Axial Resolution Research Articles

Coherent linking between confocal amplitude image and confocal phase image in dual-comb microscopy

We propose a method for integrating confocal amplitude and phase images obtained through dual-comb microscopy (DCM). DCM combines the benefits of confocal laser microscopy and quantitative phase microscopy, offering high axial resolution and scan-less imaging. By leveraging the coherence between confocal amplitude and phase images within the same DCM system, we accurately determine the number of phase wrapping iterations, thereby eliminating ambiguity in phase wrapping. We demonstrate this approach using samples with micrometer-range optical thickness and nanometer-scale surface roughness. The results demonstrate an expanded axial range, spanning from micrometers to millimeters, while maintaining nanometer-level axial resolution. This integrated DCM imaging technique enables the simultaneous acquisition of confocal amplitude image and absolute phase image, thus enhancing its potential for wide-axial-dynamic-range imaging across various applications.

Gradient transformation-weighted centroid: enhancing peak localization precision in the line chromatic confocal sensing system

Line chromatic confocal imaging (LCI) is an advanced system used for quick and accurate three-dimensional surface imaging without vertical mechanical scanning. It is extensively employed for fast industrial inspection. For high-speed and accurate measurement characteristics of the LCI technique, a rapid and accurate peak localization method is important. In this paper, we propose a gradient transform weight centroid method (GTWC) to improve the accuracy of peak positioning, without compromising high-speed characteristics. This method helps reconstruct the 3D profile at a higher axial resolution by reducing the full width at half maximum (FWHM) without altering the original structure of the LCI system. Both simulations and experiments show the feasibility and good performance of this method.

Video-rate two-photon microendoscopy using second harmonic resonance fiber scanning

We present a 2.5-mm-diameter resonant fiber scanning two-photon microendoscope with a 30-mm long forward-viewing rigid probe tip that enables video-rate imaging (20 Hz frame rate) suitable for hand-held imaging of tissues without motion artifacts. Higher-order harmonic oscillation scanning techniques are developed to significantly increase the frame rate compared to prior published fiber scanning microendoscopy designs while maintaining the field-of-view (∼125 µm), the optical resolution (1.2 µm lateral and 10.9 µm axial resolution, full width at half maximum), and the spatial sampling (1250 circumferential pixels per spiral × 20 radial pixels over the diameter; 210 spirals per frame, ∼4 spiral samples per resolvable pixel) compared to a traditional scan using the fundamental resonance. 3D printed mounts were created to reduce the cost and simplify the fabrication for the fiber scanner without compromising performance or stability (<0.3 µm drift over 84 hours). A custom long-wavelength (∼1.08 µm) femtosecond fiber laser is coupled into several meters of fiber to realize a flexible, hand-held device for long-wavelength multiphoton microendoscopy.

Tailoring the Microstructure and Porosity of Porous Piezoelectric Ceramics for Ultrasonic Transducer Application.

Porous piezoelectric ceramics and composites are advantageous for ultrasonic transducers due to their capability to decouple longitudinal and transverse modes, their improved voltage sensitivity, and their enhanced acoustic matching. However, the design and fabrication of porous piezoelectric ultrasonic transducers with excellent electromechanical properties are still challenging. In this work, porous lead zirconate titanate (PZT) ceramics with an aligned pore structure were prepared using the freeze-cast technique, and the effect of porous structure and porosity on the electromechanical parameters was investigated. The introduction of an aligned pore structure is beneficial to enhance the electromechanical properties and reduce the acoustic impedance. A high d33 (∼530 pC/N), a higher kt (∼0.676), and a lower acoustic impedance (∼10.4 MRalys) were achieved in the porous PZT ceramic with the porosity of 44 vol %. The effect of porosity and pore structure on the decoupling degree of vibration modes and ferroelectric polarization was considered to correct the homogeneous medium model, which can quantify the relationship between the kt and porosity of the porous structure. A demonstration of a piezoelectric ultrasonic transducer based on freeze-cast porous PZT ceramics was presented, which exhibits a -6 dB bandwidth of 52% and a theoretical axial resolution of 520 μm. This work therefore provides a potential alternative of piezoelectric ultrasonic transducers for nondestructive testing and imaging applications.

Rapid full-color serial sectioning tomography with speckle illumination and ultraviolet excitation

Three-dimensional (3D) high-resolution large-volume imaging has remained a challenge. Translational rapid ultraviolet-excited sectioning tomography (TRUST) achieves rapid and cost-effective whole-organ subcellular imaging through iterative optical scanning and mechanical sectioning. However, the axial resolution is limited by the mechanical sectioning thickness or the UV light penetration depth in tissue. Here, assisted with high-and-low-frequency (HiLo) microscopy (HiLoTRUST), the optical sectioning thickness has been reduced from tens of micrometers to ~5.8 µm. In addition, HiLoTRUST has attained a finer mechanical sectioning thickness (10–15 µm) compared to TRUST (50 µm). For high-content imaging as in TRUST, we employed two additional UV light-emitting diodes (LEDs) specifically for uniform illumination. The full-color imaging ability and improved axial resolution of HiLoTRUST have been validated by two-dimensional (2D)/3D imaging of various mouse organs and human lung cancer specimens. HiLoTRUST offers a cost-effective, full-color, and high-resolution 3D imaging approach, showing its great potential in 3D histology applications.

Patient‐Mounted Neuro Optical Coherence Tomography for Targeted Minimally Invasive Micro‐Resolution Volumetric Imaging in Brain In Vivo

Targeted neuroimaging plays a vital role in evaluating pathologies and guiding interventions in deep brain regions, such as biopsy, laser ablation, and deep brain stimulation. However, current neuroimaging techniques face several challenges when it comes to imaging the deep brain. These challenges include limited imaging depth, a narrow field of view, low resolution, and a lack of real‐time imaging and stereotactic deployment capabilities. To address these challenges, a patient‐mounted neuro optical coherence tomography (neuroOCT) system that combines a lightweight 5 degrees‐of‐freedom skull‐mounted robot (Skullbot) with a neuroendoscope measuring ≈0.6 mm in diameter is introduced. This innovative system enables targeted and minimally invasive neuroimaging with an axial resolution of ≈2.4 μm and a transverse resolution of around 4.5 μm. The Skullbot can be securely attached to the head and precisely deploys the neuroendoscope with an accuracy of ±1.5 mm in the transverse direction and ±0.25 mm in the longitudinal direction. This allows for motion‐insensitive stereotactic imaging within the brain. By utilizing the neuroOCT system, targeted imaging of a tumor in a brain phantom is successfully demonstrated. Furthermore, the system's capability for in vivo micro‐resolution volumetric neuroimaging of fine structures within a mouse brain is validated.

Ultrasound in Skin Cancer: Why, How, and When to Use It?

Skin cancer is the most common cancer in human beings. Ultrasound is a powerful and non-invasive imaging technique that has expanded its use in dermatology, including in the skin cancer field. The full range of critical anatomical information provided by ultrasound cannot be deduced from a naked eye examination, palpation, or other imaging techniques such as dermoscopy, confocal microscopy, magnetic resonance imaging, or PET-CT (Positron Emission Tomography-Computed Tomography). This review practically analyzes the main ultrasonographic features of the most common types of skin cancers and the performance of the locoregional staging according to the literature, which is illustrated by state-of-the-art clinical and ultrasonographic correlations. The most common types of skin cancer show recognizable ultrasonographic patterns. Among the current radiological imaging techniques, ultrasound has the highest axial spatial resolution. Compared to other imaging techniques used in dermatology, it shows the great advantage of penetrating the soft tissues thoroughly, which allows us to detect and identify the most common skin types of skin cancer, including both the primary tumor and its locoregional metastases.

Sub-60-nm isotropic 3D super-resolution microscopy through self-interference field excitation

Due to its unique optical sectioning capability, confocal laser scanning microscopy (CLSM) can provide highly sensitive, highly specific imaging of specimens in three dimensions and has been recognized as an indispensable tool for biological and medical studies. Nonetheless, the spatial resolution of CLSM is constrained by the diffraction nature, with λ/2 resolution laterally (xy) and 1.5λ resolution axially (z). To improve the imaging resolution beyond the diffraction limit as well as to achieve its isotropy, we present a strategy of mirror-assisted self-interference field excitation (SIEx) highly nonlinear microscopy. The imaging principle has been theoretically modeled and investigated in accordance with the Wolf vector diffraction theory. The experimental demonstration of isotropic three-dimensional SIEx nanoscopy, assisted with the ultrahigh-order optical nonlinearity of photon avalanching nanoparticles, was achieved utilizing a common laser-scanning microscope configuration, resulting in a lateral resolution of 54 nm (λ/15) and an axial resolution of 57 nm (λ/15) with one single beam from a low-power, continuous-wave, near-infrared laser (19kW⋅cm−2). We further extended the applicability of the SIEx scheme to biological imaging and demonstrated super-resolution imaging for immunolabeled actin filaments of BSC-1 cells with an isotropic full width at half maximum of ∼67nm (λ/13). Our facile SIEx methodology can, in principle, be seamlessly integrated with the existing and widely available laser-scanning fluorescence microscopes without adding any complexity, thereby enabling their capability of 3D isotropic super-resolution imaging.

Photoreceptor outer segment reflectivity with ultrahigh resolution visible light optical coherence tomography in systemic hydroxychloroquine use.

To evaluate outer retinal organization in normal subjects and those using hydroxychloroquine (HCQ) with ultrahigh resolution visible light optical coherence tomography (VIS-OCT). Forty eyes of 22 adult subjects were recruited from a tertiary care retina practice including controls (20 eyes, 12 subjects, mean age 40±22yrs, mean logMAR BCVA 0.19, 90% female) and subjects with a history of HCQ use (20 eyes, 10 subjects, mean age 62±17yrs, mean logMAR BCVA 0.03, 67% female). Each subject was imaged using a custom-built VIS-OCT device (axial resolution 1.3μm) and FDA-approved OCT devices. Using VIS-OCT, control subjects demonstrate 5 and 6 hyperreflective bands in the foveal and parafoveal regions, respectively, between the outer nuclear layer and Bruch's membrane. These bands demonstrate intensity profiles complementary to the known histopathologic distribution of rods and cones. In comparison to controls, subjects taking HCQ demonstrate blunting of all bands, particularly bands 2-4. In all cases of suspected or known toxicity, VIS-OCT demonstrated attenuation of band 3i and in no cases was there attenuation of other bands that was more severe than band 3i, suggesting that changes in the reflectivity of Band 3i may be the earliest identifiable sign of HCQ toxicity. VIS-OCT of the outer retina demonstrates a unique outer retinal banding pattern corresponding to photoreceptor density profiles. There is a notable attenuation of the photoreceptor outer segment reflectivity profile associated with early HCQ toxicity. This finding may be an early, and possibly reversible, sign of HCQ toxicity, primarily impacting the cones.

Comparison of intravascular ultrasound-guided with optical coherence tomography-guided percutaneous coronary intervention for left main distal bifurcation lesions: Rationale and design of the ISOLEDS trial

BackgroundPercutaneous coronary intervention (PCI) can provide benefits for anatomically suitable left main coronary artery (LMCA) lesions. When compared to traditional coronary angiography (CAG) -guided PCI, the use of intravascular ultrasound (IVUS) guidance has shown significant long-term prognostic improvements in LMCA PCI. Optical coherence tomography (OCT) offers a higher axial resolution than IVUS. However, there is currently a lack of relevant randomized controlled trials investigating the use of OCT specifically for left main distal bifurcation lesions. MethodsThe ISOLEDS trial is an ongoing multicenter study that aims to compare IVUS-guided PCI with OCT-guided PCI for patients with true LMCA distal bifurcation lesions. This prospective, randomized, controlled, non-inferiority trial will enroll a total of 664 patients with visually-defined Medina 1,1,1 or 0,1,1 classification of left main distal bifurcation lesions. The patients will be randomly assigned in a 1:1 ratio to either IVUS-guided or OCT-guided PCI. The primary endpoint is to assess the occurrence of target lesion failure (TLF) within 12 months after the procedure. After undergoing PCI, patients are required to visit the hospital for a 12-month clinical follow-up. During this clinical assessment, CAG can be performed to evaluate the status of target lesions. DiscussionThe ISOLEDS trial represents the first attempt to compare two distinct intracoronary imaging techniques for guiding PCI in patients with true LMCA distal bifurcation lesions. By evaluating and comparing the outcomes of these two imaging techniques, the trial results will aid operators in selection of the most effective approach for guiding PCI in these patients.

Demonstration of in-vivo simultaneous 3D imaging with 18F-FDG and Na131I using Compton–PET system

Simultaneous imaging of the SPECT tracer 131I and PET tracer 18F is important in the diagnosis of high- and low-grade thyroid cancers because high-grade thyroid cancers have high 18F-FDG and low 131I uptake, while low-grade thyroid cancers have high 131I and low 18F-FDG uptake. In this study, Na131I and 18F-FDG were simultaneously imaged using the Compton-PET system, in vivo. The angular resolution and sensitivity of the Compton camera with 356 keV gamma ray measured using a 133Ba point source were 12.3° and 2 × 10−5, respectively. The spatial resolution and sensitivity of PET were measured with a 22Na point source. The transaxial and axial spatial resolutions of the PET at the center of the FOV were 1.15 mm and 2.04 mm, respectively. Its sensitivity was 1.2 × 10−4. In-vivo images of the 18F and 131I isotopes were simultaneously acquired from mice. These showed that 18F-FDG was active in the heart, brown fat, and brain, while Na131I was active in the thyroid, stomach, and bladder. Artifacts were found in the Compton camera images when the activity of 131I was much lower than that of 18F. This study demonstrates the potential of simultaneous clinical imaging of 18F and 131I.

Impact of Sigmoid Sinus Anatomy on Assessing the Feasibility of the Retrofacial Access to the Entire Jugular Fossa Before Surgery.

The jugular fossa (JF) is a challenging area for surgical approaches because of its complex anatomy and proximity to neurovascular structures. The study evaluates the feasibility of the neuronavigated microsurgical transmastoid extended infralabyrinthine extradural retrofacial approach (mTEIER-A) in human head specimens for accessing the entire intraosseous JF in relation to the position of the sigmoid sinus (SS), horizontal angle of attack, and size of the SS. The mTEIER-A was performed on human head specimens. Before dissection, the position of the SS, horizontal angle of attack, and size of the SS were measured on tilted axial high resolution computed tomography scans; after dissection, access to the lateral aspect of the JF on dissected human head specimens and on postoperative high-resolution computed tomography scans was examined. The position of the SS was classified relative to a predefined reference line, and the feasibility of retrofacial access was documented. SS positions located medial to the reference line (P1) and horizontal angles >12.5° significantly enhance retrofacial access to the lateral aspect of the JF, whereas the size of the SS has a limited impact. Depending on the position of the SS and the horizontal angle of access, mTEIER-A provides sufficient retrofacial access to the lateral aspect of the JF. These findings emphasize the need for precise preoperative planning and suggest that mTEIER-A could minimize the need for more invasive approaches, potentially reducing related morbidity. Further clinical studies are recommended to validate these findings.

Lens-free on-chip 3D microscopy based on wavelength-scanning Fourier ptychographic diffraction tomography

Lens-free on-chip microscopy is a powerful and promising high-throughput computational microscopy technique due to its unique advantage of creating high-resolution images across the full field-of-view (FOV) of the imaging sensor. Nevertheless, most current lens-free microscopy methods have been designed for imaging only two-dimensional thin samples. Lens-free on-chip tomography (LFOCT) with a uniform resolution across the entire FOV and at a subpixel level remains a critical challenge. In this paper, we demonstrated a new LFOCT technique and associated imaging platform based on wavelength scanning Fourier ptychographic diffraction tomography (wsFPDT). Instead of using angularly-variable illuminations, in wsFPDT, the sample is illuminated by on-axis wavelength-variable illuminations, ranging from 430 to 1200 nm. The corresponding under-sampled diffraction patterns are recorded, and then an iterative ptychographic reconstruction procedure is applied to fill the spectrum of the three-dimensional (3D) scattering potential to recover the sample’s 3D refractive index (RI) distribution. The wavelength-scanning scheme not only eliminates the need for mechanical motion during image acquisition and precise registration of the raw images but secures a quasi-uniform, pixel-super-resolved imaging resolution across the entire imaging FOV. With wsFPDT, we demonstrate the high-throughput, billion-voxel 3D tomographic imaging results with a half-pitch lateral resolution of 775 nm and an axial resolution of 5.43 μm across a large FOV of 29.85 mm2 and an imaging depth of >200 μm. The effectiveness of the proposed method was demonstrated by imaging various types of samples, including micro-polystyrene beads, diatoms, and mouse mononuclear macrophage cells. The unique capability to reveal quantitative morphological properties, such as area, volume, and sphericity index of single cell over large cell populations makes wsFPDT a powerful quantitative and label-free tool for high-throughput biological applications.

Optical Coherence Tomography of Van Der Waals Heterostructures Using Extreme Ultraviolet Light

AbstractNew experimental methods with high out‐of‐plane spatial sensitivity combined with ultrafast temporal resolution can revolutionize the understanding of charge‐ and heat‐transfer dynamics occurring at interfaces. In this work, a step forward is taken in this direction by applying coherence tomography with extreme ultraviolet (EUV) light to different van der Waals heterostructures, which enables a 3D sample reconstruction with nanoscopic axial resolution. Furthermore, the measurements and, more in general, the approach is confirmed by ab initio calculations of the refractive index of layered materials that we compare to existing databases of empirical data. The EUV coherence tomography contrast is estimated in a broad spectral range (photon energy 65 –100 eV). This work sets the basis for the development of a new spectroscopy tool that, thanks to the temporal profile of EUV light sources and the high axial resolution of coherence tomography, can become the ideal probe of ultrafast processes occurring in van der Waals heterostructures and buried nanoscale opto‐electronic devices.

Frequency selective illumination for high aperture coherence scanning interferometry

Abstract Coherence scanning interferometry is a widely used optical topography measurement technique, which can achieve axial resolutions in the sub-nanometer regime. Nevertheless, in the lateral dimension it is inherently diffraction limited and multiple problems arise when approaching this limit. Especially for challenging surface topographies like steep slopes or small grating periods measurement artifacts start to cause massive deviations in the 3D reconstruction of the surface due to the increased influence of noise on increasingly weak signals. In this study we present an illumination approach for Linnik-type CSI, which highlights oblique incident angles of the illuminating light cone in high numerical aperture (0.95) systems. It is demonstrated, that this approach can significantly improve the signal-to-noise ratio for measurements at steep surface slopes and therefore increase the subsequent surface reconstruction.

High-resolution ultrasound imaging based on spatio-temporal MUSIC

Abstract Time-reversal MUltiple SIgnal Classification (TR-MUSIC) is known for its super-resolution capability in locating point scatterers. However, a prerequisite for the application of the TR-MUSIC method is a thorough understanding of the properties of the medium and its background Green’s function. In general, it is difficult to obtain an accurate model of the Green’s function in advance for non-uniform or complex media, necessitating the use of approximate Green’s functions. When TR-MUSIC relies on these approximations, the impact on lateral resolution may be minimal, but the axial resolution is significantly reduced. In addition, we have proposed the Range-MUSIC (R-MUSIC) method, which exploits the linear relationship between the rotation of the echo phases and the positions of the scatterers. This approach uses subbands of different frequencies, differentiating multiple point scatterers by the speed of phase rotation associated with each frequency. By analyzing the profile in the time domain of echoes within the noise subspace, R-MUSIC achieves super-resolution in the axial direction without improving lateral resolution. Therefore, our study combines R-MUSIC with TR-MUSIC to improve axial resolution while maintaining lateral resolution. Through simulation and experimental evidence, we have shown that this combined approach yields better imaging performance than either method used independently.

Line-field confocal optical coherence tomography based on tandem interferometry with a focus-tunable lens.

This article introduces an innovative line-field confocal optical coherence tomography (LC-OCT) system based on tandem interferometry, featuring a focus-tunable lens for dynamic focusing. The principle of tandem interferometry is first recalled, and an analytical expression of the interferometric signal detected is established in order to identify the influence of key experimental parameters. The LC-OCT system is based on a Linnik-type imaging interferometer with a focus-tunable lens for focus scanning, coupled to a Michelson-type compensating interferometer using a piezoelectric linear translation stage for coherence plane scanning. The system achieves axial and lateral image resolutions of approximately 1 µm over the entire imaging depth (400 µm), in line with conventional LC-OCT. Vertical section images (B-scans) of skin acquired at 14.3 fps reveal distinguishable structures within the epidermis and dermis. Using refocusing and stitching, images of a tissue phantom were obtained with an imaging depth superior to 1.4 mm. The system holds promise for LC-OCT miniaturization, along with enhanced imaging speed and extended imaging depth.

Research on 3D Reconstruction of Paleontological Fossils Based on Photoacoustic Microscopy

Abstract The focus on three-dimensional morphological analysis of endogenous trace fossils has emerged as a prominent aspect in the study of palaeobiological fossils. Photoacoustic imaging technology, renowned for its deep penetration, high resolution and non-destructiveness, holds considerable promise in exploring fossil morphology. In this work, a solid-coupling-based photoacoustic microscopic imaging system was developed, leveraging this technology to investigate small-scale physical fossils. The proposed system enabled layered imaging of various fossil specimens, achieving a lateral resolution exceeds 35 μm and an axial resolution superior to 8.8815 μm. The three-dimensional reconstruction results were obtained through image processing algorithms. This system was proved to be efficient to imaging the small-scale physical fossils.

2D spatiotemporal passive cavitation imaging and evaluation during ultrasound thrombolysis based on diagnostic ultrasound platform

Acoustic cavitation plays a critical role in various biomedical applications. However, uncontrolled cavitation can lead to undesired damage to healthy tissues. Therefore, real-time monitoring and quantitative evaluation of cavitation dynamics is essential for understanding underlying mechanisms and optimizing ultrasound treatment efficiency and safety. The current research addressed the limitations of traditionally used cavitation detection methods by developing introduced an adaptive time-division multiplexing passive cavitation imaging (PCI) system integrated into a commercial diagnostic ultrasound platform. This new method combined real-time cavitation monitoring with B-mode imaging, allowing for simultaneous visualization of treatment progress and 2D quantitative evaluation of cavitation dosage within targeted area. An improved delay-and-sum (DAS) algorithm, optimized with a minimum variance (MV) beamformer, is utilized to minimize the side lobe effect and improve the axial resolution typically associated with PCI. In additional to visualize and quantitatively assess the cavitation activities generated under varied acoustic pressures and microbubble concentrations, this system was specifically applied to perform 2D cavitation evaluation for ultrasound thrombolysis mediated by different solutions, e.g., saline, nanodiamond (ND) and nitrogen-annealed nanodiamond (N-AND). This research aims to bridge the gap between laboratory-based research systems and real-time spatiotemporal cavitation evaluation demands in practical uses. Results indicate that this improved 2D cavitation monitoring and evaluation system could offer a useful tool for comprehensive evaluating cavitation-mediated effects (e.g., ultrasound thrombolysis), providing valuable insights into in-depth understanding of cavitation mechanisms and optimization of cavitation applications.

O-PRESS: Boosting OCT axial resolution with Prior guidance, Recurrence, and Equivariant Self-Supervision

Optical coherence tomography (OCT) is a noninvasive technology that enables real-time imaging of tissue microanatomies. The axial resolution of OCT is intrinsically constrained by the spectral bandwidth of the employed light source while maintaining a fixed center wavelength for a specific application. Physically extending this bandwidth faces strong limitations and requires a substantial cost. We present a novel computational approach, called as O-PRESS, for boosting the axial resolution of OCT with Prior guidance, a Recurrent mechanism, and Equivariant Self-Supervision. Diverging from conventional deconvolution methods that rely on physical models or data-driven techniques, our method seamlessly integrates OCT modeling and deep learning, enabling us to achieve real-time axial-resolution enhancement exclusively from measurements without a need for paired images. Our approach solves two primary tasks of resolution enhancement and noise reduction with one treatment. Both tasks are executed in a self-supervised manner, with equivariance imaging and free space priors guiding their respective processes. Experimental evaluations, encompassing both quantitative metrics and visual assessments, consistently verify the efficacy and superiority of our approach, which exhibits performance on par with fully supervised methods. Importantly, the robustness of our model is affirmed, showcasing its dual capability to enhance axial resolution while concurrently improving the signal-to-noise ratio.