Concluding literature analysis of the currently existing DP frameworks and interfacing

Since 2013, multiple pathology laboratories have implemented DP tools to a certain degree in their workflow – mostly for research purposes. However, until now, very few laboratories have used a fully digital workflow for clinical diagnosis.

In the middle of 2016, the Department of Pathology at the University of Pittsburgh Medical Center integrated DP into its anatomical pathology laboratory information system for diagnostic purposes with the help of vendors (Omnyx Integrated Digital Pathology and CoPathPlus) [140]. This integration solution provides unidirectional data exchange from the pathology laboratory information system to the DPS using web services. Therefore, a

pathologist can access patient identifiers, histology, and case data directly in the DPS.

Regardless of the fact that they use the same technology (SOAP web services), the specifications and application of the system differ from the approach used for biobank purposes. However, this example provides stronger assumptions that our integrated DPS developed using web services, has practical uses for a variety of potential purposes, including clinical diagnosis.

From 2010-2016, LabPON, a pathology laboratory located in the Netherlands, which handles more than 55,000 histological cases per year, fully digitized its diagnostic workflow [141]. The entire process of implementing DP in clinical diagnostics required a significant investment of time and money. There are still challenges that create some obstacles in the process. For example, the digital images require about 450TB of storage capacity per year, but the server capacity is currently limited to 89TB. Therefore, at LabPON, the digital images are deleted after 6-8 weeks. Making a diagnosis based only on digital images is allowed in the Netherlands, but there is no regulation regarding the storing and archiving of digital microscopy images. Digital images are managed by a case viewer that is connected to the LIMS. While images are used for diagnosis, cases are being moved from the folder “In Preparation” to a “For Review” folder, and finally into the “Finished” folder to sign out the case [141].

According to these examples, it seems that the final implemented solution is mostly based on the needs of applications and the organizational environment. Additionally, as there are multiple distinct WSI technologies and LIMS systems on the market, and the reality that standardization of DP is still challenging, implementation mechanisms should be determined for specific systems that are used in a laboratory.

The HL7 Anatomic Pathology Working Group tries to enhance HL7 standards for pathology use cases. In order to facilitate interoperability of laboratory information, they have covered various aspects of pathology, such as improving the tracking of anatomic pathology specimens, integrating pathology data into the medical records, ensuring consistency of the image association, and improving the usage of tissue collection [101]. Additionally, the HL7 working group has tried to improve the transfer of data between pathology labs and clinical settings, which requires filling the gap around vocabulary (such as LOINC and ClinGen codes) for pathology laboratory results [142]. Because there are multiple components that need to be taken into account to enhance existing HL7 standards, progress in pathology units has been quite slow.

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During the last few years, several imaging applications have emerged on the market to handle WSIs, autopsy images, electron microscopic images, and other pathology images [143, 144].

In the most popular of these applications, the DICOM standard is used either for handling digital images as a file format or for image transmission to integrate digital images into a hospital’s infrastructure [145]. In the second case, when the DICOM is used for data transmission between different applications, digital image file formats should be JPEG, JPEG2000, TIFF, or DICOM itself. If the images are presented in JPEG (using the lossy compression method) format, the image quality is not sufficient enough. TIFF, JPEG2000, or DICOM file formats (despite the fact that these formats are based on the lossless methods) have several limitations for pathology images. For example, the maximum file size is limited to 4GB. The DICOM file format is still very rarely used for pathology images, as it has not been integrated into microscope image acquisition systems. There are several applications (e.g., JP2 WSI Converter) that convert some of the proprietary file formats into the standard file format.

However, the main limitation of these applications is that the metadata information is likely to be lost during the image conversion from their original formats (mostly proprietary formats) to standardized image formats (JPEG or TIFF).

Even though the DICOM standard and the PACS storage solution are not used for our integrated DPS, some specifications of the DICOM standard were taken into account. Since there was a growing interest in radiology to access DICOM objects from HTML pages via HTTP/HTTPS, the DICOM working group 27 (web technology for DICOM) developed the Web Access to DICOM Persistent Objects (WADO) standard as a web extension to DICOM. Because the PACS system is generally used as a storage solution for DICOM objects, the WADO Server is connected to the PACS system to retrieve the imaging information. According to the DICOM specification provided by working group 20 (integration of the imaging and information systems) and working group 27, data exchange involves transferring two different kinds of data – pixel data and metadata. WADO uses the web service technology to facilitate access to the images. Pixel data is retrieved by the RESTful web services and metadata is exchanged based on the SOAP-based web services [146]. From a technological point of view, the WADO standard utilizes technology similar to our developed system, but uses a different approach for various applications. Additionally, to keep the enriched metadata of the microscopic images, it is better to store them in the proprietary file format so that information is not lost.

Later, it can be freely converted into the DICOM standard when it becomes integrated into the WSI systems.

Despite the fact that the DICOM standard has significant technical limitations in pathology (discussed in Subchapter 2.3.2.3), it is still possible to roughly define the future directions of the developed system in terms of the DICOM standard. As our interfacing solution is based on the same technology (SOAP web services using XML) for metadata exchange, it allows us to suppose that our solution will be able to easily adapt to the new DICOM standard, since the imaging or metadata information is kept without any loss. Moreover, the interfacing solution can be improved along with the development of the DICOM standard in the ensuing years.

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