Semiconductor laser diodes are compact, efficient, and reliable sources of laser light that have been extensively used in laser printers, optical telecommunications, and optical disc systems. Although powers up to several tens of watts have been available from such devices, the ability to couple power into medically useful optical fibers has been limited to a few watts, restricting applications primarily to ophthalmology. To expand the medical applications of diode lasers into general surgery we have developed a 25 W medical laser diode system with a standard SMA-905 connection for 400, 600, or 1000 micrometers core medical delivery fibers. In-vitro comparisons between the 805 nm diode and 1064 nm Nd:YAG show similar vaporization and necrosis zones in contact mode but a higher absorption coefficient for the diode laser in non- contact mode. The results of clinical use in both modes demonstrate the clinical efficacy of this small compact and portable system in a wide range of surgical applications.

Significant progress has been made in the past few years in increasing power and performance of semiconductor laser diodes. Package and system designs can now be optimized to immensely improve the use and effects of laser diodes in medical health care. These micron size devices exhibit power conversion efficiencies in excess of 50%, can operate with battery power sources, and can be sterilized. Delivery systems include fiber optics or lensed output. The complete unit can be as small as 1' square and can be hermetically sealed. These characteristics, among others, make these devices ideal for medical applications. For this presentation, we summarize current laser diode technology and compare performance with solid state and gas lasers commonly used in medicine today. The benefits and advantages to a laser diode derived system are highlighted. We present data that illustrates electrical and opto- electronic characteristics and discuss several configurations which are particularly suited for use in medical procedures.

Light emitting diode (LED) array light sources currently in development offer an alternative to laser light sources in a wide range of medical applications. Previously developed as light sources for research in photosynthesis in plant growth experimentation, LED arrays have produced an average continuous output of 4 - 6 watts at a wavelength of 660 nm. This output is equivalent to the terrestrially sensed output of the sun at this wavelength at high noon. LED chips are arrayed on an alumina tile substrate that may be formed to provide optical power focused on a specified target area.

Ophthalmic applications of medical lasers have been extensively explored recently because of their market potential. Refractive surgical lasers represent one of the major development efforts due to the large population of eye disorders: about 160 million people in the USA and more than 2 billion worldwide. The first refractive laser developed was the ArF excimer laser at 193 nm in 1987 - 88 for a procedure called photorefractive keratectomy (PRK). More recently, solid state refractive lasers have also been explored for preliminary clinical trials. These lasers include Nd:YLF (picosecond at 1054 nm), doubled-Nd:YAG (nanosecond at 532 nm), Ho:YAG (microsecond at 2100 nm) and ultraviolet (UV) lasers generated from the harmonic of Ti:sapphire-laser (205 - 220 nm) and Nd:YAG (at 213 nm).

Alexandrite lasers have been developed over the past decade and are now playing an increasing role in medical research and clinical practice. The characteristics of these lasers are described including: the ability to tune their wavelength, to convert the output into other ultraviolet, visible, and infrared wavelengths, and to vary their pulse duration. Several new clinical applications and promising new areas of ongoing research utilize the unique wavelength and temporal versatility of these lasers.

Performance of the chromium-doped forsterite laser for various modes of operation is reviewed. Methods for generation of femtosecond pulses are presented. Stable transform limited tunable femtosecond pulses with FWHM of 50 fs were generated from a self mode- locked chromium-doped forsterite laser. Synchronous pumping provided the starting mechanism for self mode-locked operation.

Since January 1988 we have been using the combined Nd:YAG laser Medicalas. The laser operates on the wavelength of 1.06 micrometers with maximum output power of 100 W, and a wavelength of 1.32 micrometers with maximum output power of 30 W. Introduction of the laser into clinical practice was preceded by experimental operation, where we verified the interaction of laser emittance on both wavelengths with the tissues of colon, stomach, esophagus, and open surgery of the abdominal and thoracic cavities.

The acousto-optical Q-switched (AOQ) laser is a modification of the continuous-wave (cw) Nd:YAG laser with a quartz Q-switch modulator mounted into a laser resonator. The modulator is driven by a signal of 27.12 MHz of high frequency generation modulated by low frequency in the range of 200 to 500 kHz. Modulation causes the generation of high-peak power pulses in the kilowatts. Pulse durations are hundreds of nanoseconds, and the repetition rate depends on modulation frequency.

Laser induced retinal lesions are used to treat a variety of eye diseases. The size and location of these retinal lesions are critical for effective treatment and minimal complications. An automated system is under development for retinal photocoagulation to improve the accuracy of this treatment. Separate instrumentation systems have been developed to monitor and control lesion growth in real time to compensate for tissue inhomogeneity, and to track and compensate for retinal movement during irradiation. A real time lesion feedback control system is implemented on a UNIX based workstation. A CCD camera (30 frames/second) and coagulating laser are coaxially aligned such that images of the lesion can be acquired during laser irradiation. Parameters of these reflectance images are extracted by an image processor in real time and when certain preset thresholds are exceeded, the laser is shut off. The camera and laser legs are alternately shuttered during irradiation by a high speed spinning wheel to prevent the reflected light from the laser from interfering with the reflectance signal. This system is coupled to a fundus camera for delivery to the eye.

We have designed and are fabricating the SideFire^R laser optical fiber device incorporating a 99.95+% purity gold tip with a mirror which laterally reflects the beam at a 105 degree(s) angle to the optical fiber axis while closely maintaining the beam profile. The monolithic gold construction of the mirrored tip underlies the optical and thermal stability and the bicompatibility of the device during lasing in aqueous environments using up to 80 W of Nd:YAG 1.064 micrometers radiation. Current studies are being conducted to evaluate the use of this device in laser coagulation of the prostate as an alternative treatment to transurethral resection in treatment of benign prostatic hypertrophy.

MRI-guided interventional procedures are critically dependent on accurate localization of an MRI-compatible needle used as a guiding device for laser fiber optic therapy. We present a scheme which utilizes the 3D imaging capability of the MRI modality and the 3D image processing capability of computer workstations to automatically and time-efficiently localize and display the tip of the needle on an oblique plane which cuts through the scanned object.

Precise coordination of image acquisition relative to lesion creation is a crucial consideration for real-time MRI-monitoring of laser-tissue interaction. A hybrid laser and MRI system is described which provides an integrated environment for coordinated operation of laser and various in-vivo monitoring devices, such as MRI, and thermometry. Furthermore, the hybrid system allows programmable analysis of image data in coordination with temperature measurements.

Interstitial tumor therapy guided by imaging techniques is minimally invasive and a promising surgical approach which will become clinically practical only when effective, simple, and safe modalities for tumor excision and control of tumor vascular supply are available. In a novel experiment utilizing a 1.5 T magnetic resonance (MR) scanner, the carotid artery of a New Zealand white rabbit was identified and then clamped using the Premium Surgiclip^tm 9.0' disposable automatic clip applier. The magnetic resonance imager equipped with an angiography package was used to locate vasculature in the carotid triangle of the rabbit via fast scan techniques. The artery was then clamped with titanium clips, and repeat magnetic resonance angiography (MRA) clearly demonstrated the cessation of blood flow within the chosen vessel. The experimental results are promising, since the angiography package not only provided the visualization of the arterial vessel, but was also used to guide an MR compatible surgical instrument to the vessel, with no artifact seen.

In this study a model was developed to quantify levels of laser/cavitron energy deposition and to correlate this with MRI and histological damage. The Ho:YAG laser (2.1 micron wavelength) and cavitron were used on separate matching tissues, with exposure to succeedingly higher energy densities by an accurate and reproducible method of dosimetry. Post laser/cavitron treatments were then evaluated using the Signa 1.5 T MRI (GE Medical Systems). In this study, fast gradient echo (rapid SPGR) pulse sequence was used to visualize and quantify signal changes. Thereafter, biopsies were taken for standard H&E preparation and quantification of laser or cavitron damage. FSE and turbo flash images taken demonstrated a linear correlation between energy deposition in the tissue and signal intensity changes for the laser or signal void for the cavitron. These signal changes correlated well with the histological measurements of the same tissues. This initial study demonstrates the potential clinical feasibility of these two energy delivery systems on various tissues. Furthermore it suggests the need for future development of non-invasive quantitative techniques for real time MRI monitoring in the treatment of deep and difficult to reach tumors of the head and neck and other parts of the body.

Significant progress has been made recently in techniques and corresponding instrumentation for optical spectroscopy and imaging of tissues in vivo, based on either optical absorption/scattering, fluorescence, or Raman effects. The focus of this paper is on the principles and instrumentation required for in vivo use, particularly non-invasive clinical applications. Progress in absorption spectroscopy and imaging are emphasized in order to illustrate principles and some of the major limitations of current technologies. Possible future approaches to practical clinical instrumentation are indicated.

The diagnostic capability of an optical biopsy probe combined with a tumor selective fluorescence drug (Photofrin II^R) was tested in an in vivo animal model. The optical biopsy system is comprised of an arc lamp, an optical contact probe, and low cost detectors. We illuminated tissue with blue (405 nm) light and detected the diffusely reflected excitation light, the tissue autofluorescence (500 - 540 nm), and the drug fluorescence near 630 nm. By using the appropriate signal ratios, normal, inflamed and malignant lymph nodes could be distinguished with a high specificity and sensitivity (85 - 95%).

Our laboratory has developed a modular laser tomography system, with pulsed or amplitude modulated (MHz to GHz), near infrared lasers that deliver a probing beam to the tissue of interest through a fiber optic. After the incoming light is scattered and attenuated by the tissue, a detector or imaging fiber optic bundle delivers it to a point detector (photomultiplier tube) which is heterodyned with the modulation frequency to yield the phase delay and demodulation resulting from the light-tissue interaction. The CCD electronics are phase-locked with those of the digitizer to minimize pixel jitter and, in addition, an external clock synchronizes the detector units with the modulated laser source. The digitized time slices are integrated into four bins corresponding to four quadrants of the cross correlation period. The final processing step, a fast Fourier transform, generates the phase shift, demodulation, and average intensity data suitable for image reconstruction.

A superconducting Signa 1.5 T magnetic resonance (MR) suite was modified and multiple upgrades were introduced to make it effective and safe for minimally invasive surgical procedures guided by imaging techniques. Two MR compatible video projection cameras and monitors from Resonance Technology were installed inside the Magnetic Resonance Imaging (MR) room allowing visualization of MR and/or ultrasound (UTZ) images during surgical procedures. The interventional therapist can now stand at the patient's side and visualize MR and/or UTZ images in the room. A permanent MR compatible camera and light source were installed at the opening of the magnet bore which allows close-up visual monitoring of the patient and treatment site. MR compatible anesthesia systems (Ohmeda Company) and monitoring equipment (In Vivo Research, Inc.) are now available. A standard ultrasound (UTZ) system was modified and adapted by General Electric Medical Systems for use in this MRI suite.

The use of laser radiation for endoscopic surgery has been a significant advance in patient care. The usual modality is to use an optical fiber to deliver the light energy from the laser to the patient. However, there have been a number of incidents of the optical fiber breaking while the beam was active. Although no injuries have been reported, we investigated the hazard posed by such broken fibers to operating room (OR) personnel. Optical fibers were fractured in a manner that simulated the fractures in the ORs and the output power and divergence measured. In most cases, the laser emission was still `beam-like,' presenting a potential ocular hazard. Clearly proper use of eye protection and administrative controls are needed to avoid injuries.

This paper explores the concerns revolving around the resultant detritus of the active laser. Ocular, cutaneous, respiratory and systemic effects, and protection and prevention measures are discussed.

The excimer laser while presenting the medical community with a new and potentially exciting tool, particularly in the ophthalmic arena, (an area where laser safety policies have traditionally met with skepticism) also presents unique safety concerns. The object of this presentation is to review those safety concerns and raise user awareness. Some of these safety issues are: Ultra violet exposure, rare gas hazards, x ray exposure, training, high voltage, etc.

All healthcare professionals involved in the delivery of laser technology to patients, must develop and monitor clinical laser safety programs that ensure compliance with national, state, and local regulations, professional standards of practice, and national consensus standards. Laser safe treatment environments for patients and for personnel can be established and maintained through understanding the impact of both regulatory and advisory guidelines, comprehensive program planning, appropriate continuing education, and routine safety audits.

It is a problem of laser eye-microsurgery and a proposed new method of laser iridopuncture to aff ect the predetermined points of an incessantly moving eye. Solving the problem, we aligned a sharp "laser needle" with a TV system and slaved it electrooptically f or being always centred in a tracking window. Preliminary image processing includes histogram normalization resulting in the possibility of a f ixed threshold selection for binary quantization of an image. TV correlation-tracking realizes a minimum absolute diff erence algorithm with the size of a tracking window 16x16 pixels and the field of search 8 pixels greater in orthogonal directions. The laser beam is Bragg-diff racted on a moving sound wave in a Te02 crystal. Frequency synthesizer controls the deflection of a laser beam and operates in the range from 50 to 100 MHz quantized in 0.1 MHz steps. Maximal switch time is 1 ms. Investigations on animals and treatment of human volunteers were made. Patients with tachyarrhythmia, stomac and duodenum ulcer, chronic pancreatitis, gall­ bladder diskinesy, bronchial asthma were included into the experimental group. Laser iridopuncture, acting as a stabilizing factor improving the status of injured membranes of blood cells, giving the normalization of RR­ intervals within the 40%-limits, and a perfect healing of ulcer af ter 10-12 procedures, showed to be a perspective non-invasive method of treatment f or human diseases.

New powerfull waveguide laser is created on neodymium glass radia­ ting on wavelength. 1.06 µm . The laser generates pack of giant pulses with duration 30-40 nsec and several MW power. Total energy of the pack of pulses reaches 20 J in time period 1 msec. A bunch of neodymium glass spoke waveguides with a diameter of 1.5 mm is used as an active media. waveguide are located round the pumping lamp. Flexibility of the active elements makes possible getting any ne­ eded distribution of radiation intensity. Simple construction (without electrooptical modulators of light and traditional Fabri-Perot resonator) made possible creation of a highly reliable laser system for treatment of wounds, combustions, etc. on big surfaces.

Modern surgery widely uses both laser and low frequency ultrasonic techniques together with various modifications of contact instruments. This paper describes for the first time the feasibility of different combinations of these techniques in the medical practice. Comparative analysis of laser and ultrasound systems show that they can essentially supplement each other and, in combination, bring new efficacious results. Over time during surgical procedures, both ultrasound and lasers are used one after the other. It is also possible to use both techniques simultaneously from separate devices and separate contact tips. However combination of laser and ultrasound in one unit and in one contact tip using optical fiber and acoustic waveguide for delivery of laser and ultrasound energy is more efficient.

Much has happened since lasers were introduced into medicine in the early 1960s. In this presentation we will provide a look at the current market situation and take a look ahead. We will describe the lasers and applications that hold the most promise for the future, listing the major participants and the laser types they supply in each of these application areas. If time permits, we will also present our selections for the most significant new products introduced in 1992.