A digital pathology scanner is a machine that photographs a glass slide of tissue at high magnification and turns it into one very large digital image. A pathologist, the doctor who examines tissue for diseases such as cancer, can then read it on a screen anywhere, and an AI model can analyse it. The image is called a whole slide image.
Here is what is on the slide. When a surgeon removes a lump, the lab cuts a slice of it about 4 thousandths of a millimetre thick. The slice is placed on a glass slide and stained with dyes, so that the cells show up in pink and purple. Traditionally, a pathologist looks at the slide through a microscope, in the same building as the lab.
The scanner photographs the slide in thousands of small tiles, at about 40 times magnification. It focuses each tile and joins the tiles into one image. A single slide can become an image of 1,00,000 × 80,000 pixels, several gigabytes in size. Large labs load hundreds of slides into one scanner and leave it running overnight. There are so many images, and they are so large, that they are usually kept in low-cost cloud storage, called object storage.
Imagine a cancer hospital in Silchar, in southern Assam, that receives many biopsies and has only one pathologist. A biopsy is a small piece of tissue taken to check for disease. Each evening, the hospital's lab scans the day's 120 slides. The lab's laboratory information system (LIS) links each image to the right patient and test. The next morning, a specialist breast pathologist at a large hospital in another city opens the difficult cases on her screen. She zooms from the whole slice to single cells in seconds. An AI model has already marked the areas that look most like cancer, and has counted the dividing cells in one tumour. She checks the marks, writes her report and sends it back the same morning. Without the scanner, the glass slides would have gone by courier, which takes several days.
Digital pathology is the slide-reading version of digital radiology. The slide images can be stored and shown in the same PACS and imaging AI platform as the hospital's scans. The AI that marks likely cancer is a kind of computer vision. The tissue samples are processed in the same labs as other tests in laboratory diagnostics.
A digital pathology scanner is different from a camera fitted to a microscope. A microscope camera photographs one small area at a time, the area the doctor is looking at. The scanner captures the whole slide, so the pathologist can look anywhere on it later, and a second pathologist can look at exactly the same image.