Digital Pathology Progression

As technology advances, new niche areas for application are uncovered

Digital pathology has been around for a decade, but its slow adoption has been hampered by cost, workflow integration, system integration, and governmental regulation on whole slide imaging (WSI) systems. And despite the fanfare by pathology informatics champions and professional organizations through their meetings and educational materials, there’s still slight resistance in adoption of digital pathology in the general pathology community. Many perceive digital pathology or WSI systems as a luxury supplement to the daily clinical practice rather than a necessity.

Current Practices

Unlike radiology, with its seamless image digitization and PACS, the histopathology laboratory has to process tissue and produce glass slides. Glass slide production remains the backbone of a histopathology laboratory in the foreseeable future and is the focus of legacy laboratory information systems (LIS). Digital pathology is considered by some to be extra effort and time over and above the steps that would have to take place anyway in a histopathology laboratory. Workflow and data flow need to be adjusted for WSI system implementation, and it needs operational and network support. In most instances, WSI system runs parallel to LIS with limited integration. In the best-case scenario, whole slide digital images are appendages to cases in LIS and not the center of the cases.

The FDA labeled WSI system class III (highest risk) medical devices and has advised that WSI systems should be regulated as such (quality system regulation, good manufacturing procedures, premarket approval). It is in sharp contrast to microscopes that are regulated as class I (lowest-risk) devices and require no premarket approval. Until whole slide digital images are approved for primary diagnoses and LISs are successfully designed around whole slide digital images rather than glass slides (similar to radiology PACS), the adoption to clinical service will remain at a slow pace.

Areas for Enrichment

There are other niches, however, where WSIs have been successfully implemented, such as in education, quality assurance, research, image analysis and secondary diagnostic purposes, including telepathology for frozen sections and second opinions. All of these are considered to be important secondary functions in the practice of pathology. These secondary functions enrich and bring value proposition to pathology service. While waiting for FDA decision on WSI systems for primary diagnoses, pathologists should familiarize themselves in using WSI systems for secondary functions.

With the exorbitant amount of glass slides produced by a busy pathology practice, routine scanning of all cases/slides does not make sense, but routine scanning of pertinent or positive diagnostic slides after sign outs are feasible. WSIs are portable (accessible anywhere at anytime), easily and indefinitely archived and shared/distributed to support secondary functions. WSIs are superior to glass slides for future review after primary diagnosis has been made and the glass slide has been put away in remote storage.

As well, a good WSI system will eliminate the need for retrieval of the actual glass slides, reducing glass slide transport in general, and obviate the risk of misfiling, losing and breaking glass slides.

The most common use of digital pathology is telepathology for frozen sections and second opinions. Telepathology use in the near future will increase due to materialization of the Accountable Care Organization (ACO), which emphasizes high quality, lower cost and better outcome of patient care. Typically in this scenario, an ACO medical center will employ digital pathology to support a remote healthcare facility in providing the same high quality and subspecialized pathology service with lower cost and staffing in the remote healthcare facility.

Two Major Advances

Recently, there have been two major advances in digital pathology. The first one is the approval of certain WSI systems for routine diagnoses in Canada. Similarly, the systems have also received European Union’s CE Mark. The decision by the Canadian government to clear WSI systems is based on the need to improve access and quality of care for patients living in remote areas. These happened while the U.S. FDA is still considering approving these devices. Pathologists in the U.S. will have an opportunity to learn WSI implementation for primary diagnoses from their colleagues in Canada.

The second advance is the recently published guideline for validating WSIs for diagnoses from the College of American Pathologists and Laboratory Quality Center. The guideline was established to assist pathology laboratories in validating their own WSI systems for clinical use. It was supported by many previous studies that have shown diagnostic accuracy of WSI, either close or comparable to light microscopy. Therefore, primary diagnoses can be safely rendered using whole slide images.

Validation of the entire WSI system, involving pathologists trained to use the system, should be performed in a manner that emulates the laboratory’s actual clinical environment. It is recommended that the validation study include at least 60 routine cases per application, ­comparing intraobserver diagnostic concordance between digitized and glass slides viewed after wash out period (at least 2 weeks apart). Validation should demonstrate that the WSI system under review produces acceptable digital slides for diagnostic interpretation.

Taking Steps Forward

Converting “analog” conventional pathology to digital pathology is considered to be the first necessary step toward the future of pathology where the boundary between clinical, anatomic and molecular pathology is blurred. Both clinical and molecular pathology are digital from the beginning. The promise of image analysis, pattern recognition and data mining from WSI systems will ultimately result in valuable data to support clinical decisions and drive patient care.

The buzz of vendor neutral archive (VNA) in the recent years brings image intensive specialties – radiology, cardiology, dermatology, gastroenterology and pathology – to the forefront. The basic concept of VNA is storing medical images in standard format and interface that are neutral to vendor-specific devices. VNA potentially could eliminate departmental image storage silos and allow greater stability at archival level, despite rapid evolution and change at the higher application-level (display and workflow). All WSI systems are advocating their own propriety image format, which is counterintuitive in the eve of VNA. While many are able to save WSI in an open source format, such as JPEG 2000, those images will lose some of their attributes when opened by another vendor’s image viewer. The work on establishing standards for WSI, such as DICOM, is ongoing.

Wider adoption of digital pathology requires better workflow; availability of image standard; improved integration to the LIS, PACS or enterprise imaging system; lower cost of hardware and implementation; promotion of reimbursement for technical and diagnostic services; clarification of regulations; and pathologist acclimatization to WSI. The technology is here to stay and pathologists should embrace and familiarize with digital pathology, as it is the future of pathology.

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