Displays and Image Processing ch. 15

Image Processing in Modern Displays

• Modern display technology surpasses traditional televisions in terms of:
  • Higher frame rates
  • More lines per image

Types of Displays

• Bistable Displays:

  • Capable of displaying only two states: black and white.

• GrayScale Displays:

  • Capable of displaying multiple levels of brightness.

Display Controls

• Two primary controls on video monitors adjust the display characteristics:
  • Contrast:
  • Defines the range of light within the displayed image.
  • Scan Converters:
  • Translate information from a spoke video format and store the information for later display.
  • Alter the format of data during the writing and reading process.

Analog vs. Digital Numbers

• Analog:
  • Represents the real world, characterized by unlimited choices and continuous values.
• Digital:
  • Represents the computer world, characterized by limited choices and discrete values.

Analog Scan Converter

• Description:

  • Funnel-shaped vacuum tube with an electron gun located at the smaller end.
  • Electrons carrying information are emitted from the electron gun.
  • The larger end contains a dielectric matrix of silicon and water.
  • The dielectric matrix divides the picture into dots containing electrical storage elements, referred to as electron buckets.

• Spatial Resolution:

  • Refers to the level of detail in the image.

Limitations of Analog Scan Converters

• Image fade occurs as the silicon and water dissipate over time.
• Image flicker can occur due to switching between reading and writing modes.
• Instability can affect the quality of the image, with degradation occurring with age.

Digital Scan Converter

• Converts images into digital form.
• Advantages of digital scan converters:
  • Uniformity
  • Stability
  • Durability
  • Speed
  • Accuracy
• Key elements of digital scanning:
  • Pixel: The building block of digital pictures.
  • Bit: A binary digit representing a bistable value of 0 or 1.
  • Byte: Consists of 8 bits of computer memory.
  • Word: Memory that consists of 2 bytes.

Image Quality Factors

• Images containing numerous gray shades exhibit better contrast resolution.
• Bits per Pixel:
  • Fewer bits per pixel result in fewer shades of gray, degrading contrast resolution.
  • More bits per pixel allow for more shades of gray, enhancing contrast resolution.
• Digital images consist of pixels and bits that represent image detail, gray shades, and their spatial resolution and contrast resolution.
• An advantage of digital images is their less susceptibility to contamination compared to analog images.

Processing Digital Image Data

• Analog signals during reception are converted into digital form through an A/D (Analog to Digital) conversion.
• Digital information consists of zeros and ones and is stored in memory.
• Reflected signals undergo preprocessing before storage.

After Storage Processing

• Processing after storage in the digital scan converter is termed postprocessing.
• Information is translated back into analog form for display on an analog video display for interpretation.
• The relationship between the real world and the computer world can be characterized by:
  • Analog to digital conversion (A/D)
  • Digital to analog conversion (D/A)

Magnification Techniques

• Read Magnification:

  • Enlarges the region of interest (ROI) of an image after the image is stored.
  • The U/S (ultrasound) system scans anatomy, converting images from analog to digital form for storage.
  • The system characterizes the ROI by pixels in the magnified image, maintaining pixel count without changing spatial resolution.

• Write Magnification:

  • The process occurs post-processing where the U/S system rescans only the ROI, characterized by a greater number of pixels in the new image compared to the original ROI.
  • Write magnification cannot be used on frozen images.
  • Temporal resolution may improve if the bottom of the ROI is shallower than the original depth of view.

Advanced Imaging Techniques

• Coded Excitation:

  • Involves using very long sound pulses containing a wide range of frequencies during the pulsing process.
  • Benefits include spatial compounding, which combines images from different angles to produce a single image, reducing speckles and minimizing shadowing artifacts.
  • Limitations include a reduction in frame rate and temporal resolution.

• Frequency Compounding:

  • An advanced technique that mitigates speckle artifact noise in ultrasound images by dividing reflected signals into sub-bands of limited frequencies, creating an image within each sub-band.

• Edge Enhancement:

  • Technique to create sharper images by generating subtle bright and dark highlights on either side of image boundaries, making them appear more defined.

• Temporal Compounding:

  • Also known as persistence or temporal averaging, this technique displays information from older images alongside current images, creating a smoother image and reducing noise to produce higher image quality.

Interpolation and Emerging Technologies

• Fill-in Interpolation:

  • Constructs new simulated data points to fill in gaps of missing data in a manner unnoticeable to the observer.

• Emerging Technology - Elastography:

  • Produces images related to the mechanical properties of tissue; involves tissue deformation resulting from the sound beam.

Picture Archiving and Communication Systems (PACS)

• PACS provides three major advantages:

  • Virtually instant access to archived studies.
  • No degradation of data over extended time periods, unlike analog archiving.
  • The ability to store and forward telemedicine reports and images electronically to remote sites.

• Digital Storage:

  • Computer hard drives serve as the primary devices for digital storage used in PACS.

• DICOM (Digital Imaging and Communications in Medicine):

  • A standard that connects to PACS and facilitates the sharing and storage of medical information.