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Biomedical subjects

I Itzkan

Publications and source records attributed to I Itzkan.

25 records · Page 2Linked to original sources
PubMed1994

Interferometric surface monitoring of biological tissue to study inertially confined ablation.

We present results from the application of laser interferometry to the study of short-pulsed laser ablation of biological tissue. The mechanical response of tissue to laser-induced stress is examined under subthreshold conditions to determine its role in initiating the ablation process. A theoretical model is developed to relate this surface displacement to the pressure within the tissue and the mechanical properties of the tissue. In the experiment, a 7.5 ns pulse of 355 nm light was used to irradiate bovine shank bone, human meniscus, and an aqueous dye solution. Interferometric monitoring of the tissue surface was used to determine its motion after laser irradiation. The surface movement of bone was qualitatively consistent with the theoretical predictions of the model. The movement of meniscus and an aqueous dye solution showed additional features that are consistent with the growth and collapse of cavitation bubbles.

Animals↗
PubMed1994

Laser-induced thermoelastic deformation: a three-dimensional solution and its application to the ablation of biological tissue.

Under certain conditions, laser light incident on a target material can induce an explosive removal of some material, a process called laser ablation. The photomechanical model of laser ablation asserts that this process is initiated when the laser-induced stresses exceed the strength of the material in question. Although one-dimensional calculations have shown that short pulsed lasers can create significant transient tensile stresses in target materials, the stresses last for only a few nanoseconds and the spatial location of the peak stresses is not consistent with experimental observations of material failure in biological tissues. Using the theory of elasticity, analytical expressions have been derived for the thermoelastic stresses and deformations in an axially symmetric three-dimensional solid body caused by the absorption of laser light. The full three-dimensional solution includes three stresses, radial, circumferential and shear, which are necessarily absent in the simple one-dimensional solution. These stresses have long-lived components that exist for eight orders of magnitude longer in time than the acoustic transients, an important point when the details of dynamic fracture are considered. Many important qualitative features are revealed including the spatial location of the peak stresses, which is more consistent with experimental observations of failure.

Animals↗
PubMed1991

Wavelength dependence of pulsed laser ablation of calcified tissue.

Pulsed laser ablation of calcified biological tissue was studied at several wavelengths in the near-ultraviolet, visible, near- and mid-infrared regions of the spectrum. The primary tissue model was bovine shank bone, while human arterial calcified plaque and normal human artery wall were also studied at selected wavelengths for comparison. Laser irradiances were on the order of MW/mm2, fluences ranged up to 1000 mJ/mm2, and repetition rates varied between 0.3-10 Hz. Spot sizes on the tissue surface ranged from 150 to 850 microns. Laser craters made with wavelengths between lambda = 295 nm and lambda = 375 nm and in the lambda = 3 microns region exhibited the highest quality ablation with clean, sharp cuts following closely the spatial contour of the incident beam. Craters drilled with visible wavelengths between lambda = 450 nm and lambda = 590 nm were generally larger than the incident laser beam spot, irregular in shape and often surrounded by large flakes of tissue debris. Ablation fluence thresholds increased with wavelength through the visible wavelengths and into the mid-infrared, but dropped to their lowest values near lambda = 3 microns. Fluence thresholds obtained with the tissue under a 1 mm depth of saline were approximately twice air thresholds. Ablation yields also varied with wavelength, probably due to increased scattering in the visible region, and were the same under saline as in air.

Absorption↗
PubMed1983

In vivo spectrophotometric evaluation of normal, lesional, and laser-treated skin in patients with port-wine stains.

The influence of patient age and argon laser therapy on port-wine stains (PWS) was studied quantitatively in 16 patients aged 15-64 years using a spectrophotometer and computer graphics/statistics program. Normalized reflectance curves revealed a 10-20% decrease with age in the reflectance of normal skin from 400 nm to 650 nm, with an even more pronounced reflectance decrease in the region of peak deoxyhemoglobin absorption at approximately 555 nm. In each patient, PWS reflectance was less than that in the normal skin, as expected, and the average discrepancy increased with age from approximately 25% to 50%, with further reduction at 555 nm. The data suggest that with advancing age, both normal skin and PWS have a greater total hemoglobin content and an increased proportion of deoxyhemoglobin, consistent with increasing vascular dilation and tortuosity; and that the age-associated changes in PWS are an exaggeration of those in normal skin. Laser-treated PWS in both young and old patients had reflectance curves indistinguishable from those of untreated PWS in young patients. This implies, contrary to published clinical impressions, that in the absence of scarring the results of argon laser therapy are the same in young and old patients, but that only older patients experience a significant color shift in the lesion.

Adolescent↗
PubMed1981

Laser therapy. Basic concepts and nomenclature.

Laser therapy has been demonstrated to be effective in treating many types of cutaneous vascular and pigmented lesions. Clinical and investigative studies on lasers are being published with increasing frequency, but is difficult to interpret and compare results because of lack of use of appropriate nomenclature regarding laser energy. We suggest that scientific communication in this expanding field will be improved if all future studies state: (1) irradiance (laser flux density) at the irradiated surface in watts/cm2, (2) laser beam cross-sectional area and shape at the irradiated surface, (3) laser pulse duration or exposure time in seconds, (4) pulse repetition rate (pulsed lasers) in pulses per second, (5) treatment time segments and intervals between treatment times, (6) total treated skin area in cm2, (7) total number of applied laser pulses or exposures, and (8) the type of laser used and its spectral distribution.

Humans↗