fluoro test 2 pptx

what is fluoroscopy used for?

dynamic function studies

what does dynamic function studies mean?

active diagnosis during an examination

can we use fluoro as a positioning guide?

no

what are the two types of c arm arrangements?

- under table units

- over table units

how is a fluoroscopic xray tube similar to normal xray tubes?

they can operate for longer periods of time at much lower mA

how many inches is the tube target fixed to? why?

15" to prevent SOD

fluoroscopic range

0.5-5.0mA (average of 3)

diagnostic tube range

50-1200mA

fluoroscopy imaging chain

tube, pt, light, electron, light

after exposure from the tube travels through the patient, what does it hit?

image intensification tube

after exposure hits the image intensification tube, where does it go?

split to tv, recording media for static and dynamic images

why is the image intensifier tube important?

early fluoroscopic screens required dark adaptation

cones or rods: photopic (daylight)

cones

cones or rods: scotopic (nightlight)

rods

cones or rods: high visual acuity

cones

cones or rods: low visual acuity (10x less)

rods

image intensifiers amplify brightness to activate what?

photopic acuity

if 2000 light photons go through an image intensifier, how many do we end up with?

200,000

what do image intensification tubes do?

amplify the brightness of the image

the image intensification tube is capable of increasing image brightness _____-______ times

500-8000

primary xray beam exits the patient and strikes the ______ screen

input

the fluorescent input screen absorbs xray photons and emits what?

light photons

input fluorescent screen has 0.1-0.2mm layer of what?

sodium-activated cesium iodide phosphors (CsI)

single incident photon produces over ________ light photons

1500

why is there a thin protective coating between input screen and photocathode?

prevents any chemical interactions

photocathode material is made of what?

photoemissive metals

what is photoemission?

a photocathodes materials absorb light photons and emit electrons

the charge of electrostatic lenses do what?

accelerate and focus the electron stream

what do electrostatic lenses do to the image?

they cause the image to reverse from left to right and inferior to superior on the screen

the ______ the voltage supplied to electrostatic lenses the _______ the acceleration

greater, greater

the ______ the focal point moves toward the input screen=more magnification

closer

true or false: the appearance of magnification can be done by the electrons from the center area of the input phosphor interact with the output phosphor and contribute to the image

true

what is the formula for the magnification factor?

input screen diameter/diameter of input screen used during magnification

what charge does the anode have?

positive

the positive charge of the anode causes what?

attraction of negative electrons from photocathode

where is the anode positioned?

in front of the output screen

the anode has a hole in it where the _____ pass to the output screen

electrons

what is the output screen made of?

silver-activated zinc-cadmium sulfide phosphor

electrons strike the output screen, converted into _______ light photons that exit the tube

green

Because phosphors emit light isotropically , an opaque filter prevents most light emitted back in the direction of the input screen from returning where it would do what?

degrade image

stage 1 of the fluoroscopic imaging chain

input screen: xray photons to light

stage 2 of the fluoroscopic imaging chain

photocathode: light to electrons

stage 3 of the fluoroscopic imaging chain

output screen: electrons to light

stage 4 of the fluoroscopic imaging chain

viewing monitor: light to electronic signal

what is the minification gain?

same # of electrons compacted when going from a large input screen to a smaller output screen

the minification gain does what to the image?

increase brightness

minification gain formula

input screen diameter ^2/ output screen diameter ^2

what is the flux gain?

increase in light photons due to conversion efficiency of output screen

what does the flux gain affect?

image quality

together, minification and flux gain do what?

increased image intensity

formula for total brightness gain

minification gain x flux gain

what does auto brightness control do?

Maintains the brightness of the image by automatically adjusting the exposure factors as necessary according to subject density and desired contrast

what does auto brightness control monitor?

intensity flowing between the cathode and anode and maintains fluoroscopic density & contrast

what is auto brightness control accomplished by?

varying kVp, mA, and pulse time

true or false: auto brightness control has a relatively quick response time

false, it's slow

size distortion is primarily caused by _____

OID

magnification intensifiers do not significantly affect actual _____ distortion

size

shape distortion is caused by ________ problems

geometric

while the input screen is concave, it does not eliminate ______ distortion at output screen

edge

what is vignetting?

diminished resolution and contrast at the image periphery

how much of the image is affected by vignetting?

8-10%

what is quantum mottle caused by?

insufficient mA

for digital fluoro, the ______ ________ works in conjunction with a flat panel receptor

image intensifier

cesium iodide phosphors ________ xray photons and ______ light that is recorded by the TFT

absorb, emit

what is a limitation of digital fluoroscopy?

electronic noise

digital fluoro has a good _____ contrast resolution

low

flat panel TFT fluoroscopy ________ the image intensifier tube and video camera

replaces

true or false: digital flat panel fluoroscopy has no vignetting

true

true or false: digital flat panel fluoroscopy ensures optimum image brightness, lowest possible dose, and optimal spatial resolution

true

true or false: digital flat panel fluoroscopy uses electronic magnification but still has an increase in pt dose

false, there is no increase in pt dose due to electronic mag

true or false: digital flat panel fluoroscopy has low contrast detectability

true

single detector or multi detector: fluoroscopic tube located under the table top

multi detector

single detector or multi detector: single TFT detector used in all imaging

single detector

single detector or multi detector: single xray tube mounted above pt; scatter radiation

single detector

single detector or multi detector: fluoroscopic TFT detector on carriage

multi detector

single detector or multi detector: 2 additional TFT detectors (upright imaging/recumbent table imaging)

multi detector

single detector or multi detector advantages:

-offers expandable SIDs

-reduced pt dose

-improved spatial resolution

-greater anatomical coverage

-operate fluoro behind control booth

single detector

single detector or multi detector advantages: capability of quickly switching back and forth (static to dynamic mode)

multi detector

the greatest concentration of exposure from the patient is 90 degrees from the _______/_______ beam

patient/central

true or false: collimation improves image quality by removing scatter

true

true or false: collimation creates more pt dose

false, its less

how much reduction do dynamic and static images have?

90%

how can you reduce dose with peds pts?

removing the grid from the system, thus reducing overall dose 30-50%

tabletop exposure should not exceed _____ R/min

10

minimum source to skin distance for mobile fluoro

12 inches

minimum source to skin distance for fixed fluoro

15 inches

federal law requires audible ____ min timer

5

how does magnification increase pt dose?

the ABC increases tube output

highest energy scatter occurs at _____ degree angle to the pt

90

lead apron is _______mm Pb/eq

0.5

lead gloves is ______mm Pb/eq

0.5

lead apron (fluoro skirt) with at lease ______mm Pb/eq

0.25