Computed Tomography Technologist Practice Exam 2026 - Free CT Technologist Practice Questions and Study Guide

The shades of gray in a CT image are primarily influenced by the quantities of x-ray photons striking the detector. This is because the amount of x-ray exposure received by the detector is directly related to the attenuation of the x-ray beam as it passes through different tissues of varying densities in the body.

When x-rays are emitted from the source, they pass through the patient and are partially absorbed or scattered by the tissues. The detector then captures the remaining x-ray photons that successfully penetrate through the body and reach it. The number of photons detected varies according to the density and composition of the tissues. For instance, denser tissues like bone will absorb more x-rays, resulting in fewer photons reaching the detector, which will appear as lighter shades on the CT image. Conversely, less dense tissues will allow more photons to reach the detector, presenting as darker shades.

This variation in the number of x-ray photons hits the detector leads to different levels of brightness in the resulting image, thus defining the shades of gray seen in CT scans. The other factors listed, such as the thickness of the scanned area, type of detector used, and matrix size and DFOV, play roles in image quality and resolution but do not directly determine how shades of gray are manifested