1. Ultrasound Image Encoding
Dave Heaney
A.L.I. Technologies, Inc.
9/22/2018

2. 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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3. Several Photometric Interpretation Options
Monochrome2
Palette Color
RGB
ARGB (retired)
YBR_FULL
YBR_FULL_422
YBR_PARTIAL_422
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4. 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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5. US Image Data Elements
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6. US Image Data Elements (cont.)
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7. US Image Data Elements (cont.)
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8. 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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9. Compression Types: 1. Lossy JPEG 2. Lossless JPEG
3. Run Length Encoding
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10. Lossy JPEG Important Points:
Default lossy JPEG Transfer Syntax is JPEG Baseline 1: , 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. “10:1 JPEG Baseline1 Q=90”).
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11. Lossless JPEG Important Points:
Default lossless JPEG Transfer Syntax is Process 14:
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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12. 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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13. 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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14. 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.
9/22/2018