Probe Footprint Research Articles

Reduction of Pulsed Eddy Current Probe Footprint Using Sequentially Excited Multiple Coils

Reduction of Pulsed Eddy Current Probe Footprint Using Sequentially Excited Multiple Coils

Complete Complementary Coded Excitation Scheme for SNR Improvement of 2D Sparse Array Ultrasound Imaging.

Driving the numerous elements of 2D matrix arrays for 3D ultrasound imaging is very challenging in terms of cable size, wiring and data rate. The sparse array approach tackles this problem by optimally distributing a reduced number of elements over a 2D aperture while preserving a decent image quality and beam steering capabilities. Unfortunately, reducing the number of elements significantly reduces the active probe footprint reducing as a consequence the sensitivity and at the end the signal-to-noise ratio. Here we propose a new coded excitation scheme based on complete complementary codes to increase the signal-to-noise ratio in 3D ultrasound imaging with sparse arrays. These codes are known for their ideal auto-correlation and cross-correlation properties and have been widely used in Code-Division Multiple Access systems (CDMA). An algorithm for generating such codes is presented as well as the adopted imaging sequence. The proposed method has been compared in simulations to other coded excitation schemes and showed significant increase in the signal-to-noise ratio of sparse arrays with no correlation artifacts and no frame rate reduction. The gain in signal-to-noise ratio compared to the case where no coded excitation is used was around [Formula: see text] and the contrast was also improved by [Formula: see text] while the resolution was unchanged.

Factors influencing the Shear Wave Elastography evaluation of the patellar tendon.

There is no clear standardization for tendon Shear Wave Elastography (SWE), and data regarding the factors that influence the correctness of evaluation are scarce. We aimed to determine the intra- and interobserver agreement in patellar tendon SWE, and to establish the influence of various factors on elasticity values. We recruited 37 healthy volunteers; SWE of the patellar tendon was performed by two examiners. The following factors were analyzed: probe frequency, degree of joint flexion, size of region of interest (ROI), distance of the color box from the probe footprint, utilization of coupling gel as standoff, and the effect of physical exercise on elastic modulus values. Highest overall interobserver [k=0.767, 95%CI (0.717-0.799), p<0.001] and intraobserver agreement [k=0.920 (0.909-0.929) for examiner 1, k=0.891 (0.875-0.905) for examiner 2] was obtained with the knee in the neutral position, using the L18-5 probe. With the knee flexed at 30º and 45º, the elasticity values were higher compared to the neutral position (p<0.001). With the probe immersed in 0.25 and 0.50 cm coupling gel, the median values were lower compared to the probe placed on the skin (p=0.001, p=0.018). The ROI dimensions and the placement of the SWE box at the level of the skin or at 0.5 cm below skin did not significantly influence the elastic modulus. After physical exercise, the elasticity values decreased in the proximal and middle portion of the tendon (p=0.002, p<0.001). The best results obtained in patellar tendon SWE were with the knee in neutral position, in the proximal or middle tendon, after 10 minutes of relaxation and with the probe placed directly on the skin with minimal pressure. The size and position of ROI do not significantly influence the examination.

Study on the Effect of Metal Mesh on Pulsed Eddy-Current Testing of Corrosion under Insulation Using an Early-Phase Signal Feature

Corrosion under insulation (CUI) is a major threat to the structural integrity of insulated pipes and vessels. Pulsed eddy-current testing (PECT) is well known in the industry for detecting CUI, but its readings can be easily influenced by nearby conductive objects, including the insulation supporting metal mesh. As a sequel to our previous study, this paper focuses on the surface distribution of eddy currents at the time of the turning off of the driving voltage instead of examining the overall process of eddy current diffusion. Based on the fact that CUI takes place on the outside of the insulated specimen, the probe footprint was calculated only on the specimen surface. The corrosion depth was regarded as an increment to the probe lift-off, whose information was carried in the early PECT signal. Finite element simulations were performed to facilitate the calculation of the probe footprint and predict the signal behavior. The peak value, which appeared in the early phase of the differential PECT signal, was found to be well correlated with the corrosion depth. Further studies revealed that the mild steel mesh could result in the enlargement of the probe footprint and a decrease in the change rate of the peak value in relation to the corrosion depth. Finally, experiments were conducted to verify the simulation results. The presented findings are consistent with the previously reported results and provide a potential alternative to evaluate CUI in specific scenarios where the insulation has a fixed and uniform thickness.

Improved thickness measurement on rough surfaces by using guided wave cut-off frequency

Substantial variability is seen when thickness measurements using conventional ultrasonic time of flight measurements are carried out on rough surfaces; this makes it difficult to estimate corrosion rates when the corrosion mechanism leads to surface roughness. It has been shown that thickness measurements using guided wave cut-off frequencies (through thickness resonance frequencies) can be done at much lower frequencies than conventional time of flight thickness gauging for the same minimum thickness resolution. The lower frequency measurements are less susceptible to variations caused by surface roughness and so will give more consistent and reliable results in cases where corrosion leads to increased surface roughness. Measurements were carried out using guided wave cut-off frequencies on four plates with different surface roughness. On a plate with root mean square (rms) surface roughness of 0.3 mm, the thickness estimates followed the trend predicted from the plate geometry and probe footprint, whereas higher frequency measurements reported in the literature deviated from this trend at an rms roughness of 0.1 mm. The guided wave cut-offcut-off frequency measurements can be done using the same transduction system as that used for large area guided wave monitoring so it is possible to combine large and small area monitoring in a single unit. Frequent measurements enable the wall thickness obtained with guided wave cut-off measurements to be tracked with time, and the low susceptibility of the measurements to surface roughness means that accurate corrosion rates will be obtained.

Effects of the wire mesh on pulsed eddy current detection of corrosion under insulation

ABSTRACT Pulsed eddy current (PEC) technique has been used to detect corrosion under insulation (CUI) for decades, but whether and how the wire mesh laid in the insulation layer affects the detection remains ambiguous. This paper touches on this issue for the first time. The insulated structure was simplified to a carbon steel plate covered by a cladding with an air gap representing the insulation layer, in which the wire mesh was situated. Finite element simulations were performed on the simplified model and found that the aluminium or stainless steel wire mesh had little effect on eddy currents in the plate, while the mild steel wire mesh could cause a considerable increase in the probe footprint and a significant drop of the eddy current density. For the mild steel wire mesh, the magnetic permeability and wire diameter were the main factors affecting the probe footprint and eddy current density. Afterwards, simulations were conducted to analyse the effect of the mild steel wire mesh on the PEC probe performances for evaluating the CUI depth and found that the mild steel wire mesh led to decreases in both the PEC signal amplitude and decay rate. The simulation results were finally verified by experiments.

Analytical Method of Probe Footprint Based on Equivalent Model of Pulsed Eddy Current Field

In the pulsed eddy current testing for the local wall-thinning corrosion of ferromagnetic components, it is significative to accurately calculate the effective coverage area of the probe for analyzing the spatial resolution of corrosion detection. Based on the analytical expressions of the pulsed eddy current field of ferromagnetic plate, an equivalent model is established to analyze the probe footprint, by taking the eddy current ring in the conductor as the excitation source, and by replacing the conductor region with non-conductive and magnetic conductive medium. First, the boundary value problem of the equivalent model is solved analytically, and the contribution function of the eddy current loop is proposed to calculate the voltage signal in the detection coil induced by a single eddy current loop in the conductor. Then, the voltage induced by the eddy current field in the equivalent model is derived by integrating the contribution function in the whole conductor region, and the equivalent model is verified by comparing with the existing analytical results. Finally, combined with the thickness detection results of a steel plate with rectangular groove defects, the analysis method for the footprint of the probe is proposed using the contribution function. Considering not only the distribution of eddy current field induced by the excitation coil but also the influence of the shape and position of the detection coil, the analytical method for the probe footprint proposed in this article can provide more detailed and accurate guidance for the probe design in the eddy current testing.

Ultrasound guided internal jugular vein cannulation in infants: Comparative evaluation of novel modified short axis out of plane approach with conventional short axis out of plane approach.

Background and Aims:Central venous cannulation (CVC) through right internal jugular vein (IJV) route is routinely performed in paediatric patients undergoing major surgery and in those admitted to intensive care units. A novel technique (modified short-axis out-of-plane [MSA-OOP]) to improve first pass success rate of ultrasound-guided IJV CVC in neonates and infants is being compared with conventional SA-OOP method.Methods:A total of 120 patients were enroled in the study over a period of 6 months. All paediatric patients with age <1 year and weight <10 kg who underwent a major surgery requiring CVC were included. Patients were randomised to either of the two approaches of ultrasound-guided IJV cannulation; SA-OOP and modified SA-OOP (MSA-OOP). In modified approach, the midline of probe footprint was marked with a radio-opaque barium wire that casted a central acoustic shadow on ultrasound screen.Results:In MSA-OOP group, 83.1% of patients were cannulated in the first attempt as compared to 49.2% patients in group SA-OOP. Patients in MSA-OOP group required significantly fewer attempts for successful CVC as compared to patients in the SA-OOP group ( MSA-OOP: median = 1, interquartile range [1-1]; SAOOP: median = 2, interquartile range [1-2], P < 0.001, Mann–Whitney U-test).Conclusion:The use of MSA-OOP ultrasound technique for IJV CVC cannulation results in a higher first-attempt success rate and reduces the number of cannulation attempts.

Brain-shift compensation using intraoperative ultrasound and constraint-based biomechanical simulation.

During brain tumor surgery, planning and guidance are based on preoperative images which do not account for brain-shift. However, this deformation is a major source of error in image-guided neurosurgery and affects the accuracy of the procedure. In this paper, we present a constraint-based biomechanical simulation method to compensate for craniotomy-induced brain-shift that integrates the deformations of the blood vessels and cortical surface, using a single intraoperative ultrasound acquisition. Prior to surgery, a patient-specific biomechanical model is built from preoperative images, accounting for the vascular tree in the tumor region and brain soft tissues. Intraoperatively, a navigated ultrasound acquisition is performed directly in contact with the organ. Doppler and B-mode images are recorded simultaneously, enabling the extraction of the blood vessels and probe footprint, respectively. A constraint-based simulation is then executed to register the pre- and intraoperative vascular trees as well as the cortical surface with the probe footprint. Finally, preoperative images are updated to provide the surgeon with images corresponding to the current brain shape for navigation. The robustness of our method is first assessed using sparse and noisy synthetic data. In addition, quantitative results for five clinical cases are provided, first using landmarks set on blood vessels, then based on anatomical structures delineated in medical images. The average distances between paired vessels landmarks ranged from 3.51 to 7.32 (in mm) before compensation. With our method, on average 67% of the brain-shift is corrected (range [1.26; 2.33]) against 57% using one of the closest existing works (range [1.71; 2.84]). Finally, our method is proven to be fully compatible with a surgical workflow in terms of execution times and user interactions. In this paper, a new constraint-based biomechanical simulation method is proposed to compensate for craniotomy-induced brain-shift. While being efficient to correct this deformation, the method is fully integrable in a clinical process.

Footprint characteristics revised for field‐scale soil moisture monitoring with cosmic‐ray neutrons

AbstractCosmic‐ray neutron probes are widely used to monitor environmental water content near the surface. The method averages over tens of hectares and is unrivaled in serving representative data for agriculture and hydrological models at the hectometer scale. Recent experiments, however, indicate that the sensor response to environmental heterogeneity is not fully understood. Knowledge of the support volume is a prerequisite for the proper interpretation and validation of hydrogeophysical data. In a previous study, several physical simplifications have been introduced into a neutron transport model in order to derive the characteristics of the cosmic‐ray probe's footprint. We utilize a refined source and energy spectrum for cosmic‐ray neutrons and simulate their response to a variety of environmental conditions. Results indicate that the method is particularly sensitive to soil moisture in the first tens of meters around the probe, whereas the radial weights are changing dynamically with ambient water. The footprint radius ranges from 130 to 240 m depending on air humidity, soil moisture, and vegetation. The moisture‐dependent penetration depth of 15 to 83 cm decreases exponentially with distance to the sensor. However, the footprint circle remains almost isotropic in complex terrain with nearby rivers, roads or hill slopes. Our findings suggest that a dynamically weighted average of point measurements is essential for accurate calibration and validation. The new insights will have important impact on signal interpretation, sensor installation, data interpolation from mobile surveys, and the choice of appropriate resolutions for data assimilation into hydrological models.

The COsmic-ray Soil Moisture Interaction Code (COSMIC) for use in data assimilation

Abstract. Soil moisture status in land surface models (LSMs) can be updated by assimilating cosmic-ray neutron intensity measured in air above the surface. This requires a fast and accurate model to calculate the neutron intensity from the profiles of soil moisture modeled by the LSM. The existing Monte Carlo N-Particle eXtended (MCNPX) model is sufficiently accurate but too slow to be practical in the context of data assimilation. Consequently an alternative and efficient model is needed which can be calibrated accurately to reproduce the calculations made by MCNPX and used to substitute for MCNPX during data assimilation. This paper describes the construction and calibration of such a model, COsmic-ray Soil Moisture Interaction Code (COSMIC), which is simple, physically based and analytic, and which, because it runs at least 50 000 times faster than MCNPX, is appropriate in data assimilation applications. The model includes simple descriptions of (a) degradation of the incoming high-energy neutron flux with soil depth, (b) creation of fast neutrons at each depth in the soil, and (c) scattering of the resulting fast neutrons before they reach the soil surface, all of which processes may have parameterized dependency on the chemistry and moisture content of the soil. The site-to-site variability in the parameters used in COSMIC is explored for 42 sample sites in the COsmic-ray Soil Moisture Observing System (COSMOS), and the comparative performance of COSMIC relative to MCNPX when applied to represent interactions between cosmic-ray neutrons and moist soil is explored. At an example site in Arizona, fast-neutron counts calculated by COSMIC from the average soil moisture profile given by an independent network of point measurements in the COSMOS probe footprint are similar to the fast-neutron intensity measured by the COSMOS probe. It was demonstrated that, when used within a data assimilation framework to assimilate COSMOS probe counts into the Noah land surface model at the Santa Rita Experimental Range field site, the calibrated COSMIC model provided an effective mechanism for translating model-calculated soil moisture profiles into aboveground fast-neutron count when applied with two radically different approaches used to remove the bias between data and model.

Label-free in vivo GRIN-lens optical resolution photoacoustic micro-endoscopy

In this letter, the feasibility of label-free in vivo GRIN-lens optical resolution photoacoustic micro-endoscopy is demonstrated. An image guide with 100 000 single-mode fibers in a 1.4 mm diameter bundle in conjunction with a 0.29 pitch GRIN lens is used in order to transfer a focused scanning spot through the image guide and refocus it into tissue. A high-repetition-rate (up to 600 kHz) ytterbium fiber laser is used in order to enable near real-time imaging capability. Phantom studies indicate 6 μm resolution. The system, with ∼2 mm working distance, overcomes the penetration depth limitation and hence improves the surface laser fluence of previously reported fiber based optical resolution photoacoustic microscopy (OR-PAM). The proposed system with a sub-mm probe footprint is very flexible and now has a significant penetration depth which is another step towards clinical applications.

Label-free in vivo fiber-based optical-resolution photoacoustic microscopy

In this Letter, the capability of label-free fiber-based optical-resolution photoacoustic microscopy is demonstrated. This real-time imaging system takes advantage of image-guide fibers and a unique fiber laser. The 800 μm image-guide consists of 30,000 individual single-mode fibers in a bundle and the diode-pumped, pulsed Ytterbium fiber laser is utilized to perform up to 600 kHz repetition rate. Phantom studies indicate 7 μm resolution. The proposed setup keeps many of the powerful properties of previous tabletop OR-PAM systems, but also offers a submillimeter probe footprint and high flexibility due to the nature of the image-guide. This system could have significant clinical impact for endoscopic applications where the thin fiber can be inserted into the body.

A novel technique for ultrasound-guided supraclavicular subclavian cannulation

Objective Ultrasound-guided subclavian (SC) access is an inadequately described procedure in the current literature. We recommend using the endocavitary (EC) probe to perform supraclavicular (SUP) SC line placement and evaluate emergency medicine residents' skill and comfort in using this technique after an education session. Methods The EC probe placed in the SUP fossa was used for direct visualization of SUP SC cannulation. Fifteen residents at the University of Utah were educated on this technique. Residents were graded on their ability to visualize the SC vein and answered questions before and after the training. Residents reported their comfort with the technique using a 5-point Likert scale. Results All 15 residents correctly identified the SC vein and rated their understanding of the SUP anatomy before and after the training; average resident comfort rating was 2.9 before training and 4.4 after (95% confidence interval, 1.1-1.9; P < .001). Most residents reported significant ease of visualization and stated that they would likely attempt the procedure as their next method of central venous access. Conclusion Ultrasound-guided SUP SC central access using the EC probe may be technically advantageous because of the relatively small probe footprint and fit into the SUP fossa. All participants were able to identify the vein and reported subjective improvement in the understanding of anatomy and comfort with the procedure after a brief training session.

Characterization of Benign and Malignant Solid Breast Masses: Harmonic Versus Nonharmonic 3D Power Doppler Imaging

The aim of this study was to compare the diagnostic performance of nonharmonic ultrasound (US) and tissue harmonic imaging (THI) using three-dimensional (3D) power Doppler sonographic technique to classify benign and malignant breast tumors by vascularization. From January 2003 to February 2004, we evaluated 200 patients and one of lobular carcinoma in situ was excluded from the malignant category. One hundred and ninety-nine subjects were enrolled. All subjects with one or more breast masses were studied with 3D power Doppler US nonharmonic and harmonic technologies. Sixteen of 199 subjects were excluded because masses exceeded 3 cm limit of our US probe's footprint ( n = 5) or no harmonic Doppler information ( n = 11). A total of 97 benign and 86 pathologically proven malignant breast tumor images were analyzed. 3D power Doppler US imaging was performed using a Voluson730 US system. Three histogram indices, the vascularization index (VI), flow index (FI) and vascularization-flow index (VFI), on both nonharmonic and harmonic images were calculated for the intratumor and for shells with an outside thickness of 3 mm surrounding the breast lesion. A multilayer perception (MLP) neural network classifier used the vascularity indices to determine whether the breast tumors are benign or malignant. The receiver operating characteristic (ROC) curves are performed to estimate the diagnostic performances for nonharmonic and harmonic methods. ROC curve analysis used overall age, volume, VI, FI and VFI for both intratumor and shells with an outside thickness of 3 mm surrounding the breast lesions in nonharmonic US and THI. The area under the ROC curve (A Z) was 0.9086 and 0.9009 ( p = 0.3770). The sensitivity was 90.7% and 83.7% ( p = 0.72), respectively, and the specificity was 92.8% and 92.8% ( p = 1.00), respectively. In conclusion, the performance of 3D power Doppler US with respect to the characterization of solid breast masses as benign or malignant was not significantly improved with tissue harmonic imaging. (E-mail: darren_chen@cch.org.tw)