Spectral and scatterer-size correlation during angular compounding: simulations and experimental studies

In a previous study, theoretical expressions were derived for the correlation between ultrasonic scatterer-size estimates and their associated spectral measures when echo data are acquired from the same location but at different angles. The results were verified using simulations. In the present work, we further analyze simulation data for these conditions; in addition, we measure the correlations using a cylindrical tissue-mimicking phantom. Experimental and theoretical results show that the relationship of scatterer-size correlation to insonification angle depends on gate duration, gate type and beam profile. Some discrepancies are noted between experimental results and theoretical predictions, particularly when using smaller gated windows. The sources of the discrepancies are discussed. Experimental results using a 6-MHz linear array suggest that, to save acquisition and processing time while reducing variance, a 2 degree-3 degree angular increment step provides efficient angular compounding for scatterer-size imaging with this array. Theoretical predictions can provide estimates of expected correlations between angular acquisitions when compounding with other transducers.     

Spatial resolution in optical coherence elastography of bounded media

Dynamic optical coherence elastography (OCE) tracks mechanical wave propagation in the subsurface region of tissue to image its shear modulus. For bulk shear waves, the lateral resolution of the reconstructed modulus map (i.e., elastographic resolution) can approach that of optical coherence tomography (OCT), typically a few tens of microns. Here we perform comprehensive numerical simulations and acoustic micro-tapping OCE experiments to show that for the typical situation of guided wave propagation in bounded media, such as cornea, the elastographic resolution cannot reach the OCT resolution and is mainly defined by the thickness of the bounded tissue layer. We considered the excitation of both broadband and quasi-harmonic guided waves in a bounded, isotropic medium. Leveraging the properties of broadband pulses, a robust method for modulus reconstruction with minimum artifacts at interfaces is demonstrated. In contrast, tissue bounding creates large instabilities in the phase of harmonic waves, leading to serious artifacts in modulus reconstructions.     

Interventional 4D motion estimation and reconstruction of cardiac vasculature without motion periodicity assumption

Anatomical and functional information of cardiac vasculature is a key component in the field of interventional cardiology. With the technology of C-arm CT it is possible to reconstruct static intraprocedural 3D images from angiographic projection data. Current approaches attempt to add the temporal dimension (4D). In the assumption of periodic heart motion, ECG-gating techniques can be used. However, arrhythmic heart signals and slight breathing motion are degrading image quality frequently.To overcome those problems, we present a reconstruction method based on a 4D time-continuous B-spline motion field. The temporal component of the motion field is parameterized by the acquisition time and does not assume a periodic heart motion. The analytic dynamic FDK-reconstruction formula is used directly for the motion estimation and image reconstruction.In a physical phantom experiment two vessels of size 3.1 mm and 2.3 mm were reconstructed using the proposed method and an algorithm with periodicity assumption. For a periodic motion both methods obtained an error of 0.1 mm. For a non-periodic motion the proposed method was superior, obtaining an error of 0.3 mm/0.2 mm in comparison to 1.2 mm/1.0 mm for the algorithm with periodicity assumption. For a clinical test case of a left coronary artery it could be further shown that the method is capable to produce diameter measurements with an absolute error of 0.1 mm compared to state-of-the-art measurement tools from orthogonal coronary angiography. Further, it is shown for three different clinical cases (left/right coronary artery, coronary sinus) that the proposed method is able to handle a large variability of vascular structures and motion patterns. The complete algorithm is hardware-accelerated using the GPU requiring a computation time of less than 3 min for typical clinical scenarios.     

Differences in the compressive stress-strain response of infiltrating ductal carcinomas with and without lobular features--implications for mammography and elastography

In a previous study, it was noted that in some cases when compressive strains greater than about 5% were applied to tumors removed from the breast, there was an abrupt and irreversible change in the tissue stiffness. The data from that study were further analyzed and infiltrating ductal carcinomas with and without lobular features were selected for additional testing to explore their behavior under compressive strains from 0-10%. Fresh tumor samples were tested using a servo-hydraulic Instron testing machine to apply ramp type displacement loads to the samples. The results show that when strains greater than 5% are applied to the tumor tissue without lobular features, there is an irreversible decrease in the stiffness of the tissue while no such change is noted in the other tumor tissue. The implications for this behavior in making mammographic and elastographic images of the breast were then explored using finite element simulations to determine under what compression conditions could the critical strain threshold be reached in the tumor tissue.     

Spatial characterization of corneal biomechanical properties with optical coherence elastography after UV cross-linking

Corneal collagen cross-linking (CXL) is a clinical treatment for keratoconus that structurally reinforces degenerating ocular tissue, thereby limiting disease progression. Clinical outcomes would benefit from noninvasive methods to assess tissue material properties in affected individuals. Regional variations in tissue properties were quantified before and after CXL in rabbit eyes using optical coherence elastography (OCE) imaging. Low-amplitude (<1µm) elastic waves were generated using micro air-pulse stimulation and the resulting wave amplitude and speed were measured using phase-stabilized swept-source OCE. OCE imaging following CXL treatment demonstrates increased corneal stiffness through faster elastic wave propagation speeds and lower wave amplitudes.OCIS codes: (170.0170) Medical optics and biotechnology, (110.4500) Optical coherence tomography, (170.4580) Optical diagnostics for medicine, (170.6935) Tissue characterization     

Population dynamics under the Laplace assumption

In this paper, we describe a generic approach to modelling dynamics in neuronal populations. This approach models a full density on the states of neuronal populations but finesses this high-dimensional problem by re-formulating density dynamics in terms of ordinary differential equations on the sufficient statistics of the densities considered (c.f., the method of moments). The particular form for the population density we adopt is a Gaussian density (c.f., the Laplace assumption). This means population dynamics are described by equations governing the evolution of the population's mean and covariance. We derive these equations from the Fokker-Planck formalism and illustrate their application to a conductance-based model of neuronal exchanges. One interesting aspect of this formulation is that we can uncouple the mean and covariance to furnish a neural-mass model, which rests only on the populations mean. This enables us to compare equivalent mean-field and neural-mass models of the same populations and evaluate, quantitatively, the contribution of population variance to the expected dynamics. The mean-field model presented here will form the basis of a dynamic causal model of observed electromagnetic signals in future work.     

对比声触诊弹性成像与可视化瞬时弹性成像检测肝脏弹性北大核心CSCD

目的对比观察声触诊弹性成像(STE)与可视化瞬时弹性成像(ViTE)检测肝脏弹性的价值。方法收集478名接受腹部超声检查的受检者,根据检查结果将其分为肝纤维化组(n=147)、肝硬化组(n=162)及健康组(n=169);采用STE和ViTE测量各组肝脏弹性值,观察2种方法检测的一致性、检测成功率、稳定性及其测值的差异。结果STE和ViTE检测成功率差异无统计学意义(P>0.05),其对肝纤维化组及健康组的检测一致性均较好,对肝硬化组的一致性较差。STE及ViTE针对肝纤维化组和健康组的测量结果的稳定性均较好;对肝硬化组,STE稳定性较好,而ViTE稳定性较差。STE与ViTE所测肝纤维化组及健康组肝脏弹性值差异均无统计学意义(P均>0.05),而STE测得肝硬化组肝脏弹性值显著低于ViTE(P<0.05)。STE及ViTE对男性受试者肝脏弹性值的测值均大于女性(P均<0.05),尤以25~50岁受检者为著(P均<0.05)。结论STE与ViTE检测肝脏弹性值的成功率均较高,且对肝纤维化患者和健康人群的一致性和稳定性均较好,而用于检测肝硬化患者的一致性较差;对肝硬化患者,STE检测稳定性较好,而ViTE较差。     

A zero-crossing strain estimator for elastography

A novel zero-crossing tracking strain estimator (ZCT) has been developed for elastography. This technique is based on tracking the zero-crossings between the pre- and postcompression A-lines, and does not require global or adaptive A-line stretching. For multicompression elastography, ZCT can be implemented as a tracking scheme, where a temporal track of the zero-crossings between successive radiofrequency (RF) A-lines is obtained, or as an averaging scheme, where a cumulation of the interframe strains is performed, to yield high elastographic signal-to-noise ratio (SNR). Other advantages of the scheme include fast processing and its potential to be implemented in hardware. The limitations of the technique are the need for small compression steps due to lack of robustness when large compression steps (> 3% applied compression) are used. Simulations and experiments were performed to illustrate its utility as an alternative strain-estimation technique. This technique provides lower SNR but higher contrast-to-noise ratio (CNR) than the conventional strain-estimation techniques in elastography.     

Adaptive spectral strain estimators for elastography

In conventional elastography, internal tissue deformations, induced by external compression applied to the tissue surface, are estimated by cross-correlation analysis of echo signals obtained before and after compression. Conventionally, strains are estimated by computing the gradient of estimated displacement. However, gradient-based algorithms are highly susceptible to noise and decorrelation, which could limit their utility. We previously developed strain estimators based on a frequency-domain (spectral) formulation that were shown to be more robust but less precise compared to conventional strain estimators, In this paper, we introduce a novel spectral strain estimator that estimates local strain by maximizing the correlation between the spectra of pre- and postcompression echo signals using iterative frequency-scaling of the latter; we also discuss a variation of this algorithm that may be computationally more efficient but less precise. The adaptive spectral strain estimator combines the advantages of time- and frequency-domain methods and has outperformed conventional estimators in experiments and 2-D finite-element simulations.     

Spatial contrast sensitivity of migraine patients without aura

Visual disturbances are frequent symptoms in migraine. Since there is a possibility of separate damage in the magno- or parvo-cellular visual pathway in migraine patients, we performed a study including the measurement of static and dynamic spatial contrast sensitivity on 15 patients suffering from migraine without aura under photopic and scotopic conditions. Fifteen healthy volunteers without primary headache served as controls. The results revealed a marked decrease in contrast sensitivity at low spatial frequencies in the migraine patients. Spatial contrast sensitivity demonstrated some lateralization, as the sensitivity to low spatial frequencies obtained through separate eyes showed significantly larger side-differences in migraine patients than in control subjects. These findings suggest that the mechanisms responsible for vision at low spatial frequencies are impaired in migraine patients. This might indicate impaired function of the magnocellular pathways in this condition.     

Ultrasound elastography for the differential diagnosis of nipple retraction

Purpose

Nipple retraction is difficult to diagnose radiologically and extremely worrisome for patients. It occurs most commonly due to pathologies such as previous mastitis or an infiltrative malignancy. With this in mind, the goal of this study was to differentiate benign from malignant lesions of nipple retraction, using the differential characteristics of retroareolar area stiffness, observed by means of the new technological modality of ultrasound elastography (USE).

Materials and methods

Nineteen unilateral nipple retraction cases, including five cases of mammary ductal carcinoma posteriorly infiltrated the areola, two cases of Paget disease, and 12 cases of mastitis, were investigated. Imaging findings [gray-scale ultrasound (US) and USE analyses of the breasts’ nipple–areolar complex], pathological evaluation, and the results of 4 years of follow-up treatment were obtained. The recorded images were evaluated by two different radiologists, and all data were analyzed statistically.

Results

Statistical analysis showed that there was a strong correlation between the two radiologists’ evaluations. The US images were not diagnostic for either the malignant or benign conditions. The correlation between the diagnosis using US and the final diagnosis was calculated as 0.436 (p = 0.006). However, the USE images were more informative since the correlation ratio between the USE results and the final diagnosis was found to be 0.723 (p < 0.001). While the area under the concentration curve (AUC) values that were used for the diagnostic determination of the US results were inconclusive at 0.274 (p < 0.021), the AUC values for USE were significant, with a diagnostic value of 0.866 for all cases (p < 0.01).

Conclusion

The USE modality, which is not commonly used in routine practice, has the potential to solve the problem of differentiation of nipple retraction etiologies in the near future.     

Pixel compounding: resolution-enhanced ultrasound imaging for quantitative analysis

Accurate measurement of structural features represented in medical images is important in clinical trials and patient diagnosis. A key factor for precision is spatial resolution, which in ultrasonic imaging is limited by transducer array arrangements, transmitting frequency, and data acquisition firmware. In this paper, a variation of pixel compounding is proposed to enhance ultrasound resolution using acquired cine loops. The technique operates on a sequence of ultrasound B-scan images acquired with random motion. Subpixel registration is estimated and a maximum a posteriori (MAP) approach with the shift information is used to reconstruct a high-resolution single image. A nonhomogeneous anisotropic diffusion algorithm follows from the estimation process and is implemented to enhance the high-resolution edges. Preliminary tests using simulations and phantom studies show promising results. Pixel compounding can be a powerful preprocessing tool to assure accurate segmentation, measurement, and analysis of ultrasound images.     

Technique for rapid in vitro single-cell elastography

Statistically meaningful assays require scanning a large number of cells in a short time. Here we present a technique for rapid in vitro single-cell elastography. The technique is based on atomic force acoustic microscopy but (1) requires only a few minutes of scan time, (2) can be used on live cells briefly removed from most of the nutrient fluid, (3) does negligible harm or damage to the cell, (4) provides semiquantitative information on the distribution of modulus across the cell and (5) yields data with 1- to 10-nm resolution. We describe the new technique in detail, apply it to baby hamster kidney cells, verify the results and calibrate the images with atomic force microscope force-distance measurements. The technique enables rapid assessment of physical/biochemical signals on the cell modulus and contributes to current understanding of cell mechanics.     

剪切波弹性成像技术判断睾丸生精功能

目的探讨剪切波弹性成像技术能否判断睾丸生精功能受损严重程度。方法纳入38例无精患者(无精组)和34例少弱精患者(少弱精组),另选33名精液正常者为对照组。比较各组间睾丸体积(TV)、睾丸剪切波速度(SWV)及SWV极差的差异。绘制受试者工作特性(ROC)曲线,评估SWV及SWV极差的诊断效能。结果无精组TV明显低于其余2组(P均<0.05);少弱精组与对照组差异无统计学意义(P>0.05)。3组患者年龄差异均无统计学意义(P均>0.05)。无精组SWV及SWV极差显著高于其余2组(P均<0.05),少弱精组与对照组差异无统计学意义(P>0.05)。TV<10 ml睾丸的SWV明显高于TV≥10 ml者(P<0.05)。SWV与TV呈低度负相关(r=-0.42,P<0.05)。SWV极差与TV呈弱相关(r=-0.19,P>0.05)。依据无精组与对照组SWV及SWV极差值建立ROC曲线,SWV截断值为1.73 m/s时,AUC为0.84,敏感度为89.41%、特异度为76.53%。SWV极差为1.54 m/s时,AUC为0.75,敏感...