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Biomedical subjects

S Debray

Publications and source records attributed to S Debray.

6 recordsLinked to original sources
PubMed2001

Laser evoked potentials using the Nd:YAG laser.

Pain-related cortical potentials were evoked by skin stimulation of the face and the limbs with 5-ns-duration laser pulses delivered by a Q-switched Nd:YAG laser. Such laser pulses, in the nanosecond range, were able to induce pinprick pain sensations and to evoke reproducible laser evoked potentials (LEPs) without visible skin lesions for an energy density of less than 18 mJ/mm(2). Low energy densities, around 10 mJ/mm(2), were sufficient to reach the pain threshold and to induce LEP. The mean conduction velocity of the stimulated afferent fibers was close to 20 m/s, consistent with the stimulation of Adelta fibers. The amplitude of LEP correlated with pain perception rather than with energy density. The differences, such as wavelength and stimulus duration, between the Q-switched Nd:YAG laser we used and the lasers that are currently used in LEP studies (i.e., CO(2), argon, or Tm:YAG lasers in the millisecond range) are discussed. Our study opens novel perspectives in the LEP field of research by using a new type of laser with a very short pulse duration.

Afferent Pathways↗
PubMed1993

Laser tomography of heterogeneous scattering media using spatial and temporal resolution.

Time-resolved tomography is performed in transillumination by using 527 nm picosecond pulses from a passively mode-locked doubled Nd/glass laser and a streak camera to select photons according to their flight time. This work reports on the increase in contrast of a time-resolved profile of a 2 mm radius opaque object embedded in a scattering medium, constituted of diluted milk in a 30 mm thick cell. For spatial analysis, the emerging photons are detected through a 6 mm slit at the outlet face of the cell. Transmission profiles obtained as a function of time show that the contrast is enhanced for the shortest flight times, while the 'shadow' of the object is no longer detected after about 100 ps. Moreover, improvements in contrast are studied for different configurations of the model, to analyse separately the role of collimated and scattered photons. It is expected that such a tomographic method based on time-resolved absorption could be applied to imaging for more complex biological structures in the red and near-infra-red range.

Humans↗
PubMed1989

In vivo transillumination of the hand using near infrared laser pulses and differential spectroscopy.

In vivo dual wavelength differential spectrography was performed on the hand of an adult male, using a collimated transillumination device. A pulsed laser with sufficiently high peak power and sufficiently low energy was employed so that transillumination could be realized without thermal damage. Spectrochemical analysis based on the absorbance of oxygen transporting molecules (OTM), i.e. haemoglobin in blood vessels and myoglobin in muscles, was performed along a 70 mm scanning line within the near-red infrared range. The two wavelengths used (675 and 800 nm) were chosen on the basis of the absorption spectrum of haemoglobin. The profiles computed with differential spectrography data related to the oxygen saturation of OTM are closely correlated with X-ray densitometry of the most vascularized tissues in the hand along the scanning line. In addition, at 675 nm, the profiles are rapidly modified as a function of the oxygen supply to the hand. Considering the accuracy obtained for the spatial localization of the OTM redox state, it is expected that these results could be applied to imaging.

Adult↗
PubMed1986

Scanning spectrophotometry for the dynamic study of tissue respiration in intact organs.

For use with intact perfused organs a spectrophotometer system has been developed, both for dual-wavelength absorption measurements and for spectral scanning. A monochromator is used for illumination and scanning in the visible and near infrared. Optic fibres conduct light to the specimen under examination and from the specimen to a detecting photomultiplier. System control is exercised by a microcomputer, which also processes the collected data. The performance of the system on isolated perfused rat heart is demonstrated, in the spectral scanning mode and in the dual-wavelength mode, by studying simultaneously the kinetics of cytochrome aa3, and myoglobin oxidation-reduction.

Animals↗
PubMed1984

Imaging mammalian tissues and organs using laser collimated transillumination.

Images of mammalian organs were built up using a Laser collimated transillumination device equipped with a bidirectional scanning setup. A microcomputer was used to run the scanning process, acquisition of detected signals and images restitution. The images featured a satisfactory resolution of optical discontinuities on both sample surfaces. Light scattering within biological tissues restricted the spatial discrimination encountered with geometrical selection approach. By combining space and time resolution at various wavelengths, the production of an efficient tomospectroscopy could be envisaged.

Animals↗