Renaldas Raisutis

Principles of high-frequency ultrasonography for investigation of skin pathology

Ultrasonography is a valuable diagnostic tool widely used in medicine. During the last three decades, this non‐invasive skin imaging method has been extended to dermatology. High‐frequency ultrasonography with higher than 20 MHz scanners is well‐established for measuring tumour thickness and skin thickness when treating inflammatory skin diseases such as scleroderma or psoriasis. High‐frequency ultrasonography has become extremely helpful for the preoperative assessment of skin melanoma. The correlation between ultrasonic and histological measurements of melanomas thickness is significantly similarly good using transducers of 20, 75 or 100 MHz frequency (r range from 0.895 to 0.99) and better compared with transducers of 7.5 MHz frequency (r = 0.76). The preoperative sonographically estimated thickness of skin melanoma is sometimes overestimated, because of an underlying inflammatory infiltrate and other reasons. Assessment of skin melanoma thickness using transducers of 100 MHz frequency has better agreement with histology, compared with ultrasonography with 20 MHz transducers. However, the ultrasonic penetration depth is limited to 1.5 mm in case of 100 MHz. The newer ultrasonic techniques such as high‐frequency ultrasonography and colour Doppler sonography could be used for assessment of the tumour vascularization and its metastatic potential. The wide variety of diagnostic information provided by high‐frequency ultrasonography undoubtedly improves the management of oncological and inflammatory skin conditions and underlines its essential position in dermatological practice.

Ultrasonic Thickness Measurement of Multilayered Aluminum Foam Precursor Material

Metallic foams are prospective materials for use in the aerospace and automotive industry for crash energy absorption safety parts or lightweight constructions. During manufacturing, artifacts in the foamable precursor material or material quality variations can influence the foam structure after the foaming process; thus, such a process requires quality control. The advantage of ultrasonic techniques is the possibility to perform noncontact and one-sided access measurements online. A three-layer system consisting of a layer of aluminum foam precursor sandwiched between two aluminum sheets has been investigated. The problems of ultrasonic nondestructive characterization of such materials are due to the very similar density and ultrasound velocity of the adjacent layers, which produce very weak reflections of ultrasonic waves, and the thin layers also give overlapped reflections in the time domain. The objective of this paper was to develop an ultrasonic technique that is suitable for measurement of the total thickness and the thickness of individual layers. The proposed technique is based on the identification of object parameters. The numerical iterative deconvolution technique was investigated, analyzed, and adapted to measure the thickness of individual layers with similar density and ultrasound velocity of the multilayered aluminum foam precursor material. Theoretical analysis and experimental investigations have shown that application of the proposed numerical iterative deconvolution enables the thickness measurement of individual layers with the expanded uncertainty of less than plusmn10 mum.

Waveguide sensor for measurement of viscosity of highly viscous fluids

Ultrasonic waveguide sensor for measurement of viscosity of highly viscous fluids has been developed. The measurement principle is based on application of guided shear-horizontal SH0 mode of the Lamb waves propagating in an aluminium planar waveguide immersed in a viscous liquid. Attenuation of the guided wave depends on viscosity of the surrounding liquid and is used for viscosity estimation. The developed sensor is mechanically robust and may be used for in-line process control of viscous liquids.

Ultrasonic guided wave tomography for the inspection of the fuel tanks floor

A novel ultrasonic non-destructive technique (NDT) based on application of a transmission tomography of guided ultrasonic waves is proposed for floor inspection of large storage tanks and detection of non-uniformities, such as corrosion. The technique needs access only to the outer edge of the tank floor and does not require emptying the tank. Theoretical estimations have been verified by laboratory experiments using a scaled physical model of the tank. Estimation of the attenuation of different wave modes propagating in steel plates and determination of the losses in the lap welds showed that most suitable is S0 Lamb wave mode which possesses smallest losses and consequently enables investigation of tank floors up to average diameter 20–30 m. The in situ experiments carried out in a real 8 m diameter tank demonstrated that the developed technique could be used for reconstruction of the spatial distribution of the non-uniformities in a tank floor.

Measurement of viscosity of highly viscous non-Newtonian fluids by means of ultrasonic guided waves

In order to perform monitoring of the polymerisation process, it is necessary to measure viscosity. However, in the case of non-Newtonian highly viscous fluids, viscosity starts to be dependent on the vibration or rotation frequency of the sensing element. Also, the sensing element must possess a sufficient mechanical strength. Some of these problems may be solved applying ultrasonic measurement methods, however until now most of the known investigations were devoted to measurements of relatively low viscosities (up to a few Pas) of Newtonian liquids. The objective of the presented work is to develop ultrasonic method for measurement of viscosity of high viscous substances during manufacturing process in extreme conditions. For this purpose the method based on application of guided Lamb waves possessing the predominant component of in-plane displacements (the S0 and the SH0 modes) and propagating in an aluminium planar waveguide immersed in a viscous liquid has been investigated. The simulations indicated that in the selected modes mainly in-plane displacements are dominating, therefore the attenuation of those modes propagating in a planar waveguide immersed in a viscous liquid is mainly caused by viscosity of the liquid. The simulation results were confirmed by experiments. All measurements were performed in the viscosity standard Cannon N2700000. Measurements with the S0 wave mode were performed at the frequency of 500kHz. The SH0 wave mode was exited and used for measurements at the frequency of 580kHz. It was demonstrated that by selecting the particular mode of guided waves (S0 or SH0), the operation frequency and dimensions of the aluminium waveguide it is possible to get the necessary viscosity measurement range and sensitivity. The experiments also revealed that the measured dynamic viscosity is strongly frequency dependent and as a characteristic feature of non-Newtonian liquids is much lower than indicated by the standards. Therefore, in order to get the absolute values of viscosity in this case an additional calibration procedure is required. Feasibility to measure variations of high dynamic viscosities in the range of (20-25,000) Pas was theoretically and experimentally proved. The proposed solution differently from the known methods in principle is more mechanically robust and better fitted for measurements in extreme conditions.

Validation of Dispersion Curve Reconstruction Techniques for the A0 and S0 Modes of Lamb Waves

The properties of ultrasonic Lamb waves, such as relatively small attenuation and high sensitivity to structural changes of the object being investigated, allow performing of non-destructive testing of various elongated structures like pipes, cables, etc. Due to the dispersion effect of Lamb waves, a waveform of the received informative signal is usually distorted, elongated and overlapping in the time domain. Therefore, in order to investigate objects using the ultrasonic Lamb waves and to reconstruct the dispersion curves, it is necessary to know the relationship between frequency, phase and group velocities and thickness of the plate. The zero-crossing technique for measurement of phase velocity of Lamb waves (the A0 and S0 modes) has been investigated using modelled dispersed signals and experimental signals obtained for an aluminium plate having thickness of 2 mm. A comparison between two reconstruction methods of Lamb wave phase velocity dispersion curves, namely, the two-dimensional fast Fourier transform (2D-FFT) and zero-crossing technique, along with the theoretical (analytical) dispersion curves is presented. The results indicate that the proposed zero-crossing method is suitable for use in reconstruction of dispersion curves in the regions affected by strong dispersion, especially for the A0 mode.

Hybrid Signal Processing Technique to Improve the Defect Estimation in Ultrasonic Non-Destructive Testing of Composite Structures

This work proposes a novel hybrid signal processing technique to extract information on disbond-type defects from a single B-scan in the process of non-destructive testing (NDT) of glass fiber reinforced plastic (GFRP) material using ultrasonic guided waves (GW). The selected GFRP sample has been a segment of wind turbine blade, which possessed an aerodynamic shape. Two disbond type defects having diameters of 15 mm and 25 mm were artificially constructed on its trailing edge. The experiment has been performed using the low-frequency ultrasonic system developed at the Ultrasound Institute of Kaunas University of Technology and only one side of the sample was accessed. A special configuration of the transmitting and receiving transducers fixed on a movable panel with a separation distance of 50 mm was proposed for recording the ultrasonic guided wave signals at each one-millimeter step along the scanning distance up to 500 mm. Finally, the hybrid signal processing technique comprising the valuable features of the three most promising signal processing techniques: cross-correlation, wavelet transform, and Hilbert–Huang transform has been applied to the received signals for the extraction of defects information from a single B-scan image. The wavelet transform and cross-correlation techniques have been combined in order to extract the approximated size and location of the defects and measurements of time delays. Thereafter, Hilbert–Huang transform has been applied to the wavelet transformed signal to compare the variation of instantaneous frequencies and instantaneous amplitudes of the defect-free and defective signals.

Propagation of Ultrasonic Guided Waves in Composite Multi-Wire Ropes

Multi-wire ropes are widely used as load-carrying constructional elements in bridges, cranes, elevators, etc. Structural integrity of such ropes can be inspected by using non-destructive ultrasonic techniques. The objective of this work was to investigate propagation of ultrasonic guided waves (UGW) along composite multi-wire ropes in the cases of various types of acoustic contacts between neighboring wires and the plastic core. The modes of UGW propagating along the multi-wire ropes were identified using modelling, the dispersion curves were calculated using analytical and semi-analytical finite element (SAFE) techniques. In order to investigate the effects of UGW propagation, the two types of the acoustic contact between neighboring wires were simulated using the 3D finite element method (FE) as well. The key question of investigation was estimation of the actual boundary conditions between neighboring wires (solid or slip) and the real depth of penetration of UGW into the overall cross-section of the rope. Therefore, in order to verify the results of FE modelling, the guided wave penetration into strands of multi-wire rope was investigated experimentally. The performed modelling and experimental investigation enabled us to select optimal parameters of UGW to be used for non-destructive testing.

Automated Estimation of Melanocytic Skin Tumor Thickness by Ultrasonic Radiofrequency Data.

High‐frequency (>20‐MHz) ultrasound (US) is a noninvasive preoperative tool for assessment of melanocytic skin tumor thickness. Ultrasonic melanocytic skin tumor thickness estimation is not always easy and is related to the experience of the clinician. In this article, we present an automated thickness measurement method based on time‐frequency analysis of US radiofrequency signals.

Preoperative assessment of skin tumor thickness and structure using 14-MHz ultrasound

OBJECTIVE The aim of this study was to compare the relationship between skin tumor thickness and homogeneity and to evaluate the accuracy of 14-MHz ultrasound while measuring the thickness of different skin tumors. MATERIAL AND METHODS The ultrasonographic and histological analysis of 72 skin tumors was performed. Preoperative vertical tumor thickness (T) and structure of 12 melanomas, 34 melanocytic nevi and 26 basal cell carcinomas was assessed by 14-MHz ultrasonography. After the tumors were excised the vertical thickness measurement (Breslow index, pT) was performed by pathologist. According to the histological thickness all skin tumors were divided to thin (≤1mm) and thick (>1mm). The accuracy of the 14-MHz ultrasound measurements and correlation between the ultrasonographic and histological tumor thickness were estimated. RESULTS Homogeneous structure was assessed for all thin (≤1mm) and the majority (81.3%) of thick (>1mm) melanocytic skin tumors. Nonhomogeneous structure was estimated in thin and thick basal cell carcinomas, accordingly 42.9% and 31.9%. Measurements of T and pT correlated moderately in thick (>1mm) tumors (r=0.694), while in thin (≤1mm) tumors correlation was low (r=0.336). Moderate correlation between ultrasonographic and histological thickness was computed for melanocytic skin tumors as well as for basal cell carcinomas (r=0.564 and r=0.690). CONCLUSIONS Medium frequency ultrasound is not a reliable tool for the precise measurement of thin (≤1mm) skin tumors. Ultrasonography using a 14-MHz frequency transducer enables more precisely to measure the thickness of basal cell carcinoma than melanocytic skin tumors. The 14-MHz ultrasound is support tool to suggest the morphologic type of skin tumor.