Mitigating skin tone bias in linear array in vivo photoacoustic imaging with short-lag spatial coherence beamforming.

Photoacoustic (PA) imaging has the potential to deliver non-invasive diagnostic information. However, skin tone differences bias PA target visualization, as the elevated optical absorption of melanated skin decreases optical fluence within the imaging plane and increases the presence of acoustic clutter. This paper demonstrates that short-lag spatial coherence (SLSC) beamforming mitigates this bias. PA data from the forearm of 18 volunteers were acquired with 750-, 810-, and 870-nm wavelengths. Skin tones ranging from light to dark were objectively quantified using the individual typology angle (ITA°). The signal-to-noise ratio (SNR) of the radial artery (RA) and surrounding clutter were measured. Clutter was minimal (e.g., -16 dB relative to the RA) with lighter skin tones and increased to -8 dB with darker tones, which compromised RA visualization in conventional PA images. SLSC beamforming achieved a median SNR improvement of 3.8 dB, resulting in better RA visualization for all skin tones.

Hybrid Nanoparticles of Citrate-Coated Manganese Ferrite and Gold Nanorods in Magneto-Optical Imaging and Thermal Therapy.

The development of nanomaterials has drawn considerable attention in nanomedicine to advance cancer diagnosis and treatment over the last decades. Gold nanorods (GNRs) and magnetic nanoparticles (MNPs) have been known as commonly used nanostructures in biomedical applications due to their attractive optical properties and superparamagnetic (SP) behaviors, respectively. In this study, we proposed a simple combination of plasmonic and SP properties into hybrid NPs of citrate-coated manganese ferrite (Ci-MnFe2O4) and cetyltrimethylammonium bromide-coated GNRs (CTAB-GNRs). In this regard, two different samples were prepared: the first was composed of Ci-MnFe2O4 (0.4 wt%), and the second contained hybrid NPs of Ci-MnFe2O4 (0.4 wt%) and CTAB-GNRs (0.04 wt%). Characterization measurements such as UV-Visible spectroscopy and transmission electron microscopy (TEM) revealed electrostatic interactions caused by the opposing surface charges of hybrid NPs, which resulted in the formation of small nanoclusters. The performance of the two samples was investigated using magneto-motive ultrasound imaging (MMUS). The sample containing Ci-MnFe2O4_CTAB-GNRs demonstrated a displacement nearly two-fold greater than just using Ci-MnFe2O4; therefore, enhancing MMUS image contrast. Furthermore, the preliminary potential of these hybrid NPs was also examined in magnetic hyperthermia (MH) and photoacoustic imaging (PAI) modalities. Lastly, these hybrid NPs demonstrated high stability and an absence of aggregation in water and phosphate buffer solution (PBS) medium. Thus, Ci-MnFe2O4_CTAB-GNRs hybrid NPs can be considered as a potential contrast agent in MMUS and PAI and a heat generator in MH.

Relationship between lymphedema after breast cancer treatment and biophysical characteristics of the affected tissue.

The treatment of breast cancer is often complicated by lymphedema of the upper limbs. Standard lymphedema evaluation methodologies are not able to measure tissue fibrosis. The ultrasound aspects related to tissue microstructures of lymphedema are neglected in clinical evaluations. The objective of this study was to identify and measure the degree of impairment, topography, and biophysical alterations of subcutaneous lymphedema tissue secondary to the treatment of breast cancer by ultrasonography. Forty-two women at a mean age of 58 (±9.7) years, with unilateral lymphedema due to breast cancer treatment, were evaluated. The upper limbs were divided into affected (affected by lymphedema) and control (contralateral limb). Each limb was subdivided into seven areas, defined by perimetry, evaluated in pairs. The biophysical characteristics thickness, entropy, and echogenicity were evaluated by ultrasonography. The results showed a significant difference in the echogenicity and thickness variables between the affected and unaffected upper limb, in all the extent of the upper limb, while entropy showed no significant difference. The findings indicate that the data presented were consistent both in identifying and measuring the degree of impairment and biophysical changes in the subcutaneous tissue of lymphedema secondary to the treatment of breast cancer.

Glycerol-in-SEBS gel as a material to manufacture stable wall-less vascular phantom for ultrasound and photoacoustic imaging.

Styrene-ethylene/butylene-styrene (SEBS) copolymer-in-mineral oil gel is an appropriate tissue-mimicking material to manufacture stable phantoms for ultrasound and photoacoustic imaging. Glycerol dispersion has been proposed to further tune the acoustic properties and to incorporate hydrophilic additives into SEBS gel. However, this type of material has not been investigated to produce wall-less vascular flow phantom for these imaging modalities. In this paper, the development of a wall-less vascular phantom for ultrasound and photoacoustic imaging is reported. Mixtures of glycerol/TiO2-in-SEBS gel samples were manufactured at different proportions of glycerol (10%, 15%, and 20%) and TiO2(0% to 0.5%) to characterize their optical and acoustic properties. Optical absorption in the 500-950 nm range was independent of the amount of glycerol and TiO2, while optical scattering increased linearly with the concentration of TiO2. Acoustic attenuation and speed of sound were not influenced by the presence of TiO2. The sample manufactured using weight percentages of 10% SEBS, 15% glycerol, and 0.2% TiO2was selected to make the vascular phantom. The phantom proved to be stable during the pulsatile blood-mimicking fluid (BMF) flow, without any observed damage to its structure or leaks. Ultrasound color Doppler images showed a typical laminar flow, while the B-mode images showed a homogeneous speckled pattern due to the presence of the glycerol droplets in the gel. The photoacoustic images of the phantom showed a well-defined signal coming from the surface of the phantom and from the vessels where BMF was flowing. The Spearman's correlations between the photoacoustic and tabulated spectra calculated from the regions containing BMF, in this case a mixture of salt solutions (NiCl2and CuSO4), were higher than 0.95. Our results demonstrated that glycerol-in-SEBS gel was an adequate material to make a stable vascular flow phantom for ultrasound photoacoustic imaging.

A Novel Theranostic Platform: Integration of Magnetomotive and Thermal Ultrasound Imaging With Magnetic Hyperthermia.

OBJECTIVE: Nanotheranostic systems integrate therapeutic and diagnostic procedures using nanotechnology. This type of approach has enabled the development of methods for early detection and treatment of different pathologies. Magnetic hyperthermia (MH) has been proposed as an alternative or complementary method of cancer therapy. However, challenges such as delivering and localizing the magnetic nanoparticles (MNPs) within tissues and monitoring the temperature during the treatment hinder this technique to be effectively translated into a clinical routine. Therefore, in this study a theranostic platform has been proposed and examined to address two main issues, localizing MNPs and real-time temperature monitoring, for preclinical MH. METHODS: The system integrates magnetomotive (MMUS) and thermal ultrasound imaging with MH. An ultrasound device was used to acquire MMUS images to detect MNPs, and ultrasound thermometry to monitor the temperature. This platform was designed such that a single coil generated the magnetic field for MMUS and MH. The feasibility of the system was examined using a tissue mimicking phantom containing an inclusion filled with zinc substituted magnetite NPs. RESULTS: These MNPs were effectively used as contrast agent for MMUS and to generate heat during MH. In addition to localizing MNPs, real-time two-dimensional temperature maps were obtained with substantial concordance (ρc > 0.97) with invasive measurements using fiber optic thermometer. The heating rate was proportional to the displacements in MMUS (r = 0.92). CONCLUSION: Ultrasound thermometry was successfully used to monitor the temperature during MH. In addition, it was shown that acquiring MMUS images prior to MH can qualitatively predict the temperature distribution of the MNP-laden regions.

Tissue Characterization by Low-Frequency Acoustic Waves Generated by a Single High-Frequency Focused Ultrasound Beam.

The mechanical properties of biological tissues are fingerprints of certain pathologic processes. Ultrasound systems have been used as a non-invasive technique to both induce kilohertz-frequency mechanical vibrations and detect waves resulting from interactions with biological structures. However, existing methodologies to produce kilohertz-frequency mechanical vibrations using ultrasound require the use of variable-frequency, dual-frequency and high-power systems. Here, we propose and demonstrate the use of bursts of megahertz- frequency acoustic radiation to observe kilohertz-frequency mechanical responses in biological tissues. Femoral bones were obtained from 10 healthy mice and 10 mice in which osteoporosis had been induced. The bones' porosity, trabecular number, trabecular spacing, connectivity and connectivity density were determined using micro-computed tomography (µCT). The samples were irradiated with short, focused acoustic radiation pulses (f = 3.1 MHz, t = 15 µs), and the low-frequency acoustic response (1-100 kHz) was acquired using a dedicated hydrophone. A strong correlation between the spectral maps of the acquired signals and the µCT data was found. In a subsequent evaluation, soft tissue stiffness measurements were performed with a gel wax-based tissue-mimicking phantom containing three spherical inclusions of the same type of gel but different densities and Young's moduli, yet with approximately the same echogenicity. Conventional B-mode ultrasound was unable to image the inclusions, while the novel technique proposed here showed good image contrast.

Multiangle Long-Axis Lateral Illumination Photoacoustic Imaging Using Linear Array Transducer.

Photoacoustic imaging (PAI) combines optical contrast with ultrasound spatial resolution and can be obtained up to a depth of a few centimeters. Hand-held PAI systems using linear array usually operate in reflection mode using a dark-field illumination scheme, where the optical fiber output is attached to both sides of the elevation plane (short-axis) of the transducer. More recently, bright-field strategies where the optical illumination is coaxial with acoustic detection have been proposed to overcome some limitations of the standard dark-field approach. In this paper, a novel multiangle long-axis lateral illumination is proposed. Monte Carlo simulations were conducted to evaluate light delivery for three different illumination schemes: bright-field, standard dark-field, and long-axis lateral illumination. Long-axis lateral illumination showed remarkable improvement in light delivery for targets with a width smaller than the transducer lateral dimension. A prototype was developed to experimentally demonstrate the feasibility of the proposed approach. In this device, the fiber bundle terminal ends are attached to both sides of the transducer's long-axis and the illumination angle of each fiber bundle can be independently controlled. The final PA image is obtained by the coherent sum of subframes acquired using different angles. The prototype was experimentally evaluated by taking images from a phantom, a mouse abdomen, forearm, and index finger of a volunteer. The system provided light delivery enhancement taking advantage of the geometry of the target, achieving sufficient signal-to-noise ratio at clinically relevant depths.

Evaluation of a Computer-Aided Diagnosis System in the Classification of Lesions in Breast Strain Elastography Imaging.

Purpose: Evaluation of the performance of a computer-aided diagnosis (CAD) system based on the quantified color distribution in strain elastography imaging to evaluate the malignancy of breast tumors. Methods: The database consisted of 31 malignant and 52 benign lesions. A radiologist who was blinded to the diagnosis performed the visual analysis of the lesions. After six months with no eye contact on the breast images, the same radiologist and other two radiologists manually drew the contour of the lesions in B-mode ultrasound, which was masked in the elastography image. In order to measure the amount of hard tissue in a lesion, we developed a CAD system able to identify the amount of hard tissue, represented by red color, and quantify its predominance in a lesion, allowing classification as soft, intermediate, or hard. The data obtained with the CAD system were compared with the visual analysis. We calculated the sensitivity, specificity, and area under the curve (AUC) for the classification using the CAD system from the manual delineation of the contour by each radiologist. Results: The performance of the CAD system for the most experienced radiologist achieved sensitivity of 70.97%, specificity of 88.46%, and AUC of 0.853. The system presented better performance compared with his visual diagnosis, whose sensitivity, specificity, and AUC were 61.29%, 88.46%, and 0.829, respectively. The system obtained sensitivity, specificity, and AUC of 67.70%, 84.60%, and 0.783, respectively, for images segmented by Radiologist 2, and 51.60%, 92.30%, and 0.771, respectively, for those segmented by the Resident. The intra-class correlation coefficient was 0.748. The inter-observer agreement of the CAD system with the different contours was good in all comparisons. Conclusions: The proposed CAD system can improve the radiologist performance for classifying breast masses, with excellent inter-observer agreement. It could be a promising tool for clinical use.

Acoustic and Elastic Properties of Glycerol in Oil-Based Gel Phantoms.

Phantoms are important tools for image quality control and medical training. Many phantom materials have been proposed for ultrasound; most of them use water as the solvent, but these materials have disadvantages such as dehydration and low temporal stability if not properly stored. To overcome these difficulties, copolymer-in-oil gel was proposed as an inert and stable material; however, speed of sound for these materials is still lower than what is described for most biological tissues. Here, we propose the glycerol dispersion in oil-based gels to modify the acoustic and elastic properties of copolymer-in-oil phantoms. We manufactured copolymer-in-oil gels using styrene-ethylene/butylene-styrene (SEBS) in concentrations 8%-15%. We used 2 types of mineral oils with different viscosities. Glycerol was added in a volume fraction 0%-30% of the total amount of liquid. The acoustic (i.e., speed of sound, attenuation and backscattering) and the mechanical (i.e., density and Young's modulus) properties of the samples were within the range of values observed for soft tissues. The acoustic parameters of the samples were dependent on oil viscosity and glycerol concentration. The speed of sound ranged 1423 m/s - 1502 m/s, while the acoustic attenuation and the ultrasonic backscattering increased by adding glycerol. The density and the Young's moduli were less affected by the presence of glycerol. We conclude that glycerol can be used to control the acoustic parameters of copolymer-in-oil gels. Additionally, it opens the possibility of incorporating other oil-insoluble substances to control further properties of the phantom.

Ultrasound elastography assessment of the median nerve in leprosy patients.

INTRODUCTION: We sought to compare median nerve elasticity between leprosy patients (LPs) and healthy volunteers (HVs) using ultrasound elastography (UE). METHODS: Two radiologists independently measured the strain ratio of the median nerve/flexor digitorum superficialis muscle (MN/FDSM) of 18 LP and 18 HV using real-time freehand UE. Statistical analysis included intra-class correlation coefficients (ICC) and Mann-Whitney test. RESULTS: The MN/FDSM strain ratios of the LP and HV were 2.66 ± 1.30 and 3.52 ± 0.93, respectively (P < 0.05). We observed a significantly lower MN/FDSM strain ratio in LP with reactions (types 1 and 2 cutaneous reactions associated with or without neuritis) (2.30 ± 0.91) compared with LP without reactions (3.60 ± 1.70). We found no significant differences between HV and LP without reactions. The intra- and inter-observer ICCs were 0.50 (95% confidence interval [CI], 0.11-0.72) and 0.34 (95% CI, 0.28-0.52), respectively. CONCLUSIONS: MN/FDSM strain ratios were significantly lower in LP with reactions. UE may be useful for nerve elasticity evaluation in leprosy. Muscle Nerve 56: 393-398, 2017.

Stable phantom materials for ultrasound and optical imaging.

Phantoms mimicking the specific properties of biological tissues are essential to fully characterize medical devices. Water-based materials are commonly used to manufacture phantoms for ultrasound and optical imaging techniques. However, these materials have disadvantages, such as easy degradation and low temporal stability. In this study, we propose an oil-based new tissue-mimicking material for ultrasound and optical imaging, with the advantage of presenting low temporal degradation. A styrene-ethylene/butylene-styrene (SEBS) copolymer in mineral oil samples was made varying the SEBS concentration between 5%-15%, and low-density polyethylene (LDPE) between 0%-9%. Acoustic properties, such as the speed of sound and the attenuation coefficient, were obtained using frequencies ranging from 1-10 MHz, and were consistent with that of soft tissues. These properties were controlled varying SEBS and LDPE concentration. To characterize the optical properties of the samples, the diffuse reflectance and transmittance were measured. Scattering and absorption coefficients ranging from 400 nm-1200 nm were calculated for each compound. SEBS gels are a translucent material presenting low optical absorption and scattering coefficients in the visible region of the spectrum, but the presence of LDPE increased the turbidity. Adding LDPE increased the absorption and scattering of the phantom materials. Ultrasound and photoacoustic images of a heterogeneous phantom made of LDPE/SEBS containing a spherical inclusion were obtained. Annatto dye was added to the inclusion to enhance the optical absorbance. The results suggest that copolymer gels are promising for ultrasound and optical imaging, making them also potentially useful for photoacoustic imaging.

Focused ultrasound neuromodulation of cortical and subcortical brain structures using 1.9 MHz.

PURPOSE: Ultrasound neuromodulation is a promising noninvasive technique for controlling neural activity. Previous small animal studies suffered from low targeting specificity because of the low ultrasound frequencies (<690 kHz) used. In this study, the authors demonstrated the capability of focused ultrasound (FUS) neuromodulation in the megahertz-range to achieve superior targeting specificity in the murine brain as well as demonstrate modulation of both motor and sensory responses. METHODS: FUS sonications were carried out at 1.9 MHz with 50% duty cycle, pulse repetition frequency of 1 kHz, and duration of 1 s. The robustness of the FUS neuromodulation was assessed first in sensorimotor cortex, where elicited motor activities were observed and recorded on videos and electromyography. Deeper brain regions were then targeted where pupillary dilation served as an indicative of successful modulation of subcortical brain structures. RESULTS: Contralateral and ipsilateral movements of the hind limbs were repeatedly observed when the FUS was targeted at the sensorimotor cortex. Induced trunk and tail movements were also observed at different coordinates inside the sensorimotor cortex. At deeper targeted-structures, FUS induced eyeball movements (superior colliculus) and pupillary dilation (pretectal nucleus, locus coeruleus, and hippocampus). Histological analysis revealed no tissue damage associated with the FUS sonications. CONCLUSIONS: The motor movements and pupillary dilation observed in this study demonstrate the capability of FUS to modulate cortical and subcortical brain structures without inducing any damage. The variety of responses observed here demonstrates the capability of FUS to perform functional brain mapping.

Application of Artificial Neural Network Models in Segmentation and Classification of Nodules in Breast Ultrasound Digital Images.

This research presents a methodology for the automatic detection and characterization of breast sonographic findings. We performed the tests in ultrasound images obtained from breast phantoms made of tissue mimicking material. When the results were considerable, we applied the same techniques to clinical examinations. The process was started employing preprocessing (Wiener filter, equalization, and median filter) to minimize noise. Then, five segmentation techniques were investigated to determine the most concise representation of the lesion contour, enabling us to consider the neural network SOM as the most relevant. After the delimitation of the object, the most expressive features were defined to the morphological description of the finding, generating the input data to the neural Multilayer Perceptron (MLP) classifier. The accuracy achieved during training with simulated images was 94.2%, producing an AUC of 0.92. To evaluating the data generalization, the classification was performed with a group of unknown images to the system, both to simulators and to clinical trials, resulting in an accuracy of 90% and 81%, respectively. The proposed classifier proved to be an important tool for the diagnosis in breast ultrasound.

Verticality Perceptions Associate with Postural Control and Functionality in Stroke Patients.

Deficits of postural control and perceptions of verticality are disabling problems observed in stroke patients that have been recently correlated to each other. However, there is no evidence in the literature confirming this relationship with quantitative posturography analysis. Therefore, the objectives of the present study were to analyze the relationship between Subjective Postural Vertical (SPV) and Haptic Vertical (HV) with posturography and functionality in stroke patients. We included 45 stroke patients. The study protocol was composed by clinical interview, evaluation of SPV and HV in roll and pitch planes and posturography. Posturography was measured in the sitting and standing positions under the conditions: eyes open, stable surface (EOSS); eyes closed, stable surface (ECSS); eyes open, unstable surface (EOUS); and eyes closed, unstable surface (ECUS). The median PV in roll plane was 0.34° (-1.44° to 2.54°) and in pitch plane 0.36° (-2.72° to 2.45°). The median of HV in roll and pitch planes were -0.94° (-5.86° to 3.84°) and 3.56° (-0.68° to 8.36°), respectively. SPV in the roll plane was correlated with all posturagraphy parameters in sitting position in all conditions (r = 0.35 to 0.47; p < 0.006). There were moderate correlations with the verticality perceptions and all the functional scales. Linear regression model showed association between speed and SPV in the roll plane in the condition EOSS (R2 of 0.37; p = 0.005), in the condition ECSS (R2 of 0.13; p = 0.04) and in the condition EOUS (R2 of 0.22; p = 0.03). These results suggest that verticality perception is a relevant component of postural control and should be systematically evaluated, particularly in patients with abnormal postural control.

Comparison between shear wave dispersion magneto motive ultrasound and transient elastography for measuring tissue-mimicking phantom viscoelasticity.

Several methods have been developed over the last several years to analyze the mechanical properties of soft tissue. Elastography, for example, was proposed to evaluate soft tissue stiffness in an attempt to reduce the need for invasive procedures, such as breast biopsies; however, its qualitative nature and the fact that it is operator-dependent have proven to be limitations of the technique. Quantitative shearwave- based techniques have been proposed to obtain information about tissue stiffness independent of the operator. This paper describes shear wave dispersion magnetomotive ultrasound (SDMMUS), a new shear-wave-based method in which a viscoelastic medium labeled with iron oxide nanoparticles is displaced by an external tone burst magnetic field. As in magnetomotive ultrasound (MMUS), SDMMUS uses ultrasound to detect internal mechanical vibrations induced by the interaction between a magnetic field and magnetic nanoparticles. These vibrations generated shear waves that were evaluated to estimate the viscoelastic properties of tissue-mimicking phantoms. These phantoms were manufactured with different concentrations of gelatin and labeled with iron oxide nanoparticles. The elasticity and viscosity obtained with SDMMUS agreed well with the results obtained by traditional ultrasound-based transient elastography.

A hybrid transducer to evaluate stomach emptying by ultrasound and susceptometric measurements: an in vivo feasibility study.

Gastric emptying reflects a diversity of important physiological functions. Alternating current biosusceptometry (ACB) is an inexpensive, radiation-free, and minimally invasive method to evaluate gastric emptying, but its response depends on the spatial distribution of the magnetized material and does not provide precise anatomical information. The hybrid transducer, which combines ACB and an ultrasound probe, is an alternative to improve susceptometry measurements, namely the spatial localization of the magnetized source. In this study, initial stomach emptying, in rats, was monitored with the aid of the hybrid transducer. Yogurt mixed with ferrite particles was injected into the rat's stomach. The hybrid transducer was placed on the rat's abdomen during experiments, and the susceptometry signal and magnetomotive ultrasound (MMUS) images were saved and postprocessed. MMUS highlighted the movement of magnetic particles due to magnetic force from ACB excitation coils, and showed the rat's stomach location. In this feasibility study, we monitored the stomach emptying of 4 rats for 20 min. The mean relative ACB signal decayed by 4.6 ± 0.1%, and the mean relative area of MMUS images decreased by 4.5 ± 0.2%, after 20 min postingestion of the magnetic meal due to stomach emptying. In a second experiment, 3-D MMUS images from axial sequences were obtained by spatially translating the hybrid transducer, providing details of the stomach wall, which may enable minimally invasive detection of abnormalities. In conclusion, the MMUS image increased ACB spatial resolution and furnished additional anatomical information.

Paraffin-gel tissue-mimicking material for ultrasound-guided needle biopsy phantom.

Paraffin-gel waxes have been investigated as new soft tissue-mimicking materials for ultrasound-guided breast biopsy training. Breast phantoms were produced with a broad range of acoustical properties. The speed of sound for the phantoms ranged from 1425.4 ± 0.6 to 1480.3 ± 1.7 m/s at room temperature. The attenuation coefficients were easily controlled between 0.32 ± 0.27 dB/cm and 2.04 ± 0.65 dB/cm at 7.5 MHz, depending on the amount of carnauba wax added to the base material. The materials do not suffer dehydration and provide adequate needle penetration, with a Young's storage modulus varying between 14.7 ± 0.2 kPa and 34.9 ± 0.3 kPa. The phantom background material possesses long-term stability and can be employed in a supine position without changes in geometry. These results indicate that paraffin-gel waxes may be promising materials for training radiologists in ultrasound biopsy procedures.

Vibroacoustography for the assessment of total hip arthroplasty.

OBJECTIVES: This paper proposes imaging with 3-dimensional vibroacoustography for postoperatively assessing the uncovered cup area after total hip arthroplasty as a quantitative criterion to evaluate implant fixation. METHODS: A phantom with a bone-like structure covered by a tissue-mimicking material was used to simulate a total hip arthroplasty case. Vibroacoustography images of the uncovered cup region were generated using a two-element confocal ultrasound transducer and a hydrophone inside a water tank. Topological correction based on the geometry of the implant was performed to generate a 3-dimensional representation of the vibroacoustography image and to accurately evaluate the surface. The 3-dimensional area obtained by the vibroacoustography approach was compared to the area evaluated by a 3-dimensional motion capture system. RESULTS: The vibroacoustography technique provided high-resolution, high-contrast, and speckle-free images with less sensitivity to the beam incidence. Using a 3-dimensional-topology correction of the image, we accurately estimated the uncovered area of the implant with a relative error of 8.1% in comparison with the motion capture system measurements. CONCLUSION: Measurement of the cup coverage after total hip arthroplasty has not been well established; however, the covered surface area of the acetabular component is one of the most important prognostic factors. The preliminary results of this study show that vibroacoustography is a 3-dimensional approach that can be used to postoperatively evaluate total hip arthroplasty. The favorable results also provide an impetus for exploring vibroacoustography in other bone or implant surface imaging applications.

Vibroacoustography for the assessment of total hip arthroplasty

OBJECTIVES: This paper proposes imaging with 3-dimensional vibroacoustography for postoperatively assessing the uncovered cup area after total hip arthroplasty as a quantitative criterion to evaluate implant fixation. METHODS: A phantom with a bone-like structure covered by a tissue-mimicking material was used to simulate a total hip arthroplasty case. Vibroacoustography images of the uncovered cup region were generated using a two-element confocal ultrasound transducer and a hydrophone inside a water tank. Topological correction based on the geometry of the implant was performed to generate a 3-dimensional representation of the vibroacoustography image and to accurately evaluate the surface. The 3-dimensional area obtained by the vibroacoustography approach was compared to the area evaluated by a 3-dimensional motion capture system. RESULTS: The vibroacoustography technique provided high-resolution, high-contrast, and speckle-free images with less sensitivity to the beam incidence. Using a 3-dimensional-topology correction of the image, we accurately estimated the uncovered area of the implant with a relative error of 8.1% in comparison with the motion capture system measurements. CONCLUSION: Measurement of the cup coverage after total hip arthroplasty has not been well established; however, the covered surface area of the acetabular component is one of the most important prognostic factors. The preliminary results of this study show that vibroacoustography is a 3-dimensional approach that can be used to postoperatively evaluate total hip arthroplasty. The favorable results also provide an impetus for exploring vibroacoustography in other bone or implant surface imaging applications. .

Vibro-acoustography beam formation with reconfigurable arrays.

In this work, we present a numerical study of the use of reconfigurable arrays (RCA) for vibro-acoustography (VA) beam formation. A parametric study of the aperture selection, number of channels, number of elements, focal distance, and steering parameters is presented to show the feasibility and evaluate the performance of VA imaging based on RCA. The transducer aperture was based on two concentric arrays driven by two continuous-wave or toneburst signals at slightly different frequencies. The mathematical model considers a homogeneous, isotropic, inviscid medium. The pointspread function of the system is calculated based on angular spectrum methods using the Fresnel approximation for rectangular sources. Simulations considering arrays with 50 x 50 to 200 x 200 elements with number of channels varying in the range of 32 to 128 are evaluated to identify the best configuration for VA. Advantages of two-dimensional and RCA arrays and aspects related to clinical importance of the RCA implementation in VA, such as spatial resolution, image frame rate, and commercial machine implementation, are discussed. It is concluded that RCA transducers can produce spatial resolution similar to confocal transducers and steering is possible in the elevational and azimuthal planes. Optimal settings for number of elements, number of channels, maximum steering, and focal distance are suggested for VA clinical applications. Furthermore, an optimization for beam steering based on the channel assignment is proposed for balancing the contribution of the two waves in the steered focus.