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Year 3 Radiography > Digital Imaging > Flashcards

Digital Imaging Flashcards

1
Q

how many pixels/matrix in average image

A

256x256=65536 pixels

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2
Q

what is a pixel

A

image made up of pixels (picture elements)
each pixel has specific grey shade (black to white)
pixels arranged in a matrix of fixed dimension

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3
Q

define image sharpness

A

how well you can distinguish 2 close together objects

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4
Q

how is spatial resolution measured

A

line pairs per mm (lp/mm)

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5
Q

spatial resolution of

a. conventional film
b. human eye can resolve
c. current dental systems use

A

a. conventional film: 22lp/mm
b. human eye can resolve:8
c. current dental systems use:between 6 and 22

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6
Q

what is pixel shade

A

each pixel assigned a shade of grey depending on amount of radiation that has reached the sensor

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7
Q

what is number of grey shades dependent on

A

bit depth of image file

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8
Q

how to calculate bit depth

A

2 to power n

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9
Q

2 types of dental digital imaging technologies and name examples

A
  • direct: virtually instant image. Charge couple devices (CCDs), complementary metal oxide semi-conductor (CMOS)
  • indirect: plate must be read –> several seconds before image available. computer radiography plates
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10
Q

process of direct digital imaging

A
  1. scintillation layer converts x rays to light

2. semi-conductor based pixel array converts light to electron charge

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11
Q

compare process of CCD and CMOS

A

plate exposed to light –> energy released
CCD: light passed along pixels and read at the end
CMOS: light read from each pixel individually

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12
Q

adv/disadvantages of CCD and CMOS

A

CCD: -expensive to manufacture (have to transport charge across chip without converting)

  • create high quality low noise images
  • higher fill factor
  • better pixel uniformity
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13
Q

explain fill factor and apply to CCD/CMOS

A

how much of pixel converts light to charge.
CCD: whole pixel catches light and converts it to charge –> high fill factor
CMOS: space on each pixel for microcircuitry for detection so less efficient conversion of light energy (lower fill factor)

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14
Q

explain pixel uniformity and apply to CCD/CMOS

A

same amount of amplification from each pixel
CCD: same in all pixels because light is passed between pixels
CMOS: all individual detection –> poor pixel uniformity (bad)

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15
Q

how digital x rays are seen on pc stages

A

scintillation layer –> pixels –> wiring (voltage) –> analogue digital converter (ADC) –> converted to discreet numbers for digital signal –> image seen on PC

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16
Q

matrix number for

a. black
b. white

A

a. black: 0

b. white: 255

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17
Q

why are wireless sensors good

A

use less radiofrequency transmission (less xray exposure)

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18
Q

why are all in one digital imaging devices bad 2

A
  • have to hold it –> unsteady, blur

- operator has to stand v close to x ray –> exposure to x rays

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19
Q

2 alternative names for indirect digital imaging

A
  • photostimulable phosphor plates PSPs

- computed radiography CR

20
Q

how do PSPs work

A
  • plastic plate coated with storage phosphor material sensitive to x rays
  • phosphor stores x ray energy (like latent image in photographic film)
  • plate placed in laser reader/computer which releases photon energy as light
21
Q

what is a phosphor

A

anything that converts one energy to another ie x rays –> light

22
Q

what way round to put in phosphor plates and why

A

magnet side away from machine, otherwise would get image of magnet

23
Q

advantages of PSPs over CCD/ CMOS 5

A
  • larger variety of imaging areas
  • no bulky connecting cable
  • slimmer imaging plate (no electricity built in)
  • cost: PSP £20-50 per plate, CCD/CMOS £1000+ per sensor
  • has linear response to xrays over a wider range than most CCD/CMOS (no blooming)
24
Q

explain blooming

A

overload of pixels and bleeding in to adjacent pixels –> sensor does not respond in linear fashion to areas of high radiolucency eg pharynx

25
Q

disadvantages of PSP 3

A
  • plates must be processed within 8 hours or image faded
  • requires separate processing (reading device) –> takes longer
  • requires careful handling to prevent scratches
26
Q

define radiographic density

A

overall image blackness (denser=blacker)

27
Q

define radiographic contrast

A

degree of difference in density between structures

28
Q

Define film speed

A

sensitivity of x rays to film (F,E,D) –> how black film will get

29
Q

define detector sensitivity

A

same as film speed but for digital

30
Q

define image sharpness

what is this the same as

A

ability to display fine image detail and discriminate between adjacent structures
same as spatial resolution

31
Q

define noise

A

presence of random speckled appearance in digital image due to electronic noise

32
Q

how to overcome noise

A

increased exposure (signal)

33
Q

what 5 things can be edited using digital imaging. explain each

A
  • brightness: raises or lowers grey levels by same amount
  • contrast:
  • sharpening/edge enhancement: emphasises differences in densities
  • negative image
  • distance measurement, eg for implants/perio
34
Q

relationship between noise and exposure

A

inverse

more x ray dose –> less noise (but bad for pt)

35
Q

eg of when sharpening/edge enhancement may be used

A

to see endo files

36
Q

compare CCD,PSP,film diagnosis ability

A

equal (caries,periapical lesions, seeing endo files)

37
Q

7 disadvantages of physical archival of images /notes

A
  • space
  • staff to file/retrieve
  • can only see at one place/time
  • limited options for electronic transfer
  • only as good as person making record
  • risk of loss due to fire/flooding
  • risk of losing due to misfiling etc
38
Q

x ray archive system used here

A

picture archiving and communications system (PACS)

39
Q

PACS architecture

A

see slide. modalities (x ray machines in hosp)
–> acquisition gateways
–> DICOM storage (harddrive for city/country)
other way: can be retrieved by DICOM query/retrieve on any PACS display workstations

40
Q

what does DICOM stand for

A

digital imaging and communications in medicine

41
Q

what is DICOM

A

industry standard for communication/management of medical imaging info
PACS imaging equipment must be DICOM compliant

42
Q

advantages of digital imaging over film 6

A

-potential reduced pt dose
-instant/quickly available image
-electronic storage
-can edit image
-less consumables (sensors reusable, don’t have to buy film)
-no noxious chemicals –>safer, env favourable
(+ poss fewer processing errors)

43
Q

4 advantages of electronic storage

A
  • integrate with electronic pt notes
  • can view simultaneously at diff sites
  • electronic transfer
  • less likely to lose/damage image
44
Q

7 disadvantages of digital imaging

A
  • outlay cost
  • cross-infection control
  • bulky rigid sensors (not acceptable to pt)
  • physical damage to sensors
  • limitation on size of sensors
  • physical damage to wire on CCD/CMOS
  • images can be manipulated (fraud)
45
Q

explain the process of computed radiography

A
  • helium/neon laser releases red light
  • red light releases blue light energy from phosphor (europium-activated barium fluorohalide)
  • blue light detected by photomultiplier
  • photomultiplier converts energy light –> electrical
  • ADC: amplifies signal and converts it electric –> digital
  • image seen on workstation

Year 3 Radiography (9 decks)

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