High-Frequency Transient Elastography Prototype to Assess Skin (Dermis) Fibrosis: A Diagnostic Study in Patients with Venous Insufficiency and Controls.

PURPOSE: High-frequency transient elastography (HF-TE) is a noninvasive technique for assessing shear-wave speed and finally elasticity in thin tissue such as the skin. It has never been validated for monitoring fibrotic skin diseases. The purpose was to evaluate the potential of HF-TE to assess skin fibrosis in patients with chronic venous disorders (CVD). MATERIALS AND METHODS: This clinical study enrolled 48 patients at various stages of CVD and 48 paired healthy volunteers. Subjects underwent a clinical examination with an evaluation of Rodnan's fibrosis skin score. We studied the dermis thickness measured using ultrasound (US) and elasticity measurements using cutometer and HF-TE studied according to 3 cutaneous zones positioned on the leg. The area under the receiver operating characteristic curve (AUC) was calculated to evaluate the diagnosis performance for a combined parameter (PRL) based on a logistic regression model using both elasticity and dermal thickness. RESULTS: Patients with CVD had significantly higher values of skin elasticity than healthy subjects, 134.5 kPa and 132.1 kPa vs. 91.3 kPa, respectively. The dermis thickness also increased with escalation in CVD stage for all studied zones. The PRL parameter had an AUC value of 0.79 for all zones and stages of CVD clustered. The discriminating power of PRL increased with escalation of the CVD stage; with an AUC value of up to 0.89 for evolved stages, and a sensitivity and specificity of 0.79 and 0.89, respectively. CONCLUSION: HF-TE, coupled with a US measurement of dermis thickness, made it possible to propose a new biomarker, which proved to be a good diagnostic tool for skin fibrosis.

Inkjet-printed P(VDF-TrFE) film for high-frequency annular array.

An innovative processing to deposit P(VDF-TrFE) film on silicon wafers by an inkjet printing method was used to fabricate high-frequency annular array prototype. This prototype has a total aperture of 7.3 mm and 8 active elements. A polymer-based lens with low acoustic attenuation was added to the flat deposition on the wafer, setting the geometric focus to 13.8 mm. With a thickness of around 11 µm, the electromechanical performance of P(VDF-TrFE) films was evaluated with an effective thickness coupling factor of 22%. Electronics allowing all elements to simultaneously emit as a single element transducer was developed. In reception, a dynamic focusing, based on eight independent amplifying channels, was preferred. The center frequency of the prototype was 21.3 MHz, the insertion loss was 48.5 dB and the -6 dB fractional bandwidth was 143%. The trade-off sensitivity/bandwidth has rather favored the large bandwidth. Dynamic focusing on reception was applied and allowed to improvements in the lateral-full width at half maximum as shown on images obtained with a wire phantom at several depths. The next step, for a fully operational multi-element transducer, will be to achieve a significant increase of the acoustic attenuation in the silicon wafer.

Acoustic and Elastic Properties of a Blood Clot during Microbubble-Enhanced Sonothrombolysis: Hardening of the Clot with Inertial Cavitation.

Stroke is the second leading cause of death worldwide. Existing therapies present limitations, and other therapeutic alternatives are sought, such as sonothrombolysis with microbubbles (STL). The aim of this study was to evaluate the change induced by STL with or without recombinant tissue-type plasminogen activator (rtPA) on the acoustic and elastic properties of the blood clot by measuring its sound speed (SoS) and shear wave speed (SWS) with high frequency ultrasound and ultrafast imaging, respectively. An in-vitro setup was used and human blood clots were submitted to a combination of microbubbles and rtPA. The results demonstrate that STL induces a raise of SoS in the blood clot, specifically when combined with rtPA (p < 0.05). Moreover, the combination of rtPA and STL induces a hardening of the clot in comparison to rtPA alone (p < 0.05). This is the first assessment of acoustoelastic properties of blood clots during STL. The combination of rtPA and STL induce SoS and hardening of the clot, which is known to impair the penetration of thrombolytic drugs and their efficacy.

Low-Frequency Intrapulmonary Percussive Ventilation Increases Aerosol Penetration in a 2-Compartment Physical Model of Fibrotic Lung Disease.

In patients with fibrotic pulmonary disease such as idiopathic pulmonary fibrosis (IPF), inhaled aerosols deposit mostly in the less affected region of the lungs, resulting in suboptimal pharmacokinetics of airway-delivered treatments. Refinement of aerosol delivery technique requires new models to simulate the major alterations of lung physiology associated with IPF, i.e., heterogeneously reduced lung compliance and increased airway caliber. A novel physical model of the respiratory system was constructed to simulate aerosol drug delivery in spontaneously breathing (negative pressure ventilation) IPF patients. The model comprises upper (Alberta ideal throat) and lower airway (plastic tubing) models and branches into two compartments (Michigan lung models) which differ in compliance and caliber of conducting airway. The model was able to reproduce the heterogeneous, compliance-dependent reduction in ventilation and aerosol penetration (using NaF as a model aerosol) seen in fibrotic lung regions in IPF. Of note, intrapulmonary percussive ventilation induced a 2-3-fold increase in aerosol penetration in the low-compliance/high airway caliber compartment of the model, demonstrating the responsiveness of the model to therapeutic intervention.

Interest of the attenuation coefficient in multiparametric high frequency ultrasound investigation of whole blood coagulation process.

Previous studies [R. Libgot, F. Ossant, Y. Gruel, P. Lermusiaux, and F. Patat, Proc.-IEEE Utrason. Symp. 4, 2259-2262 (2005); R. Libgot-Calle, F. Ossant, Y. Gruel, P. Lermusiaux, and F. Patat, Ultrasound Med. Biol. 34, 252-264 (2008); F. Ossant, R. Libgot, P. Coupe, P. Lermusiaux, and F. Patat, Proc.-IEEE Ultrason. Symp. 2, 846-849 (2004)] showed the potential of an in vitro high frequency ultrasound (beyond 20 MHz) device to describe the blood clotting process. The parameters were simultaneously estimated in double transmission (DT) with the calculation of the velocity of longitudinal waves and in backscattering (BS) modes with the estimation of the integrated BS coefficient and the effective scatterer size. The aim of the present study was to show how the integrated attenuation coefficient (IAC) assessed in DT mode could provide additional information on this process, especially regarding the fibrin polymerization which is an important part of the coagulation process. A characteristic time t(a) of the variations in IAC that could be linked to fibrin formation was identified.

High frequency ultrasound device to investigate the acoustic properties of whole blood during coagulation.

This study was designed to investigate the changes in acoustic properties of whole blood during the coagulation process. High frequency (from 20 to 40 MHz) ultrasound parameters were measured both in double transmission (DT) and backscattering (BS) mode to assess sound velocity and backscatter coefficient, respectively. The integrated backscatter coefficient (IBC) and the effective scatterer size (ESS) were deducted from the backscatter coefficient. Measurements were performed on whole blood samples collected from 12 healthy volunteers. During the blood clotting process (2 h observation), acoustic parameters were measured with 15 s time resolution for the transmission parameter and 5 s (for the 5 first min) and 30 s (for the end of the observation time) for the backscattering parameters. The results obtained clearly showed that simultaneous measurements of parameters in DT and BS modes are able to identify several stages during the in vitro blood clotting process. In particular, red blood cell (RBC) aggregation can be described from the backscattering parameters and liquid-gel transition phase of blood from the sound velocity. Intra- and inter-individual dispersion of these parameters were also measured and discussed.

Very-high-frequency ultrasound corneal imaging as a new tool for early diagnosis of ocular surface toxicity in rabbits treated with a preserved glaucoma drug.

AIM: To evaluate very-high-frequency (VHF) ultrasound imaging as a new method to detect and quantify early corneal epithelium changes induced by chronic exposure to a benzalkonium-chloride-containing antiglaucoma drug. METHODS: Timolol preserved with 0.01% benzalkonium chloride solution was applied b.i.d. in 1 eye of 10 rabbits for 56 days. Unpreserved timolol solution was used as control. Ocular surface changes were assessed weekly combining clinical examinations, in vivo 60-MHz ultrasound imaging and ex vivo histological analysis. RESULTS: VHF ultrasound imaging allowed quantitative measurement of corneal epithelium thickness and qualitative imaging of toxic epithelial damage. It revealed significantly decreased epithelial thickness in vivo as early as the 21st day of treatment (40.75 +/- 1.72 microm at D0 vs. 39 +/- 2 at D21, vs. 31.9 +/- 2.98 at D56; p = 0.017 and p = 0.005, respectively). The first clinical changes appeared from the 42nd day of treatment (conjunctival redness, conjunctival staining and corneal staining; D56 compared to D0: p = 0.005, 0.01 and 0.004, respectively) and then correlated with VHF ultrasound data. Epithelial thickness measured with VHF ultrasound was correlated with histological epithelial pachymetry (p < 0.001) and with the corneal damage score assessed with scanning electron microscopy (p = 0.038). CONCLUSION: VHF ultrasound imaging provided an early in vivo diagnosis of corneal epithelium pathology induced by chronic exposure to a preserved glaucoma drug, before the first clinical evidence of ocular toxicity. It could be a new reproducible method to detect the toxicity of glaucoma medication so that therapy can then be adapted.

3-D-Printed Phantom Fabricated by Photopolymer Jetting Technology for High-Frequency Ultrasound Imaging.

In the field of high-frequency ultrasound imaging ( MHz), tools for characterizing the performance of imaging systems are lacking. Indeed, commercial phantoms are often inadequate for this frequency range. The development of homemade phantoms on the laboratory scale is often required but is hindered by the difficulty in making very small structures that must be distributed with high accuracy in 3-D space. We propose investigating the use of 3-D photopolymer printing to create resolution and calibration phantoms designed for high-frequency ultrasound imaging. The quality and importance of these phantoms are discussed from the point of view of ultrasound parameters and imaging. First, the compressional wave group velocity, acoustic impedance, and attenuation of six photopolymerized materials were measured using temporal and spectral methods in a substitution experimental setup. Measurements were performed on printed samples using a broadband-focused single-element transducer covering a large frequency range (15-55 MHz). Two 3-D phantoms incorporating different shapes and dimensions were designed and printed. Finally, 3-D acoustic images were obtained using either a mechanically driven single-element transducer or a high-frequency commercial imaging system. Three-dimensional printing enabled us to generate phantoms suitable for high-frequency imaging with complex geometry inclusions and with a surrounding material having acoustic properties close to those of human skin. The calculated SNR between the inclusion and surrounding media is approximately 50 dB. In conclusion, 3-D printing is a useful tool for directly, easily, and rapidly manufacturing ultrasound phantoms for ultrasound imaging system assessments and computational calibration or validation.

Microbubbles combined with ultrasound therapy in ischemic stroke: A systematic review of in-vivo preclinical studies.

BACKGROUND: Microbubbles (MBs) combined with ultrasound sonothrombolysis (STL) appears to be an alternative therapeutic strategy for acute ischemic stroke (IS), but clinical results remain controversial. OBJECTIVE: The aim of this systematic review is to identify the parameters tested; to assess evidence on the safety and efficacy on preclinical data on STL; and to assess the validity and publication bias. METHODS: Pubmed® and Web of ScienceTM databases were systematically searched from January 1995 to April 2017 in French and English. We included studies evaluating STL on animal stroke model. This systematic review was conducted in accordance with the PRISMA guidelines. Data were extracted following a pre-defined schedule by two of the authors. The CAMARADES criteria were used for quality assessment. A narrative synthesis was conducted. RESULTS: Sixteen studies met the inclusion criteria. The result showed that ultrasound parameters and types of MBs were heterogeneous among studies. Numerous positive outcomes on efficacy were found, but only four studies demonstrated superiority of STL versus recombinant tissue-type plasminogen activator on clinical criteria. Data available on safety are limited. LIMITATIONS: Quality assessment of the studies reviewed revealed a number of biases. CONCLUSION: Further in vivo studies are needed to demonstrate a better efficacy and safety of STL compared to currently approved therapeutic options. SYSTEMATIC REVIEW REGISTRATION: http://syrf.org.uk/protocols/.

One-step surgical removal of cutaneous melanoma with surgical margins based on preoperative ultrasound measurement of the thickness of the melanoma.

BACKGROUND: Surgical margins of melanoma vary from 5 mm to 1 or 2 cm depending on histology thickness (Breslow). This approach usually requires two surgical steps: excisional biopsy and further re-excision according to histology thickness. A previous systematic review showed that measuring melanoma thickness with high-resolution ultrasound imaging equipment correlates well with histological measurement of melanoma thickness. Therefore, we routinely determined tumour sonographic thickness in order to perform surgery as a single step. OBJECTIVES: To determine the proportion of patients who receive one-step surgery with adequate margins based on sonographic measurement of melanoma thickness and identify the reasons for differences between these two measurements. MATERIALS AND METHODS: A retrospective series of patients with melanoma, in which thickness was measured by ultrasound (20 MHz) from April 2007 to December 2015 prior to surgery. RESULTS: Ninety-nine melanomas were treated, of which 78 were removed in a single step with surgical margins based on sonometric thickness measurements; 71 of these (91%, 95% CI: 82-96) did not require re-excision, five had excessive margins, and two had insufficient margins. The correlation between the histometric and sonometric measurements was good; r=0.88. Significant absolute difference between sonometric and histometric measurements was associated with thickness, ulceration, and size of tumours, based on bivariate analysis. Thickness remained the only significant factor based on multivariate analysis. CONCLUSION: Measuring the thickness of melanoma with high-resolution ultrasound imaging equipment makes it possible to remove the melanoma in a single step with adequate margins in at least 82% of the cases in routine care.

Evaluation of high resolution ultrasound as a tool for assessing the 3D volume of blood clots during in vitro thrombolysis.

Thrombosis is a major cause of several diseases, i.e. myocardial infarction, cerebral stroke and pulmonary embolism. Thrombolytic therapies are required to induce fast and efficient recanalization of occluded vessels. To evaluate the in vitro efficacy of these thrombolytic strategies, measuring clot dissolution is essential. This study aimed to evaluate and validate high resolution ultrasound as a tool to assess the exact volume of clots in 3D and in real time during in vitro thrombolytic drug testing. This new method was validated by measuring the effects of concentration range of recombinant tissue type plasminogen activator on a blood clot during complete occlusion or 70% stenosis of a vessel. This study shows that high resolution ultrasound imaging allows for a real-time assessment of the 3D volume of a blood clot with negligible inter- and intra-operator variabilities. The conclusions drawn from this study demonstrate the promising potential of high resolution ultrasound imaging for the in vitro assessment of new thrombolytic drugs.

High-frequency ultrasound imaging for cutaneous neurofibroma in patients with neurofibromatosis type I.

Neurofibromas (NFs) are benign tumours arising from a nerve sheath, which are present in nearly all patients with neurofibromatosis type 1 (NF1). High-frequency ultrasound (HFU) systems, using frequencies over 20 MHz, were developed to improve visualization of skin tumours by means of increased resolution. To describe NFs by using HFU in patients with NF1. Anonymized HFU (25-MHz) images of NFs were randomized. Initially, two dermatologist investigators, with experience in HFU imaging of the skin, together described the ultrasound images and established eight criteria for NFs. The same task was then repeated by two other dermatologists, also with experience in HFU imaging of the skin, independently, to establish inter-observer agreement. A total of 108 NFs in 29 patients were included. Superficial and subcutaneous NFs were hypoechoic with a round to spindle shape. Plexiform NFs were ill-defined, consisting of multiple hypoechoic linear zones. Good to excellent inter-observer agreement was found for six of the eight criteria (k>0.6). This is the first series describing HFU skin imaging of NFs in patients with NF1. Lateral extension that may correspond to involvement of an adjacent nerve seems to be specific to NFs.

High-Resolution Elastography for Thin-Layer Mechanical Characterization: Toward Skin Investigation.

Interest in elasticity estimation for thin layers is increasing because of the various potential applications, including dermatology and cosmetology. In this context, we propose a dedicated elastographic system using 1-D high-frequency transient elastography (HF-TE) to estimate the 1-D Young's modulus through the dermis and hypodermis, which are the two human skin layers of interest in this study. An experimental validation of the HF-TE method was first carried out on two homogeneous tissue-mimicking hard and soft phantoms. The Young's modulus values obtained in these phantoms were compared with those obtained by two complementary shear wave propagation techniques: shear wave-induced resonance elastography (SWIRE) and supersonic shear imaging (SSI). A third two-layer thin phantom, with mechanical properties similar to those of skin, was used to validate the ability of HF-TE to distinguish layers and measure elasticity. Finally, preliminary in vivo experiments conducted on forearm and cheek skin revealed the promising performance of HF-TE in measuring elasticity in the dermis and hypodermis.

In-vivo imaging of skin under stress: potential of high-frequency (20 MHz) static 2-D elastography.

The aim of this study was to evaluate the potential of high-frequency static two-dimensional (2-D) elastography for in vivo exploration of the mechanical behavior of skin. Our device was based on the combination of a 20 MHz sonographer and a patented extensiometer device able to apply calibrated uniaxial stretching of the skin. We used a new algorithm to compute elastograms that improve elastographic signal-to-noise ratio (SNRe) without sacrificing resolution. Mechanical behavior was described according to the axial strain and lateral displacements induced in the tissue. The efficacy of the strain anpolyvinyl alcohol first evaluated in polyvinyl alcohol (PVA)-cryogel phantoms. Several in vivo experiments then were conducted, mainly with the multistretching averaging method, and demonstrated the potential of this technique in the evaluation of mechanical behavior of the dermis and the hypodermis under stress.

Spatial variation of acoustic parameters in human skin: an in vitro study between 22 and 45 MHz.

This study of spatial variance of acoustic parameters was performed on eight nonfrozen samples of female abdominal skin (women 46.5 +/- 12.2 years old), obtained during plastic surgery. Intra- and interindividual variations are discussed on the basis of estimations of three acoustic parameters (slope of attenuation- beta; integrated attenuation coefficient- IAC; integrated backscattering coefficient- IBC) and one texture parameter (based on two estimators of effective density of scatterers: alpha(2) and alpha(1/2)) as a function of surface area and depth of acquisition in the frequency range 22 to 45 MHz. Values of intraindividual variations varied from 7.1% for IAC to 23.2% for IBC, and significantly decreased at a ratio between 1.2 to 2.3 when the acquisition surface area was increased from 4 mm(2) to 1 cm(2). Interindividual variations were higher than intraindividual variations, and varied from 14.2% for alpha(1/2) to 51% for IBC. The mean values (+/- SD) for all specimens combined, estimated with a large number of independent radiofrequency (RF) lines (400) and for a surface area of exploration of 4 cm(2), were 1.06 +/- 0.17 dB cm(-1) MHz(-1) for beta, 135 +/- 37 dB cm(-1) for IAC, (3.7 +/- 1.9) x 10(-2) cm(-1) sr(-1) for IBC, 1.40 +/- 0.17 scatterers/resolution cell for alpha(2) and 1.32 +/- 0.27 scatterers/resolution cell for alpha(1/2). Finally, attenuation micro(f) and backscattering coefficient sigma(b)(f) were compared to published results for the same parameters measured in human skin.

Axial ultrasound B-scans of the entire eye with a 20-MHz linear array: correction of crystalline lens phase aberration by applying Fermat's principle.

In ophthalmic ultrasonography the crystalline lens is known to be the main source of phase aberration, causing a significant decrease in resolution and distortion effects on axial B-scans. This paper proposes a computationally efficient method to correct the phase aberration arising from the crystalline lens, including refraction effects using a bending ray tracing approach based on Fermat's principle. This method is used as a basis to perform eye-adapted beamforming (BF), with appropriate focusing delays for a 128-element 20-MHz linear array in both emission and reception. Implementation was achieved on an in-house developed experimental ultrasound scanning device, the ECODERM. The proposed BF was tested in vitro by imaging a wire phantom through an eye phantom consisting of a synthetic gelatin lens anatomically set up in an appropriate liquid (turpentine) to approach the in vivo velocity ratio. Both extremes of accommodation shapes of the human crystalline lens were investigated. The performance of the developed BF was evaluated in relation to that in homogeneous medium and compared to a conventional delay-and-sum (DAS) BF and a second adapted BF which was simplified to ignore the lens refraction. Global expectations provided by our method with the transducer array are reviewed by an analysis quantifying both image quality and spatial fidelity, as well as the detrimental effects of a crystalline lens in conventional reconstruction. Compared to conventional array imaging, the results indicated a two-fold improvement in the lateral resolution, greater sensitivity and a considerable reduction of spatial distortions that were sufficient to envisage reliable biometry directly in B-mode, especially phakometry.

Skin anisotropy in vivo and initial natural stress effect: a quantitative study using high-frequency static elastography.

BACKGROUND: Most studies on skin anisotropy are carried out in an "average" context, e.g. with an extension/compression test on the skin in vivo, the elastic modulus being estimated for the stretched zone overall. Furthermore, the natural tension of the skin is not taken into account either in the experimental protocols or in the models studied. In this study, a battery of elastographic tests was carried out to investigate forearm skin anisotropy quantitatively by measuring local through-thickness strain in the dermis by means of high frequency elastography. The biaxial tensile effect and influence of the natural forearm skin tension were also analyzed. METHODS: The elastographic test was carried out using a combination of an extensiometer device and a real time ultrasound scanner. The extensiometer was used to apply a stress cycle, i.e. stretching, holding and release, on the internal face of the forearm in vivo. Parallel to the mechanical test, 2D real time ultrasound acquisitions were performed to track local displacements and to estimate local through-thickness strain using an elastographic algorithm. Local through-thickness strain kinetics were then extracted and used as a quantified indicator. We studied anisotropy in two stretching situations: stretching parallel and stretching perpendicular to Langer's lines. Elastographic tests were performed for two upper arm/forearm angles, i.e. outstretched and bent forearm, in order to check the natural skin tension effect. RESULTS: The results showed the effectiveness of elastographic tests to describe and quantify the anisotropic behavior of the forearm skin in vivo. Elastographic results were distinctly different according to forearm positions: the anisotropic behavior was reversed from the bent forearm to the outstretched forearm. CONCLUSIONS: The local anisotropic behavior of the skin in vivo could be easily studied using the elastographic test. Nevertheless, the initial skin tension is an important parameter which strongly affects the mechanical behavior of the skin in vivo, in particular its anisotropic properties.

Mechanical skin thinning-to-thickening transition observed in vivo through 2D high frequency elastography.

This study was based on two dimensional (2D) high frequency elastography to describe quantitatively the mechanical behavior of the human dermis in vivo. The study was conducted on the forearm skin and elastographic tests were performed using a combination of two devices: an extensiometer developed for the in vivo study of the mechanical behavior of the skin using uniaxial stretching stress, and a 20MHz real time sonographer (Dermcup 2020™) for ultrasound skin imaging. The staggered strain estimation algorithm (SSE) was used to produce elastograms. A temporal cumulative technique was applied to improve elastogram quality and to monitor variations in skin strain during stretching. The influence of the natural skin tension controlled by arm bending was studied and distinctive mechanical behavior was observed for low and high mechanical stress levels. In a preliminary analysis, the reproducibility of measurements was assessed by means of coefficient of variation (CV) in 5 selected healthy volunteers.Finally, two hypotheses linked to the geometrical and structural properties of the dermis are proposed to account for the new findings described in this study.