Medical Imaging

JPEG 2000 has many characteristics which are useful to one of its target market areas, medical imaging. Some background to this has been covered in a JPEG committee document (N2782) which also gives some useful information about how JPEG 2000 works. One key aspect which often concerns the medical profession is the need to ensure that images can be communicated losslessly, without any distortions introduced by a compression process that may lead to mis-diagnosis. This often results in huge files, which can be difficult to store, handle, and communicate. JPEG 2000 can be used to encode files completely (or partially) losslessly, and provides good compression performance for this purpose (similar, for example, to that offered by JPEG's optimised method for such compression, JPEG-LS (IS 14495)). It does however have several additional features which make JPEG 2000 particularly attractive for medical imaging:

selected parts of the image can be defined as Regions of Interest - they can then be delivered before other parts of the image, or losslessly, whilst other parts of the image that are less critical use normal lossy compression. In addition, these 'ROIs' can have specific metadata associated with them - for example annotations or notes (which themselves could be in a multimedia format such as MP3 audio)
the JPEG 2000 codestream can be ordered to deliver images of lower resolution, or reduced quality, well before the full image can be transmitted. This helps significantly in browsing applications, and means that only one file is needed for several applications
extensive metadata can be included with the image, in a tight association. This means that files can be transmitted between recipients which can easily be processed, or indexed into an existing database. Some applications, such as those relating to DICOM standards, have their own sophisticated methods for handling this metadata, and JPEG are working with the DICOM committee to ensure that these two important standards can be easily integrated
many different forms of image can be usefully compressed using JPEG 2000 - for example radiological, MRI, CAT and other medical imaging modalities, which use non-visual sensors, and may use enhancement techniques such as pseudo-colouring the resulting image

One important part of the JPEG 2000 standards for medical imaging is that of Motion JPEG 2000. This is defined in Part 3 of JPEG 2000, and unlike the more well-known MPEG family of standards produced by JPEG's sister committee, does not have any form of extrapolation (and hence potential distortion) in the time domain. Each frame is a separate JPEG 2000 coded image, and may have its own specific characteristics - for example in an endoscopy, the time series could relate to spatial displacement of the sensor, rather than having a constant time between image frames. A document (N2883) outlining this specific usage of JPEG 2000 is available.

For further information, we suggest you contact either:

Alexis Tzannes - Chair of JPEG 2000 Medical Imaging Ad hoc group
or
Touradj Ebrahimi - Chair of JPEG 2000 Requirements group, and co-chair of JPEG 2000 Medical Imaging Ad hoc group