CAMRT Radiography Practice Exam

How many CT numbers are assigned to each pixel in the image matrix?

1. One half the number of all values recorded from the array detector

2. One

3. Two values for a 256-matrix, 4 values for a 512-matrix

4. The number of HU per pixel is one-tenth the display field of view

The correct answer is: One

Each pixel in a CT image matrix is assigned one CT number, which is also referred to as a Hounsfield unit (HU). This single value represents the attenuation of X-rays as they pass through a specific region of tissue, allowing for characterization of the density and composition of the materials within the scanned area. The CT number is derived from the linear attenuation coefficients of the tissue compared to a reference standard, which is water, and it helps radiologists interpret the images. Different tissues and materials have distinct attenuation characteristics, resulting in a wide range of CT numbers. This singular assignment of one CT number per pixel enables a clear and concise representation of the data in the final image. Other options unnecessarily complicate the concept of how CT numbers correspond to individual pixels or misrepresent the relationship between matrix sizes and values assigned.