DICOM and the Pathology Community Experience

Bruce Beckwith, MD

Whole Slide Imaging (WSI)

Scanner

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

Comparison of Digital ImagingRadiology

• 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

The Image Size Challenge

1 focal plane24 bit color40x magnification15 Gigabytes

10 focal planes24 bit color40x magnification3.75 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

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

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

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

WG-26 Goals

• Initial 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

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

SpecimenPhysical object

ContainerBox, Block, Slide, etc.

Is child of

n

PreparationStep

Collect, Sample, Stain, Process

Image

Isacquired

on

1

Series

1

Contains

n

1

CreatesEquipment

Modality

1 n

Study

Contains

Patient

1

Has

n

1

n

Issource

of

1

Contains

Contains1 n

n

Has1 n

1

Has

1ComponentBase, Coverslip

n

Pathology Imaging in DICOM

Base Std

Supp 122

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

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

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)

Pixel dataDimension dataPer-frame headerFixed Header

Multi-frame image object

H Solomon GE

Image Pyramid

All image objectstypically in 1 DICOM Series

Thumbnail Image

Intermediate Image

BaselineImage

Multi-frame image(single object)

Multi-frame image(single object)may include multipleZ-planes, color planes

Single frame image

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

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

Pathology Imaging Workflow

Slide prep data

Whole Slide Scanner

Images w/slide prep data

PathologyWorkstation

Images

Gross specimen

accessioning

Specimen Images

Surgical or biopsy

procedure

Images – X-ray, U/S, optical, etc.

Slide preparationCase info

PathologyOrder & Specimeninfo

Slide ID

Scanning orders

Adapted from H Solomon GE

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

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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/