M
mA the average electrical current passing through an X-ray tube during an exposure measured in milliamperes.
machine code the language the computer can understand directly; all instructions are written in binary.
machine tank developer the initial developer used in automatic processing machine and consists of developer replenisher and starter solution.
MacMillan nurses nurses based both in hospitals and in the community who provide advice on symptom control and provide psychological support for cancer patients and their families.
macrocephaly large head, not caused by hydrocephalus.
macrocyte a large red blood cell. Occurs in megaloblastic anaemia (for example, pernicious anaemia) and in association with excess alcohol intake, liver disease and hypothyroidism.
macrocytosis an increased number of macrocytes.
macrodactyly excessive development, enlargement, of the fingers or toes.
macroglossia an abnormally large tongue.
macrophages mononuclear cells, which destroy foreign bodies and cell debris by phagocytosis. Part of the monocyte–macrophage (reticuloendothelial) system, they are derived from monocytes. See also histiocytes.
macroscopic visible to the unaided eye; gross. See also microscopic.
macula densa special cells of the nephron. Forms part of the juxtaglomerular apparatus.
macula lutea (yellow spot) area of the retina responsible for clearest central vision.
magic angle artefact in magnetic resonance imaging of a joint, if a tendon lies at an angle of 55° to the static magnetic field it appears brighter on T1 and proton density weighted images but has a normal low signal on T2 weighted images, and therefore can be potentially confused with pathology.
magnesium (Mg) a metallic element needed in the body for many enzyme-catalysed reactions. Magnesium is an intracellular positively charged ion (cation) and is present in bone, and its metabolism is linked to that of calcium.
magnesium oxide used at the back of the crystal in scintillation counters to direct light back towards the sodium iodide crystal.
magnet a substance containing a north and a south pole.
magnetic disk an 8-inch double-sided, double-density disk for storing images of up to 1.2 Mbytes.
magnetic domain an area of a substance when all the atoms are pointing in the same direction.
magnetic field exists when a point of force is experienced by a magnetic pole placed at the point.
magnetic flux the lines of force through a magnetic field.
magnetic induction if a substance contains magnetic atoms and is placed in a magnetic field and the poles of the atoms become aligned magnetizing the substance.
magnetic moment a measure of the magnitude and direction of the magnetic properties of an object or particle that cause it to align with the static main field and form its own local magnetic field.
magnetic resonance the absorption of the emission of the electromagnetic energy by nuclei in a static magnetic field following excitation by a radio frequency pulse. The resonant frequency of the pulse and the emitted signal are proportional to the strength of the magnetic field.
magnetic resonance imaging (MRI; nuclear magnetic resonance (NMR)) a non-invasive technique that does not use ionizing radiation. It uses radiofrequency radiation in the presence of a powerful magnetic field to produce high-quality images of the body in any plane.
magnetic resonance signal the electromagnetic signal produced by the precession of the transverse magnetism of the spins which induce a voltage in the receiver coil which is then amplified by the receiver to form the signal.
magnetic susceptibility (χ) the ability of a substance to become magnetized or to distort a magnetic field. See also diamagnetic, paramagnetic, superparamagnetic, ferromagnetic.
magnetic tape tape that can store 180 Mbytes of information.
magnetization transfer contrast in magnetic resonance imaging when the image contrast is manipulated by selectively saturating a pool of protein bound water. By applying an off-resonance pulse (1000–2000Hz) these proteins are suppressed. As the protein bound water and the bulk water protons are in rapid exchange the saturation is transferred to the bulk phase of the water protons leading to a reduction in signal from the bulk water. Used to demonstrate small peripheral vessels and aneurysms in the brain and the detection of early demyelination or protein destruction.
magneto-optical disk a disk used to store computer data by a combination of a magnetic field on the disk and the use of a laser to write or read the information thus enabling a large quantity of data to be stored on the disk.
magnetron a piece of equipment that contains an anode and a cathode in a vacuum which are placed in a uniform magnetic field which causes the electrons to travel in a spiral, curved path from the cathode to the anode to produce radiowaves. A high-power radiofrequency oscillator used to power some linear accelerators.
magnum large or great, as foramen magnum in occipital bone.
mainframe a large computer, usually the centre of a system. Intelligent peripherals can then be attached.
major accident procedure a detailed management plan allocating staffing, resources and areas of responsibility, used in incidents where more than 15 casualties are expected.
malabsorption defective absorption of nutrients from the digestive tract.
malabsorption syndrome loss of weight and fat in the faeces (steatorrhoea), varying in severity. Caused by: (a) disease of the small intestine; (b) lack of digestive enzymes or bile salts; (c) surgical operations.
malalignment faulty alignment, for example, bones after a fracture.
malformation abnormal shape or structure; deformity.
malignant virulent and dangerous.
malignant growth (tumour) one that demonstrates the capacity to invade adjacent tissues/organs and spread (metastasis) to distant sites; often rapidly growing and with a fatal outcome. See also cancer, sarcoma.
malignant hyperpyrexia a rare inherited condition which presents in response to certain anaesthetic drugs and neuroleptic (antipsychotic) drugs; there is progressive increase in body temperature and, if untreated, may be fatal.
malignant lymphoma a malignant carcinoma of the thyroid gland which may spread to the lymph nodes or recur in the gastrointestinal tract.
malignant melanoma malignant cutaneous mole or freckle (usually); it is the most dangerous of all skin cancers. Related to overexposure to ultraviolet radiation (sunburn); most common in fair-skinned, blond/red-haired people. It is characterized by change in colour, shape, size of mole or with bleeding or itching in a mole. The prognosis depends on Breslow thickness; staging involves lymph node status, with sentinel node biopsy (SNB) now becoming an integral part along with computed tomography (CT) scan. Surgery is the only curative treatment with chemotherapy and radiotherapy of limited effectiveness.
malignant pustule virulent skin lesion. See also anthrax.
malignant tumour a growth which is not encapsulated, infiltrates adjacent tissue, causes metastases which spread to other parts of the body and may ultimately result in the death of the patient. See also cancer, sarcoma.
malleolus a part or process of a bone shaped like a hammer. external malleolus at the lower end of the fibula. internal malleolus situated at the lower end of the tibia.
mallet finger a fracture where the dorsal base of a phalanx is torn away.
malleus the hammer-shaped lateral bone of the middle ear. See also incus, stapes.
malocclusion any deviation from the normal occlusion of the teeth, often associated with an abnormal jaw relationship. See also orthodontics.
malposition any abnormal position of a part.
malpractice improper or injurious medical or nursing treatment. Professional practice that falls below accepted standards and causes harm. It may be negligence, unethical behaviour, abuse or criminal activities.
malrotation a congenital abnormality of the bowel when the distal limb of the mid gut fails to rotate on returning to the abdomen. Identified on ultrasound by looking at the placement of the blood vessels supplying the bowel.
maltase (α-glucosidase) an enzyme found in intestinal juice. It converts maltose to glucose.
maltoma low-grade β-cell lymphoma of the mucosa-associated lymphoid tissue. It may be related to Helicobacter pylori infection which, when eradicated, may lead to regression of disease.
malunion the union of a fracture in a poor position.
mammaplasty any plastic operation on the breast. See also augmentation, implant, reduction.
mammilla the nipple. A small papilla.
mammography radiographic demonstration of the breast by use of specially low-penetration (long-wavelength) X-rays. Used in the diagnosis of or screening for breast conditions including cancer.
mandible the bone forming the lower jaw.
manipulation using the hands skilfully as in reducing a fracture or hernia, or changing an abnormal fetal position to facilitate a vaginal delivery.
Mann–Whitney test a non-parametric statistical test comparing two sets of unmatched data using a table of values for U. If the results are less than the values in the table the results are significant. It is a substitute to Student’s t test for independent groups.
manometer an instrument for measuring the pressure exerted by liquids or gases. Used for example for measuring the pressure exerted by the cerebrospinal fluid during lumbar puncture, or for measuring central venous pressure.
mantle technique so called because the treatment area represents a cloak, the field dimensions are larger than the patient and therefore shielding of the lungs is required, used to treat Hodgkin’s disease. Consists of anterior and posterior parallel pair, shielding of the spinal cord may be required from the posterior field.
manual evacuation digital removal of faeces from the rectum.
manubrium a handle-shaped structure; the upper part of the sternum.
marble bones see osteopetrosis.
march fracture a type of stress fracture caused by an increase in physical activity which may so stress a metatarsal (usually the second) to produce an undisplaced self-healing hair-line crack. Management usually involves moderate rest with supportive padding and strapping for a few weeks but sometimes a walking plaster is required.
marginal cost the cost of providing the extra resources required to carry out activity above a baseline number.
mAs the average electrical current passing through an X-ray tube during an exposure multiplied by the exposure time in seconds.
mass the amount of matter in a body.
mass attenuation coefficient is the linear attenuation coefficient divided by the density of the medium the beam passes through and is used to describe the probability of an interaction occurring between the X-ray beam and the tissue.
mass number the total mass of neutrons and protons within an atom.
mast cells basophils (type of leucocyte) that have migrated to the tissues. They are located around small blood vessels and bind to IgE before producing chemicals such as histamine that are involved in inflammation and anaphylaxis.
mastectomy the surgical removal of one or both breasts due to malignant disease or the prevention of malignant disease. simple only breast tissue is removed. radical some of the muscles of the chest are removed along with the breast and axillary lymph nodes. See also lumpectomy.
mastitis inflammation of the breast. chronic mastitis the name formerly applied to the nodular changes in the breasts now usually called fibrocystic disease.
mastoid air cells extend in a backward and downward direction from the antrum.
mastoid antrum the air space within the mastoid process, lined by mucous membrane continuous with that of the tympanum and mastoid cells.
mastoid process the prominence of the mastoid portion of the temporal bone just behind the ear.
mastoidectomy drainage of the mastoid air-cells and excision of diseased tissue. cortical mastoidectomy all the mastoid cells are removed making one cavity which drains through an opening (aditus) into the middle ear. The external meatus and middle ear are untouched. radical mastoidectomy the mastoid antrum, and middle ear are made into one continuous cavity for drainage of infection. Loss of hearing is inevitable.
mastoiditis inflammation of the mastoid air-cells.
matrix the foundation substance in which the tissue cells are embedded. In digital imaging, the rows and columns of pixels on a display used to form a digital image.
maxillary sinuses two, pyramidal shaped cavities which lie on either side of the nasal cavity.
maxillofacial associated with the maxilla and face.
maxillofacial surgery branch of surgery concerned with the surgical management of developmental disorders and diseases of the facial structure.
maximum density (D Max) the maximum density which can be reached on a film under set exposure and processing conditions, determined using a characteristic curve. See also characteristic curve.
maximum intensity projection a volume rendering technique used to visualize high-intensity structures within a data acquisition. Achieved by a step by step process for producing projections from a two-dimensional or three-dimensional volume data set which is processed along selected angles. The highest data value for each pixel taken from a specific viewing angle is displayed. Used to demonstrate vascular structures in CT scanning and also in MR scanning.
McMurray’s osteotomy division of femur between lesser and greater trochanter. Shaft displaced inwards beneath the head and abducted. This position maintained by a nail plate. Restores painless weight bearing. In developmental dysplasia of the hip, deliberate pelvic osteotomy renders the outer part of the socket (acetabulum) more horizontal.
MCP block (LMPA, low melting-point alloy block) an alloy of lead, bismuth, cadmium and zinc which can be formed into individually shaped shielding blocks. These can be mounted below the head of the radiotherapy machine providing customized shielding of normal tissue.
mean the average. arithmetic mean a figure arrived at by dividing the sum of a set of values by the number of items in the set. See also central tendency statistic, median, mode.
mean dose point in radiotherapy, the central dose point when all the doses are plotted by increasing or decreasing size.
mean window level the average range of pixel values in an image.
mechanical ventilation see intermittent positive pressure ventilation.
Meckel’s diverticulum a blind, pouch-like sac sometimes arising from the free border of the lower ileum. Occurs in 2% of the population: usually symptomless. May cause gastrointestinal bleeding or intussusception.
media the middle coat of a vessel. Nutritive jellies used for culturing bacteria. See also medium.
medial associated with or near the midline, or to the middle layer of a structure.
median the middle. A central tendency statistic; the midway or middle value in a set of scores when placed in increasing order. See also mean, mode.
median line an imaginary line passing through the centre of the body from a point between the eyes to between the closed feet.
median plane a vertical plane that divides the body into right and left halves. Also called the midsagittal plane, median sagittal plane.
median sagittal plane an imaginary plane passing vertically through the mid line of the body dividing it into right and left halves.
mediastinoscopy a minor endoscopic surgical procedure for visual inspection of the mediastinum. May be combined with biopsy of the lymph nodes for histological examination, and diagnosis or staging in the case of cancer.
mediastinum the space between the lungs. Contains the heart, great vessels and the oesophagus.
medical audit systematic and critical review of medical care, including diagnosis and treatment, outcomes and quality of life.
medical ethics a set of moral values and principles of conduct for professionals working with patients.
medical jurisprudence see forensic medicine.
medical shock shock caused by the loss of circulating blood volume as a result of dehydration, haemorrhage, vomiting, diarrhoea or severe burns. Now called hypovolaemic shock.
medication a therapeutic substance or drug, administered orally or by injection intra-arterially, subcutaneously, intramuscularly, intravenously, or rectally, topically, transdermally or sublingually.
medicinal associated with a medicine.
medicine science or art of healing, especially as distinguished from surgery and obstetrics. A therapeutic substance. See also drug.
mediolateral associated with the middle and one side.
medium a substance used in bacteriology for the growth of microorganisms.
Medline computerized database of medical science and associated literature.
medulla the marrow in the centre of a long bone. The internal part of organs, for example, kidneys, adrenals and lymph nodes, etc. medulla oblongata the lowest part of the brainstem where it passes through the foramen magnum to become the spinal cord. It contains the nerve centres controlling various vital functions, for example, cardiac centres.
medullary associated with the medulla.
medullary carcinoma a malignant carcinoma of the thyroid gland which is slow growing and may have calcium present, it spreads to the lymph nodes and mediastinum.
medullary cavity the hollow centre of a long bone, containing yellow bone marrow or medulla.
medullated containing or surrounded by a medulla or marrow, particularly referring to myelinated nerve fibres.
medulloblastoma malignant, rapidly growing tumour occurring in children; usually in the midline of the cerebellum.
megacephalic (macrocephalic, megalocephalic) large headed.
megacolon of the colon. acquired megacolon associated with chronic constipation of any cause, or may occur in acute severe colitis of any cause (toxic megacolon). congenital megacolon (Hirschsprung’s disease) due to absence of ganglionic cells in a distal segment of the colon with loss of relaxation resulting in dilatation of the normal proximal colon.
megakaryocyte large multinucleated cells of the marrow that produce platelets (thrombocytes).
megaloblastic anaemia an anaemia caused by a deficiency of vitamin B12 or folate. It results in the formation of large red blood cells called megaloblasts.
megalocephalic see megacephalic.
megavoltage radiotherapy units radiotherapy units operating in the range of 4–25 megavolts, for example linear accelerators, used for external beam radiotherapy treatments.
meibomian glands sebaceous glands lying in grooves on the inner surface of the eyelids, their ducts opening on the free margins of the lids.
Meigs syndrome a benign, solid ovarian tumour associated with ascites and hydrothorax.
meiosis a stage of reduction cell division when the chromosomes of a gamete are halved in number ready for union at fertilization.
melaena black, tar-like stools. Evidence of gastrointestinal bleeding.
melanin a brown/black pigment found in hair, skin and the choroid of the eye.
melanocytes cells in the skin that produce melanin when stimulated by the pituitary hormone melanocyte stimulating hormone (MSH).
melanoma a malignant tumour arising from the pigment-producing cells (melanocytes) of the skin, or of the eye. See also malignant melanoma.
melatonin a hormone produced by the pineal body (gland) in response to the amount of light entering the eye. Influences sexual development and is involved in reproductive function. Also influences mood and various circadian rhythms, such as body temperature and sleep.
membrane a thin lining or covering substance. See also basement membrane, hyaloid membrane, mucous membrane, serous membrane, synovial membrane, tympanic membrane.
menarche when menstrual cycles commence.
meninges the surrounding membranes of the brain and spinal cord. They are the dura mater (outer), arachnoid membrane (middle) and pia mater (inner). See also meningitis.
meningioma a slowly growing fibrous tumour arising in the meninges.
meningism (meningismus) a condition describing irritation and inflammation of the meninges due normally to infection or haemorrhage and consisting of neck stiffness and photophobia.
meningitis inflammation of the meninges around the brain and spinal cord that can be due to an acute bacterial (for example, meningococcal meningitis) or viral infection, chronic infective and inflammatory conditions and occasionally malignancy.
meningocele protrusion of the meninges through a bony defect. It forms a cyst filled with cerebrospinal fluid. See also spina bifida.
meningoencephalitis inflammation of the brain and the meninges.
meningomyelocele (myelomeningocele) protrusion of a portion of the spinal cord and its enclosing membranes through a bony defect in the spinal canal. It differs from a meningocele in being covered with a thin, transparent membrane which may be granular and moist.
meniscectomy the removal of a semilunar cartilage of the knee joint, following injury and displacement. The medial cartilage is damaged most commonly.
meniscus semilunar cartilage, particularly in the knee joint. The curved upper surface of a column of liquid.
menopause the ending of menstruation. A period of time during which ovarian activity declines and eventually ceases (the climacteric). It normally occurs between the ages of 45 and 55 years. artificial menopause an earlier menopause caused by surgery or radiotherapy.
menorrhagia an excessive regular menstrual flow.
menses fluid discharged from the uterus during menstruation; menstrual flow.
menstrual relating to the menses. menstrual or uterine cycle the cyclical changes that occur as the endometrium responds to ovarian hormones. There are three phases: proliferative, secretory, and menstrual in which bleeding occurs for about 5 days. The cycle is repeated approximately every 28 days (21–35 days), except during pregnancy, from the menarche to the menopause.
menstruation the flow of blood and endometrial debris from the uterus once a month in the female. It usually starts at the age of 12–13 years in developed countries, and ceases around 50 years of age.
mentoanterior forward position of the fetal chin in the maternal pelvis in a face presentation.
mentoposterior backward position of the fetal chin in the maternal pelvis in a face presentation.
menu a set of choices presented in a computer program.
mesenchymoma a neoplasm composed of two or more cellular elements which are not usually associated with each other and fibrous tissue.
mesentery a large sling-like fold of peritoneum passing between a portion of the intestine and the posterior abdominal wall. Contains nerves, lymphatics and blood vessels.
mesial towards the front or the mid line.
mesoderm middle layer of the three primary germ layers of the early embryo. It gives rise to the cardiovascular system, lymphatic system, bone, muscles, blood, the dermis, pericardium, pleura, peritoneum, urogenital tract, gonads and the adrenal cortex. See also ectoderm, endoderm.
mesothelioma a rapidly growing tumour of the pleura (commonly), pericardium or peritoneum; usually associated with asbestos exposure at least 20 years previously. Industrially related, therefore compensation usually appropriate as few are operable and the median survival post-diagnosis is about 8 months. Therapy is almost universally palliative; generally chemo- and radioresistant.
mesovarium a double fold of peritoneum that attaches the ovary to the broad ligament.
meta-analysis a statistical summary of several research studies using complex quantitative analysis of the primary data.
metabolic associated with metabolism. basal metabolic rate (BMR) the expression of basal metabolism in terms of kJ per m2 of body surface per hour.
metabolic accumulation the concentration of a substance in the body through the metabolic process, for example, iodine in the thyroid gland.
metabolism the continuous series of chemical processes in the living body by which life is maintained. Nutrients and tissues are broken down (catabolism), new substances are created for growth and rebuilding (anabolism) and energy is released in catabolism and utilized in anabolism and heat production. See also adenosine diphosphate, adenosine triphosphate, basal metabolism.
metabolite any product of or substance taking part in metabolism. An essential metabolite one that is necessary for normal metabolism, for example, vitamins.
metacarpophalangeal associated with the metacarpal bones and the phalanges.
metacarpal bones the five bones which form that part of the hand between the wrist and fingers.
metal exchange a method of silver recovery when the fixer solution passes through a base metal which is replaced by the silver and base metal ions are released into the solution which then goes to waste.
metaphysis in a long bone, the side of the epiphyseal plate which is nearest the shaft and is the site of the production of bone during childhood. See also epiphysis.
metaplasia a change from one type of tissue to another.
metastable state when a nucleus is decaying and the length of time it takes can be measured.
metastasis the secondary spread of malignant tumour cells from one part of the body to another. Either by the lymphatic route to the lymph nodes or to distant organs via the haematogenous (blood) route or can be transplanted during surgery. Most solid tumours are not curable if metastasis has occurred.
metatarsal bones the five bones of the foot between the ankle and the toes.
metatarsophalangeal associated with the metatarsus and the phalanges.
metatarsus adductus a deformity where the forefoot is deviated towards the midline of the body in relation to the hindfoot.
methicillin-resistant Staphylococcus aureus (MRSA) strains of Staphylococcus aureus that are resistant to methicillin (not used clinically) and flucloxacillin. Causes serious and sometimes fatal infections in hospitals, and patients with MRSA are increasingly encountered outside hospital. Treatment involves vancomycin or teicoplanin, or various combinations of rifampicin, sodium fusidate and ciprofloxacin. Topical mupirocin is used to eliminate nasal or skin carriage. Infection control measures that include strict adherence to hand washing, proper environmental cleaning and isolation or patient cohorting are vital in controlling MRSA. Epidemic strains (EMRSA) have developed resistance to most antibiotics except glycopeptides, i.e. vancomycin and teicoplanin.
metritis inflammation of the uterus.
metrorrhagia uterine bleeding between the menstrual periods such as after intercourse or examination.
micelle tiny globules of fat and bile salts formed during fat digestion. Fatty acids and glycerol are transported into the intestinal cells (enterocytes) in this form, leaving the bile salts behind in the lumen of the bowel.
microcephaly an abnormally small head.
microcirculation blood flow through the arterioles, capillaries and venules. Damage to these vessels is a cause of pressure ulcers.
microglial cells a type of macrophage of the central nervous system.
micrognathia failure of the development of the lower jaw forming a receding chin.
microgram (μg) one millionth of a gram.
micrometre (μg) also still called a micron. One millionth of a metre.
microorganism (microbe) a microscopic cell. Often synonymous with bacterium but includes virus, protozoon, rickettsia, chlamydia and fungus.
microprocessor an integrated circuit that can be pre-programmed to perform a variety of tasks.
microvilli microscopic projections from the free surface of cell membranes whose purpose is to increase the exposed surface of the cell for absorption, for example, intestinal epithelium.
micturating cystogram radiographic examination that can be used to investigate urinary incontinence. Following intravenous injection of a contrast agent or, more commonly, after contrast is introduced into the bladder via a urinary catheter until micturating begins. A series of radiographs are taken during the act of passing urine.
micturition (urination) passing urine.
midbrain that section of the brain that connects the cerebrum with the pons and cerebellum.
midsagittal plane see median plane.
milligram (mg) one thousandth part of a gram.
millilitre (ml) one thousandth part of a litre. Equal to a cubic centimetre.
millimetre (mm) one thousandth part of a metre.
millimole (mmol) one thousandth part of a mole.
Milwaukee brace an orthotic device used in the corrective treatment of spinal curvature (scoliosis). It applies fixed traction between the occiput and the pelvis.
MIME (Multipurpose Internet Mail Extensions) a method of sending binary objects by email.
mineralocorticoid a group of corticosteroid hormones produced by the adrenal cortex. Involved in the regulation of electrolyte and water balance. See also aldosterone.
miscarriage spontaneous loss of pregnancy before 24 completed weeks of gestation (previously referred to as abortion). See also complete miscarriage, incomplete miscarriage, inevitable miscarriage, missed miscarriage, recurrent miscarriage, septic miscarriage, spontaneous miscarriage, threatened miscarriage, tubal miscarriage.
missed abortion a condition when a dead fetus or embryo remains in the uterus for 2 months or more before 24 weeks of age.
missed miscarriage the early signs and symptoms of pregnancy disappear and the fetus dies but is not expelled for some time. See also carneous mole.
Mitchell theory theory of latent image formation states that free silver ions come near to a shallow electron trap and deepens it, while this trap is deepened it attracts another electron and a free silver ion to form a silver atom called the pre-image centre. This then dissociates into a silver ion and an electron, the silver atom must attract a second silver ion to form a latent sub-image centre, this attracts further electrons causing a build up of silver atoms which eventually destroy the crystal lattice and allows development to take place. See also Gurney Mott theory.
mitosis nuclear (and usually cell) division, in which somatic cells divide. It involves the exact replication of chromosomes, which results in two ‘daughter’ cells that are genetically identical to the cell of origin.
mitral mitre-shaped, as the valve between the left atrium and ventricle of the heart (bicuspid valve).
mitral regurgitation (incompetence) a defect in the closure of the mitral valve whereby blood tends to flow backwards into the left atrium from the left ventricle.
mitral stenosis narrowing of the mitral orifice, usually due to rheumatic fever.
mitral valvulotomy (valvotomy) an operation to correct a stenosed mitral valve.
mixing valve a method of controlling the water and temperature of a unit by mixing the hot and cold water supplies together, found in automatic film processors.
M mode motion modulation in ultrasound imaging when a linear scan is held while a time position graph of any motion builds up. Stationary parts are shown as straight lines and moving parts as oscillations, used in cardiac work to assess distances and the movement of objects.
modal dose the most frequently occurring dose value in a chart.
mode the most frequent (common) value in a series of scores. See also central tendency statistic, mean, median.
modem (MOdulator-DEModulator) a device, also known as an acoustic coupler, which allows the computer to transmit data down a conventional telephone line.
modulation transfer function (MTF) the assessment of an imaging system’s performance at different object sizes.
Mohs’ micrographic surgery a surgical technique for microscopically controlled excision usually of a malignant skin tumour.
moist gangrene death of part of the tissues of the body, occurs when venous drainage is inadequate so that the tissues are swollen with fluid.
molar tooth multi-cusped posterior grinding tooth, placed fourth and fifth from the midline in the primary dentition, and sixth, seventh and eighth in the secondary dentition. The upper molars have three roots and the lower molars have two roots.
molar pregnancy when a hydatidiform mole develops from the placental (trophoblastic) tissue of the early embryo, it is associated with raised human chorionic gonadotrophin (HCG) and may be benign or malignant.
mole one of the seven base units of the International System of Units (SI), the measurement of amount of substance which contains as many elementary particles as there are atoms in 0.012 kilograms of carbon 12. A pigmented area on the skin, usually brown, they may be flat, some are raised and occasionally have hairs growing from them, alterations in shape, colour, size, or bleeding may be indicative of malignant changes.
molecular distortion when the electron orbits are deformed relative to the atomic nucleus.
molecular weight the sum of the atomic weights of atoms in a molecule.
molecule combination of two or more atoms to form a specific chemical substance. The smallest part of a compound that can exist on its own and retain all the properties of the compound.
molluscum contagiosum an infectious condition common in infants caused by a virus. Tiny translucent papules with a central depression are formed.
molluscum fibrosum the superficial tumours of von Recklinghausen’s disease.
momentum the product of the mass and the velocity of the body.
monarticular relating to one joint.
monitor a device similar to a television, but which receives video signals directly from the computer, rather than RE-modulated signals, giving much more accurate resolution. An anglicized version of the Rush Medicus quality assurance programme for use in hospitals.
monitor photography the imaging of the video output from CT, MRI or ultrasound unit via a camera system.
monitoring sequential recording. Term usually reserved for automatic visual display of measurements such as temperature, pulse, respiration and blood pressure. In management, looking at an activity in relation to a specification or target.
monoamine oxidase an enzyme that breaks down monoamines, such as dopamine, 5-hydroxytryptamine (serotonin) and noradrenaline (norepinephrine) in the brain.
monoarthritis arthritis affecting a single joint.
monochromatic emulsions are film emulsions that are unable to detect any colours apart from the blue part of the visible spectrum, tend to be used with calcium tungstate screens.
monocyte a phagocytic white blood cell. It migrates to the tissues to become a macrophage.
monocyte–macrophage system (reticuloendothelial system) a widely disseminated system of specialized phagocytes in the bone marrow, liver, lymph nodes, spleen, and other tissues. Functions include blood cell and haemoglobin breakdown, formation of bile pigments, removal of cell breakdown products and as part of the defences against microorganisms.
mononuclear describes a cell with a single nucleus such as a monocyte.
mononucleosis an increase in the number of circulating monocytes (mononuclear cells) in the blood.
monoplegia paralysis of only one limb.
mons veneris the eminence formed by the pad of fat which lies over the pubic bone in the female.
Monteggia fracture-dislocation fracture of the ulna associated with dislocation of the radial head.
morbidity the state of being diseased. standardized morbidity ratio (SMBR) the degree of self-reported limiting long-term illness indirectly standardized for variations in age and gender.
mortality number or frequency of deaths. mortality rate the death rate; the ratio of the total number of deaths to the total population. There are several specialized mortality rates and ratios including: childhood mortality (children aged 1–14 years), infant mortality (first year of life), maternal mortality (deaths associated with pregnancy and childbirth), neonatal mortality (first four weeks of life), perinatal mortality (stillbirths plus deaths in the first week of life), stillbirth rate. See also standardized mortality rate, standardized mortality ratio.
mortality rate the number of deaths per 1000 or other unit, of the population occurring annularly from a certain disease or condition.
Morton’s neuroma a benign tumour of the nerve cells, which typically occurs between the third and fourth toes, characterized by a thickening of the tissue that surrounds the digital nerve.
mother board the main circuit board in a computer.
motile able to move spontaneously.
motor agraphia inability to express thoughts in writing, usually due to left precentral cerebral lesions.
motor neuron the nerve cell (or neuron) that supplies the electrical input to muscles. This can be either the lower motor neuron that directly innervates the muscles and originates in the brainstem and spinal cord or the upper motor neuron that originates from the motor cortex part of the brain and innervates the lower motor neuron.
motor neuron disease a group of neurodegenerative disorders affecting the nerves that supply the muscles leading to weakness and eventually death.
motor skill the ability to perform a particular task which involves significant movement of one or more joints of the body, for example, as part of a sports skill.
motor unit a lower motor neuron and all of the muscle fibres it innervates.
mottle the granular appearance in areas of even density on a radiographic image. See also film grain, quantum mottle, structure mottle.
mouse a device for making the computer more ‘user friendly’. Instead of accessing the computer via a keypad, the mouse is used by rolling the device across a desktop, this moves a cursor to icon displays on the screen.
Mousseau-Barbin Tube a plastic intubation tube which is pulled through an oesophageal tumour by the use of a string or guidewire and is attached to the stomach with a suture. Used to maintain a free passage of food and fluid.
movement unsharpness blurring on an image due to movement of the equipment or the person which can be either voluntary or involuntary, for example heart beat.
mucin glycoprotein constituent of mucus.
mucinolysis breakdown of mucin.
mucocutaneous associated with mucous membrane and skin. mucocutaneous lymph node syndrome (MLNS) a disease affecting mainly babies and children. It is an inflammatory vasculitis characterized by fever, dry lips, red mouth and strawberry-like tongue. There is a rash on the trunk, and erythema with desquamation affecting the extremities. There is cervical lymphadenopathy, polymorphonuclear leucocytosis and a raised ESR. Also known as Kawasaki disease.
mucositis inflammation of the mucous membrane such as the lining of the mouth and throat.
mucous associated with or containing mucus, for example, mucous membrane.
mucous membrane contains glands which secrete mucus. It lines the cavities and passages that communicate with the exterior of the body.
mucous polyp a growth (adenoma) of mucous membrane which becomes pedunculated.
mucus viscid secretion of mucous glands.
multiaxial joints a joint which has movement round more than two axes, for example, the hip joint.
multicellular having many cells.
multi-leaf collimation (MLC) a method of customized beam shaping in radiotherapy without the use of lead blocks.
multilobular possessing many lobes.
multiplanar reconstruction in CT scanning, the formation of an image in any plane from the acquired axial data set.
multiple myeloma a form of bone marrow cancer resulting from the accumulation of malignant plasma cells.
multisection CT a CT scanner using multiple rows of detectors to enable several slices to be obtained at the same time thus increasing the speed of image acquisition.
multi-slice spiral CT scanner CT scanners that collect up to 64 slices (2006) of data during a spiral scan.
multivariate statistics analysis of three or more variables simultane-ously. Used to clarify the association of two variables after allowing for other variables.
Munchausen syndrome a condition characterized by frequent requests for treatment or hospitalization for a symptomatic but imaginary illness. The patient may logically and convincingly present the symptoms and history of a real disease.
Munchausen syndrome by proxy (MSP) a condition when a parent or carer frequently fabricates or induces illness in a child with the intent of keeping them in hospital or in contact with doctors.
mural associated with the wall of a structure.
murmur (bruit) abnormal sound heard on auscultation of heart or great vessels, presystolic murmur characteristic of mitral stenosis.
muscle one of the four basic tissues. Composed of specialized contractile tissue formed from excitable cells. There are three types. cardiac muscle makes up the middle wall of the heart; it is involuntary, striated and innervated by autonomic nerves. skeletal muscle is voluntary, striated and innervated by the peripheral nerves of the central nervous system. red muscle, white muscle. smooth or involuntary muscle is non-striated and involuntary and is innervated by the autonomic nerves.
muscle fibre a muscle cell. Skeletal muscle fibres are classified according to type of action and metabolism: muscle fibre type I (slow twitch) fibres are characterized by relatively slow contraction time and high aerobic capacity. They are well suited to long duration activities. muscle fibre type IIa (fast oxidative glycolytic) fibres that are classed as fast-twitch but have some of the aerobic characteristics of slow-twitch fibres. muscle fibre type IIb (fast twitch glycolytic) fibres characterized by very fast contraction time and high anaerobic capacity. muscle fibre type FT type C fibres are thought to function at the extreme end of the anaerobic metabolic range.
musculature the muscular system, or any part of it.
musculocutaneous associated with muscle and skin.
musculoskeletal associated with the muscular and skeletal systems.
mutation a gene or chromosome alteration that results in genetic changes that alter the characteristics of the affected cell. The change is transmitted through succeeding generations. Mutations may be spontaneous, or induced by agents such as ionizing radiation that alter the chromosomal DNA.
mutual induction when a changing current is passed through one conductor and produces a changing magnetic field, if another conductor is placed in the field an electromotive force will be formed in the second conductor.
mycosis fungoides a malignant skin tumour from T-lymphocytes.
mycotoxins poisons produced from fungi.
myelin the white, fatty substance that covers and insulates some nerve fibres. See also white matter.
myelitis inflammation of the spinal cord.
myeloablative describes the therapy (for example, radiotherapy, chemotherapy) given intentionally to completely ‘knock out’ the bone marrow. Used in leukaemia and often precedes a bone marrow transplant.
myeloblasts the early precursor cells of the polymorphonuclear granulocytic white blood cells.
myelocele an accompaniment of spina bifida wherein development of the spinal cord itself has been arrested, and the central canal of the cord opens on the skin surface discharging cerebrospinal fluid.
myelocytes precursor cells of polymorphonuclear granulocytic white blood cells.
myelography radiographic examination of the spinal canal by injection of a contrast agent into the subarachnoid space. Superseded by CT and MRI.
myeloid associated with the bone marrow. Associated with the granulocyte precursor cells in the bone marrow. See also leukaemia.
myelomatosis (multiple myeloma) a tumour of the bone marrow.
myelopathy disease of the spinal cord. Can be a serious complication of cervical spondylosis.
myeloproliferative disorders condition where there is proliferation of one or more of the cellular components of the bone marrow such as myelofibrosis, primary proliferative polycythaemia and thrombocythaemia. See also leukaemia.
myelosclerosis a generalized increase in bone density.
myocardial infarction death of a part of the myocardium (heart muscle) from deprivation of blood following occlusion (blockage) of a coronary artery, for example from thrombosis. The patient experiences a ‘heart attack’ with sudden intense chest pain which may radiate to arms and lower jaw. Management includes: aspirin, thrombolytic therapy, pain relief, antiemetics, oxygen therapy, bed rest, observations including continuous ECG and later mobilization and cardiac rehabilitation. Patients should be cared for in a coronary care unit for 12–24 hours because of the risk of life-threatening arrhythmias such as ventricular fibrillation, and the need for skilled staff to monitor the effects of thrombolytic therapy. See also angina pectoris, cardiac enzymes, coronary heart disease.
myocardium the middle layer of the heart wall. Formed from highly specialized cardiac muscle. See also muscle.
myofibri bundle of fibres contained in a muscle fibre.
myogenic originating in or starting from muscle.
myoglobin (myohaemoglobin) a haem-protein molecule of skeletal muscle. It is involved with the oxygen released by the red blood cells, which it stores and transports to muscle cell mitochondria where it is used to produce energy. Myoglobin escapes from damaged muscle and appears in the urine in ‘crush syndrome’.
myoma a tumour of muscle tissue.
myometrium the specialized muscular wall of the uterus.
myoneural associated with muscle and nerve.
myosarcoma a malignant tumour derived from muscle.
myositis inflammation of muscle tissue.
myotome the muscles supplied by a single spinal nerve.
myxoedema a condition caused by hypothyroidism, characterized by the swelling of the hands, face, feet and periorbital tissue.
myxoma a connective tissue tumour composed largely of mucoid material.
myxosarcoma a malignant tumour of connective tissue with a soft, mucoid consistency.
