These test patterns are used for spatial resolution measurements. The procedure is very quick, simple and accurate. The test patterns are used to evaluate film screen and digital systems, as well as magnification techniques.
Each test pattern is enclosed in plastic and has a different resolution range that is displayed in LP/mm. The patterns have varying numbers of line pair groups. Thicknesses are limited by the resolution, with a maximum thickness of 0.1 mm for test patterns up to 5 LP/mm. Radiopaque numbers indicate the resolution value of each group in LP/mm.
Line Pair Test Patterns containing two line groups of each resolution value are typically recommended for imaging systems; the groups in these types of patterns (see at right) are perpendicular to each other. These patterns are recommended when screen image or video intensifiers are to be tested. It is good practice to place them in various locations covering the entire area of an imaging field.
Star Test Patterns are used to measure focal spot size. Focal spot size can be confirmed by observing the regions of blurred image distortion which are seen when the test pattern is imaged. Photons from the various regions of the focal spot will cause blurring of the pattern due to the geometric distortions associated with different origins of the photons from the focal spot. Focal spot size can be determined by calculating the distance from the center of the pattern to the region where the blurring begins to occur.