Scanning laser ophthalmoscope Health Dictionary

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 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

An instrument for examining the interior of the EYE. There are di?erent types of ophthalmoscope; all have a light source to illuminate the inside of the eye and a magnifying lens to make examination easier.... ophthalmoscope

Positron-emission tomography is a NUCLEAR MEDICINE diagnostic technique that works by identifying positrons – positively charged electrons – given o? by substances labelled with radioactive varieties of elements. The result is three-dimensional images that identify metabolic and chemical activities of tissues, especially brain tissues. The images provide information about tissue and organ functions, and can be collated with structural images using COMPUTED TOMOGRAPHY or magnetic resonance imaging (MRI). The equipment is very expensive and available only in selected hospitals in the United Kingdom. The technique is especially valuable in the assessment of neurological disorders.... pet scanning

A speech disorder in which articulated syllables are wrongly spaced and each is given the same vocal emphasis. The condition occurs as a result of disease in the cerebellum (see BRAIN) or its connecting nerves. (See also VOICE AND SPEECH.)... scanning speech

Ways of producing images of body organs that record, process and analyse sound waves, radio waves or X-RAYS passing through or generated by the body’s tissues. ULTRASOUND scanning using high-frequency, inaudible sound waves directed at the area of the body being studied is the most generally used scanning procedure. Sound waves are re?ected more powerfully by some structures than others, and a pattern of those re?ections is detected and shown on a screen. Other screening methods include COMPUTED TOMOGRAPHY, magnetic resonance imaging (MRI), positron emission tomography (PET SCANNING) and RADIONUCLIDE scanning, which measures the di?erential uptake of radioactive materials in the body’s tissues.... scanning techniques

An abbreviation for computerized axial tomographic scanning, commonly known as CT scanning.... cat scanning

See radionuclide scanning.... isotope scanning

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

See radionuclide scanning.... radioisotope scanning

Techniques, such as radionuclide scanning and ultrasound scanning, that are used to provide information about the location, anatomy, and function of the thyroid gland.... thyroid scanning

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

A diagnostic technique in which the combined use of a computer and X-rays passed through the body at different angles produces cross-sectional images of tissues. (computed tomography) scanning has revolutionized the diagnosis and treatment of tumours, abscesses, and haemorrhages in the brain, as well as head injuries and strokes. scanning is also used to locate and image tumours, investigate diseases, and aid needle biopsy in organs of the trunk.

Newer types of scanners use a spiral technique: the scanner rotates around the body as the patient is moved slowly forwards on a bed, causing the X-ray beams to follow a spiral course. The computer produces 3-D images. Injected or swallowed contrast media (chemicals opaque to X-rays) may be used to make certain tissues more visible.... ct scanning

A diagnostic technique based on detection of radiation emitted by radioactive substances introduced into the body. Substances are taken up to different degrees by different tissues, allowing specific organs to be studied. For example, iodine is taken up mainly by the thyroid gland, so by “tagging” a sample of iodine with a radioactive marker (radionuclide), the uptake of iodine can be monitored to investigate the functioning of the gland. A radionuclide is swallowed or injected into the blood and accumulates in the target organ. It emits radiation in the form of gamma radiation, which is detected by a gamma camera to produce an image. Cross-sectional images (“slices”) can be obtained using a computer-controlled gamma camera that rotates around the patient. This specialized form of radionuclide scanning is known as (single photon emission computed tomography). Moving mation on blood flow, the movement of the heart walls, the flow of urine through the kidneys, and bile flow through the liver.

Radionuclide scanning is a safe procedure, requiring only minute doses of radiation that are excreted within hours. The radionuclides carry virtually no risk of toxicity or hypersensitivity.... radionuclide scanning

A diagnostic technique in which very high frequency sound waves are passed into the body and the reflected echoes analysed to build a picture of the internal organs or of a fetus in the uterus. The procedure is painless and considered safe.Ultrasonic waves are emitted by a transducer, which is placed on the skin over the part of the body to be viewed. The transducer contains a crystal that converts an electric current into sound waves. These pass readily through soft tissues and fluids, making this procedure useful for examining fluid-filled or soft organs.

One of the most common uses of ultrasound is to view the uterus and fetus, at any time during pregnancy, but often at 18–20 weeks. The age, size, and growth rate of the fetus can be determined; multiple pregnancies detected; and certain problems, such as neural tube defects, diagnosed. Scans may be taken early in pregnancy if problems, such as an ectopic pregnancy, are suspected.

Ultrasound scanning can also be used in newborn babies to examine the brain through a gap in the skull (for example, to investigate hydrocephalus). Ultrasound can help to diagnose disorders such as cirrhosis, gallstones, hydronephrosis, and pancreatitis, as well as problems in the thyroid gland, breasts, bladder, testes, ovaries, spleen, and eyes. The technique is also used during needle biopsy to help guide the needle.Doppler ultrasound is a modified form of ultrasound that uses the Doppler effect to investigate moving objects.

This can be used to examine the fetal heartbeat and to obtain information about the rate of blood flow in vessels.... ultrasound scanning

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

(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

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

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

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

a non-invasive instrument for measuring blood flow through tissue (e.g. skin) utilizing a laser beam.... laser doppler flowmeter

(NT scanning) an ultrasound screening test performed during pregnancy at 11 weeks of gestation that measures the maximum thickness of the translucency between the skin and the soft tissue overlying the cervical (neck) region of the spine of the fetus. Increased NT is associated with an increased risk of chromosomal abnormalities and of a wide variety of structural abnormalities (e.g. heart defects). See also ultrasound marker.... nuchal translucency scanning

an imaging system that allows a PET scan (see positron emission tomography) and a CT scan (see computerized tomography) to be performed very close together, with minimal movement of the patient between scans. This means that the images produced can be co-registered (see co-registration), giving very accurate anatomical localization (from the CT scan) of areas of increased activity (identified on the PET scan). This is very important for determining the site of disease in order to plan treatment.... pet/ct scanning

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

(single photon emission computing tomography) (in nuclear medicine) a *cross-sectional imaging technique for observing an organ or part of the body using a *gamma camera; images are produced after injecting a radioactive *tracer. The camera is rotated around the patient being scanned. Using a computer reconstruction *algorithm similar to that of a *computerized tomography scanner, multiple ‘slices’ are made through the area of interest. SPECT scanning is used particularly in cardiac nuclear medicine imaging (see MUGA scan). It differs from PET scanning in that radioactive decay gives off only a single gamma ray.... spect scanning

(helical CT scanning) a development of conventional *computerized tomography (CT) scanning in which the X-ray tube rotates continuously around the patient as he or she passes through the scanner. This allows the acquisition of images throughout a specified volume of tissue much more quickly. Since these images are digitally acquired (see digitization), *post-processing can produce images in numerous planes, without further exposure of the patient to ionizing radiation. See also multidetector computerized tomography.... spiral ct scanning

(V/Q scanning) a nuclear medicine technique in which two different isotopes are used, one inhaled (usually *xenon-133 or *krypton-81m), to examine lung ventilation, and the other injected into a vein, to examine lung perfusion. In *pulmonary embolism, the area of lung supplied by the blocked artery is not being perfused with blood – which gives a perfusion defect on the film – but has normal ventilation. This technique is highly sensitive for pulmonary embolism.... ventilation-perfusion scanning

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