Ultrasound Image Encoding

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Ultrasound Image Encoding

• Dave Heaney
• A.L.I. Technologies, Inc.

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Two Types of IODs

• Ultrasound Image IOD for single frame images
• Ultrasound Multi-frame Image IOD for multi-frame
  images such as cine and 3D acquisition.

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Several Photometric Interpretation Options

• Monochrome2
• Palette Color
• RGB
• ARGB (retired)
• YBR_FULL
• YBR_FULL_422
• YBR_PARTIAL_422

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Several Transfer Syntax Options

• Little Endian Implicit (default)
• Little Endian Explicit
• Big Endian Explicit
• Lossy JPEG (various)
• Lossless JPEG (various)
• Run Length Encoding

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US Image Data Elements
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US Image Data Elements (cont.)
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US Image Data Elements (cont.)
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US Image Data Elements (cont.)
In addition there can be the Palette Color
Elements of the LUT Module for Palette Color
Images. These will be covered in the LUT
presentation.
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Compression Types 1. Lossy JPEG 2. Lossless
JPEG 3. Run Length Encoding
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Lossy JPEG

• Important Points
• Default lossy JPEG Transfer Syntax is JPEG
  Baseline 1 1.2.840.10008.1.2.4.50, as 8 bit only
  image data.
• Data Elements must be encoded Little Endian
  Explicit.
• YBR yields a better compression ratio than RGB.
  YBR FULL 422 is most used (as per Application
  Profile).
• Photometric Interpretation, and other elements,
  must indicate last state of data prior to
  compression (YBR FULL 442 if RGB is converted
  prior to compression).
• Lossy Image Compression must be set to 01 (VR of
  CS).
• If image is later decompressed set the Derivation
  Description (0008,2111) (i.e. 101 JPEG
  Baseline1 Q90).

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Lossless JPEG

• Important Points
• Default lossless JPEG Transfer Syntax is Process
  14 1.2.840.10008.1.2.4.70.
• Data Elements must be encoded Little Endian
  Explicit.
• Can be used for Palette Color pixel data.
• Lossy Image Compression must be set to 00 (VR of
  CS).

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Run Length Encoding

• Important Points
• Data Elements must be encoded Little Endian
  Explicit.
• Can be used for Palette Color pixel data (8 and
  16 bit).
• YBR color data generally yields better
  compression than RGB data (grayscale pixel values
  reduce to a single channel). Conversion from RGB
  to YBR is slightly lossy however.
• RLE is done on byte per byte basis even for 16
  bit data. Thus for 16 bit Palette Color data the
  1st RLE segment will contain the most significant
  bytes and the 2nd segment the least significant.
  VR of Pixel Data Element will thus always be OB
  for RLE data.
• Size of the RLE Header is always 16 long words,
  64 bits, regardless of number of segments.

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US Region Calibration Module

• Important Points
• Unlike most other IODs scaling and calibration do
  not have to uniform across an entire Ultrasound
  Image. The US Region Calibration Module allows
  this specification.
• A sequence of one or more regions can be
  specified.
• Important to include to allow auto-scaling on
  workstations.
• Not only for scaling information, can be used
  for
• pixel component description
• mapping from Pixel Value to Parameter Value
• transducer frequency for a region
• doppler information
• m-line specification

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Other Notes

• Compressed pixel data is contained in the Pixel
  Data Element (7FE0,0010) which has a VR of OB or
  OW. Even though the encoding of the compressed
  data is actually done as if the VR is SQ, SQ must
  not be specified.
• Study Description (0008,1030) is widely used for
  specifying Exam Type
• Interchange of cine images generally requires
  support for lossy JPEG encoding.
• In Ultrasound images overlay data is generally
  burned in with image data. Support for bit map
  overlays may not be widespread.