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Amitonova LV. Multimode fiber endoscopes for computational brain imaging. NEUROPHOTONICS 2024; 11:S11509. [PMID: 38450327 PMCID: PMC10917391 DOI: 10.1117/1.nph.11.s1.s11509] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Figures] [Subscribe] [Scholar Register] [Received: 09/01/2023] [Revised: 01/08/2024] [Accepted: 01/31/2024] [Indexed: 03/08/2024]
Abstract
Advances in imaging tools have always been a pivotal driver for new discoveries in neuroscience. An ability to visualize neurons and subcellular structures deep within the brain of a freely behaving animal is integral to our understanding of the relationship between neural activity and higher cognitive functions. However, fast high-resolution imaging is limited to sub-surface brain regions and generally requires head fixation of the animal under the microscope. Developing new approaches to address these challenges is critical. The last decades have seen rapid progress in minimally invasive endo-microscopy techniques based on bare optical fibers. A single multimode fiber can be used to penetrate deep into the brain without causing significant damage to the overlying structures and provide high-resolution imaging. Here, we discuss how the full potential of high-speed super-resolution fiber endoscopy can be realized by a holistic approach that combines fiber optics, light shaping, and advanced computational algorithms. The recent progress opens up new avenues for minimally invasive deep brain studies in freely behaving mice.
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Affiliation(s)
- Lyubov V. Amitonova
- Vrije Universiteit Amsterdam, Department of Physics and Astronomy, Amsterdam, The Netherlands
- Advanced Research Center for Nanolithography, Amsterdam, The Netherlands
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Du Y, Dylda E, Stibůrek M, Gomes AD, Turtaev S, Pakan JMP, Čižmár T. Advancing the path to in-vivo imaging in freely moving mice via multimode-multicore fiber based holographic endoscopy. NEUROPHOTONICS 2024; 11:S11506. [PMID: 38352728 PMCID: PMC10863504 DOI: 10.1117/1.nph.11.s1.s11506] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Figures] [Subscribe] [Scholar Register] [Received: 10/30/2023] [Revised: 01/17/2024] [Accepted: 01/22/2024] [Indexed: 02/16/2024]
Abstract
Significance Hair-thin multimode optical fiber-based holographic endoscopes have gained considerable interest in modern neuroscience for their ability to achieve cellular and even subcellular resolution during in-vivo deep brain imaging. However, the application of multimode fibers in freely moving animals presents a persistent challenge as it is difficult to maintain optimal imaging performance while the fiber undergoes deformations. Aim We propose a fiber solution for challenging in-vivo applications with the capability of deep brain high spatial resolution imaging and neuronal activity monitoring in anesthetized as well as awake behaving mice. Approach We used our previously developed M 3 CF multimode-multicore fiber to record fluorescently labeled neurons in anesthetized mice. Our M 3 CF exhibits a cascaded refractive index structure, enabling two distinct regimes of light transport that imitate either a multimode or a multicore fiber. The M 3 CF has been specifically designed for use in the initial phase of an in-vivo experiment, allowing for the navigation of the endoscope's distal end toward the targeted brain structure. The multicore regime enables the transfer of light to and from each individual neuron within the field of view. For chronic experiments in awake behaving mice, it is crucial to allow for disconnecting the fiber and the animal between experiments. Therefore, we provide here an effective solution and establish a protocol for reconnection of two segments of M 3 CF with hexagonally arranged corelets. Results We successfully utilized the M 3 CF to image neurons in anaesthetized transgenic mice expressing enhanced green fluorescent protein. Additionally, we compared imaging results obtained with the M 3 CF with larger numerical aperture (NA) fibers in fixed whole-brain tissue. Conclusions This study focuses on addressing challenges and providing insights into the use of multimode-multicore fibers as imaging solutions for in-vivo applications. We suggest that the upcoming version of the M 3 CF increases the overall NA between the two cladding layers to allow for access to high resolution spatial imaging. As the NA increases in the multimode regime, the fiber diameter and ring structure must be reduced to minimize the computational burden and invasiveness.
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Affiliation(s)
- Yang Du
- University of Chinese Academy of Sciences, Hangzhou Institute for Advanced Study, Hangzhou, China
- Leibniz Institute of Photonic Technology, Jena, Germany
| | - Evelyn Dylda
- Otto-von-Guericke-University Magdeburg, Institute of Cognitive Neurology and Dementia Research, Magdeburg, Germany
- Center for Behavioral Brain Sciences, Magdeburg, Germany
| | | | - André D Gomes
- Leibniz Institute of Photonic Technology, Jena, Germany
| | | | - Janelle M. P. Pakan
- Otto-von-Guericke-University Magdeburg, Institute of Cognitive Neurology and Dementia Research, Magdeburg, Germany
- Center for Behavioral Brain Sciences, Magdeburg, Germany
- German Centre for Neurodegenerative Diseases, Magdeburg, Germany
- Leibniz Institute for Neurobiology, Magdeburg, Germany
| | - Tomáš Čižmár
- Leibniz Institute of Photonic Technology, Jena, Germany
- Institute of Scientific Instruments of CAS, Brno, Czechia
- Friedrich Schiller University Jena, Institute of Applied Optics, Jena, Germany
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Song P, Wang R, Loetgering L, Liu J, Vouras P, Lee Y, Jiang S, Feng B, Maiden A, Yang C, Zheng G. Ptycho-endoscopy on a lensless ultrathin fiber bundle tip. LIGHT, SCIENCE & APPLICATIONS 2024; 13:168. [PMID: 39019852 PMCID: PMC11255264 DOI: 10.1038/s41377-024-01510-5] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 01/30/2024] [Revised: 06/10/2024] [Accepted: 06/25/2024] [Indexed: 07/19/2024]
Abstract
Synthetic aperture radar (SAR) utilizes an aircraft-carried antenna to emit electromagnetic pulses and detect the returning echoes. As the aircraft travels across a designated area, it synthesizes a large virtual aperture to improve image resolution. Inspired by SAR, we introduce synthetic aperture ptycho-endoscopy (SAPE) for micro-endoscopic imaging beyond the diffraction limit. SAPE operates by hand-holding a lensless fiber bundle tip to record coherent diffraction patterns from specimens. The fiber cores at the distal tip modulate the diffracted wavefield within a confined area, emulating the role of the 'airborne antenna' in SAR. The handheld operation introduces positional shifts to the tip, analogous to the aircraft's movement. These shifts facilitate the acquisition of a ptychogram and synthesize a large virtual aperture extending beyond the bundle's physical limit. We mitigate the influences of hand motion and fiber bending through a low-rank spatiotemporal decomposition of the bundle's modulation profile. Our tests demonstrate the ability to resolve a 548-nm linewidth on a resolution target. The achieved space-bandwidth product is ~1.1 million effective pixels, representing a 36-fold increase compared to that of the original fiber bundle. Furthermore, SAPE's refocusing capability enables imaging over an extended depth of field exceeding 2 cm. The aperture synthesizing process in SAPE surpasses the diffraction limit set by the probe's maximum collection angle, opening new opportunities for both fiber-based and distal-chip endoscopy in applications such as medical diagnostics and industrial inspection.
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Affiliation(s)
- Pengming Song
- Department of Biomedical Engineering, University of Connecticut, Storrs, CT, 06269, USA.
| | - Ruihai Wang
- Department of Biomedical Engineering, University of Connecticut, Storrs, CT, 06269, USA
| | - Lars Loetgering
- CarlZeiss AG, Carl Zeiss Promenade, Jena, Thuringia, 07745, Germany
| | - Jia Liu
- Department of Biomedical Engineering, University of Connecticut, Storrs, CT, 06269, USA
| | - Peter Vouras
- United States Department of Defense, Washington, DC, 20301, USA
| | - Yujin Lee
- School of Electrical and Electronic Engineering, Yonsei University, Seoul, 03722, Republic of Korea
| | - Shaowei Jiang
- Department of Biomedical Engineering, University of Connecticut, Storrs, CT, 06269, USA
| | - Bin Feng
- Department of Biomedical Engineering, University of Connecticut, Storrs, CT, 06269, USA
| | - Andrew Maiden
- Department of Electronic and Electrical Engineering, University of Sheffield, Sheffield, South Yorkshire S1 3JD, UK
- Diamond Light Source, Harwell, Oxfordshire, OX11 0DE, UK
| | - Changhuei Yang
- Department of Electrical Engineering, California Institute of Technology, Pasadena, CA, 91125, USA
| | - Guoan Zheng
- Department of Biomedical Engineering, University of Connecticut, Storrs, CT, 06269, USA.
- Center for Biomedical and Bioengineering Innovation, University of Connecticut, Storrs, CT, 06269, USA.
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Wang J, Chen C, You W, Jiao Y, Liu X, Jiang X, Lu W. Honeycomb effect elimination in differential phase fiber-bundle-based endoscopy. OPTICS EXPRESS 2024; 32:20682-20694. [PMID: 38859444 DOI: 10.1364/oe.526033] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 04/10/2024] [Accepted: 05/10/2024] [Indexed: 06/12/2024]
Abstract
Fiber-bundle-based endoscopy, with its ultrathin probe and micrometer-level resolution, has become a widely adopted imaging modality for in vivo imaging. However, the fiber bundles introduce a significant honeycomb effect, primarily due to the multi-core structure and crosstalk of adjacent fiber cores, which superposes the honeycomb pattern image on the original image. To tackle this issue, we propose an iterative-free spatial pixel shifting (SPS) algorithm, designed to suppress the honeycomb effect and enhance real-time imaging performance. The process involves the creation of three additional sub-images by shifting the original image by one pixel at 0, 45, and 90 degree angles. These four sub-images are then used to compute differential maps in the x and y directions. By performing spiral integration on these differential maps, we reconstruct a honeycomb-free image with improved details. Our simulations and experimental results, conducted on a self-built fiber bundle-based endoscopy system, demonstrate the effectiveness of the SPS algorithm. SPS significantly improves the image quality of reflective objects and unlabeled transparent scattered objects, laying a solid foundation for biomedical endoscopic applications.
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Weinberg G, Kang M, Choi W, Choi W, Katz O. Ptychographic lensless coherent endomicroscopy through a flexible fiber bundle. OPTICS EXPRESS 2024; 32:20421-20431. [PMID: 38859424 DOI: 10.1364/oe.503963] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 08/22/2023] [Accepted: 04/18/2024] [Indexed: 06/12/2024]
Abstract
Conventional fiber-bundle-based endoscopes allow minimally invasive imaging through flexible multi-core fiber (MCF) bundles by placing a miniature lens at the distal tip and using each core as an imaging pixel. In recent years, lensless imaging through MCFs was made possible by correcting the core-to-core phase distortions pre-measured in a calibration procedure. However, temporally varying wavefront distortions, for instance, due to dynamic fiber bending, pose a challenge for such approaches. Here, we demonstrate a coherent lensless imaging technique based on intensity-only measurements insensitive to core-to-core phase distortions. We leverage a ptychographic reconstruction algorithm to retrieve the phase and amplitude profiles of reflective objects placed at a distance from the fiber tip, using as input a set of diffracted intensity patterns reflected from the object when the illumination is scanned over the MCF cores. Our approach thus utilizes an acquisition process equivalent to confocal microendoscopy, only replacing the single detector with a camera.
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Weinberg G, Weiss U, Katz O. Image scanning lensless fiber-bundle endomicroscopy. OPTICS EXPRESS 2023; 31:37050-37057. [PMID: 38017842 DOI: 10.1364/oe.496369] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 05/25/2023] [Accepted: 09/07/2023] [Indexed: 11/30/2023]
Abstract
Fiber-based confocal endomicroscopy has shown great promise for minimally-invasive deep-tissue imaging. Despite its advantages, confocal fiber-bundle endoscopy inherently suffers from undersampling due to the spacing between fiber cores, and low collection efficiency when the target is not in proximity to the distal fiber facet. Here, we demonstrate an adaptation of image-scanning microscopy (ISM) to lensless fiber bundle endoscopy, doubling the spatial sampling frequency and significantly improving collection efficiency. Our approach only requires replacing the confocal detector with a camera. It improves the spatial resolution for targets placed at a distance from the fiber tip, and addresses the fundamental challenge of aliasing/pixelization artifacts.
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Collard L, Piscopo L, Pisano F, Zheng D, De Vittorio M, Pisanello F. Optimizing the internal phase reference to shape the output of a multimode optical fiber. PLoS One 2023; 18:e0290300. [PMID: 37682976 PMCID: PMC10490902 DOI: 10.1371/journal.pone.0290300] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/26/2023] [Accepted: 08/04/2023] [Indexed: 09/10/2023] Open
Abstract
Pre-shaping light to achieve desired amplitude distributions at the tip of a multimode fiber (MMF) has emerged as a powerful method allowing a wide range of imaging techniques to be implemented at the distal facet. Such techniques rely on measuring the transmission matrix of the optically turbid waveguide which scrambles the coherent input light into an effectively random speckle pattern. Typically, this is done by measuring the interferogram between the output speckle and a reference beam. In recent years, an optical setup where the reference beam passes through the MMF has become an attractive configuration because of the high interferometric stability of the common optical path. However, the merits and drawbacks of an internal reference beam remain controversial. The measurement of the transmission matrix is known to depend on the choice of internal reference and has been reported to result in "blind spots" due to phase singularities of the reference beam. Here, we describe how the focussing efficiency of the calibration can be increased by several percent by optimising the choice of internal reference beam.
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Affiliation(s)
- Liam Collard
- Istituto Italiano di Tecnologia, Center for Biomolecular Nanotechnologies, Arnesano, Italy
- RAISE Ecosystem, Genova, Italy
| | - Linda Piscopo
- Istituto Italiano di Tecnologia, Center for Biomolecular Nanotechnologies, Arnesano, Italy
- Dipartimento di Ingegneria Dell’Innovazione, Università del Salento, Lecce, Italy
| | - Filippo Pisano
- Istituto Italiano di Tecnologia, Center for Biomolecular Nanotechnologies, Arnesano, Italy
- Department of Physics and Astronomy “G. Galilei”, University of Padova, Padova, Italy
| | - Di Zheng
- Istituto Italiano di Tecnologia, Center for Biomolecular Nanotechnologies, Arnesano, Italy
| | - Massimo De Vittorio
- Istituto Italiano di Tecnologia, Center for Biomolecular Nanotechnologies, Arnesano, Italy
- RAISE Ecosystem, Genova, Italy
- Dipartimento di Ingegneria Dell’Innovazione, Università del Salento, Lecce, Italy
| | - Ferruccio Pisanello
- Istituto Italiano di Tecnologia, Center for Biomolecular Nanotechnologies, Arnesano, Italy
- RAISE Ecosystem, Genova, Italy
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Kang M, Choi W, Choi W, Choi Y. Fourier holographic endoscopy for imaging continuously moving objects. OPTICS EXPRESS 2023; 31:11705-11716. [PMID: 37155799 DOI: 10.1364/oe.482923] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/10/2023]
Abstract
Coherent fiber bundles are widely used for endoscopy, but conventional approaches require distal optics to form an object image and acquire pixelated information owing to the geometry of the fiber cores. Recently, holographic recording of a reflection matrix enables a bare fiber bundle to perform pixelation-free microscopic imaging as well as allows a flexible mode operation, because the random core-to-core phase retardations due to any fiber bending and twisting could be removed in situ from the recorded matrix. Despite its flexibility, the method is not suitable for a moving object because the fiber probe should remain stationary during the matrix recording to avoid the alteration of the phase retardations. Here, we acquire a reflection matrix of a Fourier holographic endoscope equipped with a fiber bundle and explore the effect of fiber bending on the recorded matrix. By removing the motion effect, we develop a method that can resolve the perturbation of the reflection matrix caused by a continuously moving fiber bundle. Thus, we demonstrate high-resolution endoscopic imaging through a fiber bundle, even when the fiber probe changes its shape along with the moving objects. The proposed method can be used for minimally invasive monitoring of behaving animals.
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