fluoroscopy

image intensifier

electronic vacuum tube that amplifies the brightness of the fluoroscopic image

input screen

cesium iodide phosphor coated onto a curved surface of glass, titanium or steel. converts incident xray to light

photocathode

device made of photo emissive metals that absorbs light and emits electrons in a process called photoemission

electrostatic lenses

series of bands or rings of metal which have varying positive voltages. these bands pull the electrons across the tube toward the output phosphor 

accelerating anode

small ring of metal located in the neck of the ii. device has a positive charge that accelerates electrons across ii tube causing them to strike output screen with 50-75X more kinetic energy they had leaving the photocathode. hole in center allows electrons to pass through anode to output screen 

output screen 

glass base coated with zinc cadmium sulfide phosphor which accepts electrons and emits green light. the output screen is only 1 inch

minification gain

gain in brightness due to energy from large output screen being compresses to very small output screen

total brightness gain

minification gain X flux gain

conversion efficiency

a ratio of the intensity of output phosphor to input exposure rate

intensity output phosphor / mR per sec at input screen 

ABC (automatic brightness control)

maintains image brightness by automatically adjusting exposure factors (adjust technical factors as tissue thickness and density changes) 

magnification mode 

increasing the voltage supplied to focusing lenses move focal point closer to input screen, which magnifies the image at the output scree. this is accomplished by using the ii in the smallest mode. resolution improves, but patient dose also increases. image may be magnified between 1.5 to 4 times its original size 

quantum mottle 

grainy image due to insufficient radiation 

coupling devices

devices that convert light from output screen to electrons, which can then be sent on to viewing devices. CCD / CMOS / vidicon and plumbicon tubes are all coupling devices 

CCD (charged coupled device)

couples output screen to viewing device. a flat compact light sensing device that accepts light and converts it to electrons. 

CMOS (complimentary metal oxide semi conductor)

can be used instead of CCD to convert light to electrons at the output screen/ 

TV camera tube 

vidicon and plumbicon tubes: cathode xray tubes that accepts light and emit electrons. Had been used at output screen to convert signal to electrons which can then be sent on to viewing devices 

flux gain

increase in brightness due to the acceleration of electrons across the ii tube. increase in light photons due to conversion efficiency of the input screen 

veiling glare

distortion caused by light scatter at the output screen that adds background signal degrading contrast 

pincushion distortion

type of distortion where the outer portion of image is magnified more than central portion because the input screen is curved, and the output screen is flat 

vignetting 

type of image distortion. brightness is greater at the center of the image and falls off towards the edges

pulsed fluoro

exposure is pulsed at a specific number of exposures per second, rather than a continuous stream, which saves patient dose

last image hold

after a short exposure, a continuous image is held on the viewing monitor using digital memory capabilities. this minimizes exposure and reduces patient dose

multifield intensifier

intensifiers with more then one field of view selection. dualmode has two selections