Visualization of blood cell contrast in nailfold capillaries with high-speed reverse lens mobile phone microscopy.

Gregory N Mckay,Carlos Castro-González,Aurélien Bourquard,Nicholas J Durr,Álvaro Sánchez-Ferro,Nela Mohan,Ian Butterworth

doi:10.1364/boe.382376

Abstract

Quantification of optical absorption gaps in nailfold capillaries has recently shown promise as a non-invasive technique for neutropenia screening. Here we demonstrate a low-cost, portable attachment to a mobile phone that can resolve optical absorption gaps in nailfold capillaries using a reverse lens technique and oblique 520nm illumination. Resolution <4μm within a 1mm2 on-axis region is demonstrated, and wide field of view (3.5mm × 4.8mm) imaging is achieved with resolution <6μm in the periphery. Optical absorption gaps (OAGs) are visible in superficial capillary loops of a healthy human participant by an ∼8-fold difference in contrast-to-noise ratio with respect to red blood cell absorption contrast. High speed video capillaroscopy up to 240 frames per second (fps) is possible, though 60fps is sufficient to resolve an average frequency of 37 OAGs/minute passing through nailfold capillaries. The simplicity and portability of this technique may enable the development of an effective non-invasive tool for white blood cell screening in point-of-care and global health settings.

Highlights

Capillaroscopy, the microscopic evaluation of capillary organization and microvascular blood flow, is a century old technique that has shown value in a variety of clinical fields
Our experiments demonstrate that mobile phone capillaroscopy is a promising technique for point-of-care white blood cell (WBC) count screening due to its ability to resolve optical absorption gaps (OAGs)
Resolution and quantification of optical absorption gaps (OAGs) in nailfold capillaries in vivo has been shown to be an effective tool for neutropenia screening

Summary

Introduction

Capillaroscopy, the microscopic evaluation of capillary organization and microvascular blood flow, is a century old technique that has shown value in a variety of clinical fields. High speed video capillaroscopy can resolve, track, and quantify optical absorption gaps (OAGs) between red blood cells [6,7] flowing in capillaries, which are typically 150-400μm deep in the nailfold [8]. Evidence that these absorption gaps are caused by white blood cells has been demonstrated in a variety of settings including animal cremaster vasculature and in the retina, as it relates to the blue entopic phenomenon [9,10,11,12]. The WBC count generally provides a gauge of immune status, and is commonly used in diagnosing infection, cancer, immune suppression, and auto-immune disease [15,16,17,18]

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Conclusion