Dental Radiography Chapter 8

Radiolucent

refers to that portion of an image that is dark or black, structure that appears radiolucent lacks density and permits the passage of the x-ray beam (ie, air space)

Radiopaque

refers to that portion of an image that appears light or white, structures are dense and absorb or resist the passage of the x-ray beam (ie; enamel, dentin, bone)

Diagnostic image

the ideal dental image; provides a great deal of information; the images exhibit proper density and contrast, are of the same shape and size as the object exposed, and have sharp outlines

Density

The overall darkness or blackness of an image

Exposure factors

Settings for milliamperage (mA), exposure time, and kilovoltage (kVp).

Exposure time

the interval during which x-rays are produced; increase in exposure time = increase in density; x-ray timer controls exposure time by turning the few of x-rays on and off

Subject thickness

the thickness of soft tissue and bone in a patient

Contrast

the difference in the degree of blackness between adjacent on a dental image

High contrast

very high and very light areas

Low contrast

many shades of grey

Film contrast

characteristics of the film that influence radiographic contrast; (ie; inherent qualities of the film and film processing); increase in develop time or developer temp is increase in film contrast

Subject contrast

the characteristics of the subject that influence radiographic contrast; (ie; size and thickness of patient tissues; high KVP low subject contrast

Scale of contrast

the range of useful densities seen on a dental image

Short-scale contrast

dental image only shows two densities, areas of black and white; result from lower kvp, high contrast

Stepwedge

Used to demonstrate short scale contrast and long scale contrast

Sharpness

capability of the receptor to reproduce the distinct outlines of an object

Penumbra

unsharpness, or blurring of the edge

Focal spot

The tungsten target of the anode; converts bombarding electrons into x-ray photons, concentrating the electrons and creating an enormous amount of heat.; smaller focal spot area, sharper the image

Magnification

the radiographic image that appears larger then the actual size of the object it represents

Target-receptor distance

distance between source of x-rays and image receptor, longer PID and longer distance is decrease in magnification

Object-receptor distance

The distance between the object being radiographed and the image receptor, decrease in distance is decrease in magnification

Distortion

variation in the true size and shape of the object being radiographed

Object-receptor alignment

to minimize dimensional distortion, the object and receptor must be parallel to each other

X-ray beam angulation

minimizze dimensional distortion, the central xray beam must be perpendicular to tooth and the receptor

Film composition

the emulsion of faster film contains larger crystals that produce less image sharpness, smaller crystals produce sharper outlines

movement

a loss of image sharpness occurs if tube head, receptor or pt moves, image maybe nondiagnostic

low-scale contrast

dental image shows many densities or many shades of gray; results from high KVP and low contrast