(FNH) The focal nodular hyperplasia is a hypervascular, benign focal liver lesion. Various liver imaging techniques are common to differentiate FNH from a malign lesion, such as contrast enhanced ultrasound, MRI or a CT multi phase study.

The focal spot is the point where the electron beam impinges on the tube anode and from which x-rays are emitted. The size of the focal spot is determined by the size of the filament and cathode, which is determined by the manufacturer.
Most x-ray tubes have more than one focal spot size. The size of the focal spot has influence on spatial resolution. The smaller the focal spot, the better the limiting spatial resolution of the x-ray system, especially in magnification mammography. The use of a small focal spot concentrates heat onto a smaller portion of the anode therefore, more heat is generated and a longer cooling time is necessary.

(FDD) The focus to detector distance is the distance between the focal spot of the x-ray tube and the radiation detectors.

(FID) The focus to isocenter distance is the distance from the focus of the x-ray tube to the isocenter (the rotation center of the CT gantry).

A focused grid consists of lead foil strips interspersed with strips of radiolucent material that are angled in order to coincide with the shape of the beam.