Alternating current continuously changes in magnitude and direction. Commonly the current changes at a frequency of 50 - 60 Hz.

Arrhythmia rejection is a method to reject irregular RR intervals (time duration between two consecutive R waves of the electrocardiogram) in cardiac gating during cardiovascular imaging and to improve the image quality, whereby the cardiac frequency is used as the basis of the normal heart rate. The RR interval window determines the percentage variation of the heart rate. Variations of the acquired data outside the window are rejected and not used in the image reconstruction. Also one interval after the arrhythmic beat will be rejected. Arrhythmia rejection may be inappropriate for patients with certain pathologies, because if the RR interval is constant long, short, long, - all intervals would be rejected.

A cinefluorography produces a movie (cine) film from an image intensifier during x-rays examinations (often called videofluorography, cineradiography or cine). Cinefluorography is always monitored on the TV screen normally used for fluoroscopy. The image from the output screen of the image intensifier is split with a semi-transparent mirror into two output ports; one leading to the movie camera and the other to the fluoroscopy camera. Most of the light is directed to the cine camera. The image on the monitor does not suffer in quality due to the fact that the tube current for cinefluorography is about 100 times higher than for common fluoroscopy.
The x-ray generator pulses are synchronized with the movements of the cine camera, so that no x-rays are emitted when the film is moved forward to the next frame. The needed very accurate synchronization of the x-ray generator can be achieved by use of high voltage switching in the secondary circuit of the constant potential x-ray generator, by starting and stopping the inverter in a medium frequency generator or by using a grid controlled x-ray tube.

The duty cycle is the part of the operation cycle of an accelerator during which radiation is produced. The duty cycle is the product of the pulse duration and the pulse-repetition frequency.

See also Duty Cycle in MRI.

(FWTM) The width of a Gaussian or Lorentzian type curve at the tenth of its maximum height (full width at half maximum (FWHM)) and a quality measure of the sharpness of a peak (frequency peak, resolution peak) used less frequently than the FWHM measure.