Input phosphor
- Converts incoming xray into light photons
- made cesium iodide
Photocathode
Converts light photons from the input phosphor into free electrons
Electrostatic lens
- located along the full length of the image intensification tube
- directs or focuses the path of electrons from the photo cathode to the surface of the output phosphorus screen
Output phosphor
- convert electrons sent from the photocathode into light photons
- made of zinc cadmium sulfide
Flat panel detectors
- indirect sold state system, xrays converted into light and then into an electronic signal
- better stability, lower pt dose, wider dynamic range
Brightness gain
BG= minification gain x flux gain
Minification gain=
Input phosphor (squared) / output phosphor (squared)
Flux gain
-fixed factor in II tube that deals with the increase in the # of light photons exiting the tube for every light photon produced at the input end of the tube
bright light vision (photopic)
- cone cells
- concentrated at fovea of the eye
- provides high visual acuity
Low light or night vision (scotopic)
- rod cells
- distributed along periphery of eye
- provides poor visual acuity- gross detail
Vignetting
Loss of detail along the edge of the fluoroscopic image
Cine fluoroscopic device
- will give highest pt dose (10x)
- exposed by light from the output end of the image intensification tube
Automatic brightness control (ABC)
- fluoroscopic mA is directly related to the brightness of the fluoroscopic image
- light intensity is measured by a photocell at the output phosphor end of the image intensification tube
Magnification mode
- magnification of fluoroscopic image is a function of the input phosphor size
- by reducing the size of the area of the input phosphor focused to the output phosphor screen results in an electronic mag. of the image
When switching from a larger to a smaller input phosphor size, the electron focal spot moves _____ from the output phosphor, which reduces the FOV and magnifies image
Further
Magnification factor
MF= input phosphor 1/ input phosphor 2
Magnifying the fluoro image causes what
- increased pt dose
- better SR
- better CR
Patient dose increase formula
Pt dose increase = input phosphor 1 (squared) / input phosphor 2 (squared)
When in mag mode of fluoro, your focal point moves _____ to the input phosphor
Closer
When not in mag mode, focal point moves _____ to output phosphor
Closer
As the distance between the image intensifier and the fixed source of radiation decreases what happens to patient dose
Decreases
Fluoroscopy is the single greatest source of acute radiation exposure to the patient in the diagnostic radiology environment
