Dr Laurence Sutton Calderdale and Huddersfield NHS Foundation

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

Image Compression n n n 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

Definition n 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

Image Compression n n n 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

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

Open for new vocabulary? Exponential In Bytes or. . . . Yottabyte YB 1024 Bytes 1 Quadrillion can‘t imagine! Zettabyte ZB 1021 Bytes 1 Trilliard 1000 x all ever spoken words Exabyte EB 1018 Bytes 1 Trillion Petabyte PB 1015 Bytes 1 Billiard 500 Billion pages text Terabyte TB 1012 Bytes 1 Billion paper from 50, 000 trees Gigabyte GB 109 Bytes 1 Milliard 400, 000 written A 4 pages Megabyte MB 106 Bytes 1 Million Kilobyte KB 103 Bytes 1 thousand* Byte B 8 bit b ½ page A 4 written text 1 Byte new vocabulary ? – 1 Googol = 10100 Image Compression *(exact 1024 Byte)

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

or +1 age 0 to ma 15 na % ge TC me O nt Sto rag St Cost TCO total cost of ownership 1991 eh ard war e 1994 Storage TCO increases – 35 % 1997 2000 2003 2006 Source: Associate Management Group Dr. Laurence Sutton Management cost increases Ø Data availability Ø People Ø Software Ø Security Ø Facilities Ø Energy Ø Others

Image Compression n n n 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

Image Compression Lossless or Lossy n Lossless n n n Regenerated is guaranteed to be identical to the original image Also known as “reversible compression” Lossy n n 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

Image Compression

Historical n 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. ” n Today however Primary Reading of Irreversibly compressed images is not an accepted standard of practice Image Compression

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

In Plane Loss n n n 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

Some types of Image Compression n n n 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

Some types of Image Compression n n GIF and PNG are lossless LZW (PK-zip, built-in in RAID etc. ) n < 2: 1 JPEG can be lossless JPEG Lossless (Pulse Code Modulation compression) n Totally unrelated to normal “JPEG” n 2 varieties defined in DICOM n About 2. 5: 1 JPEG 2000 lossless mode n About 3: 1 Image Compression

JPEG 2000 and JPEG n n JPEG, (Lossy) Discrete Cosine Transform Technique resulting in blocky artefacts at higher level of compression. JPEG 2000, Wavelet based compression technique which allows for higher compression ratios without overt artefacts. Part of JPEG 2000 is now part of an ISO standard File ex, . jp 2 or. j 2 c Image Compression

JPEG 2000 Advantages n n n n 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

Explicit Lossy Processes JPEG Q=80 JPEG Q=50 6: 1 11: 1 J 2 k 30: 1 J 2 k 100: 1

JPIP n n n 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

Image Compression n n n 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

Canada Infoway Project n n n National EHR Storage and Network Impact of 35 M images (1. 5 PB) annually. Cost of storage versus cost of ownership. Lossy Compression could save CDN$100 M/year. Can Lossy (Irreversible) Compression be used as a standard of practice? Commissioned series of projects to evaluate…… Image Compression

Canada Infoway Project n n 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

Canada Infoway Project n n n 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

Outcomes. Review of research…. Both reviewers concluded that “based on n scientific studies, irreversible compression is a clinically acceptable option for the compression of medical images. ” n Legal Review…. n n 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

Outcomes. n Legal Review, BUT n n n 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. n Non of the regulatory bodies in Canada, USA, UK, EU, Australia have prevented or endorsed the use of imaging compression Image Compression

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

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

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

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

Mammography n n ECR 2007, German Study, Dr R Loose, Nuremberg 33 MB down to 325 KB 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

CAD CT Lung Nodule Volume Assessment. n n n 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

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

Conclusions and Caveats n Limits (Tolerance) Image Compression n n n MR/CT 10: 1 CR 20: 1 JPEG 2000 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

Next Steps. n n ? 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