4 Image receptors (1)

Question 1

what are the 2 types of radiographic film?

Answer 1

• direct action/packet film
• indirect action (used in conjunction with intensifying screens)

Question 2

what are the 2 types of digital receptors?

Answer 2

• solid-state sensors
• phosphor plates

Question 3

what is a direct film used for?

Answer 3

dental intra-oral

Question 4

what are the 2 types of solid state sensors?

Answer 4

CCD - charge-coupled device
CMOS - complimentary metal-oxide semiconductor

Question 5

what type of receptors do they use in ddh?

Answer 5

PSP (photo stimulated phosphor plates)

Question 6

briefly how do PSP plates work?

Answer 6

images are produced by interaction of x-rays with the phosphor layer on the plate, which is then scanned by a laser to produce an image

Question 7

what are the 2 sides of a phosphor plate?

Answer 7

• the pale side which has the phosphor coating (the phosphor can be various compounds, e.g. barium fluoride) this is the side the image is formed on
• the black side, this shows the size of the film and the orientation dot

Question 8

explain the stages of image formation on a PSP receptor

Answer 8

• the imaging plate is placed into the patients mouth and the phosphor coating is exposed to x-rays which cause a reaction within the phosphor (known as the stable excited state)
• the x-ray energy is stored in the electrons of the phosphor crystals (trapped signal - latent image)
• the plate is then dropped into the vista scan unit where it is scanned by a red laser (known as the unstable excited state)
• the stored energy is released as blue light
• the light is detected by the photodetector and sent to a signal digitizer (analogue to digital converter)

Question 9

how does the ADC (analogue to digital converter) convert the light into an image?

Answer 9

The ADC converts light to a digital signal (numerical value assigned to each pixel according to intensity of the detected light)
These pixels numerical values represent the various shades of grey which form the image on the monitor

Question 10

how is a PSP erased?

Answer 10

Image on plate is erased by exposing phosphor to bright light (releases any remaining trapped energy in the phosphor electrons)
= plate is ready to reuse

Question 11

What are the 4 layers which make up a charged couple device system (CCD - solid state sensors)

Answer 11

• front cover
• scintillator layer (converts x-ray energy to light)
• silicon wafer (converts light into an electrical signal)
• back cover (incorporating a cable to carry the signal to a PC) - most recent digital detectors are wireless, dont need to directly connect to the computer

Question 12

Explain how a CCD is used to produce an image

Answer 12

• X-rays hit the scintillator layer within the sensor
• this gives off light which hits the photosensitive cells within a very thin piece of silicon, these make up the pixels of the image
• electrons within each cell (pixel) are released and these form a charge which is converted to an electrical signal (voltage) which the computer converts into an image

Question 13

what does CMOS stand for?

Answer 13

complementary metal oxide semiconductors

Question 14

what does CCD stand for

Answer 14

charge-coupled device

Question 15

What is the difference between CCD and CMOS?

Answer 15

CMOS is very similar to CCD
- the only difference is the photocells are electrically isolated, therefore a signal (voltage) is sent from each individual cell (pixel) rather than lines of cells (pixels)

Question 16

What has a better quality image?

Answer 16

CCD - but CMOS catching up

Question 17

What are the advantages to digital receptors?

Answer 17

• no chemicals required to process digital images
• much faster processing images
• easy archiving (referring clinician has almost instant access)
• easy image transfer
• image manipulation - can do almost anything too it
• dose reduction - exposure factors reduced

Question 18

What are the disadvantaged of digital receptors?

Answer 18

• expensive
• easily damaged
• reduction in resolution due to pixel size (not as detailed as film)
• security issues (breaches of confidentiality
• shorter exposure times = drop in resolution of the image
• image manipulation - can make image look nothing like it originally done, can make you reliant on technology

Question 19

if exposure selection is too high, how will the image appear?

Answer 19

too dark and can appear flat, no contrast. This is because the high radiation has caused too much light to be produced in each pixel, which means there is little variation in the electrical signals which are converted to form the image

Question 20

In the dental hospital, what is the archive system used?

Answer 20

PACS - picture archiving and communication system

Question 21

What are size 4 PSP plates used for?

Answer 21

occlusal radiographs

Question 22

what are the 4 most common psp plate sizes<

Answer 22

0, 1 and 2 for periapical and bitewings
and 4 for occlusal

Question 23

What are the sizes available for solid state digital receptors?

Answer 23

Size 2 (usually only 1 size available)