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Imaging Lecture Rad 142 > Test 5 > Flashcards

Test 5 Flashcards

1
Q

Function of the laser:

A

Scans the CR imaging plate to release stored energy/latent image during image processing.

  • helium neon laser
  • solid state laser diode
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2
Q

Function of the photomultiplier tube:

A

Collects, amplifies and converts light to an electrical signal during CR image processing

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3
Q

Function of the ADC

A

Digitizes the electrical signal to produce the digital image

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4
Q

Function of the erasure cycle:

A

CR plate is erased by an intense white light after image processing. Releases any residual stored energy/latent image.

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5
Q

What are the advantages of CR digital imaging systems?

A
  • Compatibility w/ existing X-ray equipment
  • wider exposure latitude/dynamic range compared to film/screen imaging
  • ideal for use in mobile imaging.
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6
Q

What is the disadvantage of CR digital imaging systems?

A

Amount of time necessary for processing and image readout

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7
Q

What are the 4 components of the CR reader?

A

Laser
Photomultiplier/PM tube
Analog to digital converter/ADC
Erasure cycle

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8
Q

what are DR flat panel detectors?

A

an array of X-ray detectors that receive the exit radiation and convert it into electronic signals processed by a computer. Responsible for integrating the signal storage, readout, and digitizing electronics.

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9
Q

what are fixed detectors?

A

detectors permanently mounted in the table or upright bucky system that communicate directly with the computer.

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10
Q

what does indirect conversion detectors do?

A

convert exit radiation first to visible light and then to electrical charges .

  • uses cesium iodide scintillator to convert exit radiation into visible light
  • layer of amorphous silicon is what converts the visible light into electrical charges.
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11
Q

what does direct conversion detectors do?

A

converts exit radiation DIRECTLY into electrical charges with faster image reconstruction.
*amorphous selenium coated detectors is what converts the exit radiation directly into electrical charges.

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12
Q

With direct and indirect conversion detectors, what are the jobs of thin-film-transistors and the analog to digital converters (ADC)?

A

TFT-temporarily stores the electronic charge

ADC-converts varying electrical/analog signals into digital data.

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13
Q

what are the advantages of DR direct digital imaging systems?

A
  • produces higher resolution images faster than CR and film/screen imaging systems
  • lower patient exposure and dose.
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14
Q

what are the disadvantages of DR direct digital imaging systems?

A
  • incompatibility with existing X-ray equipment

- expensive

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15
Q

what is the digital image matrix composed of?

A

rows and columns of pixels (picture element). Each pixel corresponds to a shade of gray representing an area in the patient called a voxel (volume element).

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16
Q

what does bit depth determine and what does it control?

A
  • determines the # of shades of gray the system is capable of displaying in the digital image.
  • determines contrast resolution
  • controls brightness
17
Q

define brightness

A

intensity of light that represents the individual pixels in the image on the monitor

18
Q

The greater the bit depth of a digital system, the ____________.

A

the greater the # of shades of gray the system is capable of displaying on the monitor.
-high resolution=improved visibility of tissues with similar densities

19
Q

what is a histogram?

A
  • graphic display of digital data during image processing
  • shows distribution of pixel values
  • indicates low, proper or high exposure
20
Q

what is an algorithm?

A

mathematical formula applied during digital processing

21
Q

what is spatial resolution dependent on?

A
  • aquisition pixel size

- digital display pixel size

22
Q

noise/quantum mottle creates ____ signal and _____noise level in a digital image.

A

high

low

23
Q

in the SNR ratio, what represents signal?

A

of X-ray photons that strike the digital detector

24
Q

what kind of SNR is desirable in digital imaging?

A

high signal to low noise level

25
Q

what is the gray scale rendition or look up table? what is its purpose?

A
  • software applies a look up table to the values of interest during image processing.
  • purpose is to rescale the values of interest to produce an image with the proper contrast for the selected anatomy to make details visible.
26
Q

what does edge enhancement/noise suppression do?

A

improves the visibility of small, high contrast structures in the digital image

27
Q

what does contrast enhancement do?

A

alters or increases the pixel value to display different brightness levels

28
Q

what does window level control and what is the relationship?

A

-brightness (density)
-direct relationship
^ window level = ^brightness

29
Q

what does window width control and what is the relationship?

A

-contrast
-inverse relationship
window width ^ = contrast decreases

30
Q

how does the computer make up for dead/unresponsive pixels?

A

applies a correction algorithm and assigns new digital values to each dead pixel, by taking the average value of surrounding adjacent pixels

31
Q

what are the three types of image noise?

A

mechanical
optical
computer

32
Q

what are mechanical defects?

A

CR reader slow and fast scan drivers

33
Q

what are optical defects?

A

laser intensity control, scatter and light emitted by the IP

34
Q

what are computer defects?

A

electronic noise
inadequate sampling
inadequate quantization

35
Q

what is DICOM?

A
  • digital imaging and communications in medicine

- Protocol and communication standard used for info sharing between PACS and other modalities

36
Q

what does the radiology network do?

A

links all 3 computer systems: HIS RIS DICOM

37
Q

why is the resolution bar test pattern performed?

A

to evaluate the focal spot of the X-ray tube, measures effective focal spot and actual focal spot

38
Q

why is the CR dose monitoring test performed?

A

to monitor increases or decreases in radiation exposure doses.

39
Q

when and why are spatial contrast tests performed?

A

once a month, to control and correct the quality and performance of the CR digitizer system

Imaging Lecture Rad 142 (4 decks)

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