IMPAX applies two different types of compression to JPEG and wavelet images: lossless and lossy.
An image with lossless compression is compressed but the compression is fully reversible and the image can be returned to the original state as it was produced at the modality. Other terms in the industry for lossless compression are original, full fidelity, and uncompressed.
An image with lossy compression is a irreversibly compressed version of the JPEG or wavelet image. Other terms in the industry for lossy compression are compressed and non-diagnostic.
 | Note: Do not use lossy compressed images (JPEG or wavelet) when dictating mammography studies but only for reference purposes. Ensure that the client is configured to retrieve original images when dictating mammography studies. |
The benefits of being able to use these two types of image compression include:
Better system performance
As lossy image quality is sufficient for many IMPAX users and various circumstances (such as viewing prior studies), using lossy wavelet versions allows them to view images more quickly. Using lossy images reduces the number of retrieves to archive required, which reduces the overall network load by allowing more studies to be available in the online cache.
| Note: We do not recommend using lossy compression if transmitting studies that contain KOSD or GSPS objects. The KOSD (Key Object Selection Document) and GSPS (Grayscale Softcopy Presentation State) objects will refer to objects that do not exist in the transmitted study. |
Enhanced usability
Many IMPAX users, such as clinicians, are not interested in the details of image compression and format. Therefore, you can configure the system such that these users get only one type of image and do not have to make the choice of whether to display the other type instead.
Meeting diagnostic requirements
For diagnosis, lossless images may be needed to meet legal requirements and radiologists may also prefer to see the lossless images. For clinical review, however, the lossy image generally suffices and may be preferred, given its support for faster loading.
The system can be configured to meet the needs of radiologists, who often need lossless images for diagnosis but may use the lossy version in other cases. For example, they may view lossless images on workstations running on a fast, dedicated network, but view lossy images on less ideal workstations. Or, they may use lossless images for current studies but lossy versions for priors (for example, by setting up site caches such that dictated studies older than two weeks are in the web cache only). As needed, they can retrieve the original version of lossy images.
| Note: A triangle symbol appears on images that are lossy compressed. |
Lossy indicator in lower right corner
