Adaptive wavefront correction structured illumination holographic tomography.

In this study, a novel adaptive wavefront correction (AWC) technique is implemented on a compactly developed structured illumination holographic tomography (SI-HT) system. We propose a mechanical movement-free compact scanning architecture for SI-HT systems with AWC, implemented by designing and displaying a series of computer-generated holograms (CGH) composed of blazed grating with phase Fresnel lens on a phase-only spatial light modulator (SLM). In the proposed SI-HT, the aberrations of the optical system are sensed by digital holography and are used to design the CGH-based AWC to compensate the phase aberrations of the tomographic imaging system. The proposed method was validated using a standard Siemens star target, its potential application was demonstrated using a live candida rugosa sample, and its label-free three-dimensional refractive index profile was generated at its subcellular level. The experimental results obtained reveal the ability of the proposed method to enhance the imaging performance in both lateral and axial directions.

One-shot synthetic aperture digital holographic microscopy with non-coplanar angular-multiplexing and coherence gating.

This paper proposes one-shot synthetic aperture digital holographic microscopy using a combination of angular-multiplexing and coherence gating. The proposed angular-multiplexing technique uses multiple noncoplanar incident beams into the synthetic aperture to create tight packed passbands so as to extend spatial frequency spectrum. Coherence gating is performed to prevent the self-interference among the multiple beams. Based on the design guideline proposed herein, a phase-only spatial light modulator is employed as an adjustable blazed grating to split multiple noncoplanar beams and perform angular-multiplexing, and then using coherence gating based on low-coherence-light, superresolution imaging is achieved after one-shot acquisition.

Integrated dual-tomography for refractive index analysis of free-floating single living cell with isotropic superresolution.

Digital holographic microtomography is a promising technique for three-dimensional (3D) measurement of the refractive index (RI) profiles of biological specimens. Measurement of the RI distribution of a free-floating single living cell with an isotropic superresolution had not previously been accomplished. To the best of our knowledge, this is the first study focusing on the development of an integrated dual-tomographic (IDT) imaging system for RI measurement of an unlabelled free-floating single living cell with an isotropic superresolution by combining the spatial frequencies of full-angle specimen rotation with those of beam rotation. A novel 'UFO' (unidentified flying object) like shaped coherent transfer function is obtained. The IDT imaging system does not require any complex image-processing algorithm for 3D reconstruction. The working principle was successfully demonstrated and a 3D RI profile of a single living cell, Candida rugosa, was obtained with an isotropic superresolution. This technology is expected to set a benchmark for free-floating single live sample measurements without labeling or any special sample preparations for the experiments.

Coded aperture structured illumination digital holographic microscopy for superresolution imaging.

This paper proposes a coded aperture structured illumination (CASI) technique in digital holographic microscopy (DHM). A CASI wave is generated using two binary phase codes (0° and 120°) for spatial phase shifting. The generated CASI wave then interferes with a reference wave to form a coded Fresnel hologram at a single exposure with compressive sensing (CS) to avoid the temporal phase-shifting process of the structured illumination (SI). The CS algorithm is applied to retrieve the missing data of decoded phase-shifted SI-modulated waves, which are used to separate overlapped spatial frequencies for obtaining a larger spatial frequency coverage to provide superresolution imaging. Two phase-only spatial light modulators are applied to generate a directional SI pattern for obtaining a coded aperture with a suitable size to perform one-shot acquisition in the DHM system.

Resolution enhancement of spectrum normalization in synthetic aperture digital holographic microscopy.

This study describes the overlapping of spatial frequency bands for synthetic aperture in digital holography using spectrum normalization to effectively enhance the spatial resolutions of image reconstruction. Synthesized spectrum swelling induced by excessive frequency overlaps can be normalized through the inverse apodization of an adjustable window function, which is similar to the effects of suppressing low-frequency expansion and strengthening high-frequency components of the reconstructed images. The results indicated that using the normalized spectrum synthesis that requires only a few frequency bands effectively enhances the spatial resolution and phase sensitivity of reconstructed images in digital holographic microscopy.

Applications of digital holographic microscopy in therapeutic evaluation of Chinese herbal medicines.

Therapeutic use of Chinese herbal medicines (CHMs) is a new approach to treat neurodegenerative diseases, such as Alzheimer's disease and Parkinson's disease. The detection of soma volume and neurite outgrowth of living neurons is a highly relevant biomarker related to various application fields, including therapy efficacy and drug safety evaluation. Through the use of digital holographic microscopy (DHM), we may evaluate the therapeutic effect of CHMs in curing neurodegeneration. Panax ginseng has been used in traditional Chinese herbal medicine for centuries. In this study, DHM is applied to monitor the three-dimensional morphology change of retinoic acid-induced human neuroblastoma SH-SY5Y cells during Panax ginseng treatment. We demonstrate the capability of DHM to detect noninvasively SH-SY5Y cell apoptosis and rescue through the measurement of neuronal volume and neurite outgrowth regulation without any labeling reagent. Through DHM, we observed the phase images of the rapidly shrinking cells with decreasing soma volume and shortening neurite outgrowth during glutamate treatments. Then shrinkage in glutamate-induced cells is significantly alleviated during Panax ginseng treatment. The results through DHM are consistent with the result from MTT assay for assessing cell viability during Panax ginseng treatment. Thus, we suggest that application of DHM for measuring soma volume and neurite outgrowth of living neurons may be one appropriate therapeutic evaluation for CHMs.