chapter 9 - radiology

Radiant

Energy ways that are produced, charged, and emitted from a common center in the dental radiation tube

X-ray tube

Vacuum tube; produces x-rays

Cathode

Negative pole; electrode in the vaccuum tube that serves as the electron source

Filament

Fine thread; tungsten coil in the cathode focusing cup that generates the electrons

Anode

Positive pole; the target for the electron barrage to convert the electron force into protons

Focal spot

Target area where rays are projected to make the primary beam, or central beam

Collimator

To align; a device used to regulate the size of the beam leaving the tube in parallel rays, helping to avoid stray radiation

PID

Position indicating device

Aperture

Opening or port; opening in the lead colllimator disk that regulates the size of the primary beam

Filter

Aluminum disks that are placed between the collimator attachment and the exit window of the tube to absorb weak radiation

Inherent filtration

All filtration (tube wall, insulating oil, aluminum disks) devices that filter weak, longer wavelength X-rays

Added fiitration

Filtration placed outside the tube head to meet safety standards

Total filtration

The sum of inherent and added filtration, expressed in millimeters of aluminum equivalent

Milliampere control

An increase in milliamperage increases the amount of electrons available and darkens the radiograph

Milliampere

Thousand of an ampere (electric current)

Kilovolt power

1000 volt unit; controls the force that attracts the electrons to the anode; helps to determine the penetrating power and the quality/energy of the radiation rays

Exposure time

duration of the interval during which current will pass through the X-ray tube; this period may be stated as fractions of a second or impulses

Impulses

60 pulses to a second

Target film distance

Distance of the film surface from the source of radiation (target or focal spot)

Target-object distance

Distance between the anode target and the object to be radiographed

Film speed

A (slowest) to F (fastest) speed; faster speed film requires less radiation exposure time for the patient

Primary radition

Central ray of radiation emitting from the tube head and PID. This is the desired radiation and is used to expose radiographic film

Secondary radiation

Radiation given off from other matter that is exposed to the primary beam

Scattered radiation

Radiation deflected from its path during its passage through matter; may be deflected or diffused in all directions, becoming attenuated (weakened) or another form of secondary radiation

Stray radiation

Also called leakage; any radiation other than the useful beam produced from the tube head; a faulty or broken tube head may be the source of the stray radiation

Remnant radiation

Radiation rays that reach the film target after passing through the subject part being radiographed. These rays form the latent image on the fim emulsion

Ion

A particle that carries an electrical charge

Sensitivity

Ability of X-rays to penetrate and possible ionize.

Reproductive cells (genetic)

More radiosensitive than the radioresistant body tissues (somatic) cells

Cumulative effect

Long-term outcome of radiation. Repetition increases and intensifies the ionizing effect on cells for a buildup of damage.

Latent period

Time between application of a stimulus and the beginning of a response in a muscle fiber. Between exposure and the effect or detection

Acute radiation exposure

Radiation occuring from a massive short-term ionizing dose, such as an accidental exposure or explosion of radiation material

Chronic radiation exposure

Accumulated radiation cell damage from continual or frequent small exposures absorbed over a period of time

Roentgen (R)

The basic unit of exposure to radiation; the amount of X-radiation or gamma radiation needed to ionize. Coulumb per kilogram. (C/Kg = 3880 roentgens)

Rad (radiation absorbed dose)

Gray (Gy). JThe basic unit of absorbed radiation dose equal to 100 ergs (energy units) per fram of tissue or 1 rad = cGy

Rem

Sievert (Sv). The unit of ionizing radiation needed to produce the same biological effect as 1 roentgen (R) of radiation

Rbe (relative biological effectiveness)

Unit of measurement used to determine amount of biological absorption effects on body tissues by different types of radiation energy

Coulomb

International electromagnetic measurent abbreviated as C; 1 C per kilogram is equal to 3880 roentgens

Maximum permissble dose (MPD)

Highest rate of exposure permissible for the occupationally exposed person.

Erythema dose

Radiation overdose that produces redness of the skin

Erythema

Redness

ALARA

As low as reasonable achievable; a policy of using the lowest amount of radiation exposure as possible. Proper exposure and protection aids, use of fast films, good techniques in exposure and developing, questioning the patient regarding recent exposures and the correct calculations or control settings

Dosimeter

Giving measure; operator's radiation monitoring device with ionizing chamber or a device to indicate exposure and measure accumulated doses of radiation; available in the form of a film badge, pen, ring, and so on

Lead apron/thyrocervical collar

Patient apparel with lead protection for genetic cells in the torso and the thyroid glands in the cervical area

Lead barriers, shields

Devices used by operators to block out scattered radiation

Phantom

Practice mannequin containing tooth and head structures to imitate the actual condition.

DXTTR

Dental X-ray Teaching and Training Replica; or Dexter

Periapical film packet

Size 0 (pedodontic size) 1 (adult anterior) or 2 (adult anterior and posterior) used for the intraoral periapical view of the entire tooth or teeth in a given area along with adjacent tissues and oral structures

Bitewing film packet

(also called interproximal radiograph size 3); film used to record crown and interproximal views of both arches while in occlusion

Film speeds

Film are rated A to F according to the amount of exposure needed with A needing the most time

Occlusal film packet

size 4; film that may be used intraorally or extraorally to expose large areas (2-1/4" x 3"); these film packets may contain more than one film and are marked and color-coded to identify the amount of film enclosed

Extraoral films

Radiographs exposed outside the oral cavity; larger in size and loaded in a film cassette or wrapped for protection from light rays

Cephalometric

Headplates, extraoral radiographs of the head used in orthodontic and oral surgery, and sometimes in prosthodontist dentistry

Cepahl

Head

Metric

Measure

Cephalostat

A device used to stabilize the patient's head in a plane parallel to the film and at right angles to the central ray of the X-ray beam; it is used for large radiographs of the head

Panoramic radiograph

A special radiograph capturing a view of the entire dentition with the surrounding structures on one film. Extraoral film is placed in the machine's cassette and rotates around the patient at the same speed as the tube head rotation, providing a panoramic view. Popular in orthodontics and oral surgery

NOMAD

Lightweight, battery energized, and capable of exposing either conventional film or digital images

Intensifying screen

A lining of calcium tungstate phosphors or rare earth within the cassette that gives off a bluish light (calcium tungstate) or green glow (rare earth) when exposed to radiation; this combination of light and radiation forms a latent image of the film faster and reduces exposure time

CCD (Charge coupled device)

Solid-state sensor that may or may not be wired to the computer workstation

Pixels

Picture elements

PSP (photostimulatable phosphor device)

Cordless, indirect sensor plate that absorbs radiation to complete a latent image; the sensor plate is placed in a barrier wrap, put in a positioning device, and then exposed using conventional exposure techniques; the plate is then processed by placing it into a scanner that will absorb the captured pixel information, compute the photon energy, and translate the image onto the screen or monitor

Contrast

Variations in shades from black to white. A radiograph exhibiting many variations in shades is considered to posses long-scale. Increased kilovoltage helps to produce this effect

Density/brightness

Amount of film blackening associated with the percentage of light transmitted through a film. An increase or decrease in density is accomplished by an increase or decrease in milliamperage and exposure time (mA/second)

Detail

Point-to-point delineation or view of tiny structures in a radiograph image. Proper exposure, handling factors, and kVp selection provide good detail

Definition/smoothness

Outline sharpness and clarity of image exhibited on a radiograph

Penumbra

Movement of the film, patient, or tube head is the most common cause of poor definition or fuzzy outline

Paene

Nearly

Umbra

Shadow

Noise

Low and high frequency components that hamper reception and computation of digital singals

Radiolucent

Describes a radiograph that appears dark, or the ability of a substance to permit passage of X-rays, thereby causing the radiographic film to darken

Radius

Ray

Pacus

Dark

Radiopaque

Portion of the radiograph that appears light, or the ability of a substance to resist X-ray penetration, thereby causing a light area on the film

Lucent

Light

Bisecting angle

Central x-ray beam is directly perpendicular with an imaginary bisecting line of the angle formed by the plane of the film and the long axis of the tooth. Technique called short cone technique

Paralleling

Film packet is placed parallel to the long axis of the tooth and at a 90 degree (right) angle to the central X-ray beam. Called extension cone or right-angle technique

Sagittal plane

Also called midsaggital plane; imaginary vertical line bisecting the face into a right and left half; important during exposure to determine positioning of the patient

Ala-tragus line

Imaginary line frm the ala (wing) of the nose to the tragus (skin protection anterior to acoustin meatus), center of ear. THis line is important for positioning the patient in the bisecting-angle technique

Frankfort plane

Imaginary line from the tragus of the ear to the floor of the orbit that is used to align the maxillary arch parallel to the floor; used mostly for extraoral films. Many machines that expose large extraoral films and digital images have a stabilizing chin rest or an aiming light to ensure this directional position

Positive angulation

Angulation achieved by pointing the end of the PID downward also called plus angulation. Mandibular exposures are incisors (+40 degrees), cuspids (+45 degrees), bicuspids/premolars (+30 degrees), and molars (+20 degrees)

Negative angulation

Angulation achieved by positioning the PID upward; also called minus angulation. Mandibular exposures are incisors (-15 degrees), cuspids (-20 degrees), bicuspids/premolars (-10 degrees), and molars (-5 degrees)

Zero angulation

Angluation achieved by PID placement parallel to the floor.

Horizontal angulation

Direction of the central X-ray beam in a horizontal plane (side to side). The central beam must be placed perpendicular to the film front and teeth alignment. The error observed with improper horizontal angulation is called overlapping or cone cutting

Vertical angulation

Direction of the central X-ray beam in an up or down position. Improper vertical angulation results in from foreshortening or elongation errors

PID

Position indicating device, formerly called a cone; may be a long cone (12-16 inches) or a short cone (8 inches); may be a round or rectangular, open-ended tube. Used to collimate and direct the central beam, and it also determines the target-surface distance

Film-holding instrument

Device used to place and retain the film or sensor in the oral cavity during exposure

Blue

Anterior placement

Yellow

Posterior placement

Red

Bitewing placement

Green

Endodontic placement

Biteblock

A device inserted between the teeth to hold the film during exposure, made of foam, wood or plastic

Individual film holder

A grip device, such as Rinn's Eezee-grip, that will hold one film or one sensor for exposure in the mouth. Mostly used in a small mouth or difficult areas, the loaded film holder is put into position and held by the patient's bite or finger pressure

Bite loop/tab

Paper tab or a celluloid circle placed around periapical film, enabling the film to be used in a bitewing position. This combination is used in place of a commercially manufactured interproximal film. Some of these are constructed to assist with stabilizing and holding the digital sensors in the film-holding device

Film-safe container

A lead-lined container used to hold exposed films until processing; protects the film from exposure to scattered or secondary rays during exposure of films

Full mouth survey (FMS or FMX)

Multiple exposures of the oral cavity showing crown and root area in a series of radiographic views; when arranged in proper sequence, these films or images give a survey or view of the condition of the entire mouth

Bitewing survey (BWS or BWX)

Two or four film exposures of the posterior view to observe the crowns of maxillary and mandibular posterior teeth; anterior bitewing exposure is also possible

Edentulous survey

Radiographic survey of a patient wihtout teeth

Radiograph processing

Procedure for bringing out the latent image on a film and making the exposure permanent; the procedure involves developing, rinsing, fixing, washing, and drying; processing may be completed in an automatic film processor or by manual methods in a processing tank

Developing

Chemical process using the chemical elon to bring out contrast and another chemical, hydroquinone, to show contrast in films. This brings out latent image on the film's silver halines that were affected or darkened by radiation