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 Superseded by CT and MRI.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.
detector a device used to measure the amount of radiation transmitted through a patient. Modern CT units typically use solid state ceramic detectors. See also scintillation detector.
detergent a cleansing agent, for example, cetrimide.
deterioration progressive impairment of function: worsening of the patient’s condition.
determinants of health factors that may influence the health of an individual, or differences in health between individuals, apart from age, sex and constitution (physiological, genetic factors). These could be social and economic, environmental or psychological factors that increase the risk of ill health or disease (for example, heart disease, cancers, diabetes). These determinants, or indicators, are associated with better or worse health of populations as measured by mortality (standardized mortality ratios), valid measures of morbidity or self-reported health status (for example, health surveys, census, standardized illness ratios). For example, higher infant mortality may be associated with environmental factors, healthcare provision, social and community support, maternal deprivation and poverty. There may also be a cultural and behavioural perspective. See also morbidity, mortality.
deterministic effect an effect that always occurs, with radiation dose it is an effect which occurs above a specific dose, skin reddening, hair loss, temporary depression of blood count, death. See also stochastic effect.
detoxication the removal of the poisonous property of a substance.
detrusor an expelling muscle such as that of the urinary bladder. detrusor instability failure to inhibit reflex detrusor contraction. See also incontinence.
developer a chemical which reacts with exposed film and reduces exposed silver bromide crystals to black metallic silver by donating electrons to the crystals.
developing agent the chemical which reduces exposed silver bromide crystals to metallic silver for example, a combination of phenidone and hydroquinone.
developmental dysplasia of the hip (DDH) also known as congenital dislocation of the hip. The term DDH is useful in describing the varying causes and severity of the condition. There is poor development of the acetabulum which allows the head of the femur to dislocate.
dextrocardia transposition of the heart to the right side of the thorax.
diabetes a disease characterized by the excretion of large quantities of urine, and therefore excessive thirst.
diabetes insipidus a rare form of diabetes caused if the production of antidiuretic hormone decreases.
diabetes mellitus a condition resulting from a deficiency in the amount of insulin produced by the pancreas.
diabetic a person suffering from diabetes.
diabetic coma a loss of consciousness in a patient with diabetes mellitus if the disease is undiagnosed or if insulin has been omitted.
diagnosis the art or act of distinguishing one disease from another. differential diagnosis is the term used when making a correct decision between diseases presenting a similar clinical picture.
diagnostic associated with diagnosis, evidence in diagnosis.
diagnostic ultrasonography information is derived from echoes which occur when a controlled beam of sound energy crosses the boundary between adjacent tissues of differing physical properties.
dialyser (artificial kidney) the machine used to remove waste products from the blood in the case of renal failure, the membrane used for dialysis.
dialysis process by which solutes are removed from solution by diffusion across a porous membrane; requires the presence of a favourable solute gradient. See also haemodialysis, peritoneal dialysis.
diamagnetic a substance that will slightly reduce the strength of the magnetic field in which it is placed, the magnetic field induced is opposed to that of the surrounding magnetic field and has negative magnetic susceptibility. See also paramagnetic, superparamagnetic, ferromagnetic.
diamagnetism the influence of an applied magnetic field on the electrons orbiting the nuclei within the substance is rarely permanent. See also paramagnetism, ferromagnetism.
diapedesis the passage of cells from within blood vessels through the vessel walls into the tissues.
diaphragm the dome-shaped muscular partition between the thorax above and the abdomen below. Any partitioning membrane or septum. A cap which encircles the cervix to act as a barrier contraceptive, reliable when fitted correctly and used correctly with a spermicidal chemical.
diaphragmatic hernia see hiatus hernia.
diaphysis the shaft of a long bone.
diarrhoea a change from the established bowel rhythm characterized by an increase in frequency and fluidity of the stools, may cause dehydration, hypokalaemia (low potassium levels in the blood), malabsorption of nutrients and perianal soreness. Causes include infection, food sensitivity, laxative misuse, drugs such as antibiotics, dietary change, anxiety, colorectal cancer (alternating with constipation) and some systemic diseases.
diarthrosis a synovial, freely movable joint.
diastasis a separation of bones without fracture.
diastema a naturally occurring space between two teeth.
diastole the relaxation filling period of the cardiac cycle. See also systole.
diastolic dysfunction the inability of the left ventricle of the heart to spring back after it has opened.
diastolic notching during an ultrasound procedure, a sudden and temporary dip towards the base line of the image display during the relaxation period of the cardiac cycle.
diathermy the passage of a high-frequency electric current through the tissues causing heat to be produced. When both electrodes are large, the heat is diffused over a wide area according to the electrical resistance of the tissues. In this form it is widely used in the treatment of inflammation, especially when deeply seated (for example, sinusitis, pelvic cellulitis). When one electrode is very small the heat is concentrated in this area and becomes great enough to destroy tissue. In this form (surgical diathermy) it is used to stop bleeding at operation by coagulation of blood, or to cut through tissue.
dichroic fog used to be seen when a film was manually processed and was caused by development continuing in the fixer, it appears as a pink stain if viewed by transmitted light and greenish blue when viewed by reflected light.
DICOM (Digital Imaging and COmmunications in Medicine) a project to bring manufacturers together to agree standardization in computerized image transfer and communications so that clinical information can be communicated among all specialities.
dicrotic (associated with, or having) a double beat, as indicated by a second expansion of the artery during diastole.
dicrotic notch the second rise in the arterial tracing caused by the closure of the aortic valve (that between the left ventricle and the aorta). See also anacrotic.
dielectric a substance that acts as an electrical insulator and can contain an electric field.
dielectric constant (K) is the ratio of the capacitance of the capacitor with the dielectric to the capacitance with a vacuum between the plates of the capacitor.
dietetics the interpretation and application of the scientific principles of nutrition to feeding in health and disease.
dietitian one who applies the principles of nutrition to the feeding of an individual or a group of individuals. Dietitians are employed in a range of hospital and community settings, the food industry, by local authorities and by national and international agencies, for example, WHO.
differential blood count the estimation of the relative proportions of the different leucocyte cells in the blood. The normal differential count is: polymorphonuclear 65–70%, lymphocytes 20–25%, monocytes 5%, eosinophils 0–3%, basophils 0–0.5%. In childhood the proportion of lymphocytes is higher.
differential diagnosis making a correct decision between diseases presenting a similar clinical picture. See also diagnosis.
differentiation the process during which cells and tissues expand the ability to perform specialized functions that distinguish them from other cell types. Cancer cells are graded by their degree of differentiation.
diffuse periostitis inflammation of the periosteum of long bones.
diffusion when water and other small molecules in tissue undergo random microscopic, parallel movement which can be measured by magnetic resonance techniques, for example, distinguishing cysts from solid tumours, strokes, and cerebrospinal fluid dynamic studies.
digestion the process by which food is changed so that it can be absorbed by the body.
digital literally to do with numbers, now refers to the electronic production of films and computer images. In computing, represents a quantity changing in steps which are discrete. See also analogue.
digital compression pressure applied by the fingers, usually to an artery to stop bleeding.
digital imaging system the production of a digital radiographic image by reading an imaging plate and then displaying an image on a computer screen (digital radiography) or reading the signal from a television camera attached to an image intensifier (digital fluoroscopy) (see figure on p. 124).
digitalis leaf of the common foxglove containing glycosides, such as digoxin.
digital radiography the production of a digital radiographic image by reading an imaging plate and then displaying an image on a computer screen.
digital scanner equipment used to produce a digital image from a conventional radiographic film by passing light through the image and recording the intensity of the light.
digital signal the measurement of a signal in terms of numbers rather than a continuously varying value producing higher-quality image transfer to computers and television monitors.
digital subtraction angiography a method of increasing the contrast between vessels containing radiographic contrast agent and the background. A digital radiograph with contrast agent is superimposed on a reversed digital image without contrast agent thus removing most of the background information.
digitally reconstructed radiograph the electronic capture, manipulation and storage of X-rays to form a two- or three-dimensional radiographic image. In radiotherapy, computer reconstructions of radiographs from CT slices made to imitate the divergent X-ray beam.
Block diagram of the major components of a digital imaging system.
From Principles of radiological physics, 3rd edn, D T Graham, 1996, Churchill Livingstone, Edinburgh, with permission.
digital verification the use of either silicon diodes or ionization chambers placed in the exit beam during radiotherapy treatment to confirm the correct dose of radiation is being administered to the patient.
digital versatile disk (DVD) a 120-mm sheet of aluminium covered with layer of acetate and an outer layer of metal and with a polycarbonate backing. Used in computing to store data in digital form which can be read by a laser.
digiti minimi quinti varus (congenital overlapping fifth toe) the smallest toe lies on the dorsum of the base of the fourth toe in a medially deviated position. It may be bilateral or unilateral.
dilatation stretching or enlargement. May occur physiologically, pathologically or be induced artificially.
dilatation and curettage (D and C) by custom refers to dilating the uterine cervix to obtain an endometrial sample by curettage. See also hysteroscopy.
dilatation and evacuation (D and E) dilatation of the cervix and evacuation of a fetus under anaesthetic for therapeutic termination of pregnancy or for the removal of a dead fetus in the second trimester of pregnancy.
dilution analysis when a known quantity of radioactive material is introduced into a space or cavity in a patient to enable the volume of the space to be calculated in radionuclide imaging.
diode a device containing an anode and a cathode in a vacuum and allows electrons to flow in one direction only, from the cathode to the anode.
dioxide oxide containing two atoms of oxygen in each molecule, for example, CO2.
dipeptidases digestive enzymes that split dipeptides (paired amino acids) into individual amino acids.
2,3-diphosphoglycerate (2,3-DPG) substance present in red blood cells that decreases the affinity of haemoglobin for oxygen, thus allowing oxygen to be released to the tissues.
diplegia symmetrical paralysis of legs, usually associated with cerebral damage.
diploid (2n) describes a cell with a full set of paired chromosomes. In humans the diploid number is 46 chromosomes (44 autosomes and 2 sex chromosomes) arranged in 23 pairs in all cells except the gametes.
direct cost a cost that can be directly attributed to the budget of a specific department, for example pharmacy costs in a given department.
direct current electricity the flow of electrons in only one direction.
direct exposure films films used without intensifying screens, for example, for intra-oral dental films.
disarticulation amputation at a joint.
discectomy surgical removal of a disc, usually an intervertebral disc.
discogenic arising in or produced by a disc, usually an intervertebral disc.
discography the introduction of a radiographic contrast agent into the nucleus of a spinal disc.
discrete distinct, separate, not merging. For example, used to describe some types of skin lesion.
discrete wedges individual wedges produced with a limited range of angles, usually 15ö, 30ö, 45ö, and 60ö which are fitted to the light beam diaphragm during radiotherapy treatment.
disease any deviation from or interruption of the normal structure and function of any part of the body. It is manifested by a characteristic set of signs and symptoms and in most instances the aetiology, pathology and prognosis is known.
disimpaction separation of the broken ends of a bone that have been driven into each other during the impact which caused the fracture. Traction may then be applied to maintain the bone ends in good alignment and separate.
disinfectant an agent that destroys or inhibits the growth of microorganisms, but not necessarily spore. The term is usually reserved for chemical germicides that are too corrosive or toxic to be applied to tissues, but which are suitable for application to inanimate objects.
disinfection the removal or destruction of harmful microbes but not usually bacterial spores. It is commonly achieved by using heat or chemicals.
disinfestation eradication of an infestation, especially of lice (delousing).
disk a circular plastic disc coated with magnetic material used for storing computer data. Disks are usually high-speed devices.
dislocation displacement of organs, or the articular surfaces of joints. The disruption of the joint is such that the articular surfaces no longer form a working joint. It may be congenital, spontaneous, traumatic or recurrent. Treatment may include reduction under anaesthetic.
disobliteration (rebore) removal of that which blocks a vessel, most often intimal plaques in an artery, when it is called endarterectomy.
dispersed daylight system a number of units of different sizes that are used to load films into cassettes and a cassette unloader that is fixed to an automatic film processor.
disposable items articles that are used only once and then discarded thus reducing cross-infection.
dissecting aneurysm a localized dilation of an artery, usually the aorta, when the outer and middle layers of the vessel wall are separated longitudinally. Rupture of the aneurysm may be fatal in less than 1 hour.
dissection separation of tissues by cutting. When a group of lymph nodes are totally excised it is referred to as a block dissection of nodes: it is usually part of the treatment for cancer.
disseminated widely spread or scattered.
disseminated intravascular coagulation (DIC) an abnormal overstimulation of coagulation processes characterized by a rapid consumption of clotting factors which leads to microvascular thrombi and bleeding. It is associated with conditions leading to inadequate organ perfusion, such as hypovolaemia and/or sepsis.
dissociation separation of complex substances into their components. Ionization; when ionic compounds dissolve in water they dissociate or ionize into their ions.
distal farthest from the head or source. See also proximal.
distribution server in a PACS system a method of storing and sending images to an external user, the images can be encrypted to prevent unauthorized viewing.
diuresis increased production/secretion of urine.
diuretics substances that increase the secretion of urine by the kidney.
divers’ paralysis see decompression illness.
diverticulitis inflammation of a diverticulum (a pouch or sac protruding from the wall of a tube or hollow organ).
diverticulosis a condition in which there are many pouch-like hernias (diverticula) in the intestines. Colonic diverticula increase in frequency with age. May be asymptomatic, bleed, become infected or perforate.
diverticulum (diverticula) a pouch or sac protruding from the wall of a tube or hollow organ. May be congenital or acquired.
dizygotic relating to two zygotes. Describes non-identical twins that develop from two separate zygotes.
dolor pain; usually used in the context of being one of the five classical signs and symptoms of inflammation – the others being calor, loss of function, rubor and tumor.
domain name used to locate an organization or individual on the internet.
dominant describes a gene with the ability to override the expression of other recessive genes. dominant genes are expressed in both the homozygous state and the heterozygous state. Examples of dominant gene expression include: normal skin and hair pigmentation and Huntington’s disease.
dominant hemisphere on the opposite side of the brain to that of the preferred hand. The dominant hemisphere for language is the left in most right-handed people and about a third of left-handed people.
dongle any device used to protect software from piracy.
dopa a compound formed in an intermediate stage during the synthesis of catecholamines, for example, adrenaline (epinephrine), from tyrosine.
dopamine a monoamine neurotransmitter. It functions in the central nervous system, especially the basal nuclei. Reduced levels are associated with Parkinson’s disease. Used intravenously in some types of shock to increase cardiac output and blood flow to the kidneys.
dopants impurities introduced into a crystal structure to control its characteristics. See also activators, killers.
doping the addition of impurities to a substance, in extrinsic semiconductors impurities are added to the silicon or germanium to increase the electrical conductivity.
Doppler effect when ultrasound echoes are reflected from a moving structure they are changed in frequency, the amount and direction depends on the velocity, the direction of the moving interface and the position of the observer. Moving towards an object produces an increase in the reflected frequencies and moving away from the object produces a decrease in frequency.
Doppler scanner equipment used in ultrasound imaging to monitor a moving substance, for example, the flow of blood or the beating heart.
Doppler scanning combines ultrasonography with pulse echo. Doppler ultrasound technique can be used to calculate cardiac output and stroke volume by measuring blood flow in the aorta via a probe passed into the oesophagus. Used to monitor haemodynamic status and response to treatment.
Doppler shift a measurement obtained by subtracting the known frequency of the original transmitted ultrasonic waveform from the reflected waveform.
Doppler technique can be used to measure the velocity of blood flow through a vessel to determine the degree of occlusion or stenosis.
dorsal associated with the back, or the posterior part of an organ.
dorsal decubitus radiograph patient is supine and the central ray passes through the body from side to side.
dorsiflexion bending backwards. In the case of the great toe – upwards.
dorsipalmar radiograph a radiograph of the hand with the palm in contact with the cassette.
dorsiplantar a radiograph of the foot with the sole in contact with the cassette.
dorsocentral at the back and in the centre.
dorsolumbar associated with the lumbar region of the back.
DOS (Disk Operating System) the software which controls the computer disk drive.
dose build-up each layer of tissue produces recoil electrons which in turn deposit their kinetic energy through several other layers of tissue. The energy in each layer will be determined by the number of electrons passing through the layer plus the absorbed kinetic energy.
dose-equivalent limits the maximum dosage of radiation an individual can receive over a specific period of time in sieverts.
dose volume histogram a graphical representation of dose distribution in a specific anatomical structure.
dosimeter, dosemeter a device worn by personnel or placed within equipment to measure incident X-rays or gamma rays. thermoluminescent dosimeters, using lithium fluoride powder impregnated into plastic discs, are used in personnel monitoring. Previously, photographic film in a special filter holder was used. See also film badges, thermoluminescent dosimeters, solid state radiation detector, Geiger–Muller counter.
dots per inch a measure of image quality, the higher the number the better the image quality.
doubling time time over which a tumour will double in size. A mark of tumour virulence and occasionally an indicator of chemoresponsiveness (faster doubling time often associated with high growth fraction and occasionally with higher chemoresponsiveness).
download to transfer information from one computer to another.
Down’s syndrome a congenital condition in which there is learning disability and facial characteristics that include: oval tilted eyes, squint and a flattened occiput. The chromosome abnormality is of two types: (a) Primary trisomy, caused by abnormal division of chromosome 21 (at meiosis). This results in an extra chromosome instead of the normal pair: the infant has 47 chromosomes and is often born of an older mother. (b) Structural abnormality involving chromosome 21, with a total number of 46 chromosomes, one of which has an abnormal structure as the result of a special translocation. Such infants are usually born of younger mothers and there is a higher risk of recurrence in subsequent pregnancies.
drillers’ disease (vibration syndrome) caused by using vibrating machinery, resulting in cysts in the bones of the wrist and sometimes the hand.
drive wire a wire used to hold a single radioactive source and cause it to oscillate over a prescribed length of a catheter.
drop attacks periodic falling because of sudden loss of postural control of the lower limbs, without vertigo or loss of consciousness. Usually followed by sudden return of normal muscle tone, allowing the person to rise, if uninjured.
droplet infection pathogen transmission in droplets of moisture such as during coughing or talking.
drug the generic name for any substance used for the prevention, diagnosis and treatment of diagnosed disease and also for the relief of symptoms. See also prescription only medicines, general sales list.
drug dependence a state arising from repeated administration of a drug on a periodic or continuous basis (WHO, 1964). Now a preferable term to drug addiction and drug habituation.
drug interaction occurs when the action of one drug is affected by another drug, beverage or food taken previously or simultaneously.
drug misuse term increasingly used to describe the illegal use of drugs. Substance misuse includes solvents and alcohol, as well as drugs.
drug reaction an adverse reaction to a drug.
drug resistance the increasing problem caused by the ability of some microorganisms to develop resistance to certain antibiotics, for example, vancomycin-resistant enterococci and methicillin-resistant Staphylococcus aureus.
drug tolerance a situation where the therapeutic effects of a drug lessen over time, which necessitates the administration of a larger dose to achieve the same benefit.
drug trials several levels of testing occurring during the development of new drugs. (a) phase I trials where small numbers of healthy volunteers (usually male) are given small doses and monitored for adverse reactions. Blood samples are tested to determine drug distribution and excretion. (b) phase II trials involve patients, and the new drug’s efficacy is compared with existing treatments. (c) phase III trials involve large multiple centre studies carried out before the drug is approved and licensed for use by the appropriate bodies. See also Committee on Safety of Medicines. (d) phase IV trials take place after the drug has been approved for clinical use. Aim to monitor and report adverse and idiosyncratic reactions not seen earlier.
dry gangrene death of part of the tissues of the body, occurs when the drainage of blood from the affected part is adequate; the tissues become shrunken and black.
dual dosemeter two independent ionization chambers, that measure the integrated dose at the isocentre and feed signals to two independent dosimeters each capable of terminating a radiotherapy treatment exposure at a predetermined level. It provides a system of fail safe dose delivery control.
dual filament two filaments in an X-ray tube to enable either broad or fine focus to be selected.
Dubowitz score assesses gestational age.
Duchenne muscular dystrophy an X-linked recessive disorder affecting only boys. The disorder usually begins to show between 3 and 5 years and is characterized by progressive muscle weakness and loss of locomotor skills. Death usually occurs during the teens or early twenties from respiratory or cardiac failure.
duct a tube for carrying away the secretions from a gland.
ductless glands endocrine glands.
ductus arteriosus a fetal blood vessel connecting the left pulmonary artery to the aorta, to bypass the lungs in the fetus. At birth the duct closes, but if it remains open it is called persistent or patent ductus arteriosus, a congenital heart defect.
ductus venosus connection between the umbilical vein and inferior vena cava in the fetal circulation. Closes at birth.
Dukes’ classification a staging system for colorecal tumours, A – confined to mucosa and submucosa; B – involvement of the musculature, C – metastatic involvement to regional lymph nodes; D – metastasized to distant organ tissues. It is based on the degree of tissue invasion and metastasis.
dulac technique positioning the patient so that the area of interest is in the centre of a sphere.
duodenal atresia closure of the duodenum, seen on ultrasound as a double bubble appearance of a fluid-filled, distended stomach and duo-denal cap.
duodenal ulcer a peptic ulcer occurring in the duodenal mucosa. The majority are associated with the presence of the bacterium Helicobacter pylori in the stomach. Other factors include NSAIDs, smoking and genetic factors. Epigastric pain may occur some time after meals or during the night. The pain may be relieved by food, antacids and vomiting. The ulcer can bleed, leading to haematemesis and/or melaena, or it can perforate. Severe scarring following chronic ulceration may produce pyloric stenosis and gastric outlet obstruction. Management includes: (a) general measures; smoking cessation, avoiding foods that cause pain, avoiding aspirin and NSAIDs; (b) antibiotic drugs to eradicate H. pylori; (c) drugs to reduce gastric acid; H2 receptor antagonists, for example, ranitidine, proton pump inhibitors, for example, omeprazole, antacids based on calcium, magnesium or aluminium salts; (d) rarely surgical treatment, for example, after perforation.
duodenitis inflammation of the duodenum.
duodenojejunal associated with the duodenum and jejunum.
duodenoscope a side-viewing flexible fibreoptic endoscope.
duodenostomy a surgically made fistula between the duodenum and another cavity, for example, cholecystoduodenostomy.
duodenum the fixed, curved, first portion of the small intestine, connecting the stomach above to the jejunum below.
duplex scan a method of using real time imaging, colour and Doppler at the same time to demonstrate heart, blood vessels and in obstetrics.
duplicating film film used to produce exact copies of radiographs by direct contact printing.
duplitized films radiographic films in which the emulsion is coated on both sides of the base.
Dupuytren’s contracture painless, chronic flexion of the digits of the hand, especially the third and fourth, towards the palm. The aetiology is uncertain but some cases are associated with hepatic cirrhosis.
dura mater the outer meningeal membrane. See also falx cerebri, meninges, tentorium cerebelli.
duty of care the legal responsibility in the law of negligence that a person must take reasonable care to avoid causing harm.
DVD (Digital Versatile Disk) a single- or double-sided disk used to record information from a computer using a laser to burn the surface of the disk.
DVI (Direct Video Interface) a specialist computer connector for flat-panel computer monitors.
dwarf person of stunted growth. May be due to growth hormone deficiency. Also occurs in untreated congenital hypothyroidism and juvenile hypothyroidism, achondroplasia and other conditions.
dwarfism arrested growth and development as occurs in congenital hypothyroidism, and in some chronic diseases such as intestinal malabsorption, renal failure and rickets.
dwell time the positioning of a radioactive source within a catheter for different intervals of time.
dye sensitizing increasing the spectral sensitivity of the film by adding impurities to the film emulsion, because it is done by adding coloured dyes can be called spectral sensitizing.
dynamic CT in early CT scanners when a number of scans were performed in rapid succession to demonstrate blood flow, now no longer used.
dynamic imaging the monitoring of the change in radioactive uptake over time in radionuclide imaging.
dynamic incremental CT in early CT scanners, when a number of dynamic CT scans were performed at different levels in the body, now no longer used.
dynamic range in ultrasound imaging the difference between the maximum and minimum values in a set of data, that is how many degrees of black and white are found in the grey scale image.
dynamic wedge a wedge angle produced by the rapid movement of the beam collimators, which does not affect the beam quality.
dysarthria a speech disorder that results from a problem in muscular control of the mechanisms of speech. It is caused by damage to either the central or the peripheral nervous system, or both. Loss of muscular control may involve incoordination and/or slowness and weakness. The problem may affect articulation, phonation, prosody, resonance and respiration.
dyschondroplasia a disorder of bone growth resulting in normal trunk, short arms and legs.
dysdiadochokinesia impairment of the ability to perform alternating movements, such as pronation and supination, in rapid, smooth and rhythmical succession; a sign of cerebellar disease but also seen in the so-called ‘clumsy child’ with minimal brain damage.
dysfunctional a body or a system which is unable to function normally.
dysgammaglobulinaemia impaired immunoglobulin production in terms of quantitative or qualitative humoral immunity. There are numerous primary and secondary causes including common variable immuno-deficiency, X-linked agammaglobulinaemia, X-linked hyper-IgM syndrome, myeloma and transient hypogammaglobulinaemia of infancy.
dysgenesis malformation during embryonic development.
dysgerminoma a rare ovarian tumour, benign or of low-grade malignancy. It originates from primitive/undifferentiated gonadal cells and occurs in young women.
dyskaryosis abnormality of nuclear chromatin, indicating a malignant or premalignant condition.
dyskeratosis abnormal keratin production by epithelial cells; may indicate malignancy.
dyskinesia (clumsy child syndrome) impairment of voluntary movement.
dysmaturity signs and symptoms of growth retardation at birth. See also low birthweight.
dysmelia limb malformation, including missing limbs or shortening of limbs.
dysmenorrhoea painful menstruation. It may be spasmodic or primary dysmenorrhoea, most often affecting young women once ovulation has become established, or congestive or secondary dysmenorrhoea usually affecting women in their late twenties and may be associated with pelvic pathology, such as fibroids or endometriosis.
dysphagia difficulty in swallowing. Dysphagia can occur in a variety of medical conditions including oesophageal cancer, cerebral palsy, motor neuron disease, cerebrovascular accident, dementia and head and neck cancer. The difficulty in swallowing may be experienced with fluids and/or solid food. The extent of difficulty can range from a mild to a very severe problem. Assessment and management of dysphagia is best conducted by a multidisciplinary team that may include a gastroenterologist, specialist nutrition nurse, dietitian, speech and language therapist. The composition of the team will be determined by the needs of the patient, the medical condition underlying the swallowing problem, whether surgery is indicated, the clin-ical setting and the aim of treatment (curative or palliative).
dysphasia also sometimes known as aphasia. Dysphasia is a disorder of language and has nothing to do with intelligence level or an intellectual disorder. It is most commonly associated with cerebrovascular accident affecting the left side of the brain, but can occur after a head injury or brain surgery. Dysphasia can affect the ability to understand language and also the use of language for expression. The presentation of dysphasia varies greatly and those affected have very different skills and difficulties. It is important that detailed, individual consideration is given to their difficulties. The understanding of language includes understanding both what is said and what is written. Likewise, expression includes both verbal expression and written expression. Discrepancies between the level of understanding and expression of language are common. Most often, people with dysphasia have problems both in comprehension and in expression although the degree of impairment in each may vary. Assessment and treatment of dysphasia needs a detailed understanding and breakdown of language. Speech and language therapists can provide therapy to assist individuals and their carers to improve their communication. Dysphasia has a considerable impact on most areas of life such as relationships, work and leisure activities. Rehabilitation takes time and may last many months. People affected by dysphasia can become very withdrawn and isolated if they do not receive sufficient support. See also aphasia.
dysphonia abnormality in the speaking voice such as hoarseness.
dysplasia developmental abnormality of tissues and organs, often referring to a premalignant condition and graded according to severity.
dyspnoea difficulty in, or laboured, breathing.
dyspraxia lack of voluntary control over muscles, particularly the orofacial ones.
dysraphism incomplete closure of a crease or ridge, for example of the neural tube.
dyssynergia loss of fluency of movement; poor sequencing and timing of movements; loss of coordination of muscles that normally act in unison, particularly the abnormal state of muscle activity due to cerebellar disease.
dystaxia difficulty in controlling voluntary movements.
dystonia a movement disorder in which there is the abnormal posturing of a part of the body, examples of which are spasmodic torticollis and writer’s cramp.
dystrophy any abnormal condition caused by poor nutrition which usually results in muscle degeneration. See also muscular dystrophy.
