De-scattering with Excitation Patterning (DEEP) Enables Rapid Wide-field Imaging Through Scattering Media

Very interesting stuff from the people at MIT regarding imaging through scattering media. Recently, multiple approaches taking advantage of temporal focusing (TF) increased efficiency inside scattering media when using two-photon microscopy have been published, and this goes a step further.

Here, the authors use wide-field structured illumination, in combination with TF, to obtain images with a large field-of-view and a slow number of camera acquisitions. To do so, they sequentially project a set of random structured patterns using a digital micromirror device (DMD). Using the pictures acquired for each illumination pattern in combination with the point-spread-function (PSF) of the imaging system allows to recover images of different biological samples without the typical scattering blur.

Optical design and working principle of the system. Figure extracted from “De-scattering with Excitation Patterning (DEEP) Enables Rapid Wide-field Imaging Through Scattering Media,” Dushan N. Wadduwage et al., at https://arxiv.org/abs/1902.10737

De-scattering with Excitation Patterning (DEEP) Enables Rapid Wide-field Imaging Through Scattering Media

by Dushan N. Wadduwage et al., at arXiv.

Abstract:

From multi-photon imaging penetrating millimeters deep through scattering biological tissue, to super-resolution imaging conquering the diffraction limit, optical imaging techniques have greatly advanced in recent years. Notwithstanding, a key unmet challenge in all these imaging techniques is to perform rapid wide-field imaging through a turbid medium. Strategies such as active wave-front correction and multi-photon excitation, both used for deep tissue imaging; or wide-field total-internal-refection illumination, used for super-resolution imaging; can generate arbitrary excitation patterns over a large field-of-view through or under turbid media. In these cases, throughput advantage gained by wide-field excitation is lost due to the use of point detection. To address this challenge, here we introduce a novel technique called De-scattering with Excitation Patterning, or ‘DEEP’, which uses patterned excitation followed by wide-field detection with computational imaging. We use two-photon temporal focusing (TFM) to demonstrate our approach at multiple scattering lengths deep in tissue. Our results suggest that millions of point-scanning measurements could be substituted with tens to hundreds of DEEP measurements with no compromise in image quality.

Rapid broadband characterization of scattering medium using hyperspectral imaging

People at LKB (and St. Andrews) keep shining light into scattering media. This time, they have developed a cool approach for measuring the multispectral Transmission Matrix (MSTM) of a medium. This knowledge allows to control each spectral component of a light beam when travelling through the medium, which permits to shape, for example, the spectral and temporal profiles of light pulses. This is quite nice, as can be used to generate tight focci inside biological tissues, improving the performance of nonlinear microscopy techniques.

Usually, the measurement of the MSTM entails a long iterative process (basically you just measure the TM for each spectral channel you want to characterize). This is not always possible (usually you do not have a laser with all the wavelengths you need to measure), and also tends to be slow (which is a problem if you want to measure the MSTM of a changing medium). Here the authors tackle this problem by performing a wavelength-to-spatial mapping, thus measuring the spatio-spectral information in just one shot of a CCD camera. To do so, they use a clever design with a lenslet array and a dispersion grating. In this way, the total time it takes to acquire the MSTM is reduced in ~2 orders of magnitude. Elegant, simple, and fast.

Design concept for the spectral measurements using a lenslet array and a single CCD sensor. Extracted from “Rapid broadband characterization of scattering medium using hyperspectral imaging,” A. Boniface et al., https://www.osapublishing.org/optica/abstract.cfm?uri=optica-6-3-274

Rapid broadband characterization of scattering medium using hyperspectral imaging

by Antoine Boniface et al., at Optica

Abstract:

Scattering of a coherent ultrashort pulse of light by a disordered medium results in a complex spatiotemporal speckle pattern. The form of the pattern can be described by knowledge of a spectrally dependent transmission matrix, which can in turn be used to shape the propagation of the pulse through the medium. We introduce a method for rapid measurement of this matrix for the entire spectrum of the pulse based on a hyperspectral imaging system that is close to 2 orders of magnitude faster than any approach previously reported. We demonstrate narrowband as well as spatiotemporal refocusing of a femtosecond pulse temporally stretched to several picoseconds after propagation through a multiply scattering medium. This enables new routes for multiphoton imaging and manipulation through complex media.