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Yr 3 - Radiology > Digital imaging > Flashcards

Digital imaging Flashcards

1
Q

What are pixels arranged on?

A

A matrix of fixed direction

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2
Q

How many pixels in a 256 matrix?

A

256 X 256 = 65535 pixels

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3
Q

What happens to the resolution when using finer pixels?

A

Sharper

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4
Q

What does the spatial resolution go up to using a conventional film?

A

22 lp/mm

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5
Q

What resolution can the human eye resolve up to without magnification?

A

8lp/mm

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6
Q

Why are our films of higher resolution than the eye can resolve?

A

So we can appreciate greater detail (magnification) if wanted

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7
Q

What resolutions do current dental systems have?

A

Between 6 and 22 lp/mm

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8
Q

What is pixel shade?

A

Each pixel is assigned a shade of grey depending on the amount of radiation that has reached the sensor Typically more radiation = blacker but can be inverted

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9
Q

What is the number of shades possible dependent on?

A

The bit depth of the image 1 bit = 2 shades (2^1) 2 bit = 4 shades (2^2) 6 bit = 64 shades (2^3) Deeper but depth = uses more memory

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10
Q

What are the different types of digital image recording available.?

A

Direct digital Indirect digital

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11
Q

What is direct digital?

A

Produces virtually instant image (seconds) Uses charge coupled devices (CCDs) or complementary metal oxide semi-conductor (CMOS) = solid state circuitry (I.e. On a circuit board)

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12
Q

What is indirect digital?

A

Computed radiography plate is put through a reading machine before the image is available (I.e. Several seconds)

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13
Q

How is a digital image constructed?

A

Pixels each had electric grey shade ranging between black and white (only a fixed number of shades between the two of which only 250 are identifiable by the human eye)

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14
Q

What is the two stage process for digital direct 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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15
Q

How does a charge coupled direct digital device (CCD) deal with the electric charge generated?

A

The electron charge is passed from one pixel to the next and is read out at the end (has a single amplifying component)

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16
Q

How does a metal oxide semi conductor (CMOS) direct digital device deal with the electric charge generated?

A

The electron charge is read from each pixel individually (each pixel has microcircuitry built in)

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17
Q

What are charge coupled devices?

A

Expensive to manufacture (have to transport the charge across the chip without distortion) Created high quality, low noise images Higher “fill factor” Better pixel uniformity

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18
Q

What are complementary metal oxide semiconductors active pixel sensors?

A

Lower power requirements than CCDs Easier to manufacture Cheaper Light sensitivity Noisier than CCD -> individually amplify slightly different amounts = noise

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19
Q

How does it become a displayed image?

A

X-ray -> light -> energy -> ADC (analogue to digital converter) -> digital signal (discrete numbers) -> displayed image (0= black & 255 = white on 8 bit depth film)

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20
Q

How do we apply infection control to digital sensors?

A

Put them in plastic wraps

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21
Q

How do wireless sensors work?

A

Use radio frequency transmission

22
Q

What are the bad things about all in one devices (take image, send X-ray, have a digital sensor and screen all in one)?

A

Must be held in hands = blueprint Needs operator to stand close to the X-ray tube

23
Q

What does indirect digital imaging use?

A

Computed radiography = photo stimulatorable phosphor plate (PSPs)

24
Q

How does a photostimulable phosphor plate work?

A

Converts one type of radiation into another (X-rays to log) = plastic plate coated with a storage phosphor material = sensitive to X-ray (stored by the phosphor) = phosphor plate placed in laser reader/ computer = releases the photon energy as light (must be unwrapped before this = quick to avoid bleaching) = NOT instant image generation

25
Q

What light is shined at the plate to readout the X-ray energy?

A

He/Ne laser 633nm Shined on plate = releases blue light Passes through photomultiplier tube = image

26
Q

What happens to the phosphor plates once the X-ray has been read out?

A

Intense light is aimed at it to erase the energy stored in the plate and it is recycled

27
Q

What is the phosphor material found in the photo stimulated phosphor plates?

A

Europium activated barium fluorohalide

28
Q

What starts to happen to the image on the plates after it is taken?

A

Slowly degrades

29
Q

What does the photomultiplier do?

A

Converts the light signal into an electrical signal

30
Q

What are the sizes of photostimulated phosphor plates?

A

Same sizes as traditional films = fits into conventional holders - uses magnet go go into processing machine (must make sure magnet is on back of film pack otherwise it will cause a white spot on the radiograph)

31
Q

What are the advantages of direct digital imaging (CCD and CMOS)?

A

Larger variety of imaging areas No bulky connecting cable Slimmer imaging plate

32
Q

What are the advantages of using indirect digital imaging?

A

Has a linear response to X-rays over a wider range than most direct = copes with wider range of densities Cost of a PSP £20-£50 per plate (vs CCD/CMOS = £1000+ per plate

33
Q

What is blooming?

A

The overload of pixels & bleeding of signal into adjacent pixels = not reacting linearly and radiation too high to be captures = black area with no detail) N.b. This is more of a problem with direct rather than indirect digital imaging

34
Q

What are the disadvantages of Indirect digital photostimulated phosphor plates in comparison to the direct methods?

A

Plates must be processed within 8 hours (image fades) Requires separate processing = takes longer Requires careful handling of plates to prevent scratches

35
Q

What is radio graphic density?

A

Overall image blackness

36
Q

What is radiographs if contrast?

A

Degree of difference in density between structures

37
Q

What is film speed?

A

Sensitivity of film to X-rays

38
Q

What is detector sensitivity?

A

The digital version of film speed

39
Q

What is image sharpness?

A

Ability to display fine image detail and discriminate between adjacent structures

40
Q

What is noise?

A

Presence of random speckled appearance in digital image due to electronic noise May be over come by increased exposure

41
Q

How can digital images be manipulated?

A

Brightness Contrast

42
Q

What does alteration of brightness do?

A

Raises or lowed all the grey levels by the same amounts (If too bright or dark lose quality of image)

43
Q

How does image noise relate to exposure?

A

Image noise decreases with an increase in exposure Optimal exposure = compromise between image quality and dose

44
Q

How can you measure distances on a digital X-ray?

A

Use the computer programme to measure I.e. Distance from cups tip to apex

45
Q

Which is better CCD (direct digital) or PSP(indirect digital) or film?

A

None! Generally performance is equal in all for detecting caries, periapical lesions and visualising endodontic files

46
Q

What are the key things to remember to do when putting patient radiographs in their notes?

A

Must be accurately labelled Must be accessible Stored without loss or corruption Medico legal implications for improper storage

47
Q

What are the disadvantages of physical archival of images/ notes?

A

Requires a lot of space Requires staff to manage physical archive and retrieve records as required May only be viewed in one place at a time Limited options for electronic transfer Only as good as the person making the records Risk of data loss due to fire/ flooding Risk of losing notes due to misfiling etc.

48
Q

What is the picture archiving and communications systems (PACS)?

A

An electronic archive Received multiple modalities (digital X-ray, CT, MRI) Images visible simultaneously on workstations in multiple locations within the trust Image manipulation possible Integrated with radiology information systems (RIS) = bookings/requests got X-rays and shows history of X-rays

49
Q

What is the digital imaging and communications in medicine (DICOM)?

A

Industry standard for communication and management of medical imaging information Imaging equipment for PACS must be DICOM compliant The language imaging systems use to talk to each other = can view it in other systems

50
Q

What are the advantages of digital imaging compared to film?

A

Potential for reduced radiation dose Instant/ quickly available image Electronic storage = intention with electronic patient notes (able to view simultaneously at different sites, electronic transfer, reduce likelihood of losing image) Scope for image manipulation Reduced consumables = sensors reusable (no foil or film packets) No noxious chemicals (safer environmentally and fewer processing errors)

51
Q

What are the disadvantages of digital imaging?

A

Initial outlay cost Cross infection control Bulky rigid sensor Physical damage to sensors Limited on size of sensors (especially for solid states) Physical damage to wire in CCD/ CMOS Images may be manipulated fraudulently

Yr 3 - Radiology (9 decks)

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