Elsevier

Human Pathology

Volume 37, Issue 12, December 2006, Pages 1543-1556
Human Pathology

Original contribution
Eye-movement study and human performance using telepathology virtual slides. Implications for medical education and differences with experience

https://doi.org/10.1016/j.humpath.2006.08.024Get rights and content

Summary

A core skill in diagnostic pathology is light microscopy. Remarkably little is known about human factors that affect the proficiency of pathologists as light microscopists. The cognitive skills of pathologists have received relatively little attention in comparison with the large literature on human performance studies in radiology. One reason for this lack of formal visual search studies in pathology has been the physical restrictions imposed by the close positioning of a microscope operator's head to the microscope's eyepieces. This blocks access to the operator's eyes and precludes assessment of the microscopist's eye movements. Virtual slide microscopy now removes this barrier and opens the door for studies on human factors and visual search strategies in light microscopy. The aim of this study was to assess eye movements of medical students, pathology residents, and practicing pathologists examining virtual slides on a digital display monitor. Whole histopathology glass slide digital images, so-called virtual slides, of 20 consecutive breast core biopsy cases were used in a retrospective study. These high-quality virtual slides were produced with an array-microscope equipped DMetrix DX-40 ultrarapid virtual slide processor (DMetrix, Tucson, Ariz). Using an eye-tracking device, we demonstrated for the first time that when a virtual slide reader initially looks at a virtual slide his or her eyes are very quickly attracted to regions of interest (ROIs) within the slide and that these ROIs are likely to contain diagnostic information. In a matter of seconds, critical decisions are made on the selection of ROIs for further examination at higher magnification. We recorded: (1) the time virtual slide readers spent fixating on self-selected locations on the video monitor; (2) the characteristics of the ways the eyes jumped between fixation locations; and (3) x and y coordinates for each virtual slide marking the sites the virtual slide readers manually selected for zooming to higher ROI magnifications. We correlated the locations of the visually selected fixation locations and the manually selected ROIs. Viewing profiles were identified for each group. Fully trained pathologists spent significantly less time (mean, 4.471 seconds) scanning virtual slides when compared to pathology residents (mean, 7.148 seconds) or medical students (mean, 11.861 seconds), but had relatively prolonged saccadic eye movements (P < .0001). Saccadic eye movements are defined as eye movements between fixation locations. On the other hand, the pathologists spent significantly more time than trainees dwelling on the 3 locations they subsequently chose for zooming. Unlike either the medical students or the residents, the pathologists frequently choose areas for viewing at higher magnification outside of areas of foveal (central) vision. Eye movement studies of scanning pathways (scan paths) may be useful for developing eye movement profiles for individuals and for understanding the difference in performances between novices and experts. They may also be useful for developing new visual search strategies for rendering diagnoses on telepathology virtual slides.

Introduction

Light microscopy is a core technology of diagnostic pathology. In the teaching of light microscopy skills to medical students and pathology residents, much of the training is done in an apprenticeship mode. Typically, the student and the teacher share a multiheaded light microscope to view histopathology slides together, discuss a case, and generate a diagnosis. Although some features of the morphology may be highlighted by the system operator using an embedded arrow-pointer system, the approach relies on the assumption that both participants are actually seeing the same things and have comparable cognitive processes. These premises have never been actually validated.

In the field of pathology, proficiency testing is gaining in importance. There is considerable interest in developing new quantitative and qualitative measures of pathologist performance in their clinical activities. Also, with increasing subspecialization in surgical pathology, it is of interest to find better threshold measures of competency, both in terms of diagnostic accuracy and efficiency. New technologies, such as virtual microscopy, have the potential to improve training. The recent development of virtual slides and their growing acceptance as a substitute for conventional light microscopy in educational programs and testing encourages the development of innovative training and assessment tools [1], [2], [3], [4], [5], [6]. Virtual slides have the potential to become the technology of choice for telepathology clinical activities as well [7], [8], [9], [10].

From the perspective of being able to study the skills of light microscopists, virtual slides represent a major technological breakthrough. Because the pathologist views virtual slides at a distance on a video monitor, the pathologist and the microscope are physically disengaged. This physical space between the virtual slide reader and the video monitor becomes available for the insertion of the analytical equipment used by cognitive psychologists and physiologists to study human activities during virtual slide viewing, much in the way that these studies have been carried out in radiology in the past [11], [12], [13], [14], [15], [16], [17], [18], [19], [20], [21].

Our objective in this study was to take advantage of virtual slide technology to compare the eye movements of virtual slide readers with different levels of experience. Using sophisticated, highly accurate, eye tracking instrumentation typically used in radiology studies, we analyzed the eye movements of medical students, residents, and practicing pathologists. Our results show that eye movement studies of scanning pathways (scan paths) may be useful for developing eye movement profiles for individuals and, potentially, for understanding the differences in performances of individuals with various amounts of experience. If we could identify distinctive viewing stereotypes for each level of experience, it suggests the possibility that eye movement monitoring could serve as a basis for the creation of innovative pathology training routines and improve the effectiveness of pathology digital imaging as well. Such information would also be useful in the design of telepathology workstations in the future and the training of telepathologists. This report is the first in a series of papers on the applications of telepathology virtual slides and the implementation of telepathology virtual slide diagnostic networks.

Section snippets

DMetrix virtual slide images

Twenty breast core biopsy surgical pathology cases were digitized using the previously described DMetrix DX-40 virtual slide processor (DMetrix, Inc, Tucson, Ariz) [10]. In brief, the DMetrix ultrarapid virtual slide scanner uses a novel array microscope as an imaging engine and can produce 1.5 × 1.5-cm virtual slides (the industry de facto standard for assessing virtual slide processing rates) in less than 1 minute [10]. The DMetrix DX-40 processor scans images at 0.47 μm per pixel resolution

Breast core biopsies

Fig. 4 shows the thumbnail images of the virtual slides of the 20 breast core biopsy cases used in this study. Each case included several core breast biopsies seen as multiple pieces of tissue on each glass slide.

Preferred zoom locations

Each slide reader selected, by pointing at specific locations on the monitor, 3 preferred zoom locations per image. Fig. 5 shows one of the low-magnification virtual slide images with the 3 preferred zoom locations from each of the 9 slide readers. Using the 5° useful visual field, we

Discussion

Until now, little has been known about perceptual and cognitive factors that influence performance of light microscopy. Do top experts have different cognitive processes? Do they use more effective search strategies for examining histopathology slides? Are their eye movements better developed? Can the special skills of experts be taught to novices? Can the transition from a novice to an expert level of competence be accelerated? Although we may think of expert pathologists as unusually gifted

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    Disclosures: Dr Ronald S. Weinstein and Dr Michael R. Descour are cofounders of DMetrix, Inc, and have equity in the company. Lynne Richter serves as a consultant to DMetrix and has stock options.

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