DICOM and the Pathology Community Experience Bruce Beckwith, MD Pathology is in a transition phase, moving from analog to digital images. We are 10-15 years behind radiology.

Whole Slide Imaging (WSI) Scanner This file is 110,000 by 75,000 pixels, almost 8 GIGApixels. Uncompressed, it would take about 24 GB of storage, even compressed, it is almost 2GB

Pathology Disciplines Tissue (Surgical) Pathology Tissue from biopsies, resections & autopsies Cytology Individual cells from smears/scrapings or fluids Clinical laboratory Blood smears, protein electrophoresis, etc.

Surgical Pathology Workflow Pathology workflow starts with a specimen Dissection Chemical processing Cut thin sections and place on glass slides Stain with a variety of techniques Chemical Immunochemical in-situ hybridization

Why Move To Digital Imaging? Location independence Sharing of images with clinicians Enables new analysis techniques Computerized screening of pap smears Image analysis for quantitation of special stains ? Computer aided diagnosis for other specimens Remote frozen sections, immediate sharing of cases with consultants Computer aided detection in mammography 5

Comparison of Digital Imaging Radiology Digital acquisition Manageable file size Many clinician interpretable Cost savings compared to analog Computer aided detection for mammograms Pathology Mainly analog data which is digitized Very large file size in pathology Some clinician interpretable Incremental costs in addition to analog Computer assisted screening for pap smears

Resolution Challenge Pathologists need to be able to zoom in quickly Also need rapid pan and focus across the entire slide

The Image Size Challenge 1 focal plane 24 bit color 40x magnification 15 Gigabytes 10 focal planes 24 bit color 40x magnification 3.75 Terabytes

Navigation Challenge Main challenge is rapid pan, zoom, focus, advancing to next slide Intuitive “driving” of the slide will help transition Some equipment is trying to recreate microscope “feel”

Slide Navigation Device Perhaps there will Kinect like input possible in the near future.

DICOM Digital Imaging and Communications in Medicine Voluntary standards organization Image exchange standard for CLINICAL images 27 working groups Anyone with a material interest may participate Version 3 of standard released 1992 Started as partnership of ACR and NEMA Driven by the radiology community Most working groups address radiology areas, but dentistry, endoscopy, cardiology, etc are represented by working groups Has been instrumental in arriving at the current state of radiology where imaging systems are widely interoperable with both pacs and ris. 11

DICOM Overview Communication standard High level standard, conceptual Facilitates interchange, doesn’t mandate internal storage formats within PACS Image object definitions are central Widely adopted in radiology Addresses workflow as well as images Specimen vs patient Workflow analogy Put up comparison side by side 12

Pathology in DICOM Visible light supplement approved 1999 Incomplete and rarely used Doesn’t support the complexity of Pathology practice Pathology WG needed Created WG-26 Fall 2005 Has met about 20 times Representatives from most major pathology imaging vendors Also pathologists, consultants and researchers 90+ subscribers to email listserve 60+ organizations >10 countries Make the point pathology/lab driven 13

WG-26 Goals Initial goals: Long term goals: Extend minimal capabilities to describe specimens in DICOM Create a mechanism to allow exchange and use of whole slide microscopic images within DICOM Long term goals: Other imaging modalities, such as multi-spectral images, electron microscopy, flow cytometry, clinical lab images Pathology presents specific challenges and opportunities to DICOM. In particular: 1. Some pathology-related image formats do not as yet have applicable DICOM Information Object Definitions. Examples include whole slide images, high-order multi-spectral images, flow cytometry, electron microscopy and others. [Note – Flow cytometry applications have much technical overlap with imaging modalities, even though they do not form an image. It will be important to make imaging standards that have cross-application utility between flow cytometry and immuno-histo-chemistry.] 2. Many pathology processes (for example, flow cytometry) provide challenges in distinguishing "objective" image data from "interpretive" image information. These challenges will include specifying standards for pathology specific markup that would reliably distinguish "unprocessed" from "processes" image data, image annotations from primary image data and "constructed" images from "raw" images, etc. Future Work Items • Structured Reports and/or Evidence Documents in Pathology involving full demographic information; • Correlation of radiologic and pathologic images, including image-guided biopsies; • Coding information based upon existing WHO codification, SNOMED-CT and also ADICAP thesaurus; • Navigating in a hierarchy of images by means of annotations of images and/or drawings (e.g., gross imaging annotated with blocks’ localization); • Dealing with Tissue Micro Arrays (one slide for hundreds of patients) with a link to patient information; • Integration of automated image analysis tools with WSI. 14

Supplement 122 Specifies a specimen description model which allows description of: Type of specimen Procurement and processing steps Sampling methods Physical attributes of slides Final text approved June 2008 This was a necessary first step to allow full use of pathology images with needed clinical data in DICOM Attributes will generally come from the LIS if available These are attributes which are needed to understand and interpret the image The pathologist’s report is not part of this specimen description 15

Pathology Imaging in DICOM Base Std Supp 122 The initial DICOM framework works ok for limited cases such as specimen mammography, but breaks down when more complicated information is needed. Supp 122 added support for a variety of new concepts and relationships Disambiguates specimen and container Container is target of image Container may have more than one specimen Specimens have a physical derivation (preparation) from parent specimens When more than one specimen in an imaged container, each specimen is distinguished (e.g., by position or color-coding) 16

Implementation Issues Supp 122 has the needed data elements, BUT most AP LIS Systems don’t have these data at the SPECIMEN level, if at all Unique slide ID may not be explicitly present No ability to identify subregions of a slide/block Staining and fixation information often co-mingled Specimen descriptions difficult to parse out from large text blocks Dictionaries may be poorly implemented Mention Gilberston study from Case presented at APIII 2007. Problems with the information in LIS, not really with DICOM model 17

Supplement 145 – Whole Slide Images Need a new DICOM Image Object Definition Challenges Vast size Need for intuitive and fast viewing interface DICOM specific issues Image pixel dimensions limited to 64k x 64k Image size description limited to 4GB Desirable to be backwards compatible Efficient sub-region access Most DICOM services assume entire image transmission Most DICOM IOD’s are concerned with much smaller images and they assume complete image transfer (e.g. image store, image move). 18

Tiling and Multi-frame encoding Whole Slide Image divided into tiles Each tile encoded into a frame of multi-frame image object Per-frame header gives spatial location for each tile: X, Y, and Z (focal plane) Multi-frame image object Fixed Header Per-frame header Dimension data Pixel data H Solomon GE 19

typically in 1 DICOM Series Image Pyramid Single frame image Thumbnail Image Multi-frame image (single object) Intermediate Image Multi-frame image (single object) may include multiple Z-planes, color planes Facilitates rapid zooming to precompute multiple resolution levels May add 33% to the size of the file. Baseline Image All image objects typically in 1 DICOM Series H Solomon GE

Localizer image “flavor” Thumbnail image (single frame) plus navigation links to each frame at each resolution Each tile of other resolution images has its corresponding area identified in thumbnail Full description of target tiles Object Unique ID and frame number Resolution Z-plane, color Multiple target frames can overlap Different resolution, Z-plane, color, etc. Presentation and any interactive behavior is not defined in standard Mention sparse tiling Mention that there is significant overhead but the multiresolution pyramid improves performance H Solomon GE

Supplement 145 - Next Steps Supplement approved August 2010 DICOM is now able to handle most pathology and lab images Most slide scanner vendors have been involved, along with some PACS vendors Need to engage LIS vendors and publicize these changes Pathologists can educate their LIS vendors, talk to hospital PACS administrators and talk to imaging vendors encouraging all of them to support this new digital workflow for pathology.

Pathology Imaging Workflow Case info Pathology Order & Specimen info LIS / APLIS Slide preparation Slide prep data Slide ID Scanning orders Pathology Workstation Gross specimen accessioning Images Specimen Images Whole Slide Scanner Surgical or biopsy procedure Our attention up to now has been on the WSI image itself, the output from a whole slide scanner modality. However, that scan process must be seen as just one step in the entire anatomic pathology workflow, which begins with collection of the specimen in a surgical or biopsy procedure, or even earlier with the original screening exam. Detailed discussion of this workflow is not within the scope of this presentation, but I will briefly address specimen management in DICOM as specified in Supplement 122. Images w/ slide prep data Images – X-ray, U/S, optical, etc. PACS Adapted from H Solomon GE 23

Image Sharing Currently some pathologists include snapshots in reports Tumors, specimen margins, unusual findings, etc WSI allows ability to review slides remotely with clinicians The ability to correlate slides with other images would be useful Gross specimen images Endoscopy images Radiology images

Challenges to Wider Adoption Storage and bandwidth PACS storage is relatively expensive Don’t want to transfer entire huge files Pathology systems need to become more image centric (as opposed to report centric) EMR’s need to be able to accept or connect to images and display correctly Security, credentialing, optimized viewers, etc

Summary WG-26 has created supplements to incorporate modern digital pathology within DICOM The collaboration of DICOM, IHE and HL7 has led to a broad based standards effort for digital pathology The availability of a digital workflow for images will enable major changes in the practice of pathology DICOM support for radiology, pathology, surgery, and radiation therapy opens the door for true integration of data from these areas Easy quantitation, collaboration In the next 5-10 years expect major change to more automated processes in anatomic pathology and widespread adoption of wsi 26 26

Acknowledgements Members of DICOM WG-26 Harry Solomon, mentor to WG-26 IHE Anatomic Pathology WG HL7 Anatomic Pathology WG DICOM Website: http://medical.nema.org/