Digital Radiography Flashcards

1
Q

Digital radiography uses what type of systems

A
  1. Direct detectors

2. Cassetteless system

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2
Q

What is the organizational approach to digital radiography

A
  1. Capture element
  2. Coupling element
  3. Collection element
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3
Q

Capture element

A

Where the x-ray is captured

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4
Q

Coupling element

A

That which transfers the x-ray generated signal to the collection element.

Coupling means attaching

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5
Q

Three types of collection elements

A

Photodiode
Charge-Coupled Device
Thin Film Transistor

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6
Q

2 light sensitive devices that collect photons

A

Photodiode

Charge-coupled device

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7
Q

Charge sensitive device that collects electrons

A

Thin film transistor

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8
Q

CCD are used in

A

Military use
Astronomy
Digital photography

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9
Q

What is a charge-coupled device

A

Silicone-based semi conductor that converts visible light photons into electrons.

A highly sensitive light sensitive solid-state device.

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10
Q

3 advantages of charge coupled device

A

Sensitivity—- ability of CCD to detect and respond to low levels of visible light which promotes lower dose.

dynamic range- ability of CCD to respond to a wide range of light intensity,

Size is very small so it is well-suited for DR applications

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11
Q

Charge couple devices have linear radiation response therefore

A

Image contrast is unrelated to x-ray exposure.

At low x-ray exposure CCD response is greater than filmscreen. Resulting in lower patient dose.

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12
Q

Describe indirect DR Cesium Iodide/CCD

A

Charge coupled devices can be tiled to receive the light from an area x-ray beam as it interacts with a scintillation phosphor such as cesium iodide.

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13
Q

What is the benefit of cesium iodide

A

It has a high photoelectric capture; so x-ray interaction is high and patient dose is lowered.

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14
Q

What are the steps from x-ray beam in cesium iodide CCD indirect DR

A

X-ray interacts with cesium iodine a scintillation phosphor which gives off light and interacts with fiber optic bundles and Is sent down to charge couple device array.

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15
Q

What is the challenge with cesium Iodide CCD indirect DR.

A

Creating a seamless Image at the end of each CCD in the tiled arrangement (The cross areas don’t capture image)
Solution is interpolation of pixel values at each tile interface (The lines get airbrushed out by interpolation)

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16
Q

Cesium Iodide/amorphous Silicon (indirect DR)

A

An indirect DR process by which x-rays are converted first to light then to an electric signal.

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17
Q

Cesium Iodide/amorphous Silicon (indirect DR)

Uses cesium iodide scintillation phosphor to?

A

Capture x-ray

Cesium iodide is coated over an active matrix array of amorphous silicon photodiodes.

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18
Q

Cesium Iodide/amorphous Silicon (indirect DR)

From X-ray

A

X-rays interact with cesium iodine and produce light.
The light interacts with the amorphous silicon to produce a signal.
The signal is stored in the thin film transistors until readout.

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19
Q

Cesium Iodide/amorphous Silicon (indirect DR)

Image receptor

A

Image receptor is made into individual pixels with each having a light sensitive face of cesium iodide with a capacitor and a thin film transistor embedded.

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20
Q

Challenge of Cesium Iodide/amorphous Silicon (indirect DR)

A

A large portion of the face of the pixel is covered by electronic components that are not sensitive to light.
20% does not contribute to the image.

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21
Q

Cesium Iodide/amorphous Silicon (indirect DR)

The percentage of pixel face sensitivity to x-ray is known as the

A

Fill factor

Currently this is 80%

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22
Q

Dilemma for indirect DR

A

As pixel size decreases the spatial resolution increases but at the expense of patient dose. This because as pixel size decreases, the fill factor decreases and x-ray intensity must be increased to maintain signal strength.

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23
Q

One solution for Dilemma of indirect DR

A

One solution is to use gadolinium Oxysulfide instead of Cesium Iodide which can be made thicker without compromising spatial resolution.

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24
Q

Direct Capture DR

A

Amorphous Selenium

No phosphor coating is used.

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25
Q

Direct Capture DR

From X-ray

A

X-rays interact directly with a thin layer of Amorphous Selenium, which produces a charged pair (by Direct Ionization of selenium) known as electron hole pairs (EHP). The EHP is the signal that charges the active matrix array of thin film transistors.
Charge is collected by a storage capacitor and remains there until read out by the switching action of the thin-film transistor.
A/D Convertor
Sent to computer

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26
Q

Advantage of direct capture DR

A

Spatial resolution is improved because there is no spreading of light.
Latent image is more accurate.

27
Q

Disadvantage of direct capture DR

A

Increased patient does because there is no spread of light.

It takes more radiation to release enough electrons to adequately charge the capacitor.

28
Q

What is the capture element and a coupling element in Direct capture DR

A

Amorphous Selenium

a-Se

29
Q

What are the readout electronics of direct capture DR

A

Data line and gate switches

30
Q

How many capacitors are in a flat panel detector

A

9 million

31
Q

Digital fluoroscopy equipment includes

A

Computer
Video monitors
A complex operating Console

32
Q

Digital fluoroscopy accommodate what process easily

A

Subtraction

33
Q

What is rapidly replacing the TV camera tube in the fluoroscopy chain

A

Charge coupled devices, photosensitive silicon chips

34
Q

PACS stands for

A

Picture archiving and communication system

35
Q

PACS allows for what ? digital form

A

Display
Interpretation
And storage of medical images

36
Q

Long term storage of images

A

Archive

37
Q

Display

A

Work stations can display old and new images

38
Q

PACS Communications

A

Archive, workstations and all modalities are networked together

39
Q

PACS changed what two things

A

The type of storage space required for medical images.

Role of film librarian

40
Q

5 advantages of PACS

A
  1. The problem of lost films is almost eliminated
  2. Fast access to prior studies
  3. Can do multiple modality exams on the same patient
  4. Can view the same exam from various workstations at the same time
  5. Workflow efficiencies
41
Q

Disadvantages of PACS 4

A
  1. High initial cost
  2. Lower reliability than film based systems (downtime/disaster)
  3. Learning curve for radiologists and staff
  4. Potential decrease in diagnostic ability (file compression/archive)
42
Q

Three principal components of PACS

A
  1. Display system
  2. The network
  3. The storage system
43
Q

Teleradiography

A

The process of remote transmission and viewing of images to workstations in other areas of the hospital or to radiologist offsite.
PACS

44
Q

Digitizer

A

A device that converts in analog radiograph to a digital image by the use of laserbeam technology

45
Q

DICOM stands for

A

Digital imaging and communications in medicine

46
Q

What type of digital detector do we use at St. Francis

A

Indirect

Amorphous silicon technology

47
Q

What is the detector size and number of pixels, of digital detector do we use at St. Francis

A

The detector measures 41 x 41 cm
detector provides 4 million pixels of data.
Each pixel delivers up to 16 bits of data.

48
Q

What is the role of cesium iodide in the indirect detector used at St. Francis

A

Since amorphous silicon cannot absorb x-rays directly, a scintillator material cesium iodine converts x-rays into visible light.

49
Q

3 advantages of cesium iodide/a-Si indirect detector used at St. Francis

A
  1. Wide dynamic range: long scale contrast, improved contrast resolution.
  2. Less repeats
  3. No darkroom Needed
50
Q

Where is the latent image stored in both indirect and direct DR

A

The matrix of uncharged and charged capacitors in the flat panel detectors

51
Q

Advantage of indirect DR

A

Lower patient dose due to the use of phosphors which spread light

52
Q

Disadvantage of the indirect method

A

Light scatters, degrading spatial resolution of the latent image, by exposing adjacent detectors.

53
Q

The amount of charge stored in the capacitor is proportional to

A

The amount of xRay energy that exposed that detector

54
Q

What reads the current as it passes through the TFT row by row

A

Gate switches and data lines.

55
Q

The current is amplified and passed through the ? Then to a computer

A

A/D converter

56
Q

The digital information is stored in the computer as

A

An array.

57
Q

An indirect DR needs – mR exposure and direct needs –mE exposure

A
  1. 5

1. 0

58
Q

DR image qualities are all related to

A

Pixel size

59
Q

Why do we can press large files

A

Large files have more pixels to send; more traffic and slower transmission results.

60
Q

10:1 compression means

A

Every 10 pixels we are only storing one pixel

61
Q

Two types of software artifacts

A

Preprocessing includes dead pixels

Compression artifacts which actually represents a lack of data.

62
Q

What is a histogram

A

A graph of frequency of occurrence versus digital value intervals

63
Q

Interpolation is

A

The mathematical process of assigning a value to a dead pixel based on the recorded values of adjacent pixels.

64
Q

Photodiode

A

A solid state device that converts light into an electric current.
Light photon collector.