S
saccular aneurysm a dilation of only a part of the circumference of an artery.
sacculation appearance of several saccules.
saccule a minute sac. A small fluid-filled sac in the membranous labyrinth of the inner ear. See also utricle.
sacral associated with the sacrum.
sacroanterior describes the position of the breech in the pelvis when the fetal sacrum is in the anterior part of the maternal pelvis.
sacrococcygeal associated with the sacrum and the coccyx.
sacroiliac associated with the sacrum and the ilium.
sacroiliitis inflammation of a sacroiliac joint. Involvement of both joints characterizes conditions such as ankylosing spondylitis, Reiter’s syndrome and psoriatic arthritis.
sacrolumbar associated with the sacrum and the loins.
sacroposterior describes the position of the breech in the pelvis when the fetal sacrum is in the posterior part of the maternal pelvis.
sacrum the triangular bone lying between the fifth lumbar vertebra and the coccyx. It consists of five vertebrae fused together, and it articulates on each side with the innominate bones of the pelvis, forming the sacroiliac joints.
saddle joints synovial joints that allow flexion, extension, abduction, adduction and some axial rotation, for example, the first carpometacarpal joint.
safelights lights covered with optical filters to enable staff to work in a darkened room without the film emulsion being affected by the light.
sagittal plane the anteroposterior plane of the body.
sagittal sinuses venous channels (sinuses) that drain blood from the brain.
sagittal suture the immovable joint between the two parietal bones.
saliva fluid secreted by the salivary glands. It contains water, mucus and salivary amylase.
salivary associated with saliva.
salivary calculus a stone formed in the salivary ducts.
salivary glands the glands which secrete saliva, i.e. the parotid, submandibular (submaxillary) and sublingual glands.
salpingitis acute or chronic inflammation of the uterine (fallopian) tubes. See also hydrosalpinx.
salpingogram radiological examination of tubal patency by retrograde introduction of contrast agent into the uterus and along the uterine tubes. Being superseded by ultrasound examination.
salpinx a tube, especially the uterine (fallopian) tube or the eustachian tube.
salvage therapy treatment given to a site where previous treatments have failed and the disease has recurred.
sample the particular subset chosen from a population.
saphenous apparent; manifest. The name given to two superficial veins in the leg, the great (long) and the small (short), and to the nerves accompanying them.
sarcoidosis a granulomatous disease of unknown aetiology in which histological appearances resemble tuberculosis. May affect any organ of the body, but most commonly presents as a condition of the skin, lymph nodes or the bones of the hand.
sarcoma malignant tumour of connective tissue, muscle, nerve, bone (osteosarcoma), usually first seen as a painless swelling. Treatment options include surgery, radiotherapy and chemotherapy usually in combination. See also Ewing’s tumour.
sarcomatosis a condition in which sarcomata are widely spread throughout the body.
sartorius the ‘tailor’s muscle’ of the thigh, since it flexes one leg over the other.
saturated fatty acids those fatty acids having no double bonds in their structure. Most originate from animal sources. High dietary intake is associated with arterial disease.
saturation in magnetic resonance imaging, a non-equilibrium state where equal numbers of spins are aligned with and against the magnetic field. This occurs immediately following a 90° radio frequency pulse with the longitudinal magnetization aligned in the transverse plane.
saturation analysis a technique to determine the concentration of a hormone or chemical in a small sample of blood or urine.
scald a burn caused by hot liquid or vapour.
scalp the hair-bearing skin which covers the cranium.
scalp cooling technique used to minimize or prevent alopecia associated with the administration of cytotoxic drugs such as doxorubicin.
scan an image built up by movement along or across the object scanned, either of the detector or of the imaging agent, to achieve complete coverage, for example, ultrasound scan.
scan delay the time between the start of the contrast agent injection and the onset of CT scanning.
scan limits start and end points of data acquisition.
scanners a device which enables documents, pictures, etc. to be held as a digital image.
scan time the time taken for data acquisition.
scaphoid boat-shaped, as a bone of the tarsus and carpus.
scaphoid fracture commonly occurs as a result of compression of the scaphoid, when there is a fall onto the outstretched hand in hyperextension. Commonly, if the fracture involves the proximal third of the scaphoid, there is a high risk of non-union and threat of avascular necrosis, due to the poor blood supply.
scapula the shoulder blade – a large, flat triangular bone.
scattered when photons hit an object and are deflected from their original path, they may or may not loose energy as a result.
scattergram in statistics, where two variables are represented by a single plot against an x and y axis.
scattering cross section the area of the patient, measured in cm2 or barns, that lies in the X-ray field, the larger the area the higher the probability that the radiation will interact with the tissue.
Scheuermann’s disease osteochondritis of the spine affecting the ring epiphyses of the vertebral bodies. Occurs in adolescents.
Schilling test estimation of absorption of radioactive vitamin B12 for investigation of the cause of vitamin B12 deficiency.
Schlatter’s disease (Osgood–Schlatter disease) osteochondritis of the tibial tubercle.
Schlemm’s canal a channel in the inner part of the sclera, close to its junction with the cornea. It drains excess aqueous humour and maintains normal intraocular pressure.
Schmorl’s nodes erosion of the bodies of the vertebrae, due to pressure from the nucleus pulposus. Narrowing of the disc space may occur.
Schottky defect the result of removing an atom completely from a structure.
Schwann cells neuroglial cells of the peripheral nervous system. They are concerned with the production of the myelin sheath that surrounds some nerve fibres.
schwannoma a benign, encapsulated tumour arising from the neurilemma of the peripheral, cranial or autonomic nerves.
sciatica entrapment of the sciatic nerve during its course from the lower back to the leg causing pain which runs down the back of the leg to the heel and which can lead on to weakness such as foot drop and sensory loss in the lower leg.
scintillation counters a device used to detect small quantities of X or γ radiation from a patient using either a detector in crystalline form or as a liquid scintillation material. Gamma rays from the patient strike the detector and are converted to photons, which pass through a photomultiplier producing a pulsed voltage corresponding to the original radioactivity.
scintillation detector a device for measuring radiation emitted from a patient using a sodium iodide crystal and a photomultiplier tube.
scintillation efficiency the percentage of quantal energy stopped by a phosphor which is changed to useful light photons.
scintillography (scintiscanning) visual recording of radioactivity over selected areas after administration of suitable radioisotope.
sclera the ‘white’ of the eye, the opaque bluish-white fibrous outer coat of the eyeball covering the posterior five-sixths; it merges into the cornea at the front.
sclerocorneal associated with the sclera and the cornea, as the circular junction of these two structures.
sclerodactyly deformity affecting the fingers. There is fixed, partial flexion of the fingers with subcutaneous calcification. Ulceration of the finger tips may occur. Associated with scleroderma.
scoliosis lateral curvature of the spine, which can be congenital or acquired and is due to abnormality of the vertebrae, muscles and nerves.
score in statistics, the total number of responses.
scotopic vision dark-adapted vision.
screen asymmetry the production of a pair of intensifying screens when the back screen is slightly faster than the front to compensate for any absorption that may have taken place which reduces the amount of energy reaching the screen.
screen contact test a perforated metal sheet is placed on a radiographic cassette and an exposure of 55 kV at a 2-metre focus-film distance, the film is processed and when viewed at 4 metres any dark areas indicate loss of screen film contact.
screen unsharpness blurring of an image due to the phosphor size and thickness, the presence of an absorption/reflective layer or if a dye is used in the intensifying screen construction. It can also be influenced by poor screen/film contact.
screening a preventive measure to identify potential or incipient disease at an early stage when it may be more easily treated. It is carried out in a variety of settings, including primary care, hospitals, and clinics for antenatal care, and well babies, well men and well women clinics. Screening checks include: mammography, cervical cytology, blood pressure checks, checks for diabetes mellitus, faecal occult blood, prostatic specific antigen test for prostate cancer, ultrasound and triple blood test during pregnancy. The screening process may cause anxiety even when no abnormality is found (negative result).
scrolling the movement of text or data on the display screen of a computer.
scrotum the pouch of pigmented skin in the male which contains the testes.
scurvy a lack of vitamin C, radiographically the periosteum is raised and osteoporosis is present.
search engine a database of key words that internet users can access to find information on the web.
sebum the secretion of the sebaceous glands; it contains fatty acids, cholesterol and dead cells.
secondary care health care indirectly accessed via primary care. Usually refers to specialist medical and surgical services provided in hospitals.
secondary collimation a method of varying the radiation field size to suit individual treatment areas or diagnostic examinations. See also applicators.
secondary haemorrhage occurs about 10 days after an injury and is always due to sepsis.
secondary radiation the ejection of electrons from a substance after it has been bombarded with charged particles of sufficient energy.
secondary radiation barrier a barrier that protects from the effects of scattered radiation or leakage from the X-ray tube or housing. See also primary radiation barrier.
secondary solute used in liquid scintillation counting to absorb photons emitted by the primary solute and re-emit them as photons of a longer wavelength therefore increasing the efficiency of the detection by photomultiplier tubes.
secondary tumour refers to a primary cancer that has spread to other distant sites in the body, such as colorectal cancer spreading to the liver. See also metastasis.
secretin a hormone produced in the duodenal mucosa, which causes secretion of pancreatic juice, and with other regulatory peptides inhibits gastric secretion and motility.
secretion a fluid or substance, formed or concentrated in a gland and passed into the gastrointestinal tract, the blood or to the exterior.
secretory involved in the process of secretion: describes a gland which secretes.
sector probe an ultrasound probe with a small footprint used for intercostal and cardiac imaging.
sedation the production of a state of lessened functional activity.
sedative an agent which reduces functional activity by its action on the nervous system. See also anxiolytic.
Seldinger catheter a special catheter and guide wire for insertion into an artery, along which it is passed to, for example, the heart.
selection unit remote-controlled unit for placing, for example, radioactive caesium-137 into body cavities.
selectivity the ability of a developing agent to differentiate between exposed silver halide and unexposed silver halide and therefore only converting the exposed crystals to metallic silver. An agent which has no effect on either the metallic silver in the developed image or the gelatine in which it is suspended.
Selectron a proprietary device which stores sealed radioactive sources of caesium, iridium or cobalt in a shielded container in readiness for intracavitary treatment in the uterus, cervix or vagina. In recent years extended to other body sites such as bronchus and oesophagus.
self induction occurs when a current-carrying conductor induces a magnetic field in itself and the current changes.
sella turcica pituitary fossa located on sphenoid bone.
semen seminal fluid. Fluid ejaculated during coitus. It comprises spermatozoa from the testes and the secretions from the prostate gland, seminal vesicles and bulbourethral glands.
semicircular canals three fluid-filled canals contained within the bony labyrinth of the internal ear. Orientated in the three planes of space they are part of the vestibular apparatus concerned with dynamic equilibrium and balance.
semiconductor a solid device that contains a conduction band and valence band and allows current to flow in one direction only. Intrinsic semiconductors are chemically pure and have a perfect regulation of atoms in the crystal lattice, extrinsic semiconductors have impurities added to improve electrical conductivity. See also diodes and triodes.
semilunar shaped like a crescent or half moon.
semilunar cartilages the crescentic interarticular cartilages of the knee joint (menisci).
seminal associated with semen.
seminal vesicle two tubular accessory glands behind the male bladder. They produce a thick alkaline fluid, which forms some 60% of semen volume.
seminiferous carrying or producing semen such as the seminiferous tubules, the site of spermatogenesis.
seminiferous tubule coiled tube in the testis for carrying semen.
seminoma a neoplasm of the testis that is highly radiosensitive; subtype of germ cell tumour.
semipermeable describes a membrane which is permeable to some substances in solutions, but not to others.
senescence normal physical and mental changes in increasing age.
sensible perspiration the term used when there are visible drops of sweat on the skin.
sensitivity the ability of a detector, for example a film or intensifying screen, to register very small quantities of radiation, the more sensitive the detector the wider the range of intensities can be detected. The counting efficiency of a gamma camera in counts per second per megabecqueral. The ability of a test to accurately identify a condition or disease in affected individuals, such as mammography screening for breast cancer.
sensitometer an exposure device for printing a pre-determined image onto a film.
sensitometry a method of measuring blackening on a film, plotting a characteristic curve, producing measurements from the curve and therefore comparing different films or film screen combinations. See also characteristic curve.
sensory associated with sensation. sensory nerves those which transmit impulses from peripheral receptors to the brain and spinal cord.
sensory agraphia inability to interpret the written word, due to lesions in the posterior part of the left parieto-occipital region.
sentinel node biopsy (SNB) procedure used in staging (mainly) breast cancer and melanoma where (blue) dye is injected at the primary tumour site and traced to the nearest nodal basin where the first node involved with tumour will accumulate the dye; resection of that node may improve the cure rate.
sepsis infection of the body by pus-forming bacteria.
septal thickness the thickness of the lead between the holes in a collimator of a gamma camera.
septic abortion see miscarriage.
septicaemia the multiplication of living bacteria in the bloodstream causing infection.
septic arthritis arthritis caused by infection in the joint.
septic miscarriage one associated with uterine infection.
septic shock shock caused by infection.
septum a partition between two cavities, e.g. between the nasal cavities.
sequestering agent softens hard water, in developer EDTA sodium salt is used to prevent precipitation of calcium and magnesium salts onto the surface of the film.
sequestrum a piece of dead bone which separates from the healthy bone but remains within the tissues.
serial port an external socket on older computers used to plug in a mouse or a modem.
serosa a serous membrane, e.g. the peritoneal covering of the abdominal viscera.
serotonin a monoamine formed from tryptophan (amino acid). Liberated by blood platelets after injury and found in high concentrations in the CNS and gastrointestinal tract. It is a vasoconstrictor, inhibits gastric secretion, stimulates smooth muscle and acts as a central neurotransmitter. It is also involved in pain transmission and perception, and sleep–wake cycles. Also called 5-hydroxytryptamine (5-HT).
serous membrane a lubricating membrane lining the closed cavities, and reflected over their enclosed organs.
server a central computer in a network that provides services and files to other computers, therefore enabling computers to communicate with each other.
service provider an organization that offers connections to the internet.
sesamoid bone a small area of bone formation in muscle tendons such as the patella.
set-up the accurate positioning of a patient in preparation for the delivery of radiotherapy treatment.
Sever’s disease (calcaneal epiphysitis) occurs in children and is caused by damage to the bone–cartilage layer in the heel resulting in pain.
sexually acquired reactive arthritis (SARA, Reiter’s disease) often caused by infection with Chlamydia trachomatis, but intestinal infections can also be the triggering event. Arthritis occurs together with conjunctivitis or uveitis, urethritis (or cervicitis in women), and sometimes psoriasis. See also reactive arthritis.
S°zary syndrome a leukaemic form of mycosis fungoides.
shaded surface display algorithms the generation of a three-dimensional outline of the surface of a patient or object from a set of stored images.
shadow mask a thin, perforated metal plate found in colour monitors to accurately focus the electron beam onto the phosphor and therefore improve image quality.
shadow tray a sheet of Perspex or perforated aluminium sheet in the form of a tray or table to hold shielding blocks during radiotherapy.
shared segment part of a computer network that is used by several nodes.
sharps a term used to define items that could cause harm to a person handling them, including needles, scalpels, broken ampoules, cannulae.
shelf operation an operation to deepen the acetabulum in developmental dysplasia of the hip, involving the use of a bone graft. Performed at 7–8 years, after failure of conservative treatment.
shell body temperature that outside the body core. Varies between sites, for example, 35°C at the forehead and 20°C in the feet.
shells see beam direction shells, patient shell.
Shenton’s line a line drawn along the medial border of the neck of femur and the superior border of the obturator foramen forming an even, continuous arc. If this arc is disrupted or displaced it indicates a fractured neck of femur or a hip dislocation.
shield the shield forms the external casing of an X-ray tube.
shielding blocks heavy metal blocks placed on a shadow tray to protect parts of the body that are in the beam of radiation but do not require treatment. They are a means of shaping the beam to individual volumes. See also lead shielding, MCP blocks.
shock a condition when the cardiovascular system is incapable of delivering oxygen and nutrients to the cells. Causes include haemorrhage and dehydration (hypovolaemic shock), heart failure (cardiogenic shock), infection (septic shock) and allergic reaction (anaphylactic shock). See also anaphylactic shock, electric shock, cardiogenic shock, hypovolemic shock, vasovagal shock, medical shock, neurogenic shock, septic shock.
short bone bones that are cuboidal in shape and are formed by cancellous bone with a thin covering of compact bone, for example the carpal bones.
shoulder a synovial ball and socket joint formed by the glenoid cavity of the scapula and the head of humerus. In photography the area of the characteristic curve where the film’s reaction to exposure slows. See also characteristic curve.
shoulder girdle formed by the clavicle and scapula on either side.
shrinking field technique phased treatments, in radiotherapy, where a larger volume is treated first and then the volume is shrunk to allow higher doses to be delivered to the target volume while ensuring that tolerance doses to critical structures is not exceeded.
sialogram radiographic image of the salivary glands and ducts, after injection of an opaque contrast agent.
sialography the radiographic examination of the salivary glands following the direct injection of a contrast agent.
sialolith a stone in a salivary gland or duct.
sickle cell disease an inherited blood disorder.
side-effect any physiological change other than the wanted one from a drug, e.g. oral iron causes the side-effect of black faeces. Also covers undesirable drug reactions. Some are predictable, being the result of a known metabolic action of the drug, e.g. hair loss with cytotoxic drugs. Unpredictable reactions can be: (a) immediate: anaphylaxis, angio-oedema, (b) erythematous: all forms of erythema, including nodosum and multiforme and purpuric rashes, (c) cellular eczematous rashes and contact dermatitis, (d) specific, e.g. light-sensitive eruptions with griseofulvin (antifungal).
siderosis excess of iron in the blood or tissues. Inhalation of iron oxide into the lungs can cause one form of pneumoconiosis.
sievert (Sv) the SI unit (International System of Units) for radiation dose equivalent. A measure of total biological effects of a beam of radiation. It has replaced the rem.
sighing long, slow inspiration followed by rapid expiration.
sigmoid shaped like the letter S.
sigmoid flexure the S-shaped bend at the lower end of the descending colon. It is continuous with the rectum below.
sigmoidoscopy the visual examination of the rectum and sigmoid colon using an instrument which contains a light.
sign test a statistical test used to compare two sets of results using a normal distribution table and a sign test table; the results must be equal to or less than the results on the tables to be significant.
signal in imaging it is the information required from the system, for example a radiograph, and the minimum-sized object that can be seen by a system.
signal gain the electrical signal for a specific intensity of absorbed radiation.
signal-to-noise ratio the ratio of the signal width to the unwanted energy (noise). In magnetic resonance imaging it can be improved by (a) increasing the number of signal excitations, (b) increasing the field of view, or (c) increasing the strength of the main magnetic field used.
significance the numerical probability that the results of an experiment are meaningful.
silicone a water-repellent compound. Used in dressings, as sheets, foams and gels, where it fits exactly the contours of the granulating wound to provide an ideal environment for wound healing. Also used as implants in breast reconstruction.
silicosis a form of pneumoconiosis or industrial dust disease found in metal grinders, stone-workers, etc.
silver bromide a chemical used as part of a film emulsion and has a peak sensitivity of 430 nm and is not sensitive to wavelengths above 480 nm.
silver collection used fixing solution is stored and then collected in bulk along with unwanted radiographs to enable the silver to be commercially reclaimed.
silver estimating papers special papers used to measure the quantity of silver remaining in a solution.
silver halides silver compounds that have a natural spectral sensitivity in the blue part of the visible spectrum. See also silver bromide.
silver recovery methods of recovering silver from either the fixer solution or unwanted radiographs. See also silver collection, metal exchange, electrolytic silver recovery.
simple fracture a break in bone continuity where there is no break in the skin surface.
simulator used in radiotherapy treatment localization and planning. This is a specialized unit housing a diagnostic X-ray tube to identify the treatment beam–patient geometry by using an image intensifier, an isocentric therapy unit and a collimation unit.
single photon emission computed tomography (SPECT) a specialist gamma camera which rotates round the patient and a number of two-dimensional images are taken and stored on a computer. See also positron-emission tomography.
sinoatrial node see sinus node.
sinus a hollow or cavity within a bone, especially the nasal air sinuses. A channel containing blood, especially venous blood, e.g. the sinuses of the brain. Any abnormal blind tract or channel opening onto the skin or a mucous surface.
sinus arrhythmia an increase of heart rate on inspiration, decrease on expiration.
sinusitis inflammation of a sinus, used exclusively for the paranasal sinuses.
sinus node (sinoatrial) the pacemaker of the heart. Part of the specialized tissue that forms the conducting system of the heart. It is situated at the junction of the superior vena cava and the right atrium. It initiates the wave of cardiac contraction. See also pacemaker.
sinusoid a dilated channel into which arterioles or veins open in some organs, e.g. liver, and which act in place of the usual capillaries.
sinus rhythm normal rhythm of the heart.
SIR (Serial Infra Red) a wireless communication system for computers.
SI unit abbreviation for the Syst°me International d’Unit°s, the French name for the International System of Units. (See figures on p. 346).
skeleton the bony framework of the body, supporting and protecting the soft tissues and organs and acting as attachments for muscles. See also appendicular skeleton, axial skeleton.
Skene’s glands two small glands at the entrance to the female urethra; the lesser vestibular or paraurethral glands.
skewed distribution a statistical term that describes any distribution of scores where there are a greater number of values on one side of the mean than the other, i.e. not symmetrical. See also normal distribution curve.
| Quantity | Unit of measurement | Symbol |
|---|---|---|
| Length | metre | m |
| Mass | kilogram | kg |
| Luminous intensity | candela | cd |
| Electric current | ampere | A |
| Amount of substance | mole | mol |
| Temperature | kelvin | K |
| Time | second | s |
a From Principles of radiological physics, 3rd edn, 1996, D T Graham, Churchill Livingstone, Edinburgh, with permission.
skill mix the level, range and variety of skills of the staff in a department, unit or team which is needed to meet the organizational outcomes.
skin the tissue which forms the outer covering of the body; it consists of two layers, the outer epidermis (cuticle), dermis (true skin) and the appendages; nails, glands and hair.
skin fold thickness an anthropometric measurement used as part of nutritional assessment.
skin shedding skin is continually shedding its outer keratinized cells as scales. As the skin has a natural bacterial flora, the scales are a potential source of infection for susceptible patients. See also psoriasis.
skin-sparing effect seen in megavoltage radiotherapy treatment machines where the maximum radiation dose is delivered below the skin surface.
skull the bony framework of the head, the face and cranium.
slice a single, reconstructed CT image.
Position of the bones of the skull (anterior aspect).
From Bones and joints, 4th edn, Chris Gunn, 2002, Churchill Livingstone, Edinburgh, with permission.
Position of the bones of the skull (lateral aspect).
From Bones and joints, 4th edn, Chris Gunn, 2002, Churchill Livingstone, Edinburgh, with permission.
Position of the bones of the skull (cranial cavity).
From Bones and joints, 4th edn, Chris Gunn, 2002, Churchill Livingstone, Edinburgh, with permission.
slice interval in CT scanning, the distance between reconstructed slices.
slice thickness in modern CT scanners, reconstructed slice thickness can be selected to provide various slice thicknesses from a single data acquisition.
slip ring equipment to allow electrical power to be transferred from a stationary power source onto a continuously moving gantry to allow continuous motion; used in spiral or helical CT scanning.
slipped disc prolapsed intervertebral disc. See also prolapse of an intervertebral disc.
slipped epiphysis displacement of an epiphysis, especially the upper femoral one. See also epiphysis.
slough septic tissue which becomes necrosed and separates from the healthy tissue.
small bowel enema the examination of the small bowel by introducing barium sulphate via a nasogastric tube, directly into the duodenum or the first part of the jejunum.
small for dates small for gestational age.
small for gestational age (SGA) babies who weigh less than expected for a given gestational age. They are either constitutionally small or suffer from growth restriction. See also low birthweight.
Smith’s fracture a fracture of the lower end of the radius and ulna with forward displacement of the radius. See also Colles’ fracture.
Smith–Petersen nail a trifin, cannulated metal nail used to provide internal fixation for intracapsular fractures of the femoral neck.
‘smudge’ cells cells that have been ruptured when making a blood film.
snapping hip syndrome a snapping sensation either heard or felt in the hip during movement of the joint. The nature of the signs and symptoms will indicate whether the structure at fault is more likely to be the iliotibial band or the iliopsoas tendon.
sodium (Na) metallic element. A major extracellular cation concerned with the composition of fluid compartments and neuromuscular function.
sodium bicarbonate (sodium hydrogen carbonate) acts as a buffer in the blood. Administered intravenously to correct metabolic acidosis.
sodium chloride often used in intravenous fluids to replace fluids and correct electrolyte levels.
sodium citrate used as an in vitro anticoagulant, for example for stored blood.
sodium hydroxide a developer accelerator.
sodium hypochlorite a powerful disinfectant used, in suitable dilutions, in many situations, such as dealing with environmental contamination with blood and other body fluids.
sodium pump an active transport mechanism (needing ATP) that pumps sodium ions through semipermeable cell membranes.
sodium sulphite a fixer preservative.
soft palate situated at the posterior end of the palate and consisting of muscle covered by mucous membrane.
soft rollers part of the film transport system in an automatic film processor and are found where films crossover into another section and squeeze any excess liquid out of the film; they are made of a neoprene-type substance.
software the programs run by the computer.
solar keratosis a warty skin lesion due to sun exposure which may progress to cancer.
solar plexus a large network of sympathetic (autonomic) nerve ganglia and fibres in the upper abdomen. It supplies the abdominal organs.
solar plexus punch a blow to the abdomen that results in an immediate inability to breathe freely.
solarization when an increase in exposure results in a decrease in density on a film and therefore a reverse image can be obtained. See also characteristic curve.
solenoid consists of several coils of wire joined together to produce magnetic lines of force. If soft iron is placed inside the loops of wire it becomes magnetized.
solid state radiation detector a silicon diode used to measure the activity of electron beams or megavoltage photon beams.
solute substance dissolved in a solvent.
solution a fluid that contains a dissolved substance or substances. saturated solution one in which the maximum amount of a particular substance is dissolved.
solvent an agent that is capable of dissolving other substances (solutes). The component of a solution that is present in excess. In photography used to dilute chemicals for example when making up developer, developer replenisher and fixer; the solvent used is water.
solvent misuse the practice of inhaling volatile substances, such as those in some adhesives, solvents and fuels, to produce euphoria and intoxication. Characterized by odour on clothes and hair, redness and blistering around the nose and mouth, and behaviour changes. Dependence, local damage to the nasal mucosa and organ damage, e.g. the brain, may result. Death may be caused by asphyxia or toxicity. See also drug misuse.
somatic relating to the body such as somatic cells (body cells), as distinct from the gametes.
somatic nerves nerves controlling the function of voluntary, skeletal muscle.
somatostatin (growth hormone release-inhibiting hormone, GH-RIH) a peptide found in the brain where it is a nerotransmitter, the gastrointestinal tract and the pancreas.
somatostatin receptors are found in the pituitary, pancreas, upper gastrointestinal tract, small cell lung cancer, tumours of the ovary, cervix, endometrium, breast, kidney, larynx, paranasal sinus, salivary glands, some skin tumours and tumours in the salivary glands. They are useful in imaging a variety of tumours.
somatotrophin see growth hormone.
somnolence syndrome periods of drowsiness, lethargy, loss of appetite and irritability in children following radiotherapy treatment to the head.
sonograph graphic record of sound waves.
sonography the means by which a sonograph is recorded and interpreted.
sound the result of mechanical energy travelling through matter as a wave, producing alternating compression and rarefaction resulting in vibration.
source isolation is used for patients who are sources of microorganisms that may be transmitted from them to infect others. See also containment isolation, protective isolation.
source organ an organ where radioactivity is accumulated and therefore irradiates associated organs.
source stick protocol the instructions to be followed if a machine housing a radioactive source remains in the ‘beam on’ position at the end of the planned exposure, i.e. the beam does not terminate.
Souttar tube an intubation tube which comprises flexible metal coils; the tube is pushed through an oesophageal tumour to enable the free passage of food and fluid.
spam unrequested email, usually advertising products or services.
spasticity marked rigidity of muscles.
spatial divided into partitions.
spatial detail see spatial resolution.
spatial distortion when a gamma camera does not accurately distinguish between an object and its surroundings.
spatial filtering a method of improving an electronic image by modifying the pixel values that surround the area.
spatial frequency the change in brightness value of a region of an electronic image per unit distance. If an area has low spatial frequency there is little change in brightness over distance but with high spatial values there can be a large change in brightness over a small distance.
spatial resolution the smallest distance between two objects that can be visually seen on an imaging system.
specific activity the ratio per unit mass of radioactive to non-radioactive atoms in an element.
specific dynamic action (SDA) the increase in body temperature and metabolism that occurs when energy is used in the assimilation of ingested food. Protein foods in particular cause a sustained increase in basal metabolic rate that lasts for some hours.
specific gravity the weight of a substance, as compared with that of an equal volume of pure water, the latter being represented by 1000.
specific heat the energy in joules which is required to raise the temperature of 1 kilogram of the body by 1 kelvin unit.
specific ionization the number of ion pairs produced per millimetre by a charged particle passing through a medium.
specificity the ability of a detector to respond to a specific type and energy of radiation. The ability of a test to accurately identify non-affected individuals, such as a screening test.
specific resistance of a substance is obtained when a current is measured after passing through opposing surfaces of a 1 metre cube of the material.
speckling the graininess of an ultrasound image which is caused by scatter.
spectral Doppler trace in ultrasound, a greyscale picture of a waveform showing all its components.
spectral emission the colour of light emitted by an object. In intensifying screen, lanthanum oxybromide blue, gadolinium oxysulphide green, barium fluorochloride ultraviolet and calcium tungstate blue.
spectral sensitizing increasing the spectral sensitivity of a film by adding impurities to the film emulsion, because it is done by adding coloured dyes and therefore can be called dye sensitizing, colour sensitizing or optical sensitizing.
spectral sensitivity the range of wavelengths of electromagnetic radiation that a film emulsion or the human eye is sensitive to.
speculum an instrument used to hold the walls of a cavity apart, so that the interior of the cavity can be examined or treated. See also nasal speculum, vaginal speculum.
speech recognition software, which allows computers to be operated by human voice commands.
speech synthesis software which allows computers to ‘talk’ to the user.
speed distance travelled in unit time, unit metre per second. In photography, the screen speed is the ability of the phosphor to convert radiation to light, generally the faster the screen the less image detail when comparing the same phosphor, but this does not apply to comparisons between conventional and rare earth screens. The film speed is the ability of the film to respond to exposure, the faster the film, the less exposure will be required to produce a comparable image, on a characteristic curve; generally, the nearer the curve is to the vertical axis the faster the film. See also characteristic curve.
speed classification a means of comparing different film screen combinations, it is an arbitrary scale based on 100 and combinations range between 50 and 800.
sperm an abbreviated form of the word spermatozoon or spermatozoa.
sperm count an infertility test where semen is examined for volume, sperm numbers, morphology, motility and chemical composition.
spermatic associated with or conveying semen.
spermatic cord suspends the testis in the scrotum and contains the testicular artery and vein and the deferent duct (vas deferens).
spermatogenesis the process of development of spermatozoa, consisting of two stages, firstly spermatogonia become spermatocytes which develop into spermatids, secondly, spermiogenesis, the spermatids become spermatozoa.
spermatorrhoea involuntary discharge of semen without orgasm.
spermatozoon a mature, male gamete (germ cell).
sphenoid a wedge-shaped bone at the base of the skull containing the sphenoidal sinus.
spherical aberration the difference in focussing between the edge and the centre of a lens.
sphincter a circular muscle, contraction of which serves to close an orifice.
sphingolipid sphingosine combined with a lipid. A constituent of biological membranes, especially in the brain.
sphingomyelin a phospholipid formed from sphingosine found as part of biological membranes.
sphingomyelinase an enzyme concerned with the metabolism and storage of lipids.
sphingosine a constituent of sphingolipids and sphingomyelin.
sphygmomanometer an instrument used for non-invasive measurement of arterial blood pressure. Some utilize a column of mercury, but are generally being replaced with aneroid (not containing a liquid) devices.
spica a bandage applied in a figure-of-eight pattern.
spicule a small, spike-like fragment, especially of bone.
spigot plastic peg used to close a tube.
spin echo the reappearance of a magnetic resonance signal after the initial signal has disappeared following a 90° radio-frequency pulse followed by the application of a 180° radiofrequency pulse.
spin-lattice relaxation time (T1, longitudinal relaxation time, T1 relaxation time) in magnetic resonance imaging, the time taken for the spins to give the energy obtained from the initial radio-frequency impulse, back to the surrounding environment and return to equilibrium. It represents the time required for the longitudinal magnetization (Mz) to go from 0 to 63% of its final maximum value.
spin-spin relaxation time (transverse or T2 relaxation time) the time required for the transverse magnetization to decay to about 37% of its maximum value and is the characteristic time constant for loss of phase coherence among spins orientated at an angle to the static main magnetic field.
spina bifida a congenital defect in which there is incomplete closure of the neural canal, usually in the lumbosacral region.
spina bifida occulta a congenital defect that does not affect the spinal cord or meninges. It is often marked externally by pigmentation, a haemangioma, a tuft of hair or a lipoma which may extend into the spinal canal.
spina bifida cystica an externally protruding spinal lesion. It may vary in severity from meningocele to myelomeningocele. The condition can be detected during pregnancy by an increased concentration of alphafetoprotein in the amniotic fluid or by ultrasonography.
spinal associated with the spine.
spinal accessory nerve the eleventh pair of cranial nerves. They supply the muscles of the larynx and pharynx, and the muscles of the neck and shoulder to control movement of the head and shoulders.
spinal anaesthetic a local anaesthetic solution injected into the subarachnoid space, so that it renders the area supplied by the selected spinal nerves insensitive.
spinal column see vertebral column.
spinal cord a structure which lies in the spinal column, reaching from the foramen magnum to the first or second lumbar vertebra. It is a direct continuation of the nervous tissue of the medulla oblongata.
spinal cord compression (SCC) pressure on the spinal cord. Often caused by a tumour (which is commonly metastatic tumour from lung, breast or gastrointestinal cancers). Early diagnosis is vital to prevent permanent effects such as paralysis. Treatment usually involves corticosteroids and radiotherapy.
spinal nerves 31 pairs leave the spinal cord and pass out of the spinal canal to supply the periphery of the body.
spine a popular term for the bony spinal or vertebral column. A sharp process of bone.
spiral CT scan the patient table is moved at a constant speed through the CT gantry while the X-ray tube rotates around the patient; the technique improves the time taken to record the scan and improves contrast and opacification.
spiral fracture a break in a bone which twists round the bone, the most common site is the shaft of the tibia.
spiritual distress may occur when a person’s spiritual beliefs are derived from a particular religion, which requires the person to observe certain practices in everyday living activities, e.g. the preparation of food, types of food eaten, fasting, attending public worship, prayer, personal hygiene and type of clothing. Distress is likely if they are unable to conform to the teachings of their religious faith such as might occur during illness and hospitalization.
spirometer an instrument for measuring the air capacity of the lungs.
Spitz–Holter valve a special valve used to drain hydrocephalus.
splanchnic associated with or supplying the viscera.
spleen a lymphoid, vascular organ immediately below the diaphragm, at the tail of the pancreas, behind the stomach. It is part of the monocyte-macrophage (reticuloendothelial) system. Functions include the destruction of worn out blood cells, filtering the blood of debris and providing a site for lymphocyte proliferation and antibody production.
splenocaval associated with the spleen and inferior vena cava, usually referring to anastomosis of the splenic vein to the inferior vena cava.
splenomegaly enlargement of the spleen.
splenoportal associated with the spleen and hepatic portal vein.
splenoportogram radiographic demonstration of the spleen and hepatic portal vein after injection of a radiopaque contrast agent. Superseded by ultrasound examination.
splenorenal associated with the spleen and kidney, as anastomosis of the splenic vein to the renal vein; a procedure carried out in some cases of portal hypertension.
spindle cell sarcoma malignant tumours of epithelial tissue.
splenomegaly abnormal enlargement of the spleen.
split course therapy radiotherapy where a gap is planned between the first and second halves of treatment to enable patients to recover from acute reactions to treatment.
split emulsion film a film having two emulsions, one on top of each other on the same side of the base, one layer providing high contrast and the other high maximum density, used for mammography.
spondylitis inflammation of the spine. See also ankylosing spondylitis.
spondylography a method of measuring and studying the degree of kyphosis by directly tracing the line of the back.
spondylolisthesis forward displacement of lumbar vertebra(e).
spondylosis degenerative disease of the whole spine, with osteophyte formation on either side of the intervertebral disc. Often associated with osteoarthritis of the apophyseal (facet) joints.
spontaneous abortion see spontaneous miscarriage.
spontaneous emission when an atom absorbs a photon and releases the absorbed energy as a photon of light.
spontaneous fracture one occurring without appreciable violence; may be synonymous with pathological fracture.
spontaneous miscarriage one which occurs naturally without inter- vention.
sprain injury to the soft tissues surrounding a joint, resulting in discoloration, swelling and pain. There is stretching or tearing of a ligament or capsular structure of a joint.
spreadsheet a program which allows forecasting and financial planning.
Sprengel’s shoulder deformity congenital high scapula, a permanent elevation of the shoulder, often associated with other congenital deformities, for example the presence of a cervical rib or the absence of vertebrae.
squamous cell carcinoma carcinoma arising in squamous epithelium; epithelioma.
squamous epithelium the non-glandular epithelial covering of the external body surfaces.
SSL (Secure Socket Layer) a method of verifying the identity of system users and Web sites.
staging process of measuring how advanced a tumour is and to which sites it has spread; may be locally advanced or metastatic. In stage 1 the tumour is confined to the organ of origin, stage 2 local lymph nodes are invaded, stage 3 distant lymph nodes are invaded or local spread beyond the original organ and stage 4 blood-borne metastases are present. Usually involves imaging with computed tomography, bone scan and often surgery. It includes tumour (T) size, nodal (N) status and metastatic (M) sites present/absent.
standard a level or measure against which the performance of an activity can be monitored.
standard contrast emulsions once the most common film emulsion types with a low base fog, an average gradient of 2.6 and a maximum density of 3.5. See also characteristic curve.
standard deviation (SD) in statistics, a method of grouping data on either side of the mean of a graph, in a normal distribution curve 68% of the data will be covered in one standard deviation above and below the mean. A measure of dispersion of scores around the mean value. It is the square root of variance.
standard error (SE) in statistics, a measure of variability of many mean values of different samples from a population. Used to calculate the chance of a sample mean being smaller or bigger than that for the population.
standardized mortality rate the ratio of the observed numbers of deaths in a given region to the expected number of deaths in a given region multiplied by 100.
standardized mortality ratio (SMR) allows comparisons to be made between the death rates in populations with different demographic structures. It involves the application of national age-specific mortality rates to local populations so that a ratio of expected deaths to actual deaths can be calculated. The comparative national figure is, by convention, 100 and, for example, a local figure of 106 means that there is an increased risk of 6%, whereas a local figure of 94 indicates a risk 6% lower.
standby system a system which automatically shuts down sections of an automatic film processor when not in use to reduce running costs and conserve energy.
stapes the stirrup-shaped medial bone of the middle ear. See also incus, malleus.
staphylococci Gram-positive, non-mobile bacteria normally present on the skin and mucous membranes.
Starling’s law of the heart states that the force of myocardial contraction is proportional to the length (stretching) of the ventricular muscle fibres. Increased stretching results in the next contraction being more powerful.
starter solution a solution containing a weak acid and bromide ions which is used with new developer in automatic processing machines to depress the activity of the developer until a number of films have been processed; the processed films produce bromide ions and therefore the solution will no longer need to be added.
start-up costs the costs, such as the purchase of equipment, that occur at the start of a project.
statement an instruction in a computer program.
Statistical Package for the Social Sciences (SPSS) software package often used in the analysis of quantitative data.
statistical significance in research, an expression of how likely it is that a set of results happened by chance, e.g. 0.05, 0.01 and 0.001 levels. See also P value.
statistics scientific study of numerical data collection and its analysis and evaluation.
status epilepticus a condition where there is a rapid succession of epileptic fits.
steatorrhoea the presence of excess fat in the faeces.
steering coils produce magnetic fields to ensure that an electron beam is positioned at the centre of a tube and that is then positioned on the correct aspect of the target in a linear accelerator.
Steinmann’s pin an alternative to the use of a Kirschner wire for applying skeletal traction to a limb. It has its own introducer and stirrup.
stellate ganglion a large collection of nerve cells (ganglion) on the sympathetic chain in the root of the neck.
stellate ganglionectomy surgical removal of the stellate ganglion.
stenosis abnormal narrowing of a channel or opening.
stent device used to provide a shunt or keep a tube or vessel open. For example stent insertion into the bile duct to relieve obstructive jaundice, stenting the ureters to overcome urinary obstruction, and stenting the oesophagus for palliation of dysphagia caused by oesophageal cancer. See also transjugular intrahepatic portasystemic stent shunting.
stepwedge a piece of equipment which is made up of different thicknesses of aluminium with a layer of copper on the base; wedges are calibrated so that when radiographed each step produces an exact increase or decrease in density on the film. See also characteristic curves.
stercobilin the brown pigment of faeces; it is formed from stercobilinogen which is derived from the bile pigments.
stereotactic radiotherapy where multiple beams of radiation are given to a tumour over a number of days to destroy the tumour.
stereotactic surgery where multiple beams of radiation are focused on a tumour and the total dose given destroys the tumour. See also radiosurgery.
sterile free from microorganisms.
sterilization activity that kills or removes all types of microorganisms including spores. It is accomplished by the use of heat, radiation, chemicals or filtration. Making incapable of reproduction.
sternoclavicular associated with the sternum and the clavicle.
sternocleidomastoid muscle a strap-like neck muscle arising from the sternum and clavicle, and inserting into the mastoid process of temporal bone.
sternocostal associated with the sternum and ribs.
steroids a large group of organic compounds (lipids) that have a common basic chemical structure: three 6-carbon rings and a 5-carbon ring. They include: cholesterol, bile salts, vitamin D precursors, sex hormones and the corticosteroid hormones.
sterol chemicals with the basic steroid structure combined with an alcohol group such as cholesterol.
stertorous noisy breathing, cheeks puffed in and out with each breath.
stillbirth birth of a baby, after 24 weeks’ gestation, that shows no sign of life.
Still’s disease term seldom used, having been superseded by systemic onset juvenile idiopathic arthritis. See also juvenile idiopathic arthritis.
stimulant an agent that causes functional activity of an organ.
stimulated emission when an excited atom absorbs a photon and releases two light photons.
stochastic effect one in which the probability of the effect occurring is governed by chance, therefore all doses of radiation carry some risk and the stochastic effects produced by radiation on an individual include radiation-induced cancer and genetic effects. See also deterministic effects.
stock control the method of storing and recording purchased items for example film to ensure that the oldest is used first and all film is used before its expiry date.
stoma the mouth; any opening. See also colostomy, ileostomy, urostomy.
stoma care nurse specialist nurse who advises on the management of bowel and urinary stomas.
stomach the most dilated part of the digestive tube, situated between the oesophagus and the duodenum; it lies in the epigastric, umbilical and left hypochondriac regions of the abdomen. The wall is composed of four coats: serous, muscular, submucous and mucous. It produces gastric juice containing digestive enzymes, hydrochloric acid and mucus.
stone calculus; a hardened mass of mineral matter.
stove-in chest there may be multiple anterior or posterior fractures of the ribs (causing paradoxical respiration) and fractures of sternum, or a mixture of such fractures.
straight line portion the part of the characteristic curve which is used in radiography to determine the gamma, contrast, average gradient, useful exposure range, useful density range, film latitude and film speed. See also sensitometry.
strandquist isoeffect curves a series of tolerance dose curves to relate total radiotherapy dose to overall treatment time.
strain overuse or stretching of a part. A group of microorganisms within a species. To pass a liquid through a filter.
strangulated hernia hernia in which the blood supply to the organ involved is impaired, usually due to constriction by surrounding structures.
Strategic Health Authority a body responsible for strategic health planning for a geographical area with a population of many millions (for example, the English counties of Cambridgeshire, Norfolk and Suffolk). They are also responsible for the performance management of the Primary Care Trusts (PCTs) within that area.
strategic management the management function concerned with longer-term future strategy. Financial and resource planning. See also operational management.
stratified arranged in layers.
stratum a layer or lamina, e.g. the various layers of the epithelium of the skin, i.e. stratum granulosum, stratum corneum.
streptococci Gram-positive spherical bacteria.
stress fracture (fatigue fracture) a bone fracture resulting from repeated loading with relatively low magnitude forces. Can be caused by a number of factors including overtraining, incorrect biomechanics, fatigue, hormonal imbalance, poor nutrition and osteoporosis.
stress incontinence occurs when the intra-abdominal pressure is raised as in coughing, giggling and sneezing; there is usually some weakness of the urethral sphincter muscle coupled with anatomical stretching and displacement of the bladder neck.
striae streaks; stripes; narrow bands. Occur when the abdomen enlarges such as with obesity, tumours and pregnancy, when the marks are called striae gravidarum they are red at first and then become silvery-white. Striae may also occur as a side-effect of corticosteroid therapy.
stricture a narrowing, especially of a tube or canal, due to scar tissue or tumour.
stridor a harsh breathing sound caused by partial obstruction of the larynx or trachea.
stroke (cerebrovascular accident) interference with the blood flow in the brain due to embolism, haemorrhage or thrombosis. Signs and symptoms range from weakness and tingling in a limb through to paralysis of limbs, incontinence of faeces and urine and loss of speech.
stroke volume (SV) the volume of blood pumped out of the heart by each ventricular contraction.
stroma the blood supply and supporting structures of a tumour above the size of about 2mm.
strontium (Sr) a metallic element present in bone. Isotopes of strontium are used in radionuclide scanning of bone.
strontium-90 (90Sr) a radioisotope with a half-life of 28 years produced during atomic explosions. It is dangerous when it becomes integrated within bone tissue where turnover is slow. Used to treat the cornea by being incorporated in a rolled silver foil and bonded into a silver applicator.
structure localization a method of accurately locating small, impalpable lesions using ultrasound, CT scanning or using a localizing grid and conventional radiography.
structure mottle an uneven radiographic image due to the fact that it is not possible to evenly disperse the phosphor crystals throughout the binder when manufacturing intensifying screens and therefore light from the intensifying screens is not uniformly produced.
Stryker bed a proprietary bed. Designed to allow rotation of patients to the prone or supine position. Main uses include spinal injuries and burns.
Student’s paired test a parametric test for statistical significance. Used to test differences in mean values for two related measurements such as those obtained from the same subject. See also Wilcoxon test.
Student’s t test for independent groups a parametric test for statistical significance. Used to test differences in mean values of two groups. See also Mann–Whitney test.
stupor a state of semi-unconsciousness, occurs in some mental illnesses when the patient does not move or speak and makes no response to stimuli.
styloid long and pointed; resembling a pen or stylus.
subarachnoid haemorrhage (SAH) the loss of blood from a vessel in the brain which leaks into the subarachnoid space. This is typically due to an intracerebral aneurysm or arteriovenous malformation and can be fatal. Blood is present in the cerebrospinal fluid (CSF).
subarachnoid space the space beneath the arachnoid membrane, between it and the pia mater. It contains cerebrospinal fluid.
subcarinal below a carina, usually referring to the carina tracheae.
subclavian beneath the clavicle.
subcutaneous beneath the skin.
subdural beneath the dura mater; between the dura and arachnoid membranes.
subdural haematoma (SDH) the accumulation of blood beneath the dura lining the skull that can occur after head trauma. It develops slowly and may present as a space-occupying lesion with vomiting, papilloedema, fluctuating level of consciousness, weakness, usually hemiplegia on the opposite side to the clot. Finally there is a rise in blood pressure and a fall in pulse rate.
subendocardial immediately beneath the endocardium.
subject contrast the contrast seen on a radiograph varies with the body part being imaged and will change with the size of the area, the density and atomic number of the tissue, the quality of radiation and the use of contrast agents.
subjective contrast the observer’s opinion of the contrast seen on an image; it depends on the viewing conditions, and the observer’s ability to see differences on the film.
sublethal damage damage caused by radiation that is insufficient to cause death of the cell.
subliminal inadequate for perceptible response. Below the level of consciousness.
sublingual beneath the tongue.
subluxation incomplete dislocation of a joint.
submandibular below the mandible.
submaxillary below the maxilla.
submucosa the layer of connective tissue beneath a mucous membrane.
submucous beneath a mucous membrane.
submucous resection (SMR) surgical correction of a deviated nasal septum.
suboccipital beneath the occiput; in the nape of the neck.
subperiosteal beneath the periosteum of bone.
subphrenic beneath the diaphragm.
subroutine a self-contained part of a computer program which can be returned to time and time again.
substrate a chemical acted upon and changed by an enzyme in a chemical reaction.
substratum an adhesive layer that attaches the emulsion to the film base, or the phosphor layer to the reflective layer of an intensifying screen.
succenturiate lobe an accessory lobe of the placenta.
sucrase intestinal enzyme that converts sucrose to glucose and fructose.
sucrose a disaccharide that is hydrolysed into glucose and fructose during digestion. It occurs naturally in sugar and is added to many manufactured foods. Frequent consumption of sucrose causes dental disease.
suction the process of sucking. The removal of gas or fluid from a cavity by means of reduced pressure.
sudden infant death syndrome (SIDS, cot death) the unexpected sudden death of an infant, usually occurring overnight while sleeping in a cot, but may occur under other situations. The commonest mode of death in infants between the ages of 1 month and 1 year, neither clinical nor postmortem findings being adequate to account for death. Overheating, sleeping in the prone position, respiratory illness and infection, and being in an environment where people smoke, have all been implicated as risk factors. Parents/carers are now recommended to put babies to sleep on their backs, at the foot of the cot to prevent them wriggling under bedclothes, not to overheat the room, not to smoke in the same room and to seek advice from a health professional if the baby seems unwell.
sulcus a furrow or groove, particularly those separating the gyri (convolutions) of the cerebral cortex.
sulphuric acid chemical used as the acid in a fixer solution with aluminium sulphate hardener.
superadditivity the combined activities of two chemicals is greater than the sum of their separate activities, for example phenidone and hydroquinone used in developer.
supercoat a thin layer of gelatine that is coated on the outer surface of a film or the thin layer of cellulose acetobiturate on an intensifying screen, to protect from mechanical damage.
superficial near the surface such as the superficial veins of the leg.
superior in anatomy, the upper of two parts.
supernumerary in excess of the normal number; additional. supernumerary bones include os trigonum, os tibial externum and os vesalii. Such abnormalities of sesamoid bones and supernumerary bones rarely directly cause problems in the paediatric foot but may result in soft-tissue lesions. Their presence is confirmed radiographically.
supernumerary digits see polydactyly.
superparamagnetic a substance which is 100–1000 times more susceptible to magnetism than a paramagnet. See also diamagnetic, paramagnetic, superparamagnetic, ferromagnetic.
supervised area a type of designated area where a person is likely to receive a dosage of radiation in excess of one third the dose in a controlled area; access to the area is limited to those people whose presence is necessary.
supinate turn or lay face or palm upward. See also pronate.
supinato that which supinates, usually applied to a muscle. See also pronator.
supine lying on the back with face upwards, of the hand with palm upwards. See also prone.
suppository medicine, contained in a base that melts at body temperature, placed inside the rectum.
supraclavicular above the clavicle.
supracondylar above a condyle.
supracondylar fracture a fracture affecting the lower end of the humerus or femur. The former may interfere with the blood supply to the forearm.
supraorbital above the orbits.
supraorbital ridge the ridge covered by the eyebrows.
suprarenal above the kidney. See also adrenal.
suprasternal above the sternum.
surface applicator used in brachytherapy where the external surface of the patient is treated by locally applied sources held in shaped applicators.
surfactant a mixture of phospholipids secreted by type II pneumocytes. It reduces surface tension in the alveoli, allows lung inflation and prevents alveolar collapse between breaths. See also pneumocytes.
surgical mask a mask to cover the nose and mouth to prevent contamination of a sterile area by droplet infection. Worn to protect the wearer from airborne infection.
survey a data collection method. Includes: interview, postal, telephone, or via the internet.
survival rate the proportion of patients who survive for a certain number of years, usually five, used for measuring the success of treatment for cancer.
suspensory ligaments supporting or suspending such as those supporting the lens of the eye.
suture the junction of cranial bones. In surgery, a stitch or series of stitches used to appose the edges of a surgical or traumatic wound. Also describes the placement of such stitches. See also ligature.
swab a small piece of cotton wool gauze. See also filamented swab.
swallowing (deglutition) part voluntary and part involuntary activity with three stages: oral (buccal), pharyngeal and oesophageal. See also dysphagia.
sweat the secretion from the sweat (sudoriferous) glands. Contains water, electrolytes (mainly sodium and chloride) and waste. Sweat production is primarily concerned with temperature regulation but has a small excretory role.
sweat gland see apocrine glands, eccrine.
swept gain used in ultrasound scanners to give an image of even brightness when scanning homogeneous tissue.
sympathetic nervous system part of the peripheral nervous system (PNS), it describes a division of the autonomic nervous system (ANS). It is composed of a chain of ganglia on either side of the vertebral column and nerve fibres having thoracolumbar outflow. It opposes the parasympathetic nervous system and is usually involved with body stimulation. Its action is augmented by adrenaline (epinephrine) and noradrenaline (norepinephrine).
symphalangism the fusion of phalanges in one digit.
symphysis a fibrocartilaginous union of bones such as the symphysis pubis.
symptoms any indication of disease perceived by a patient.
synapse the gap between the axon of one neuron and the dendrites of another, or the gap between the axon and a gland or muscle. Most operate chemically but a few are electrical. The synapse permits the passage of an impulse across the gap. This is achieved chemically by the release of calcium ions and a neurotransmitter such as acetylcholine.
synarthroses fibrous joints with virtually no movement.
synchondrosis a type of cartilaginous joint with minimal movement, for example, the sternocostal joints.
syncope a simple faint or loss of consciousness due to cerebral ischaemia.
syncytium a mass of tissue with several nuclei. Boundaries between individual cells are absent or poorly defined.
syndactyly (syndactylism, syndactylia, zygodactyly, webbed toes) a term applied to a total or partial fusion of adjacent digits. It is very common, usually bilateral and often familial. Multiple syndactyly occurs in hands and feet associated with other anomalies, as in Apert’s syndrome, an autosomal dominant disorder – acrocephalosyndactyly. Treatment is not required for webbing of the toes.
syndesmoses joints held together by a ligament or membrane, for example inferior tibiofibular joint.
syndrome a group of signs and symptoms typical of a distinctive disease, which often occur together and form a distinctive clinical picture.
synergism (synergy) the harmonious working together of two agents, such as drugs, microorganisms, muscles, etc.
synergistic action that brought about by the cooperation of two or more muscles, neither of which could bring about the action alone.
synovial cavity the potential space in a synovial joint.
synovial fluid the fluid secreted by the membrane lining a freely movable joint cavity.
synovial joint (diarthroses) the main group of joints found in the body; the ends of the bone are covered with articular hyaline cartilage and there is synovial fluid within the joint cavity which is secreted by the synovial membrane which lines the fibrous capsule that surrounds the joint.
synovial membrane the membrane lining the intra-articular parts of bones and ligaments. It does not cover the articular surfaces.
synovioma a tumour of synovial membrane; it can be benign or malignant.
synovitis inflammation of a synovial membrane.
syntax error two words which are shown on the computer display when an incorrect input or statement has been made.
syphilis a sexually transmitted disease.
syringe an instrument for holding fluid or air for injection, for aspirating fluid or irrigating body cavities. It is a hollow tube with a tight-fitting piston; a hollow needle or a thin tube can be fitted to the end.
syringe shield a device made of either metal with a high atomic number or thick Perspex which is designed to protect the hands of staff when handling syringes containing radioactive material.
syringomyelia a disease of the spinal cord with associated muscular wasting of the upper limbs.
syringomyelocele the most severe form of meningeal hernia (spina bifida). The central canal is dilated and the thinned-out posterior part of the spinal cord is in the hernia.
syrinx a cyst-like cavity in the spinal cord.
systematic review a systematic approach to literature reviews of both published and unpublished material that lessens bias and random errors.
Syst°me International d’Unit°s (SI, International System of Units) system of measurement used for scientific, technical and medical purposes. There are seven base units: ampere, candela, kelvin, kilogram, metre, mole and second, and various derived units, e.g. pascal, becquerel, etc. (See figures on p. 346)
systemic circulation oxygenated blood leaves the left ventricle and, after flowing through the aorta throughout the body tissues, returns deoxygenated to the right atrium of the heart.
systole the contraction phase of the cardiac cycle, as opposed to diastole.
systolic function the measurement of the ventricular contraction of the heart.
systolic murmur a cardiac murmur occurring between the first and second heart sounds due to valvular disease, e.g. mitral systolic murmur.
