Introduction

The Royal College of Pathologists of Australasia (RCPA) has received funding from the Australian Government Department of Health under the Specialist Training Program to support the development of this Digital Microscopy Education and Training Manual (DMM). This manual is based on the RCPA Guidelines for Digital Microscopy in Anatomical Pathology and Cytology October 2015.

The DMM contains training modules on

  • Technical specifications
  • Image Processing
  • Communication and Networks
  • Privacy, Confidentiality and Security
  • Quality and Compliance
  • Professional Practise Training and Competency

The RCPA recognises the rapid advances in the field of digital microscopy. The Part 1 Small Biopsy Exam in Anatomical Pathology exam is now digital microscopy based and there are many educational modules on the RCPA website which utilise this technology. There is also a requirement for laboratories using this technology to ensure safe and secure implementation for diagnostic purposes.

Digital microscopy can be used interchangeably with virtual microscopy and for the purposes of these education modules, digital microscopy (DM) will be the preferred terminology used. The captured images of the entire glass slide of stained tissue is often referred to as whole slide images (WSI).

Digital microscopy aims to emulate conventional light microscopy in a computer-generated manner. It involves two components: digitisation of the glass slide and viewing of WSI along with associated viewing applications. 2 D or 3D images are scanned or acquired from glass slide WSI with X and Y axis, and sometimes Z-axis, capability. WSI are captured with either A x20 or x40 objective lens. The higher the magnification of the objective lens used in the scanning process, the higher the resolution of the acquired image. The WSI are then viewed on a monitor or screen. Grouped aggregates of pixels are stored and loaded for viewing either as horizontal strips/lines or alternatively as squares/rectangles called tiles, depending on the file format (which is vendor-specific). Bandwidth requirements for viewing of WSI are not high because the entire image file does not need to be transferred. The image is generally stored on a remote server, and only segments of the entire image selected are transferred as required.< /p>

A digital microscopy system comprises of;

  1. A slide feeder and scanner which digitise glass slides in a linear or tiled pattern, which is then stitched together by software, to create a high-resolution image. This image can be captured through bright field or fluorescence or both. The quality of WSI can also vary from scanner to scanner. Walkowski and colleagues demonstrated, through both automated objective assessment and subjective pathologist opinion, that there was a marked difference in quality factor of WSI acquired with two different scanners.

    01. Walkowski, S. and Szymas, J. (2011). Quality evaluation of virtual slides using methods based on comparing common image areas. Diagn Pathol, 6 (Suppl 1), S14. doi: 10.1186/1746-1596-6-S1-S14

  2. A storage server stores files compressed into reduced image size to be reconstructed quickly for viewing. Data compression is important especially with 3D WSI. There are two types of image compression (lossless and lossy); with lossy compression, although there is some loss of detail (compression artefacts) it is most appropriate for diagnostic and educational digital microscopy because of the associated large amounts of data. Ideal compression ratios, pixel resolution, monitor resolution and contrast ratios have been determined for optimal diagnostic accuracy.

    02. Kalinski, T., Zwönitzer, R., Grabellus, F., Sheu, S.-Y., Sel, S., Hofmann, H., . . . Roessner, A. (2009). Lossy compression in diagnostic virtual 3-dimensional microscopy—where is the limit? Hum Pathol, 40(7), 998-1005. doi: 10.1016/j.humpath.2008.12.010

  3. A computer workstation for viewing, with high quality display monitor, ergonomic navigation control device, software application and adequate communication and network communication.
  4. A Laboratory Information Systems (LIS) to retrieve request and patient data.
Increased usage of digital microscopy in recent years has been primarily driven by developments in technology, scanners, image quality and resolution. Storage costs have declined. Image transmission and networks including cloud storage solutions are continually improving.

03. Farahani N et al. Whole slide imaging in pathology: advantages, limitations, and emerging perspectives. Pathology and Laboratory Medicine International. 2015. 7: 23-33.

In addition to technical issues, regulatory and validation requirements and standards have yet to be adequately addressed..

04. Pantanowitz L et al. Review of the current state of whole slide imaging in pathology. J Pathol Inform. 2011. 2: 36.

Many consider the use of digital microscopy a transformation of practice. The change to digital microscopy should be considered a transition which has implications for implementation so the applications for this technology can be more readily appreciated and accepted.

05. http://www.vmscope.com/virtuelle-mikroskopie.html

Some of the main benefits of using digital microscopy include:

  • Group viewing and discussion
  • Teleconsultation over the internet in real time
  • Telepathology
  • Images can be stored for documentation, medical reports and meetings
  • Resolution of a digital slide is known, so distances and areas can be measured accurately
  • Digital images will not deteriorate
  • Quicker and more efficient retrieval
  • Computer aided diagnosis (CAD)

Telepathology is the process by which diagnostic pathology is performed on transmitted digital slide images that are viewed at a distant site in real-time on a display screen rather than by conventional light microscopy with glass slides. Telepathology can be used for histopathology and cytopathology specimens, blood films/bone marrow morphology, immunofluorence and microbiological assessments of cultures. Telepathology can assist in solving pathology service issues and shortages, particularly in rural areas, and facilitate expert and referral consults. The Royal College of Pathologists (RCPA) Position Statement Telepathology.

Understanding the Integration of digital microscopy into laboratory workflow

This flowchart shows the integration of the conventional and digitalised pathways required within a LIS. It highlights the overlap between the processes and why digitalisation is best considered to be a transition and not a transformation of microscopy.

The implementation of digital pathology has been slower than the implementation of digital images into radiology. This is partly due to differences in image acquisition between the two specialties. In radiology, images begin as digital data whereas in pathology, images are converted from an analogue form into digital format. Other differences include Picture Archiving and Communication System (PACS) and associated standards Digital Imaging and Communications in Medicine (DICOM) available for radiology, larger file size and associated metadata of pathology digital images, and workflow efficiencies in radiology.

04. Pantanowitz L et al. Review of the current state of whole slide imaging in pathology. J Pathol Inform. 2011. 2: 36.

Three-dimensional focus has also traditionally been necessary with a light microscope for diagnosis, a feature that is not important for reporting a radiology image.

Despite significant improvements in technology, adoption of digital microscopy has been limited to niche practices.

04. Pantanowitz L et al. Review of the current state of whole slide imaging in pathology. J Pathol Inform. 2011. 2: 36.

However, as the technology improves, applications for diagnosis, education and research offered by this technology will broaden.

These modules aim to provide guidance when implementing digital microscopy in the workplace for diagnostic use in histopathology and cytology.
A Competencies check-list is provided at the end of each module to encapsulate the main concepts. These can be incorporated into laboratory procedure manuals and can also act as a self-testing and competence assessment guide for continuing professional development.

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