Whole Slide Scanning & High Content Analysis

In Whole Slide Scanning and High Content Analysis (HCA) applications fast image acquisition is essential due to the large number of fields to be acquired and analyzed.

When a large area or multiple wells are to be sampled, a motorized stage is incorporated to automate field selection. The use of scientific-grade CCD camera with high sensitivity (and low noise) can help reduce the required duration of exposure per field, which helps improve the throughput of the system. Although a CCD camera with a small area may provide a faster frame rate, the time required to scan a whole slide depends on several parameters.

A typical cycle usually includes the following steps: (1) stage translation (2) stage settling (3) illumination & exposure (4) readout.

The above steps are repeated until all the fields have been traversed, and the entire slide has been successfully scanned. In an system that is optimized for minimum latency and highest throughput, readout can take place while the stage is moving to the next position. A high throughput system can benefit greatly from a camera which has precise asynchronous reset and exposure controls as well as a robust, high bandwidth interface such as Gigabit Ethernet or CameraLink.

Assuming a camera exposure of 100ms, and a stage operating at a 10mm/sec (or 10µm/ms) translation rate and a 20ms settling time, the following table shows a first-order calculation of the total amount of time required to scan a slide area of 15mm x 15mm with cameras of different resolutions at a 10X magnification:

Note: The number of fields/slide is calculated by dividing the slide area (15mm x 15mm) by the Field of View area in each case. For example, in the case of the DVC-340 in the above table, the number of fields/slide = (15mm x 15mm)/(474µm x 355µm) = 1338.

The table below shows the same calculation for a higher magnification (20X), with all other conditions unchanged. With camera exposure = 100ms, stage translation rate = 10mm/sec (or 10µm/ms), stage settling time = 20ms settling time, slide area of 15mm x 15mm under a 20X magnification:

The rationale for using higher resolution scientific-grade cameras for Whole Slide Scanning is amply demonstrated by the above calculations. As Whole Slide Scanning applications seek to increase the magnification, higher resolution cameras have a increasingly significant effect on the throughput.