Flurorscopy

Question 1

what is the input fluorescent screen consist of? (material)

Answer 1

cesium iodide

Question 2

how many light photons would a single 25-keV incident photon typically produce?

Answer 2

1,500 light photons

Question 3

about how much of the incident beam does the input screen absorb?

Answer 3

66% of the beam - producing a good conversion efficiency

Question 4

what does the photocathode do with the photons that the input screen creates?

Answer 4

emits them into electrons

Question 5

what does the input screen do w the absorbed xrays?

Answer 5

emits photons

Question 6

what is the job of the photocathode?

Answer 6

absorbs photons from input screen and turns them into electrons

Question 7

what is the process that happens in the photocathode called?

Answer 7

photoemission (similar to thermionic emission, except the stimulation is light instead of heat)

Question 8

what are the electrostatic lenses?

Answer 8

series of charged electrodes

Question 9

where are the electrostatic lenses located?

Answer 9

inside the glass envelope of the tube/image intensifier

Question 10

how are the electrostatic lenses similar to the focusing cup in the xray tube?

Answer 10

the charge of the lenses accelerates & focusesthe electron stream, which carries the fluoroscopic image

Question 11

where is the anode located in the image intensifier?

Answer 11

inside glass envelope, and immediately in front of the output screen

Question 12

how much kV is the anode usually supplied w?

Answer 12

25 kV

Question 13

why does the anode have a hole in the center of it?

Answer 13

to permit accelerated electrons to pass through the anode field and onto output screen

Question 14

what are the electrons converted into once they strike the output screen?

Answer 14

green lught photons that exit the tube

Question 15

what does the output screen absorb?

Answer 15

electrons

Question 16

what is a measurement of the increase in image intensity achieved by an image intensification tube?

Answer 16

total brightness gain

Question 17

what is the total brightness gain determinded by?

Answer 17

minification gain & flux gain

Question 18

what occurs as a result of the same number of electrons that were produced at the large input screen being compressed into the area of the small output screen?

Answer 18

minification gain

Question 19

what is a measurement of the increase in light photons due to the conversion efficiency of the output screen?

Answer 19

flux gain

Question 20

what is the shape of the input screen?

Answer 20

concave

Question 21

what is a blotchy or grainy appearance caused by insufficient radiation to create a uniform image?

Answer 21

quantum mottle

Question 22

what is a semiconducting device capable of storing a charge from light photons striking a photosensitive surface?

Answer 22

charge-coupled device (CCD)

Question 23

how is the video signal emitted?

Answer 23

in a raster scanning pattern

Question 24

what is the primary advantage of CCDs?

Answer 24

extremely fast discharge time, which eliminates image lag

Question 25

what helps CCDs prolong their life?

Answer 25

by operating at lower voltages

Question 26

how do digital fluoroscopy units process the image?

Answer 26

from the image coming from the CCD by sending an analog signal through an ADC (analog-to-digital converter)

Question 27

what does TFTs replace that are in nondigital fluoro systems?

Answer 27

they replace the image intensifier

Question 28

tabletop exposure should not exceed what rate?

Answer 28

10 R/min

Question 29

what is the minimum source-to-skin distance for mobile fluoroscopic equipment?

Answer 29

12” (30 cm)

Question 30

what is the minimum source-to-skin distance for stationary fluoro equipment?

Answer 30

15” (38 cm)

Question 31

what is the federal law for a timer in fluoro?

Answer 31

5 minute audible timer

Question 32

what is the required lead shield thickness for the bucky slot cover and the drapes?

Answer 32

0.25 mm/Pb