Volume Holographic Imaging System Research Articles

Two-photon fluorescence imaging of subsurface tissue structures with volume holographic microscopy.

.Significance: Two-photon (2P) fluorescence imaging can provide background-free high-contrast images from the scattering tissues. However, obtaining a multiplane image is not straightforward. We present a two-photon volume holographic imaging (2P-VHI) system for multiplane imaging.Aim: Our goal was to design and implement a 2P-VHI system that can provide the high-contrast optically sectioned images at multiple planes.Approach: A 2P-VHI system is presented that incorporates angularly multiplexed volume holographic gratings and a femtosecond laser source for fluorescence excitation for multiplane imaging. A volume hologram with multiplexed gratings provides multifocal observation, whereas nonlinear excitation using a femtosecond laser helps in significantly enhancing both depth resolution and contrast of images.Results: Standard fluorescent beads are used to demonstrate the imaging performance of the 2P-VHI system. Two-depth resolved optical-sectioning images of fluorescently labeled thick mice intestine samples were obtained. In addition, the optical sectioning capability of our system is measured and compared with that of a conventional VHI system.Conclusions: Results demonstrated that 2P excitation in VHI systems provided the optical sectioning ability that helps in reducing background noise in the images. Integration of nonlinear fluorescence excitation in the VHI provides some unique advantages to the system and has potential to design multidepth optical sectioned spatial–spectral imaging systems.

Volume holographic spatial-spectral imaging systems [Invited

In this paper, we present an overview of the recent developments in applications of volume holographic imaging techniques in microscopy. In these techniques, three-dimensional imaging incorporates multiplexed volume holographic gratings, which are formed in phenanthrenequinone poly(methyl methacrylate) (PQ-PMMA) photopolymer and act as spatial-spectral filters, to obtain multiplane images from a volumetric object without scanning. We introduce recent major roles of volume holography in different imaging modalities, including large-capacity spatial-spectral multiplane microscopy, digital holographic microscopy, and structured Talbot (or speckle) illumination fluorescence imaging. Among various imaging applications of volume holography, simultaneous multiplane fluorescence microscopy for collecting spatial-spectral information is distinct and has great potential for hyperspectral imaging. Depth selective spatial-spectral information from an object is particularly useful for designing a high-resolution microscope in real-time operation. We further discuss volume holography in particle trapping and beam shaping. In addition, we investigate future prospects of volume holography in microscopy as well as endoscopy.

Volume holographic imaging endoscopic design and construction techniques.

A reflectance volume holographic imaging (VHI) endoscope has been designed for simultaneous in vivo imaging of surface and subsurface tissue structures. Prior utilization of VHI systems has been limited to ex vivo tissue imaging. The VHI system presented in this work is designed for laparoscopic use. It consists of a probe section that relays light from the tissue sample to a handheld unit that contains the VHI microscope. The probe section is constructed from gradient index (GRIN) lenses that form a 1:1 relay for image collection. The probe has an outer diameter of 3.8 mm and is capable of achieving 228.1 ?? lp / mm resolution with 660-nm Kohler illumination. The handheld optical section operates with a magnification of 13.9 and a field of view of 390 ?? ? m × 244 ?? ? m . System performance is assessed through imaging of 1951 USAF resolution targets and soft tissue samples. The system has also passed sterilization procedures required for surgical use and has been used in two laparoscopic surgical procedures.

Reduction of blurring in broadband volume holographic imaging using a deconvolution method.

Volume holographic imaging (VHI) is a promising biomedical imaging tool that can simultaneously provide multi-depth or multispectral information. When a VHI system is probed with a broadband source, the intensity spreads in the horizontal direction, causing degradation of the image contrast. We theoretically analyzed the reason of the horizontal intensity spread, and the analysis was validated by the simulation and experimental results of the broadband impulse response of the VHI system. We proposed a deconvolution method to reduce the horizontal intensity spread and increase the image contrast. Imaging experiments with three different objects, including bright field illuminated USAF test target and lung tissue specimen and fluorescent beads, were carried out to test the performance of the proposed method. The results demonstrated that the proposed method can significantly improve the horizontal contrast of the image acquire by broadband VHI system.

Spectral selective fluorescence molecular imaging with volume holographic imaging system

A compact volume holographic imaging (VHI) method that can detect fluorescence objects located in diffusive medium in spectral selective imaging manner is presented. The enlargement of lateral field of view of the VHI system is realized by using broadband illumination and demagnification optics. Each target spectrum of fluorescence emitting from a diffusive medium is probed by tuning the inclination angle of the transmission volume holographic grating (VHG). With the use of the single transmission VHG, fluorescence images with different spectrum are obtained sequentially and precise three-dimensional (3D) information of deep fluorescent objects located in a diffusive medium can be reconstructed from these images. The results of phantom experiments demonstrate that two fluorescent objects with a sub-millimeter distance can be resolved by spectral selective imaging.

Progress in volume holographic imaging system

Volume holographic imaging system (VHIS) incorporates a volume hologram grating (VHG) as the critical optical field processing component in a new imaging system.High spectral resolution and high sensitivity in obtaining 3D information at multi-depths are achieved without time consuming scanning mechanism and complex reconstruction algorithms by utilizing the Bragg diffraction selectivity and degeneracy properties.We briefly introduced the system structures and principles,then we presented intensively on how these VHGs were devised and VHIS were configured into the qualified spectral VHIS (S-VHIS) and multiplexed VHG imaging systems.The superiorities over conventional imaging systems and the features to be improved of VHIS were summarized and discussed. Key words: Volume holographic imaging system; Volume hologram grating; Spectral imaging; 3D multi-depth imaging

Simultaneous multiplane imaging of human ovarian cancer by volume holographic imaging

Ovarian cancer is the most deadly gynecologic cancer, a fact which is attributable to poor early detection and survival once the disease has reached advanced stages. Intraoperative laparoscopic volume holographic imaging has the potential to provide simultaneous visualization of surface and subsurface structures in ovarian tissues for improved assessment of developing ovarian cancer. In this ex vivo ovarian tissue study, we assembled a benchtop volume holographic imaging system (VHIS) to characterize the microarchitecture of 78 normal and 40 abnormal tissue specimens derived from ovarian, fallopian tube, uterine, and peritoneal tissues, collected from 26 patients aged 22 to 73 undergoing bilateral salpingo-oophorectomy, hysterectomy with bilateral salpingo-oophorectomy, or abdominal cytoreductive surgery. All tissues were successfully imaged with the VHIS in both reflectance- and fluorescence-modes revealing morphological features which can be used to distinguish between normal, benign abnormalities, and cancerous tissues. We present the development and successful application of VHIS for imaging human ovarian tissue. Comparison of VHIS images with corresponding histopathology allowed for qualitatively distinguishing microstructural features unique to the studied tissue type and disease state. These results motivate the development of a laparoscopic VHIS for evaluating the surface and subsurface morphological alterations in ovarian cancer pathogenesis.

Volume Holographic Reflection Endoscope for In-Vivo Ovarian Cancer Clinical Studies.

We present the design for an endoscopic system capable of imaging tissues of the ovary at two selected imaging depths simultaneously. The method utilizes a multiplexed volume hologram to select wavefronts from different depths within the tissue. It is the first demonstration of an endoscopic volume holographic imaging system. The endoscope uses both gradient index (GRIN) optical components and off the shelf singlet lenses to relay an image from the distal tip to the proximal end. The endoscope has a minimum diameter of 3.75 mm. The system length is 30 cm which is connected to a handle that includes the holographic components and optics that relay the image to a camera. Preliminary evaluation of the endoscope was performed with tissue phantoms and calibrated targets, which shows lateral resolution ≈ 4 μm at an operating wavelength of 660 nm. The hologram is recorded in phenanthraquinone doped poly methacrylate and is designed to produce images from two tissue depths. One image is obtained at the tissue surface and the second 70 μm below the surface. This method requires no mechanical scanning and acquires an image at the camera frame rate. The preliminary ex-vivo results show good correlation with histology sections of the same tissue sections.

Dual-grating confocal-rainbow volume holographic imaging system designs for high depth resolution

Confocal microscopy rejects out-of-focus light from the object by scanning a pinhole through the image and reconstructing the image point by point. Volume holographic imaging systems with bright-field illumination have been proposed as an alternative to conventional confocal-type microscopes that does not require scanning of a pinhole or a slit. However, due to wavelength-position degeneracy of the hologram, the high Bragg selectivity of the volume hologram is not utilized and system performance is not optimized. Confocal-rainbow illumination has been proposed as a means to remove the degeneracy and improve optical sectioning in these systems. In prior work, two versions of this system were illustrated: the first version had a separate illumination and imaging grating and the second used a single grating to disperse the incident light and to separate wavelengths in the imaging path. The initial illustration of the dual-grating system has limited depth resolution due to the low selectivity of the illumination grating. The initial illustration of the single-grating system has high depth resolution but does not allow optimization of the illumination path and requires high optical quality of the holographic filters. In this paper we consider the design and tolerance requirements of the dual-grating system for high depth resolution and demonstrate the results with an experimental system. An experimental system with two 1.8 mm thick planar holograms achieved a depth resolution of 7 μm with a field of view of 1.9 mm and a hologram dispersion matching tolerance of ±0.008°.

Phase-contrast volume holographic imaging system

A phase-contrast volume holographic imaging system for three-dimensional contrast enhancement is presented. The system utilizes a spatial filter placed on a conjugate plane to the volume holographic pupil to simultaneously enhance weak phase information at different depths within an object. The proposed system was validated with experimental image data obtained in mouse colon samples and quantitative measurements of modulation transfer function as well.

Confocal-rainbow volume holographic imaging system

The performance of broadband volume holographic imaging system in terms of depth selectivity is investigated. The mechanism for depth resolution degradation is explained. In order to overcome this resolution degradation, a novel imaging device, the confocal-rainbow volume holographic imaging system, is proposed. Modeling and experimental validation of the performance of this novel imaging system indicates that depth resolution <16 μm is achievable. The lateral resolution of this device is <2.5 μm along a field of view of 300 μm×100 μm.

Spatial–spectral volume holographic systems: resolution dependence on effective thickness

The resolution dependence of spatial-spectral volume holographic imaging systems on angular and spectral bandwidth of nonuniform gratings is investigated. Modeling techniques include a combination of the approximate coupled-wave analysis and the transfer-matrix method for holograms recorded in absorptive media. The effective thickness of the holograms is used as an estimator of the resolution of the imaging systems. The methodology, which assists in the design and optimization of volume holographic simulation results based on our approach, are confirmed with experiments and show proof of consistency and usefulness of the proposed models.

Analysis of diffracted image patterns from volume holographic imaging systems and applications to image processing

Diffracted image patterns from volume holograms that are used in volume holographic imaging systems (VHISs) are investigated. It is shown that, in VHISs, prior information about the shape and spectral properties of the diffracted patterns is important not only to determine the curvature and field of view of the image, but also for image registration and noise removal. A new methodology to study numerically and analytically the dependence of VHIS diffraction patterns with the hologram construction parameters and the readout wavelength is described. Modeling and experimental results demonstrate that, in most cases, VHIS diffracted shapes can be accurately represented by hyperbolas.

90°临面入射体全息成像系统的深度分辨率

90°临面入射体全息成像系统的深度分辨率

Simulations and experiments of aperiodic and multiplexed gratings in volume holographic imaging systems.

A new methodology describing the effects of aperiodic and multiplexed gratings in volume holographic imaging systems (VHIS) is presented. The aperiodic gratings are treated as an ensemble of localized planar gratings using coupled wave methods in conjunction with sequential and non-sequential ray-tracing techniques to accurately predict volumetric diffraction effects in VHIS. Our approach can be applied to aperiodic, multiplexed gratings and used to theoretically predict the performance of multiplexed volume holographic gratings within a volume hologram for VHIS. We present simulation and experimental results for the aperiodic and multiplexed imaging gratings formed in PQ-PMMA at 488nm and probed with a spherical wave at 633nm. Simulation results based on our approach that can be easily implemented in ray-tracing packages such as Zemax® are confirmed with experiments and show proof of consistency and usefulness of the proposed models.

Optical design for a spatial-spectral volume holographic imaging system

Spatial Spectral Holographic imaging system (S(2)-VHIS) is a promising alternative to confocal microscopy due to its capabilities to simultaneously image several sample depths with high resolution. However, the field of view of previously presented S(2)-VHIS prototypes has been restricted to less than 200μm. This paper presents experimental results of an improved S(2)-VHIS design which have a field of view of ~1mm while maintaining high resolution and dynamic range.

Laser-induced fluorescence imaging of subsurface tissue structures with a volume holographic spatial-spectral imaging system

A three-dimensional imaging system incorporating multiplexed holographic gratings to visualize fluorescence tissue structures is presented. Holographic gratings formed in volume recording materials such as a phenanthrenquinone poly(methyl methacrylate) photopolymer have narrowband angular and spectral transmittance filtering properties that enable obtaining spatial-spectral information within an object. We demonstrate this imaging system's ability to obtain multiple depth-resolved fluorescence images simultaneously.

Simulation and optimization of volume holographic imaging systems in Zemax^®

We present a new methodology for ray-tracing analysis of volume holographic imaging (VHI) systems. Using the k-sphere formulation, we apply geometrical relationships to describe the volumetric diffraction effects imposed on rays passing through a volume hologram. We explain the k-sphere formulation in conjunction with ray tracing process and describe its implementation in a Zemax UDS (User Defined Surface). We conclude with examples of simulation and optimization results and show proof of consistency and usefulness of the proposed model.

Imaging using volume holograms

We present an overview of imaging systems that incorporate a volume hologram as one of the optical field processing elements in the system. We refer to these systems as volume holographic imaging (VHI) systems. The volume hologram is recorded just once, and the recording parameters depend on the functional requirements of the imaging system. The recording step offers great flexibility in designing application-specific imaging systems. We discuss how a VHI system can be configured for diverse imaging applications ranging from surface profilometry to real-time hyperspectral microscopy, and summarize recent developments in this field.