Discussion

The aim of this article is to share the experience of using WSI for primary diagnostics in a medium routine pathology practice. The integration of WSI in the routine workflow was performed in a stepwise manner starting with minor adjustments of specimen handling, followed by two validation studies, finally resulting in implementing primary WSI based diagnostics for part of the routine work.

Studying the validity of WSI was a crucial point. The results of the two validation studies were very promising and encouraged the pathologists to start with primary WSI based diagnostics as part of the routine work. This was applied at first for breast needle core biopsies and later extended to other body systems. The gradual introduction of WSI based diagnosis in the daily routine was a very important step that revealed difficulties and problems associated with WSI based diagnostics, and allowed for timely finding solutions.

This trial showed that about 82.1% of scanned cases could be digitally signed out successfully. The main reasons for not being able to sign out the remaining cases were image quality, followed by logistical and technical problems. Image quality is expected to improve when focusing algorithms become faster and better, allowing for focusing on may be every pixel instead of a few fields scattered over the section. Another aspect that we had not expected to influence the process was the variation of thickness of the object glass. Unpredictable solitary or groups of slides appeared to have a thickness just under or above the tolerance of the automatic focusing range of the scanner. Although this variation could not be managed by the glass slide manufacturer, in newer versions of the hardware this problem has been solved. Some adjustment to the laboratory work, especially central placing of the tissue on the glass slides, will help to avoid incomplete scans. Also in tissues with low optical density the parameters for scanning can be adjusted, resulting in a higher sensitivity and complete images. Guaranteed network access and speed will probably require available Information technology (IT) support, which may not be easy to arrange for smaller laboratories. For a better flow of the routine work, WSI should be stored in an appropriate way so that the pathologist will be able to access them without delay preferably linked to the pathology report and stored in a sustainable digital archive for later referral if needed. The current work approach is that the pathologist accesses over the network the WSI stored on an external hard disk on which digital slides from the same case are stored in one a folder carrying the case number. For the time being, the existing storage system and accessibility are adequate for the department work. Nevertheless, there were about 61 cases with logistic problems where the pathologist could not locate the WSI or there were network problems which were responsible for case deferral. Performing scanning of all the tissue specimens on a daily basis would require a larger storage environment and easier access (eg, by using a storage area network). To this end, linking WSI to the pathology report would be of great advantage. It will not be necessary for the pathologist to open different files (the current work approach) to access WSI but can smoothly open the same pathology database where the patient history, macroscopic images and WSI are stored together. Linking of WSI with the patient history and pathology report has been successfully implemented in the University Medical Center Utrecht, which facilitates image retrieval for revision, clinico-pathological conferences and research.7 The same or very similar approach will be adopted in AMCH in the near future to overcome logistic problems.

Some technical laboratory errors and the need of extra stain were responsible for case deferral in 105 cases. The same could be encountered if the diagnosis was performed by glass slides and conventional microscope. Rescanning of glass slides with technical errors would be an option to enrich and complete the department's digital archive. However, this would not serve the primary goal of having WSI available in a timely and complete manner to perform WSI based routine diagnostic analysis in a medium-sized routine pathology lab. Most of the cases which required extra procedure were from skin lesions where the pathologists need extra information to complete the diagnosis by asking for extra stain, deeper sections, internal consult or even asking for the glass slide when the digital image information does not satisfy the diagnostic needs. In this study, we have only four cases where the presence of glass slide was necessary to complete the diagnosis; two of them to check the double refraction in gingival and skin infection as this feature cannot be supported in WSI. Perhaps the easiest category to start primary digital diagnosis with may be Gastro-intestinal (GI) and breast biopsies.16 ,17 Table 4 details these cases.

There was a remarkable variation (27%–90%) between the four pathologists in successfully diagnosing cases digitally. Although information as to the exact reasons for deferring cases was incomplete, this shows that adaptation of digital diagnosis may differ between pathologists when starting routine digital diagnosis.

Scanning of the complete daily production of pathology routine work will become possible shortly with the introduction of scanners which are able to scan standard glass slides at 40× in less than 1 min. Primary diagnostics on WSI will facilitate pathology routine workflow through easy image sharing and retrieval and it will not be time consuming anymore to ask for a second opinion for difficult cases. Storing microscopic information in a digital from has also many advantages over storing physical slides since WSI can be stored permanently with constant quality. These images can be used for different applications such as teaching, research and revision. Performing quality assurance (QA) and teleconsultation based on WSI is less time consuming obviating the time needed to send glass slides to far places. This will be more efficient if a national storage or image exchange facility would be present where pathologists could look up digital slides from different institutes for teleconsultation and telerevision. Furthermore, WSI can be used for image analysis which will likely improve diagnostic accuracy and productivity.9 ,18

Primary diagnostics based solely on WSI was applied also in Kalmar County Hospital, Sweden. In this hospital, digitisation of the whole daily production of histopathological specimens was initiated around the same time as in AMCH and has resulted in a situation where 75% of the diagnostics are performed digitally in addition to teleconsultations for frozen sections from other hospitals without local pathologists. Assessing the feasibility of primary WSI based diagnostics is ongoing currently in the University of Pittsburgh Medical Center, USA,5 University Medical Center Utrecht, The Netherlands16 ,17 ,19 and University Medical Center Nijmegen in collaboration with AMCH (manuscript in preparation). In addition, the Digital Pathology Association has presented two papers at the Pathology Vision conference 2011 discussing the high level validation approach of WSI for primary diagnostics. The continuous efforts aimed for validating WSI for primary diagnostics will help eventually in wide use and acceptance of WSI for this purpose. A recent review (via Medscape) has discussed the legal aspects of primary diagnostics using WSI. In this review, it was stated that according to the available documentation it would be sufficient to have local descriptions of the workflow process and to monitor the performance of the individual pathologists, an approach very similar to that for monitoring the quality of conventional microscopy.

QA and quality control have not been worked out for primary digital pathology diagnosis, but are clearly an important issue. Guidelines are, for example, needed as to the desired resolution, completeness of the scans, colour depth, compression ratios, quality of focus, and duration and quality of storage. When starting primary digital diagnosis, it seems wise to have an initial period of full QA of about 50 cases in major diagnostic areas for every pathologist, and then to do random QA in about every 50th case.

In conclusion, the quality of the currently produced WSI is sufficient for primary diagnostics in histopathology. Large scale scanning of the whole daily routine production in histopathology should be accompanied by some modifications regarding adequate and timely image retrieval and controlling scanning errors. Solving these issues is necessary before complete replacement of glass slides within pathology work could be achieved. Still, with the currently available technology, it seems that at least 82.1% of routine pathology can be signed out digitally.