Seeing clearly: Imaging in the face distortion

Microscopy in small organisms and tissues is a challenge for modern optics. Adaptive optics corrects distortions in the light entering or exiting tissues generating optimal conditions for imaging or photo-stimulation. Using segmentation of the microscope objective’s rear aperture we have established a method of adaptive correction that is compatible with wide-field illumination geometries.

HFSP Program Grant holder Jennifer Curtis and colleagues
authored on Mon, 13 August 2012

The potential applications for microscopy in biological science have expanded greatly in the last decade as progress has been made both in molecular labeling techniques and optics technology.  One of the major fronts in this expansion is the interrogation and stimulation of processes in living organisms using light.  As result of heterogeneities in shape and tissue composition significant distortion of the light passing through organisms is common.  This results in difficulty focusing on fine details of the subject even when they are within the resolving power of the microscope.  To meet these challenges there is an increasing focus on adaptive optical systems that can measure and correct the optical distortions, known as aberrations, encountered when working with complex organisms.

Figure: Images of the actin cytoskeleton in bovine pulmonary artery endothelial cells captured without aberration correction (left) and with aberration correction (right). Scale bar 5 micrometers.

Adaptive optics uses devices, called spatial light modulators (SLM), which provide real-time control over properties of propagating light.  In particular, these devices are used to correct the types of aberrations found in microscopy.  However, for aberration correction to be useful the aberrations must first be measured and quantified.

We have shown that both measurement and correction of aberrations can be achieved in a wide-field fluorescence microscope through the introduction of a spatial light modulator into the microscope’s emission path.  The spatial light modulator performs two tasks here.  First, it allows for selective image formation using only small parts of the optical wavefront.  Aberrations cause these images to move across the surface of the camera with the displacement providing a measurement of the angle at which light is traveling.  Once measured, any deviation from propagation parallel to the optic axis can be corrected immediately using the spatial light modulator.  The correction is optimized using interferometry to ensure that each part of the wavefront converges in phase to achieve constructive interference.  Significant improvement in optical resolution and image quality are observed when this technique is applied to the correction of aberrations in a wide-field fluorescence microscope.  The ability to image more clearly not only has benefits for feature identification, but also for the precise targeting of features for photo-stimulation in opto-genetics research.

Text by Jan Scrimgeour

Reference

Aberration correction in wide-field fluorescence microscopy by segmented-pupil image interferometry. J. Scrimgeour and J. E. Curtis. (2012) Optics Express, 20(13), 14534-14541.

Pubmed link

Optics Express link