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Novel Servomotor Lets Microscope Scan Fast

Jul 1, 2005 12:00 PM

Pathologists need no longer peer through microscopes scrutinizing tissue samples, thanks to a digital slide-imaging system from Aperio Technologies Inc., San Diego. The ScanScope system uses three direct-drive, PZT-based servomotors to position slides under microscope optics. A CCD imaging chip recording 15×15-mm slides one line at a time digitizes them 20 times faster than with comparable devices. The system inserts the slide under the microscope at a constant velocity to ensure images align without image artifacts.

But slide surfaces can be rough on a microscopic scale. So optics must follow tissue contours to keep focus as the sample moves under the lens.

Aperio worked with automation distributor Minarik Automation and Control, San Diego, to devise a motion system that would do so. PZT motors from Nanomotion Inc., Ronkonkoma, N.Y., operate as servomotors to focus the lens and position the slide. Two PZT motors powering the X and Y axes position slides under the lens. The Z-axis motor focuses the image with micrometer-scale resolution. The focus motor also holds and brakes the lens mechanism, a feat not possible with other servosystem designs.

Aperio says its line-scanning technique works better than methods used in other slide-scanning systems. The usual approach displays one small rectangle of slide at a time in a step-and-repeat process. This makes it tough to follow tissue contours accurately because focus is limited to one focal position per image tile. In contrast, PZT motors focus the microscope orders of magnitude faster than that possible with ordinary scanners.