Lossy compression provides viable option for storing medical images

Radiology departments need not fear irreversible compression of medical images, according to a Canadian review of the medical literature.

Two independent reviewers concluded that lossy compression is clinically acceptable for image compression, said Peter Bak, Ph.D., project director of diagnostic imaging architecture for Canada Health Infoway. The organization promotes adoption of electronic health information systems in Canada.

Some data loss does occur with lossy compression, which leads to concern that a misdiagnosis could result if relevant information was lost, he said Thursday at the SCAR meeting.

Bak and colleagues commissioned two independent researchers to systematically review the research on lossy compression. They scanned radiology and related journals, surveyed radiologists in the U.S. and Canada, and sampled professional radiology organizations in both countries for position statements on the use of irreversible image compression. The reviewers studied 120 papers, most dating from 1998.

They found that two main compression algorithm categories are currently in use: discrete cosine transform-based and wavelet-based algorithms.

The researchers also discovered that different modalities and anatomic structures have different compression tolerances; there is no one-size-fits-all compression scheme. Their consensus was that a 50:1 compression ratio is acceptable for large-matrix images, with 25:1 optimal. An acceptable ratio for small-matrix images is 20:1, with 10:1 optimal.

Acceptable compression ratios varied between modalities, from 40:1 for MRI and up to 90:1 for nuclear medicine studies.

The adoption of electronic health records will require optimum use of networking capabilities among institutions, and compressing images can go a long way toward achieving that goal, according to Bak.

The Canadian Association of Radiologists has endorsed lossy compression for primary reads.

"We in Canada have a good motive to use lossy compression. We see lossy compression as having a positive impact on our national EHR plans if we can make it happen," he said.

Investigation of the barriers to and drivers of lossy compression adoption will require more than a research review, Bak said. In the future, more work will be done to determine legal risks, assess regulatory frameworks, determine economic impact, and provide clinical and performance evaluations.