ReviewVirtual slides: an introduction
Introduction
Virtual slides have been around in a usable form since the early 1990s and, as a technology, are increasing in maturity. They have many innovative uses in education and training, and are becoming an essential tool in research practice. However, their use in routine diagnosis has yet to come. This review aims to give a basic introduction to virtual slides, assuming no prior knowledge of the subject, and to discuss the issues around virtual slides in diagnosis.
Section snippets
What is a virtual slide
A virtual slide is a digital image produced by scanning a glass pathology slide at high resolution. Typically, virtual slide scanners use standard microscope lenses and light sources to obtain a microscopic image of the tissue. A robotic system sequentially moves the lens or slide so that the entire slide is scanned. The resulting image is captured electronically with an image capture device similar to those seen in digital cameras (a so-called CCD or CMOS chip) to record all of the image data
Producing a virtual slide
Virtual slides differ from the image seen down the microscope in several ways due to the methods applied to acquire and store them. A summary of the important steps in producing virtual slides follows.
Viewing virtual slides
Virtual slides are viewed using specialized software (Figure 1); most virtual slide vendors have custom built software for their own slides. All of the viewing systems have similar basic features reminiscent of software to navigate maps – the image is displayed in a window; a small thumbnail of the whole slide displays the current ‘location’ on the slide; the pathologist can zoom in and out by using buttons on the screen or keyboard, and can pan by using similar controls or by ‘dragging and
Advantages and disadvantages of virtual slides
The advantages and disadvantages of virtual slides are listed in Table 1.
Undergraduate teaching
With an increasing trend in medical schools away from microscope based tutorials, there is a risk that teaching of basic pathology will suffer. Several medical schools have developed e- learning based approaches to teaching microscopy – for example, see the excellent WebPath site.1 While this is undoubtedly of benefit, viewing static images does not offer the same interactivity as using a microscope. However, medical students tend to dislike using microscopes as they take practice to use them.
Virtual slides in diagnosis
Virtual slides are already a success in education and training. However, in the area of diagnosis they are not in routine use. Although there are some laboratories that do use virtual slides for routine diagnostic work (mostly in the US, some in Scandinavia), the technology does not have formal US FDA or UK HTA approval for diagnostic use – so pathologists using it would essentially be using an unproven technology and doing so at their own risk.
Before discussing the reasons why virtual slides
Conclusions
With the costs of scanners and computer storage dropping, and the enormous potential benefits of virtual slides, adoption of the technology will surely become more widespread. Impediments such as cost and the significant investment required in IT infrastructure (for storage, backup, and image transfer) will be balanced against the system performance improvements possible using virtual slides. However, there is still much work to be done before virtual slides become a safe and efficient
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