A - Glossary of Terms

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A - Glossary of Terms

a, an	prefixes signifying without, lack of, eg atypical is not characteristic of type.
ab, abs	prefixes signifying away from, departure, eg abduct is to draw away from median plane or axis.
abdomen	(ab-do´men) the portion of the trunk between the diaphragm and pelvis.
abdominal aorta	(ab-do´men-al a-or´tua) the continuation into the abdomen of the thoracic aorta, which divides into the two common iliac arteries. The aorta is the largest artery in the body; it supplies oxygenated blood to the abdominal and pelvic organs and the legs.
abduct	(ab-duk) to draw away from mid line of the body.
abduction	(ab-duk´shun) describes the movement of a body part away from the axis or midline of the body.
ablation	(ab-la shun) radiofrequency ablation is a treatment technique that uses high-frequency alternating electrical current to destroy tissue cells by heating them.
abnormal	(ab-nor'-mal) irregular, deviation from usual form or condition.
abrasion layer	the protective covering of gelatin enclosing an emulsion.
abscess	(ab-ses) a localized infection consisting of pus surrounded by inflamed tissue.
absolute age-response relationship	The increased incidence of a disease is a constant number of cases after a minimal latent period.
absolute risk	The incidence of a malignant disease in a population within 1 year for a given dose, it is expressed as number of cases/ 10 to the power of 6 persons/rem.
absorb	(ab-sorb') to suck in, as in a sponge; to assimilate fluids or other substances from skin.
absorbed dose	The amount of energy transferred to matter by ionising radiation per unit mass at a given location, expressed in rad (100 erg/g) or gray (1 J/kg) The thermalisation of tissue by the absorption of ultrasound energy, expressed as a rise in temperature (degress C).
absorber	Any material absorbing ionising radiation.
absorption	(ab-sorp´shun) the transport of molecules across epithelial membranes into the body fluids. in radiology - the reduction in intensity of a beam of ionising radiation due to its passage through a material that blocks some of the incident radiation.
absorption blur	The characteristic of the subject affecting subject contrst.
absorption unsharpness	The unsharpness in the image due to variations in absorption throughout a three-dimensional structure, caused by the particular shape of that structure. For example, a spherical object projects “unsharp” edges onto film.
acanthion	(a-kan'the-on) point at centre of base of anterior nasal spine.
acanthomeatal line	(a-kantho-me-a'tal) imaginary line extending from external auditory meatus to acanthion.
acceleration	The rate of change of velocity with time.
acceleration of gravity	The constant rate at which objects falling to the Earth accelerate.
accelerator	A device that increases the velocity of electrically charged atomic particles A sodium carbonate solution that allows the developing agent to break down the protective coating on film.
accessory organs	(ak-ses´uo-re) organs that assist with the functioning of other organs within a system eg splenunculi is accessory splenic tissue.
acetic acid	In processing film, an organic acid used during the developing proces to remove developer remaining in the emulsion after latent image formation (the chemical used in the stop bath in wet film processing) see stop bath.
accommodation	(ua-kom´´uo-da´shun) a process whereby the focal length of the eye is changed by automatic adjustment of the curvature of the lens to bring images of objects from various distances into focus on the retina.
acetabulum	(as´´ue-tab´yuu-lum) a socket in the lateral surface of the pelvis with which the head of the femur articulates.
acetaminophen	a drug that reduces pain and fever but not inflammation. A member of the family of drugs called analgesics, it is found in many over-the-counter medications
achalasia	Failure of the lower esophageal sphincter to relax because of absence or destruction of cells in the myenteric nerve plexus, which results in difficulty swallowing
achilles tendon	(ua-kil´=ez) see tendo calcaneous.
acoustic	(a-koos'tik) pertaining to sound or organs of hearing
acromegaly	(ak´´ro-meg´ua-le) a condition caused by the hypersecretion of growth hormone from the pituitary gland after maturity and characterized by enlargement of the extremities, such as the nose, jaws, fingers, and toes.
acromioclavicular joint	The articulation between the acromion process and the clavicle.
acromion	greek akros = summit and omos = shoulder, hence, the tip of the shoulder.
acromion process	The bony vertical extension of the scapula, above the glenohumeral joint.
activator	Chemical, usually acetic acid in the fixer and sodium carbonate in the developer, used to neutralise the developer and swell the gelatin.
active layer	Fluorescennt material (commonly calcium tungstate) in a binding medium used in intensifying screens. There is a direct relationship between active layer thickness and the speed of the screen, and an inverse relation between active layer thickness and resolution of the radiographic image.
active memory	Data can be stored or accessed at random from anywhere in main memory in approximately equal amounts of time, regardless of where the data is stored.
activity	The number of atoms in a radioisotope that are decaying each second.
actual focal-spot size	The area on the anode target that is exposed to electrons from the tube current.
acutance	A measure of sharpness of image determined by the distinction of the boundary between the subject and background, see penumbra, umbra.
acute	(a-kut) Having a sudden onset and running a short but relatively severe course, an acute disease opposed to chronic.
acute radiation syndrome	Radiation sickness that occurs in humans after whole-body doses of 1Gy (100 rad) or more of ionising radiation delivered over a short time.
adaptation	The adjustment of the eye to dim light or red light necessary when viewing a fluoroscopic image without intensification. Pupil size changes automatically to control the amount of light reaching the retina.
added filtration	Any filtering material placed in the path of an emitted X-ray beam after it leaves the tube.
Addison's planes	(ad'i-sons) imaginary planes used to divide the abdomen into nine regions for descriptive purposes
adduct	(ad-ukt) the movement of a body part toward the axis or midline of the body.
adduction	(ad-uk´shun) the movement of a body part toward the axis or midline of the body.
adenine	A nitrogenous organic base that attaches to a deoxyribose molecule.
adeno	(ad'en-o) a gland; of or pertaining to a gland; as adenitis is inflammation of a gland.
adenoids	(ad´ue-noidz) the tonsils located in the nasopharynx; pharyngeal tonsils.
adenoma	(ade-no'mah) benign tumour of glandular origin.
adenopathy	(ad'e-nop'ath-e) Enlargement of the lymphatic glands.
adherent	(ad-her'ent) clinging or sticking together.
adhesion	(ad-he'zhun) union or sticking together of two surfaces.
adhesive layer	Bonding agent fixing emulsified silver halide gelatin to the polyester basein radiographic film. (A protective covering of gelatin that encloses the emulsion).
adipose	(ad'i-pos) fat, fat in cells of adipose tissue.
adnexa	(ad-nek'sah) appendages or conjoined parts ie adnexa in pelvis is contains ovary and fallopian
adnexal	(ad-nek'sal) Pertaining to the uterine appendages (ovaries, fallopian tubes and ligaments).
adrenal gland	the gland located superior to the kidney which is responsible for the production of epinephrine.
adventitia	(ad´´ven-tish´ua) the outermost epithelial layer of a visceral organ; also called serosa.
aerated	(a'er-at-ed) filled with air eg the lungs.
aerial oxidation	Oxidation that occurs when air is introduced into the developer when it is mixed, handled and stored.
afferent	(af´er-ent) conveying or transmitting to.
afferent arteriole	(ar-tir´e-=ol) a blood vessel within the kidney that supplies blood to the glomerulus.
afferent neuron	(noor´on) see sensory neuron.
afterglow	Phosphorescence in an intensifying screen.
age-response function	The pattern of change in radiosensitivity as a function of phase in the cell cycle.
aggregate	(ag're-gat) grouped or clustered together.
agitation	Moving film in solutions during processing. Failure to agitate film can result in streaking and loss of uniformity.
ailment	(ai'li-ment) a bodily disorder or chronic disease.
air bronchogram	The radiographic shadow of an air-filled bronchus peripheral to the hilum and surrounded by airless lung (whether by virtue of absorption of air or replacement of air or both). The air is visible within the bronchus because the lung surrounding the bronchus is airless. Visualization of an air bronchogram usually implies the presence of an airspace filling process.
air contrast	Tecchnique of using air to outline soft tissue structures for radiographic contrast on film.
air dose	Quotient of the mean energy imparted to air by ionising radiation divided by the mass of air.
air gap technique	A method of reducing scattered radiation to the film by separating the film and the object being examined by some distance. Eg: the practice of moving the image receptor 10 to 15cm from the patient so that fewer scattered X-rays interact with the image receptor, which enhances contrast of a radiograph.
ala	(a'lah) wing, wing like process or part
alar	(a'lar) pertaining to an ala eg alar process of sacrum.
ALARA	The principle that radiation exposure should be kept as low as reasonably achievable, economic and social factors being taken into account.
albumin	(al-byoo´min) a water-soluble protein produced in the liver; the major component of the plasma proteins.
algia	(al'ji-ah) suffix denoting pain eg arthralgia is pain in a joint.
algorithm	A computer adapted mathematical calculation applied to raw data during image reconstruction.
aliment	(al'i-ment) that which nourishes
alimentary canal	(al'i-men'ta-re) the tubular portion of the digestive tract.
allantois	(ua-lan´to-is) an extraembryonic membranous sac involved in the formation of blood cells. it gives rise to the fetal umbilical arteries and vein and also contributes to the formation of the urinary bladder.
allergy	(al-er-gee) a hypersensitive reaction to common, often harmless substances, most of which are found in the environment.
alnico	An alloy of aluminium, nickel and cobalt; one of the more useful magnets produced from ferromagnetic material.
Alpha partcile	The particulate form of ionising radiation consisting of two protons and two neutrons. The nucleus of helium. Emitted from the nucleus of a radioactive atom.
alternating current (AC)	The oscillation of electricity in both directions in a conductor.
aluminium equivalent	The thickness of aluminium equal to the object to be radiographed, that will offer similar attenuation under similar exposure conditions.
alveolar sacs	(al-ve´uo-lar) a cluster of alveoli that share a common chamber or central atrium.
alveolus	(al-ve´uo-lus) two meanings; 1.an individual air capsule within the lung. the alveoli are the basic functional units of respiration. 2.the socket that secures a tooth (tooth socket).
amber filter	A filter that transmits light with wavelengths longer than 550nm, which is above the spectral response of blue-sensitive film.
ambi	(am'be) prefix meaning both eg ambilateral means affecting both sides.
ammeter	An instrument that measures current.
ammonium thiosulfate	Liquid fixing agent.
amniocentesis	(am´´ne-o-sen-te´sis) a procedure in which a sample of amniotic fluid is aspirated to examine suspended cells for various genetic diseases.
amnion	(am´ne-on) a developmental membrane surrounding the fetus that contains amniotic fluid.
amniotic sac	(am´ne-otic sac) membrane filled with fluid within the abdomen that holds the embryo/fetus.
amorphous	Without shape or definite form.
ampere (A)	The Si unit of electric charge. 1A=1C/s
amphiarthrosis	(am´´fe-ar-thro´sis) a slightly movable articulation in a functional classification of joints.
amplification	Magnifying ionisation impulses for measurement in radiation detection instruments.
amplitude	The width of a waveform (maximum height of a wavelength crest) Travel distance of an X-ray tube suring a tomographic exposure.
ampulla	(am-pool´a) a local dilatation of a duct or tube.
ampulla of vater	(am-pool'a of va´ter) also known as the hepatopancreatic ampulla, is formed by the union of the pancreatic duct and the common bile duct. The ampulla is specifically located at the major duodenal papilla.
anabolism	The process of synthesising smaller molecules into a larger macromolecule.
anal canal	(a´nal) the terminal tubular portion of the large intestine that opens through the anus of the gi tract.
analgesia	(anal-je'ze-ah) diminished sensibility to pain.
anaphase	The second phase of mitosis, during which chromatids repel one another and migrate along the mitotic spindle to opposite sides of the cell.
anastomosis	(ua-nas´tuo-mo´sis) an interconnecting aggregation of blood vessels or nerves that form a network plexus.
anatomic	(an'a-tom'ik) of pertaining to or dealing with bosy structure
anatomical position	(an´´ua-tom´u1-kal) an erect body stance with the eyes directed interior, the arms at the sides, the palms of the hands facing interior, and the fingers pointing straight down.
anatomy	(ua-nat´uo-me) the branch of science concerned with the structure of the body and the relationship of its organs.
anechoic	Not containing internal echoes (on ultrasound).
anemia	(a-ne´me-a) an abnormal reduction in the red blood cell count, hemoglobin concentration, or hematocrit, or any combination of these measurements. this condition is associated with a decreased ability of the blood to carry oxygen.
anesthesia	Drugs used to induce loss of sensation for the patient in preparation for operative procedures.
anesthesiologist	A physician specializing in the controlled loss of sensation through anesthesia.
anesthetic	A drug that temporarily produces the loss of ability to sense pain or other sensations.
aneurysm	(an-yur-izm) A ballooning out of a segment of artery caused by disease or weakness in the vessel wall. It may lead to rupture and serious or fatal bleeding.
angina	(an-jye-nah) Cramp-like pain that comes and goes, and is made worse by physical effort. It is a sign that the tissue or organ supplied by a narrowed artery is not getting enough blood or oxygen.
angina pectoris	(an-ji´nua pek´tuo-ris) a thoracic pain, often referred to the left pectoral and arm area, caused by myocardial ischemia.
angiocardiography	(an-je-o-kar-de-o-gra-fe) X-ray imaging of the heart and great vessels made visible by injection of a (radio-opaque) contrast solution.
angiogenesis	(an-ge-o-gen-isis) Formation of new blood vessels.
angiogram	(an-ge-o-gram) An imaging study depicting blood vessels. In a conventional angiogram, a (radio-opaque) contrast is injected into the bloodstream and x-rays are taken to visualize the blood vessels. In other instances, CT or MRI can be used to create three-dimensional pictures of blood vessels.
angiographic	(an-je-o-graf-ik) Relating to or utilizing angiography.
angiography	(an-je-o-gra-fe) A medical imaging technique used to visualise the inside, or lumen, of blood vessels and organs of the body which are made visible by injection of a (radio-opaque) contrast solution.
angioma	(anje-o-mah) tumour composed largely of blood vessels.
angioplasty	(an-je-o-plas-te) Reconstitution or reopening of a blood vessel; may involve balloon dilation, mechanical stripping of the inside of the blood vessel, forceful injection of a elastic filamentous protein, or placement of a stent.
angle of louis	The point of junction between the manubrium and the body of the sternum.
angstrom (An)	The unit of measure of wavelength.
anion	A negatively charged ion, attracted to the anode.
ankle joint	The joint between the two bones of the lower leg (tibia and fibula) and the talus of the foot.
ankylosis	(angki-lo'sis) abnormal union of two or more normally seperate bones, immobility of a joint caused by disease, injury or surgical procedure.
annulus fibrosus	Tough hyaline cartilaginous rim of an intervertebral disc.
anode	The positively charged electrode of an X-ray tube which contains the target and from which X-rays are emitted. Anodes may be either stationary or rotating.
anomaly	(a-nom'al-e) marked irregularity or deviationfrom normal standard of structural formation.
ante	(an'te) prefix denoting before (in time or place).
antegrade	(an'te-grad) moving in the direction considered normal.
antebrachium	(an´´te-bra´ke-em) the forearm.
anteflexion	the forward angle of the normal uterus on the cervix. (see anteversion, retroflexion, retroversion)
anterior	(ventral) toward the front; the opposite of posterior, or dorsal.
anterior pituitary	(pu1-too´u1-ter-e) see adenohypophysis.
anterior root	the anterior projection of the spinal cord, composed of axons of motor neurons.
anterior tibial artery	Artery originating from the popliteal artery and branching into the posterior and anterior tibial recurrent, and lateral and medial anterior malleolar arteries, and lateral and medial malleolar retes.
anteroposterior	(anter-o-pos-ter'i-er) (AP) directed or extending from front to back. A subject position where X-rays enter the anterior portion of the subject and exit posteriorly for image production.
anteversion	The forward bending position of the normal uterus on the backward sloping vagina. (see anteflexion, retroversion, retroflexion).
anthropomorphic	Human characteristics.
anti	(an'ti) prefix signifying - against, counter or opposite
antibiotics	A class of medications used to treat bacterial infections by killing or inhibiting the growth of bacteria.
antibodies	Substances within the body that neutralize body toxins and bacteria.
anticoagulant	Substance that suppresses or delays coagulation of the blood.
anticoagulant therapy	(an-tI-co-ag-u-lant ther-a-pe) The use of anticoagulant drugs to reduce or prevent intravascular or intracardiac clotting. drugs commonly used for this are warfarin, heaprin or clexane.
antigen	The molecular configuration of an antibody that attacks a particular type of invasive or infectious agent.
antiseptic	(anti-sep'tik) any substance that will prevent/retard growth of microorganisms
antiplatelet drug	A medication that interferes with the normal function of blood platelets and thereby reduces the tendency for blood to clot; commonly called a blood thinner.
antrum	greek antron = cave, hence a space in a bone or organ.
anus	(a´nus) the terminal opening of the gi tract.
aorta	(a-or´tua) the major systemic vessel of the arterial system of the body, emerging from the left ventricle of the heart.
aortic arch	the superior left bend of the aorta between the ascending and descending portions.
AP	acronym for anterioposterior view. Where the central ray enters the anterior part of the body and exits through the posterior.
apex	(a´peks) the tip or pointed end of a conical structure.
aperture	(ap'er-chur) Opening, orifice or mouth A circular opening for the patient in the gantry of a computed tomographic or magnetic resonance imaging sysem. The fixed collimation of a diagnostic X-ray tube, as in an aperture diaphragm. The variable opening before the lens of a cine or photospot camera.
aperture diaphragm	A simple beam restricting device that attaches a lead lined metal diaphragm to the head of an X-ray tube.
apneustic center	(ap-noo´stik) a collection of nuclei(nerve cell bodies) in the brain stem that participates in the rhythmic control of breathing.
apocrine gland	(ap´uo-krin) a type of sweat gland that functions in evaporative cooling. it may respond during periods of emotional stress.
aponeurosis	(ap´´uo-noo-ro´sis) greek apo = from, and neuron = tendon (later applied to nerve cell and its fibres), fibrous or membranous sheet like tendon.
apophyseal	(ap-of-iz'e-al) of or pertaining to an apophysis
apophysis	(a-pof'i-sis) anuy outgrowth or offshoot; process of bone
appendicitis	An inflammation of the appendix, usually caused by a blockage and a subsequent infection.
appendix	(Veriform appendix) appendage of the caecum.
appendicular	latin appendere = to hang on. Of, relating to, or consisting of an appendage or appendages, especially the limbs eg appendicular skeleton.
apex of heart	the bottom most portion of the heart, formed by the left ventricle.
appose	(a-poz') to bring two surfaces in juxtaposition or proximity, as in reduction of a fracture
aqueduct	(ak'we-dukt) canal for movement of fluid; as in aqueduct of of sylvius - the passage connecting third and fourth ventricles
aqueous	(a´kwe-us) of or nature of water
aqueous humor	(a´kwe-us) the watery fluid that fills the anterior and posterior chambers of the eye.
arachnoid mater	(ua-rak´noid) the weblike (greek: arakhnes=spider) middle covering (meninx) of the central nervous system. joined to the pia mater by thin strands of tissue and covered by the dura mata (see meninges)
arachnoid membrane	A thin membrane enclosing the brain and spinal cord. The subarachnoid space lies between the arachnoid membrane and the spinal cord.
areola	(a-re-o'-lah) minute space; coloured ring around mammory nipple
arbor vitae	(ar´bor vi´te) the branching arrangement of white matter within the cerebellum.
archival quality	Referring to the fact that the image does not deteriorate with age but remains in its original state.
area beam	The X-ray beam pattern that is usually shaped like a square or rectangle and that is used in conventional radiography and fluoroscopy.
arm	the portion of the upper extremity from the shoulder to the elbow. (see brachium, forearm, antibrachium).
array processor	The part of the computer that handles raw data and performs the mathematical calculations necessary to reconstruct the digital image.
arrector pili muscle	(ah-rek´tor pih´le) the smooth muscle attached to a hair follicle that, upon contraction, pulls the hair into a more vertical position, resulting in "goose bumps."
arrhythmia	An abnormal rhythm of the heart.
arteriogram	a radiograph of arteries after they have been injected with a contrast medium.
arteriography	Radiography of arteries exposed to contrast media.
arteriole	(ar-tir´e-=ol) a minute arterial branch.
arteriosclerosis	(ar-tir´´e-o-sklue-ro´sis) any one of a group of diseases characterized by thickening and hardening of the artery wall and in the narrowing of its lumen.
arteriovenous anastomoses	(ar-tir´´e-o-ve´nus ua-nas´´tuo-mo´s=ez) direct connections between arteries and veins that bypass capillary beds.
arteriovenous fistula	(ar-tir´´e-o-ve´nus-fist-ula) An abnormal connection between an artery and a vein. This can be surgically created for hemodialysis but can also be caused by trauma.
arteriovenous malformation (AVM)	An abnormal communication between an artery and vein that may be present at birth or may result from injury or infection. Blood may flow directly from the artery to the vein, bypassing the small vessels where oxygen and tissue nutrients are exchanged. These malformations are often found in the brain and spinal cord, but may occur anywhere in the body.
artery	(ar´tue-re) a blood vessel that carries blood away from the heart.
arthritis	(arth-rI-tis) Inflammation of a joint or a state characterised by inflammation of joints.
arthrology	(ar-throl´uo-je) the scientific study of the structure and function of joints.
arthrogram	A radiographic examination of a joint after the introduction of contrast medium.
arthrosis	(ar-thro-sis) any joint or juncture uniting two bones
articular cartilage	(ar-tik´yuu-lar kar´tu1-lij) a hyaline cartilaginous covering over the articulating surface of the bones of synovial joints.
articular fossa	a hollow of depressed area within a joint.
articular surface	the surfaces of bone or cartilage which form a joint.
articulation	(ar-tik´´yuu-la´shun) a joint.
artifact	In radiology, something artificial that appears on a medical image but is not a part of the living tissue being examined. The image distortion could be due to a surgical metal clip, necklace, watch, mobile phone or a problem with the imaging equipment.
arytenoid cartilages	(ar´´ue-te´noid) a pair of small cartilages located on the superior aspect of the larynx.
ascending aorta	The portion of the aorta that originates from the left ventricle and gives rise to the right and left coronary arteries.
ascending colon	(ko´lon) the portion of the large intestine between the cecum and the hepatic flexure.
ascites	(a-sitez) accumulation of fluid in the chest and abdomen in the setting of liver failure.
asepsis	(a-sep'sis) method of preventing and of maintaining freedom from infection
aseptic	(a-septik) free from septic material
aspirate	(as'pi-rat) withdrawal of a fluid from the body by suction, usually though a needle or syringe.
aspiration	(aspi-ra'shun) a drawing out by suction, removal of fluids from a a cavity.
assimilation	(a-simi-lat'shun) conversion of material into living tissue
asthenia	(as-the'ne-ah) loss of strength
asthenic	(as-the'ne'ik) pertaining to asthenia or weakness, a patients body habitus that is small and frail.
asthma	(az'mah) disease characterised by recurrent attacks of paroxysmal breathing.
astigmatism	(ua-stig´mua-tiz´´em) unequal curvature of the refractive surfaces of the eye (cornea and/or lens), so that light entering the eye along certain meridians does not focus on the retina.
ataxia	(a-tax'si-ah) condition characterised by inability inability to coordinate voluntary muscular movements.
atelectasis	(ate-lek'ta-sis) Less-than-normal inflation of all or part of a lung with corresponding diminution in volume, often resulting in loss of the normal lucency of the affected portion of lung.
attenuation	the reduction in intensity of an x-ray beam by absorption and scattering processes as it transverses matter.
atherosclerosis	(ath´´er-o-skle-ro´sis) a common type of arteriosclerosis found in medium and larger arteries in which raised areas within the tunica intima are formed from smooth muscle cells, cholesterol, and other lipids. these plaques occlude arteries and serve as sites for the formation of thrombi.
atlas	Cervical vertebrae (C1) (the atlas) sits atop C2 (the axis) and can rotate about the dens which is a vertical post arising from C2.
atom	The smallest particle of an element that cannot be divided or broken by chemical means.
atomic mass	The relative mass of a specific isotope of an element.
atomic mass number (A)	The number of protons plus the number of neutrons in the nucleus.
atomic mass unit (amu)	The mass of a neutral atom of an element, expressed as one twelfth the mass of carbon, which has been arbitrarily assigned value of 12.
atomic number (Z)	The number of protons in the nucleus.
atony	(at'o-ne) lack of normal tone or vitality.
atresia	absence or closure of a body orifice or tubular organ.
atretic	(ua-tret´ik) without an opening. atretic ovarian follicles are those that fail to ovulate.
atrioventricular bundle	(a´´tre-o-ven-trik´yuu-lar) a group of specialized cardiac fibers that conduct impulses from the atrioventricular node to the ventricular muscles of the heart; also called the bundle of his or av bundle.
atrioventricular node	(a microscopic aggregation of specialized cardiac fibers located in the interatrial septum of the heart that are a part of the conduction system of the heart; av node.
atrioventricular valve	(a cardiac valve located between an atrium and a ventricle of the heart; av valve.
atrium	(a´tre-um) latin = entrance hall; either of the two superior chambers of the heart that receive venous blood.
atrophic	(a-trof'ik) Wasted, pertaining to or characterised by atrophy.
atrophy	(at´ro-fe) A gradual wasting away or decrease in the size of a tissue or an organ.
attachments	May mean either an origin or insertion of a muscle.
attenuation	(a-ten-yu-a-shun) Loss of energy of a beam due to absorption, scattering, beam divergence, and other causes as the beam propagates through a medium. (see absorption)
atypical	(a-tip'i-kal) unusal, not characteristic of type.
auditory	(aw´du1-tor-e) pertaining to the structures of the ear associated with hearing.
auditory tube	a narrow canal that connects the middle ear chamber to the pharynx; also called the eustachian canal.
auricle	(aw'rik'l) two meanings; 1.the fleshy pinna of the ear. 2. an ear-shaped appendage of each atrium of the heart.
auricular line	(aw-rik'u-lar) line passing through external auditory meatus and perpendicular to frankfurt horizontal plane.
auricular point	(aw-rik'u-lar) centre of external suitory meatus
auscultating	latin ausculto = to listen to, hence, auscultation, the act of listening to a bodily activity.
automatic brightness control (ABC)	A feature on a fluoroscope that allows the radiographer to select an image-brightness level that is subsequently maintained automatically by varying the KVp, the mAs or both.
automatic exposure control (AEC)	A feature that determins radiation exposure during radiographyy in most X-ray imaging systems.
automatic film processing	A system incorporating processor, transporters, water, recirculation, replenishment and dryer sub systems which automatically processes film from developer through dried product.
automatic shutter	A sensing device which limits beam size by adjusting focus-film distance to film format by opening or closing collimator shutters.
autonomic nervous system	(aw´´to-nom´ik) The sympathetic and parasympathetic portions of the nervous system that function to control the actions of the visceral organs and skin.
autoradiography	Production of an image by the photographic recording of natural radiation.
autotransformer	A transformer located in the operating console that controls the KVp, it has one winding of wire and varies voltage and current by self-induction.
autotransformer law	The principle stating that the voltage received and the voltage provided are in direct relation to the number of turns of the transformer enclosed by the respective connections.
av groove	A groove on the surface of the heart which separates the atria from the ventricles.
average gradient	Measure of radiographic contrast. A numerical expression of the relative average contrast properties of a film and processing combination for a specified exposure, represented by the slope of a straight line connecting specific density points on a characteristic curve.
axial	Pertaining to axis of the body, part or thing, directed along axis or centre line.
axial tomography	Conventional tomography in which the plane of the image is parrallel with the long axis of the body and results in sagittal and coronal images.
axilla	(ak-sil´a) the depressed hollow commonly called the armpit.
axillary lymph node dissection	Surgical exploration and removal of lymph nodes from the armpit area, as a part of breast cancer surgery. Some or all of these lymph nodes are examined under a microscope by a pathologist to see if malignant cells are present.
axillary lymph nodes	(ax-il-are limf nodz) Numerous nodes around the axillary (below the shoulder joint) veins which receive the lymphatic drainage from the upper limb, scapular region and pectoral region (including mammary gland); they drain into the subclavian trunk.
axillary vein	the continuation of the basilic vein which ends at the lateral border of the first rib, becoming the subclavian vein.
axis	(ak'sis) straight line, real or imaginary, passing through centre of the body. cervical vertebrae (C1) (the atlas) sits atop C2 (the axis)
axon	(ak´son) the elongated process of a nerve cell that transmits an impulse away from the cell body of a neuron.
azygos	(az'i-gos) an unpaired part, especially an azygous vein or an azygous lobe of lung.
azygos arch	(az'i-gos) the point where the azygous vein arches over the root of the right lung to empty into the superior vena cava.
azygos lobe	(az'i-gos) a normal variant produced by an indentation in the Rt upper lobe of the lung. It is produced by invagination of the azygous vein. This is not a true lobe, since it does not have a separate bronchus.
azygoesophageal recess	an area of lucency on an AP chest radiograph representing a portion of the Right lower lobe that crosses the midline anterior to the spine, and ends at the azygous vein and or the esophagus.
azygous vein	a vertical paraspinal vein that connects the superior venae cava with abdominal veins.

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