High Axial Resolution Research Articles

High Frequency Ultrasound Image Recovery Using Tight Frame Generative Adversarial Networks.

In ultrasound imaging, there is a trade-off between imaging depth and axial resolution because of physical limitations. Increasing the center frequency of the transmitted ultrasound wave improves the axial resolution of resulting image. However, High Frequency (HF) ultrasound has a shallower depth of penetration. Herein, we propose a novel method based on Generative Adversarial Network (GAN) for achieving a high axial resolution without a reduction in imaging depth. Results on simulated phantoms show that a mapping function between Low Frequency (LF) and HF ultrasound images can be constructed.

Metamaterial-Assisted Photobleaching Microscopy with Nanometer Scale Axial Resolution.

The past two decades have witnessed a dramatic progress in the development of novel super-resolution fluorescence microscopy technologies. Here, we report a new fluorescence imaging method, called metamaterial-assisted photobleaching microscopy (MAPM), which possesses a nanometer-scale axial resolution and is suitable for broadband operation across the entire visible spectrum. The photobleaching kinetics of fluorophores can be greatly modified via a separation-dependent energy transfer process to a nearby metamaterial. The corresponding photobleaching rate is thus linked to the distance between the fluorophores and the metamaterial layer, leading to a reconstructed image with exceptionally high axial resolution. We apply the MAPM technology to image the HeLa cell membranes tagged with fluorescent proteins and demonstrate an axial resolution of ∼2.4 nm with multiple colors. MAPM utilizes a metamaterial-coated substrate to achieve super-resolution without altering anything else in a conventional microscope, representing a simple solution for fluorescence imaging at nanometer axial resolution.

Simultaneous photoacoustic microscopy, spectral-domain optical coherence tomography, and fluorescein microscopy multi-modality retinal imaging

The goal of this study is to further develop a multi-modality eye imaging system and evaluate its feasibility of acquiring images of different modalities simultaneously. An integrated multimodality imaging system combining spectral-domain optical coherence tomography (SD-OCT), photoacoustic microscopy (PAM), and fluorescence microscopy (FM) was developed, and its performance for eye imaging was validated on multiple clinically-relevant retinal disease models in vivo in rabbits. OCT imaging allows for visualization of the different anatomic retinal layers with high axial resolution. PAM can be used to image vasculature, angiogenesis, and hemorrhages. The leakage of neovascularization can be verified with FM and fluorescein dye. Simultaneous imaging with OCT, PAM, and FM ensures co-registration of the three modalities without being affected by motion artifacts caused by breathing, body or eye movements, and heartbeat. This simultaneous multi-modality eye imaging system could be a new tool for applications both in ophthalmology and other fields.

Increased SNR in acousto-optic imaging via coded ultrasound transmission.

Acousto-optic imaging (AOI) is a non-invasive method that uses acoustic modulation to map the light fluence inside biological tissue. In many AOI implementations, ultrasound pulses are used in a time-gated measurement to perform depth-resolved imaging without the need for mechanical scanning. However, to achieve high axial resolution, it is required that ultrasound pulses with few cycles are used, limiting the modulation strength. In this Letter, we develop a new approach to pulse-based AOI in which coded ultrasound transmission is used. In coded-transmission AOI (CT-AOI), one may achieve an axial resolution that corresponds to a single cycle, but with a signal-to-noise ratio (SNR) that scales as the square root of the number of cycles. Using CT-AOI with 79 cycles, we experimentally demonstrate over four-fold increase in SNR in comparison to a single-cycle AOI scheme.

High axial resolution and long field of view for light-sheet fluorescence microscopy via double-beam aperture

We propose a simple method based on the use of interference of the double-beam aperture to enhance both the axial resolution and field of view of light-sheet fluorescence microscopy. The double-beam aperture placed in the pupil plane generates multiple-spot intensity patterns in which the size of central lobe reduces. By scanning this intensity pattern along x -axis, the light sheet is generated. By satisfactorily choosing the numerical apertures of illumination lens and detection lens, only the central light sheet is used to achieve image, so the axial resolution of light-sheet fluorescence microscopy is enhanced. Both the numerical apertures of the illumination lens and detection lens of 0.3 and 1.1, respectively, are employed to perform the simulation results. The simulation results indicated that both the axial resolution and field of view are improved in comparison to the Gaussian light-sheet. Additionally, in order to remove a small amount of the existing outside lobes, we propose a subtraction method. The simulation results demonstrated that our technique can eliminate the outside lobes in the system point spread function of the double-beam aperture beam light sheet.

Multi-incidence digital holographic profilometry with high axial resolution and enlarged measurement range.

In this work, multi-incident digital holographic profilometry for microscale measurements is presented. This technique assembles the set of object fields from captured holograms for generation of the longitudinal scanning function (LSF). Numerical propagation is used for refocusing, and thus, the LSF can be determined at any given plane along the optical axis. The LSF takes maximum value for in focus object points, which are used to obtain full-field height distribution of the sample. This principle is the base of proposed measurement technique. Three capturing holograms strategies, which give control over the shape of the LSF, unambiguous measurement range, axial resolution, and noise immunity, are discussed. The conclusions of this work are supported by numerical and experimental results.

Automated Defect Inspection Algorithm Incorporated Spectral-Domain Optical Coherence Tomography for Optical Polarizing Thin Films

Optical polarizing thin film is an optical filter enables light waves of a specific polarization pass through while blocking light waves of other polarizations. Optical polarizing thin films control the brightness of back-light unit for LCD (liquid crystal display) panel, which is essential to produce LCD modules. Defect inspection of polarizing thin films is an important feature during the manufacturing process that is helpful to improve the product quality. In the current study, an automated defect inspection algorithm is introduced and incorporated with a well-known non-destructive and non-contact optical inspection method called spectral domain optical coherence tomography (SD-OCT) to pre-identify defective sub-surface as well as top-surface locations of optical polarizing thin films Polarizing thin films employed in this study consist of 6 layers. The tomographic information, layer information, and defective locations were sufficiently identified through the SD-OCT system owing high-axial resolution. The acquired results indicate the possible application of the proposed system in optical polarizing thin films for the quality assurance.

A Self Aligning Macroscopic Selective Plane Illumination Microscope with Near Uniform Axial Resolution

A key compromise in selective plane illumination microscopy (SPIM) is the tradeoff between optical confinement, axial resolution, and field of view (FOV). Recent advancements have demonstrated that high axial resolution can be maintained over a large FOV by optical engineering of the light sheet or by scanning the thinnest portion of a Gaussian focus across the FOV. These methods require precise synchronization between the translating focus of the exciting Gaussian to the programmable shutter of a scientific CMOS camera.

A DESCRIPTIVE STUDY OF MR DEFECOGRAPHY FOR EVALUATION OF OBSTRUCTED DEFECATION SYNDROME

Objective:-This study aims to ascertain the role of MR Defecography in the evaluation of obstructed defecation syndrome (ODS) with objective to describe spectrum of MR Defecography findings in obstructed defecation syndrome (ODS) and describe a number of reference lines and measurement points used to diagnose and grade pelvic floor disorders and Document the MRI appearance of disorders associated with ano-rectal dysfunction. MR Defecography demonstrated the profile of obstructed defecation syndrome on the basis of MR defecography and demonstrate its utility in simultaneous & objective evaluation of all three pelvic compartments. This diagnostic modalities provide a detailed pelvic floor anatomy and functional evaluation, as well as their respective abnormalities, making a precise diagnosis and provides valuable information on treatment planning & decrease chance of postoperative recurrence.
 Subjects and Methods: It was Cross-sectional and prospective (quantitative) hospital based descriptive type of observational study carried out at a tertiary hospital SMS hospital, jaipur. Chosen the patients diagnosed with ODS as per Rome criteria (III) whose colonoscopy or rectosigmoidoscopy, had been done to rule out other findings from Feb 2018 to September 2019.MR defecography (static and dynamic) with 3 T (PHILIPS INGENIA) MRI system having tunnel configuration. After written and informed consent, patient was positioned supine in MR machine gantry . Static imaging performed in the axial T1WI high resolution, axial, coronal and sagittal T2WI high resolution images at rest for anatomical evaluation. Following this,after ultrasound gel instilled in the patient’s rectum and intravaginaly ,dynamic imaging were taken in the midsagittal plane through the anal canal using a T2 weighted sequence. This sequence was ran for almost 2 min, while the patient performs various maneuvers (Kegel (squeeze), valsalva menuvere (strain), and defecation). MR defecography structurally and functionally evaluated in all 3 pelvic floor compartments and associated defects noted and grading of specific findings like organ specific prolapse, pelvic floor relaxiation and descent were measured.
 Results: In our study most common findings were pelvic floor descent and anorectal junction descent in 92.68% cases each followed by rectocele in 82.93% cases. Among the females, vaginal/uterine prolapse were observed in 65.31% cases. Least common findings were paradoxical contraction (8.54%) and sigmoidocele (0%). Significant difference was observed in MRI functional parameters in resting state and during defecation/maximal strain position, utilising HMO system for pelvic floor relaxation and descent, as significant difference (p <0.001S) was observed in all parameters including H line, M line, bladder base descent, cervical/vaginal and anorectal junction descent during resting state and during defecation/maximal strain position. Out of 82 conservative biofeedback therapy was given to 79.27 % patients, surgical management was done in (7.32%) and combination of both therapies was given in 13.41% of cases. Out of 82 patients 68.29% showed benefit from management and showed improvement on follow and 31.71% patients were not improved on follow up.
 Conclusion: As complete survey of the entire pelvis is necessary before surgical repair Magnetic resonance imaging permits evaluation of all three pelvic compartments and as we demonstrated in our study more than one compartment are frequently affected in obstructed defecation syndrome. Static MR Imaging can be also useful to identify the defects responsible for pelvic organ prolapse and stress urinary incontinence, and so help perform site specific repair in surgery, to avoid the high recurrence rates.Findings reported at dynamic MR imaging of the pelvic floor are valuable for selecting candidates for surgical treatment and for indicating the most appropriate surgical approach as detection rate of pathologies increased during defecation / maximal straning as concluded by our study.

Dual differential confocal method for surface profile measurement with a large sensing measurement range.

To meet the requirements of the large sensing measurement range and high axial depth resolution for profile measurement, a dual differential confocal method (DDCM) is proposed in this paper. The DDCM uses the confocal signal to process separately the signal of two pinholes with axial offset, and it adds the two processed signals to obtain an axial response curve with a large slope and linear response range, thereby achieving a high-precision surface profile measurement with no axial scanning. Preliminary experiments show that the DDCM has a sensing measurement range of 0.54 µm and an axial resolution of 1 nm at the numerical aperture of 0.9. Furthermore, the sensing measurement range of the DDCM is approximately 2.9 times that of the differential confocal microscopy.

Relationship between the source size at the diffuser plane and the longitudinal spatial coherence function of the optical coherence microscopy system.

Coherence properties of light sources are indispensable for optical coherence microscopy/tomography as they greatly influence the signal-to-noise ratio, axial resolution, and penetration depth of the system. In the present paper, we report the investigation of longitudinal spatial coherence properties of a pseudothermal light source (PTS) as a function of the laser spot size at the rotating diffuser plate. The laser spot size is varied by translating a microscope objective lens toward or away from the diffuser plate. The longitudinal spatial coherence length, which governs the axial resolution of the coherence microscope, is found to be minimum for the beam spot size of 3.5 mm at the diffuser plate. The axial resolution of the system is found to be equal to an $\sim{13}\,\,{\rm \unicode{x00B5}{\rm m}}$∼13µm at 3.5 mm beam spot size. The change in the axial resolution of the system is confirmed by performing the experiments on standard gauge blocks of a height difference of 15 µm by varying the spot size at the diffuser plate. Thus, by appropriately choosing the beam spot size at the diffuser plane, any monochromatic laser light source can be utilized to obtain high axial resolution irrespective of the source's temporal coherence length. It can provide speckle-free tomographic images of multilayered biological specimens with large penetration depth. In addition, a PTS avoids the use of any chromatic-aberration-corrected optics and dispersion-compensation mechanism unlike conventional setups.

Light-sheet engineering using the Field Synthesis theorem

Recent advances in light-sheet microscopy have enabled sensitive imaging with high spatiotemporal resolution. However, the creation of thin light-sheets for high axial resolution is challenging, as the thickness of the sheet, field of view and confinement of the excitation need to be carefully balanced. Some of the thinnest light-sheets created so far have found little practical use as they excite too much out-of-focus fluorescence. In contrast, the most commonly used light-sheet for subcellular imaging, the square lattice, has excellent excitation confinement at the cost of lower axial resolving power. Here we leverage the recently discovered Field Synthesis theorem to create light-sheets where thickness and illumination confinement can be continuously tuned. Explicitly, we scan a line beam across a portion of an annulus mask on the back focal plane of the illumination objective, which we call C-light-sheets. We experimentally characterize these light-sheets and demonstrate their application on biological samples.

Variable-Angle Nanoplasmonic Fluorescence Microscopy: An Axially Resolved Method for Tracking the Endocytic Pathway.

The study of endocytosis, which encompasses diverse mechanisms in biology, requires the utilization of high axial resolution to monitor molecular behavior on both the cell surface and interior of the cell. We have designed a novel axially resolved fluorescence microscopic technique, termed variable-angle nanoplasmonic fluorescence microscopy. The proof-of-principle of this approach is achieved by selectively following the events in the vicinity of a cell membrane or in a cell. We use a 30 nm Au-coated semitransparent coverslip as the nanoplasmonic chip to achieve both surface plasmon resonance excitation and critical angle excitation by tuning the incident angles. This approach leads to improved axial resolution compared to total internal reflection fluorescence microscopy, which is a common imaging technique in cell biology. It offers a unique opportunity to semiquantitatively determine fluorophore axial distributions in the cell. Observing the epidermal growth factor receptor-mediated endocytosis in Caski cells clearly demonstrates the potential application of this new method for cell biology studies.

Ultrahigh Resolution Polarization Sensitive Optical Coherence Tomography of the Human Cornea with Conical Scanning Pattern and Variable Dispersion Compensation.

Noninvasive corneal imaging is essential for the diagnosis and treatment control of various diseases affecting the anterior segment of the eye. This study presents an ultrahigh resolution polarization sensitive optical coherence tomography instrument operating in the 840 nm wavelength band that incorporates a conical scanning design for large field of view imaging of the cornea. As the conical scanning introduces a dispersion mismatch depending on the scanning angle, this study implemented variable, location dependent, numerical dispersion compensation in order to achieve high axial resolution throughout the imaged volume. The corneal images were recorded in vivo in healthy volunteers showing various details of corneal structures.

Improvement of Performance Degradation in Synthetic Aperture Extension of Enhanced Axial Resolution Ultrasound Imaging Based on Frequency Sweep.

We are studying a method based on the carrier frequency sweep for axial high resolution ultrasonic imaging to provide the range resolution that corresponds to the carrier wavelength. The first proposal for this type of method was based on the focused pulse transmission. Then, to improve the frame rate, the method was extended to a synthetic aperture-type method that transmits divergent pulses. While the method is effective in terms of the frame rate, degradation of the enhanced axial resolution performance is a concern. Therefore, using finite element method simulations and simple experiments, the performance of the synthetic aperture method with high axial resolution is evaluated via comparison with the original method using focused pulses. The evaluation confirmed that the performance degradation of the synthetic aperture method is caused by weakness in the transmitted wave intensity and deterioration of the phase coherence in the reception beamforming. Based on this result, we propose a method that is less affected by the latter cause and show its effectiveness.

Divided-aperture subtraction-differential confocal method with nanoscale axial resolution

In this paper, a divided-aperture subtraction-differential confocal method (DASDCM) is proposed to meet the requirements of nanoscale noncontact height measurements for precision machining, materials science, and biology. The DASDCM divides the spot on the detection focal plane into two groups of circular detection areas, which are symmetrical to the optical axis and consist of two concentric detection pinholes with different sizes in each group. Then, the DASDCM uses a subtraction of the intensity signals received from the two detection pinholes in each group to suppress the interference of the nonconjugated information on the intensity signal; it also uses the differential subtraction of two obtained circular detection signals to obtain a sensitive axial response curve. Thereby, the DASDCM greatly improves the axial resolution while considering the signal-to-noise ratio and axial dynamic range of the system and can realize surface height measurement without axial scanning by using the linear range of the axial response curve. Theoretical analysis and preliminary experiments show that DASDCM has an axial resolution of 2nm with a laser wavelength of λ=632.8 nm and a numerical aperture of NA=0.8. It provides an effective technique for nanoscale height detection with high axial resolution.

Light‐sheet Imaging to Characterize Vascular Development in Murine Retina

The advent of light-sheet fluorescence microscopy (LSFM) has revolutionized the imaging of the cardiovascular system, allowing for visualizing the 3-D intact vascular network with high-spatiotemporal resolution and minimal photobleaching. We introduce the custom-built LSFM combined with simplified passive CLARITY (SPC) method to study the vascular development in murine retina bypassing the flat-mount sample preparation. This imaging strategy enables the rapid acquisition of entire retina with a single scan to interrogate vascular development and study angiogenesis. For the sample preparation, we dissected the retina from C57BL/6 mice at P10 for clearing. The clearing method was modified based on the previous passive CLARITY method. In brief, mouse retinas were fixed in 4% Paraformaldehyde (wt/vol) for 2 hours and transferred to the Eppendorf filled with monomer solution (4% Acrylamide (wt/vol), 0.05% Bis-Acrylamide (wt/vol), and 0.25% VA-044 initiator (wt/vol) in PBS) and incubated overnight. After thorough incubation, we put the sample in 37 degrees water bath for hydrogel polymerization for 4 hours. The retinal were then placed into a clearing solution comprised of 4% w/v sodium dodecyl sulfate (SDS) and 1.25% w/v boric acid (pH 8.5). The samples were incubated at 37 °C until cleared (Figure 1B). Our clearing method allowed for the generation of tissue-hydrogel hybrids to support the intact bowl shape structure of the retina. After the SPC, the retinas were washed with PBS and incubated with Biotinylated GS I4B lectin in 1:20 dilution for overnight and secondary antibody Alexa-488 conjugated streptavidin with 1:100 dilution for 2 days to complete the staining on vasculature. Our in-house dual-sided illumination LSFM applied a continuous wave laser with triple wavelengths as the illumination source. The detection module was installed perpendicular to the illumination plane, and it was composed of a stereo microscope with a 1X magnification objective (NA = 0.25), a scientific CMOS and a set of filters (Figure 1A). The lateral resolution and axial resolution of this LSFM system are 3.25 μm and 5 μm respectively. The cleared retinas were immersed in the refractive index (RI) matching solution (RI: 1.46–1.4844) with 1% agarose solution was mounted in a Borosilicate glass tubing (RI = 1.47) to reduce refraction and reflection among various interfaces. We succeeded in imaging the 3-D vascular network (Figure 1C), demonstrating the feasibility of this strategy to provide a structural analysis of the microvascular development. In addition, the adapted SPC preserved the native structure of the retina comparing to the flat-mount. It further reduces the complexity for clearing by removing vacuum chamber and nitrogen tank. This advanced imaging strategy is not limited to the shallow primary plexus layer for morphometric measurements but providing an accessibility for investigating the deeper secondary vascular plexus in murine. Unlike traditional confocal or wide-field imaging of the flat-mount retina, LSFM allows for rapid scanning with high axial resolution and low photo-bleaching, enabling 3D spatial localization of the tissue structure and cellular events with multi-channels of fluorescence. Support or Funding Information NIH (5R01HL083015-10) Figure 1Open in figure viewerPowerPoint A. Schematic diagram of a dual-sided illumination for the light-sheet fluorescent microscope. B. P10 mouse retinas before SPC (left), after clearing was complete (right) at day 7 of the clearing. C. 3-D perception of Alexa-488 labeled retina samples in ROI displaying the 3D vascular network. Scale bar: (B) 1 mm (C) 200 μm for. M1-10: mirror; PH: pinhole; ND: neutral density filter; BE: beam expander; S: slit; CL1-2: cylindrical lens; L1-4: achromatic doublets; Ob1-2: objective This abstract is from the Experimental Biology 2019 Meeting. There is no full text article associated with this abstract published in The FASEB Journal.

Effect on the longitudinal coherence properties of a pseudothermal light source as a function of source size and temporal coherence.

In the present Letter, a synthesized pseudothermal light source having high temporal coherence (TC) and low spatial coherence (SC) properties is used. The longitudinal coherence (LC) properties of the spatially extended monochromatic light source are systematically studied. The pseudothermal light source is generated from two different monochromatic laser sources: He-Ne (at 632nm) and DPSS (at 532nm). It was found that the LC length of such a light source becomes independent of the parent laser's TC length for a large source size. For the chosen lasers, the LC length becomes constant to about 30μm for a laser source size of ≥3.3 mm. Thus, by appropriately choosing the source size, any monochromatic laser light source depending on the biological window can be utilized to obtain high axial resolution in an optical coherence tomography (OCT) system irrespective of its TC length. The axial resolution of 650nm was obtained using a 1.2 numerical aperture objective lens at a 632nm wavelength. These findings pave the path for widespread penetration of pseudothermal light into existing OCT systems with enhanced performance. A pseudothermal light source with high TC and low SC properties could be an attractive alternative light source for achieving high axial resolution without needing dispersion compensation as compared to a broadband light source.

Nondestructive Measurement of Conformal Coating Thickness on Printed Circuit Board With Ultra-High Resolution Optical Coherence Tomography

Conformal coating (CC) is widely used to protect printed circuit board from corrosion, mold growth, and electrical failures. To ensure effective protection, the thickness of the CC layer needs to be well controlled. However, to date, the coating thickness is usually measured in a destructive way under microscopes. In this paper, we proposed to use optical coherence tomography (OCT) to measure the CC thickness nondestructively. Specifically, to obtain a good accuracy in thickness measurement, we constructed a spectral domain OCT with the ultra-high axial resolution to image the CC layer in three dimensions and developed an image segmentation algorithm to detect the CC layer from the OCT images. Finally, we evaluated the effectiveness of the proposed method by comparing it with the conventional method, and the results demonstrate that the measurement by our method is consistent with that by the microscope. This also indicates that OCT with high axial resolution can potentially be used to measure the CC thickness accurately and nondestructively.

Coronary vessel intimal sequence extraction based on prior boundary constraints in optical coherence tomography image

Optical coherence tomography (OCT) is a new technique applied in cardiovascular system. It can detect vessel intimal, small structure of plaque surface and discover small lesions with its high axial resolution and quantification character. Especially with the application of OCT in characterization of coronary atherosclerotic plaque, diagnosis and treatment strategy making, optimizing percutaneous coronary intervention therapy and assessment after stent planting make the OCT become an efficient tool for cardiovascular disease diagnosis and treatment. This paper presents a novel coronary vessel intimal sequence extraction method based on prior boundary constraints in OCT image. On the basis of conventional Chan-Vese model, we modified the evolutionary weight function to control the evolutionary rate of boundary by adding local information of boundary curve. At the same time, we added the gradient energy term and intimal boundary constraint term based on priori boundary condition to further control the evolutionary of boundary curve. At last, coronary vessel intimal is extracted in a sequence way. The comparison with vessel intimal, manual segmented by clinical scientists (golden standard), indicates that our coronary vessel intimal extraction method is robust to intimal boundary blur, distortion, guide wire shadow and plaque disturbs. The results of this study can be applied to clinical aid diagnosis and precise diagnosis and treatment.