What does a ray sum measure in a CT scan?

A ray sum measures the attenuation occurring along a ray in a CT scan. In computed tomography, a ray is a straight line through the object being imaged, and attenuation refers to the reduction in intensity of the X-ray beam as it passes through different tissues. Each tissue type has a unique density and composition, affecting how much it attenuates the rays.

During a CT scan, the X-ray tube rotates around the patient, creating multiple rays that traverse the body from various angles. The data collected along these rays is used to calculate the attenuation values, which contribute to forming a cross-sectional image. Therefore, the ray sum effectively represents the total attenuation encountered along that specific ray path.

Understanding this concept is crucial because it highlights the basis of how CT images are constructed, allowing for the visualization of internal structures based on their density differences. Each attenuation measurement contributes to the final reconstructed image, which assists radiologists in diagnosing medical conditions.