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New light-sheet technique probes deeper into turbid samples

16 Apr | By Kishan Dholakia
New light-sheet technique probes deeper into turbid samples
An attenuation-compensated Airy light-sheet microscope

A new method of using light to scan the human body, developed by researchers at the University of St Andrews, could result in less intrusive and more effective diagnosis for patients.

 

The new technique allows the light to be shaped so it can reach greater depths within biological tissue: enabling high quality three-dimensional (3D) images to be acquired. It can also allow detailed 3D images of biological specimens to be made without dissection or having to rotate specimens and take multiple images which are then fused together.

 

A neuron in a section of mouse brain tissue imaged with the new technique. Scale bar: 20 microns.

 

 

Study lead-author Jonathan Nylk, of the Optical Manipulation Group at the School of Physics and Astronomy. said: “We’ve recently discovered particular beam shapes that retain their shape when travelling through (turbid) biological tissue. These beams, called Airy beams and Bessel beams, resist the effects of scattering but they still become dimmer as they travel deeper, so it remains challenging to collect enough signal back through the tissue to form an image.”

 

“Now we show that these beams can be further enhanced to give us more control over their shape, such that they actually get brighter as they propagate. When this increase in intensity is matched with the decrease in intensity caused by travelling through tissue, a strong signal and a clear image can still be acquired from deep within the sample.”

 

This latest research builds on previous advances in “light-sheet imaging”, in which a thin sheet of light cuts across the sample like a razor blade to section the sample – but without actually cutting or damaging it. The use of curved Airy light-sheets was shown to give sharp images over a volume ten times larger than previously possible.

 

This most recent development allows the technique to be used deeper within biological specimens. The picture above shows the shapes of the light beams that "slice" through the tissue in the earlier experiments (top row), and the improved versions of these light beams that stay brighter for longer longer (bottom row), as can be seen by the more intense beam further to the right (deeper in to the tissue) than the original beams.

 

 

The picture above shows the Airy light-sheet that is used in the imaging (green) and the fluorescence it excites from the sample (red). The attenuation-compensated beam remains brighter further to the right (deeper in to the tissue). The greyscale image under these beam profiles are images taken by scanning the beams over cells from a keelworm. The lower image shows  the improved contrast at deeper penetration achieved with the new beam. The image of a keelworm (Spirobranchus lamarcki) shows the individual cell nuclei through the operculum, an appendage which is sacrificed to predators for escape and can be regrown. It's particularly useful for regeneration studies.


The new techniques are expected be useful, not only for light-sheet microscopy, but also for pushing the limits of a whole range of other optical imaging techniques. It is hoped that the development will lead to improved understanding of biological development, cancer, and diseases such as Alzheimer, Parkinson, and Huntington that affect the human brain.

 

The paper "Light-sheet microscopy with attenuation-compensated propagation-invariant beams" represents an exciting collaboration between researchers from the Schools of Physics & Astronomy, Biology, Medicine and The Scottish Oceans Institute, and was published in the 6th April issue of Science Advances.

 

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