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Dr Laurence Sutton Calderdale and Huddersfield NHS Foundation Trust Halifax West Yorkshire

Dr Laurence Sutton Calderdale and Huddersfield NHS Foundation Trust Halifax West Yorkshire. Is Lossy Compression of Image Data detrimental to Image Interpretation? Will Lossy Compression Become standardised Practice?. Image Compression. Definition. Do we need to compress image data?

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Dr Laurence Sutton Calderdale and Huddersfield NHS Foundation Trust Halifax West Yorkshire

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  1. Dr Laurence SuttonCalderdale and HuddersfieldNHS Foundation TrustHalifax West Yorkshire Is Lossy Compression of Image Data detrimental to Image Interpretation? Will Lossy Compression Become standardised Practice? Image Compression

  2. Image Compression • Definition. • Do we need to compress image data? • Compression Methods. • Canada Health Infoway Project. • Technical and Clinical Evaluation. • Medico-Legal Aspects (Regulations). • Next Steps? Image Compression

  3. Definition • Image Compression is used to reduce the amount of Memory required to store the Image data – without degrading the (visual) quality of the image to an unacceptable level Image Compression

  4. Image Compression • Definition. • Do we need to compress image data? • Compression Methods. • Canada Health Infoway Project. • Technical and Clinical Evaluation. • Medico-Legal Aspects (Regulations). • Next Steps? Image Compression

  5. Image Data Explosion …fuelled by clinical advancements 18800 Number Of Slices (Millions) • ~ 20 million CT slices produced by one imaging department • 10 Tera Bytes of data in 1 year • Speed, Storage, and Interpretation a HUGE challenge 10300 6300 3600 2700 2000 1900 1100 444 8 Slice 16 Slice Single Slice 4 Slice VCT 64 now a reality Technology not standing still 640 slices 40 slices 160 slices 80 slices Dr. Laurence Sutton

  6. Open for new vocabulary? *(exact 1024 Byte) new vocabulary ? – 1 Googol = 10100 Image Compression

  7. Online Storage Long Term Storage 2nd Copy Storage Management # of Retrievals 10% Digital Film 1 Year Time (Years) Dr. Laurence Sutton

  8. Storage management +10 to 15% TCO Cost Storage hardware –35% 1991 1994 1997 2000 2003 2006 Source:Associate Management Group TCO total cost of ownership • Management cost increases • Data availability • People • Software • Security • Facilities • Energy • Others Storage TCO increases Dr. Laurence Sutton

  9. Image Compression • Definition. • Do we need to compress image data? • Compression Methods. • Canada Health Infoway Project. • Technical and Clinical Evaluation. • Medico-Legal Aspects (Regulations). • Next Steps? Image Compression

  10. Image CompressionLossless or Lossy • Lossless • Regenerated is guaranteed to be identical to the original image • Also known as “reversible compression” • Lossy • A form of image compression where the regenerated image is not guaranteed to be identical to the original image • Also known as “irreversible compression” Image Compression

  11. Image Compression

  12. Historical • SCAR Paper 2000,Bradley J. Erickson “ Increasing evidence suggests that some forms of irreversible compression can be used with no measurable degradation in aesthetic or diagnostic value.” • Today however Primary Reading of Irreversibly compressed images is not an accepted standard of practice Image Compression

  13. Do we need to compress Image Data? • Compression is a form of information processing. • The latter we do all the time and throw away data! • Selected fluoroscopy Images • Selected CT slices sent to PACS • Representative US Images • System and Technique information loss (In Plane Loss) Image Compression

  14. In Plane Loss • In Plane Loss • Not saving CT raw data • Low dose techniques (quantum noise) • Applying and saving only one CT reconstruction algorithm • Cleanup and interpolation in CR/DR • Any form of image processing (information theory!) • 8 or 10 bit display/windowing of 12-16 bit data • Displaying any part of an image at less than 1:1 zoom • Non-linear, badly calibrated monitors • Archiving on Film • (lossy compression) Image Compression

  15. Some types of Image Compression • Joint Photographic Experts Group JPEG (ISO/IEC). (OSI) • Graphic Interchange Format GIF (LZW) • Potable Network Graphics PNG • WWW. Image File Formats • GIF and PNG are lossless • JPEG can be lossless Image Compression

  16. Some types of Image Compression • GIF and PNG are lossless • LZW (PK-zip, built-in in RAID etc.) • < 2:1 • JPEG can be lossless • JPEG Lossless (Pulse Code Modulation compression) • Totally unrelated to normal “JPEG” • 2 varieties defined in DICOM • About 2.5:1 • JPEG 2000 lossless mode • About 3:1 Image Compression

  17. JPEG2000 and JPEG • JPEG, (Lossy) Discrete Cosine Transform Technique resulting in blocky artefacts at higher level of compression. • JPEG2000, Wavelet based compression technique which allows for higher compression ratios without overt artefacts. • Part of JPEG2000 is now part of an ISO standard • File ex, .jp2 or .j2c Image Compression

  18. JPEG2000 Advantages • Superior Compression Performance. • Lossless and Lossy Compression. • Error Resilience. • Ideally suited to photographic type images. • Smoothing Artefacts at high compression levels • Regenerated Images are less Noisy and cleaner! • JPIP compression streamlining protocol. Image Compression

  19. Explicit Lossy Processes JPEG Q=80 6:1 JPEG Q=50 11:1 J2k 30:1 J2k 100:1

  20. JPIP • Uses the minimum bandwidth required. • Ability to only download the requested part of the image. • Quick view of a large image at low resolution. • Ability to pull more data for higher resolution images of smaller parts of the image. • Reduces computer processes at server and client ends. Image Compression

  21. Image Compression • Definition. • Do we need to compress image data? • Compression Methods. • Canada Health Infoway Project. • Technical and Clinical Evaluation. • Medico-Legal Aspects (Regulations). • Next Steps? Image Compression

  22. Canada Infoway Project • National EHR • Storage and Network Impact of 35M images (1.5PB) annually. • Cost of storage versus cost of ownership. • Lossy Compression could save CDN$100M/year. • Can Lossy (Irreversible) Compression be used as a standard of practice? • Commissioned series of projects to evaluate…… Image Compression

  23. Canada Infoway Project • Research conducted so far and the evaluation of the effects on Image Quality…..2 Independent Reviews. • Legal Implications of using Irreversible compression…..2 Independent Reviews. • Current Regulations around the world…..1 review • The outcome of the reviews is such that the CAR is motivated to adopt Irreversible Compression as a standard and to such an end ……. Image Compression

  24. Canada Infoway Project • Clinical Review in conjunction with Infoway to assess the most appropriate compression ratios for a variety of different body parts for each modality. • Canadian Association of Radiologist endorsement of the resulting Guidelines. • Results SIIM (SCAR) June 2007 Rhode Island. Image Compression

  25. Outcomes. • Review of research…. Both reviewers concluded that “based on scientific studies, irreversible compression is a clinically acceptable option for the compression of medical images.” • Legal Review…. • Presume no visual impact on the quality of the Image. • Main risk is Tort of Negligence. • Reduce risk by universal adoption of the standard. • Respectable minority of Radiologists Image Compression

  26. Outcomes. • Legal Review, BUT • Can not alter the Medical Record once it has been approved. • Requirement to compress the image prior to the Primary Read. • BUT, that is ok isn't it? • In this country the report is still the legal document. • Regulatory Review. • Non of the regulatory bodies in Canada,USA,UK,EU,Australia have prevented or endorsed the use of imaging compression Image Compression

  27. Technical and Clinical Review. • A Review and Comparison of Medical Image Compression Algorithms August 2004 Kirk W. Finnis, PhD Atamai Inc., 100 Perth Drive, Suite 500, London, Ontario, Canada Image Compression

  28. Technical and Clinical Review. Research Review And Assessment of Compression performance. Comparisons of different algorithms between Medical Images and Standard Image sets. *Lossy Compression of Medical Images. Image Compression

  29. Technical and Clinical Review. • Effects of Lossy Compression on Diagnosis. • Usually centred on one modality and a Pathology. • Dental • CT and MR • CXR • Digital Angiograms • Mammograms • Ultrasound Image Compression

  30. Image Compression

  31. Image Compression

  32. Image Compression

  33. CXR • Slone, Muka & Pilgram, • http://radiology.rsnajnls.org Image Compression

  34. Mammography • ECR 2007, German Study, Dr R Loose, Nuremberg • 33MB down to 325KB using standard wavelet compression. • No statistically significant impact on quality or visible differences in images for compression rates up to 100:1 • Significant Impact on storage costs and the provision of Teleradiology services Image Compression

  35. CAD CT Lung Nodule Volume Assessment. • Jane B Ko et al, Radiology 2005;237:83-88 • Low dose CT technique, ROI • No significant difference 10:1 • Difference observed at 20:1 • Reduced volume measurements. • Need to be aware of the issues in Computer Aided Techniques Image Compression

  36. Summary Metrics used by researchers to assess compression algorithms included: • Quantitative measures - a measure of image quality – Mean Squared Error (MSE) – Peak Signal to Noise Ratio (PSNR) • Qualitative measures - a measure of diagnostic quality – Difference Image and Histogram – Receiver Operating Characteristics (ROC) analysis Image Compression

  37. Conclusions and Caveats • Limits (Tolerance) Image Compression • MR/CT 10:1 • CR 20:1 • JPEG2000 adopted as a DICOM Standard • Rapid Adoption by the Imaging Community. • Medico-Legal uncertainties exist. • Evidence supports the safe adoption of Lossy compression for storage and compression without compromising diagnostic quality. Image Compression

  38. Next Steps. • ? Case for adoption of Lossy Compression in the UK • Royal College Approval of process to validate the case for Lossy Compression. • Adopt Lossy Compression as a safe standard for the purpose of diagnosing from medical images. • Consider potential issues around computer aided measurements. Image Compression

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