A novel noninvasive second-harmonic-generation tomographic method of mapping the structure of animal tissues by use of 100-fs laser pulses at 625nm is described. Subsurface structures were measured with this approach, which is potentially a symmetry-sensitive tool for optical histological reconstruction.
We have measured UV fluorescence excited through two-photon absorption from native chicken tissue, using 600-nm, 500-fs pulses from a R6G dye laser. The observed emission signal was found to depend quadratically on the excitation intensity. The two-photon excitation-induced fluorescence spectrum is attributed to tryptophan residues in proteins.
We report on an analysis ofdiffuse reflectance spectra measured in conjunction with the fluorescence from normal human breast tissues and malignant breast tumors. The diffuse reflectance spectra from excised, air-equilibrated, human breast tissue samples show lower fractions of oxygenated hemoglobin and higher content offerric (Fe3) heme in malignant breast tumor samples than in normal breast tissues. Normaltissues are found to be easily deoxygenated and reoxygenated, but malignant tumors usually do not change their state as much. An analysis oftissue oxygenation parameters will be discussed with respect to an enhancement ofpredictive power offluorescence diagnostic method. The oxygenation state of tissues may be used as an additional marker in cancer diagnostics.
Second harmonic and two photon fluorescence generated by focused 100 fs ultrashort laser pulses were used to image subsurface structures of highly scattering biological tissues. By scanning the focal point of the incident laser beam, 2-D sectional images ofthe tissue subsurface structure properties, such as symmetry and molecular compositions are obtained.
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