Laser has become an unavoidable tool in modern medicine and provides healthcare professionals with exceptional levels of precision and control. The medical sector harnesses the unique properties of focused light beams at specific wavelengths and opens up a diverse range of medical applications that enhance diagnostic accuracy, enable minimally invasive procedures, and contribute to improved patient outcomes. Lasers play an important role in various medical disciplines, showcasing their impact on surgeries, diagnostics, dermatology, ophthalmology, and beyond. The integration of lasers into medical practices not only illustrates technological advancement but also represents significant progress towards more effective and patient-friendly healthcare solutions.

The major applications of laser in medicine include:

• Dentistry
• Surgery
• Cancer treatment (Therapy)
• Ophthalmology
• Dermatology
• Cardiology
• Diagnostic Imaging
• Pain Management

The use of light in treating illness has been known for thousands of years. The ancient Greeks and Egyptians used sunlight for therapy, and they even linked it to their god Apollo, who was designated responsible for both light and healing. However, the potential of light in medicine was revealed only after the invention of lasers 50 years ago.

History

The invention of the laser in 1960 by Theodore Maiman opened the path for exploration into its potential applications in medicine. The unique characteristics of lasers, including directivity, impulse capability for short pulses, and monochromaticity made it more significant. 

Early medical uses of lasers emerged in 1961 when Dr. Charles J. Campbell successfully employed a ruby laser to eliminate an angiomatous retinal tumor with a single pulse. Dr. Leon Goldman, in 1963, utilized the ruby laser for treating pigmented skin cells. The argon-ionized laser, with a preferred wavelength of 488 nm - 514 nm, became the choice for retinal detachment treatment. Kumar Patel and colleagues developed the carbon dioxide laser in the early 1960s for not only medical purposes but also found applications in welding and drilling. The integration of optical fiber since 1970 broadened laser applications, particularly in endocavitary procedures through endoscopic channels.

In the 1970s, the argon laser found use in gastroenterology and pneumology. Dr. Peter Kiefhaber pioneered endoscopic argon laser photocoagulation for gastrointestinal bleeding. Additionally, he played an important role in introducing the Nd:YAG laser for controlling gastrointestinal bleeding. Urology saw the introduction of lasers by Dr. Hofstetter in 1976. The late 1970s witnessed the emergence of photodynamic therapy, facilitated by laser dye. 

From the early 1980s, lasers became indispensable tools in ophthalmology, gastroenterology, and facial and aesthetic surgery. In 1981, the American Society for Laser Medicine and Surgery was founded by Goldman, Dr. Ellet Drake, and others, marking the specialization of certain medical branches with lasers. The Francophone Society of Medical Lasers, founded in the same year, served a similar purpose under the leadership of Maurice Bruhat. The end of the 20th century witnessed the establishment of laser medicine centers, initially in the OECD and later more broadly in the 21st century. The historic Lindbergh Operation in 2001, involving surgeons in New York and doctors and a patient in Strasbourg, utilized lasers among other technologies.

Major lasers used in medicine include:

• CO₂ lasers
• Diode lasers
• Dye lasers
• Excimer lasers
• Fiber lasers
• Gas lasers
• Free electron lasers
• Semiconductor diode lasers

Outcome of Laser-Tissue Interactions

Laser radiation interacts with biological tissue, and the outcomes are dependent upon the laser beam's energy, exposure duration, and wavelength. The possible interaction outcomes are:

1. Photoablation: Utilizing high-energy laser wavelengths in the ultraviolet spectrum, photoablation breaks down long-chain tissue polymers into smaller, volatile fragments. This process, often employing Excimer lasers, occurs in nanoseconds.
2. Photocoagulation: Employing thermal energy, photocoagulation induces mass shrinkage in tissues, expelling water, altering color, and compromising mechanical integrity. Cells in the treated area perish, forming a region of dead tissue known as a photocoagulation burn. Photocoagulation finds applications in tumor destruction, treatment of eye conditions (e.g., diabetic retinal disorders), and hemostatic laser surgeries for bloodless incisions or vessel cessation.
3. Photomechanical (Photodisruptive) Mode: This mode necessitates nanosecond or shorter pulses with an extremely high spatial density of photons. Nd:YAG lasers operate based on this principle.
4. Photochemical Reactions (Photodynamic Therapy): Relying on laser beam's wavelength, photochemical reactions are prevalent in photodynamic therapy. Exogenous chromospheres, or photosensitizers, absorb laser energy at low intensities. Activated by the laser's specific wavelength, these molecules can induce chemical reactions in the surrounding tissue. Photodynamic therapy is primarily applied in tumor treatment.
5. Photovaporization: Absorption of higher energy laser light leads to vaporization of intracellular and extracellular water in the target tissue. This method, utilized by the carbon dioxide laser, also treats adjacent blood vessels and results in a nearly bloodless surgical field.

When a human body interacts with laser, the light transfer photon energy through absorption. These body tissues heated by lasers between 50°C and 100°C, undergoes disordering of protein and bio-molecule through photocoagulation. During surgery, laser-induced photocoagulation causes tissues to shrink as water is expelled at these temperatures. The heated region undergoes color changes and loses mechanical integrity. Cells in the photocoagulated area die and render the tissue non-functional and easily removable. This laser-induced photocoagulation process finds application in tumor destruction, treating eye conditions like diabetes-induced retinal disorders, and achieving bloodless incisions or excisions in laser surgery.

When intense laser power densities are applied, tissues heat beyond 100°C that leads to water boiling and evaporation. As 70% of body tissue comprises water, this phenomenon, known as photo-vaporization, transforms the tissue into a gas. Photo-vaporization allows for complete tissue removal and make it suitable for skin rejuvenation, resurfacing, and bloodless incisions or excisions in laser surgery. The rapid elevation of tissue temperature to over 100°C for photo-vaporization necessitates the application of high power density in a pulsed mode. In general, power density up to 10W/cm² results in tissue heating, while 10 - 100W/cm² induces photocoagulation. Power density exceeding 100W/cm² is necessary for photo-vaporization.

Notably, a laser can be utilized for photo-vaporization in focused mode and photocoagulation in defocused mode. Excimer lasers, especially in the ultraviolet range, possess the ability to break chemical bonds without substantial tissue heating and result in photochemical ablation. This type of ablation yields clean-cut incisions with a limited thermal interaction zone.

Different lasers and processes cater to various applications. Pulsed infrared lasers, for instance, are ideal for skin rejuvenation, employing selective absorption for photo-vaporization. In hair removal, the melanin pigment in hair and follicles is best targeted using the ruby laser. Pulsed dye lasers, operating in the yellow region, are effective for removing port-wine stains by absorbing in the presence of hemoglobin in blood vessels. Lasers for ophthalmological purposes include argon and excimer lasers. Visible lasers, like the green argon laser, are popular for retina operations, taking advantage of transparency to the cornea and crystalline lens.

Effects of Laser-Tissue Interactions

The interaction of laser beams with biological tissues produces various effects, each with distinct applications and implications in medical treatments. From thermal and mechanical effects to tissue-welding and photochemical reactions, lasers have become integral in surgical and therapeutic interventions. The laser's interaction with various tissues gives rise to one or more of the following effects:

• Thermal Effect: The tissue's temperature elevation induces various biological effects. Beyond 40°C, the dominant process is protein denaturation which disrupts cell activity and potentially causes cell death. At temperatures exceeding 60°C, protein coagulation occurs and reaches vaporization of H₂O at 100°C, and carbonization at temperatures beyond 250°C, leading to tissue vaporization. The extent of the thermal effect depends on laser wavelengths, power density, and the optical and thermal properties of the tissue. For instance, the CO₂ laser at 10.6 microns is fully absorbed which results in heat generation with carbonization and vaporization, while the Nd:YAG laser (1.06 microns) induces tissue coagulation at considerable depth.
• Mechanical Effect: Pulse lasers are often used to treat kidney stones. This pulsed laser energy applied to a stone's surface causes fragmentation. High-power density laser pulses may release a column of electrons that forms a "plasma bubble" or cavitation bubble. The expansion of this bubble alters the stone's physical microstructure and leads to fragmentation. The holmium laser is commonly employed for heating and vaporizing water and organic matter in stones, making them brittle.
• Tissue-Welding Effect: Laser energy aids in collagen structure interdigitation and filling gaps with minimal peripheral tissue destruction. This process finds application in procedures like vasovasostomy, urethral reconstruction, pyeloplasty, and bladder augmentation. It promotes immediate sealing, improved healing with minimal scarring, and the maintenance of luminal continuity.
• Photochemical Effect: Based on the selective photoactivation of a specific drug, this effect transforms the drug into a toxic compound. The formation of toxic metabolites results in cellular death.

Advantages of Using Lasers in Medical Applications:

The application of lasers in medicine has ushered in a new era of advanced diagnostics, precision surgery, and therapeutic interventions. Here are some key advantages of using lasers in medical applications:

• Precision and Accuracy: Lasers can be precisely controlled, allowing surgeons to target specific tissues or cells with accuracy. This precision minimizes damage to surrounding healthy tissues, making laser procedures less invasive.
• Minimally Invasive Surgery: Laser technology enables minimally invasive surgeries that reduce the need for large incisions. This leads to faster recovery times, shorter hospital stays, and decreased post-operative pain.
• Bloodless Procedures: In many laser surgeries, the intense beam of light cauterizes blood vessels as it cuts and results in minimal bleeding. This bloodless quality is particularly advantageous in delicate surgeries.
• Reduced Scarring: Laser incisions are often smaller than those made with traditional surgical tools which leads to reduced scarring. This is especially important in cosmetic and reconstructive procedures.
• Sterilization and Disinfection: Laser beams can be used for sterilization and disinfection purposes. They can effectively kill bacteria, viruses, and other pathogens and reduce the risk of infections in surgical and medical settings.
• Pain Management: Low-level laser therapy (LLLT) is employed for pain management and tissue healing. It stimulates cellular activity that promotes tissue repair and reduces pain in conditions like arthritis and sports injuries.
• Less Anesthesia Required: In some laser procedures, the level of anesthesia needed is reduced compared to traditional surgeries contributing to faster recovery times and fewer side effects.
• Versatility Across Specialties: Lasers find applications across multiple medical specialties, including dermatology, urology, gastroenterology, and more. Their versatility makes them valuable tools in diverse healthcare settings.

Disadvantages of Using Lasers in Medical Applications:

While lasers bring many benefits to medical applications, there are also certain disadvantages and challenges associated with their use. Some of the disadvantages include:

• Cost: Laser equipment and maintenance can be expensive. The initial cost of acquiring laser technology and ongoing expenses for maintenance, training, and upgrades may pose financial challenges for healthcare facilities.
• Specialized Training: The operation of laser systems often requires specialized training. Medical professionals need to acquire the necessary skills and knowledge to handle laser equipment safely. This can lead to increased training costs and time.
• Eye Safety: Laser beams can be harmful to the eyes. Adequate precautions must be taken to protect both medical personnel and patients from accidental exposure. Laser safety measures, including protective eyewear, are crucial to prevent eye injuries.
• Limited Penetration Depth: The penetration depth of laser light in biological tissues is wavelength-dependent. Some lasers may have limited penetration, restricting their effectiveness in treating deeper tissues or larger areas.
• Tissue Absorption Variability: The absorption of laser energy by different tissues varies based on factors such as color, composition, and water content. This variability can impact the predictability and consistency of laser treatments.
• Risk of Burns: Despite precise targeting, high-powered lasers can still pose a risk of thermal injury to surrounding tissues. This risk increases with higher power levels and longer exposure times.
• Potential for Overheating: Continuous-wave lasers, if not controlled properly, can generate significant heat. This may lead to overheating of tissues and surrounding structures, potentially causing damage or complications.
• Limited Standardization: Standardization of laser procedures may be lacking across different medical institutions and specialties. This can result in variations in techniques and makes it challenging to establish universal protocols.
• Incompatibility with Certain Materials: Some materials used in medical implants or devices may not be compatible with laser procedures. This limitation can restrict the use of lasers in patients with specific medical devices.
• Risk of Infection: In certain laser procedures, especially those involving the opening of tissues, there is a risk of infection. Proper aseptic techniques are crucial to minimize this risk.
• Smoke and Plume Hazards: Laser surgeries can produce smoke or plumes, which may contain harmful substances. Inhalation of this smoke can pose health risks to both medical staff and patients who require proper ventilation systems.

Click here to know more about the Effects of Laser Radiation on Human Body.