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Vidicon camera is a term which commonly used for all types of television cameras. (Strictly, a vidicon is a

TV camera tube in which the target material is made of Sb2S3.) The principle of operation of the vidicon

camera is typical of that for other types of TV camera tubes, i.e. vidicon, plumbicon, saticon, pasecon

and newicon tubes. The vidicon camera tube is also sometimes called a hivicon tube.

Television camera or video camera, the camera used in X-ray fluoroscopic and digital imaging for

converting the dynamic optical image into a standard video signal. Because of the recent importance

that digital X-ray imaging has assumed, the television camera has been significantly refined to provide

improved image resolution, increased dynamic range, and improved temporal resolution over the

cameras used in non-medical imaging applications. Colour video cameras are not used in medical X-ray

imaging. Points of importance include the light sensor, the image scanner, and the scanning format.

Although many types of video cameras are available, the camera basically consists of a small electronic

vacuum tube surrounded by coils (focusing coils, horizontal and vertical deflecting coils). The image

receptor (target) is composed of a thin field of photoconductive material. In one of the most commonly

used video cameras, the vidicon, the photoconductive material is usually antimony sulphide (Sb2S3)

suspended as globules in a mica matrix. In a plumbicon, the material is lead monoxide (PbO). The target

is mounted next to a conducting plate (the signal plate) which is in turn mounted on a glass face plate.

Each globule is about 0.025 mm in diameter and is insulated from the neighbouring globules and from

the signal plate by the mica matrix. The light from the image is focused through the glass plate, the

signal plate and mica matrix onto the photoconducting globules, and photoelectrons are emitted in

proportion to the intensity of light. These electrons are attracted to the anode and are immediately

removed from the tube. The globules are capacitively coupled to the signal plate, and the residual

positive charge on the globules causes current to flow onto the signal plate. After exposure and

emission of the photoelectrons, a residual image that is an exact replica of the light image focused on

the target is stored in the photoconductor as a positive charge distribution.

The stored image is read out by scanning an electron beam across the globules. The electron beam is

emitted from the cathode, which is located at the opposite end of the camera tube from the target. The

cathode is heated indirectly by an internal electric coil. This heating causes electrons to be emitted from

the cathode by thermionic emission, creating an electron cloud. These electrons are formed into a beam

by the control grid which begins the electron acceleration towards the target. This cathode/grid

assembly is called an electron gun because it shoots the electrons out of the end of the control grid. The

electrons are accelerated by a 250 V potential difference toward the anode, which consists of a fine wire

mesh in front of the signal plate. The signal plate is at a lower potential than the anode, and the

electrons are decelerated as they approach the plate, reaching a net energy of about 25 eV. This

decelerating field also straightens the path of the electrons, causing them to strike perpendicularly to

the signal plate.

The electron beam is focused to a fine point as it hits the target and is scanned over the target by the

deflecting coils. The beam discharges each globule, discharging the capacitor and causing current to flow

from the signal plate. This current equals the charge stored in the photoconductor. By scanning the

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electron beam across the entire surface of the photoconductor, the entire image can be detected. The

output signal, the video signal, is a one-dimensional voltage versus time curve presentation of the two-

dimensional image. The video signal is amplified and later used in the "reverse" process in a television

monitor. In digital fluoroscopy DF systems, the signal can be digitized and transferred to a computer

memory for appropriate processing of the image.