InstantScope: a low-cost whole slide imaging system with instant focal plane detection

Abstract

We report the development of a high-throughput whole slide imaging (WSI) system by adapting a cost-effective optomechanical add-on kit to existing microscopes. Inspired by the phase detection concept in professional photography, we attached two pinhole-modulated cameras at the eyepiece ports for instant focal plane detection. By adjusting the positions of the pinholes, we can effectively change the view angle for the sample, and as such, we can use the translation shift of the two pinhole-modulated images to identify the optimal focal position. By using a small pinhole size, the focal-plane-detection range is on the order of millimeter, orders of magnitude longer than the objective's depth of field. We also show that, by analyzing the phase correlation of the pinhole-modulated images, we can determine whether the sample contains one thin section, folded sections, or multiple layers separated by certain distances - an important piece of information prior to a detailed z scan. In order to achieve system automation, we deployed a low-cost programmable robotic arm to perform sample loading and $14 stepper motors to drive the microscope stage to perform x-y scanning. Using a 20X objective lens, we can acquire a 2 gigapixel image with 14 mm by 8 mm field of view in 90 seconds. The reported platform may find applications in biomedical research, telemedicine, and digital pathology. It may also provide new insights for the development of high-content screening instruments.

Angular light modulator using optical blinds

“…A key aspect of whole slide imaging is to determine the defocus distance of the sample in high speed. We have demonstrated the use of pinhole-modulated cameras for high-speed autofocusing [10,11]. In these previous demonstrations, the pinhole was placed at an off-axis position of the Fourier plane to achieve angular selectivity and we need to use a lens system to relay the pinhole to the Fourier plane of the objective lens.…”

“…In Fig. 4(b), we plotted the defocus distance as a function of the translational shifts of the captured images (the translational shift was identified by maximizing the phase correlation curve [10]). From this experiment, we can see that the reported ALM can be used for high-speed autofocusing.…”

“…These images can then be back-projected for 3D tomographic refocusing [8,9]. By using a fixed slat angle in the device, we can convert the incident-angle information into intensity variations for wavefront sensing; we can also introduce a translational shift to the defocused object for high-speed autofocusing [10].…”

A High Precision Laser-Based Autofocus Method Using Biased Image Plane for Microscopy

“…There have been countless camera-based products with autofocusing function, but most of these instruments adopt the image sharpness-based method to estimate the focal position. These methods are rather timeconsuming since the prefocus process is a searching process over the whole focusing range with steps of different intervals [1,2]. The focusing accuracy is often limited by the image content in the microscopic view [3].…”

Autofocus method for automated microscopy using embedded GPUs

“…Secondly, to propose an efficient low-cost implementation based on the limited resources of an embedded GPU System on Chip architecture, able to fulfill the time constraints of an automated optical microscope. In contrast to other faster autofocusing approaches [11,12] our method is specifically designed to deal with TB samples, which makes the processing more computationally demanding. It implies the usage of custom filters for removing impurities from the samples.…”