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 Being superseded by ultrasound examination.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.
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