CR and DR systems

Question 1

what does CR and DR stand for

Answer 1

computed radiography

digital radiography

Question 2

what are the components of a conventional film/cassette

Answer 2

cassette front
intensifying screens (scintillated layer)
radiographic film
lead foil
cassette back

Question 3

what is the intensifying screen of a film made of

Answer 3

(phosphors)
green glow: gadolinium oxysulphate
blue glow: caesium iodide

Question 4

why is a XR film dual sided with screens

Answer 4

increased detectability so reduced dose

Question 5

why is a darkroom lit up red

Answer 5

because the films contain phosphor which is green or blu sensitive

Question 6

what do you use to retain a latent image in XR film

Answer 6

silver halides

Question 7

how is the image produced from a XR film

Answer 7

retained image using silver halides

then silver is removed from image via chemical processing leaving a hardened film

Question 8

what are the 5 components of a CR system

Answer 8

1. mechanical drive
2. laser scanner and mirror
3. light channelling guide
4. light collection
5. white light

Question 9

describe the function of all 5 components of CR system

Answer 9

• mechanical drive takes in cassette opens removes and replaces plate, closes then returns to slot
• laser scanner and mirror usies helium-neon and excited the plate with red beam to cause it to emit blue light
• light guider guides it
• light collection uses photomultiplier tube or charged couple device to change from analog to digital
• white light is used to erase plate

Question 10

exactly how are latent images read

Answer 10

laser energy excites electrons releasing them from traps in conduction back back down into the valance band with excess energy emitted as light

light picked up by photomultiplier tube, converted to digital signal, building up line by line to create digital image

Question 11

why does a DR detector need a docking stand

Answer 11

to download images if made remotely and recharge battery

Question 12

why does a DR detector need internal support

Answer 12

provides structure of image matrix (usually glass)

Question 13

what is the use of an antenna in a DR wireless detector

Answer 13

data sent by wifi to computer for image to be viewed

Question 14

where is the processed image from a dr detector sent to?

Answer 14

PACS
picture archive communication system

Question 15

what are the 2 ways xrays are converted into electrons in DR

Answer 15

direct DR: amorphous silicon or selenium converts energy directly into electrons

indirect DR: XR converted into light by scintillator then into electrons

Question 16

what are the 2 materials that convert energy into electrons in direct DR

Answer 16

selenium or amorphous cilicon

Question 17

explain the process of indirect DR

Answer 17

1. xrays converted to light with thallium-activates caesium iodide scintillator needed CsI:Th
2. light converted to electrons by thin-film transistor
3. electrons converted to digital signal by matrix of hydrogenated amphorae silicone a-Si:H
4. signal passes along integrated electronic circuits
5. data transmitted by electronic amplifier circuits around edge of panel

Question 18

what can happen if you drop the DR detector and what will show up on the image because of it

Answer 18

-break glass
-break wires connecting readout circuit
-fracture crystals
-seperate scintillator from TFT

shows up as lines and patches missing

Question 19

what does TFT stand for

Answer 19

thin-film transistor

Question 20

what can happen if u let the DR detector get too hot

Answer 20

melts the glue binders

Question 21

what happens if you overexpose a DR detector and why

Answer 21

burns out image as its so sensitive

missing data in the lower tissue thicknesses

Question 22

what can happen to image if you let back scatter reach DR detector

Answer 22

shows reflected shadow of electrons or battery as its so sensitive

Question 23

what can happen to the image if you expose the DR detector for too long or short at the correct mAs

Answer 23

too long = overstimulation and blue

too short = lines forming as not enough time to collect data