A peak is a maximum of activity.

Photo Peak is short for photoelectric absorption peak, the maximum energy measured in a gamma ray absorption spectrum.

(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.

A fluoroscope projects x-ray images in a video sequence (movie) onto a screen monitor.
Early generation fluoroscopes presented particularly difficult viewing challenges for radiologists. The human retina contains two types of image receptors. Cones (central vision) operate better in bright light, while rods (peripheral vision) are more sensitive to blue-green light and low light. Therefore, the radiologists wear red goggles to filter out blue-green wavelengths to allow the rods to recover peak sensitivity before viewing fluoroscopic images.
To avoid this time consuming accommodation, the industry developed the image intensifier tube in the 1950s. Due to the high amount of individual images during a fluoroscan, a very sensitive amplifier is needed to cut down radiation exposure. Until today, image intensifiers amplify the faint light emitted by the fluorescing screen and the images can be viewed on a monitor. Recently, digital technique replaces the large and bulky image intensifier with flat-panel technology.
Various other components of a fluoroscope system include a gantry, patient table, x-ray tube, filters, collimators, images sensor, camera and computer, most similar to other radiographic systems.
A fluoroscopy system provides the view of moving anatomic structures and is valuable in performing procedures that require continuous imaging and monitoring, such as barium studies, gastrointestinal function tests, cardiac functions, studies of diaphragmatic movement, or catheter placements. A number of technologies are available to record images created during fluoroscopic (fluorographic) exams.

(FWHM) The full width at half maximum is a parameter to characterize the width of a peak on a graph. In nuclear medicine, the FWHM is used to determinate the energy resolution of gamma camera systems.