An automatic and accurate x-ray tube focal spot/grid alignment system for mobile radiography: System description and alignment accuracya)
The AMX- modified with the AGA system. The modifications shown are (a) camera and LED lamp array housing mounted in front of the collimator, (b) grid tunnel mounted on the cassette bin door, (c) alignment button mounted on the side of the collimator, (d) optical target arm mounted on the top of the horizontal extension arm, and (e) housing for vertical drive motor.
The custom grid tunnel with the target arm attached to the left dock. The arm may be attached to either the left or right dock by the technologist as desired.
Schematic showing major electrical subsystems and components of the AGA system. All components shown are added except the three components in the AMX- box.
Images of the optical target captured from the video camera: (a) Background image (LED array off), (b) foreground image (LED array on), and (c) background-corrected image. Note that a ball of crumpled aluminum foil used as a distracter for these pictures is visible near the center of (a) and (b) but not in (c).
Camera calibration jig. The camera is positioned a known distance above a grid of dots spaced by 1 cm. The larger central dot identifies the center of the reference plane.
Radiographic alignment jig. The upper and lower plates contain radio-opaque objects; the positions of these objects in the acquired image are analyzed to determine the location of the focal spot.
Accuracy of camera position measurements for different focal spot positions. The vertical axis is the difference between the focal spot positions determined by camera measurement and by radiographic measurement. The horizontal axis is the radiographic position measurement.
Clinical chest images of a patient acquired 12–24 h apart (a) without a grid and (b) with 15:1 grid aligned using AGAS.
Results of laboratory test comparing manual and automatic alignment. The alignment error is calculated from the optical measurement of the relative positions of the collimator and the optical target.
Accuracy of camera measurements of the focal spot position.
Results of laboratory test of automatic alignment. The alignment error is calculated from radiographic measurements of the focal spot position.
Accuracy of clinical alignment over 23 alignment procedures. The alignment error is calculated from optical measurements of the focal spot position.
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