X ray beam is filtered to:

 # X ray beam is filtered to:

A. Soften the beam

B. Restrict beam size

C. Remove long wavelength  X rays

D. Remove short wavelength x rays

The correct answer is C. Remove long wavelength X rays.

Although an x-ray beam consists of a continuous spectrum of x-ray photon energies, only photons with sufficient energy to penetrate through anatomic structures and reach the image receptor (digital or film) are useful for diagnostic radiology. Low-energy photons that cannot reach the receptor contribute to patient risk but do not offer any benefit. Consequently, it is desirable to remove these low-energy photons from the beam. This removal can be accomplished in part by placing a metallic disk (filter) in the beam path. A filter preferentially removes low-energy photons from the beam, while allowing high-energy photons that are able to contribute to making an image to pass through.

Energy of x-rays depends directly on its frequency (E~f) and inversely related to wavelength (E~1/λ). Electromagnetic waves with higher frequencies have proportionally higher energies. The wave with the shorter wavelength, will have higher frequency. Since we know that the energy scales directly with the frequency we know that the wave that has the shorter wavelength will have higher energy.

Reference: Oral Radiology Principles and Interpretation, 7th Edition, White and Pharoah, Page no 10

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