Research over the last 40 years has provided information on laser-tissue interactions and led to the development of many lasers used for a variety of dermatologic procedures. In this review, we discuss the current state of laser use in dermatology including the treatment of vascular lesions, tattoo removal, treatment of pigmented lesions, hair removal and laser skin resurfacing. In addition, we note several issues which need to be addressed in order to achieve an improved therapeutic outcome without adverse effects.
Thermal modification of joint capsular tissue has gained great popularity in the orthopedic community as a treatment method for joint instability since this new operative technique was introduced in 1994. Heating joint capsular tissue to approximately 60 to 80°C by laser or radiofrequency (RF) energy produces significant dimensional alterations (shrinkage and thickening) of the tissue treated, resulting in postoperative stabilization of the joint. Initial clinical trials in patients with shoulder instability indicated that the majority of the patients were able to return to high-level athletic performance following thermal modification of joint capsular tissue. A series of in vitro experimental studies demonstrated that the joint capsular tissue could be shortened by up to 45% through the application of laser or RF energy, although significant loss of the tissue’s mechanical properties and thermal damage of the tissue were observed with higher energy applications. In vivo experimental studies demonstrated initial deleterious effects of thermal energy application, followed by an active reparative response by cellular fibrous tissue with concomitant improvement of mechanical properties. Other studies using a different animal model showed that despite significant immediate postoperative tissue shrinkage, the tissue stretches over time if the tissue is subjected to physiological loading. Based on these scientific studies, it is proposed that thermal modification of joint capsular tissue relies not only on the initial effect (shrinkage), but to a great extent, the tissue’s biological response (repair of the thermally modified tissue with new thicker tissue) to achieve postoperative joint stability. Currently, arthroscopic thermal modification of shoulder joint capsular tissue is performed clinically at many hospitals, with generally good to excellent outcomes to date. Development and improvement of thermal energy delivery devices are actively being investigated for various clinical applications. Recently, the treatment of other joint disorders such as patellar instability have been examined. In addition, the potential for thermal modification of other musculoskeletal tissues such as cartilage is being explored. Thermal modification of musculoskeletal tissues have the potential to enhance joint stability and may become a prominent modality in the treatment of joint disorders. However, it should be emphasized that thermal treatment does cause initial deleterious effects on the tissue’s properties, and that long term results have yet to be evaluated. Carefully controlled clinical and scientific studies should further clarify the advantages and disadvantages of this technique.
The shape of the cornea of the eye can be modified to correct permanently for near-sightedness or far-sightedness. Heat energy can be delivered to the cornea for this purpose in order to elevate the collagen in mid-cornea to its shrinkage temperature of about 60 °C. When a suitable pattern of shrinkage is created in the peripheral cornea, the central cornea may steepen or flatten in response, and this change in curvature may serve as a refractive correction. This paper reviews the following methods for heating the cornea for this purpose: conduction, radio-frequency, laser, and microwave.
After decades of attempts to occlude the fallopian tube thorough mechanical, cautery, and chemical techniques, no practical solution has yet attained wide clinical success and usage. An historical tour of prior techniques such as caustic chemicals, polymer injections, implants, and mechanical or thermal techniques is provided herein. Promising contemporary methods employ heat as a technique for lesioning the fallopian tube, although the original work in thermal treatment dates back to 1878. Recent studies performed in animal models employ microwave or radiofrequency devices that have the potential to succeed as transcervical solutions, accomplishing tubal ligation without surgery. In cases where an implant is used instead of energy delivery to thermally ablate, the natural peristalsis of the fallopian tube causes these implants to migrate and become expelled. Failure equates to unwanted pregnancy or ectopic pregnancy, a pregnancy outside of the uterus. Thermal techniques have the advantage of leaving no foreign body behind and can be carefully monitored and controlled in both the temperature and time domains. The energy sources include conductive sources, laser, cryogenic, microwave and radiofrequency devices. The most promising studies utilize thermal methods with the temperature monitored and well regulated. This will assure consistent, circumferential lesion formation, occlusion of the tube through fibrosis, and clinical success.
Blood vessels are anatomically and mechanically complex tissue structures. The particular architecture of arteries, veins and capillaries affects their response in therapeutic heating applications. This work summarizes the signal anatomic features of blood vessels for engineers and scientists, introduces the primary underlying physical principles which describe their function and response to external heating for clinicians, and provides a few representative examples of heating applications. It is by no means complete — such a work would be at least two orders of magnitude longer — but, we hope, provides an adequate survey of the pertinent literature so that the interested can locate more substantial treatments of the subject.
The safe and effective use of interstitial thermal therapy (ITT, radiofrequency ablation) for treatment of lung neoplasms was examined in a preclinical model. Lesions were reproducibly created in normal lung parenchyma and were affected by conductive heat loss via air and blood flow and the presence of bronchi. These observations of controlled injury to lung tissue suggest that clinical application would be appropriate and may yield advantages to selected patients with lung neoplasms (lung cancer, pulmonary metastases, etc.) or other pulmonary diseases.
In the past three decades many investigators have tried to apply thermally-mediated ablative procedures for the treatment of musculoskeletal neoplasms. Much of this preliminary work has been performed in animal models and small limited clinical studies. These studies have shown the techniques of cryosurgery, microwave, and radioffequency (RF) to have some utility in specific clinical situations and specific tumors . To date the most widely utilized techniques are cryosurgery in the operative setting of malignant or locally recurrent neoplasms without cross-sectional image guidance and percutaneous radiofrequency ablation of osteoid osteomas with computed tomographic (CT) guidance. This paper will briefly review the various thermallymediated techniques. Since RF ablation is currently the only minimally invasive modality being applied to bone tumors the specifics of RF ablation in the treatment of benign and malignant tumors will be the primary focus of discussion.
From a reading of recent neurosurgical literature with a search focus on intracranial applications, a list of thermal agents and related minimally invasive techniques was drawn; this list was supplemented by our own research experience. Thermal agents which are either implemented in clinical practice or undergoing active research include: radioffequency current, laser light, microwave electromagnetic radiation, ultrasound and cryogens. Therapies include percutaneous coagulation of small targets which are less than half of one cubic centimeter as for rhizotomy for trigeminal neuralgia and pallidotomy for kinetic disorders, as well as interstitial hyperthermia and/or coagulation of large tumors which range up to centimeters in diameter. Implementation of a thermal agent for therapy evolves in a dynamic interaction between the specific technology and an understanding cf the tissue properties governing the agent’s therapeutic effect. Minimally invasive techniques require methods to define, visualize and approach targeted tissue, and to monitor (and thereby control) the extent of the thermal ‘lesion.’ Over the twentieth century, concomitant with advances in neurosurgery and radiology, technologies have been developed with which to approach the twenty-first century in pursuit of these minimally invasive thermal interventions which are, as of yet, new and underdeveloped.
Catheter-based techniques have been used successfully in the treatment of many patients with various cardiac rhythm problems, including A-V nodal reentrant tachycardia, accessory pathways, and other atrial and ventricular arrhythmias. These techniques have had limited success in the treatment of disorders such as ventricular tachycardia in the setting of prior myocardial infarction. New techniques are needed to create the larger lesions required for treatment of such conditions. In addition, conditions such as atrial fibrillation and atrial flutter require new catheter-based techniques for linear ablation. As a result, a wide range of energy sources have been investigated and developed.
Drilling holes in myocardial tissue using high-power lasers has shown to be effective in relieving angina in patients in an end-stage coronary heart disease who do not respond to medication and are unsuitable for standard revascularization techniques. An overview is presented of the interaction of various laser systems with myocardial tissue and the many experimental and clinical studies that have been conducted to elucidate the mechanism of the therapeutic effect of transmyocardial (laser) revascularization (TMR or TMLR). An angina relief of 2 classes with an acceptable mortality (5 - 10 %) and morbidity (20 - 30 %) rate is achieved in the majority of patients. Adverse effects can be minimized by critical patient selection and by a percutaneous approach (PMR). There is no significant difference in the results between the treatment modalities. The acute beneficial effect of TMLR might be attributed to sympathetic denervation. The combined thermal and mechanical injury has shown to provoke an angiogenic response that may be enhanced by adding growth factors. Consequent improvement of the myocardial reperfusion and functionality has been observed but needs further verification with, e.g., high-resolution scintigraphic techniques. Based on the experience in over 7000 patients, TMLR shows to be an effective and safe procedure resulting in a significant improvement in the quality of life for a carefully selected patient group suffering from end-stage coronary disease.
Treating disease with little alteration has long been a goal of medical science. During the past quarter century, technological advances have brought forth minimally invasive approaches to the surgical diagnosis and treatment of cancer. In the domain of breast cancer, a less invasive sentinel lymph node biopsy may replace axillary lymphadenectomy for many patients, and image guided core biopsies have minimalized the degree of surgical intervention needed for tissue diagnosis. This mirrors the primary treatment of breast cancer that over the past century has progressed from mastectomy to breast preservation with a progressively diminishing operative field.
Percutaneous image-guided ablative therapies using thermal energy sources such as radiofrequency, microwave, high intensity focused ultrasound, cryotherapy, and laser have received much recent attention as minimally-invasive strategies for the treatment of focal malignancy in the liver. Potential benefits of these techniques include the ability to ablate tumor in non-surgical candidates, reduced morbidity as compared to surgery, and the potential to perform the procedure on an outpatient basis. This article will present an overview of the principles and techniques used for thermal ablation, as well as review the results of published clinical trials.
There are numerous diseases and abnormal growths and conditions that afflict the skin and underlying superficial tissues. In addition to cancers such as primary, recurrent, and metastatic melanomas and carcinomas, there are many non-malignant conditions such as psoriasis plaques, port wine stains, warts, and superficial cut and bum wounds. Many of these clinical conditions have been shown responsive to treatment with thermal therapy - either low temperature freezing (cryotherapy),. moderate temperature warming to about 41-45°C (hyperthermia), or high temperature (>50°C) ablation or coagulation necrosis therapy. Because both very low and very high temperature therapies are for the most part non-selectively destructive in nature, they normally are used for applications where therapy can be localized precisely in the desired target and some necrosis of adjacent normal tissues is acceptable. With the exception of precision controlled cryotherapy or laser surgery (e.g. wart, mole, tattoo and port wine stain removal) or focal thermal surgery of small deep-seated nodules, it is generally preferred to use moderate thermal therapy (hyperthermia) in the treatment of skin and subcutaneous tissue disease in order to preserve the protective barrier characteristic of intact skin within the target region while inducing more subtle long term therapeutic improvement in the disease condition. This type of subtle thermal therapy is usually administered in combination with one or more other therapies such as radiation or chemotherapy - something with a differential effect on the target and surrounding normal tissues that can be magnified by the adjuvant use of heat.
A great number of women suffer from abnormal uterine bleeding. Most do not want to undergo a hysterectomy and have searched for an alternative treatment. Ablation of the endometrium has become a viable alternative. Initially, surgical applications utilized thermal ablation by passing a rolling electrode, energized by monopolar radiofrequency (RF) energy, to ablate the inner uterine lining. This procedure was done under visual guidance and required practiced surgical skills to perform the ablation. It was not possible to assess subsurface damage. More recently, various energy systems have been applied to the endometrium such as lasers, microwaves, monopolar and bipolar RF, hot fluid balloons, and cryotherapy. They are being used in computer controlled treatments that obviate the user’s skill, and utilize a self-positioning device paired with a temperature monitored, thermal treatment. Finite element models have also been created to predict heating profiles with devices that either rely on conductive heating or that deposit power in tissue. This is a very active field in terms of innovation with creative solutions using contemporary technology to reduce or halt the bleeding. Devices and minimally invasive treatments will offer choices to women and will be able to replace a surgical procedure with an office-based procedure. They are very promising and are discussed at length herein.
This paper reviews the application of MRI as a non-invasive technique for accessing temperature in thermal therapies. Two MR parameters, T1 relaxation and proton resonance frequency (PRF), have shown temperature sensitivity that is measurable with MRI. A third temperature dependent parameter associated with the self-diffusion of water, referred to as the apparent diffusion coefficient (ADC), is not intrinsic to nuclear magnetic resonance (NMR), but can be measured using MRI. These three parameters have been useful for quantitatively mapping temperature distributions in vivo. Each requires a tailored imaging technique. Each has pros and cons with regard to a given application. At this point in the development of MR image guided temperature mapping, the PRF shift technique is preferable, particularly with regard to non-invasive thermal ablation procedures. This approach has problems with stability and motion in procedures that require heating for extended time periods. Further development of MRI thermometry is required for long duration procedures.
Cautery, the application of hot fluids, burning sticks, hot coals or heated metal rods for treatment of disease, has been used to control of bleeding and treat wounds, ulcers and tumors since Neolithic times. [1-6] It has only been in the last 130 years that various electromagnetic energy sources have been exploited to produce heat for thermal medical treatments. [1, 7,8] These sources include lasers (light) and radiofrequency, microwave frequency and ultrasound generators.  Currently, the heat generated by the interaction of these energy frequencies with targeted biologic tissues is being used to treat superficial and deep lesions for a variety of lesions in several different organs.
The use of diagnostic ultrasound as a tool for noninvasive temperature feedback, image guidance, and damage assessment is described. The physical principles allowing for such applications are discussed along with the underlying scattering models. It is shown that temperature changes on the order of 0.1 °C can be detected with a spatial resolution on the order of 1 mm. It is further shown that temperature variations can be tracked up to nearly 20 °C from baseline for relatively long durations. In addition to temperature feedback, the potential for using ultrasound for damage assessment is discussed. Finally, the latest efforts on new self-guided ultrasonic phased array systems for imaging and therapy are discussed. The paper is concluded with a discussion of the future directions that will ultimately define the role of diagnostic and therapeutic ultrasound in the general area of image-guided surgery.
The desire for noninvasive monitoring of thermal therapy is readily apparent given its intent to be a minimally-invasive form of treatment. Electromagnetic properties of tissue vary with temperature; hence, the opportunity exists to exploit these variations as a means of following thermally-based therapeutic interventions. The review describes progress in electrical impedance tomography and active microwave imaging towards the realization of noninvasive temperature estimation. Examples are drawn from the author's experiences with these technologies in order to illustrate the principles and practices associated with electromagnetic imaging in the therapy monitoring context.
Five non-pharmacological, experimental, prostate (benign hyperplasia/cancer) treatment modalities including transurethral radiofrequency thermotherapy (TURT); transurethral microwave thermotherapy (TUMT); transurethral and transrectal microwave thermotherapy (TUMT/TRMT); interstitial laser coagulation (ILC); and interstitial cryotherapy (IC), are evaluated. These and other similar techniques are currently in various stages of development and clinical use. Most of these modalities produce relatively similar effects in tissue; however, each has pathophysiologic features and potential complications which may preference its use in a specific anatomical and/or disease situation. All treatments were performed using the canine prostate model, by the same investigators. Our studies have shown that although the canine prostate does not respond to injury exactly as the human prostate does, the effects are similar enough to be conceptually, and often specifically, valuable from efficacy and safety standpoints. Two of the five treatments evaluated (TURT, TUMT/TRMT) resulted in marked dilation of the prostatic urethra without significant parenchymal effect. Three of the treatments (IC, ILC, TUMT) resulted in parenchymal ablation with only minor dilation of the urethra. Although each technique has encouraging experimental findings, ultimate success will be determined by further definition of the instrumentation technique and appropriate clinical implementation.
Benign prostatic hyperplasia is a frequent benign disease that often requires surgical intervention. Prostate cancer affects 250,000 men annually, with surgery and radiation therapy the common form of treatment. Numerous biological and clinical investigations have demonstrated that HT in the 41-45°C range can significantly enhance clinical responses to radiation therapy, and has potential for enhancing other therapies such as chemotherapy, immunotherapy, and gene therapy. Furthermore, high temperature hyperthermia (greater than 50°C) alone is being used for selective tissue destruction as an alternative to conventional invasive surgery. Thermal techniques are being utilized to complement existing courses of treatment or provide minimally invasive alternative to surgery with less complications, and morbidity for each of these diseases. This article reviews a selection of heating technology and strategies specific to prostate thermal therapy, which are either in clinical use or currently under development. Transurethral, transrectal, and interstitial systems are discussed for RF current, laser, microwave, ultrasound, and thermal conduction heating technology.