In which modality does bone attenuate or weaken x-ray photons?

• A. CT
• B. MRI
• C. Attenuation
• D. Detective Quantum Efficiency

Answer: (A)

Bone dampens x-ray photons because its density and atomic structure cause strong absorption and scattering of the beam. In computed tomography, an x-ray tube sends photons through the body from many angles and detectors measure how much the beam is attenuated at each position. The varying attenuation, especially the high attenuation from bone, is what creates the contrast and allows CT to reconstruct cross-sectional images. MRI, on the other hand, relies on magnetic fields and radiofrequency signals rather than x-rays, so attenuation of x-rays isn’t the basis for its images. Attenuation is simply the physical process, not an imaging modality, and Detective Quantum Efficiency is a detector performance measure, not a modality. Thus, the modality that uses bone attenuation of x-rays to form images is computed tomography.