The Royal College of Radiologists' issued the following advice regarding compression of images:

"Compression may be used to reduce the storage space required for digital images. Standard compression algorithms can achieve "lossless" image compression up to a ratio of approximately 3:1. More dramatic space savings may be obtained with lossy compression, where some image data is lost permanently, but to a degree that may not be significant in clinical practice. In circumstances where it is impractical to store lossless images indefinitely, such lossy compression is clearly preferable to the deletion of images. Where lossy compression is applied it is important to ensure the levels chosen are appropriate so that images remain clinically useful. The compression algorithm must be approved and supported by DICOM (Digital Image Communications in Medicine)" extract from BFCR(06)4, Retention and Storage of Images and Radiological Patient Data.

The full text may be seen at the follow web address:

http://www.rcr.ac.uk/docs/radiology/pdf/ITguidance_Retention_storage_images.pdf

This guidance also states:

"The main regulatory bodies in the UK, EU, USA, Canada and Australia neither prevent nor endorse lossy compression for medical images. This risk of using lossy compression is no more than in conventional practice provided that the diagnostic quality of the image is not reduced and that the decision use lossy compression was made at an institutional level as a matter of public policy and resource allocation and there was support from at least a respectable minority of radiologists"