Johns Hopkins team develops ultra-miniaturised endoscope

Lens-free endoscope, based on optical fibre, produces high-quality images of firing neurons without damaging brain tissues

Placing and operating cameras inside living organisms is a major goal of engineers working with surgeons. However, there is an obvious problem: such devices tend to be bulky and therefore pose a risk of damaging the tissues they are imaging and passing through to reach their targets. Miniaturising endoscopes inevitably compromises the image quality they produce.

endoscope
(A) Simplified illustration of widefield illumination imaging using a multicore fibre and lens. (B) Our distal lensless imaging approach using a coded aperture. Diagram courtesy of the researchers

But the Johns Hopkins team, led by electrical and computer engineer Mark Foster, claims they have avoided this problem by constructing a lens-free endoscope the width of a few human hairs, capable of examining neurons firing in the brains of animals as small as mice and rats, without causing damage.

endoscope
A to C shows beads on a slide imaged by a bulk microscope. D to F are the beads when viewed from a conventional lens-based microendoscope. G to I are the raw images from the research team’s new ultra-miniaturized lens-free microendoscope. J to L are images G to I after computational reconstruction. Credit: Mark Foster

The minimum size for an endoscope with a lens is around half a millimetre. Lens-free devices, based on optical fibres, scan an area pixel by pixel, but previous versions have tended to bend in use and lose their image quality. Foster’s team tipped their device with a coded aperture, a flat grid that randomly blocks light by creating a projection in a known pattern. This is akin to randomly poking a piece of aluminium foil and letting light through all of the small holes. Although this technique creates a messy image, that image provides rich information about where the light originates, and that information can be computationally reconstructed into a clearer image.

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In their experiments, described in Science Advances,  Foster’s team looked at beads in different patterns on a slide and obtained sharp images. Moreover, the device does not need movement to focus on objects at different depths; instead, computational refocusing can determine where light originates in three dimensions. Therefore, unlike conventional endoscopes, the device does not need to be moved around to focus.