Chapter 9: Radiography

Radiant

Energy that is given off from a central source

X-ray tube

Also known as vacuum tube, produces X-rays

What is known as vacuum tube?

X-ray tube

Cathode

(negative Pole) Electrode in the vacuum tube that serves as the electrons source

Filament

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

Anode

(positive pole) the target for the electronic barrage to convert the electron Force into photons

Focal spot

Target area where rays are projected to make the primary beam, or Central beam; the smaller focal spots produces a better image

Collimator

(to align) a device used to regulate the size of the beam leaving the tube and parallel rays, helping to avoid stray radiation thoughts also term as diaphragm, it is usually shaped similar to a lead washer or on the connective end of the PID (position indicating device) that also has lined wall to assist collimation

What does PID stand for?

Position indicating device

Aperture

(opening or port) opening in the lead collimator disc 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.

The three types of filtration are

Inherent filtration, added filtration, total filtration

Inherent filtration

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

Added filtration

Filtration placed outside the tube head to meet safety standards

Total filtration

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

Milliampere control

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

Kilovolt power

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 (60 pulses to a second) the amount of exposure that a patient actually receives is measured and milliampere seconds

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 radiation

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

Secondary radiation

Radiation given off from other matter that 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

Attenuated

Weakened

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 this

Remnant radiation

Radiation rays that reach the film Target after passing through the subject part being radiograph. These rays form the latent image on the film emulsion

Ion

Particle that carries an electrical charge

Sensitivity

Ability of x-rays to penetrate and possibly ionize the body.

More sensitive

Younger cells are blank than older thicker cells

Reproductive cells (genetic)

Which body cells are more radiosensitive than the radio resistant body tissues (somatic)cells?

Cumulative effect

Long-term effect of radiation resulting from multiple exposures.

Latent period

The time interval between the exposure and the effect or detection of radiation

Mutation effect

Abnormal growth or is development resulting from radiation affecting a genetic change

Acute and chronic radiation exposure

What are the two types of X radiation exposure that damages the body cells?

Acute radiation exposure

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

Chronic radiation exposure

Accumulated radiation effects from continual or frequent exposures (thus the need for questioning the patient asked to when the last x-ray was taken)

Roentgen (R)

The basic unit of exposure to radiation; the international unit is the coulomb per kilogram

3,880

C/kg is how many Roentgens?

Rad (radiation absorbed dose)

International unit is gray (Gy); calculated as equal to 100 ergs energy units per gram of tissue

Rem (roentgen equivalent measure)

International unit is sievert (Sv), which is the unit of ionizing radiation needed to produce the same biological effect as one roentgen ® 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 measurement abbreviated as C; 1C per kilogram is equal to 3,880 Roentgens

Maximum permissible dose (mpd)

Maximum x-ray exposure permissible for the exposed person. Formula for calculating this factor is (5 REM per year )- (age - 18)x 5 REM per year equals

Erythema dose

Radiation exposure that produces a temporary redness of the skin

ALARA

Policy of using the lowest amount of radiation exposure possible. Measures to accomplish this include proper exposure and protection aids, use a fast films, good technique and exposure and developing, questioning the patient regarding recent exposure, and the correct calculations or control settings

As low as reasonably achievable

What does ALARA stand for?

Dosimeter

Measures the amount of stray or secondary x-ray exposure with a device that contains the ionizing chamber; available in the form of a film badge, pen, ring, and so on

Lead apron / thyrocervical collar

Patient apparel with lead protection for genetics (sex) 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

Device used for practice in learning radiation exposure techniques, a practice mannequin containing tooth and head structures to imitate the actual condition

DXTTR (Dexter)

Which is a popular model for phantom?

Periapical film packet

Most commonly used radiographic film for intraoral exposure. Use for view of the entire tooth or teeth in a given area along with adjacent tissues and oral structures

Bitewing film packets

Film used to record crown and enter proximal views of both arches while in occlusion; use intraorally with attached by tab

Interproximal radiograph, size 3

What is also a name for bite-wing film packet?

Film speeds

Comparison rate of exposure time needed by the film for proper exposure

Occlusal film packet

Radiographic film use intraorally or extra orally for exposure of larger areas. May contain more than one film and are marked and color coded to identify the amount of film and enclosed.

Extraoral films

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

Cephalometric film

Large radiographic film for exposure of the head. Use an orthodontic, oral surgery, and sometimes in prosthodontic dentistry.

Cephalostat

Pin used to center and stabilize the head during x-ray exposure. Use for large radiographs of the head

Panoramic radiograph

Special radiograph that exhibits the entire dentition area on one film. Popularly used in orthodontics and oral surgery

Intensifying screens

Fluorescent treated cassette screen to reduce patient radiation exposure. Lined with calcium tungstate phosphors or rare Earth within the cassette that gives off of bluish light or green glow when exposed to radiation.

Rare Earth

Which intensifying screen gives off more light than calcium tungstate, making its exposure time shorter?

CCD (charge coupled device) sensor

A solid state sensor that may or may not be wired to the computer workstation. The sensor and center wire are barrier wrapped and inserted into a positioning device for insertion and exposure in the mouth. The same placement and alignment technique used for conventional film exposure applied

Pixels

Picture elements.

0 (Black) to 256 (White)

Pixels exposed to radiation are a sign a grade shade color number from?

PSP (photostimulatable phosphor device) sensor

Cordless, indirect sensor plate that absores radiation to complete a latent image.

CCD and PSP

What are the two main types of sensors used for digital radiographs?

Contrast

Variations in shades from black to white. A radiograph exhibiting many rate variations in shades is considered to possess long scale contrast. Increase kilovoltage helps to produce this effect

Density / brightness

Amount of film blackening associated with the percentage of light transmitted through a film. A increase or decrease in this is accomplished by an increase or decrease in milliamprage and exposure time

Detail

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

Definition / smoothness

Outline sharpness and clarity of image exhibited on a radiograph.

Movement of the film, patient, or tube head. Penumbra (shadow).

What is the most common cause of poor definition or fussy outline and what is it called?

Noise

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

Radiolucent

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

Radiopaque

The 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

Sagittal plane

Imaginary vertical line by selecting the face into a right and left half; important during exposure to determine positioning of the patient

Midsagittal plane

Sagittal plane is also called?

Ala-tragus line

Imaginary line from the ala (wing) of the nose to the tragus (skin projection anterior to acoustic meatus), center of ear. 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; use mostly for extra oral films. Many machines have a stabilizing chin rest or aiming light to ensure this directional position.

Positive angulation