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.

The gantry tilt is the angle between the vertical plane, and the plane containing the x-ray beam and the detector array. The gantry angulation allows aligning the selected anatomic region with the scanning plane.
A CT gantry can typically be angled up to 30° forward or backward. However, the gantry angulation is determined by the manufacturer and varies among CT systems. In a series of CT scans made with a tilted gantry the anatomy shifts in location from scan to scan.

The gantry aperture is the opening through which the table with the patient moves for the examination. Typical diameters of the gantry range from 50 to 85 cm. The gantry aperture diameters between 70 and 85 cm are useful for biopsy procedures and obese patients. Larger gantry apertures allow for easier handling of the biopsy equipment.
The scanning field of view in which the CT data are acquired is smaller than the gantry aperture diameter.

A computed tomography (CT) scanner is used to create cross-sectional slices of different objects. The medical version of CT system scans the human body for tumors or other abnormalities, other versions are used for non-destructive testing in the industry.
The CT imaging system includes the moveable gantry and patient table or couch. The gantry is a frame that contains the x-ray source, collimators, filters, detectors, a data acquisition system (DAS), rotational components including slip ring systems and all associated electronics. The x-ray tube and detector system are mounted opposite each other, allowing a rapid and synchronous rotation around the patient table.
In older CT scanners a small generator supplied power to the x-ray tube and the rotational components via cables for operation. Up to the 4th generation the CT tube and detectors rotate together around the patient for each slice. CT systems with slip ring technology (the x-ray tube rotates around a stationary ring of detectors) operate without cables and provides continuous rotation of the gantry components without interference of cables. Spiral CT scanners work with a continuous table movement while the x-ray tube is rotating around the patient.

Overview about CT scanner generations:
See also Contrast Media Injector, Dual-Head CT Power Injector, Syringeless CT Power Injector.

The isocenter in x-ray imaging is the space through which the central ray of the radiation beams passes.
The CT isocenter is defined by intersection of the gantry axis of rotation. In case of a cylindrical CT type, the isocenter is at the center of the gantry bore.
In radiation oncology the isocenter is defined by the beam centerline of a medical accelerator or cobalt unit. Typically, the isocenter is located 1 m from the radiation source.