Nondestructive inspection of metal specimen using tone-burst vibro-acoustography

Even though the pulse-echo ultrasonic technique is commonly used for the assessment of metal structures, it has some inherent limitations. Vibro-acoustography (VA) is a relatively new ultrasonic technique which has demonstrated a great potential in revealing defects in objects, however it is traditionally used to analyze the integrity of specimens made of low-stiffness materials. This work presents the evaluation of the performance of VA technique for the inspection of a steel structure, which was manufactured with defects of known geometry on its inner surface. All the inspection process was done automatically, from the data acquisition to the image processing for characterizing the defects. Experimental results show that VA was able to identify and characterize even the smallest defects in the structure, with a diameter of 2 mm. In addition, the results show that VA was able to characterize the artificial defects in the steel structure with almost the same errors as the traditional pulse-echo method, which indicates a potential use of VA in the inspection of materials with high mechanical stiffness.

Ex vivo vibro-acoustography characterization of osteoporosis in an experimental mice model

Background

Osteoporosis is a highly prevalent multifactorial osteometabolic disease, classically diagnosed, in vivo, by dual energy X-ray absorptiometry (DXA). This study evaluated osteoporosis, ex vivo, using vibro-acoustography (VA), an elastographic technique based on ultrasound radiation force.

Methods

Three groups of mice femurs were used: (I) control group (CG), (II) osteoporosis group (OG) and (III) treated osteoporosis group (TOG), in which the animals received pamidronate, an antiresorptive drug. Evaluation was performed in an acoustic tank, using two high frequency focused beams produced by a confocal ultrasonic transducer. A hydrophone registered the low frequency acoustic response (AR) of bone samples. We used micro-computed tomography (microCT) as the reference standard and evaluated the correlation between VA and microCT parameters.

Results

The spectral analyses of the ARs with estimated area under the curve (AUC) values (mean; st. dev.) were, respectively, 1.29e^-07 and 9.32e^-08 for the CG, 3.25e^-08 and 2.16e^-08 for the OG, and 1.50e^-07 and 8.37e^-08 for the TOG. VA differentiated the experimental groups (P<0.01) and the results were reproducible [interclass correlation coefficient (ICC): 0.43 (95% CI: 0.15-0.71)]. There was also a statistically significant association between VA and microCT connectivity (Conn.) (r=0.80; P<0.01) and connectivity density (Conn. D) (r=0.76; P<0.01).

Conclusions

These results encourage further studies aimed at evaluating the potential use of VA for the diagnosis of osteoporosis as a relatively low-cost and radiation-free alternative to DXA.

Biomimetic phantom with anatomical accuracy for evaluating brain volumetric measurements with magnetic resonance imaging

Purpose: Brain image volumetric measurements (BVM) methods have been used to quantify brain tissue volumes using magnetic resonance imaging (MRI) when investigating abnormalities. Although BVM methods are widely used, they need to be evaluated to quantify their reliability. Currently, the gold-standard reference to evaluate a BVM is usually manual labeling measurement. Manual volume labeling is a time-consuming and expensive task, but the confidence level ascribed to this method is not absolute. We describe and evaluate a biomimetic brain phantom as an alternative for the manual validation of BVM. Methods: We printed a three-dimensional (3D) brain mold using an MRI of a three-year-old boy diagnosed with Sturge-Weber syndrome. Then we prepared three different mixtures of styrene-ethylene/butylene-styrene gel and paraffin to mimic white matter (WM), gray matter (GM), and cerebrospinal fluid (CSF). The mold was filled by these three mixtures with known volumes. We scanned the brain phantom using two MRI scanners, 1.5 and 3.0 Tesla. Our suggestion is a new challenging model to evaluate the BVM which includes the measured volumes of the phantom compartments and its MRI. We investigated the performance of an automatic BVM, i.e., the expectation-maximization (EM) method, to estimate its accuracy in BVM. Results: The automatic BVM results using the EM method showed a relative error (regarding the phantom volume) of 0.08, 0.03, and 0.13 ( ± 0.03 uncertainty) percentages of the GM, CSF, and WM volume, respectively, which was in good agreement with the results reported using manual segmentation. Conclusions: The phantom can be a potential quantifier for a wide range of segmentation methods.

Patient-specific neurosurgical phantom: assessment of visual quality, accuracy, and scaling effects

BACKGROUND

Training in medical education depends on the availability of standardized materials that can reliably mimic the human anatomy and physiology. One alternative to using cadavers or animal bodies is to employ phantoms or mimicking devices. Styrene-ethylene/butylene-styrene (SEBS) gels are biologically inert and present tunable properties, including mechanical properties that resemble the soft tissue. Therefore, SEBS is an alternative to develop a patient-specific phantom, that provides real visual and morphological experience during simulation-based neurosurgical training.

RESULTS

A 3D model was reconstructed and printed based on patient-specific magnetic resonance images. The fused deposition of polyactic acid (PLA) filament and selective laser sintering of polyamid were used for 3D printing. Silicone and SEBS materials were employed to mimic soft tissues. A neuronavigation protocol was performed on the 3D-printed models scaled to three different sizes, 100%, 50%, and 25% of the original dimensions. A neurosurgery team (17 individuals) evaluated the phantom realism as "very good" and "perfect" in 49% and 31% of the cases, respectively, and rated phantom utility as "very good" and "perfect" in 61% and 32% of the cases, respectively. Models in original size (100%) and scaled to 50% provided a quantitative and realistic visual analysis of the patient's cortical anatomy without distortion. However, reduction to one quarter of the original size (25%) hindered visualization of surface details and identification of anatomical landmarks.

CONCLUSIONS

A patient-specific phantom was developed with anatomically and spatially accurate shapes, that can be used as an alternative for surgical planning. Printed models scaled to sizes that avoided quality loss might save time and reduce medical training costs.

Preliminary results of vibro-acoustography evaluation of bone surface and bone fracture

Background

Vibro-acoustography (VA) uses two co-focused ultrasound beams with slightly different frequencies. The beams interact and generate a low-frequency focus to excite an object.

Methods

A two-element confocal ultrasound transducer with central frequency at 3.2 MHz was used to generate the low-frequency excitation (30 kHz) and the response of the bone to that excitation was acquired by a dedicated hydrophone. The face of the confocal transducer was positioned parallel to the surface of the bone at a focal length of 7 cm. The hydrophone was fixed to the side of the transducer, out of the path of the ultrasonic beam.

Results

The resulting image clearly showed the bone fracture with resolution of 0.25 mm and high contrast with well-defined borders.

Conclusions

In this paper, we present preliminary results of VA imaging of bone surface and of bone fracture using an experimental set-up. Our results encourage future studies using VA to evaluate bone fractures.

Reproducibility of abdominal fat assessment by ultrasound and computed tomography

Objective:

To test the accuracy and reproducibility of ultrasound and computed tomography (CT) for the quantification of abdominal fat in correlation with the anthropometric, clinical, and biochemical assessments.

Materials and Methods:

Using ultrasound and CT, we determined the thickness of subcutaneous and intra-abdominal fat in 101 subjects-of whom 39 (38.6%) were men and 62 (61.4%) were women-with a mean age of 66.3 years (60-80 years). The ultrasound data were correlated with the anthropometric, clinical, and biochemical parameters, as well as with the areas measured by abdominal CT.

Results:

Intra-abdominal thickness was the variable for which the correlation with the areas of abdominal fat was strongest (i.e., the correlation coefficient was highest). We also tested the reproducibility of ultrasound and CT for the assessment of abdominal fat and found that CT measurements of abdominal fat showed greater reproducibility, having higher intraobserver and interobserver reliability than had the ultrasound measurements. There was a significant correlation between ultrasound and CT, with a correlation coefficient of 0.71.

Conclusion:

In the assessment of abdominal fat, the intraobserver and interobserver reliability were greater for CT than for ultrasound, although both methods showed high accuracy and good reproducibility.

Evaluation of postural balance in mild cognitive impairment through a three-dimensional electromagnetic system

Introduction

Elderly people with cognitive impairment are at greater risk for falls; thus, an understanding of the earliest stages of cognitive decline is necessary.

Objective

To compare postural balance between elderly people with and without mild cognitive impairment using a three-dimensional system.

Methods

Thirty elderly people with mild cognitive impairment and thirty healthy elderly subjects were selected. Static posturography was performed using three-dimensional electromagnetic equipment and the following parameters were evaluated: maximum displacement, mean speed and total trajectory. Open- and closed-eye stabilometric variable comparisons between groups and within each group were carried out, and a relationship between the Mini Mental State Examination and the total trajectory of all elderly subjects was determined.

Results

The analysis among open- and closed-eye conditions showed a significant difference in maximum anteroposterior displacement in the control group and a significant difference in all stabilometric variables in the mild cognitive impairment group. A significant difference between the groups in all variables in the closed-eye condition was observed. There was a strong correlation between cognitive performance and total trajectory.

Conclusion

Evaluations showed decrease in balance in elderly people with mild cognitive impairment. Presence of anteroposterior displacement can be an early sign of postural control impairment, and the evaluation with visual restriction can be useful in detecting small postural instabilities.

Chirp- and random-based coded ultrasonic excitation for localized blood-brain barrier opening

Chirp- and random-based coded excitation methods have been proposed to reduce standing wave formation and improve focusing of transcranial ultrasound. However, no clear evidence has been shown to support the benefits of these ultrasonic excitation sequences in vivo. This study evaluates the chirp and periodic selection of random frequency (PSRF) coded-excitation methods for opening the blood-brain barrier (BBB) in mice. Three groups of mice (n  =  15) were injected with polydisperse microbubbles and sonicated in the caudate putamen using the chirp/PSRF coded (bandwidth: 1.5–1.9 MHz, peak negative pressure: 0.52 MPa, duration: 30 s) or standard ultrasound (frequency: 1.5 MHz, pressure: 0.52 MPa, burst duration: 20 ms, duration: 5 min) sequences. T1-weighted contrast-enhanced MRI scans were performed to quantitatively analyze focused ultrasound induced BBB opening. The mean opening volumes evaluated from the MRI were mm3, mm3and mm3 for the chirp, random and regular sonications, respectively. The mean cavitation levels were V.s, V.s and V.s for the chirp, random and regular sonications, respectively. The chirp and PSRF coded pulsing sequences improved the BBB opening localization by inducing lower cavitation levels and smaller opening volumes compared to results of the regular sonication technique. Larger bandwidths were associated with more focused targeting but were limited by the frequency response of the transducer, the skull attenuation and the microbubbles optimal frequency range. The coded methods could therefore facilitate highly localized drug delivery as well as benefit other transcranial ultrasound techniques that use higher pressure levels and higher precision to induce the necessary bioeffects in a brain region while avoiding damage to the surrounding healthy tissue.

Two-dimensional simulations of displacement accumulation incorporating shear strain

Using ultrasound images to track large tissue deformations usually requires breaking up the deformation into steps and then summing the resulting displacement estimates. The accumulated displacement estimation error therefore depends not only on the error in each step but also on the statistical relationships between estimation steps. These relationships have not been thoroughly studied. Building on previous work with one-dimensional (1-D) simulations, the work reported here measured error variance for single-step and accumulated displacement estimates using two-dimensional (2-D) numerical simulations of ultrasound echo signals, subjected to both normal and axial shear strain as well as electronic noise. Previous results from 1-D simulations were confirmed, showing that errors due to electronic noise are negatively correlated between steps and accumulate slowly, while errors due to strain are positively correlated and accumulate quickly. These properties hold for both normal and axial shear strain. An analysis of 2-D kernel size for tissue under normal and axial shear strain was also performed. Under axial shear strain, error variance tends to increase with larger lateral kernel sizes but decrease for larger axial kernel sizes; the opposite relationship holds under normal strain. A combination of these two types of strain limits the practical kernel size in both dimensions.

A hybrid transducer to magnetically and ultrasonically evaluate magnetic fluids

Ultrasound, magnetic fields, and optical techniques have been explored for clinical diagnosis and therapy. However, these techniques have limitations. In this study, we constructed and characterized a transducer to magnetically and ultrasonically investigate samples labeled with magnetic particles. The transducer is a hybrid system consisting of an ac biosusceptometer (ACB) and an ultrasonic transducer. The basic operation principle consisted of measuring the magnetization and microvibrations of ferromagnetic particles (37 and 70 μm) mixed in yogurt and excited by an external alternating magnetic field generated by the ACB's excitation coils. The vibration of the ferromagnetic particles was measured in phantoms using a Doppler ultrasonic transducer; we verified the sensitivity to detecting the vibrations at low concentrations of ferromagnetic material (~1%). The responses of the susceptometer and Doppler ultrasound linearly depended on the voltage level applied to the magnetizing coils at low ferromagnetic particle concentrations (⩽ 5%). We also conducted a repeatability test on the prototype, which indicated a deviation of 0.94% and 0.25% in the Doppler and susceptometric measurements, respectively. We can conclude that the hybrid transducer technique has potential clinical applications.

A pilot study on the evaluation of postural strategies in young and elderly subjects using a tridimensional electromagnetic system

Abstract

One resorts to various postural strategies while attempting to maintain balance.

Objective

To assess the postural strategies adopted by young and elderly subjects in varying sensory conditions by using a system of tridimensional electromagnetic sensors positioned on the projection of the first thoracic vertebra and on the sacral region. Postural oscillation values for young and elderly subjects were also reported.

Method

This observational cross-sectional study enrolled 25 young and 16 elderly individuals. A Polhemus™ device equipped with two sensors was used to assess postural oscillation parameters (maximum displacement, mean velocity, and trajectory). Data acquisition was carried out with subjects standing while undergoing a 90-second test in four sensory conditions: eyes opened, eyes closed, on a stable surface, and on an unstable surface.

Results

Sensors 1 and 2 presented significant cross-correlations in all sensory conditions for both groups (r > 0.99; p < 0.001). No statistically significant differences were seen when the cross-correlations for both groups were compared.

Conclusion

This study presented an important tool to analyze postural oscillation and assess the postural strategies of young and elderly subjects in different sensory conditions. Young and elderly individuals presented strong correlations between sensors (ankle strategy), but no statistically significant differences were seen between groups.

A new method to analyze the subjective visual vertical in patients with bilateral vestibular dysfunction

OBJECTIVE

The aim of this study was to assess the subjective visual vertical in patients with bilateral vestibular dysfunction and to propose a new method to analyze subjective visual vertical data in these patients.

METHODS

Static subjective visual vertical tests were performed in 40 subjects split into two groups. Group A consisted of 20 healthy volunteers, and Group B consisted of 20 patients with bilateral vestibular dysfunction. Each patient performed six measurements of the subjective visual vertical test, and the mean values were calculated and analyzed.

RESULTS

Analyses of the numerical values of subjective visual vertical deviations (the conventional method of analysis) showed that the mean deviation was 0.326±1.13º in Group A and 0.301±1.87º in Group B. However, by analyzing the absolute values of the subjective visual vertical (the new method of analysis proposed), the mean deviation became 1.35±0.48º in Group A and 2.152±0.93º in Group B. The difference in subjective visual vertical deviations between groups was statistically significant (p<0.05) only when the absolute values and the range of deviations were considered.

CONCLUSION

An analysis of the absolute values of the subjective visual vertical more accurately reflected the visual vertical misperception in patients with bilateral vestibular dysfunction.

Influência da obesidade e da força de preensão palmar no equilíbrio postural estático de idosas ativas

O objetivo deste estudo foi investigar a influência da obesidade e da força de preensão palmar (FPP) no equilíbrio postural estático de idosas ativas nas condições de olhos abertos e fechados. Participaram 31 idosas (16 eutróficas e 15 obesas). A idade média e o Índice de Massa Corpórea (IMC) das eutróficas foram, respectivamente, 68,3±2,7 anos e 23,4±1,6kg/m², e das obesas 69,1±2,7 anos e 33,5±3kg/m². A FPP foi avaliada usando um dinamômetro (JAMAR). O equilíbrio postural estático foi avaliado usando um sistema tridimensional nas condições de olhos abertos (OA) e fechados (OF), durante 90 segundos cada condição. A FPP das idosas eutróficas foi 25,1±4,6kgf e das obesas foi 24,8±5,2kgf, não havendo diferenças significativas. No equilíbrio postural, foram observadas diferenças significativas entre os grupos apenas no deslocamento máximo a-p com AO (p=0,04) e OF (p<0,01), com as idosas obesas apresentando menor deslocamento a-p em relação às eutróficas. Não houve correlação entre o deslocamento máximo a-p com IMC e a FPP. No presente estudo FPP não influenciou o equilíbrio postural estático, enquanto a obesidade foi fator determinante de menor deslocamento ântero-posterior de idosas ativas.

Análise do equilíbrio postural estático utilizando um sistema eletromagnético tridimensional

Abstract

Aim

Study design

Material and Method

Results

Conclusion

Evaluation of delayed neuronal and axonal damage secondary to moderate and severe traumatic brain injury using quantitative MR imaging techniques

BACKGROUND AND PURPOSE

Traumatic brain injury (TBI) is a classic model of monophasic neuronal and axonal injury, in which tissue damage mainly occurs at the moment of trauma. There is some evidence of delayed progression of the neuronal and axonal loss. Our purpose was to test the hypothesis that quantitative MR imaging techniques can estimate the biologic changes secondary to delayed neuronal and axonal loss after TBI.

MATERIALS AND METHODS

Nine patients (age, 11-28 years; 5 male) who sustained a moderate or severe TBI were evaluated at a mean of 3.1 years after trauma. We applied the following techniques: bicaudate (BCR) and bifrontal (BFR) ventricle-to-brain ratios; T2 relaxometry; magnetization transfer ratio (MTR); apparent diffusion coefficient (ADC); and proton spectroscopy, by using an N-acetylaspartate/creatine (NAA/Cr) ratio measured in normal-appearing white matter (NAWM) and the corpus callosum (CC). The results were compared with those of a control group.

RESULTS

BCR and BFR mean values were significantly increased (P < or = .05) in patients due to secondary subcortical atrophy; increased T2 relaxation time was observed in the NAWM and CC, reflecting an increase in water concentration secondary to axonal loss. Increased ADC mean values and reduced MTR mean values were found in the NAWM and CC, showing damage in the myelinated axonal fibers; and decreased NAA/Cr ratio mean values were found in the CC, indicating axonal loss.

CONCLUSIONS

These quantitative MR imaging techniques could noninvasively demonstrate the neuronal and axonal damage in the NAWM and CC of human brains, secondary to moderate or severe TBI.

Acoustic elastography under dynamic compression using one-dimensional track motion

This work provides an detailed analysis of a method for ultrasound-based elasticity image formation using dynamic compression technique. Radiofrequency (RF) data acquired from a homogenous phantom, where both mechanical and acoustic proprieties were set equivalent to biologic tissues, were used to validate our results. Local strains were obtained by speckle tracking of the acoustic scatterers motion between a pair of RF echo fields acquired when the phantom was dynamically deformed at low frequency (approximately 1 Hz). In this work we investigated the dynamic compression technique as an alternate to the conventional quasi-static compression. In particular, we studied the improvement on strain estimation by varying the size of 1-D kernel during the tracking between the pre- and pos-deformed RF fields.

Spatiotemporal evaluation of human colon motility using three-axis fluxgates and magnetic markers

An alternative method to study the mechanical activity of the human colon in fasting and postprandial states is presented. The method is based on measurements of the magnetic fields produced by a magnetic marker, a small cylindrical NdBFe magnet, when it was ingested by the subjects. A portable magnetic probe, consisting of two digital three-axis fluxgate magnetometers, arranged in a first-order electronic gradiometer, was implemented for this research. Measurements were taken in 16 healthy male subjects. Contractile activity frequency measurements were taken along the colon length, including the ascending, transverse and descending sections, as well as the rectal sigmoidal section. Values for the contractile activity frequency of 2-5 cycles min(-1) were measured. The set-up is simple, low-cost and suitable for use in an unshielded environment.

Euterpe Olerácea (Açaí) as an alternative oral contrast agent in MRI of the gastrointestinal system: preliminary results

Using contrast agents is a common practice in medical imaging protocols. Paramagnetic properties of certain compounds present in contrast agents can affect magnetic resonance imaging (MRI) signals. For abdominal applications, they are usually injected, but may also be administered orally. However, their use as a routine technique is limited, mainly due to the lack of appropriate oral contrast agents. We herein present the preliminary characterization and results for implementation of Euterpe Olerácea (popularly named Açaí) as a possible clinical oral contrast agent for MRI of the gastrointestinal tract. The pulp of Açaí, a fruit from the Amazon area, presented an increase in T(1)-weighted MRI signal, equivalent to that of gadolinium-diethyltriamine pentaacetic acid, and a decrease in T(2)-weighted images. We looked for intrinsic properties that could be responsible for the T(1) signal enhancement and T(2) opacification. Atomic absorption spectra revealed the presence of Fe, Mn and Cu ions in Açai. The presence of such ions contribute to the susceptometric value found of chi = -4.83 x 10(-6). This finding assents with the hypothesis that image contrast changes were due to the presence of paramagnetic material. The first measurements in vivo demonstrate a clear increase of contrast, in T(1)-weighted images, due to the presence of Açaí. Consistently, the opacification in a T(2)-weighted acquisition was evident, revealing a good contrast on bowel walls of gastric tissues.

Theoretical evaluation of the susceptometric measurement of iron in human liver by four different susceptometers

This paper is an evaluation of liver iron quantification using a simulated magnetic susceptibility measurement in the hepatic region. Susceptometers having homogeneous and non-homogeneous magnetizing fields coupled with axial second-order and planar first-order gradiometric magnetic detectors were considered. The intensity of magnetic flux threading the detector coils was evaluated considering samples with volume and susceptibility equivalent to liver iron, tissue and lung air individually. These volumes were represented by cylindrical and spherical geometries. The main sources of error in quantifying iron overload in susceptometric measurement of hepatic tissue were evaluated for four configurations of the susceptometer.