Laser-Tissue Interactions

Future Applications of Lasers in Surgery and Medicine: A Review

The experimental use of lasers in surgery and medicine began only shortly after the development of the first working laser system. However, the development of practical, effective, and safe surgical lasers has been lengthy with many obstacles and delays. Today the laser is used for a wide variety of surgical operations. The fundamental limits and potential for future applications of lasers in surgery and medicine are discussed.

Production of a uniform cellular injury by raster scanning of cells for the study of laser bioeffects

Efforts to understand laser bioeffects in cells and tissues have been hindered by a nonuniform cellular response of the specimen, resulting in graded biochemical effects. In addition, the small beam diameters of commonly used lasers limit the number of cells expressing a response to numbers inadequate for the study of biochemical effects. For a limited emission power, expansion of the beam diameter reduces the irradiance, thus requiring longer exposure durations to produce a cellular response. Cultured human retinal epithelial cells were exposed as a single spot ("tophat" exposure) from a carbon dioxide (CO(2)) laser operating at 10.6 microm or scanned with a raster system and compared with thermal injury produced with heated saline for short periods (1-9 s) at relatively high temperature (55-70 degrees C). Cell viability and induction of the 70 kDa heat shock protein were evaluated as indicators of the cellular response. Initial attempts to use a tophat (uniform energy distribution) exposure resulted in a nonuniform cellular response (and nonuniform energy distribution) due to diffraction effects from the 2-mm selection aperture. However, raster scanning for appropriate times with the CO(2) laser yielded uniform cell viability and heat shock protein synthesis that were comparable to dipping cells in heated saline. Because scanning results in a homogeneous exposure of cells, the described scanning technique may be applied to studies of cellular responses to other lasers to evaluate photochemical and photomechanical effects.

Numerical study on the thawing process of biological tissue induced by laser irradiation

Most of the laser applications in medicine and biology involve thermal effects. The laser-tissue thermal interaction has therefore received more and more attentions in recent years. However, previous works were mainly focused on the case of laser heating on normal tissues (37 degrees C or above). To date, little is known on the mechanisms of laser heating on the frozen biological tissues. Several latest experimental investigations have demonstrated that lasers have great potentials in tissue cryopreservation. But the lack of theoretical interpretation limits its further application in this area. The present paper proposes a numerical model for the thawing of biological tissues caused by laser irradiation. The Monte Carlo approach and the effective heat capacity method are, respectively, employed to simulate the light propagation and solid-liquid phase change heat transfer. The proposed model has four important features: (1) the tissue is considered as a nonideal material, in which phase transition occurs over a wide temperature range; (2) the solid phase, transition phase, and the liquid phase have different thermophysical properties; (3) the variations in optical properties due to phase-change are also taken into consideration; and (4) the light distribution is changing continually with the advancement of the thawing fronts. To this end, 15 thawing-front geometric configurations are presented for the Monte Carlo simulation. The least-squares parabola fitting technique is applied to approximate the shape of the thawing front. And then, a detailed algorithm of calculating the photon reflection/refraction behaviors at the thawing front is described. Finally, we develop a coupled light/heat transport solution procedure for the laser-induced thawing of frozen tissues. The proposed model is compared with three test problems and good agreement is obtained. The calculated results show that the light reflectance/transmittance at the tissue surface are continually changing with the progression of the thawing fronts and that lasers provide a new heating method superior to conventional heating through surface conduction because it can achieve a uniform volumetric heating. Parametric studies are performed to test the influences of the optical properties of tissue on the thawing process. The proposed model is rather general in nature and therefore can be applied to other nonbiological problems as long as the materials are absorbing and scattering media.

Neodymium: yttrium-aluminum-garnet long impulse laser for the elimination of superfluous hair: experiences and considerations from 3 years of activity

This study examined the results obtained with a modern apparatus for laser hair removal (neodymium: yttrium-aluminum-garnet [Nd:YAG] laser at long impulses with a wave-length of 1,064 nm; Q-switched laser) over a follow-up period of 3 years. A large heterogeneous group of 480 patients was taken into consideration. These patients were treated according to a standard protocol with monthly checkups and a personalized protocol at deferred appointments. The results, discovered by means of the most objective procedure possible, were retrieved and put into a graph showing two different curves for the repopulation of hair. In their clinical travels, the authors observed an average variable regrowth of 40% to 65%, allowing them to affirm that laser hair removal using Nd:YAG at long impulses is decisively efficient in obtaining long-term results. The use of a protocol (denominated "prolonged monthly checkup") with laser sessions at ever-decreasing periods permits, among other things, more outstanding and advantageous results for the patient. Thanks to more efficiently synchronized phases of the biologic hair cycle, this shortens and moves the telegenic phases closer and also renders the anagenic phases (those in which the selective photoermolysis on the pilipheric follicle proves to be efficient) more efficient. Personalization of the treatment relative to the monthly health checkup sessions is of fundamental importance to the scope of obtaining the best results in terms of cost-benefit rate, provided submassimal fluxes are (i.e., those well-tolerated by the patient) used. All this allows hair removal that is not definitive, but which becomes progressively permanent (i.e., characterized by ever-growing periods of lack of hair sustained by sporadic maintenance laser sessions based on the individual's necessity).

Laser surgery: an approach to the pediatric patient

Revolutionary advances in laser research and technology have led to expanded dermatologic laser applications. With the wide range of lasers now available, a large spectrum of skin conditions in the pediatric population can be successfully treated or, in some cases, completely eradicated. Laser treatment of the pediatric population poses a unique challenge for the clinician on a variety of levels. Physically, the composition of many vascular and pigmented lesions changes as children age making them more resistant to laser therapy. Thus, in many cases, treating lesions at an early age has resulted in clearing in fewer sessions and with decreased complications. Mechanically, lasers and laser settings used for the treatment of adult lesions may have to be adjusted for the smaller vessels and the unpredictable nature of scarring with children's skin. For vascular lesions, the pulsed dye laser is considered the laser of choice for its efficacy and low-risk profile, whereas the Q-switched, pigment-specific lasers are ideal for most childhood pigmented lesions, allowing for single pigment cell destruction. Other conditions such as acne and acne scars, psoriasis, keloids, warts and hypertrichosis that traditionally have been treated with a variety of modalities are now being managed safely with laser surgery. Other issues specific to the pediatric population include the determination of suitable anesthesia, the provision of size-appropriate safety equipment, and the assessment and management of patient and parent anxiety. The use of lasers specifically designed for structural differences in pediatric lesions and the recognition of emotional issues surrounding a young patient during laser surgery are critical components of successful treatment.

LEARNING OBJECTIVE

At the conclusion of this learning activity, participants should be familiar with the mechanism of laser technology, current trends in the use of lasers for skin lesions in the pediatric population, and the issues specific to treating a patient with laser surgery.

The curative potential of intraluminal bronchoscopic treatment for early-stage non-small-cell lung cancer

Bronchoscopic treatment modalities such as lasers, electrocautery, cryotherapy, photodynamic therapy, and brachytherapy are potentially curative for patients with very-early-stage non-small-cell lung cancer (NSCLC) in the central airways. Previously, studies had primarily focused on the effectiveness of surgery, surgical bronchoplasty, and photodynamic therapy. The cure rate of intraluminal bronchoscopic treatment is strongly related to the patient's functional status and tumor stage. Intraluminal tumors are curable bronchoscopically when they are accessible to the fiberoptic bronchoscope, strictly intraluminal, and superficial with visible proximal and distal tumor margins. Early-stage cancer infiltrating deeper into the bronchial wall may already harbor metastases to the regional lymph nodes; hence, curative intraluminal treatment is not feasible. The use of new diagnostic tools (eg, high-resolution computed tomography, autofluorescence bronchoscopy, and endobronchial ultrasound) may improve staging to select the category of patients in whom intraluminal bronchoscopic therapy with curative intent is appropriate. An accurate intraluminal tumor staging will improve our ability to exploit the curative potential of many bronchoscopic techniques for complete tumor eradication in patients with very-early-stage intraluminal NSCLC in their central airways. The use of bronchoscopic treatment as a less morbid alternative than surgical resection will benefit patients most when tumor is detected at the earliest stage possible.

Penetration of the laser light into the skin in vitro

BACKGROUND AND OBJECTIVE

Knowledge of the optical parameters of the skin is important for all kinds of phototherapy. We analyzed penetration of laser light and proved different optical properties of in vitro specimens of normal skin and granular tissue from skin ulcers.

STUDY DESIGN/MATERIALS AND METHODS

An He-Ne laser (lambda = 632.8 nm, output 50 mW) and a semiconductor laser (lambda = 675 nm, output 21 mW) were used. The distribution of laser radiation was detected by a CCD camera and evaluated by the image analysis software DIPS.

RESULTS

Transmittance in granular tissue was about 2.5 times higher than that in normal skin. In the thickest skin sample (2 cm), approximately 0.3% of He-Ne laser and 2.1% of semiconductor laser light penetrated.

CONCLUSIONS

The results demonstrate the percentage of incident light penetrating the individual skin layers in different localizations on the skin surface, which is a decisive factor for the selection of the radiation dose.

Thermal effects in excimer laser trephination of the cornea

BACKGROUND

Excimer laser trephination, as an alternative to mechanical trephination of the cornea in penetrating keratoplasty, is expected to reduce long-term postkeratoplasty astigmatism. Trephination with high energy densities may induce thermal epithelial alterations when metal aperture masks are used.

METHODS

Ninety porcine eyes fixed in an artificial anterior chamber (20 mmHg) were trephined with a 193-nm excimer laser in order to study the effect of the temperature on the cornea and the aperture mask during and after termination of the laser exposure. Energy levels tested were in the range used in patients. A pyroelectric infrared sensor connected to a PC via an analog-digital converter was used. With a high-speed sampling routine written in C+2 it was possible to monitor on line the temperature in a focus 0.8 mm in diameter.

RESULTS

In donor trephination the maximum temperature increase of the metal mask was 11 K (donor tissue 6.1 K, repetition rate 30/s). During recipient trephination the maximum temperature increase of the mask was 9.4 K (7.5 K on the cornea). An increase in the repetition rate and a decrease in the rotation speed resulted in greater temperature increase of the exposed cornea or metal mask.

CONCLUSIONS

Online monitoring of cornea and mask surface temperatures during excimer laser trephination is possible using high-speed sampling equipment. Appropriate adjustment of repetition rate and rotation speed may reduce thermal effects, especially in donor trephination.

Clinical uses of lasers in dermatology

The accessibility of the skin to examination and study has permitted dermatologists to play an extremely important role in defining the clinical usefulness and limitations of many laser systems as well as developing innovative concepts, techniques and devices that further improved the effectiveness of laser treatment. As new laser technology evolved over the years, dermatologists have also helped define the specificity of laser-tissue interaction and employed the newly developed laser technologies in innovative ways which further expanded the usefulness of these devices. One of the most important concepts to be developed by dermatologists--selective photothermolysis--has led to the creation of a series of laser systems which have provided numerous unique advantages in the management of many common vascular and pigmented conditions of the skin and mucous membranes, even in infants and children. The net result of these technologic advances has been the creation of new and effective treatment techniques which have been so profoundly superior to existing technology that they have been rapidly incorporated into the daily practice of most dermatologists.

Ophthalmic effects of low-energy laser irradiation

Laser irradiation at subthreshold energies exerts various effects on the eye and other parts of the body, mainly the skin and nervous system, through a mechanism that has yet to be adequately explained. The ocular bioeffects are manifested mostly in the retina, but also in other ocular tissues. This review outlines the reported effects of low-energy laser irradiation on nonophthalmological tissues and organs, including those of the nervous system, with special emphasis on the optic nerve. It also details the ophthalmic phenomena induced by low-energy laser irradiation and examines claims of its therapeutic efficacy in several eye diseases, such as keratitis, glaucoma and macular degeneration.

Bronchoscopic treatment of lung tumors

Several bronchoscopic techniques for the treatment of patients with tracheobronchial pathology have become available during the last decade. Technical development and additional instruments have provided the bronchoscopist with several alternatives for bronchoscopic therapeutic interventions. The majority of patients with malignant tracheobronchial neoplasm have a dismal prognosis. Palliation is the main aim of the treatment. However, in patients with an early-stage tumor, bronchoscopic treatment may have a curative potential. Resectability, after tumor reduction by a bronchoscopic treatment, may be improved. This article discusses various bronchoscopic techniques, the advantages and disadvantages of each method and the possible benefit which can be derived from such a treatment.

Argon and diode laser treatment of benign eyelid lesions

This study reports the experience of 14 patients (15 lesions) treated with the argon or diode laser for small, benign eyelid conditions. The technique is suitable for use by ophthalmic surgeons because the lesions are localised, the surgery can be performed precisely to maintain adequate lid function and cosmesis, and both the argon and diode laser viewing systems and delivery systems provide excellent control for the surgery. There were no complications from the laser surgery, and the surgical aims of lesion clearance, good cosmesis and function were fulfilled in all patients. The advantages in lid surgery of the diode and argon lasers over the carbon dioxide laser are highlighted.

Effect of steroids or tissue precooling on edema and tissue thermal coagulation after CO2 laser impact

The carbon dioxide laser is frequently used in laryngeal microsurgery. Some surgeons have empirically used preoperative steroids or precooling with ice prior to laser impact to limit the resultant tissue thermal coagulation and/or edema. An animal model was designed to quantitatively test these effects. Depillated areas of rat skin were exposed to a CO2 beam of 1 mm diameter at 15 W for 0.1 sec after either administration of Decadron (0.25 mg/kg) immediately prior to impact or precooling more than 10 degrees C below basal body temperature. Measurement of edema was quantitated as extravasation of Evans's blue dye that had been injected intravenously. Tissue thermal coagulation was measured on hematoxylin and eosin stained histologic sections. In comparison to controls, statistically significant reduction in edema was seen only at the 24 hour time period after laser exposure for the steroid group (P less than .002) but not for the precooling group. Tissue thermal coagulation was significantly smaller for both the steroid and the ice group (P less than .006 and P less than .001, respectively) when compared to controls.

The effects of laser energy on the arterial wall

Laser energy has been proposed as a method of resecting atherosclerotic plaque since the mid 1960s. However, only over the past several years have we come to understand some of the unique interactions of the laser with cardiovascular tissue. In laser angioplasty a major challenge has been choosing the optimal laser and duration of laser exposure to achieve adequate resection of plaque, while minimizing such complications as thrombosis, perforation, embolization, aneurysm formation, and accelerated atherosclerosis. Ultimately we must develop a more selective laser that resects plaque while leaving adjacent arterial wall uninjured. This review describes the physics of laser energy, the different lasers available for use in the cardiovascular system, laser-arterial wall interactions, and some of the limitations of laser angioplasty.

Side effects in excimer corneal surgery. Corneal thermal gradients

Thermal loading is a significant side effect during excimer laser surgery of the cornea. The maximal temperature rise, which is dependent on fluence and repetition rate of the radiation, amounts to 20 degrees C in excised corneas and 7.5 degrees C in the in situ cornea. The temperature decreases exponentially with increasing distance from the incision with a half-value distance of 610 +/- 100 micron. Exposure parameters are recommended to avoid temperature rises greater than 11 degrees C.