Compton scattering is the deflection of gamma- and x-ray photons by electrons.

See also Compton Continuum, Compton Effect, Air Kerma, Filter Grid, Focused Grid, Grid Efficiency, and Compton Arthur Holly.

Contrast is the relative difference of intensities in two adjacent regions of an image. When referring to computed tomography (CT), contrast is defined as a difference in Hounsfield units between structures. The measurement of contrast resolution in CT imaging involves determining how easy it is to differentiate tissues whose CT density is similar to that of their surroundings. An image lacks contrast when there are no sharp differences between black and white. Brightness refers to the overall lightness or darkness of an image.
The contrast between air, soft tissue, and bones in x-ray and CT images is based on their different absorption of x-rays. Differences in tissue density, thickness and changes of the x-ray spectrum have consequences for image contrast, image noise as well as patient dose.
Optimized tube current, collimation, pitch and image reconstruction improves the contrast. Higher image contrast is produced by increased slice thickness, smaller matrix, and large field of view which results in large voxel size; high mAs to reduce noise; low pass filter.

See also Contrast Enhanced Computed Tomography.

The gantry is a ring-shaped structure, containing the x-ray tube, collimators, filters, data acquisition system (DAS), associated electronics such as gantry angulation motors, rotational components including slip ring systems and the detector array in a CT or radiation therapy system. The table control, to regulate the gantry tilt and laser (or high intensity) lights are included within, or mounted on the gantry serving as anatomical positioning guides. To scan the patient, the patient table is moved through the gantry aperture.
The rotating arm on which an accelerator head is mounted is also called gantry. This gantry can rotate 360 degrees around its axis.

Grids are used in a test phantom to check the quality of x-ray images. Such a grid may consist for example, of gold structures on a silicon surface and a grid period length of 2 micrometer with space wide in between of 1 micrometer.
Filter grids are also used in x-ray imaging to reduce noise contributed by scatter.

Inherent filtration refers to a permanently implemented filter in the useful beam. Inherent filtration includes the window of the x-ray tube and any permanent enclosure for the tube or source.