John A. Parrish

Selective thermal effects with pulsed irradiation from lasers: from organ to organelle.

Specific damage by selectively absorbed, pulsed lasers can be predicted based on physical models. Thermally mediated alterations can be confined to pigmented targets from the level of subcellular organelles (e.g., mela-nosomes) to large multicellular tissue structures (e.g., blood vessels) by the appropriate manipulation of wavelength and pulse duration. Highly selective damage to human cutaneous microvessels in vivo is shown to occur after 0.3-mus 577-nm dye laser pulses; the epidermis and dermal structures other than vessels are spared. Observations in an animal model suggest that hemorrhage or, at lower doses, selective intravascular coagulation and permanent microvascular hemostasis occur. Highly selective damage to melanized cells and to single melanosomes in situ was shown to occur after single 20-ns 351-nm pulses from a XeF excimer laser. Basal-cell- and melanocyte-specific necrosis is followed by gross hypo-pigmentation. In this case there is no evidence of vascular damage. The most likely modes of selective alterations include localized thermal denaturation, vaporization, and shock-wave generation. Means of predicting and controlling histologically selective radiant heating effects in skin are suggested.

Comparative Thermal Modeling Of Er:YAG, Ho:YAG And CO 2 Laser Pulses For Tissue Vaporization

We will present a thermal model for laser pulses with pulse widths small compared to the materials thermal time constant. This model will then be used to generate computer plots of the zones of vaporized tissue as well as the predicted tissue temperature rise. Using published values of absorption coefficients, we will predict the vaporization energy thresholds for Er:YAG (2.94μm), Ho:YAG (2.1μm) and CO2 (10.6μm) laser pulses. We will also examine the extent of the thermally denatured zone surrounding the zone of vaporization. Using typical energies available from these lasers we will then predict material removed per pulse, and per second.

Low Energy Laser Biostimulation: New Prospects For Medical Applications

The therapeutic benefits of light-energy is not a new concept to the modern world. Documented applications from ancient times tell of the therapeutic effects of ordinary sun-light to treat such common ailments as painful body joints, wounds, compound fractures and tetanus. The discovery of laser light in the 1960s, opened up new prospects for the medical use of light. Laser light differs from other forms of electromagnetic spectrum in that a single wavelength rather than a spectrum of wavelengths is emitted. Since the early 1970s, low-energy laser radiation has been reported to enhance wound healing rates, reduce edema, and relieve musculoskeletal pain. There is no detectable thermal effect of this laser on the tissue being treated. The effects are considered to occur as a result of photochemical, non thermal effects of the laser beam. Photons are absorbed by the tissue being treated and, in turn, produce positive therapeutic effects such as reduction of pain and edema. Pre-clinical and clinical evaluations are, presently, underway to document the safety and efficacy of low energy laser therapy, which represents a significant advance in the non-invasive treatment of pain.

Cholesterol Levels Assessed With Photon Correlation Spectroscopy

The technique of quasi-elastic light scattering spectroscopy or photon correlation spectroscopy has been used to non-invasively monitor changes in the lens of the eye which could lead to lens opacification and cataract development. We have made quasi-elastic light scattering measurements from the eyes of normal and cholesterolemic rabbits. This report describes an exploratory investigation of the effects of a high cholesterol diet on the lens of the rabbit eye. The goal in making these measurements was to provide a non-invasive assessment of systemic atherosclerotic involvement in these rabbits.

A Medical Excimer Laser System For Corneal Surgery And Laser Angioplasty

The authors report the design criteria and performance of the ExciMeda UV200 medical excimer laser system. A beam delivery system for controlled photoablative machining of variable power optical lenses in organic material is described. Some of the potential applications of this delivery system in corneal surgery are presented. The uses of the UV200 laser system in other areas of medical research are discussed and, in particular, its application i the field of laser angioplasty is outlined. There has been considerable interest recently in the use of excimer lasers in a variety of fields in medicine. The ultraviolet, high peak power beam emitted by an excimer laser has been shown to be capable of producing very clean and precise cuts in organic material. In particular, cuts can be made in biological material with minimal disturbance of the material adjacent to the cut. For example, tissue can be cut in such a way as to produce negligible charring or vacuolization in adjacent areas of the tissue. This is in marked contrast to the results when organic material is cut by a continuous wave laser such as an Argon ion laser, or c.w. CO2 laser. The potential applications in clinical settings which are suggested by this feature of the interaction of tissue with excimer laser radiation have been largely unrealized outside the laboratory as yet. A primary reason for this is that, until recently, excimer lasers have been available only in a form that was suitable for the scientific laboratory. These lasers required large amounts of space, were not mobile once installed, and required con nection to external sources of water cooling, vacuum exhaust, a high current electrical supply, and a variety of gas bottles including the gases F2 and C12. These systems were not designed with clinical applications in mind, and thus provided unnecessary performance features at the cost of added complexity. They also posed potential electrical and gaseous safety hazards not suitable for a clinical environment. In addition, the output from these system could not be easily delivered to a target site due to the absence of any built-in beam delivery system such as an articulated arm, or fiber-optic delivery system . Several months ago, Summit Technology introduced the worlds first medical excimer laser, the ExciMedTM UV200. This laser system is shown in Figure 1. It has been specifically designed for research applications in a clinical environment and incorporates a number of important design features.

Light-Induced Conformational Changes Of Lens Proteins: Photochemistry And Photophysics Of The Process

Sensitized photooxidation causes a change in the tertiary structure of lens crystalline. The subtle variations observed in the nature of these changes are attributed to the difference in the inherent tertiary structure of the crystallins. Each active species of oxygen, a product of the sensitized reaction, has a distinct role in this process. Sensitizer molecules also exhibit a certain specificity regarding the photoinduced conformational changes of these proteins.

The Control Of Neodymium YAG Laser Fiber Optics Hyperthermia With Magnetic Resonance Imaging

Experiments were performed to investigate the feasibility of combining laser heating of tissues while controlling the temperature changes by magnetic resonance imaging (MRI). A great potential exists for applications in cancer treatment and in scientific research.

Comparison Of Percutaneous Laser Discectomy With Other Modalities For The Treatment Of Herniated Lumbar Discs And Cadaveric Studies Of Percutaneous Laser Discectomy

Current modalities for treating a herniated lumbar disc include standard open discectomy, microsurgical discectomy, chemonucleoysis and percutaneous discectomy. The Food and Drug Administration has not yet approved percutaneous laser discectomy for clinical investigation. The investigators believe that percutaneous laser discectomy combines the efficacy of both chemonucleoysis and percutaneous discectomy with the safety of both open standard discectomy and microsurgical discectomy. The investigators removed two lumbar discs from a cadaveric spine and weighed each of them. The two lumbar discs weighed in the range of 13.654 grams and 15.713 grams, respectively. The investigators initiated several series of 10 firing cycles from a surgical carbon dioxide laser system. In each firing cycle the surgical carbon dioxide laser system delivered a beam of light energy having an output power of 18.0 watts at pulse duration of 0.045 second at the rate of 15 pulses per second for a period of 6 seconds and vaporized approximately 325 milligrams of disc material. Based on the findings of other investigators reported in the literature relating to percutaneous discectomy the investigators postulated that 10 to 20 firing cycles are required to vaporize 30 to 40% (2.4 to 6.4 grams) of the disc material. The investigators initiated two series of 10 firing cycles in order to perform laser discectomy in a third lumbar disc of the cadaveric spine in situ. The investigators harvested and then bisected the laser-treated third lumbar disc for gross review. Their gross findings indicated a high probability of success For percutaneous laser discectomy.

Studies On Endoscopic Local Hyperthermia Using Nd-YAG Laser

Attempting a new method of laser irradiation for depressed gastric carcinoma, using a newly developed interstitial probe and laser attenuator, we applied local hyperthermia with prolonged low watt contact irradiation. Experimental studies were performed with this probe, using BDF1 mice injected hypodermically with Lewis lung carcinoma. A laser power of 2.0 w at the tip of fiber produced the most desirable temperature curve, about 43 - 60°C at the irradiation site. Clinical applications were carried out on 15 patients with early gastric carcinoma (mainly depressed), 10 preoperative pilot cases and 5 inoperable cases. In follow-up operations and biopsies gastric carcinoma was found to have completely dis-appeared in 2 of the preoperative and 4 of the inoperable cases. In the remaining 8 preoperative cases residual traces of carcinoma were found at the margin of the laser ulcer, but not at the bottom of it. We propose that endoscopic local hyperthermia using interstitial probe and low power irradiation (2.0 W) is the safest and most suitable method of dealing with depressed carcinoma.

Experimental Studies Of Endoscopic Local Hyperthermia With Contact Nd-YAG Laser

We have been studying experimentally and clinically to evaluate the histological effects and safety of the therapeutic Nd-YAG laser endoscopy by the contact method with new ceramic endoprobes comparing wit Li those by the non-contact method with single quartz fiber. In this paper, we would like to discuss possibilities of clinical application of endoscopic local hyperthermia using Nd-YAG laser (Laserthermia) with computer control system. Newly developed computer controlled Laserthermia may possible to apply for the treatment of the malignant tumor in the gastrointestinal (GI) tract.