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SEM II - Exposure > DR Digital Imaging > Flashcards

DR Digital Imaging Flashcards

0
Q

Digital

A

A device or system that represents information as continuously variable numerical values.

Example - digital watch

CR and DR are digital

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1
Q

Analog

A

A device or system that represents information as continuously variable physical quantities.

Example - mechanical watch

X-ray film

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2
Q

FPD Flat Panel Detector (DR Imaging Plate)

A

Takes the place of cassettes and readers; 3 different types:
Tethered (w/cord)
Fixed (mounted in Bucky)
Wireless (uses radio signal sent from FPD to base)

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3
Q

Capture element

A

Remnant X-ray energy is captured.

Indirect DR - amorphous Sillicon
- converts X-ray to visible light

Direct DR - amorphous selenium
- converts X-ray directly to electrons

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4
Q

Coupling element

A

Transfers X-ray generated signal to collection element

Indirect DR - amorphous silicon
- light sent to photoconductive material

Direct DR - amorphous selenium
-electrons sent to TFT

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5
Q

Collection element

A

Collects photons or electrons to be quantified - assigned a digital value

Indirect DR -TFT - electrons from photoconductive material collected by TFT

Direct DR - TFT - electrons from amorphous selenium collected by TFT

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6
Q

Algorithm

A

A finite sequence of instructions, an explicit step by step procedure for solving a problem, often used for calculation and data processing. A computers mathematical “recipe”, not one size fits all

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7
Q

Sampling

A

The process used to digitize the spatial information in an image, typically achieved by dividing an image into a square or rectanglar array of sampling points.

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8
Q

Spatial resolution

A

The ability to see really small structures, the field of view, matrix size

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9
Q

Pixel size

A

Measured from side to side of the pixel, a less accurate measure, does not account for dead zones

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10
Q

Pixel pitch

A

Measures center of pixel to center of other; takes into consideration dead zones, a more accurate assessment.

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11
Q

Pixel density

A

/mm

the number of pixels per given area

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12
Q

Amorphous

A

having no shape or organization

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13
Q

Indirect Conversion Flat Panel Detectors

A

Detector that uses thin layers of amorphous silicon with an array of photodiodes - coated w/Photostimulable phosphor that emits light - converted to an electrical charge, signal sent to ADC to convert to digital signal. High QDE - lower patient dose; loss of resolution due to divergence of light emitted.

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14
Q

Amorphous Silicon (a-Si)

A

Phosphor material - emits light when stimulated

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15
Q

Direct Conversion Flat Panel Detectors

A

Uses a amorphous selenium coated TFT that directly converts X-ray to electrical signals. Absorbs remnant radiation in the selenium layers that are collected by capacitors, then sent to the ADC to convert to digital.
No light conversion = no light divergence

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16
Q

Amorphous Selenium (a-Se)

A

Absorbs X-ray - converts directly to electrons (no light divergence)

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17
Q

TFT - Thin Film Transistor

A

Collect electric charges, positioned in a matrix, detects charges on a pixel by pixel basis.
Capable of very high spatial resolution (greater than 20lp/mm)

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18
Q

AMA - Active Matrix Array

A

Amorphous silicon, capacitor, and TFT assembly

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19
Q

DEL - Detector Element

A

Small square capable of recording a certain number of electrons.

The smallest possible dot of information.

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20
Q

Capacitor

A

Temporarily collects electrical signal

21
Q

Matrix

A

The layout of cells in rows and columns containing pixels/voxels. The larger the matrix, the better the resolution.

22
Q

Hounsfeld Units/CT Numbers

A

a quantitive scale for describing radio density calculated by comparing the linear attenuation coefficient of each pixel

23
Q

Dot/matrix image

A

A 2 dimensional patterned array, used to represent characters, symbols and images

24
Q

LP/mm - Line Pairs per Millimeter

A

The measure of image sharpness. The ability of the human eye to see the number of high contrast pairs of lines appearing in the space of a single mm.

25
Q

Pixel

A

the smallest component of a picture, 2 dimensional - length x width.
Each pixel corresponds to a shade of gray.

26
Q

Voxel

A

3 dimensional, volume element (CT scan) each voxel corresponds to a shade of gray representing a volume within a patient.

27
Q

Dynamic Range/Bit Range/Bit Depth/Pixel Depth

A

The range of gray shades that can be assigned to a pixel, the higher the range, the more gray shades available to display the image.

28
Q

scintillation

A

xray photons are converted to light within the flat panel detector by a layer of cesium iodide amorphous silicon

29
Q

The divergent properties of light

A

Spreads out across all directions.

30
Q

The goal of ALL digital imaging systems is to convert X-ray energy into electron energy, Why?

A

Because electrons can be counted, either individually or as a sum negative charge. Counting something allows you to assign it a digital value. Computer can store info held as numbers(digital info held as binary code), but they cannot store analog information.

31
Q

Digitizing

A

The process of converting colors, shades, and shapes held as analog info into numbers

32
Q

Signal

A

Wanted anatomical information

- the voltage from the CCD/TFT

33
Q

Noise

A

Unwanted electrical interference

- the voltage supplying the CCD/TFT creates electron noise

34
Q

Noise interferes with

A

The purity of the voltage signal which occurs from therapy exposure

35
Q

Signal to noise ratio

A

A high signal to noise ratio indicates little noise

A low signal to noise ratio indicates lots of noise

36
Q

Quantum mottle

A

Noise

Too few X-rays in the beam to adequately form an image

37
Q

Structure mottle

A

Uneven distribution and/or size of phosphor crystals

38
Q

Monitors

A

DAC devices

39
Q

Contrast resolution

A

The ability to distinguish adjacent structures that have similar densities.

Rated in Bit depth

Aka pixel depth/bit range/dynamic range

40
Q

Latitude

A

Margin for technique error

41
Q

More grays =

A

Greater latitude

42
Q

Windowing

A

Allows the radiographer to alter the image contrast and density. Achieved by altering window width or window level

43
Q

Window width

A

Changes the range of gray tones
Increasing = longer scale of contrast (low contrast)
Decreasing = shorter scale of contrast (high contrast)

44
Q

Window level

A

Adjusts the overall optical density (also referred to brightness)

Raising = increase in overall density

Lowering = decrease in overall density

45
Q

Dose creep

A

Overexposing the patient only to let auto rescaling take care of making the image optimal
(Bad)

46
Q

Look up table (LUT)

A

A table of predetermined luminance values depending on anatomy.

Controls automatic rescaling

Results in image having appropriate brightness and contrast

47
Q

Veil glare

A

Glares a great distraction to the eye

48
Q

Shuttering should never be used

A

To mask poor collimation

49
Q

Background removal or shutter border

A

Underexposed borders around the collimation edges allow excell light to enter eyes

SEM II - Exposure (6 decks)

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