fluoroscopy VOCAB

image intensifier

electronic vacuum tube that amplifies the brightness of the fluoroscopic image

input screen

cesium iodide phosphor coated noto a curved surfacf glass, titanium, or steel

converts incident x-ray to light

photocathode

device made of photoemissive metals (cesium and antimony) that absorbs light and emits electrons in a process called photomission

electrostatic lenses

series of bands or rins of metal which have varying positive voltages

the bands pull the electrons across the tube toward the output phosphor

• accelerate and focus the electron stream

accelerating anode

small ring of metal located in the neck of the image intensifier

device has a positive charde that accelerates electrons across the image intensifier tube causing them to strike the output screen with 50-75 times more kinetic energy than they had leaving the phtotcathode (flux gain)

hole in the center allows electrons to pass thorugh anode to output screen

output screen

glass base coated within zinc cadmium sulfide phosphor which accepts electrons and emits green light

only 1 inch

minification gain

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

how to calculate total brightness gain

minification gain x flux gain

conversion efficiency

a ratio of the intensity of output phosphor to inpu texposure rate

intensity output phosphor / mR per sec at the input screen

automatic brightness control (ABC)

maintains image brightness by automatically adjusting exposure factors

adjusts technique when tissue densities change

magnification mode

increasing the voltage supplied to focusing lenses moves focal spot closer to input screen, which magnifies the image at the output screen

• uses smallest mode of image intensifier

• improves resolution

• improved pt dose

• can be magnified 1.5-4 times the 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

examples:

• CCD

• CMOS

• Vidicon nd Plumbicon tubes

carged coupled device (CCD)

couples output screen to viewing devices

a flat, compact light sensing device that accepts light and converts it to electrons

more sensitive than video tubes, operate at lower voltages, acceptable resolution, not as fragile

more commonly used and better quality than CMOS

complimentary metal-oxide semi-conductor (CMOS)

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

cheeper and usess less power than a CCD but worse quality

TV camera tube

vidicon and plumbicon tubes

cathode ray tubes that accept light and emit electrons which can then be sent to the viewing device

flux gain

increase in brightness due to the acceleration of electrons across the image intensifier tube

increase in light photons due to conversion efficiency of the output screen

veiling glare

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

pincushion distortion

the outer portion of image is magnified more than the 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 toward the edges

occurs as a consequence of pincushion distortion or from scattered light near the coupling device

pulsed fluoro

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

last image hold

after a short exposure, a continuous image is held on the viewing monitor using digital memory capabilities

minimizes exposure and reduces pt does

multifield intensifier

intensifiers with han one field of view selection (size of input screen)

dualmode has two selections, trimode has three