The accuracy of dynamic predictive autofocusing for whole slide imaging

Abstract

Context:Whole slide imaging (WSI) for digital pathology involves the rapid automated acquisition of multiple high-power fields from a microscope slide containing a tissue specimen. Capturing each field in the correct focal plane is essential to create high-quality digital images. Others have described a novel focusing method which reduces the number of focal planes required to generate accurate focus. However, this method was not applied dynamically in an automated WSI system under continuous motion.Aims:This report measures the accuracy of this method when applied in a rapid continuous scan mode using a dual sensor WSI system with interleaved acquisition of images.Methods:We acquired over 400 tiles in a “stop and go” scan mode, surveying the entire z depth in each tile and used this as ground truth. We compared this ground truth focal height to the focal height determined using a rapid 3-point focus algorithm applied dynamically in a continuous scanning mode.Results:Our data showed the average focal height error of 0.30 (±0.27) μm compared to ground truth, which is well within the system's depth of field. On a tile by tile assessment, approximately 95% of the tiles were within the system's depth of field. Further, this method was six times faster than acquiring tiles compared to the same method in a non-continuous scan mode.Conclusions:The data indicates that the method employed can yield a significant improvement in scan speed while maintaining highly accurate autofocusing.

A Comprehensive Study of Telecytology Using Robotic Digital Microscope and Single Z-Stack Digital Scan for Fine-Needle Aspiration-Rapid On-Site Evaluation

“…[7] Moreover, the advances in slide scanning technology have improved known issues such as uniformity of plane of focus, data storage requirement, and image quality. [8] The sufficiency of improvement is supported by the fact that a small number of institutions have started to pioneer on-site slide scanning for the frozen section as an alternative for the remotely controlled robotic microscope. [4]…”

Autofocus methods of whole slide imaging systems and the introduction of a second-generation independent dual sensor scanning method

“…A recent study demonstrates that this method is feasible and can generate high quality images. [ 6 ] The study compared the gold standard “stop motion” imaging (which stops at each tile and performs a 50 z-plane focus calculation), to continuous IDS scanning. The two methods showed little variance in the z-position at each tile, indicting IDS imaging is highly accurate compared to the ground truth.…”

An automated slide scanning system for membrane filter imaging in diagnosis of urogenital schistosomiasis

“…However, it is less effective when the sample's location varies due to tissue topography variations. [15][16][17][18] Realtime image-based autofocusing offers several approaches, including dual sensor scanning, 19 beam splitter arrays, 20 tilted sensors, 21 phase detection, [22][23][24] deep learning [25][26][27][28][29][30] and dual-LED illumination. [31][32][33][34][35] These methods do not require a pregenerated focus map and can handle samples with varying topography.…”

“…One major challenge of this method is its time‐consuming nature. Additionally, skipping tiles can reduce the focus map surveying time but comes at the expense of accuracy in the resulting focus map 19 . Various FoM measures have been used in the literature, initially introduced by Brenner and his colleagues 36 …”