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.
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