Higher Harmonic Imaging Research Articles

High throughput wide field second harmonic imaging of giant unilamellar vesicles.

Cell-sized giant unilamellar vesicles (GUVs) are an ideal tool for understanding lipid membrane structure and properties. Label-free spatiotemporal images of their membrane potential and structure would greatly aid the quantitative understanding of membrane properties. In principle, second harmonic imaging is a great tool to do so, but the low degree of spatial anisotropy that arises from a single membrane limits its application. Here, we advance the use of wide-field high throughput SH imaging by SH imaging with the use of ultrashort laser pulses. We achieve a throughput improvement of 78% of the maximum theoretical value and demonstrate subsecond image acquisition times. We show how the interfacial water intensity can be converted into a quantitative membrane potential map. Finally, for GUV imaging, we compare this type of nonresonant SH imaging to resonant SH imaging and two photon imaging using fluorophores.

High-order harmonic generation in the water window from mid-IR laser sources

We investigate the harmonic response of neon atoms to mid-IR laser fields ($2000--3000$ nm) using a single active electron (SAE) model and the fully ab initio all-electron $R$ matrix with time dependence (RMT) method. The laser peak intensity and wavelength are varied to find suitable parameters for high-harmonic imaging in the water window. Comparison of the SAE and RMT results shows qualitative agreement between them as well as parameters such as the cutoff frequency predicted by the classical three-step model. However, there are significant differences in the details, particularly in the predicted conversion efficiency. These details indicate the possible importance of multielectron effects, as well as a strong sensitivity of quantitative predictions on specific aspects of the numerical model.

Diagnostic Value of High Frame Rate Contrast-enhanced Ultrasonography and Post-processing Contrast Vector Imaging for Evaluation of Focal Liver Lesions: A Feasibility Study

This study evaluated the feasibility of contrast vector imaging (CVI) to characterize focal liver lesions. From July to October 2019, we prospectively enrolled 30 patients with focal liver lesions (hepatocellular carcinoma [HCC] [n = 19], metastasis [n = 8], combined HCC-cholangiocarcinoma [CC] [n = 1], intra-hepatic CC [n = 1] and sclerosed hemangioma [n = 1]). Contrast-enhanced ultrasound (CEUS) was performed with high frame rate contrast harmonic imaging technique by one radiologist, and post-processing CVI was obtained and analyzed by two radiologists. On combined CVI with CEUS, the staining pattern was significantly predominant in HCCs (9/11, 81.8%), while peripheral rim was frequent in non-HCCs (5/8, 62.5%) (p = 0.020). HCCs exhibited feeding arteries (8/11, 45.5%) and high velocity variance (10/11, 90.9 %), whereas non-HCCs showed detour pattern (4/8, 50.0%) with either a high or low velocity variance (4/8, 50.0%, both), with no significant inter-group differences (p = 0.052 and 0.080, respectively). In conclusion, CVI was feasible and provided quantitative and multi-parametric information of different types of hepatic tumors.

A 35 MHz/105 MHz Dual-Element Focused Transducer for Intravascular Ultrasound Tissue Imaging Using the Third Harmonic.

The superharmonic imaging of tissue has the potential for high spatial and contrast resolutions, compared to the fundamental and second harmonic imaging. For this technique, the spectral bandwidth of an ultrasound transducer is divided for transmission of ultrasound and reception of its superharmonics (i.e., higher than the second harmonic). Due to the spectral division for the transmission and reception, transmitted ultrasound energy is not sufficient to induce superharmonics in media without using contrast agents, and it is difficult that a transducer has a −6 dB fractional bandwidth of higher than 100%. For the superharmonic imaging of tissue, thus, multi-frequency array transducers are the best choice if available; transmit and receive elements are separate and have different center frequencies. However, the construction of a multi-frequency transducer for intravascular ultrasound (IVUS) imaging is particularly demanding because of its small size of less than 1 mm. Here, we report a recently developed dual-element focused IVUS transducer for the third harmonic imaging of tissue, which consists of a 35-MHz element for ultrasound transmission and a 105-MHz element for third harmonic reception. For high quality third harmonic imaging, both elements were fabricated to have the same focus at 2.5 mm. The results of tissue mimicking phantom tests demonstrated that the third harmonic images produced by the developed transducer had higher spatial resolution and deeper imaging depth than the fundamental images.

Material discrimination and mixture ratio estimation in nanocomposites via harmonic atomic force microscopy.

Harmonic atomic force microscopy (AFM) was employed to discriminate between different materials and to estimate the mixture ratio of the constituent components in nanocomposites. The major influencing factors, namely amplitude feedback set-point, drive frequency and laser spot position along the cantilever beam, were systematically investigated. Employing different set-points induces alternation of tip–sample interaction forces and thus different harmonic responses. The numerical simulations of the cantilever dynamics were well-correlated with the experimental observations. Owing to the deviation of the drive frequency from the fundamental resonance, harmonic amplitude contrast reversal may occur. It was also found that the laser spot position affects the harmonic signal strengths as expected. Based on these investigations, harmonic AFM was employed to identify material components and estimate the mixture ratio in multicomponent materials. The composite samples are composed of different kinds of nanoparticles with almost the same shape and size. Higher harmonic imaging offers better information on the distribution and mixture of different nanoparticles as compared to other techniques, including topography and conventional tapping phase. Therefore, harmonic AFM has potential applications in various fields of nanoscience and nanotechnology.

High harmonic exploring on different materials in dynamic atomic force microscopy

In atomic force microscopy (AFM), high-frequency components consisted in dynamic tip-sample interaction have been recently demonstrated as a promising technique for exploring more extensive material properties. Here we present an exploratory study of high harmonic atomic force microscopy by force-spectroscopy and high harmonic imaging. Since these components are very weak compared to the fundamental response, we firstly designed a high harmonic cantilever by tuning the second order flexural resonance frequency to an integer 6 times of its fundamental mode (i.e. ω 2=6 ω 1). Moreover, it is verified that high harmonic can discern extra features than topographies on different samples with amplitude/frequency modulation (AM/FM) dynamic AFM mode. In AM mode, the first resonance amplitude and 6th harmonic amplitude were discussed. The 6th harmonic is more sensitive than the first order response. In FM mode, it is noted that the decaying rate of the 6th harmonic frequency is approximately 6 multiples to the slope of the fundamental frequency shift when the tip approaches to the surface of sample. This non-destructive method was also adopted to investigate the local interlayer coupling and intercalation in the two-dimensional graphene films tentatively.

Corrosion process monitoring by AFM higher harmonic imaging

The atomic force microscope (AFM) was invented in 1986 as an alternative to the scanning tunnelling microscope, which cannot be used in studies of non-conductive materials. Today the AFM is a powerful, versatile and fundamental tool for visualizing and studying the morphology of material surfaces. Moreover, additional information for some materials can be recovered by analysing the AFM’s higher cantilever modes when the cantilever motion is inharmonic and generates frequency components above the excitation frequency, usually close to the resonance frequency of the lowest oscillation mode. This method has been applied and developed to monitor corrosion processes. The higher-harmonic imaging is especially helpful for sharpening boundaries between objects in heterogeneous samples, which can be used to identify variations in steel structures (e.g. corrosion products, steel heterogeneity). The corrosion products have different chemical structures because they are composed of chemicals other than the original metal base (mainly iron oxides). Thus, their physicochemical properties are different from the primary basis. These structures have edges at which higher harmonics should be more intense because of stronger interference between the tip and the specimen structure there. This means that the AFM’s higher-harmonic imaging is an excellent tool for monitoring surficial effects of the corrosion process.

Cantilever optimization for applications in enhanced harmonic atomic force microscopy

Structural design and optimization of atomic force microscopy (AFM) cantilevers were performed with multi-objectives to tailor one or more higher-order resonance frequencies to be integer multiples of the fundamental one and to keep the minimum change of stiffness. The tuning of frequency properties was achieved by altering mass distribution of the cantilever via cutting a rectangular slot. Rayleigh-Ritz method and finite element analysis were incorporated in the optimizations of slot dimension and position. The determined structure was fabricated on a conventional AFM cantilever by using focused ion beam etching. Higher harmonic imaging with the micromachined cantilever on a two-component polymer blend was subsequently performed. Experiments and theoretical simulations demonstrated that the harmonic amplitude contrast was improved up to at least 3 times. The enhancement of harmonic signals can benefit the discrimination of materials with different elastic properties.

Higher Harmonic Imaging of Anomalies and Defects in Thin Plates by Local Resonance

Higher Harmonic Imaging of Anomalies and Defects in Thin Plates by Local Resonance

Higher-harmonic Imaging of Artificial Closed Flaws with Variable Gaps

Higher-harmonic Imaging of Artificial Closed Flaws with Variable Gaps

Retrospective Analysis of Ultrasound-Detected Bleeding Complications after Ultrasound-Guided Transcutaneous Kidney Biopsies

The aim of this retrospective single-center study was to examine ultrasound-detected complications after diagnostic parenchymal renal biopsies. After 471 ultrasound-guided kidney biopsies (225 native kidneys and 246 renal allografts), ultrasound revealed hematomas (21.9%), arterio-venous fistulas (8.9%), active bleeding (1.1%) and hematuria (0.4%). Only 0.8% of all patients required invasive intervention such as coiling (n = 3) and surgical procedures (n = 1). Three episodes of bleeding (0.6%) were solved with manual compression. One patient (0.2%) needed an irrigation catheter because of hematuria. Furthermore, six patients (1.3%) received blood transfusion. Ultrasound-guided biopsies are safe. With modern ultrasound machines using multi-frequency transducers with high resolution and harmonic imaging, even marginal bleeding after renal biopsy is detected.

Multiphysics analysis of an asymptotically correct piezoelectric sensor under static and dynamic load

This paper presents a versatile platform named V ariational A symptotic M ethod (VAM), to model and analyze a piezoelectric cantilever sensor under static and dynamic load. Variational asymptotic method is a mathematically rigorous dimentional reduction methodology and has been previously used to model different structures which can be defined by an energy functional having one or more small inherent parameters; but, it has never been explicitly applied to capture the multiphysics behavior of a sensor. Piezoelectric based sensing technology has seen an explosive growth in the last decade with its various applications in different domain, such as energy harvesters, aerospace application, soft robotics, wind turbine, biomechanics, etc. So, an efficient mathematical model is highly required to get a better insight of the multiphysics behavior of an electromechanical structure. The present study highlights the capability of the theory to effectively capture the electromechanical response of a piezo-sensor under any static or dynamic load. The example problems considered in this present study include a single layer piezo-sensor as well as a double layer piezo-sensor bonded with aluminum. For static analysis, we have testified the model under a constant tip load. The discussed method effectively captures the voltage distribution across the thickness of the structure which is one of the fundamental parameter for a sensor model. The response accuracy obtained through variational asymptotic method is very good compared with the 3D simulation response performed in ABAQUS. For dynamic analysis a single layered piezo-sensor has been studied under a tip harmonic force. The structure response is studied for both damped as well as undamped conditions. Displacement and corresponding voltage output for specific excitation frequency which is close to its first natural frequency has been studied. The model efficacy under dynamic load has been validated with the experimental study performed by Ly et al. (2011). The present model has numerous potential applications like in PZT cantilever design for chemo-sensing, disease diagnostic, energy harvesting for self powered electronics, AFM higher harmonic imaging etc. The present theory along with the piezoelectric physics have been implemented in a modified version of VABS II (2004).

Enhancing the optical lever sensitivity of microcantilevers for dynamic atomic force microscopy via integrated low frequency paddles

A method is presented to enhance the optical lever sensitivity in dynamic atomic force microscopy (AFM) by nearly an order of magnitude over a wide frequency bandwidth. This is achieved by fabricating or releasing a paddle with a soft hinge close to the free end of the AFM microcantilever such that the paddle resonance frequency is well below the fundamental resonance frequency of the microcantilever. We show a significant increase in signal to noise ratio when cantilever motion is observed at the paddle for AFM systems that are not limited by thermal noise. Also, any effects due to the excitation of the second eigenmode were decoupled by locating the paddle at the node of the second eigenmode. We use these probes for higher harmonic imaging in amplitude modulated AFM (AM–AFM) on a standard polymer blend made of polystyrene and low density polyethylene. We demonstrate significantly improved contrast in higher harmonic images when observing cantilever motion at the paddle. Thus this microcantilever design can improve significantly conventional cantilever performance for dynamic AFM and is compatible with low-cost, high yield microfabrication processes.

Polarization contrast of nanoscale waveguides in high harmonic imaging

The optical polarization response of a structured material is one of its most significant properties, carrying information about microscopic anisotropies as well as chiral features and spin orientations. Polarization analysis is therefore a key element of imaging and spectroscopy techniques throughout the entire spectrum. In the case of extreme ultraviolet (EUV) radiation, however, both the preparation and detection of well-defined polarization states remain challenging. As a result, polarization-sensitive EUV microscopy based on table-top sources has not yet been realized, despite its great potential, for example, in nanoscale magnetic imaging. Here, we demonstrate polarization contrast in coherent diffractive imaging using high harmonic radiation and investigate the polarization properties of nanoscale transmission waveguides. We quantify the achievable polarization extinction ratio for different waveguide geometries and wavelengths. Our results demonstrate the utility of slab waveguides for efficient EUV polarization control and illustrate the importance of considering polarization contrast in the imaging of nanoscale structures.

ピッチキャッチ斜角入射による表面及び表面直下の微細欠陥の高調波可視化

ピッチキャッチ斜角入射による表面及び表面直下の微細欠陥の高調波可視化

Fast Stiffness Mapping of Cells Using High-Bandwidth Atomic Force Microscopy.

The cytoskeleton controls cellular morphology and mediates the mechanical interactions between a cell and its environment. Atomic force microscopy (AFM) has the unique capability to map cytoskeletal mechanics and structures with nanometer resolution. However, whole-cell cytomechanical imaging with conventional AFM techniques is limited by low imaging speed. Here, we present fast nanomechanical mapping of cells using high-bandwidth AFM (HB-AFM), where >10(6) nanoindentation measurements were acquired in ∼10 min-a task that would take weeks to finish using conventional AFM. High-bandwidth measurements enabled capture of the entire tip-sample interaction for each tap on cells, engendering a new measurement ("force phase") that exceeds the contrast of conventional tapping mode and enabling spectral visualization of >10 harmonics. The abundance of measurements allowed discovery of subtle cytomechanical features, including the stiffness of fibers of the cellular spectrin network in situ. This approach bridges HB-AFM and high-harmonic imaging and opens future opportunities for measuring the dynamic mechanical properties of living cells.

J0420303 水浸高調波法による繰返負荷過程における塑性域変化の可視化

J0420303 水浸高調波法による繰返負荷過程における塑性域変化の可視化

High throughput second harmonic imaging for label-free biological applications.

Second harmonic generation (SHG) is inherently sensitive to the absence of spatial centrosymmetry, which can render it intrinsically sensitive to interfacial processes, chemical changes and electrochemical responses. Here, we seek to improve the imaging throughput of SHG microscopy by using a wide-field imaging scheme in combination with a medium-range repetition rate amplified near infrared femtosecond laser source and gated detection. The imaging throughput of this configuration is tested by measuring the optical image contrast for different image acquisition times of BaTiO₃ nanoparticles in two different wide-field setups and one commercial point-scanning configuration. We find that the second harmonic imaging throughput is improved by 2-3 orders of magnitude compared to point-scan imaging. Capitalizing on this result, we perform low fluence imaging of (parts of) living mammalian neurons in culture.

An improved time-base transformation scheme for computing waveform deformation during nonlinear propagation of ultrasound

Nonlinear propagation plays an important role in various applications of medical ultrasound, like higher harmonic imaging and high intensity focused ultrasound (HIFU) treatment. Simulation of nonlinear ultrasound fields can greatly assist in explaining experimental observations and in predicting the performance of novel procedures and devices. Many numerical simulations are based on the generic split-step approach, which takes the ultrasound field at the transducer plane and propagates this forward over successive parallel planes. Usually, the spatial steps between the planes are small and the diffraction, attenuation, and nonlinear deformation may be treated as separate substeps. For the majority of methods, e.g., for all KZK-type methods, the nonlinear substep relies on the implicit solution of the one-dimensional Burgers equation, which is implemented using a time-base transformation. This generally works fine, but when the shock wave regime is approached, reduced spatial steps are required to avoid time points to cross over, and the method can become notoriously slow. This paper analyses the fundamental difficulty with the common time base transformation, and provides an alternative that does not suffer from the mentioned slowdown. Numerical results will be shown to demonstrate that this alternative will allow much larger spatial steps without compromising the numerical accuracy.

Higher-harmonic imaging of the plastic zone in front of a fatigue crack tip

The plastic zone in front of a small fatigue crack in an SM 400 steel plate of 4 mm thickness is imaged by immersion local resonance technique, in which a plate sample is excited to resonance vibrations in the thickness direction by long-tone burst waves of large amplitude and a high-pass filter extracts higher-harmonic components from the received ultrasonic signal. For a sample with Luders’ lines, the crack tip plastic zone and cracked area are clearly imaged by the 5th harmonic amplitude of the incident resonance frequency. Also, a higher-harmonic time-delay image exhibits the crack tip plastic zone.