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Biomedical subjects

S Gabay

Publications and source records attributed to S Gabay.

At least 19 recordsLinked to original sources
PubMed1997

Modelling the assessment of port wine stain parameters from skin surface temperature following a diagnostic laser pulse.

BACKGROUND AND OBJECTIVE: Laser treatment of port wine stains (PWS) has become an established clinical modality over the past decade. However, in some cases full clearance of the PWS cannot be achieved. To improve the clinical results, it is necessary to match the laser treatment parameters to the PWS anatomy on an individual patient basis. Therefore, knowledge of the PWS structure is of great importance. The objective of this study is to describe a diagnostic method to assess the PWS blood vessels depth and diameter from the skin surface temperature-time course following a diagnostic laser pulse. STUDY DESIGN/MATERIALS AND METHODS: The Monte Carlo (MC) method was used to calculate the deposited laser energy into a port wine stain skin model following irradiation by a diagnostic laser pulse at 577 nm. The heat equation was solved numerically, using the deposited energy profile as the source term, yielding the temperature-time course at the skin surface. Subtraction of "bloodless" skin signal from that of the skin containing blood vessels gives us the net contribution of a heated dermal blood vessel to the skin surface temperature-time behaviour. RESULTS: The net blood vessel signal shows heat-diffusion behaviour and was found to be sensitive to the dermal blood vessel depth and diameter. The time delay for the peak signal temperature to occur depends quadratically on the blood vessel depth. The peak temperature relates linearly to the blood vessel diameter. The degree of epidermal melanin content can also be determined from the immediate temperature rise of the signal. CONCLUSION: The proposed method easily enables assessment of the blood vessel depth and diameter as well as the epidermal melanin content in a skin model. The method can be applied to a real PWS when using the adjacent normal skin as a reference.

Blood Vessels↗
PubMed1989

Excimer laser-processed donor corneal lenticules for lamellar keratoplasty.

We used the 193-nm argon-fluoride excimer laser to cut plano corneal lenticules from fresh corneal tissue for lamellar keratoplasty. The laser was used to cut away all corneal tissue outside a specially designed mold, which was developed to obtain a corneal lenticule of 10 mm in diameter and a constant thickness of 0.3 mm. The surface topography of the excimer laser-cut corneal lenticule was smoother and more regular on scanning electron microscopy than a hand-cut corneal lenticule, and the thickness was constant around the surface. No thermal or mechanical damage to the cornea was observed on light microscopy in the area adjacent to the cut.

Cornea↗
PubMed1988

Retinal thermal response to copper-vapor laser exposure.

A thermal model has been used for the interaction of an annular laser beam of a high-repetition-rate pulsed laser (copper-vapor laser) with the retina of a rabbit. The model predicts the temperature rise at each retinal point, during and after the laser exposure, as a function of pulse energy, exposure time, and pulse repetition rate. The retinal effects for each set of treatment parameters were estimated according to the predicted temperature rise and were found to be identical with our previous experimental results. The character of the interaction between the copper-vapor laser and the retina can be pretuned by the laser pulse repetition rate to fit the requirements of various treatments, permitting multiple uses of this laser for ophthalmic treatments.

Animals↗
PubMed1988

The retinal effects of copper vapor laser exposure.

The copper vapor laser is a pulsed gas laser which emits energy in two wavelengths simultaneously: 510.6 nm (green) and 578.2 nm (yellow). Each pulse has a duration of 15 nsec, maximal energy of 3 mJ and a peak power of more than 100 kW. It is a variably high repetition rate laser, in the range between 1 kHz and more than 20 kHz. We studied its interaction with the rabbit retina, while using two different repetition rates, 4 kHz and 18 kHz. The histological analysis of the lesion produced by 4 kHz repetition rate showed undesired retinal effects, similar to those caused by other pulsed lasers. On the other hand, the histological examination of the lesion produced by the 18 kHz repetition rate showed a desired coagulation effect, limited to the outer retinal layers, and comparable to a lesion produced by a continuous wave (CW) laser.

Animals↗
PubMed1977

Quipazine exacerbation of a hyperkinetic syndrome: involvement of brain dopamine and serotonin.

Quipazine (5-25 mg.kg-1, s.c.) was given to rats in which a hyperkinetic syndrome had been previously induced by administration of beta,beta'-iminodipropionitrile (IDPN). Quipazine produced a significant increase in the circling behavior and choreiform head and neck movements, characteristic of the syndrome. This response could be blocked by pretreatment with the serotonin antagonists, SQ10, 631 (25 mg.kg-1, i.p.) and methysergide (5.0 mg.kg-1, i.p.), as well as the dopamine receptor antagonist, haloperidol (0.5 mg.kg-1, i.p.). These observations are discussed with respect to the nature of the involvement of brain serotonergic and dopaminergic systems in quipazine action on these hyperkinetic disturbances.

Animals↗
PubMed1975

Regional neurochemical studies on the effect of beta, beta'-iminodipropionitrile (IDPN) in the rat.

A permanent hyperkinetic syndrome, characterized by excitation, choreiform head and neck movements and circling, which has led to it being called collectively the "ECC-syndrome," is induced in rats by the daily IP administration of beta, beta'-iminodipropionitrile (IDPN), 300 mg/kg, for 7 days. The levels of the biogenic amines, norepinephrine (NE), dopamine (DA), serotonin (5-HT) and its metabolite 5-hydroxyindoleacetic acid (5-HIAA), were measured in the striatum, midbrain, medulla, cortex, and cerebellum on the day the syndrome appeared (day 7) and one week later (day 14). The biogenic amine most affected by IDPN administration was 5-HT. On day 7, striatal 5-HT levels increased and 5-HIAA levels decreased while in the medulla and midbrain, 5-HIAA levels increased. On day 14, significant reductions in both 5-HT, in the midbrain, striatum, and cortex, and 5-HIAA, in all regions except the cortex, were observed. NE was markedly increased in the medulla, midbrain, and striatum on day 7, whereas on day 14 it was found to be within the normal range in these same regions. With the exception of a slight, but significant, increase in the cortex on day 7, DA levels in all regions were found to be relatively unaffected by IDPN administration on both day 7 and day 14. In an attempt to detect degenerative changes which might be taking place in the brain and which might provide an explanation for the permanency of the behavioral disturbances, the uptake of [3H]-labeled NE, DA, and 5-HT into synaptosomal-rich preparations of striatum and the uptake of NE and 5-HT into the midbrain area were compared between normal and syndromized rats on both day 7 and day 14. Small changes were observed but they were not statistically significant. The alterations of 5-HT and 5-HIAA levels in several regions of the brain under the conditions examined may indicate that IDPN's neurotoxicity primarily affects 5-HT-containing neurones. The active membrane transporting system of the nerve endings studied, however, remained relatively intact. This latter finding eliminates the possibility that neuronal degeneration in these areas is responsible for the decreased 5-HT and 5-HIAA levels or is the pathology underlying the permanency of the syndrome. These results are evaluated in terms of a possible model for hyperkinetic disorders.

Animals↗