Institute for Diagnostic Imaging Research

This article discusses a number of modern techniques used for the analysis of works of art. The most widely used approaches as well as lesser known ones are outlined in terms of their applications and the kind of information on the condition of artworks that can be extracted. Special attention is paid to the method of thermographic analysis of works of pictorial art. The principles of the technique, various computational approaches, and safety concerns are discussed. A set of examples is provided for the demonstration of the capabilities of thermographic assessment, including a range of real canvas and panel paintings exhibited in museums and in private collections.

The availability of a non-invasive express method for the in vivo measurement of both sound velocity and thickness of the human skull bone would be of great benefit to various transcranial ultrasonic imaging and treatment applications. This paper investigates two ultrasonic methods that measure both parameters and are based on the variable focus technique. All the experiments described in this paper were conducted on specially prepared custom skull bone phantoms, including flat and deformed samples, designed and developed in our laboratory. The first method uses a single immersion 2.25 MHz ultrasonic transducer consecutively focused on the front and back surfaces of the sample. The accuracy and precision of this method are demonstrated via single point measurements on flat samples with and without porosity. The measurement results from a specimen with the randomly curved back surface show the possibility of obtaining the inner profile of the skull bone. The second presented method is a practical modification of the variable focus technique for the linear phased array case. The method was tested on flat and curved skull bone phantoms with and without inner porosity showing higher measurement accuracy and simpler practical realization than its scanning counterpart.

In the various stages of developing diagnostic and therapeutic equipment, the use of phantoms can play a very important role in improving the process, help in implementation, testing and calibrations. Phantoms are especially useful in developing new applications and training new doctors in medical schools. However, devices that use different physical factors, such as MRI, Ultrasound, CT Scan, etc will require the phantom to be made of different physical properties. In this paper we introduce the properties of recently designed new materials for developing phantoms for ultrasonic human body investigation, which in today's market make up more than 30% in the world of phantoms. We developed a novel composite material which allows fabrication of various kinds of ultrasound bone phantoms to mimic most of the acoustical properties of human bones. In contrast to the ex vivo tissues, the proposed material can maintain the physical and acoustical properties unchanged for long periods of time; moreover, these properties can be custom designed and created to suit specific needs. As a result, we introduce three examples of ultrasound phantoms that we manufactured in our laboratory: cortical, trabecular and skull bone phantoms. The paper also presents the results of a comparison study between the acoustical and physical properties of actual human bones (reported in the referenced literatures) and the phantoms manufactured by us.

A new adaptive beamforming algorithm for imaging via small-aperture 1-D ultrasonic-phased arrays through composite layered structures is reported. Such structures cause acoustic phase aberration and wave refraction at undulating interfaces and can lead to significant distortion of an ultrasonic field pattern produced by conventional beamforming techniques. This distortion takes the form of defocusing the ultrasonic field transmitted through the barrier and causes loss of resolution and overall degradation of image quality. To compensate for the phase aberration and the refractional effects, we developed and examined an adaptive beamforming algorithm for small-aperture linear-phased arrays. After accurately assessing the barrier's local geometry and sound speed, the method calculates a new timing scheme to refocus the distorted beam at its original location. As a tentative application, implementation of this method for trans-skull imaging of certain types of head injuries through human skull is discussed. Simulation and laboratory results of applying the method on skull-mimicking phantoms are presented. Correction of up to 2.5 cm focal point displacement at up to 10 cm depth under our skull phantom is demonstrated. Quantitative assessment of the method in a variety of temporal focusing scenarios is also reported. Overall temporal deviation on the order of a few nanoseconds was observed between the simulated and experimental results. The single-point adaptive focusing results demonstrate strong potential of our approach for diagnostic imaging through intact human skull. The algorithms were implemented on an ultrasound advanced open-platform controlling 64 active elements on a 128-element phased array.

Indoor localization of staff and patients based on radio frequency identification (RFID) technology has promising potential application in the healthcare sector. The use of an active RFID in real-time indoor positioning system without any sacrifice of localization accuracy is intended to provide security, guidance and support service to patients. In this paper maximum likelihood estimation along with its Cramer-Rao lower bound of the locations of active RFID tags are presented by exploring the received signal strength indicator which is collected at the readers. The performance of real-time localization system is implemented by using an extended Kalman filter (EKF).

Abstract: This paper aimed to study the correlation between Real Time Integrated Weld Analyzer measurements and peel test results. The experiment involved study of weld nuggets for different combinations of sheet thicknesses, welding time and current of mild steel samples. The intent was to assess the potential use of a real time integrated ultrasonic system in the industrial environment allowing nondestructive evaluation of 100% of the spot welds produced. The results showed high correlation between nugget penetration into the sheets and nugget size measured ultrasonically and destructively, for all evaluated parameters.

The thickness of a resistance spot weld resulting from electrode indentation is an important quality control parameter for estimating the final nugget diameter and identifying the occurrence of expulsion. An ultrasound transducer has been installed in a welding electrode allowing for evaluation of a spot weld during welding, using echo pulses. In such a system, the unknown increase in temperature during welding increases time of flight through the weld, while geometric contraction of the plates decreases it. These opposing effects often give false representations of the true weld thickness. This paper proposes a novel method of separating these effects. This is done using signal and image processing of successive A‐scans to identify the solid‐liquid nugget interface, where the melting temperature of the material is known. This paper demonstrates how the final weld thickness can be determined very accurately at the point in time when the nugget completely solidifies. It can also be shown that excessive indentation accompanied by a sudden decrease in time‐of‐flight during welding can be used to determine if an expulsion has occurred.

Hydroxyapatite is a widely used material used for the bioactivation of an implant’s surface. A promising hydroxyapatite coating approach is the kinetic deposition of powder particles. The possibility of solid-state deposition improvement through the merging of Aerosol Deposition and Low Pressure Cold Spraying techniques is a promising prospect for improving the deposition efficiency and the quality of coatings. The objective of the paper is to study the possibilities of hydroxyapatite coating structure modification through changes in the coating process and post-heat treatment. The novel Aerosol Cold Spraying system joining Low Pressure Cold Spraying and Aerosol Deposition was used for the deposition of coatings. The coating’s post-processing was conducted using two techniques: Spark Plasma Sintering and Pressureless Sintering. The coating’s structure was examined using scanning, transmission, and light microscopy, and X-ray diffraction. Substrate–coating bond strength was assessed using a tensile test. Homogenous buildup using Aerosol Cold Spraying of hydroxyapatite was achieved. Various pores and microcracks were visible in the sprayed coatings. The deposition process and the thermal post-processing did not lead to significant degradation of the hydroxyapatite phase. As a result of the Spark Plasma Sintering and Pressureless Sintering at 800 °C, an increase in tensile adhesion bond strength and crystal size was obtained.

Abstract The main purpose of this study was to form cold sprayed copper coatings on A 516 low carbon steel, which is considered a prospective material for manufacturing used nuclear fuel containers. The 3 mm-thick Cu coatings were formed using the high pressure cold spray method with N2 as the propellant gas. To increase the adhesion strength of the deposited coatings a copper sublayer was formed first, using He as the propellant gas. The deformation of copper particles during the deposition process was studied. The obtained SEM images of the Cu layer-A 516 low carbon steel substrate cross-sections demonstrated that the Cu sublayer had a dense microstructure, and local jet-metallic mixing areas. The Cu particles were deformed considerably more severely in the sub-layer than in the following layers. The steel substrate underwent severe deformation due to the impact of Cu particles. The mutual severe deformation of Cu particles and steel substrate resulted in a considerable increase of adhesion strength up to 120MPa. The structure of coatings and coating-substrate interface was studied by OIM, SEM and EDS.

Used for centuries in the clinical practice, audible percussion is a method of eliciting sounds by tapping various areas of the human body either by finger tips or by a percussion hammer. Despite its advantages, pulmonary diagnostics by percussion is still highly subjective, depends on the physician's skills, and requires quiet surroundings. Automation of this well-established technique could help amplify its existing merits while removing the above drawbacks. In this work, clinical percussion signals from normal volunteers are decomposed into a sum of exponentially damped sinusoids (EDS) whose parameters are determined using the Matrix Pencil Method. Some EDS represent transient oscillation modes of the thorax/abdomen excited by the percussion event, while others are associated with the noise. It is demonstrated that relatively few EDS are usually enough to accurately reconstruct the original signal. It is shown that combining the frequency and damping parameters of these most significant EDS allows for efficient classification of percussion signals into the two main types historically known as "resonant" and "tympanic." This classification ability can provide a basis for the automated objective diagnostics of various pulmonary pathologies including pneumothorax. The algorithm can be implemented on an embedded platform for the battlefield and other emergency applications.

OBJECTIVE: Background theory and a new algorithm for single-point adaptive focusing in transmission mode through ultrasonic barriers via one-dimensional phased arrays were reported in part I. In this paper the algorithm is further extended and implemented into a full adaptive beamforming process, including complete transmission and reception modes. METHODS: Corrected time delay patterns, adapted to the local acoustical and geometrical properties of the barrier, are calculated and applied in both modes. Further, an adaptive imaging process is also developed that implements the proposed beamforming process for two-dimensional imaging through randomly shaped multilayered phase-aberrating structures. The method is optimized for the case of human skull as the ultrasound barrier and its application for transcranial imaging is discussed. RESULTS: Laboratory results of adaptive imaging through realistic skull-mimicking phantoms are presented. The algorithms are implemented on a 64-channel ultrasound open-source phased array platform controlling a standard 128-element biomedical phased array. Irregularly shaped reflectors with characteristic dimensions of the order of ∼0.5 mm to ∼4.5 mm were used as targets behind the skull phantoms in our experiments. Minimum and maximum distortional target displacements of 2.2 mm and 25.3 mm (in 12 cm depth) were observed in sonograms when uncompensated time delays were used. By contrast, the positioning errors ranged from 0.0 to 0.9 mm when our algorithm was employed. CONCLUSION AND SIGNIFICANCE: The adaptive imaging results demonstrate strong potential of the proposed technique for diagnostic imaging of acoustically reflective head injuries directly through intact human skull.

Abstract Surface preparation is very important for reliable adhesive bonding of cold sprayed coatings to the substrate. In this work, the grit blasting of low-carbon A516 steel substrates with Al2O3 particles was studied and the roughness parameters Ra and Rt of the grit blasted surfaces were then measured. The influence of alumina grit size on the roughening of the A516 steel substrate, and the resulting effect on the roughness of the Cu coating – steel interface were studied. The results showed that variations of the grit blast size had significantly affected the resultant surface roughness of the substrate. The adhesive strength of the formed copper coatings on A516 steel substrates depends on the surface roughness and hardness of the base material. The adhesive strength about 110-200MPa was achieved. The specific features of the Cu coating-A516 steel interface topography were examined and discussed.

This paper examines the utilization of the time reversal matched filtering method to resolve the location of an acoustic point source beneath a skull phantom (variable thickness layer), without the removal of this layer. This acoustical process is examined experimentally in a water tank immersion system containing an acoustic source, a custom-made skull phantom, and a receiving transducer in a pitch-catch arrangement. The phantom is designed to approximately model the acoustic properties of an average human skull bone (minus the diploe layer), while the variable thickness of the phantom introduces a variable time delay to the acoustic wave, relative to its entry point on the phantom. This variable delay is measured and corrected for, and a matched filtering time reversed process is used to determine the location of the point source. The results of the experiment are examined for various positions of the acoustic source behind the phantom and compared to the reference cases with no phantom present. The average distance between these two cases is found to be 4.36 mm, and within the expected deviation in results due to not accounting for the effects of refraction.

The present study investigates the feasibility, accuracy, and precision of 3-D profile extraction of the human skull bone using a custom-designed ultrasound matrix transducer in Pulse-Echo. Due to the attenuative scattering properties of the skull, the backscattered echoes from the inner surface of the skull are severely degraded, attenuated, and at some points overlapped. Furthermore, the speed of sound (SOS) in the skull varies significantly in different zones and also from case to case; if considered constant, it introduces significant error to the profile measurement. A new method for simultaneous estimation of the skull profiles and the sound speed value is presented. The proposed method is a two-folded procedure: first, the arrival times of the backscattered echoes from the skull bone are estimated using multi-lag phase delay (MLPD) and modified space alternating generalized expectation maximization (SAGE) algorithms. Next, these arrival times are fed into an adaptive sound speed estimation algorithm to compute the optimal SOS value and subsequently, the skull bone thickness. For quantitative evaluation, the estimated bone phantom thicknesses were compared with the mechanical measurements. The accuracies of the bone thickness measurements using MLPD and modified SAGE algorithms combined with the adaptive SOS estimation were 7.93% and 4.21%, respectively. These values were 14.44% and 10.75% for the autocorrelation and cross-correlation methods. Additionally, the Bland-Altman plots showed the modified SAGE outperformed the other methods with -0.35 and 0.44 mm limits of agreement. No systematic error that could be related to the skull bone thickness was observed for this method.

The work addresses the important role of conservation science in the pre-restoration diagnostics of paintings. The authors demonstrate how mid-infrared (3-5 m band) methods, namely, Pulse thermography, Pulse Phase thermography and Principal Component thermography, can be used for the analysis of wood-based and canvas-based paintings, illustrating the power of this approach in the detection of delaminations, degraded regions, as well as uncovering scenes which have been painted over (pentimenti). The results of the application of thermographic methods are compared with the results achieved through Near-Infrared reflectography (0.7-1.1 m band) which is recognized as one of most conventional methods for art diagnostics.

In this paper, the mechanisms of laser ultrasound response formation in monocrystalline silicon are discussed. The ultrasound waves in the test specimen were generated with laser pulses of two different wavelengths and registered with a piezoelectric transducer. The amplitude of the measured signal was found to be a nonlinear function of the laser radiation intensity. It was shown, that the observed nonlinearity is related to the features of optical absorption and thermoelastic sources formation in the material. A simple model taking into account temperature dependencies of the thermal conductivity and thermal expansion coefficient was developed. An excellent agreement between experimental and simulation for different wavelengths was demonstrated.

A finite-difference model based on the implicit approach for simulations of basic thermographic experiments is discussed. A specific sparse-matrices format was successfully utilized in order to accelerate the solution of a large system of equations while simulating each time step, as well as reducing the computer memory consumption.

In recent years, deep learning-based algorithms for image super-resolution (SR) have been increasingly thriving. However, in most existing algorithms, the model takes the whole low-resolution (LR) image as input and treats the low-frequency (LF) and high-frequency (HF) contents in the image equally. Considering the nature of Bicubic down-sampling, which is the most used degradation in SR models, high-resolution (HR) and LR images share the most part of the LF in the image while differing in HF. To this end, this paper proposes a model that separates frequencies in the image with an enhanced octave convolution (EOctConv) layer. EOctConv applies channel attention to highlight HFs in the image while considering the relation between the weighted HFs with LFs, respectively. Separating image frequencies not only eases the learning of the relation between LR and HR images, it can significantly enable the model to focus most of the computation on recovering the lost details. The proposed model incorporates significantly fewer numbers of parameters which is indeed a remarkable factor to considerably reduce the computation time and complexity yet compares favorably with recent results in literature qualitatively and quantitatively on benchmark datasets.

It is common knowledge in the medical field that fingernails may potentially be a useful biomarker in assessing certain disorders of the body by both their appearance and texture. With the use of a hand-held, portable ultrasonic device a user may have the ability to quantitatively assess the progression of fingernail properties on-the-spot and over the long term. This device would be applicable to both clinical and cosmetic applications alike. Its application in the medical field to chemotherapy patients in a pilot study is also introduced. No device is currently on the market to quantitatively investigate the properties of fingernails hence this would be the first of its kind. This paper outlines the hardware, software and applications of the ultrasonic probe prototype for use by certified professionals or by the general public.

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