Informatics, digital & computational pathology

Digital and whole slide imaging

Digital imaging fundamentals & standards

Last author update: 8 September 2021
Last staff update: 8 September 2021

Copyright: 2021,, Inc.

PubMed Search: Digital imaging[title] pathology "last 5 years"[dp]

Snehal S. Sonawane, M.B.B.S., M.D.
Dariusz Borys, M.D.
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Cite this page: Sonawane SS, Borys D. Digital imaging fundamentals & standards. website. Accessed June 16th, 2024.
Definition / general
  • Dynamic, image based environment that enables the acquisition, management and interpretation of pathology information generated from a digitized glass slide
Essential features
  • Specialized field of pathology involved with data management based on information generated from digitized specimen slides
  • Glass slides are converted into digital images with the aid of specialized scanning machines (glass slide scanners); slides can then be viewed, managed, shared and analyzed utilizing computer based technology
  • Digital images can be viewed locally or can be made accessible for viewing remotely via viewing software and internet
  • Digital images can be archived and maintained in an information management system, which allows for archival and intelligent retrieval
  • These computer based systems can be potentially trained in deep learning (DL) exercises to perform pattern recognition based tasks (artificial intelligence)
  • Image analysis tools can be utilized to derive objective quantification measures from digital slides and deep learning neural networks can be of use to identify certain regions and objects on the digital slides (e.g. Ki67 labeling cells)
  • Digital images allow information sharing for diagnostics, prognosis, education and research
  • 2 main types:
    • Static: utilizes still images
    • Interactive / dynamic digital pathology: utilizes real time images
  • Often used interchangeably with virtual microscopy, digital pathology, telepathology
Components of digital imaging
  • Scanner (image acquisition)
  • Image management (data and messages, including integration in laboratory information system [LIS])
  • Viewing software
  • Image storage system
  • Image evaluation and analysis systems (Pathobiology 2016;83:99)
  • Frozen section diagnosis in remote areas
  • Primary diagnosis of pathology specimens in clinical use
  • Assessment of immunohistochemistry and in situ hybridization
  • Telepathology expert consultation
  • Requesting second opinion
  • Remote working
  • Insourcing and outsourcing of the work
  • Multidisciplinary team tumor board
  • Cytology screening
  • Quality assurance
  • Diagnostic validations for clinical trials
  • Quantitation of hormone receptor (e.g. HER2 studies in breast cancer)
  • 3 dimensional visualization of anatomical structures
  • Education
  • Research
  • Continuing medical education in pathology (Arch Pathol Lab Med 2021 May 18 [Epub ahead of print], J Biophotonics 2012;5:327)
Implementation steps
  • Imaging technology: find the imaging scanner for the size and requirements of your lab, taking the intended use into consideration
  • Information technology infrastructure: determine all the infrastructure that you will need to accommodate a digital pathology system, including network, storage and security
  • Digital workflow: define the workflow stages, personnel carrying out each task and quality control parameters (Pathology 2019;51:1)
  • Validation of the system: for the validation process, utilize the guidelines published by the College of American Pathologists (see below)
  • Train the staff
  • Compare the new and old systems
  • Evaluate the new system
  • Once digitalized, images can be read anywhere, which facilitates flexibility and remote working
  • Digital images can be archived for reviewing, teaching and research
  • Better use of professional time
  • Ability to annotate the images for presentation, sharing and collaboration
  • Reduced loss of mailed pathology material
  • Viewing multiple digital images at the same time and the ability to perform synchronous viewing
  • Easy image portability and retrieval
  • Allows faster diagnosis of urgent cases and faster access to ancillary studies
  • Allows outsourcing for research
  • Facilitates faster second opinions and consults
  • Reduced risk of patient / slide misidentification errors
  • Rapid case retrievals, decreased slide damage and loss
  • Allows automatic and compressive diagnostic audits
  • Facilitates more accurate and convenient cancer staging
  • Ergonomic advantage, as it allows various working positions and reduces musculoskeletal problems
  • Financial benefits include reduced locum cost, travel costs, reduced archival and retrieval cost and increased productivity by consultants and pathologists
  • Research and development opportunities and improves collaboration (J Clin Pathol 2017;70:1010)
  • Reference: Pathol Lab Med Intl 2015;2015:23
  • Expensive instrument
  • Unstable technology: possibility of network, software and hardware failure
  • Requires high speed internet
  • Image quality: requires high magnification scanners
  • Lack of a universal format for virtual slide data
  • Storage of the digital data
  • Lack of standards / regulatory barriers
  • Cost effectiveness
  • Acceptance by pathologists
  • Lab information systems that are not yet ready to handle digital imaging (inability to handle high throughput routine work) (Histopathology 2017;70:134)
  • Reference: Pathol Lab Med Intl 2015;2015:23
Diagrams / tables

Images hosted on other servers:

Comparison of digital pathology and traditional workflow

Digital imaging standards
  • Difficult to define a standard for pathology images due to various imaging and nonimaging parameters
  • Need for established guidelines for digital imaging
  • Standards discussed here are more relevant for whole slide imaging (WSI) and clinical practice of pathology
  • Digital Pathology Association has published a set of guidelines for WSI in clinical practice and various organizations have made an effort to define the guidelines for the standardization of digital; below are technical recommendations for digital imaging system implementation and optimal use
  • Reference: J Pathol Inform 2017;8:51
Technical recommendations
  1. Architecture
    • Can be any of these 3 types: client server solution, web application or service oriented architecture
    • Should be suitable to all personnel who are doing pathology related work
    • Should be able to incorporate into other information systems, such as LIS, electronic medical record and patient database (Pathobiology 2016;83:99, J Pathol Inform 2017;8:51)
  2. Communication network
    • Should have capacity to transmit the images in a timely manner without degradation or distortion
    • Estimated internet speed at the main site should be able to dedicate at least 175 Mbps network capacity for digital imaging and dedicate 1 Gbps full duplex connection between scanner and cloud archive to ensure appropriate performance
    • For optimal viewing performance, recommended minimum bandwidth of 2 Mbps (Pathobiology 2016;83:99, J Pathol Inform 2017;8:51)
  3. Scanner capacity and design
    • Scanners vary not only by their scanning modality but also by scanning time and slide loading capacity
    • High throughput scanners can load up to 400 slides (Arch Pathol Lab Med 2019;143:222)
    • Scanners should:
      • Be designed in such a way that ensures safety of the glass slides throughout the process of scanning
      • Have identification function in order to identify the barcodes associated with the glass slides
      • Be equipped with an autofocus function
      • Provide details to user about the quality of the scanned image
    • Z axis scanning function will lower the rescanning rates and allow the creation of:
      • 3D images that allow navigation in the z axis
      • Enhanced / extended focusing mode to create the best single slide
    • Before implantation, the scanner type, performance and quality must be assessed based on institutional needs, such as sample size, sample type, anticipated turnaround time, etc. (Arch Pathol Lab Med 2019;143:222, J Pathol Inform 2017;8:51)
  4. Scanning speed:
    • Affected by image compression, network bandwidth, scanning magnification and storage; all these parameters should be of matching capacity so that the scanner can work at its fullest potential
    • Other tasks, such as slide loading, calibration, image transmission and storage should be added to the scanning time to give a fair estimate of when the image will be available
    • Standard scanner takes around 10 minutes to scan an area of 1.5 cm2 using 40x objective (J Pathol Inform 2014;5:15)
  5. Storage / data archive
    • There should be defined policies and procedures for adequate short term and long term storage of the archived slide data, depending on the relevant laws and regulations and particular situations
    • Guidelines by CAP (USA), RCP (UK), and FAGP (Germany) recommend data preservation for at least 10 years
    • Guidelines from the JSP (Japan) recommend permanent preservation of the WSI data for a minimum of 5 years
    • Digital Pathology Association (DPA) recommends redundant storage systems
    • 2 storage approaches: selective image storage or every image storage
    • Hot storage for more recent slides, versus cold storage for older slides (Pathobiology 2016;83:99, J Pathol Inform 2017;8:51)
    • JSP (Japan) guidelines recommends that data from the past 5 years be preserved in hot storage for immediate reference of recent cases
    • Hybrid solutions, such as local and cloud based storage (Arch Pathol Lab Med 2021 May 18 [Epub ahead of print])
    • Multisite organization may utilize hub and spoke models (Arch Pathol Lab Med 2021 May 18 [Epub ahead of print])
  6. Image quality for optimal viewing
    • Image resolution of 0.5 μm/pixel (effective viewing magnification: 20x) or better
    • Rescanned slides should be < 5%
    • Reference: J Clin Pathol 2015;68:499
  7. Image compression
  8. Image format
  9. Digital slide viewer and human interface
    • Slide viewer must have the ability to load and navigate the images and should support annotation and side by side visualization (J Pathol Inform 2014;5:14)
    • Display devices can be flat screen monitors or tablet PCs for telepathology utilization
    • Elements taken into consideration while selecting the display devices are: type of display, light source, resolution of the display, contrast ratio, color temperature and profile, speed and capacity of the graphic memory cards
    • Other factors, such as room lighting, window placements and distance from the viewer's eye levels should be kept in mind
    • These display devices should be validated at regular intervals to monitor and maintain performance
    • Display device characteristics:
      • Horizontal resolution: ≥ 1,280 - 2,560 pixels
      • Screen size (diagonal): ≥ 17 - 27 inches
      • Luminance: ≥ 170 - 300 cd/m2
      • Luminance ratio: ≥ 250 - 1,600:1
      • Pixel pitch: ≤ 0.33 mm
      • Minimum luminance: ≥ 0.5 cd/m2
    • Image viewing software should allow observation field display (macro images), annotation function, screen capture functionality and side by side viewing capability
    • Must be fast enough to support the daily workflow of the pathologists by creating a worklist
    • Viewer must support multiple file formats from different sources
    • Telepathology refresh time of 1 second (J Pathol Transl Med 2020;54:437, Pathobiology 2016;83:99, J Pathol Inform 2017;8:51)
  10. Monitor / display
    • Display devices should be compatible with the file formats generated by the scanner and should support the network operations available in any given institute
    • Display devices with horizontal resolution of approximately 2,000 pixels (2K) is optimal (for example, a 24 inch monitor with 1,920 × 1,200 pixels and 0.27 pixel pitch is the minimum recommended resolution)
    • As per the current guidelines, pathologists should determine if the image or monitor is satisfactory for the purpose of its intended use
    • Some technical specifications are:
      • Diagonal dimension of the display distance should be about 80% of the viewing distance
      • Screen should be able to display the image at the originally acquired spatial resolution
      • Viewing devices should be color calibrated
      • Actual contrast (still images) should be 1,000 - 1,600:1
      • Brightness of the display device should be with a luminance of 300 candela (cd)/m2 or higher (Pathobiology 2016;83:99, J Pathol Inform 2017;8:51)
  11. Mobile device use
  12. Security and privacy
    • Security and privacy safeguards should be set in accordance with federal, state, local and hospital guidelines to maintain data integrity
    • Bar coding of the slides is recommended to maintain and ensure the valid electronic chain of custody (Pathobiology 2016;83:99, J Pathol Inform 2017;8:51)
  13. Interoperability
    • Will allow exchange of information between different systems
    • Digital imaging systems should be integrated not only with LIS but with other clinical systems, such as medical imaging system, dermatology, radiology and clinical images in a patient encounter LIS via accepted standards, such as HL7 and IHE (Integrating Healthcare Enterprise)
    • Digital pathology system should follow standards defined by DICOM and below is the list of international standards:
      • IHE: Anatomic Pathology Technical Framework
      • DICOM Supplement 122: Specimen Module and Revised Pathology SOP Classes
Validation of WSI system for diagnostic purpose in pathology (2021 CAP guidelines)
  • Laboratories must validate the WSI systems before use
  • The College of American Pathologists has proposed guidelines for validation of the WSI; the recommendations are below:
    1. Validation process should include a sample set of at least 60 cases for 1 application or use cases (e.g. H&E stained sections of fixed tissue, frozen sections, hematology) that reflect the spectrum and complexity of specimen types and diagnoses likely to be encountered during routine practice; the validation should include another 20 cases to cover additional applications, such as immunohistochemistry or other special stains if these applications are relevant to an intended use and were not included in the 60 cases mentioned above
    2. Validation study should establish diagnostic concordance between digital and glass slides for the same observer (i.e. intraobserver variability); if concordance is less than 95%, laboratories should investigate and attempt to remedy the cause
    3. Washout period of at least 2 weeks should occur between viewing digital and glass slides
    4. If using a previously validated scanner for a new, materially different use case, a full validation for the new use case with documentation is needed
    5. If replacing a scanner of the same make / model for previously validated applications, calibration of images for same slides scanned with each scanner with documentation is acceptable (also known as a function check)
      • If deploying scanners of the same make / model as previously validated at multiple sites across a hospital network, assess applications, network and histology issues at each site to determine if full validation is required for each new scanner with documentation
      • If replacing a scanner with different make / model, full validation with documentation is needed
    6. If introducing scanners of different make / model to multiple sites across a hospital network, full validation with documentation for at least 1 site with assessment of applications, network and histology issues at additional sites to determine if full validation is required for each new scanner
    7. If introducing completely different viewing software, including software from the same vendor where legacy software has been sunset, start with calibration of images between old and new software to determine if full validation is required with documentation; if employing an upgrade of software from the same vendor, calibration of images between old and upgraded software with documentation potential function check or partial validation is dependent upon the criticality and extent of the upgrade
    8. If replacing / upgrading displays at pathologist workstations, calibrate image quality between old and new displays with or without documentation
    9. Remote locations / change in network: if allowing primary diagnosis to be remotely performed outside the hospital network (e.g. pathologist’s home), a full validation with documentation is needed
  • If there is a change in pathology or hospital network, calibrate archived images immediately before and after the network changes are made, either with or without documentation (Arch Pathol Lab Med 2021 May 18 [Epub ahead of print])
    Board review style question #1
    For optimal viewing performance the minimum recommended bandwidth is

    1. 1 Mbps
    2. 2 Mbps
    3. 3 Mbps
    4. 5 Mbps
    Board review style answer #1
    Board review style question #2
    What is the recommended acceptable rescanning rate for a digital scanner?

    1. < 1%
    2. < 5%
    3. < 7%
    4. < 10%
    Board review style answer #2
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