both solvents, like cyclohexanethiol and dicyclohexydisulphide, special compounds were obtained in methanol and in DMF, because of the involvement of the respective solvent in the reaction. Yields of reduced compounds were lower in methanol owing to compound that hindered the reduction (cyclohexylketal). With increasing temperature and duration the amount of reduced compounds increased. Further experiments have shown that 1,1-cyclohexanedithiol is likely to be a necessary intermediate for the reduced products. The experiments give evidence to the 'pyrite hypothesis', which postulates that the FeS/FeS2, redox system was of importance for the origin of life.

Compression of picosecond pulses from a solid-state laser using self-phase modulation in graded-index fibers.

We report the compression by a factor of 7 of 2-microJ pulses of 5-psec duration from a mode-locked Nd:phosphate glass laser. The pulses were chirped and their spectrum broadened while traveling through a graded-index core fiber. After amplification to 500 microJ, they were finally compressed by traveling through a dispersive delay line, and 0.7-psec pulse widths were achieved.