When noise increases in an image, what two factors also increase while one decreases?

The correct choice identifies the relationship between noise in CT images and the influences of matrix size and collimation. As noise increases in an image, the matrix size, which refers to the number of pixels used to form the image, must also increase to maintain detail and resolution. This is because a larger matrix allows for finer resolution and can help reduce the perception of noise by averaging out pixel values.

At the same time, collimation refers to how much of the patient is included in the scan and how finely the beam is directed. When noise in the image is higher, collimation is typically increased to enhance image quality by reducing scatter radiation and improving the clarity of the image.

Conversely, aperture size is affected negatively in this scenario; as noise increases, it becomes more challenging to retain high image quality, leading to a decrease in aperture size. Hence, the first two factors increase while aperture size decreases, maintaining a balance between quality and image clarity amidst higher noise levels.