D
D log E curve applies to a particular film or film/screen combination and is the curve which results when the density is plotted against the log of relative exposure. See also characteristic curve.
dacryocystography rarely used radiographic examination of the tear drainage apparatus following the introduction of a positive contrast agent. Superseded by CT and MRI.
dactylitis inflammation of finger or toe. The digit becomes swollen due to periostitis. Associated with congenital syphilis, tuberculosis, sarcoid.
dark adaptation adjustments made by the eye in reduced light or darkness. The pupils dilate, cones function ceases, rhodopsin is formed and the rod activity increases. See also light adaptation.
data items of information, usually collected for a specific purpose, for example to be used in the analysis of a problem.
data analysis describes statistical analyses of data.
database software designed to store information in a systematic way, and at the same time to allow easy retrieval and manipulation of all data.
data compression in computing, the reduction in size of information to decrease transferred film size.
data processing the storage, sorting and analysis of data, usually electron-ically with computers.
data protection rules relating to information held about individuals, such as in Data Protection Act 1998. In computing only registered users can hold information about individuals on computer and all patients have a right under this act to see any records concerning themselves or their treatment.
data set the data relating to a specific group such as a particular age group.
dating scan an ultrasound scan taken between 11 and 14 weeks, using the crown–rump length to accurately age the fetus.
daughter radionuclide a nucleus after it has decayed. See also radioactive decay.
day care centre outpatient centres that provide company, psychological and nursing support.
day case surgery the provision of surgery for out-patients who will return home the same day.
day hospital a centre which patients attend daily. Recreational and occupational therapy and physiotherapy often provided. Greatest use is in the services for older people and those with mental health problems.
daylight systems a system which enables the loading and unloading of radiographic film without the use of a darkroom. See also dispersed daylight system, centralized daylight system.
deafness a partial or complete loss of hearing. See also conductive deafness, congenital deafness.
deamination removal of an amino group (NH2) from organic compounds such as excess amino acids.
debility a condition of weakness with lack of muscle tone.
döbridement the removal of foreign matter and contaminated or devitalized tissue from or adjacent to a wound. chemical/medical döbridement is accomplished by the external application of a substance to the wound, such as a specific wound dressing. surgical döbridement is accomplished by using surgical instruments and aseptic technique.
debugging the correction and, much more importantly, the finding of errors or bugs in a computer program.
decalcification the removal of mineral salts, as from teeth in dental caries, bone in disorders of calcium metabolism.
deceleration time used in cardiac ultrasound work to measure the function of a mitral valve, for example, a long mitral E wave deceleration time indicates diastolic dysfunction.
decibel (dB) a unit of sound intensity (loudness).
decidua the endometrial lining of the uterus thickened and altered for the reception of the fertilized ovum. It is shed at the end of pregnancy.
decidua basalis that part which lies under the embedded ovum and forms the maternal part of the placenta.
decidua capsularis that part which lies over the developing ovum.
decidua vera the decidua lining the rest of the uterus.
deciduous by convention refers to the teeth of the primary dentition.
deciduous teeth temporary teeth in children, 20 in number and lettered abcde in each quadrant of the mouth.
decompression removal of pressure or a compressing force.
decompression (of bladder) in cases of chronic urinary retention, by continu-ous or intermittent drainage via catheter inserted per urethra.
decompression (of brain) achieved by removing a circular area of the skull (trephining) in order to evacuate clot.
decompression illness results from sudden reduction in atmospheric pressure, as experienced by divers on return to surface, aircrew ascending to great heights. Caused by bubbles of nitrogen which are released from solution in the blood; symptoms vary according to the site of these. The condition is largely preventable by proper and gradual decompression technique. Variously described as ‘bends, chokes and creeps’ depending on the symptomatology. Originally called caisson disease when identified as a hazard for divers. Later recognized as a complication of high altitude.
decontamination the method of removing foreign material such as radioactive substances for the safety of the individual.
decubitus the position of the person when lying down.
decubitus ulcer (pressure sore, bedsore) a breakdown of the skin due to pressure or immobility, usual sites are buttocks, heels, elbows, shoulders.
decussation intersection; crossing of nerve fibres at a point beyond their origin, as in the optic and pyramidal tracts.
deep vein thrombosis (DVT) thrombus forming in a deep vein such as those in the legs or pelvis. It is associated with slowing of blood flow, abnormal or inappropriate clotting processes, or damage to veins. A thrombus may break off to form an embolus that travels in the venous circulation, through the heart to the lungs. See also pulmonary embolus.
defecation voiding of faeces per anus.
defibrillation the application of a direct current (DC) electric shock to arrest ventricular fibrillation of the heart and restore normal cardiac rhythm.
defibrillator equipment for the application of a direct electric current to the heart to arrest ventricular fibrillation and restore normal cardiac rhythm.
deflection when an ultrasound beam is refracted and therefore causes objects to appear to be in a different location from where they actually occur.
degaussing a method of demagnetizing a cathode ray tube if the shadow mask becomes magnetized.
degeneration deterioration in quality or function. Regression from more specialized to less specialized type of tissue.
deglutition swallowing, a complex process that is partly voluntary, partly involuntary.
dehydration loss or removal of fluid. In the body this condition arises when the fluid intake fails to replace fluid loss. This is liable to occur when there is bleeding, diarrhoea, excessive exudation from a raw area as in burns, excessive sweating, polyuria or vomiting, and usually upsets the body’s electrolyte balance. If suitable fluid replacement cannot be achieved orally, then parenteral administration must be instituted.
delayed union longer than expected healing of a fracture.
deliberate self-harm (DSH) wilful non-fatal act(s) carried out in the knowledge that it was potentially harmful. Examples include self-poisoning (overdose), self-cutting and self-mutilation.
delirium abnormal mental condition based on hallucinations or illusion. May occur in high fever, in mental health problems, or be toxic in origin.
delirium tremens results from alcoholic intoxication and is represented by a picture of confusion, terror, restlessness and hallucinations.
Delphi technique a research method where a consensus of expert opinion is obtained during a multiple-step process where the contributors are asked to rate a number of items, for example, research priorities, in order of importance.
deltoid muscle muscle acting at the shoulder.
dementia (organic brain syndrome – OBS) an irreversible organic brain disease causing disturbance of memory and personality, deterioration in personal care, impaired cognitive ability and disorientation. See also presenile dementia, Creutzfeldt–Jakob disease.
demographic indices such as age distribution, birth and mortality rates, occupation and geographical distribution. They are used to obtain a profile of a given population, compare different areas and plan services.
demography the study of population.
demyelination destruction of the myelin sheaths surrounding nerve fibres. Can occur in the peripheral nerves (for example, Guillain–Barrö syndrome), or in the central nervous system (for example, multiple sclerosis).
dendrite (dendron) one of the branched filaments which are given off from the body of a nerve cell. That part of a neuron which transmits an impulse to the nerve cell.
dendritic cell an antigen-presenting cell that presents a processed antigen to B and T lymphocytes bearing antigen-specific receptors. They are thought to be the cells important in determining the type of immune response generated against an antigen.
Dennis Browne splints splints used to correct congenital talipes equinovarus (club foot).
densitometer an instrument for measuring the relative density of different steps on a film. See also sensitometry.
density the amount of blackening on a radiographic or photographic film and is the log of the opacity.
dental amalgam a compound of a basal alloy of silver and tin with mercury, used for restoring teeth. See also amalgam.
dental attrition non-carious, mechanical wearing of teeth, either through normal mastication or as a result of parafunctional habits, for example, bruxism.
dental caries a microbial disease of the calcified tissues of the teeth, characterized by demineralization of the inorganic portion and destruction of their organic substance.
dental enamel hard, acellular calcified tissue covering the crown of a tooth.
dental erosion non-carious wearing away of the surfaces of the teeth due to chemical causes.
dental formulae a method of identifying individual teeth: adult teeth are numbered and children’s teeth have letters.
dental hygienist dental auxiliary trained to scale and clean teeth, carry out certain preventive procedures and give oral hygiene instruction to the prescription of a dentist.
dental implant artificial structure implanted surgically into the alveolar bone, usually made from titanium.
dental plaque soft deposit of bacteria and cellular debris that rapidly forms on the surface of a tooth in the absence of oral hygiene.
dental pulp tissue consisting of blood vessels, nerves and connective tissue that occupies the core of the crown and the root canal(s) of a tooth.
dental restoration the process of replacing part or all of a tooth by artificial means; also the term given to the type of replacement used, for example, filling, crown, bridge.
dental scaling the removal of calculus, using special instruments, from the surfaces of the teeth.
dental therapist dental auxiliary who is trained to carry out certain dental operative procedures to the prescription of a dentist.
dentate having natural teeth present.
dentine calcified organic hard tissue forming the bulk of the crown and roots of teeth and surrounds the pulp cavity. See also tooth.
dentist any person who practices dentistry, and is qualified and licensed to do so.
dentistry profession concerned with the diagnosis, prevention and treatment of diseases of the teeth and their supporting tissues, including their restoration and replacement. See also conservative dentistry, cosmetic dentistry, forensic dentistry, paediatric dentistry, preventative dentistry, prosthetic dentistry.
dentition the natural teeth collectively in an individual.
dento-alveolar abscess localized collection of pus within the alveolar bone, of dental origin.
denture a removable dental prosthesis. May be partial or full (replacing some, or all, of the teeth in either jaw respectively).
deoxygenation the removal of oxygen.
deoxyribonucleic acid (DNA) a double-strand nucleic acid molecule found in the chromosomes of all organisms (except some viruses). DNA (as genes) carries the coded instructions for passing on hereditary characteristics. DNA is a polymer formed from many nucleotides. These consist of the sugar deoxyribose, phosphate groups and four nitrogenous bases: adenine (A), guanine (G), thymine (T) and cytosine (C). Adenine and guanine are purine bases, and thymine and cytosine are pyrimidine bases. The nucleotide units are bound together to form a double helix with the adenine of one strand opposite the thymine of the other and the same for guanine and cytosine.
dependent variable one that depends on the experimental conditions.
depolarization in excitable cells the inside of the membrane becomes electrically positive with respect to the outside. Occurs during the transmission of a nerve impulse. See also polarized.
depressant a drug that reduces functional activity of an organ.
depressed fracture an indentation in the bone, usually occurs in the skull, when the bone is hit by a hard object or when a bone presses on an underlying organ such as the lungs.
depression a hollow place or indentation. A downward or inward movement or displacement. Diminution of power or activity. An emotional disorder characterized by feelings of profound sadness, may be classified by severity (mild/moderate/severe), by the presence of somatic symptoms (anorexia, weight loss, impaired libido, sleep disturbance, etc.) and by the presence or absence of psychotic symptoms. Recognized cognitive symptoms include hopelessness, helplessness, guilt, low self-esteem and suicidal thoughts. The previous description of reactive versus endogenous depression is outdated and not thought to be relevant to treatment or prognosis.
deprivation indices a set of census variables and weightings used to assess levels of deprivation within a specific community or population. They include: levels of unemployment, single-parent households, pensioners living alone and households without a car. See also Jarman index.
dermatitis inflammation of the skin (by custom limited to an eczematous reaction). See also eczema, atopic dermatitis, industrial dermatitis.
dermatitis herpetiformis (hydroa) an intensely itchy skin eruption of unknown cause, most commonly characterized by papules and vesicles, which remit and relapse. Associated with coeliac disease (gluten-induced enteropathy).
dermatofibroma a small round, painless lump usually found on the extremities.
dermatologist medically qualified individual who studies skin diseases and is skilled in their treatment. A skin specialist.
dermatology the science which deals with the skin, its structure, functions, diseases and their treatment.
dermatomyositis an autoimmune connective tissue disease mainly affecting the skin and muscles. Presents with a characteristic skin rash and muscle weakness. Can be associated with an underlying malignancy in more elderly people. See also collagen.
dermis the true skin; the cutis vera; the layer below the epidermis.
dermoid associated with or resembling skin.
dermoid cyst a cyst which is congenital in origin and usually occurs in the ovary. It contains elements of hair, nails, skin, teeth, etc.
descriptive epidemiology the retrospective analysis of the relationship between disease and suspected cause of the disease.
descriptive statistics that which describes or summarizes the observations of a sample. See also inferential statistics.
desensitization process of reducing subsequent immediate-type hypersensitivity reactions to venoms and other allergens by repeated injection of minute quantities of allergen in order to modulate the immune response away from the harmful allergic type reaction to a less pathological response. A behavioural therapy used for phobias where people are helped to overcome their irrational fear. There is a gradual introduction to the object or situation through imagining the object, looking at pictures or by eventually confronting the real thing.
desiccation drying out. There can be desiccation of the nucleus pulposus, thus diminishing the cushioning effect of a healthy intervertebral disc.
designated area an area where radiation is being used and therefore there are restrictions placed on who can be present in the area, areas are described as being controlled or supervised.
desloughing the process of removing slough from a wound.
desquamation shedding of the upper layers, usually of the skin either in flakes or powdery form.
detached retina separation of the neurosensory retina from the pigment epithelium. May be caused by retinal tears or holes, fibrous traction on the retina, or by exudation of fluid under the neurosensory retina.
detained patient a person with a mental disorder who has been detained under the relevant legislation such as the Mental Health Act.
detected quantum efficiency (DQE) is the relationship between the density of useful quanta of light and the density of radiation quanta falling on the detector. Ideally this should be as near to 100% as possible.
detection acuity the ability of an individual to see the presence of small objects.
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