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RT 212 > 6. CCD and CMOS > Flashcards

6. CCD and CMOS Flashcards

1
Q

The oldest indirect-conversion digital radiography systems used to acquire the digital image

A

Charged-Coupled Devices (CCD)

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2
Q

In a CCD system:

A
  1. X-ray photons interact with a scintillation
    material and the signal is transmitted by lenses
    or fiber optics to the CCD.
  2. During the transmission process, the lenses
    reduce the size of the projected visible light
    image.
  3. Transfer the image to one or small capacitors
    that convert the light into an electrical charge.
  4. This charge is stored in a sequential pattern
    released line by line and sent to an analog-to-digital converter (ADC)
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3
Q

Charged-Coupled Devices (CCD) chip is made up of a

A

polysilicon layer, a silicon dioxide layer, and a silicon substrate

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4
Q

coated with a photosensitive material & contains

the electronic gates

A

Polysilicon Layer

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5
Q

an insulator

A

Silicon Dioxide Layer

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6
Q

contains the charge storage area

A

Silicon Substrate

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7
Q

Bucket Brigade Scheme (CCD)

A 
1. Each pixel or detector element (del) 
contains three electrodes that hold 
the electrons in an electrical 
potential well. 
2. The dels are formed by voltage gates that opens and closes like 
gates to allow the flow of electrons. 
3. To collect the charge on the silicon  chips, the voltage sign within each del is change, moving the electrons 
by rows down the columns until the 
readout row is reached
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8
Q

del

A

detector element

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9
Q

Most CCD chips range from ____

A

2 to 4 cm

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10
Q

The scintillator 2 main Types of Phosphors

A
  • Structured

- Unstructured

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11
Q

produce more light spread when stimulated by X-rays, thereby decreasing the efficiency of the detector

A

Unstructured

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12
Q

powder-like grains

A

Unstructured (Gadolinium oxysulfide)

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13
Q

Unstructured phosphor used in Digital Radiography

A

Gadolinium oxysulfide (Gd2O2S)

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14
Q

allows greater detection of X-rays

than Gd2O2S scintillator

A

Structured

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15
Q

almost no light spread

A

Structured

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16
Q

spatial resolution is higher

A

Structured

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17
Q

needlelike crystals

A

Structured (Cesium Iodide)

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18
Q

Structured phosphor used in Digital Radiography

A

Cesium Iodide (CsI)

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19
Q

Powder phosphors used for Computed Radiography

A

Barium Fluoride Bromide

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20
Q

Needle phosphors used for Computed Radiography

A

Cesium Bromide

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21
Q

used to focus light onto the CCD chip

A
  • Lens

- Fiberoptics

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22
Q

The amount of electrons produced relative to the incident light from the scintillator is the _______ of the CCD

A

quantum efficiency (Detective Quantum Efficiency)

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23
Q

3 Common Noise Types

A
  1. Statistical noise
  2. Dark current noise
  3. Amplification noise
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24
Q

noise created by the lack of light

photons from the scintillator

A

Statistical Noise

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25
Q

occurs when the CCD chip operates

without radiation stimulation

A

Dark Current Noise

26
Q

common to digital systems

A

Amplification Noise

27
Q

during manufacturing, some pixels may not

work, the more bad pixels present, the worse the detector efficiency

A

Amplification Noise

28
Q

the ____ the cost of the CCD, the ___ the number of defects

A

lower,

higher

29
Q

CCD Applications

A
  1. Digital Fluoroscopy
  2. Stereotactic Breast Biopsy
  3. Digital Mammography
  4. General Radiography
30
Q

In general radiography, CCD’s may be tiled in a ____ to a single CCD

A

16 x 12 array

31
Q

CCD Advantages

A
  1. Relatively inexpensive and much more simple

2. Modular design, easy to repair, replace & upgrade

32
Q

CCD Greatest Disadvantages

A
  1. Demagnification requires pixel to reduce in

size, which reduces DQE

33
Q

CMOS

A

Complementary Metal Oxide

Semiconductors Systems

34
Q

developed by NASA

A

Complementary Metal Oxide Semiconductors Systems (CMOS)

35
Q

use a scintillator that when struck by X-ray photons, convert the X-rays into light
photons and store them in capacitors

A

Complementary Metal Oxide Semiconductors Systems (CMOS)

36
Q

each pixel or detector element (del) has its
own amplifier, which is switched off and on
by circuitry within the pixel, converting the
light photons into electrical charges

A

Complementary Metal Oxide Semiconductors Systems (CMOS)

37
Q

is a semiconductor

A

Complementary Metal Oxide Semiconductors Systems (CMOS)

38
Q

is a solid chemical element or compound that conducts electricity under
some conditions, making it a good medium for
the control of electrical current

A

Semiconductor

39
Q

move photogenerated charge from pixel to pixel and convert it to voltage at output node

40
Q

imagers convert charge to voltage inside each pixel

41
Q

most popular semiconductor

42
Q

base material for most integrated circuit

43
Q

Antimony (Sb) atomic number

44
Q

Boron (B) atomic number

45
Q

Arsenic (As) atomic number

46
Q

Carbon (C) atomic number

47
Q

Germanium (Ge) atomic number

48
Q

Selenium (Se) atomic number

49
Q

Sulfur (S) atomic number

50
Q

Tellurium (Te) atomic number

51
Q

Silicon (S) atomic number

52
Q

greater pixel fill factor

53
Q

more susceptible to noise

54
Q

lower light sensitivity

55
Q

uses very little power

56
Q

inexpensive

57
Q

lower quality

58
Q

lower sensitivity

59
Q

lower resolution

60
Q

Charged-coupled device is based on the principle of _____

A

Photoelectric effect

61
Q

represents the number of electrons it collected, then this information is sent to the computer

62
Q

CCD’s uses a thin wafer of ______ to produce electrons from photons because it easily releases electrons with visible light

RT 212 (10 decks)

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