High Spatial Resolution Imaging Techniques Research Articles

The tradeoffs between grating lobes and larger array pitch using null subtraction imaging

Null Subtraction Imaging (NSI) is a new beamforming technique for producing B-mode images that results in high spatial resolution and low computational cost compared to other high-spatial resolution imaging techniques. Previous work has demonstrated that in addition to a narrow main lobe and low side lobes, NSI can also reduce or mitigate grating lobes. Grating lobes can appear when the wavelength of ultrasound is larger than the pitch of the array and these grating lobes can result in imaging artifacts. Lower grating lobes on a larger pitch array could allow larger linear arrays for abdominal imaging with lower element count. Experiments were conducted to quantify the tradeoff between grating lobe levels and pitch size when using NSI. NSI was able to reduce grating lobes by up to 19dB with an element pitch of five times the wavelength. The effects of the DC offset (a tunable parameter of NSI) on grating lobe reduction were also testedand found that NSI with a lower DC offset provides greater reduction in grating lobes, with up to 40dB reduction. The level of grating lobe reduction versus the depth of a target was also testedand found a slight decrease in grating lobe reduction at greater depths.

Risk stratification in cardiomyopathies (dilated, hypertrophic, and arrhythmogenic cardiomyopathy) by cardiac magnetic resonance imaging.

Cardiac magnetic resonance imaging (CMR) is a non-invasive, multiplanar, and high spatial resolution imaging technique, which represents the current gold standard for the evaluation of biventricular volumes and function. Furthermore, unlike other methods, it has the great advantage of characterizing the myocardial tissue by identifying the presence of alterations, such as oedema and focal and diffuse fibrosis. In particular, the late gadolinium enhancement technique makes it possible to identify areas of focal fibrosis that often constitute the substrate for the triggering of threatening ventricular arrhythmias at the basis of sudden cardiac death. For this reason, the use of CMR in the study of cardiomyopathies has become of primary importance, both for the differential diagnosis and for patient risk stratification. In this brief review, the ability of CMR in prognostic stratification of patients with dilated, hypertrophic, and arrhythmogenic cardiomyopathy will be analysed. In particular, the role of CMR in the prediction of arrhythmic risk and in the decision-making process for the implantation of a cardiac defibrillator will be examined.

A comparison of two high spatial resolution imaging techniques for determining carbide precipitate type and size in ferritic 9Cr-1Mo steel

Two high spatial resolution imaging techniques, focused gallium ion beam imaging in conjunction with XeF2 gas (FIB/XeF2) and high-speed atomic force microscopy (HS-AFM), were used to analyse 9Cr-1Mo ferritic steel samples, which had been exposed for extended periods to hot CO2 gas containing traces of CO, H2, H2O and CH4. The carbide precipitates embedded in the metal matrix were observed and their morphology, size and spatial distribution were quantified using these two techniques. The lower resolution of the FIB/XeF2 imaging technique suggested that small carbide precipitates (<50 nm) may be missed, while the existence of a limited flow layer introduced by sample preparation may influence the HS-AFM results. The gallium ion beam was used to remove a thin oxide layer of approximately 50 nm from sample surfaces prior to FIB/XeF2 imaging, avoiding the influence of surface contamination. HS-AFM provided higher resolution (∼5 nm) than FIB/XeF2 imaging. A quantitative comparison of the experimental data confirmed the value of both FIB/XeF2 and HS-AFM for imaging carbide precipitates, while clarifying their strengths and limitations.

Near-field speckle imaging of light localization in disordered photonic systems

Optical localization in strongly disordered photonic media is an attractive topic for proposing novel cavity-like structures. Light interference can produce random modes confined within small volumes, whose spatial distribution in the near-field is predicted to show hot spots at the nanoscale. However, these near-field speckles have not yet been experimentally investigated due to the lack of a high spatial resolution imaging techniques. Here, we study a system where the disorder is induced by random drilling air holes in a GaAs suspended membrane with internal InAs quantum dots. We perform deep-subwavelength near-field experiments in the telecom window to directly image the spatial distribution of the electric field intensity of disordered-induced localized optical modes. We retrieve the near-field speckle patterns that extend over few micrometers and show several single speckles of the order of λ/10 size. The results are compared with the numerical calculations and with the recent findings in the literature of disordered media. Notably, the hot spots of random modes are found in proximity of the air holes of the disordered system.

Intrinsic signal optical imaging of visual brain activity: Tracking of fast cortical dynamics

Hemodynamic-based brain imaging techniques are typically incapable of monitoring brain activity with both high spatial and high temporal resolutions. In this study, we have used intrinsic signal optical imaging (ISOI), a relatively high spatial resolution imaging technique, to examine the temporal resolution of the hemodynamic signal. We imaged V1 responses in anesthetized monkey to a moving light spot. Movies of cortical responses clearly revealed a focus of hemodynamic response traveling across the cortical surface. Importantly, at different locations along the cortical trajectory, response timecourses maintained a similar tri-phasic shape and shifted sequentially across cortex with a predictable delay. We calculated the time between distinguishable timecourses and found that the temporal resolution of the signal at which two events can be reliably distinguished is about 80 milliseconds. These results suggest that hemodynamic-based imaging is suitable for detecting ongoing cortical events at high spatial resolution and with temporal resolution relevant for behavioral studies.

Thin-cap fibroatheroma rupture is associated with a fine interplay of shear and wall stress.

In this review, we summarized the effect of mechanical factors (shear and wall stress) on thin-cap fibroatheroma formation and rupture. To make this review understandable for a biology-oriented audience, we start with detailed definitions of relevant mechanical metrics. We then describe how biomechanics has supported histopathologic efforts to understand the basis of plaque rupture. In addition to plaque rupture, biomechanics also contributes toward the progression of thin-cap fibroatheroma through a multitude of reported mechanobiological mechanisms. We thus propose a new mechanism whereby both shear stress and wall stress interact to create thin-cap fibroatheromas. Specifically, when regions of certain blood flow and wall mechanical stimuli coincide, they synergistically create inflammation within the cellular environment that can lead to thin-cap fibroatheroma rupture. A consequence of this postulate is that local shear stress is not sufficient to cause rupture, but it must coincide with regions of local tissue stiffening and stress concentrations that can occur during plaque progression. Because such changes to the wall mechanics occur over a micrometer scale, high spatial resolution imaging techniques will be necessary to evaluate this hypothesis and ultimately predict plaque rupture in a clinical environment.

Label-free detection of anticancer drug paclitaxel in living cells by confocal Raman microscopy

Confocal Raman microscopy, a non-invasive, label-free, and high spatial resolution imaging technique is employed to trace the anticancer drug paclitaxel in living Michigan Cancer Foundation-7 (MCF-7) cells. The Raman images were treated by K-mean cluster analysis to detect the drug in cells. Distribution of paclitaxel in cells is verified by calculating the correlation coefficient between the reference spectrum of the drug and the whole Raman image spectra. A time dependent gradual diffusion of paclitaxel all over the cell is observed suggesting a complementary picture of the pharmaceutical action of this drug based on rapid binding of free tubulin to crystallized paclitaxel.