Laser doppler flowmeter Health Dictionary

  1. Health Encyclopedia
  2. Laser Doppler Flowmeter

Laser Doppler Flowmeter: From 1 Different Sources

Excimer Laser

A type of laser that is used to remove thin sheets of tissue from the surface of the cornea (see EYE), thus changing the curvature of the eye’s corneal surface. The procedure is used to excise diseased tissue or to correct myopia (see REFRACTION), when it is known as photorefractive keratectomy or lasik.... excimer laser

Laser

Laser stands for Light Ampli?cation by Stimulated Emission of Radiation. The light produced by a laser is of a single wavelength and all the waves are in phase with each other, allowing a very high level of energy to be projected as a parallel beam or focused on to a small spot.

Various gases, liquids and solids will emit light when they are suitably stimulated. A gassed laser is pumped by the ionising e?ect of a high-voltage current. This is the same process as that used in a ?uorescent tube. Each type of laser has a di?erent e?ect on biological tissues and this is related to the wavelength of the light produced. The wavelength determines the degree of energy absorption by di?erent tissues, and because of this, di?erent lasers are needed for di?erent tasks. The argon laser produces light in the visible green wavelength which is selectively absorbed by HAEMOGLOBIN. It heats and coagulates (see COAGULATION) tissues so can be used to seal bleeding blood vessels and to selectively destroy pigmented lesions. The carbon-dioxide laser is the standard laser for cutting tissue: the infra-red beam it produces is strongly absorbed by water and so vaporises cells. Thus, by moving a ?nely focused beam across the tissue, it is possible to make an incision.

The two main uses of laser in surgery are the endoscopic (see ENDOSCOPE) photocoagulation of bleeding vessels, and the incision of tissue. Lasers have important applications in OPHTHALMOLOGY in the treatment of such disorders as detachment of the retina and the diabetic complications of proliferative retinopathy and of the cornea (see EYE, DISORDERS OF). The destruction of abnormal cells – a sign of pre-malignancy – in the CERVIX UTERI is done using lasers. The beams may also be used to remove scar tissue from the FALLOPIAN TUBES resulting from infection, thus unblocking the tubes and improving the chances of CONCEPTION. Lasers also have several important applications in DERMATOLOGY. They are used in the treatment of pigmented lesions such as LENTIGO, in the obliteration of port-wine stains, in the removal of small, benign tumours such as verrucas, and ?nally in the removal of tattoos.

Low-intensity laser beams promote tissue healing and reduce in?ammation, pain and swelling. Their e?ect is achieved by stimulating blood and lymph ?ow and by cutting the production of PROSTAGLANDINS, which provoke in?ammation and pain. The beams are used to treat ligament sprains, muscle tears and in?amed joints and tendons.

The three great advantages of lasers are their potency, their speed of action, and the ability to focus on an extremely small area. For these reasons they are widely used, and have allowed great advances to be made in microsurgery, and particularly in FIBREOPTIC ENDOSCOPY.... laser

Doppler Effect

A change in the frequency with which sound waves from a given source reach an observer when the source is in rapid motion with respect to the observer.

Approaching sounds appear higher in pitch (frequency) than sounds that are moving away.

This is because the wavelengths of the sound from an approaching source are progressively foreshortened, whereas the wavelengths from a receding source are stretched.

The Doppler effect is used in ultrasound scanning techniques.

An emitter sends out pulses of ultrasound (inaudible highfrequency sound) of a specific frequency.

When these pulses bounce off a moving object (blood flowing through a blood vessel, for example), the frequency of the echoes is changed from that of the emitted sound.

A sensor detects the frequency changes and converts the data into useful information (about how fast the blood flows, for example).

Doppler ultrasound techniques are also used to monitor fetal heartbeat, to detect air bubbles in dialysis and heart–lung machines, and to measure blood pressure.... doppler effect

Laser Treatment

Use of a laser beam in a variety of medical procedures. Highintensity laser beams cut through tissue and cause blood clotting. They can be used in surgery and to destroy abnormal blood vessels. Lasers are frequently used in ophthalmology to treat eye disorders, in gynaecology (for example, to unblock fallopian tubes), and to remove birthmarks and tattoos.... laser treatment

Argon Laser

a type of *laser that utilizes argon gas to produce a beam of intense light, used especially in eye surgery to treat disease of the retina (e.g. diabetic retinopathy) or glaucoma (as in argon laser *trabeculoplasty). See also photocoagulation.... argon laser

Diode Laser

a type of laser whose medical uses include treating diseases of the retina, by producing small burns in the retina (see photocoagulation), and selected cases of glaucoma (cyclophotocoagulation). It is also used for treating varicose veins (see endovenous laser treatment).... diode laser

Endovenous Laser Treatment

(EVLT) a minimally invasive procedure to treat *varicose veins. A laser fibre (usually an 810-nm *diode laser) contained within a sheath is fed into the vein by ultrasound guidance and slowly withdrawn as it is fired, thereby delivering laser energy that causes irreversible destruction and eventual ablation of the vein.... endovenous laser treatment

Femtosecond Laser

a laser that emits optical pulses with a duration of femtoseconds (fs; 1 fs = 10?15 s), allowing micrometer-level accuracy and needle– or blade-free surgery. It has the potential to carry out lens extraction or cataract surgery through a pin-prick incision.... femtosecond laser

Flowmeter

n. an instrument for measuring the flow of a liquid or gas. Anaesthetic equipment has to be fitted with flowmeters so that the administration of anaesthetic gases in different proportions can be controlled. Flowmeters are widely used by asthma sufferers to measure their ability to expire air.... flowmeter

Holmium:yag Laser

a type of *YAG laser that uses a short-pulsed high-energy beam with a wavelength of 2100 nm to cut, perforate, and fragment tissue. It has a penetration of 0.4 mm. This laser is used in the fragmentation of urinary tract calculi (stones) and in *enucleation of the prostate gland.... holmium:yag laser

Doppler Ultrasound

a diagnostic technique that utilizes the fact that the frequency of sound or light waves changes when they are reflected from a moving surface (the Doppler effect). It is used to study the flow in blood vessels and the movement of blood in the heart. The frequency detector may be part of an ultrasound imaging probe, which displays an image of the anatomy on a monitor. Simultaneously the Doppler signal from a particular point on the ultrasound image can be displayed superimposed on the anatomical position (duplex imaging). Using electronic techniques, direction and velocity of blood flow can each be allocated different colours and displayed on a colour monitor over the anatomical image (colour flow ultrasound imaging). Power Doppler, a modification of this technique, is more sensitive at detecting flow but does not give information on direction of flow. Doppler ultrasound is a valuable technique to detect vessel thrombosis, such as deep vein thrombosis, and can be safely used in pregnancy without the risk of ionizing radiation. It is extensively used in vascular surgery to assess the status of the blood vessels before surgery, especially in carotid surgery. Doppler measurement of the fetal middle cerebral vessels (MCA Doppler) can predict fetal anaemia as the resistance in these vessels is increased. This noninvasive technique has supplanted serial amniocentesis/fetal cord blood sampling in cases of *haemolytic disease of the newborn. Doppler of other fetal vessels (e.g. the ductus venosus) is used as a screening method for fetal chromosomal and cardiac defects and, later, fetal growth restriction. [C. J. Doppler (1803–53), Austrian physicist]... doppler ultrasound

Laser-assisted Uvulopalatoplasty

(LAUP) laser surgery to the palate, which is used in the treatment of *obstructive sleep apnoea.... laser-assisted uvulopalatoplasty

Scanning Laser Ophthalmoscope

see ophthalmoscope.... scanning laser ophthalmoscope

Selective Laser Trabeculoplasty

(SLT) see trabeculoplasty.... selective laser trabeculoplasty

 yag Laser

a type of *laser whose active medium is a crystal of yttrium, aluminium, and garnet. It is used for cutting tissue, for example in lens *capsulotomy or *iridotomy. Specialized types (e.g. the *holmium:YAG laser) are used for various specific purposes....  yag laser

Health encyclopedia icon Health Encyclopedia

Recent Searches