Advances in Digital Pathology

The frontiers of pathologists’ views are being extended.

Digital Pathology

Digital pathology plays a critical role in modern pathology practice and is increasingly becoming required technology within the laboratory environment. Advances in computing power, faster networks and cheaper storage has enabled pathologists to manage images more easily and flexibly than in the last decade. Laboratory information systems (LIS) have started to exploit these capabilities, and as a result we are beginning to see an increase in capture, storage, manipulation and retrieval of digital images handled by the LIS.

A digital image is composed of thousands of tiny pixels of color, shades of gray, or black and white. Computer monitors display digital pictures by dividing the display screen into millions of pixels, arranged in rows and columns. Pathology practices routinely use digital images acquired by video/digital cameras, which they may utilize in real-time (e.g., live streaming) and/or store locally or remotely within integrated networks.

In practices where digital images are incorporated into sign out and reporting, they often have multiple cameras, network connectivity to an image server and the pathologists’ workstations, and integrated or modular integration of these digital images with their LIS.

Imaging software is highly varied and serves many functions. For example, software for image processing permits annotation and also allows the images to be adjusted for brightness, contrast, hue and resolution, which may be extremely useful for editing pathologic images for clinical use. Image-embedded reports may improve the care of patients by providing the clinician with added insight into the patient’s disease process.

Applications of Digital Pathology

As pathology practices increasingly utilize digital pathology and in so doing generate many types of digital images, this presents ­significant challenges in labeling, storage and management within a healthcare organization. These images have many clinical applications-deployment in pathology reports, for conferences, presentations, quality assurance studies, research and the creation of digital slide teaching.

Another application of digital pathology is telepathology, which allows diagnosis to be performed at a distance by an expert. Three general approaches to telepathology use static, dynamic and hybrid systems.

Static (or “store-and-forward”) telepathology requires that the referring individual capture a collection of digital images for transmission to the consultant. A disadvantage is the loss of control by the consulting telepathologist.

Dynamic systems are remote-controlled microscopes that give the pathologist a live view of the distant image while allowing them to remotely control the microscope. The advantage to dynamic systems is that they give the consultant flexibility in distant viewing. Disadvantages include the expensive and proprietary nature of the host and client stations and the high bandwidth needed to view image data.

Hybrid telepathology systems combine the features of static and dynamic systems by coupling remote-controlled microscopy with high-resolution still image capture and retrieval. This approach requires a lower bandwidth while still providing high-quality images for diagnostics, reporting and archiving.

Current and future developments in telepathology are focusing on three areas:

  • the adoption of open standards that will allow intersystem operability,
  • the integration of telepathology into the LIS to facilitate image databases, reporting and billing capabilities, and
  • the increasing use of whole slide imaging (WSI) in clinical practice.

Whole Slide Imaging

In the last two decades, digital imaging in pathology has seen advances in whole slide imaging (WSI), which allows entire slides to be imaged (digitized or scanned) and stored at high resolutions. The WSI is an image file that is a nearly identical digitized reproduction of all the material (e.g., tissue section or cytology specimen) on the glass slide with full zooming functionality, allowing the pathologist to focus on any region of interest on the slide.

The images currently produced by whole slide scanners are of diagnostic quality. With available viewing software, it is also possible to have annotations and clinical metadata presented with this image, resulting in a virtual microscope with all the clinical information needed to sign out the case.

In the last decade, vendors have produced increasingly capable automated, high-speed whole slide imagers. A typical imaging robot today can read barcodes on glass slides and capture and compress an image of a slide with a 1.5×1.5 cm tissue section within 1-3 minutes. The quality of focusing is limited by multiple optical and mechanical para-meters, notably numerical aperture (NA) of the objective and movement resolution on the vertical (z-) axis.

Newer devices are implementing non-traditional optics, illumination and sensors designed specifically for very high-speed image capture resulting in significant improvements in speed, throughput and resolution. All WSI scanners come with automatic algorithms to determine the optimal focus (focal planes) throughout the slide.

Many studies have demonstrated the ­utility of WSI in teaching, quality assurance assessment, consultation, telepathology, image analysis and research use. WSI files are usually formatted as multi-resolution “pyramids” that contain multiple images comprising multiple magnifications. Every vendor has its own proprietary file format, and efforts are under way toward a universal interchange standard (DICOM supplements 122 and 124).

Looking Forward

Nevertheless, despite some of the hurdles that still need to be overcome, this is an exciting time in pathology. Digital pathology tools are making it possible to integrate imaging into all aspects of pathology reporting, including anatomical, clinical and molecular. WSI will continue and progress toward true digital “slideless” and “paperless” laboratories in the future.

The LIS also will continue to evolve, making it easier to be able to integrate images in the pathology workflow. Advanced algorithms and computer-aided diagnostic techniques will be increasingly used.

Other enhancements in digital pathology on the horizon include improved imaging techniques such as 3D tissue reconstruction and advanced imaging tools such as optical coherence tomography that offer superior ultra-high resolution, non-invasive views in many dimensions of the pathology specimen.

Current applications of digital pathology and future enhancements of these tools are extending the frontiers of the pathologist’s view beyond a microscopic slide and enabling a true integration of knowledge beyond present limits and boundaries.

Suggested Reading

Parwani AV, Feldman M, Balis U, Pantanowitz L. Digital imaging. In: Pantanowitz L, Balis UJ, Tuthill JM (editors). Pathology Informatics: Theory & Practice. ASCP Press. 2012; 15:231-256.

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