Nd:YAG surgical lasers are in general use, particularly in

gastroenterology, urology, gynecology, and general surgical applications, to

photocoagulate, cut, or vaporize tissue. Nd:YAG laser energy penetrates more

deeply into tissue than energy emitted by CO2, potassium titanyl phosphate

(KTP/532, also called frequency-doubled Nd:YAG), or argon lasers and affects a

larger volume of tissue. With their wide ranges of both power and spot size,

Nd:YAG lasers can photocoagulate blood vessels at low power densities (e.g., for

treatment of vascular tumors and anomalies) and vaporize tumors at high power

densities (e.g., for treatment of solid tumors such as esophageal squamous

carcinoma).

In addition, Nd:YAG surgical laser energy (1,064 nm wavelength) can be

delivered through flexible silica fibers and can pass through clear fluids,

unpigmented tissue, and the top layer of the skin, making Nd:YAG lasers more

effective than other types of lasers in treating certain medical conditions. For

example, Nd:YAG surgical lasers are used to control excessive uterine bleeding

and bleeding gastrointestinal ulcers; to relieve the intensity of painful symptoms

caused by otherwise inoperable highly vascular tumors of the respiratory tract,

stomach, and brain; and to destroy prostate, rectal, and bladder tumors.

There are two types of Nd:YAG lasers—general surgical and ophthalmic—and

each has a specific application. The Nd:YAG ophthalmic laser produces a very

short-pulsed, low-energy photodisruptive effect (measured innanoseconds and

millijoules), while the Nd:YAG surgical laser usually uses a continuous wave or

pulsed continuous wave and delivers greater amounts of energy (measured in

seconds and joules), producing a photoablative effect. The Product Comparison

chart also includes a non-ablative Nd:YAG laser designed for laser skin

rejuventation, wrinkle reduction, acne, and acne scar treatments. The laser

energy penetrates the upper to deep tissue layers to stimulate collagen

production or to shrink sebaceous glands.

Frequency-doubled Nd:YAG lasers pass Nd:YAG laser energy through a KTP or

other special crystal, doubling the frequency and halving the wavelength to 532

nm. This wavelength is visible (green) and is absorbed primarily by pigmented

tissue to a depth of 1 to 2 mm. It is used largely in otolaryngology, gynecology,

and dermatology and in general surgical procedures such as laparoscopic

cholecystectomy. Physicians have also begun using high-powered (e.g. 80 W)

KTP lasers to treat benign prostate hyperplasia (BPH) because the wavelength is

excellent for hemostatis and transmits through water. One manufacturer now

offers a frequency doubled double-pulse Nd:YAG (FREDDY) laser for lithotripsy

treatments which simultaneously emits two pulses with 532 nm and 1032 nm and

wavelengths.

Combining an Nd:YAG laser with a CO2 laser adds a beam that can vaporize

surface tissue with little thermal effect on nearby healthy tissue structures. CO2

lasers emit invisible infrared beams of 10,600 nm wavelength that effectively

vaporize water and are efficient cutting tools. Low-powered Nd:YAG lasers are

also available for dental procedures.

Principles of operation

Lasers are designated by their active medium, which emits light of a single

predominant wavelength. Input energy from a light (or other energy) source

interacts with the medium within the laser tube to cause the emission of a

narrow beam, or pencil, of high-energy light. In Nd:YAG lasers, the medium

consists of neodymium (Nd), a rare-earth element, dispersed or doped in a solid

crystal of yttrium-aluminum-garnet (YAG). This laser emits a single wavelength

(1,064 nm) of near-infrared light, which is in the invisible portion of the

electromagnetic spectrum. This wavelength is minimally absorbed in tissue, with

maximal penetration. It is absorbed primarily by tissue chromophores, is less

well absorbed by blood, and is minimally absorbed by water. The Nd:YAG laser

penetrates tissue up to 10 mm and is highly scattered so that it is converted into

heat, producing a photothermal destructive effect.

Like most laser systems, Nd:YAG systems consist of a lasing medium (i.e., an

Nd:YAG doped crystal rod), a laser pump or energy source, and an optical

resonating cavity containing mirrors. Other components may include cooling

systems and aiming beams. The reflective ellipsoidal laser cavity contains the

solid Nd:YAG rod and flash lamp (pump) at the ellipse’s foci. The laser pump,

which is typically an incoherent visible optical light source, supplies energy to

the rod in the form of photons. When electrons in the medium (Nd:YAG) absorb

these photons, they become excited and move to a higher, less stable energy

level. This creates a state called a population inversion, in which more of the

atoms in the medium are in the excited state than in the ground state. The

instability of this state culminates in a certain moment when some atoms release

their photons. These newly released photons stimulate the excited electrons to

decay back to their original energy levels with the emission of identical photons.

Because the original photons and the emitted photons have identical

wavelengths, they leave the atoms in phase. This process initiates a reaction

called stimulated emission, in which a cascading wave of reactions causes a

great number of identical photons to be released at the same moment. The light

produced by stimulated emission is coherent and monochromatic. A collimated

beam is created when this light is reflected in a resonator chamber between two

mirrors, one of which is partially reflective and allows the parallel waves to exit

the optical cavity. Directing the invisible beam of the Nd:YAG or CO2 laser to the

target tissue requires an aiming beam—a second, low-power laser that produces

a visible beam of light, allowing the surgeon to verify the area to be treated

before activating the laser. This can be either a helium-neon (He-Ne) laser,

producing a red, orange, or yellow guiding light, or a filtered xenon lamp,

producing a red, blue, or white light. Integrated optics align the aiming beam

with the invisible therapeutic beam to ensure that both travel the same path. In

some laser systems, the aiming beam’s brightness and/or color can be adjusted.

A separate aiming beam is not needed for the KTP laser; however, a

nontherapeutic low-power KTP beam is used to highlight the area to be treated.

Because Nd:YAG surgical lasers convert electrical energy to light energy

inefficiently, a cooling system is needed to prevent heat damage to the laser.

Most laser cooling systems use a self-contained internal radiator and fan

assembly to circulate cooling water through the laser head; earlier cooling

systems required external plumbing. Nd:YAG surgical laser energy is focused

into small, flexible, silica fibers that connect to the laser aperture, usually found

on the side of the laser unit. These fibers can be passed through flexible or rigid

endoscopes to apply laser energy within body cavities or closed anatomic spaces,

such as the stomach, uterus, bladder, and respiratory passages. Some fibers

have specially shaped crystal contact tips and require cooling by the passage of a

nonflammable gas or liquid through the fiber to prevent overheating of the tip.

Laser energy heats the contact tip, and the heat is used to treat the tissue.

Delivery of the Nd:YAG laser energy to tissue can be achieved in one of several

ways. Catheters can be used to deliver the optical fibers through blood vessels.

Bare fibers are suitable for introduction into confined cavities through

endoscopes because of their narrow diameter. Since the laser light leaves the

fiber typically with a divergence of 20 to 30 degrees, the diverging beam may be

used for superficial treatment of large areas. If a small spot is required for a

high-precision application, a focusing lens can be placed in front of the fiber tip.

For contact cutting or vascular recanalization, a fiber tip allows contact-mode

operation so that the tip is in physical contact with the tissue. Contact-mode

lasing may be used to apply energy locally for precise tissue destruction with

minimal lateral damage. Endoscopes with multiple channels allow the surgeon to

perform other procedures (e.g., suctioning). In addition, micromanipulators and

handpieces can be used for applications in which the laser beam energy must be

focused on a specific area or when fine control of beam movement is necessary.

The KTP/532 laser can be used with handpieces, micromanipulators, and

endoscopes.

CO2 delivery systems consist of a hollow articulated arm with mirrors set in

articulating joints so that the beam can be aimed in any direction. The end of the

arm has an accessory attachment (e.g., handpiece, laparoscope) with a focusing

lens to control the spot size and focal length of the beam, enabling the surgeon

to vary the power density and the effect of the laser energy on the tissue. (For a

more detailed description of CO2 laser delivery systems, see the Product

Comparison titled Lasers, Carbon Dioxide, Surgical/Dermatologic.)

Early Nd:YAG laser surgeries were performed with a free-beam technique; that is, the laser fiber

remained several millimeters away from the tissue during lasing. Limitations of the free-beam method

included deep tissue penetration, lack of tactile sensation for the surgeon, and an inability to focus the

laser beam. Some manufacturers provide wavelength conversion contact tips for Nd:YAG lasers, which

attach to the end of the laser fiber. This allows surgeons to cut and coagulate tissue by direct contact,

with minimal effect on nearby tissue. The contact tips are shaped crystals of synthetic sapphire or

ceramic that are screwed into a metal ferrule on the end of the laser fiber. Laser energy is concentrated

at the end of the contact tip, where it is converted mostly to heat energy so that the laser works like a

hot knife and enables precise tissue destruction. Other manufacturers provide silica tips of various

shapes to deliver laser energy by direct contact with tissue. Contact tips provide the surgeon with tactile

feedback; the tissue effect depends on the tip’s shape and coating (e.g., frosted tips emit a small amount

of laser energy and provide greater hemostasis) and the energy output. Contact tips can be used for 8 to

10procedures, depending on the surgeon’s skill. Some manufacturers provide disposable contact fibers

with integral shaped tips. Adhering tissue can cause silica fibers to absorb laser energy, raising them to

very high temperatures. As a result, the fibers can burn, melt, or chip and become unable to deliver

laser energy uniformly. To prevent this from occurring, some silica fiber systems need a supply of

cooling gas (e.g., air, CO2, nitrogen) or cooling liquid flowing around the fiber to protect the tip.

Pressurized gas can be supplied from the hospital’s piped medical gas system, an external tank, or an

integral system, and gravity or a pump can provide liquid flow; either can be increased during laser

operation and decreased when not needed. It should be noted that gas cooling of Nd:YAG fiber tips has

been associated with a risk of fatal gas embolism. This issue is described in detail in the Reported

Problems section below. KTP and Nd:YAG surgical lasers can be used in a continuous-wave mode or a

pulsed mode. In the continuous-wave mode, the laser delivers energy continuously as long as the

footswitch is depressed. In the pulsed mode, the laser fires repetitive short pulses at a selected exposure

duration. This mode allows the tissue to cool down during the interval between pulses so that the

energy can be delivered with more precise thermal effects and less chance of thermal spread to adjacent

tissue. In both the continuous-wave mode and the pulsed mode, the user adjusts the power output and

the exposure time; in the pulsed mode, the rate of repetition can also be adjusted. As a safety feature,

most laser units have power meters that can be used to compare the power output at the tip of the fiber

and at the laser head and automatically adjust the laser’s output power so that the power delivered from

the fiber’s tip matches the desired power. Because laser fibers are very small (typical diameters are 0.4

to 1 mm) and delicate, they are easily broken or damaged by overheating. Damaged fibers can sustain

substantial energy transmission loss at their tips; fibers with excessive transmission loss (e.g., >30%)

can melt and ignite from the energy absorbed by the fiber. A calibration mode can be used to assess the

transmission loss of the fiber. Other safety features include interlocks that turn off the laser or block the

beam with a shutter when a laser fiber is not connected, a removable key to prevent unauthorized

operation of the laser, and a visual and/or audible alarm signal of laser beam emission. Other safety and

alarm features alert users to gas- and water-cooling-system malfunctions (e.g., low water pressure, high

temperature, blocked gas line). Nd:YAG lasers operate from either a 120 or 240 VAC single- or three-

phase electrical system; many require substantial power. The CO2 laser, in a combination unit, requires

240 VAC, and the KTP/Nd:YAG laser may require up to 240 VAC. Hospitals must provide appropriate

electrical services and sometimes special high amperage outlets in the expected areas of use (e.g.,

operating room [OR], cystoscopy or endoscopy rooms).