Which statement about basis images in CBCT is true?

• A. Hundreds of basis images (frames) captured around the patient
• B. Basis images are not used in CBCT
• C. Basis images are the final reconstructed volume
• D. Basis images are not related to angular information

Answer: (A)

Basis images in CBCT are the individual projection frames captured as the X-ray source and detector rotate around the patient. There are typically hundreds of these frames collected over a full rotation to provide sufficient angular sampling. These frames are the data the reconstruction algorithm uses to estimate the 3D volume; they are not the final image themselves. Because each frame corresponds to a specific viewing angle, basis images are inherently tied to angular information. Therefore, describing hundreds of basis images captured around the patient accurately reflects their role in CBCT.