Tubestand / Bucky Alignment for Stationary Radiographic Systems

 

Alignment of x-ray tube and receptor also ensures alignment of the radiographic grid. The function of a grid is to absorb radiation that is has been scattered and is no longer traveling from the direction of the tube's focal spot. To operate properly, the grid must be laterally aligned with the x-ray beam and be at the proper distance from the focal spot. Grid misalignment can cause various types of cutoff which can reduce the radiation penetrating the grid thus necessitating an increase in patient dose. It may also produce artifacts on the image.

If the lateral center of the grid is not aligned with the central x-ray beam, there will be a uniform reduction in the intensity of radiation reaching the receptor. This effect can occur either because of lateral misalignment or due to tilting of the grid with respect to the central beam.

Because there is a uniform reduction in beam intensity, there is no identifying image abnormality to alert the interpreting physician. And because beam intensity to the receptor is reduced, its effect must be offset by a compensatory increase in technique and thus patient dose.




Most grids are focused and thus must be operated within a designated distance range from the focal spot. If the distance of the grid from the focal spot is not within the designated range, the lateral center of the image will appear darker than the periphery.

 



If both the distance of the grid from the focal spot is not within the designated range and the grid is laterally decentered (or tilted), one side of the image will appear darker than the other. This effect can be dangerous since it has the potential to mimic a medical condition.

 

Misalignment can also cause inconsistencies in phototiming. Phototimer sensor fields are located at fixed positions and if the bucky is not aligned with the x-ray beam, sensors will not be positioned properly which can cause a change in the exposure time and thus patient radiation dose.

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