What units are used to express the spatial frequency?

Spatial frequency is a concept used to describe the detail of an image in terms of the frequency of its detail structures over a given unit distance. It represents how often structures within an image occur within a specific region and is expressed in terms of line pairs per millimeter.

Line pairs consist of one dark line and one light line, which together serve as a measure to assess the resolving power of imaging systems. The higher the spatial frequency, the finer the details that can be resolved in the image. Hence, using line pairs per millimeter allows radiographers and technicians to quantify the image quality and resolution effectively.

Other units, such as Hertz, refer to cycles per second but are not typically used for spatial frequency in imaging. Decibels are a measure of intensity or power level, often used in acoustics or signal processing rather than spatial frequency. Pixels per inch pertains to digital image resolution rather than the spatial frequency in the context of how detail is perceived. Therefore, line pairs per millimeter is the appropriate unit for expressing spatial frequency in radiographic imaging.