D - Glossary of Terms

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D - Glossary of Terms

dacryo	(dak'ri-o) Combining form denoting relation to tears or to lacrimal apparatus.
dark adaptation	The process by which the eye adapts itself to a lower level of ambient illumination when entering a darkened room.
Data acquisition system (DAS)	A computer-controlled electronic amplifier and switching device to which the signal from each radiation detector of a multislice spiral computed tomographic scanning system is connected.
dead man switch	A safety switch that closes a circuit only by continuous pressure from the instrument operator.
debility	(de-bil'i-te) Weakness, lack or loss of strength.
decay curve	The activity of a radioactive source, measured in becquerels, plotted against time.
deciduous	(de-sid´u-us) Pertaining to something shed or cast off in a particular sequence. Deciduous teeth are shed and replaced by permanent teeth during development.
decimal system	A system of numbers based on multi¬ples of 10.
decubitus	(de-ku'bi-tus) lying down eg dorsal decubitus is lying on back and lateral decubitus is lying on the side.
decussation	(dek´´uh-sa´shun) A crossing of nerve fibres from one side of the CNS to the other.
deep	Far, or further, from the surface opposite of superficial.
deep lymph nodes	Small masses of lymphatic tissue that connect lymph vessels in the deep fascia.
defecation	(def´´e-ka´shun) The elimination of faeces from the rectum through the anal canal and out the anus.
deglutition	(de´´glu-tish´un) The act of swallowing.
demarcate	To set or mark the limits of.
demarcation	(de''mar-kashun) Act ot process of marking off boundaries, line of seperation, between healthy and diseased tissue.
dendrite	(den´dr-ite) A nerve cell process that transmits impulses toward a neuron cell body.
de novo	From the beginning; anew.
dens	(denz) Odontoid process of second cervical vertebra.
densitometer	Instrument that measures the optical density of exposed film.
density	The opacity of a radiographic shadow to visible light. A qualitative expression‎ of the degree of film blackening, usually expressed in terms of the blackening of one film or shadow with respect to another.
density difference (DD)	The difference between the step with an average optical density closest to 2.2 and the step with an average optical density closest to, but not less than, 0.5.
density gradient	A numerical value that refers to contrast values on film; the higher the number, the higher the contrast. It is determined from a films characteristic curve by dividing the value of the vertical rise by the value of the horizontal rise.
dentin	(den´tin) The main substance of a tooth, covered by enamel over the crown of the tooth and by cementum on the root.
dentition	(den-tish´un) The number, arrangement, and shape of teeth.
denture	(den'tur) Artifical teeth.
deoxyribonucleic acid (DNA)	Molecule that carries the genetic information necessary for cell replication. The target molecule of radiobiology.
dependent	in a relaxed state, lying down
depression	(de-presh'un) Hollow area, concavity, decrease of functional activity or mental vitality.
depth dose	Radiation dose at a specific depth within an object. It is usually measured on percentage of surface dose.
derived quantities	Any secondary quantity derived from a combination of one or more of the three base quantities, such as mass, length, and time.
dermal papilla	(pa-pil´a) A projection of the dermis into the epidermis.
dermato	(der'ma-to) Prefix denoting relation to skin eg dermatoma is a skin tumor.
dermatomes	the strip of skin supplied by one spinal nerve (sensory).
dermis	(der´mis) The second, or deep, layer of skin beneath the epidermis.
descending aorta	The portion of the aorta from the arch to its division in the abdomen into the common iliac arteries.
descending colon	The segment of the large intestine that descends on the left side from the level of the spleen (splenic flexure) to the level of the left iliac crest (sigmoid colon).
desquamation	Ulceration and denudation of the skin.
detail	The degree of sharpness of structural lines on a radiograph.
detective quantum efficiency (DQE)	The percentage of x-rays absorbed by the screen.
detector array	Group of detectors and interspace material used to separate them. The image receptor in computed tomography.
detergent	(de-ter'jent) Any cleansing agent, a medicine used to cleanse wounds.
detergent rinse	A technique used to shorten film drying time. After final wasing and before drying, films are rinsed in a weak detergent solution (5ml/41ml of water).
deterministic effect	A biologic response whose severity varies with radiation dose. A dose threshold usually exists.
developer	The chemical solution that converts the latent image on film to a visible image. It consistsof a developing agent (hydroquinone), an accelerator (sodium carbonate), a preservative (sodium sulfite) and a restrainer (potassium bromide) to prevent unexposed silver bromide crystals in film from blackening.
developing	The stage of processing during which the latent image is converted to a manifest image.
developing agent	A chemical, usually phenidone, hydroquinone, or Metol, that reduces exposed silver ions to atomic silver.
development	The chemical reduction of the silver-halide ions to metallic silver of the exposed grains of the film emulsion.
development fog	An artifact that results from crystals that had not been exposed reducing to metallic silver as a result of the lack of a restrainer.
dextral	(deks'tral) Of or pertaining to the right side, opposed to sinistral.
dextro	(deks'tro) Prefix denoting relation to right side, eg dextrocardia is transposition of heart to the right side of the chest.
dextrosinistral	(deks''tro-sin'is-tral) Extending from right to left; as a dextrosinistral plane.
diagnosis	(di''ag-no'sis) Art or act of determining character of a disease from existing symptoms; also conclusion reached.
diagnostic mammography	Examination performed on patients with symptoms or elevated risk factors for breast cancer.
diagnostic-type protective tube housing	Lead-lined housing enclosing an x-ray tube that shields leakage radiation to less than 100 mR/hr at 1 m.
diapedesis	(di´´a-ped-e´-sis) The migration of white blood cells through the endothelial walls of blood capillaries into the surrounding connective tissues.
diaphragm	(di´a-fram) A sheet like dome of muscle and connective tissue that separates the thoracic and abdominal cavities. In medical imaging - An x-ray tube head attachment consisting basically of a sheet of lead with a hole that determines the size and shape of the primary beam.
diaphysis	(di-af´i-sis) The shaft of a long bone.
diarrhoea	(di´´a-re´a) Abnormal frequency of defecation accompanied by abnormal liquidity of the feces.
diarthrosis	(di´´ar-thro´sis) A type of functionally classified joint in which the articulating bones are freely movable; also called a synovial joint.
diastole	(di-as´to-le) The sequence of the cardiac cycle during which a heart chamber wall is relaxed.
dichroic stain	Two-colored stain that appears as a curtain effect on the radiograph.
diencephalon	(di´´en-sef´a-lon) A major region of the brain that includes the third ventricle, thalamus, hypothalamus, and pituitary gland.
diffraction	The phenomenon of the preferential scattering of a beam of radiation in certain directions when passing through a course grained absorber.
diffraction mottle	A mottle superimposed on a radiographic image due to the diffraction of incident radiation.
differential X-ray absorption	The process by which different numbers of x-ray photons are attenuated by matter, due to differences in the densities of the various components of the matter. When the attenuating matter is human tissue, the process of differential x-ray absorption is responsible for the creation of the radiographic image.
digestion	(di-jes'chun) The process by which larger molecules of food substance are broken down mechanically and chemically into smaller molecules that can be absorbed.
digital fluoroscopy (DF)	A digital x-ray imaging system that produces a series of dynamic images obtained with an area x-ray beam and an image intensifier.
digital radiography (DR)	Static images produced with either a fan x-ray beam intercepted by a linear array of radiation detectors or an area x-ray beam intercepted by a photostimulable phosphor plate or a direct-capture solid-state device.
dimagnetic	Nonmagnetic materials that are unaffected when brought into a magnetic field.
dimensional stability	The property that allows the base of radiographic film to maintain its size and shape during use and processing so that it does not contribute to image distortion.
diode	Vacuum tube with two electrodes, a cathode, and an anode.
diploe	(dip´lo-e) The spongy layer of bone positioned between the inner and outer layers of compact bone.
diploic space	(dip'lo-ic) The medullary space between the dense cortical bone of inner and outer tables of the flat calvarial bones of the skull, composed of cancellous bone and bone marrow
dipolar	Referring to a molecule with areas of opposing electric charges.
direct current (DC)	The flow of electricity in only one direction in a conductor.
direct-current motor	An electric motor in which many turns of wire are used for the current loop and many bar magnets are used to create the external magnetic field.
direct effect	Effect of radiation that occurs when the ionising radiation interacts directly with a particularly radiosensitive molecule.
direct-exposure film	Film used without intensifying screens.
dis	(dis) Prefix denoting abscence, reversal or seperation.
disaccharide	A sugar.
disarticulation	(dis''ar-tik''u-la'shun) Amputation at a joint with separation of joint.
disc / disc space	(disk) The space between the vertebrae, formed from a fibrous ring (the annulus) and a central "cushion" (nucleus pulposis)
discography	Radiography of intervertebral discs exposed to contrast media.
dissociation	The process of separating a whole into parts.
dispersion	(dis-per'shun) Act of separating or state of being separated, as finely divided particles of a substance dispersed through a medium.
distal	(dis´tal) Further away from the midline or origin; the opposite of proximal.
distance	See inverse square law.
distortion	Unequal magnification of different portions of the same object, lack of (geometric) proportionality.
diverticulitis	(di''ver-tik''u-li'tis) Inflammation of a diverticulum or diverticula.
diverticulosis	(di''ver-tik''u-lo'sis) Multiple diverticula of any cavity or passage, most commonly of colon.
diverticulum	(di''ver-tik'u-lum) A blind sac or pocket branching off from a main cavity or canal.
dolicho	(dol'i-ko) Prefix meaning long and narrow eg dolichofacial is along narrow face.
dolichocephalic	(dol''i-ko-se-fal'ik) Having a long narrow head.
dorsal	(dor´sal) Pertaining to the back or posterior portion of a body part; the opposite of ventral; also called posterior.
dorsal root ganglion	The ganglia associated with the spinal nerves are called dorsal root ganglia. Ganglia are a biological tissue mass, most commonly a mass of nerve cell bodies.
dorsalis pedis artery	The continuation of the anterior tibial artery, that branches into the lateral and medial tarsal, arcuate, and deep plantar arteries
dorsiflexion	(dor´´se-flek´shun) Movement at the ankle as the dorsum of the foot is elevated.
dorsum	(dor-sum) Latin = back. During development, the lower limb rotates medially so that extensors are at the front, flexors at the back, the knee points forward (not backward like the elbow) and the dorsum of the foot is at the front, not the back.
dorsum sellae	The posterior bone margin of the pituitary fossa, that is the superior limit of the sphenoid bone. The dorsum sellae forms the boundary between the middle and posterior cranial fossae in the midline.
dose	(dos) Proper quantity of a medicine to be taken at one time or within a specified time A general term used to denote a quantity of radiation absorbed by living tissue. Quantity of X-radiation adminstered therapeutically at one time or over a period. see also Gray
dose equivalent (H)	The radiation quantity that is used for radiation protection and that expresses dose on a common scale for all radiations. Expressed in rem or sievert (Sv).
dose limit (DL)	The maximum permissible dose. Dosimeter An instrument that detects and measures exposure to ionising radiation.
dose rate	The rate at which radiation is delivered or received.
dosimeter	A monitoring device used for measuring or eval‎uating the absorbed dose or exposure. It is normally worn by radiographers to detect and record the radiation received. Often called a thermoluminescent device (TLD)
dosimetry	The practice of measuring the intensity of radiation.
double contrast examination	An examination of the colon that uses air and barium for contrast.
double emulsion film	Radiographic film that has an emulsion coating on both sides of the base and a layer of supercoat over each emulsion.
double-helix	Configuration of DNA that is shaped like a ladder twisted about an imaginary axis like a spring.
doubling dose	That dose of radiation expected to double the number of genetic mutations in a generation.
dropsy	(drop'se) Abnormal accumulation of fluid in cellular tissue or in a cavity of body (also called hydrops).
drug	(drug) Any chemical substance used, internally or externally in treatment of disease.
dryer system	A rapid drying mechanism in the automatic film processor. It uses a series of squeeze rollers to remove surface moisture from the film and a forced hot air system to complete drying.
drying	Film must be dried after washing. This is accomplished with controlled heat or time. A detergent rinse after washing will shorten drying time.
ductus arteriosus	(duk´tus ar-tir´´e-o´sus) The blood vessel that connects the pulmonary trunk and the aorta in a fetus.
ductus deferens	(def´er-enz) pl. ductus deferentia A tube that carries spermatozoa from the epididymis to the ejaculatory duct; also called the vas deferens or seminal duct.
ductus venosus	(ven-o´sus) A fetal blood vessel that connects the umbilical vein and the inferior vena cava.
duodenum	(du´´o-de´num) The first portion of the small intestine that leads from the pylorus of the stomach to the jejunum.
duplicating film	A single-emulsion film that is exposed to ultraviolet light or blue light through the existing radiograph to produce a copy.
duplicating printer	A light controlled, exposure regulating device for duplicating radiographs by exposing copying film.
duplication	A technqiue for photographically reproducing a radiographic image. See duplicating film.
duodenal bulb	The portion of the duodenum that forms the superior flexure with the pylorus.
dura mater	(du'ra ma´ter) The outermost meninx.
dynamic range	The range of values that can be displayed by an imaging system; shades of gray.
dys	(dis) prefix denoting difficulty or pain eg dyspnea which is labored or painfull breathing. abnormality or impairment eg dysarthrosis which is malformation of a joint.
dysphagia	Difficulty swallowing
dysplasia	Disordered growth or faulty development of various tissues or body parts.
dyspnea	(disp-ne'ah) Labored or painful breathing.
dysuria	(dis-u'ri-ah) Difficult or painful urination