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With early PACS, radiologists thought that they needed 4-6 monitors. ... non-uniformity, erasure - blub problems. How else can Morie OCCUR? quantum mottle ... – PowerPoint PPT presentation

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Title: ARRT%20


1
ARRT Other DIGITAL Terms Defined
  • April 2009
  • Wk 9/10 RT 255

2
Display Workstations
  • Conventional film/screen radiography uses large
    multiviewer lightboxes.
  • With early PACS, radiologists thought that they
    needed 4-6 monitors.
  • Now, the number of monitors has dropped to an
    average of 2.
  • Development of viewing software and better
    hardware.

3
Name the 3 types of monitors
4
Name the 3 types of monitors
  • Two major types of monitors with a third type
    gaining acceptance
  • CRT (?)
  • LCD (?)
  • Plasma screen

5
3 types of monitors
  • CRT (cathode ray tube)
  • LCD (liquid crystal display)
  • Plasma screen

6
Medical Use of Monitors
  • Most medical monitors used to display
    radiographic images are monochrome
    high-resolution monitors.
  • Early displays used were primarily CRTs, but as
    the LCD technology has gotten better, more LCDs
    are taking the place of the older CRTs.

7
Image Display MONITORS
ARRT DEFINITIONS
  • viewing conditions
  • (i.e.,luminance,ambient lighting)
  • spatial resolution
  • contrast resolution/dynamic range
  • DICOM gray scale function
  • window level and width function

8
viewing conditions luminance,ambient lighting
  • How does this affect viewing images
  • ? Different monitors

ARRT DEFINITIONS
9
viewing conditions luminance,ambient lighting
  • How does this affect viewing images?
  • Surrounding light impacted what was seen on image
    now
  • With different monitors
  • LCD gives more light.
  • LCD can be used in areas
  • with a high amount of ambient light.
  • dark rooms not necessary

10
Technologist workstation monitors are used in
brightly lighted areas. So monitor luminance, the
brightness of a monitor display, is an important
consideration. Also, the monitor must allow a
technologist to visualize enough detail to
discern motion and that the recorded lines are
sharp and visible.
11
Monitor Advantages and Disadvantages
  • Most consumers want a monitor that can provide
    the highest resolution for the best price.
  • Most radiology applications have traditionally
    used the CRT because of its superior resolution,
    but as the LCD technology has progressed, more
    and more departments are buying the more slim and
    light weight LCDs to replace the bulky CRTs.

12
MONITORSDisplay Workstations
  • Early PACS reading rooms required supplemental
    air-conditioning to offset the heat from multiple
    CRTs.
  • Resolution and orientation of the monitor is also
    a factor in determining which type of monitor is
    to be used.
  • Most cross-sectional imaging is read on a 1K
    square monitor.
  • Most computed radiography (CR) and digital
    radiography (DR) images are read on at least a
  • 2K portrait monitor

13
LCD
  • 1.3 megapixels
  • to 5 megapixels.
  • mammography imaging
  • at least 5 megapixel resolution is required.  

14
CRT
  • The CRT is the most popular monitor on the
    market.
  • It consists of a cathode and anode within a
    vacuum tube.
  • Cathode boils off a cloud of electrons, and then
    a potential difference is placed on the tube.
  • A stream of electrons is sent across to the
    anode, which in the case of the monitor is a
    sheet of glass coated with a phosphor layer.

15
CRT
  • Electrons strike the phosphor on the glass.
  • Impact causes the glass to emit a color based on
    the intensity of impact and area that the
    electrons strike.
  • The electrons interact with a red, green, or blue
    dot to form the color and image that is being
    sent from the video card signal.

16
CRT
  • Electron beam starts in the upper left hand
    corner and scans across the glass from side to
    side and top to bottom.
  • Once beam reaches the bottom, it starts back over
    at the top left.
  • Most monitors have 350 lines to be scanned.

17
LCD
  • LCD produces images by shining or reflecting
    light through a layer of liquid crystal and a
    series of color filters.
  • Monitor is two pieces of polarized glass with a
    liquid crystal material between the two.
  • Light is allowed through the first layer of
    glass.

18
LCD
  • When a current is applied to the liquid crystal,
    it aligns and allows light in varying intensities
    through to the next layer of glass through color
    filters.
  • Light forms the colors and images seen on the
    display.

19
LCD Display Workstations
  • LCD has dropped in price and has risen in
    quality.
  • LCD will soon take over PACS display market
    because of its size, resolution, and lack of heat
    production.
  • LCD requires less maintenance.

20
CRT vs LCD
  • CRT
  • Luminance higher in the center
  • Lower measurable black levels
  • Phosphor granularity adds to spatial noise
  • Viewable area smaller than stated size
  • Better color reproduction
  • More responsive on redraw
  • More rugged
  • Aspect ratio 43
  • LCD
  • Less veiling glare
  • Consumes less energy
  • Increased spatial resolution
  • Larger viewing area by described size
  • Display limited to designed resolution
  • Can position screen
  • Smaller footprint and lighter
  • Widescreen aspect ratio 169

21
Monitors more terms
  • Aspect ratio
  • Ratio is the width of the monitor to the height
    of the monitor.
  • Most CRT monitors have an aspect ratio of 43,
    and LCD monitors have a ratio of 169.
  • Viewable area
  • The viewable area is measured from one corner of
    the display to the opposite corner diagonally.

22
Plasma Display
  • Plasma monitors are new to the consumer market.
  • They have been used in government and military
    applications since the late 1960s.
  • They are made up a many small fluorescent lights
    that are illuminated to form the color of the
    image.
  • Monitor varies the intensities of the various
    light combinations to produce a full range of
    color.

23
Image Display MONITORS
  • viewing conditions
  • (i.e.,luminance,ambient lighting)
  • spatial resolution
  • contrast resolution/dynamic range
  • DICOM gray scale function
  • window level and width function

24
MONITORS Spatial Resolution
ARRT DEFINITIONS
  • Spatial resolution refers to the amount of detail
    present in any image.
  • Phosphor layer thickness and pixel size
    determines resolution in CR.
  • The thinner the phosphor layer is, the higher
    resolution.
  • Film/screen radiography resolution at its best is
    limited to 10 line pairs per millimeter (lp/mm).
  • CR resolution is 2.55 lp/mm to 5 lp/mm, resulting
    in less detail.

25
MONITOR RESOLUTION
26
digital image characteristics
ARRT definitions
  • spatial resolution
  • sampling frequency
  • DEL (detector element size)
  • receptor size and matrix size
  • image signal (exposure related)
  • quantum mottle
  • SNR (signal to noise ratio) or
  • CNR (contrast to noise ratio)

27
Spatial Resolution
  • A radiograph typically does not show soft tissue
    structures
  • Digital image shows not only the soft tissue but
    also the edge of the skin.
  • Giving the appearance of more detail.

28
MONITORScontrast resolution/dynamic range
  • Appearance of more detail is due to the wider
    dynamic recording range / contrast resolution
  • and does not mean that there is additional
    detail
  • Because so many more densities are recorded in CR
    (wide dynamic range), images appear more
    detailed.

29
contrast resolution
  • The contrast resolution of a monitor is the
    difference between the maximum and minimum
    luminance of the display.

30
Exposure Latitudeor Dynamic Range
  • CR and DR
  • Contain a detector that can respond in a linear
    manner
  • as compared to S shape of HD Curve
  • Exposure latitude is wide, allowing the single
    detector to be sensitive to a wide range of
    exposures.

31
Why do digital systems havesignificantly greater
latitude?
  • Linear response give the imaging plates greater
    latitude
  • Area recieving little radiation can be enhanced
    by the computer
  • Higher densities can be separated and brought
    down to the visibile density ranges
  • (Brightness in DR replaces density)

32
Monitors - RESOLUTION
  • Pixel is a basic picture element on a display.
  • A pixel is any of the small discrete elements
    that together constitute an image.
  • Resolution - of pixels contained on a display
  • Relationship
  • More pixels in an image, the higher the
    resolution more information that can be
    displayed.
  • Resolution also is defined as the process or
    capability of distinguishing between individual
    parts of an image that are adjacent.

33
Nyquist frequency
  • The highest spatial frequency that can be
    recorded by a digital detector.
  • is determined by the pixel pitch.
  • The Nyquist frequency is half the number of
    pixels/mm.
  • A digital system with a pixel density of 10
    pixels/mm would have a Nyquist frequency of 5
    line pair/mm.

34
sampling frequency
ARRT definitions
  • The frequency that a data sample is acquired from
    the exposed detector.
  • It is expressed in pixel pitch and pixels per mm.
  • Sampling frequency may be determined by receptor
    size depending on the vendor.
  • KODAK 8x10 better detail than 14x17
  • Use of the smallest imaging plate possible for
    each exam results in the highest sampling rate.
  • When the smallest possible imaging plate is
    selected, a corresponding matrix is used by the
    computer algorithm to process the image.

35
Pixel picture element,
  • the smallest area represented in a digital image.
  • A digital radiography image consists of a matrix
    of pixels which is typically several thousand
    pixels in each direction.
  • Pixel density A term that describes the number
    of pixels/mm in an image. Pixel density is
    determined by the pixel pitch.

36
DEL (detector element size)receptor size and
matrix size
  • a pixel or picture element.
  • The typical number of pixels in a matrix range
    from about 512 512 to 1024 1024 and can be as
    large as 2500 2500.
  • The more pixels there are, the greater the image
    resolution.
  • The image is digitized by position (spatial
    location) and by intensity (gray level).

37
DELs detector elements
  • DELs collect electrons that are extracted from
    the detector assembly and converted into a
    digital value by an ADC. That process creates the
    image that displays on our monitor.
  • DEL size controls the recorded detail, or spatial
    resolution, for the flat-panel device. The
    technologist cant change the size of the DEL,
    which is fixed for that piece of equipment.
  • .

38
Detective Quantum Efficiency
  • Known as the fill factor, the larger the area of
    the TFT photodiodes, the more radiation can be
    detected and the greater amount of signal
    generated.
  • Consequently, the greater the area of the TFT
    array, the higher the DQE.
  • Over 1 million pixels are read converted

39
FILL FACTOR
  • A field-effect transistor (FET) or silicon TFT
  • Isolates each pixel element
  • Reacts like a switch to send the electrical
    charges to the image processor

40
Detective Quantum Efficiency
  • How efficiently a system converts the x-ray input
    signal into a useful output image is known as
    detective quantum efficiency, or DQE.
  • DQE is a measurement of the percentage of x-rays
    that are absorbed when they hit the detector.

41
Detective Quantum Efficiency
  • In other words, CR records all of the phosphor
    output. Systems with higher quantum efficiency
    can produce higher-quality images at a lower
    dose.
  • Indirect and direct DR capture technology has
    increased DQE over CR.
  • However, DR direct capture technology, because it
    does not have the light conversion step and
    consequently no light spread, increases DQE the
    most.

42
SNR (signal to noise ratio) orCNR (contrast to
noise ratio)
ARRT definitions
  • SNR (signal to noise ratio) there is always a
    very small electric current flowing in any
    circuit - is called background electronic noise.
  • It is similar to the fog on a radiograph in that
    it conveys no information and serves only to
    obscure the electronic signal.
  • CNR (contrast to noise ratio) measure for
    assessing the ability of imaging an procedure to
    generate clinically useful image contrast.
  • gives an objective measure of useful contrast.

43
Image Display
  • spatial resolutioncontrast resolution/dynamic
    range

44
  • What is a 3-D array of Pixels ?
  • A voxel (a volumetric pixel) is a volume element,
    representing a 3-D value space. A pixel which
    represents 2D image data.

45
Pixel Pitch
  • The space from the center of a pixel to the
    center of the adjacent pixel. It is measured in
    microns (µm).
  • Pixel pitch is determined by sampling frequency
    for cassette-based PSP systems and by DEL spacing
    for TFT flat panel.

46
The Nyquist Theorem
  • Theorem states that when sampling a signal, the
    sampling frequency must be greater than twice the
    bandwidth of the input signal so that the
    reconstruction of the original image will be
    nearly perfect.
  • At least twice the number of pixels needed to
    form the image must be sampled.
  • If too few pixels are sampled, the result is a
    lack of resolution.

47
Monitors Display Workstations
  • Pixels are arranged in a matrix.
  • Common screen resolutions found on todays
    monitors are the following
  • 1280 1024 (1K)
  • 1600 1200 (2K)
  • 2048 1536 (3K)
  • 2048 2560 (5K)

48
Monitors DOT PITCH
  • Dot pitch is the measurement of how close the
    dots are located to one another within a pixel.
  • The smaller the dot pitch of a display, the finer
    the resolution.
  • Dot pitch may be expressed as aperture grille
    pitch or slot pitch.

49
Monitors REFRESH RATE
  • Refresh rate or vertical scanning rate
  • Refresh rate is a measure of how fast the monitor
    rewrites the screen or the number of times that
    the image is redrawn on the display each second.
  • Refresh rate helps to control the flicker seen by
    the user.
  • The higher the refresh rate, the less flicker
    will be seen.
  • Most refresh rates on todays computer are set
    between 60 and 75 Hz the image is redrawn 60 to
    75 timers per second.

50
Image Display MONITORS
  • viewing conditions
  • (i.e.,luminance,ambient lighting)
  • spatial resolution
  • contrast resolution/dynamic range
  • DICOM gray scale function
  • window level and width function

51
MONITOR RESOLUTION
  • DICOM gray scale function calibration of
    monitors to the same standard communication of
    images
  • Window level affects brightness (density) - B
  • Window width function affects contrast/gray scale
    - A

windowing and level
52
MONITOR Image Manipulation and Enhancement
Functions
  • Window/level
  • This is a default function of the left mouse
    button.
  • By depressing and holding down the mouse button
    and moving the mouse up and down and left and
    right, the window and level can be adjusted.
  • Window (width) represents the range of gray
    values.
  • Level represents the center value of the range.
  • A change in the window and level appears to
    change the brightness and contrast of the image.

53
Image Manipulation and Enhancement Functions
  • Other Tools Annotations
  • Annotations are NOT to be used
  • to label left or right to indicate the patients
    side.
  • Annotations are used to indicate prone or supine,
    30 minutes, upright or flat.
  • Any other image information is appropriate.
  • Radiologist will place arrows or circles around
    pathologic or questionable areas.

54
MONITOR Image Manipulation and Enhancement
Functions
  • Pan, zoom, and magnify
  • Tools are used primarily by the
  • radiologist to increase the size of an area on
    the image.
  • Magnify usually magnifies a square area of the
    image
  • Pan and zoom functions are usually used together.
  • Image is first zoomed up to the desired
    magnification level then Pan icon is activated.
  • Zoomed image can be moved around to view the
    different areas of the image.

55
Image Manipulation and Enhancement Functions
  • Measurements
  • Size of a pixel is a known
  • so the software
  • has the ability to measure
  • structures on the image
  • based on this.
  • Angle measurement.
  • Can give an angle measurement between two
    structures
  • Commonly used when reading spine studies

56
Image Manipulation and Enhancement Functions
  • Measurements
  • Region of interest
  • Measurement tool determines the pixel intensity
    of a certain area.
  • Each type of tissue or fluid has a different
    intensity of reading.
  • Radiologist can make a determination whether
    something is solid or fluid.
  • Each pixel can have a gray
  • level between 0 (20) and 4096 (212).
  • The gray level will be a factor
  • in determining the quality of the image

57
DR
58
Monitor Navigation Functions
  • Hanging protocols
  • Can be viewed
  • 11 41 etc
  • Protocol can also be specified to show the
    previous exam on one monitor and the current exam
    on the other
  • Once set, the most efficient study navigation is
    determined.

59
Image Management Functions
  • Patient demographics
  • Patient demographics
  • must be correct.
  • If demographics are not correct at the archive
    level, the images could be lost.
  • Changes should only be made when the information
    is absolutely known to be wrong.
  • Many hospitals allow only certain persons the
    access to change demographics just to keep the
    errors to a minimum.

60
Image Management Functions
  • Query/retrieve icon
  • Used to retrieve on demand any studies from the
    archive
  • Allows user to query a study on multiple fields
  • Patients name or identification
  • Date of service
  • Modality
  • Diagnosis code or comment field

61
WINDOW LEVEL / WIDTHWhich one controlsDenisty
(brightness) ?Contrast
What else control these in DIGITAL IMAGING?
62
Enhanced Visualization Image Processing
  • Takes image diagnostic quality to a new level
  • Increases latitude while preserving contrast
  • Process decreases windowing and leveling
  • Virtually eliminates detail loss in dense tissues

63
Contrast / Denisty (Brightness)
  • CR and DR
  • Kilovoltage peak still influences subject
    contrast, but radiographic contrast is primarily
    controlled by an image processing look-up table.
    LUT
  • Milliampere-second setting has more control over
    image noise, whereas density is controlled by
    image-processing algorithms.

64
Physician Review Stations Monitors
  • Step-down model of the radiologists reading
    station (lower res)
  • Some functions reduced
  • One of the most important features
  • is ability to view current and previous reports
    with images.
  • Many vendors are integrating
  • the RIS functions
  • with PACS software.

65
Technologist QC Stations
  • review images after acquisition but before
    sending them to the radiologist
  • May be used to improve or adjust image-quality
    characteristics
  • May be used to verify patient demographic
    information
  • Placed between the CR and DR acquisition
    modalities as a pass-through to ensure that the
    images have met the departmental quality standard

66
Technologist QC Station
  • Generally has a 1K monitor
  • Does not have the resolution capabilities of the
    radiologists reading station
  • Care required of technologist when manipulating
    images not to change the appearance too much from
    original acquired image

67
The File Room Workstation
  • Workstation may be used to
  • look up exams for a physician
  • or to print copies of images
  • for the patient to take to an
  • outside physician.
  • Many hospitals are moving away from printing
    films because of the cost.
  • Hospitals are moving toward burning compact disks
    (CDs) with the patients images.

68
(No Transcript)
69
Image Receptors
ARRT definitions
  • digital image characteristics
  • spatial resolution
  • sampling frequency
  • DEL (detector element size)
  • receptor size and matrix size
  • image signal (exposure related)
  • quantum mottle
  • SNR (signal to noise ratio) or
  • CNR (contrast to noise ratio)

70
image signal (exposure related) Exposure
Indicators
  • The amount of light given off by the imaging
    plate is a result of the radiation exposure that
    the plate has received.
  • The light is converted into a signal that is used
    to calculate the exposure indicator number, which
    is a different number from one vendor to another.

71
Digital artifacts
  • Grid Lines Appear as grid cutoff.
  • Moire (Aliasing)
  • wavy artifact occurs because the grid lines and
    the scanning laser are parallel.
  • When the spatial frequency is greater than the
    Nyquist frequency
  • Maintenance (e.g., detector fog) When errors
    occur in equipment performance, corrective action
    must occur. These corrections will generally be
    done by service personnel employed by the vendor.
  • non-uniformity, erasure - blub problems

72
How else can Morie OCCUR?
73
quantum mottle
ARRT definitions
failure of an imaging system to record densities
usually caused by a lack of x-ray
photons. PHOTON STARVED KVP MAS HOW IS
THIS AFFECTED IN DR / CR?
74
Image Receptors
ARRT definitions
  • digital image characteristics
  • spatial resolution
  • sampling frequency
  • DEL (detector element size)
  • receptor size and matrix size
  • image signal (exposure related)
  • quantum mottle
  • SNR (signal to noise ratio) or
  • CNR (contrast to noise ratio)

75
Image Acquisition and Readout
  • PSP (photo-stimulable phosphor)
  • flat panel detectors
  • (direct and indirect)

76
CR Imaging Plate
  • Construction
  • Image recorded on a thin sheet of plastic known
    as the imaging plate - PSP
  • Consists of several layers
  • Phosphor?

77
Imaging Plate
  • Phosphor?
  • BARIUM FLUORO HALIDE WITH A EUROPIUM BASE

78
Digital Radiography
  • Two types of digital radiography
  • Indirect capture DR
  • Machine absorbs x-rays and converts them to
    light.
  • CCD or thin-film transistor (TFT) converts light
    to electric signals.
  • Computer processes electric signals.
  • Images are viewed on computer monitor.

79
Digital Radiography
  • Direct capture DR
  • Photoconductor absorbs x-rays.
  • TFT collects signal.
  • Electrical signal is sent to computer for
    processing.
  • Image is viewed on computer screen.

80
Image Acquisition and Readout
  • flat panel detectors
  • Phosphors?
  • direct Am SELENIUM
  • indirect Am SILICON

81
  • Digital Systems
  • electronic collimation
  • grayscale rendition or look-up table (LUT)
  • edge enhancement/
  • noise suppression
  • contrast enhancement
  • system malfunctions (e.g., ghost image, banding,
    erasure, dead pixels, readout problems, printer
    distortion)

82
Image Data Recognitionand Preprocessing shutter
  • Agfa uses the term collimation, Kodak uses the
    term segmentation, and Fuji uses the phrase
    exposure data recognition.
  • All systems use a region of interest to define
    the area where the part to be examined is
    recognized and the exposure outside the region of
    interest is subtracted.

83
  • So in essence, rescaling provided an acceptable
    image, despite an excess level of exposure to the
    receptor.
  • What about the dose to the patient?
  • Excessive  exposure to receptor without
    rescaling.
  • Excessive  exposure to receptor with rescaling.

84
  • Rescaling the image pixel values to appear
    appropriate, display properly, can lead to
    overexposing a patient. The visual cue to the
    technologist that overexposure has occurred isnt
    present. With an analog system, a technologist
    would have seen the image on the left as it came
    out of the processor and used the excessive
    density of the image as a visual cue to repeat
    the image. Rescaling forces a technologist to
    look elsewhere for signs that a proper exposure
    was used to produce an image.

85
Dose creep
  • refers to the potential to gradually increase
    patient exposure over time.
  • However, a technologist lacks visual feedback
    that additional radiation is being used to
    produce the images

86
DAP
  • The dose area product (DAP) meter is a device
    that may be interlinked with the x-ray unit to
    determine the actual patient entrance skin
    exposure dose with accurately calibrated
    equipment. Currently, no standards are
    established for using a dose area product meter

These two radiographs show the difference in
entrance skin exposure measured by the DAP meter.
The area with a smaller exposure field size
carries a lower exposure without reducing image
quality
87
Image EvaluationBrightness and Contrast in
Images
  • Exposure Field Recognition Error
  • Gross Overexposure
  • Excessive Scatter Striking the Receptor
  • Excessive Fog on the Receptor
  • Grid Cutoff
  • Intra-Field or Off-Focus Radiation
  • Wrong Menu Selection

88
ARRT SPECS - DIGITAL
  • PACS
  • HIS (hospital information system) - work list
  • RIS (radiology information system)
  • DICOM
  • Workflow (inappropriate documentation, lost
    images, mismatched images, corrupt data)

89
PACS
  • Image is stored on a computer retrieval and
    viewing system for digital imaging examinations.
  • The PACS software provides tools that enable a
    PACS operator to manipulate images.
  • The basic image manipulations possible are
    magnification and minification of an image
    altering image brightness and contrast and
    annotating the image using text, symbols, lines
    and arrows.

90
Picture Archival andCommunication Systems
  • Networked group of computers, servers, and
    archives to store digital images
  • Can accept any image that is in DICOM format
  • Serves as the file room, reading room,
    duplicator, and courier
  • Provides image access to multiple users at the
    same time, on-demand images, electronic
    annotations of images, and specialty image
    processing

91
RIS Data Storage
  • Less ERRORS
  • A radiology information system, or RIS, is a data
    system for patient-related functions in the
    radiology department. Examples of functionality a
    RIS provides within a radiology department
    include (but are not limited to)
  • scheduling
  • appointments
  • collecting and displaying orders for radiologic
    examinations
  • storing and displaying patient data
  • tracking patients
  • providing patient and order data to a PACS
    storing and distributing radiology reports
    providing billing services and  providing a
    database to track and project trends.

92
HIS
  • A hospital information system, or HIS, is a paper
    and/or data system that manages the
    administrative, financial and clinical
    information necessary to operate a hospital or
    health care system

93
Health Level 7 (HL7)
  • HL7 are the software standards established for
    exchanging electronic information in health care.
    PACS is mainly concerned with images and data
    associated with images, whereas HL7 sets
    standards for transmitting text-based information
    throughout a medical center.

94
Next
  • ODIA - Register
  • Review Modules 5 6 ( 11 ??)
  • Do study test at end of modules -
  • ?Print out certificate of completion
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