Applications and implications of whole-slide imaging in breast pathology

Technological advances in whole slide imaging (WSI) technology and artificial intelligence (AI) applications in recent years have resulted in increasing adoption of this paradigm shift technology. This brings with it many advantages, new challenges, and potential adaptations to the microscopic assessment of specimens that pathologists need to be aware of. This article describes the applications and implications of WSI within the context of the reporting of breast pathology specimens. Challenging diagnostic entities in digital breast pathology are presented and the key areas in which AI could be useful in breast pathology are highlighted.     

Whole slide images for primary diagnostics of gastrointestinal tract pathology: a feasibility study

During the last decade, whole slide images have been used in many areas of pathology such as teaching, research, digital archiving, teleconsultation, and quality assurance testing. However, whole slide images have as yet not much been used for up-front diagnostics because of the lack of validation studies. The aim of this study was, therefore, to test the feasibility of whole slide images for diagnosis of gastrointestinal tract specimens, one of the largest areas of diagnostic pathology. One hundred gastrointestinal tract biopsies and resections that had been diagnosed using light microscopy 1 year before were rediagnosed on whole slide images scanned at ×20 magnification by 5 pathologists (all reassessing their own cases), having the original clinical information available but blinded to their original light microscopy diagnoses. The original light microscopy and whole slide image-based diagnoses were compared and classified as concordant, slightly discordant (without clinical consequences), and discordant. The diagnoses based on light microscopy and the whole slide image-based rediagnoses were concordant in 95% of the cases. Light microscopy and whole slide image diagnosis in the remaining 5% of cases were slightly discordant, none of these were with clinical or prognostic implications. Up-front histopathologic diagnosis of gastrointestinal biopsies and resections can be done on whole slide images.     

Virtual microscopy and digital pathology in training and education

Traditionally, education and training in pathology has been delivered using textbooks, glass slides and conventional microscopy. Over the last two decades, the number of web-based pathology resources has expanded dramatically with centralized pathological resources being delivered to many students simultaneously. Recently, whole slide imaging technology allows glass slides to be scanned and viewed on a computer screen via dedicated software. This technology is referred to as virtual microscopy and has created enormous opportunities in pathological training and education. Students are able to learn key histopathological skills, e.g. to identify areas of diagnostic relevance from an entire slide, via a web-based computer environment. Students no longer need to be in the same room as the slides. New human-computer interfaces are also being developed using more natural touch technology to enhance the manipulation of digitized slides. Several major initiatives are also underway introducing online competency and diagnostic decision analysis using virtual microscopy and have important future roles in accreditation and recertification. Finally, researchers are investigating how pathological decision-making is achieved using virtual microscopy and modern eye-tracking devices. Virtual microscopy and digital pathology will continue to improve how pathology training and education is delivered.     

Colour in digital pathology: a review

Colour is central to the practice of pathology because of the use of coloured histochemical and immunohistochemical stains to visualize tissue features. Our reliance upon histochemical stains and light microscopy has evolved alongside a wide variation in slide colour, with little investigation into the implications of colour variation. However, the introduction of the digital microscope and whole‐slide imaging has highlighted the need for further understanding and control of colour. This is because the digitization process itself introduces further colour variation which may affect diagnosis, and image analysis algorithms often use colour or intensity measures to detect or measure tissue features. The US Food and Drug Administration have released recent guidance stating the need to develop a method of controlling colour reproduction throughout the digitization process in whole‐slide imaging for primary diagnostic use. This comprehensive review introduces applied basic colour physics and colour interpretation by the human visual system, before discussing the importance of colour in pathology. The process of colour calibration and its application to pathology are also included, as well as a summary of the current guidelines and recommendations regarding colour in digital pathology.     

Localization of Diagnostically Relevant Regions of Interest in Whole Slide Images: a Comparative Study

Whole slide digital imaging technology enables researchers to study pathologists’ interpretive behavior as they view digital slides and gain new understanding of the diagnostic medical decision-making process. In this study, we propose a simple yet important analysis to extract diagnostically relevant regions of interest (ROIs) from tracking records using only pathologists’ actions as they viewed biopsy specimens in the whole slide digital imaging format (zooming, panning, and fixating). We use these extracted regions in a visual bag-of-words model based on color and texture features to predict diagnostically relevant ROIs on whole slide images. Using a logistic regression classifier in a cross-validation setting on 240 digital breast biopsy slides and viewport tracking logs of three expert pathologists, we produce probability maps that show 74 % overlap with the actual regions at which pathologists looked. We compare different bag-of-words models by changing dictionary size, visual word definition (patches vs. superpixels), and training data (automatically extracted ROIs vs. manually marked ROIs). This study is a first step in understanding the scanning behaviors of pathologists and the underlying reasons for diagnostic errors.     

Accuracy is in the eyes of the pathologist: The visual interpretive process and diagnostic accuracy with digital whole slide images

Digital whole slide imaging is an increasingly common medium in pathology, with application to education, telemedicine, and rendering second opinions. It has also made it possible to use eye tracking devices to explore the dynamic visual inspection and interpretation of histopathological features of tissue while pathologists review cases. Using whole slide images, the present study examined how a pathologist’s diagnosis is influenced by fixed case-level factors, their prior clinical experience, and their patterns of visual inspection. Participating pathologists interpreted one of two test sets, each containing 12 digital whole slide images of breast biopsy specimens. Cases represented four diagnostic categories as determined via expert consensus: benign without atypia, atypia, ductal carcinoma in situ (DCIS), and invasive cancer. Each case included one or more regions of interest (ROIs) previously determined as of critical diagnostic importance. During pathologist interpretation we tracked eye movements, viewer tool behavior (zooming, panning), and interpretation time. Models were built using logistic and linear regression with generalized estimating equations, testing whether variables at the level of the pathologists, cases, and visual interpretive behavior would independently and/or interactively predict diagnostic accuracy and efficiency. Diagnostic accuracy varied as a function of case consensus diagnosis, replicating earlier research. As would be expected, benign cases tended to elicit false positives, and atypia, DCIS, and invasive cases tended to elicit false negatives. Pathologist experience levels, case consensus diagnosis, case difficulty, eye fixation durations, and the extent to which pathologists’ eyes fixated within versus outside of diagnostic ROIs, all independently or interactively predicted diagnostic accuracy. Higher zooming behavior predicted a tendency to over-interpret benign and atypia cases, but not DCIS cases. Efficiency was not predicted by pathologist- or visual search-level variables. Results provide new insights into the medical interpretive process and demonstrate the complex interactions between pathologists and cases that guide diagnostic decision-making. Implications for training, clinical practice, and computer-aided decision aids are considered.     

Being fully digital: perspective of a Dutch academic pathology laboratory

The introduction of fast and robust whole slide scanners has facilitated the implementation of ‘digital pathology’ with various uses, the final challenge being full digital diagnostics. In this article, we describe the implementation process of a fully digital workflow for primary diagnostics in 2015 at the University Medical Centre in Utrecht, The Netherlands, as one of the first laboratories going fully digital with a future‐proof complete digital archive. Furthermore, we evaluated the experience of the first 2 years of working with the system by pathologists and residents. The system was successfully implemented in 6 months, including a European tender procedure. Most pathologists and residents had high confidence in working fully digitally, the expertise areas lagging behind being paediatrics, haematopathology, and neuropathology. Reported limitations concerned recognition of microorganisms and mitoses. Neither the age of respondents nor the number of years of pathology experience was correlated with the confidence level regarding digital diagnostics. The ergonomics of digital diagnostics were better than those of traditional microscopy. In this article, we describe our experiences in implementing our fully digital primary diagnostics workflow, describing in depth the implementation steps undertaken, the interlocking components that are required for a fully functional digital pathology system (laboratory management, hospital information systems, data storage, and whole slide scanners), and the changes required in workflow and slide production.     

Fibrocartilaginous mesenchymoma of bone: a single‐institution experience with molecular investigations and a review of the literature

Whole slide imaging is being used increasingly in research applications and in frozen section, consultation and external quality assurance practice. Digital pathology, when integrated with other digital tools such as barcoding, specimen tracking and digital dictation, can be integrated into the histopathology workflow, from specimen accession to report sign‐out. These elements can bring about improvements in the safety, quality and efficiency of a histopathology department. The present paper reviews the evidence for these benefits. We then discuss the challenges of implementing a fully digital pathology workflow, including the regulatory environment, validation of whole slide imaging and the evidence for the design of a digital pathology workstation.     

Interobserver and intraobserver reproducibility in digital and routine microscopic assessment of prostate needle biopsies

Advances in whole slide digital imaging in the past decade necessitate validation of these tools in each organ system in advance of clinical adoption. We assessed reproducibility in reporting prostate needle biopsy parameters among urologic pathologists using routine and digital microscopy in a consultation/second opinion-like setting. Four urologic pathologists evaluated a single core level from 50 diagnostically challenging needle biopsy specimens by routine microscopy and whole slide digital imaging. Interobserver and intraobserver agreement were calculated for primary and secondary Gleason grades, Gleason score, tumor quantitation (percentage and size in millimeters), and perineural invasion. Interobserver agreement for routine microscopy was excellent for primary Gleason grade (κ = 0.72) and good for all other parameters (κ ranging from 0.36 to 0.55). Whole slide digital imaging assessment yielded similar agreement for all parameters. Intraobserver agreement for primary Gleason grade and Gleason score was very good to excellent for all pathologists (all κ ≥ 0.65 and ≥ 0.73, respectively). Size of tumor in millimeters consistently displayed higher levels of agreement than percentage of tumor across media and pathologists. Digital assessment of routinely reported cancer parameters on prostatic needle biopsy for a given scanned core level is comparable to that of routine microscopy. These findings imply that histologic interpretation using dynamic whole slide images may accurately simulate routine microscopic evaluation in the consultation setting. Implementation of whole slide digital imaging in these scenarios may significantly reduce the workload of large referral centers in the near future and impact the manner in which pathologists seek second opinion consultation on challenging cases.     

An array microscope for ultrarapid virtual slide processing and telepathology. Design, fabrication, and validation study

This paper describes the design and fabrication of a novel array microscope for the first ultrarapid virtual slide processor (DMetrix DX-40 digital slide scanner). The array microscope optics consists of a stack of three 80-element 10 x 8-lenslet arrays, constituting a "lenslet array ensemble." The lenslet array ensemble is positioned over a glass slide. Uniquely shaped lenses in each of the lenslet arrays, arranged perpendicular to the glass slide constitute a single "miniaturized microscope." A high-pixel-density image sensor is attached to the top of the lenslet array ensemble. In operation, the lenslet array ensemble is transported by a motorized mechanism relative to the long axis of a glass slide. Each of the 80 miniaturized microscopes has a lateral field of view of 250 microns. The microscopes of each row of the array are offset from the microscopes in other rows. Scanning a glass slide with the array microscope produces seamless two-dimensional image data of the entire slide, that is, a virtual slide. The optical system has a numerical aperture of N.A.= 0.65, scans slides at a rate of 3 mm per second, and accrues up to 3,000 images per second from each of the 80 miniaturized microscopes. In the ultrarapid virtual slide processing cycle, the time for image acquisition takes 58 seconds for a 2.25 cm2 tissue section. An automatic slide loader enables the scanner to process up to 40 slides per hour without operator intervention. Slide scanning and image processing are done concurrently so that post-scan processing is eliminated. A virtual slide can be viewed over the Internet immediately after the scanning is complete. A validation study compared the diagnostic accuracy of pathologist case readers using array microscopy (with images viewed as virtual slides) and conventional light microscopy. Four senior pathologists diagnosed 30 breast surgical pathology cases each using both imaging modes, but on separate occasions. Of 120 case reads by array microscopy, there were 3 incorrect diagnoses, all of which were made on difficult cases with equivocal diagnoses by light microscopy. There was a strong correlation between array microscopy vs. "truth" diagnoses based on surgical pathology reports. The kappa statistic for the array microscopy vs. truth was 0.96, which is highly significant (z=10.33, p <0.001). There was no statistically significant difference between rates of agreement with truth between array microscopy and light microscopy (z=0.134, p >0.05). Array microscopy and light microscopy did not differ significantly with respect to the number/percent of correct decisions rendered (t=0.552, p=0.6376) or equivocal decisions rendered (t=2.449, p=0.0917). Pathologists rated 95.8% of array microscopy virtual slide images as good or excellent. None were rated as poor. The mean viewing time for a DMetrix virtual slide was 1.16 minutes. The DMetrix virtual slide processor has been found to reduce the virtual slide processing cycle more than 10 fold, as compared with other virtual slide systems reported to date. The virtual slide images are of high quality and suitable for diagnostic pathology, second opinions, expert opinions, clinical trials, education, and research.     

Digital pathology: current status and future perspectives

During the last decade pathology has benefited from the rapid progress of image digitizing technology. The improvement in this technology had led to the creation of slide scanners which are able to produce whole slide images (WSI) which can be explored by image viewers in a way comparable to the conventional microscope. The file size of the WSI ranges from a few megabytes to several gigabytes, leading to challenges in the area of image storage and management when they will be used routinely in daily clinical practice. Digital slides are used in pathology for education, diagnostic purposes (clinicopathological meetings, consultations, revisions, slide panels and, increasingly, for upfront clinical diagnostics) and archiving. As an alternative to conventional slides, WSI are generally well accepted, especially in education, where they are available to a large number of students with the full possibilities of annotations without the problem of variation between serial sections. Image processing techniques can also be applied to WSI, providing pathologists with tools assisting in the diagnosis-making process. This paper will highlight the current status of digital pathology applications and its impact on the field of pathology.     

Whole-slide imaging in cytopathology: state of the art and future directions

Whole slide imaging (WSI) has been increasingly adopted for digital evaluation of surgical pathology specimens. Unlike histological slides, cytological preparations frequently display a heterogeneous distribution of cells throughout slides in different focal planes sometimes admixed with obscuring material, therefore requiring multiple scanning planes which significantly lengthens image acquisition and evaluation times. Although examination of digital images can be more advantageous than conventional glass slides, the challenges of focusing, scanning and screening cytological specimens and the associated increase in scan times and data storage needs have limited the routine application of WSI in cytopathology practice. Emerging digital systems designed to overcome image acquisition obstacles coupled with artificial intelligence algorithms augmenting screening of digital cytology slides offer innovative solutions to address these limitations. The aim of this review is to critically address the potential benefits and pitfalls of employing WSI in cytopathology practice and to introduce promising state-of-the-art solutions on the horizon.     

Digital Pathology Consultations—a New Era in Digital Imaging, Challenges and Practical Applications

Digital pathology has grown dramatically in the last 10 years and has created opportunities to not only support the triaging of difficult cases among specialists within an organization, but also enable remote pathology consultations with external organizations across the world. This study investigated one organization's need for a vendor agnostic Digital Pathology Consultation workflow solution that overcomes the challenges associated with the transfer of large studies across a local area network or across the Internet. The organization investigated is a large multifacility healthcare organization that consists of 20 hospitals spread across a wide geographical area. The organization has one of the largest academic pathology departments in the USA, with more than 100 diagnostic anatomic pathologists. This organization developed a set of web-based tools to support the workflow of digital pathology consultations and allow the viewing of whole slide images. The challenges and practical implementations of two different use cases are addressed: the occasional end user (professional or patient) requesting a second opinion and the external laboratory or hospital looking for an established consultative relationship with a large volume of cases. The solution presented in this study addresses the challenges associated with the distribution of large images and the lack of established imaging standards, while providing for a convenient and secure portal for pathologist report entry and distribution.     

Use of whole slide imaging in surgical pathology quality assurance: design and pilot validation studies

By imaging large numbers of slides automatically at high resolution, modem automated whole slide imaging (WSI) systems have the potential to become useful tools in pathology practice. This article describes a pilot validation study for use of automated high-speed WSI systems for surgical pathology quality assurance (QA). This was a retrospective comparative study in which 24 full genitourinary cases (including 47 surgical parts and 391 slides) were independently reviewed with traditional microscopy and whole slide digital images. Approximately half the cases had neoplasia in the diagnostic line. At the end of the study, diagnostic discrepancies were evaluated by a pathology consensus committee. The study pathologists felt that the traditional and WSI methods were comparable for case review. They reported no difference in perceived case complexity or diagnostic confidence between the methods. There were 4 clinically insignificant discrepancies with the signed-out cases: 2 from glass slide and 2 with WSI review. Of the 2 discrepancies reported by the WSI method, the committee agreed with the reviewer once and the original report once. At the end of the study, the participants agreed that automated WSI is a viable potential modality for surgical pathology QA, especially in multifacility health systems that would like to establish interfacility QA. The participants felt that major issues limiting the implementation of WSI-based QA did not involve image acquisition or quality but rather image management issues such as the pathologist's interface, the hospital's network, and integration with the laboratory information system.     

Anatomical pathology is dead? Long live anatomical pathology

The standard diagnostic instrument used for over 150 years by anatomical pathologists has been the optical microscope and glass slide. The advent of immunohistochemistry in the routine laboratory in the 1980s, followed by in situ hybridisation in the 1990s, has increased the armamentaria available to the diagnostic pathologist, and this technology has led to changed patient management in a limited number of neoplastic diseases. The first decade of the 21 century has seen an increasing number of publications using proteomic technologies that promise to change disease diagnosis and management, the traditional role of an anatomical pathologist. Despite the plethora of publications on proteomics and pathology, to date there are actually limited data where proteomic technologies do appear to be of greater diagnostic value than the standard histological slide. Though proteomic techniques will become more prevalent in the future, it will need the expertise of an anatomical pathologist to dissect out and validate this added information.     

Reconciliation of diverse telepathology system designs. Historic issues and implications for emerging markets and new applications

Telepathology, the distant service component of digital pathology, is a growth industry. The word "telepathology" was introduced into the English Language in 1986. Initially, two different, competing imaging modalities were used for telepathology. These were dynamic (real time) robotic telepathology and static image (store-and-forward) telepathology. In 1989, a hybrid dynamic robotic/static image telepathology system was developed in Norway. This hybrid imaging system bundled these two primary pathology imaging modalities into a single multi-modality pathology imaging system. Similar hybrid systems were subsequently developed and marketed in other countries as well. It is noteworthy that hybrid dynamic robotic/static image telepathology systems provided the infrastructure for the first truly sustainable telepathology services. Since then, impressive progress has been made in developing another telepathology technology, so-called "virtual microscopy" telepathology (also called "whole slide image" telepathology or "WSI" telepathology). Over the past decade, WSI has appeared to be emerging as the preferred digital telepathology digital imaging modality. However, recently, there has been a re-emergence of interest in dynamic-robotic telepathology driven, in part, by concerns over the lack of a means for up-and-down focusing (i.e., Z-axis focusing) using early WSI processors. In 2010, the initial two U.S. patents for robotic telepathology (issued in 1993 and 1994) expired enabling many digital pathology equipment companies to incorporate dynamic-robotic telepathology modules into their WSI products for the first time. The dynamic-robotic telepathology module provided a solution to the up-and-down focusing issue. WSI and dynamic robotic telepathology are now, rapidly, being bundled into a new class of telepathology/digital pathology imaging system, the "WSI-enhanced dynamic robotic telepathology system". To date, six major WSI processor equipment companies have embraced the approach and developed WSI-enhanced dynamic-robotic digital telepathology systems, marketed under a variety of labels. Successful commercialization of such systems could help overcome the current resistance of some pathologists to incorporate digital pathology, and telepathology, into their routine and esoteric laboratory services. Also, WSI-enhanced dynamic robotic telepathology could be useful for providing general pathology and subspecialty pathology services to many of the world's underserved populations in the decades ahead. This could become an important enabler for the delivery of patient-centered healthcare in the future.     

Critical comparison of 31 commercially available digital slide systems in pathology

Advances in new technologies for complete slide digitization in pathology have allowed the appearance of a wide spectrum of technologic solutions for whole-slide scanning, which have been classified into motorized microscopes and scanners. This article describes technical aspects of 31 different digital microscopy systems. The most relevant characteristics of the scanning devices are described, including the cameras used, the speed of digitization, and the image quality. Other aspects, such as the file format, the compression techniques, and the solutions for visualization of digital slides, (including diagnosis-aided tools) are also considered. Most of the systems evaluated allow a high-resolution digitization of the whole slide within about 1 hour using a x40 objective. The image quality of the current virtual microscopy systems is suitable for clinical, educational, and research purposes. The efficient use of digital microscopy by means of image analysis systems can offer important benefits to pathology departments.     

A multisite performance study comparing the reading of immunohistochemical slides on a computer monitor with conventional manual microscopy for estrogen and progesterone receptor analysis

A multisite study was conducted to assess the performance of the Aperio digital pathology system (Aperio Technologies, Vista, CA) for reading estrogen receptor (ER) and progesterone receptor (PR) slides on a computer monitor. A total of 520 formalin-fixed breast tissue specimens were assayed at 3 clinical sites for ER and PR (260 each). Percentage and average staining intensity of positive nuclei were assessed. At each site, 3 pathologists performed a blinded reading of the glass slides using their microscopes initially and later using digital images on a computer monitor. Comparable percentages of agreements were obtained for manual microscopy (MM) and manual digital slide reading (MDR) (ER, percentage of positive nuclei with cutoffs: MM, 91.3%-99.0%/MDR, 91.3%-100.0%; PR, percentage of positive nuclei with cutoffs: MM, 83.8%-99.0%/MDR, 76.3%-100.0%). Reading ER and PR slides on a computer monitor using the Aperio digital pathology system is equivalent to reading the slides with a conventional light microscope.     

Loss of fidelity in scanned digital images compared to glass slides of brain tumors resected using cavitron ultrasonic surgical aspirator

Conversion of glass slides to digital images is necessary to capitalize on advances in computational pathology and could potentially transform our approach to primary diagnosis, research, and medical education. Most slide scanners have a limited maximum scannable area and utilize proprietary tissue detection algorithms to selectively scan regions that contain tissue, allowing for increased scanning speed and reduced file size compared to scanning the entire slide at high resolution. However, very small and faintly stained tissue fragments may not be recognized by these algorithms, leading to loss of fidelity in the digital image compared to the glass slides. Cavitron ultrasonic surgical aspirator (CUSA) is frequently used in brain tumor resections, resulting in highly fragmented specimens that are used for primary diagnosis. Here we evaluated the rate of loss of fidelity in 296 digital images from 40 CUSA‐resected brain tumors scanned using a Philips Ultra Fast Scanner. Overall, 54% of the slides (at least one from every case) showed loss of fidelity, with at least one tissue fragment not scanned at high resolution. The majority of the missed tissue fragments were small (<0.5 mm), but rare slides were missing fragments greater than 5 mm in greatest dimension. In addition, 19% of the slides with missing tissue showed no indication of loss of fidelity in the digital image itself; the missing tissue could only be appreciated upon review of the glass slides. These results highlight a potential liability in the use of digital images for primary diagnosis in CUSA‐resected brain tumor specimens.     

The future of telepathology for the developing world

Physician shortages are acute in developing countries, where disease burden is the greatest and resources for health care are very limited. A lack of pathologists in these countries has lead to delays in diagnosis and misdiagnoses that adversely affect patient care and survival. The introduction of telepathology into countries with limited resources for health care is but one of multiple approaches that can be used to alleviate the problem. Telepathology is the electronic transmission of digital images that can be used for education and diagnostic consultation. A basic system consists of a microscope with a mounted digital camera linked to a computer. The ability to produce histologic slides, to repair and maintain equipment, and to provide training are also needed for the successful use of this technology. iPath is a Web-based, open platform, software application which was developed at the University of Basel, Switzerland, for telepathology and which brings together pathologists from around the world to provide telepathology support for diagnostic consultation and provides education to centers with limited resources. The use of virtual-slide technology to provide a digital image of an entire glass slide is another technology for diagnostic consultation and pathology education. This technology requires more costly resources to support it, which may limit its utility in many areas. Telepathology can generate collections of digital images and virtual slides needed for training indigenous pathologists in their countries to become self-sufficient. Thus, the long-term goal of this technology is to improve patient care and survival.