Error analysis and reliability of zero-order Lamb mode inversion for waveguide characterization.

In recent years, several fitting techniques have been presented to reconstruct the parameters of a plate from its Lamb wave dispersion curves. Published studies show that these techniques can yield high accuracy results and have the potential of reconstructing several parameters at once. The precision with which parameters can be reconstructed by inverting Lamb wave dispersion curves, however, remains an open question of fundamental importance to many applications. In this work, we introduce a method of analyzing dispersion curves that yields quantitative information on the precision with which the parameters can be extracted. In our method, rather than employing error minimization algorithms, we compare a target dispersion curve to a database of theoretical ones that covers a given parameter space. By calculating a measure of dissimilarity (error) for every point in the parameter space, we reconstruct the distribution of the error in that space, beside the location of its minimum. We then introduce dimensionless quantities that describe the distribution of this error, thus yielding information about the spread of similar curves in the parameter space. We demonstrate our approach by considering both idealized and realistic scenarios, analyzing the dispersion curves obtained numerically for a plate and experimentally for a pipe. Our results show that the precision with which each parameter is reconstructed depends on the mode used, as well as the frequency range in which it is considered.

Tapering of the interventricular septum can affect ultrasound shear wave elastography: An in vitro and in silico study.

Shear wave elastography (SWE) has the potential to determine cardiac tissue stiffness from non-invasive shear wave speed measurements, important, e.g., for predicting heart failure. Previous studies showed that waves traveling in the interventricular septum (IVS) may display Lamb-like dispersive behaviour, introducing a thickness-frequency dependency in the wave speed. However, the IVS tapers across its length, which complicates wave speed estimation by introducing an additional variable to account for. The goal of this work is to assess the impact of tapering thickness on SWE. The investigation is performed by combining in vitro experiments with acoustic radiation force (ARF) and 2D finite element simulations, to isolate the effect of the tapering curve on ARF-induced and natural waves in the heart. The experiments show a 11% deceleration during propagation from the thick to the thin end of an IVS-mimicking tapered phantom plate. The numerical analysis shows that neglecting the thickness variation in the wavenumber-frequency domain can introduce errors of more than 30% in the estimation of the shear modulus, and that the exact tapering curve, rather than the overall thickness reduction, determines the dispersive behaviour of the wave. These results suggest that septal geometry should be accounted for when deriving cardiac stiffness with SWE.

Optimization of acoustic coupling for bottom actuated scattering based subsurface scanning probe microscopy.

The characterization of buried nanoscale structures nondestructively is an important challenge in a number of applications, such as defect detection and metrology in the semiconductor industry. A promising technique is Subsurface Scanning Probe Microscopy (SSPM), which combines ultrasound with Atomic Force Microscopy (AFM). Initially, SSPM was used to measure the viscoelastic contrast between a subsurface feature and its surrounding medium. However, by increasing the ultrasonic frequency to >1 GHz, it has been shown that SSPM can also measure acoustic impedance based contrasts. At these frequencies, it becomes difficult to reliably couple the sound into the sample such that the AFM is able to pick up the scattered sound field. The cause is the existence of strong acoustic resonances in the sample, the transducer, and the coupling layer-the liquid layer used to couple the sound energy from the transducer into the sample-in combination with the nonlinearity of the tip-sample interaction. Thus, it is essential to control and measure the thickness of the coupling layer with nanometer accuracy. Here, we present the design of a mechanical clamp to ensure a stable acoustic coupling. Moreover, an acoustic method is presented to measure the coupling layer thickness in real-time. Stable coupling layers with thicknesses of 700 ± 2 nm were achieved over periods of 2-4 h. Measurements of the downmixed AFM signals showed stable signal intensities for >1 h. The clamp and monitoring method introduced here makes scattering based SSPM practical, robust, and reliable and enables measurement periods of hours.

A sensitive optical micro-machined ultrasound sensor (OMUS) based on a silicon photonic ring resonator on an acoustical membrane.

With the increasing use of ultrasonography, especially in medical imaging, novel fabrication techniques together with novel sensor designs are needed to meet the requirements for future applications like three-dimensional intercardiac and intravascular imaging. These applications require arrays of many small elements to selectively record the sound waves coming from a certain direction. Here we present proof of concept of an optical micro-machined ultrasound sensor (OMUS) fabricated with a semi-industrial CMOS fabrication line. The sensor is based on integrated photonics, which allows for elements with small spatial footprint. We demonstrate that the first prototype is already capable of detecting pressures of 0.4 Pa, which matches the performance of the state of the art piezo-electric transducers while having a 65 times smaller spatial footprint. The sensor is compatible with MRI due to the lack of electronical wiring. Another important benefit of the use of integrated photonics is the easy interrogation of an array of elements. Hence, in future designs only two optical fibers are needed to interrogate an entire array, which minimizes the amount of connections of smart catheters. The demonstrated OMUS has potential applications in medical ultrasound imaging, non destructive testing as well as in flow sensing.

Single pulse frequency compounding protocol for superharmonic imaging.

Second harmonic imaging is currently accepted as the standard in commercial echographic systems. A new imaging technique, coined as superharmonic imaging (SHI), combines the third till the fifth harmonics, arising during nonlinear sound propagation. It could further enhance the resolution and quality of echographic images. To meet the bandwidth requirement for SHI a dedicated phased array has been developed: a low frequency subarray, intended for transmission, interleaved with a high frequency subarray, used in reception. As the bandwidth of the elements is limited, the spectral gaps in between the harmonics cause multiple (ghost) reflection artifacts. A dual-pulse frequency compounding method aims at suppressing those artifacts at a price of a reduced frame rate. In this study we explore a possibility of performing frequency compounding within a single transmission. The traditional frequency compounding method suppresses the ripples by consecutively emitting two short Gaussian bursts with a slightly different center frequency. In the newly proposed method, the transmit aperture is divided into two parts: the first half is used to send a pulse at the lower center frequency, while the other half simultaneously transmits at a slightly higher center frequency. The suitability of the protocol for medical imaging applications in terms of the steering capabilities was performed in a simulation study with INCS and the hydrophone measurements. Moreover, an experimental study was carried out to find the optimal parameters for the clinical imaging protocol. The latter was subsequently used to obtain the images of a tissue mimicking phantom containing strongly reflecting wires. Additionally, the images of a human heart in the parasternal projection were acquired. The scanning aperture with the developed protocol amounts to approximately 90°, which is sufficient to capture the cardiac structures in the standard anatomical projections. The theoretically estimated and experimentally measured grating lobe levels are equal to -28.3 dB and -35.9 dB, respectively. A considerable improvement in the axial resolution of the SHI component (0.73 mm) at -6 dB in comparison with the third harmonic (2.23 mm) was observed. A similar comparison in terms of the lateral resolution slightly favored the superharmonic component by 0.2 mm. Additionally, the images of the tissue mimicking phantom exhibited the absence of the multiple reflection artifacts. The in-vivo acquisition allows one to clearly observe the dynamic of the mitral valve leaflets. The new method is equally effective in eliminating the ripple artifacts associated with SHI as the dual-pulse technique, while the full frame rate is maintained.

Randomized clinical trial of ultrasound-guided foam sclerotherapy versus surgery for the incompetent great saphenous vein.

BACKGROUND: New minimally invasive treatment modalities, such as ultrasound-guided foam sclerotherapy (UGFS), are becoming more popular. In a multicentre randomized controlled non-inferiority trial, the effectiveness and costs of UGFS and surgery for treatment of the incompetent great saphenous vein (GSV) were compared. METHODS: Patients with primary great saphenous varicose veins were assigned randomly to either UGFS or surgical stripping with high ligation. Recurrence, defined as reflux combined with venous symptoms, was determined on colour duplex scans at baseline, 3 months, 1 year and 2 years after initial treatment. Secondary outcomes were presence of recurrent reflux (irrespective of symptoms), reduction of symptoms, health-related quality of life (EQ-5D(™)), adverse events and direct hospital costs. RESULTS: Two hundred and thirty patients were treated by UGFS and 200 underwent GSV stripping. The 2-year probability of recurrence was similar in the UGFS and surgery groups: 11·3 per cent (24 of 213) and 9·0 per cent (16 of 177) respectively (P = 0·407). At 2 years, reflux irrespective of venous symptoms was significantly more frequent in the UGFS group (35·0 per cent) than in the surgery group (21·0 per cent) (P = 0·003). Mean(s.d.) hospital costs per patient over 2 years were €774(344) per patient for UGFS and €1824(141) for stripping. CONCLUSION: At 2-year follow-up, UGFS was not inferior to surgery when reflux associated with venous symptoms was the clinical outcome of interest. UGFS has the potential to be a cost-effective approach to a common health problem. Registration numbers: NCT01103258 (http://www.clinicaltrials.gov) and NTR654 (http://www.trialregister.nl).

Drop foot, a rare complication following Müller's phlebectomy.

In this article we present a case of a temporary foot drop after ambulatory phlebectomy. The temporary nerve blockage was caused by anaesthetic infiltration. In treating varicose veins using the technique of Müller, care must be taken for transient nerve palsies.

A comparison of twice-daily calcipotriol ointment with once-daily short-contact dithranol cream therapy: a randomized controlled trial of supervised treatment of psoriasis vulgaris in a day-care setting.

BACKGROUND: Calcipotriol has become a first-line treatment for psoriasis. Its efficacy and safety have been shown in many comparative clinical trials carried out in outpatients. In a comparative study in patients visiting the outpatient department once every 14 days, it was shown that calcipotriol was more effective and better tolerated compared with dithranol. OBJECTIVES: To compare the clinical efficacy of calcipotriol ointment with that of dithranol cream in a supervised treatment regimen. METHODS: In a multicentre randomized controlled trial in six centres in the Netherlands, 106 patients with chronic plaque psoriasis were included, 54 receiving calcipotriol ointment twice daily and 52 dithranol cream once daily. Patients were treated at the day-care centre, using the care instruction principle of daily visits during the first week and twice-weekly visits subsequently for up to 12 weeks. RESULTS: This study failed to prove that calcipotriol is as efficacious as dithranol when used in a day-care setting (noninferiority test). The mean percentage reduction in Psoriasis Area and Severity Index from baseline to end of treatment was 57.0% in the calcipotriol group vs. 63.6% in the dithranol group. However, the two-sided test for superiority indicated no statistically significant difference between the treatment groups (P = 0.39). At the end of treatment, 15% of the patients treated with calcipotriol ointment and 25% of those treated with dithranol cream did not require any further treatment. Although calcipotriol ointment appeared to be more effective during the first 8 weeks, a difference was no longer apparent at 12 weeks. In comparison with the high number of drop-outs due to cutaneous side-effects in the calcipotriol group, the frequency of a tolerable degree of irritation appeared to be higher in patients treated with dithranol. However, concomitant corticosteroid treatment of dithranol irritation in seven patients may have contributed to this difference between both treatments. Moreover, patients receiving therapy with calcipotriol ointment experienced fewer application-related skin and subcutaneous tissue disorders than patients treated with dithranol cream: 21 of 53 (40%) and 37 of 52 (71%), respectively. This difference is statistically significant (P = 0.001). CONCLUSIONS: The hypothesis that calcipotriol ointment might be at least as effective as dithranol cream in the day-care setting could not be proven in the present study. Whereas calcipotriol has become a mainstay in the routine outpatient treatment of psoriasis not requiring a day-care setting, dithranol treatment, being difficult as a routine outpatient therapy, has increased efficacy and improved tolerability if the treatment is carried out in a day-care setting.

Detecting broken struts of a Björk-Shiley heart valve using ultrasound: a feasibility study.

The Björk-Shiley (BScc) mechanical heart valve has extensively been used in surgery from 1979 to 1986. There is, compared with equivalent valve types, increased occurrence of unexpected mechanical failure of the outlet strut of the valve, with a high incidence of mortality, when it occurs. Many approaches have been attempted to noninvasively determine BScc valve integrity. None of the approaches resulted in adequate assessment, mostly due to a lack of either sensitivity or specificity demonstrated in in vitro and/or in vivo studies. In our study we analyze leg movement of the BScc valves outlet strut during the cardiac cycle with ultrasound. For a broken strut, the movement of both legs will be significantly different, whereas the difference will be negligible for an intact strut. BScc valves were mounted in the mitral position in an in vitro pulse duplicator system. A focused single-element transducer was used to direct ultrasound on a leg of the outlet strut. Correlation-based time delay estimation was used to estimate differences in time of flight of the outlet strut echoes to determine outlet strut leg movement. The movement of an intact valve and a valve with a single-leg fracture with both ends grating against each other (SLF), the most difficult fracture to diagnose, has been studied. The results showed no significant difference in movement between both legs of the outlet strut of the intact BScc valve (amplitude of movement 9.2 microm +/- 0.1 microm). Whereas for the defective valve, the amplitude of movement of the broken leg of the SLF valve was 12 microm +/- 1.6 microm vs. 8.6 microm +/- 0.1 microm for the intact leg. In conclusion, the proposed method has shown to be feasible in vitro and has potentials for in vivo detection of BScc valve outlet strut fracture.

Constipation presenting as recurrent vulvovaginitis in prepubertal children.

Vulvovaginitis is the most common gynecologic problem in premenarcheal girls. We describe 3 patients with recurrent vulvovaginitis caused by bacterial infection who responded to treatment of constipation with resolution of the vulvovaginitis. There were no recurrences during the follow-up period of 15 to 36 months. We propose that underlying constipation should be added to the list of possible causes of recurrent vulvovaginitis.