Configuring Compression

By default, current versions (1.9.6 or later) of the Gateway software are configured to use Diagnostically acceptable irreversible compression (DAIC, or "lossy") compression for locally storing studies, as well as transmitting studies to OnePacs, for all study types other than conventional radiography and mammography studies. (CR and MG studies use lossless compression, at a compression ratio of approximately 3:1). For lossy compression, the JPEG2000 algorithm with a compression ratio of 8:1 is used. The JPEG2000 algorithm was selected due to an established body of research demonstrating JPEG2000 to have optimal characteristics as a compression algorithm for medical imaging, including the ability to maintain excellent image quality even at high compression ratios (see “JPEG2000 Compression of Medical Imagery”, Proc. of SPIE Vol. 3980, Feb. 2000). The 8:1 ratio chosen for the default OnePacs installation is a conservative figure.

DAIC at the ratios used by this software rarely if ever would lead to any human-perceptible difference in image characteristics. The American College of Radiology and other similar bodies in other jurisdictions have stated that DAIC is acceptable for all uses in radiology including long-term archiving, provided that the image quality is checked by appropriate qualified personnel and found acceptable. The DAIC used by this software follows guidelines issued by the ACR, including algorithm selection. Please review your imaging studies for confirmation of image quality prior to usage. If you which to change any compression settings, such as to store all studies lossless, please refer to the OnePacs documentation for configuration instructions.

Some users may wish to change the default compression settings, either to utilize reversible compression, or to increase or decrease the compression ratio.

The compression used can be configured in the jmx-console, reached in a web browser at the following URL:

(On the gateway machine itself) http://localhost:8080/jmx-console

After login to the jmx console, select the “Service=StoreSCP” option. Scroll down the screen to find the “CompressionRules” item. Into the text box containing the compression rules, you may paste in one of the following options:


StringFunction
JPLLCompress all studies with JPEG lossless
J2KICompress all studies with JPEG2000 lossy


You may also edit the “LossyCompressionQuality” item to change the compression ratio. The default value is 0.12, signifying an approximately 8 to 1 compression ratio (that is, the final image will be 0.12 times the size of the original uncompressed image). JPLL generally leads to a ratio of about 3.5, with the compressed image approximately 0.29 the size of the original image. Thus, as configured by default in the OnePacs system, J2KI will generally result in approximately 2.4 x greater achieved compression than J2LL.

Implications of Compression for Archiving

Whatever compression method you choose at the Gateway will determine how studies are stored in the OnePacs system. If you are archiving studies with OnePacs, you may choose to either archive studies in a lossless format, or with lossy compression. Using lossy compression has the advantage of reducing file size, which reduces storage costs and transmission times. However, some facilities/groups may wish to archive studies only using lossless compression.

If you wish to have all studies for one or more facilities managed in the OnePacs system using only lossless compression, simply configure the Gateway(s) for such facility(ies) to utilize lossless compression. If studies are compressed using lossless compression at the Gateway, they will remain compressed with lossless compression for the remainder of their life cycle with OnePacs, including permanent archiving, if applicable.

The American College of Radiology, American Association of Physicists in Medicine, and Society of Imaging Informatics jointly issues a "Technical Standard for Electronic Practice of Medical Imaging", last revised December 2017.  In part the standard reads:


Compression may be defined as mathematically reversible (lossless) or irreversible (lossy). Reversible compression may always be used, since by definition there is no impact on the image. Irreversible compression may be used to reduce transmission time or storage space only if the quality of the result is sufficient to reliably perform the clinical task. The type of body part, the modality, and the objective of the study will determine the amount of compression that can be tolerated.

The term “diagnostically acceptable irreversible compression” (DAIC) refers to mathematically irreversible compression that does not affect a particular diagnostic task [5]. DAIC may be used under the direction of a qualified physician with no reduction in clinical diagnostic performance by either the primary image interpreter or decision makers reviewing the images. From a practical perspective, this means that any artifacts generated by the compression scheme should not be perceptible by the human viewer or are at such a low level that they do not interfere with interpretation.

The ACR and this technical standard make no general statement on the type or amount of compression that is appropriate to any particular modality, disease, or clinical application to achieve the diagnostically acceptable goal. The scientific literature and other national guidelines may assist the responsible physician in choosing appropriate types and amounts of compression, weighing the risk of degraded performance against the benefits of reduced storage space or transmission time. The type and amount of compression applied to different imaging studies transmitted and stored by the system should be initially selected and periodically reviewed by the responsible physician to ensure appropriate clinical image quality, always considering that it may be difficult to evaluate the impact on observer performance objectively and reliably.