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hobson contrast > Digital imaging > Flashcards

Digital imaging Flashcards

(64 cards)

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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
Thin Film Transistors (TFTs)
-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
26
DELs collect .. | Direct conversion
the electrons that represent individual components of the image
27
Number of electrons deposited in the individual DEL corresponds to .. (Direct conversion)
amount radiation that strikes each area
28
As electrons are extracted from TFT, they are sent to the | direct conversion
ADC which sends the signal to the computer | -DELs automatically and immediately erase
29
Indirect Conversion DR
- 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
Charged Coupled Devices (CCD)
- Photosensitive silicon chips - Light from scintillator strikes silicon CCD chip - Electric signal from CCD sent to computer
31
Complimentary Metal Oxide Semiconductor (CMOS)
- Developed by nasa - Uses a scintillator material - Converts x-ray photons to light photons - STORES light photons in capacitors
32
Matrix
Made up of pixels and voxels
33
Spatial resolution dependent on
matrix size
34
Spatial Resolution in Digital Imaging Systems—dependent on:
- matrix size - pixel size - grayscale bit depth
35
in a Matrix..
-numerical values arranged in a square of rows and columns -Each square is a pixel
36
Pixel is
-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
Matrix size is expressed in terms of
total number of pixels
38
Larger matrix =
- smaller pixels | - Smaller pixels = greater spatial resolution
39
Detector Elements (DELs)
- 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
Fill Factor
how much the dell is receiving or recording information
41
Sampling Frequency
-number of pixels sampled per millimeter -Controls spatial resolution in CR -More pixels sampled, means increased spatial resolution
42
Low sampling frequency =
fewer samples = larger pixel size = lower spatial resolution
43
High sampling frequency =
smaller pixel size = higher spatial resolution
44
IP selection
-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
Nyquist Frequency
-Determines maximum spatial resolution for a given sampling frequency -desired spatial resolution (X) is desired, the sampling frequency must be 2(X)
46
Grayscale
-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
Pixel Bit Depth
-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
Contrast-to-Noise Resolution (CNR )
is a method of describing the contrast resolution compared with the amount of noise in the image
49
Digital images with a higher CNR will
increase the visibility of anatomic tissues
50
Modulation Transfer Function (MTF)
- Ability of imaging system to record spatial frequencies - Divides spatial resolution into individual components - Mathematical calculation
51
Signal-to-Noise Ratio
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
High signal-to noise ratio indicates a..
highly efficient system that displays little noise or has higher spatial resolution
53
Detective Quantum Efficiency
-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
Higher DQE indicates a receptor is more efficient in converting
the input signal and therefore lower exposure to the patient
55
DQE of 1 = 100% or no loss of information
100% or no loss of information
56
↑Absorption Efficiency = ↑Conversion Efficiency=
↑DQE
57
↑ DQE =
↓ Patient Dose
58
Gray scale bit depth range
• Ranges from 8-32 bits
59
Bit depth of 8=
256 hades of gray
60
Digital systems 14 Bit =
16,384 shades of gray
61
A Priori>
compares exposure data to a | single standardized data set
62
Neural
predefined data is matched with | exposure data extracted from IR
63
-Photostimuable phosphors have the ability to not only | absorb energy, they can also
STORE and release | energy
64
analog to digital converter (ADC)
changes analog signal to digital values

hobson contrast (3 decks)

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