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Digital imaging Flashcards

1
Q

Digital imaging history

A
  • starter 1970’s (CT)
  • Fugi was the first corp. (1980’s)
  • DR became later with less work than CR
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2
Q

In digital the info is received by the IR as

A

analog signal an converted to digital/numerical signal

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3
Q

reason to go for Digital Radiography

A

Faster, Cheaper, Safer, Better

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4
Q

DR advantages

A 
Increased contrast resolution
Throughput (immediately) 
Post Processing ability
Electronic transmission of images
Large dynamic range
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5
Q

Digital Radiography (DR)

A

Flat-panel detectors (2 types)
1) Direct conversion/capture without scintillator
2) Indirect conversion/capture with scintillator
- Charge-Coupled Device (CCD)
- Complementary Metal Oxide Semiconductors
(CMOS)

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6
Q

CR Cassette has

A

-Cassette holds the Imaging Plate (IP) or (PSP)
-Lightweight plastic or carbon fiber
-Inner surfaces (front and back) are lined with a felt-like
material that prevents electrostatic charging of the IP
-Back panel contains lead foil to minimize backscatter
-chip for info

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7
Q

Layers of the phosphor plate

A
  • protective
  • phosphor (active part)
  • conductor
  • support
  • back shield
  • lacking
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8
Q

PSP/IP how is coated?

A
  • IP is coated with emulsion/phosphor on one (1) side

- Phosphor side is placed face up in cassette

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9
Q

PSP plate storage has..

A

-Europium-doped (activated) stores energy
-Barium Fluorohalide crystals (BaFx:EU2+)
-X in the formula above indicates that certain halides
are interchangeable (bromide, iodide, gadolinium,
strontium

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10
Q

Chemical Formulas

A

BaFBr:Eu (bromide)
BaFI:Eu. (iodide)

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11
Q

TURBID PHOSPHOR

A

-shaped in round way all directions

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12
Q

beam interacts with electrons in the ..

CR

A

photostimuable phosphor crystals.

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13
Q

Stimulates or gives energy to electrons in the crystals, allowing them to enter the ..

A

conductive layer where they are trapped in an area known as “F” .traps, color, or phosphor centers

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14
Q

Phosphor crystals develop a series of defects called

A

“metastable” sites or ‘F’ centers (farbzentren), or color centers, throughout the lattice structure of the phosphor crystals

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15
Q

needle shape phosphor

A

once direction

better spatial resolution

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16
Q

IP stores the energy of the remnant beam in the form of..

A

latent image

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17
Q

Latent image is composed of

A

high energy electrons charges stored in the F centers,

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18
Q

IP is insterted in a reader , the reader scans by finely focused neon-helium laser beam in ..

A

a raster pattern (the way we read, line by line from left to right)

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19
Q

Electrons return to lower energy state photostimulated luminescence (PSL)

A

they release blue-purple light, go back to valance band

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20
Q

Quantization

A

analog image into matrix and each pixel is assigned digital number or brightness value

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21
Q

whether use cassette or not DR uses..

A

Flat Panel detectors with Thin-film-Transistor (TFT)

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22
Q

Direct detector uses a photoconductor material that directly converts..

A

x-ray photons into an electronic signal

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23
Q

Flat panel detector array replaces ..

A

the Bucky assembly

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24
Q

Direct Conversion

A

-Amorphous(dosent have distinct structure) selenium
(photoConductor) directly converts x-ray photons to
electrons
-Thin Film Transistors (TFTs) collect the electrons
-TFT is a complex circuit device that collects the
electrons emitted by the selenium
-Within the TFT are areas called detector elements or
DELs

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25
Q

Thin Film Transistors (TFTs)

A

-Small photosensitive detector elements (DELs)(pixels)
-Each DEL contains a photodiode that absorbs the
electrons and generates an electrical charge
-A field-effect transistor or silicon TFT isolates each
pixel elements and reacts like a switch to send the
electrical charges to the image processor
-Look-Up-Table applied and histogram created

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26
Q

DELs collect ..

Direct conversion

A

the electrons that represent individual components of the image

27
Q

Number of electrons deposited in the individual DEL corresponds to ..
(Direct conversion)

A

amount radiation that strikes each area

28
Q

As electrons are extracted from TFT, they are sent to the

direct conversion

A

ADC which sends the signal to the computer

-DELs automatically and immediately erase

29
Q

Indirect Conversion DR

A
  • 2 step process> x-ray photons are converted to light,
    light photons are converted to an electrical signal
    -Scintillator needed, usually a phosphor (gadolinium
    oxysulfide or cesium iodide)
    -Amorphous silicon used as a photoDetector to convert
    light into an electrical charge
30
Q

Charged Coupled Devices (CCD)

A
  • Photosensitive silicon chips
  • Light from scintillator strikes silicon CCD chip
  • Electric signal from CCD sent to computer
31
Q

Complimentary Metal Oxide Semiconductor (CMOS)

A
  • Developed by nasa
  • Uses a scintillator material
  • Converts x-ray photons to light photons
  • STORES light photons in capacitors
32
Q

Matrix

A

Made up of pixels and voxels

33
Q

Spatial resolution dependent on

A

matrix size

34
Q

Spatial Resolution in Digital Imaging Systems—dependent on:

A
  • matrix size
  • pixel size
  • grayscale bit depth
35
Q

in a Matrix..

A

-numerical values arranged in a square of rows and
columns
-Each square is a pixel

36
Q

Pixel is

A

-the smallest element in a digital image
-Each pixel represents a discrete numerical value
(brightness or shades of grey)
-Each pixel can be identified by its column and row
(address or location)

37
Q

Matrix size is expressed in terms of

A

total number of pixels

38
Q

Larger matrix =

A
  • smaller pixels

- Smaller pixels = greater spatial resolution

39
Q

Detector Elements (DELs)

A
  • Pixel size in DR is determined by the DELs
  • receives the remnant beam and collects the signal
  • Each DEL has a switch and a storage area
40
Q

Fill Factor

A

how much the dell is receiving or recording information

41
Q

Sampling Frequency

A

-number of pixels sampled per millimeter
-Controls spatial resolution in CR
-More pixels sampled, means increased spatial
resolution

42
Q

Low sampling frequency =

A

fewer samples = larger pixel size = lower spatial resolution

43
Q

High sampling frequency =

A

smaller pixel size = higher spatial resolution

44
Q

IP selection

A

-Size is critical due to image display
-CR readers scan approximately 2000 x
2000 pixels
-Using smallest IP possible results in highest
sampling frequency

45
Q

Nyquist Frequency

A

-Determines maximum spatial resolution for a given
sampling frequency

-desired spatial resolution (X) is desired, the sampling frequency must be 2(X)

46
Q

Grayscale

A

-number of different shades of gray the imaging
system is able to display

-Depends on pixel bit depth

-Systems that can display greater number of shades of
gray has better contrast resolution

47
Q

Pixel Bit Depth

A

-Determines number of density values
-Affects density and contrast of system
-Controlled by ADC
10 bit (210 = 1024)
12 bit (212 = 4096)* standard
16 bit (216 = 65,536)

48
Q

Contrast-to-Noise Resolution (CNR )

A

is a method of describing the contrast resolution compared with the amount of noise in the image

49
Q

Digital images with a higher CNR will

A

increase the visibility of anatomic tissues

50
Q

Modulation Transfer Function (MTF)

A
  • Ability of imaging system to record spatial frequencies
  • Divides spatial resolution into individual components
  • Mathematical calculation
51
Q

Signal-to-Noise Ratio

A

SNR is the ratio of useful data (signal) to useless data (noise)

Method to describe strength of the radiation exposure compared to the amount of noise in the image

52
Q

High signal-to noise ratio indicates a..

A

highly efficient system that displays little noise or has higher spatial resolution

53
Q

Detective Quantum Efficiency

A

-Measures a receptor’s ability to create an output
signal the accurately represents the input signal (x-ray
beam). Measurement of the efficiency of an image
receptor in converting x-ray exposure it receives into a
quality radiographic image
-As DQE, Conversion efficiency or absorption efficiency
increases, Exposure Decreases

54
Q

Higher DQE indicates a receptor is more efficient in converting

A

the input signal and therefore lower exposure to the patient

55
Q

DQE of 1 = 100% or no loss of information

A

100% or no loss of information

56
Q

↑Absorption Efficiency =

↑Conversion Efficiency=

57
Q

↑ DQE =

A

↓ Patient Dose

58
Q

Gray scale bit depth range

A

• Ranges from 8-32 bits

59
Q

Bit depth of 8=

A

256 hades of gray

60
Q

Digital systems 14 Bit =

A

16,384 shades of gray

61
Q

A Priori>

A

compares exposure data to a

single standardized data set

62
Q

Neural

A

predefined data is matched with

exposure data extracted from IR

63
Q

-Photostimuable phosphors have the ability to not only

absorb energy, they can also

A

STORE and release

energy

64
Q

analog to digital converter (ADC)

A

changes analog signal to digital values

hobson contrast (3 decks)

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