6. CCD and CMOS

Question 1

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

Answer 1

Charged-Coupled Devices (CCD)

Question 2

In a CCD system:

Answer 2

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)

Question 3

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

Answer 3

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

Question 4

coated with a photosensitive material & contains

the electronic gates

Answer 4

Polysilicon Layer

Question 5

an insulator

Answer 5

Silicon Dioxide Layer

Question 6

contains the charge storage area

Answer 6

Silicon Substrate

Question 7

Bucket Brigade Scheme (CCD)

Answer 7

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

Question 8

del

Answer 8

detector element

Question 9

Most CCD chips range from ____

Answer 9

2 to 4 cm

Question 10

The scintillator 2 main Types of Phosphors

Answer 10

• Structured

- Unstructured

Question 11

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

Answer 11

Unstructured

Question 12

powder-like grains

Answer 12

Unstructured (Gadolinium oxysulfide)

Question 13

Unstructured phosphor used in Digital Radiography

Answer 13

Gadolinium oxysulfide (Gd2O2S)

Question 14

allows greater detection of X-rays

than Gd2O2S scintillator

Answer 14

Structured

Question 15

almost no light spread

Answer 15

Structured

Question 16

spatial resolution is higher

Answer 16

Structured

Question 17

needlelike crystals

Answer 17

Structured (Cesium Iodide)

Question 18

Structured phosphor used in Digital Radiography

Answer 18

Cesium Iodide (CsI)

Question 19

Powder phosphors used for Computed Radiography

Answer 19

Barium Fluoride Bromide

Question 20

Needle phosphors used for Computed Radiography

Answer 20

Cesium Bromide

Question 21

used to focus light onto the CCD chip

Answer 21

• Lens

- Fiberoptics

Question 22

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

Answer 22

quantum efficiency (Detective Quantum Efficiency)

Question 23

3 Common Noise Types

Answer 23

1. Statistical noise
2. Dark current noise
3. Amplification noise

Question 24

noise created by the lack of light

photons from the scintillator

Answer 24

Statistical Noise

Question 25

occurs when the CCD chip operates | without radiation stimulation

Answer 25

Dark Current Noise

Question 26

common to digital systems

Answer 26

Amplification Noise

Question 27

during manufacturing, some pixels may not | work, the more bad pixels present, the worse the detector efficiency

Answer 27

Amplification Noise

Question 28

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

Answer 28

lower, | higher

Question 29

CCD Applications

Answer 29

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

Question 30

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

Answer 30

16 x 12 array

Question 31

CCD Advantages

Answer 31

1. Relatively inexpensive and much more simple | 2. Modular design, easy to repair, replace & upgrade

Question 32

CCD Greatest Disadvantages

Answer 32

1. Demagnification requires pixel to reduce in | size, which reduces DQE

Question 33

CMOS

Answer 33

Complementary Metal Oxide | Semiconductors Systems

Question 34

developed by NASA

Answer 34

Complementary Metal Oxide Semiconductors Systems (CMOS)

Question 35

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

Answer 35

Complementary Metal Oxide Semiconductors Systems (CMOS)

Question 36

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

Answer 36

Complementary Metal Oxide Semiconductors Systems (CMOS)

Question 37

is a semiconductor

Answer 37

Complementary Metal Oxide Semiconductors Systems (CMOS)

Question 38

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

Answer 38

Semiconductor

Question 39

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

Answer 39

CCDs

Question 40

imagers convert charge to voltage inside each pixel

Answer 40

CMOS

Question 41

most popular semiconductor

Answer 41

Silicon

Question 42

base material for most integrated circuit

Answer 42

Silicon

Question 43

Antimony (Sb) atomic number

Answer 43

51

Question 44

Boron (B) atomic number

Answer 44

5

Question 45

Arsenic (As) atomic number

Answer 45

33

Question 46

Carbon (C) atomic number

Answer 46

6

Question 47

Germanium (Ge) atomic number

Answer 47

32

Question 48

Selenium (Se) atomic number

Answer 48

34

Question 49

Sulfur (S) atomic number

Answer 49

16

Question 50

Tellurium (Te) atomic number

Answer 50

52

Question 51

Silicon (S) atomic number

Answer 51

14

Question 52

greater pixel fill factor

Answer 52

CCD

Question 53

more susceptible to noise

Answer 53

CMOS

Question 54

lower light sensitivity

Answer 54

CMOS

Question 55

uses very little power

Answer 55

CMOS

Question 56

inexpensive

Answer 56

CMOS

Question 57

lower quality

Answer 57

CMOS

Question 58

lower sensitivity

Answer 58

CMOS

Question 59

lower resolution

Answer 59

CMOS

Question 60

Charged-coupled device is based on the principle of _____

Answer 60

Photoelectric effect

Question 61

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

Answer 61

Capacitor

Question 62

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

Answer 62

silicon