(DQA) This procedure is used by system operators to verify an x-ray system, gamma camera, or CT scanner operation based on relevant image quality parameters like e.g., geometric distortion, x-ray yield, signal to noise ratio. The quality assurance should carry out according to instructions of the manufacturer.

See also Acceptance Checking, Calibration and Calibration Factor.

A phantom is an artificial object of known size and composition that is imaged to test, adjust or monitor the linearity, sensitivity, homogeneity, imaging performance and geometric aspects of CT scanners, gamma cameras or other radiographic systems. A phantom can be a fluid-filled container or bottle including structures of various materials, sizes and shapes.

See also Daily Quality Assurance and Acceptance Checking.

(PSF) The point spread function describes the response of an imaging system to a point or impulse input. A hypothetical point object will generally have an extended (blurred) image resulting from the imaging process; this is the point spread function characterizing the imaging process. Considering any object as composed of an assembly of point objects, knowledge of the PSF permits the prediction of how the object will be imaged, assuming linearity of the imaging process.

See also Resolution, Phantom and Daily Quality Assurance.