New quantitative data processing methods could enable ultrasound as a potential diagnostic method for hip implant integration monitoring. For development of such methods, suitable acoustic simulation tools are essential. In this work, a novel 1D FDTD simulation tool for multilayer structures, considering frequency-dependent properties, is introduced, particularly meeting the special needs of this application. Simulation results show excellent agreement with experimental data, confirming accurate prediction of wave propagation in multilayer systems.

Since COVID-19, clean indoor air has become more of a focus due to airborne viruses. Conventional filters often fail to capture ultrafine particles. This work investigates how standing ultrasonic fields manipulate aerosols for more efficient cleaning. Gor’kov theory and FEM simulations used to evaluate the acoustic forces on particles. Experiments by light refractive vibrometry and high-speed camera observations confirm the model quality.

This paper explores an alternative approach to ultrasonic flow measurement using guided acoustic waves in cylindrical modes. Unlike conventional methods with diagonal sound propagation, the entire pipe including the fluid is excited to vibrate, reducing path-dependent correction factors. A ring-shaped sensor was developed for a DN15 steel pipe. Results show a signal time shift 2.5 times greater than with Lamb wave-based sensors, adjustable over distance. This approach enables precise, non-invasive flow measurement across various pipe diameters.

Background, Motivation and Objective

Hip joint prostheses (HJP) are increasingly common with an aging population. The most frequent complication is aseptic loosening, linked to bone resorption and a growing soft tissue gap between bone and implant. However, integration monitoring and loosening diagnosis still rely on expensive, static X-ray imaging. Ultrasound, despite cheaper, dynamic, and radiation-free, is not yet viable due to its limits in resolving tissue beyond the bone.

This work presents how a novel quantitative ultrasound (QUS) data processing approach could improve HJP monitoring by quantitatively assessing osteointegration. While the basic concept was already tested on artificial models, we now show first clinical results for ultrasonic thickness measurements of the bone-implant gap at hip implant patients compared to X-ray imaging.

Statement of Contribution/Methods

Our approach is based on an analysis of raw (RF) beamformed ultrasonic data. A scan line perpendicular to the bone surface is extracted and a certain signal range following the dominant bone reflection is transformed to the frequency domain using a Fast Fourier Transform (FFT) (a). The gap thickness, indicating local osteointegration quality and potential loosening signs, is then determined by evaluating the frequency spacing of minima in the amplitude spectrum.

To demonstrate the potential of our QUS method, we analyzed ultrasonic scans from six HJP patients at one fixed position each (sagittal and transversal) using a handheld scanner (C3 HD3, Clarius, Canada) and compared the measured gap thicknesses with x-ray images.

Results/Discussion

(b) shows the gap thicknesses determined using our QUS method in comparison with the visual assessment of corresponding X-ray images. Despite the small sample size and some simplifying assumptions used for this first feasibility test, the clear trend highlights the approach’s potential for assessing local implant integration. The cases where no gap could be seen in the x-ray image illustrate its potential for gap detection beyond X-ray resolution limits.

Besides gap thickness, our QUS approach could also reveal elasticity changes in the soft-tissue gap, potentially indicating critical biofilm formation. Further steps also include extending our method to an automated thickness detection during dynamic scanning and integrating results into B-mode images, e. g., using color coding.

This study is focused on optimizing electromagnetic acoustic transducer (EMAT) sensors for enhanced ultrasonic guided wave signal generation in steel cables using CAD and modern manufacturing to enable contactless ultrasonic signal transmission and reception. A lab test rig with advanced measurement and data processing was set up to test the sensors’ ability to detect cable damage, like wire breaks and abrasion, while also examining the effect of potential disruptors such as rope soiling. Machine learning algorithms were applied to improve the damage detection accuracy, leading to significant advancements in magnetostrictive measurement methods and providing a new standard for future development in this area. The use of the Vision Transformer Masked Autoencoder Architecture (ViTMAE) and generative pre-training has shown that reliable damage detection is possible despite the considerable signal fluctuations caused by rope movement.

The study presents a unifying methodology for characterizing micromixers, integrating both experimental and simulation techniques. Focusing on Dean mixer designs, it employs an optical evaluation for experiments and a modified Sobolev norm for simulations, yielding a unified dimensionless characteristic parameter for the whole mixer at a given Reynolds number. The results demonstrate consistent mixing performance trends across both methods for various operation points. This paper also proposes enhancements in the evaluation process to improve accuracy and reduce noise impact. This approach provides a valuable framework for optimizing micromixer designs, essential in advancing microfluidic technologies.

Der künstliche Hüftgelenkersatz ist eine der häufigsten und etabliertesten Operationen in der Orthopädie und Unfallchirurgie. Mehr als 200 000 Implantationen pro Jahr allein in Deutschland geben zahlreichen Menschen wieder Beweglichkeit, Flexibilität und Unabhängigkeit. Doch schon nach 3 Jahren müssen mehr als 3 Prozent dieser Hüftprothesen wieder ersetzt werden und diese Wahrscheinlichkeit steigt mit jedem Jahr weiter an. Ursächlich sind hauptsächlich Lockerungen, eine mangelnde knöcherne Integration der Prothese nach der Operation oder Knochenfrakturen im Bereich des Implantatschafts, die in biologischen und biomechanischen Veränderungen an der Knochen-Implantat-Grenze begründet liegen.

Eine quantitative und lokale Zustandsbewertung dieses Knochen-Implantat-Grenzbereichs könnte solche Veränderungen früh erkennen, aber auch das Einwachsen einer Prothese überwachen, sodass der Arzt früh reagieren und entsprechende Maßnahmen einleiten kann. Eine solche Bewertung könnte die üblichen klinischen Diagnoseverfahren, wie die klassische Röntgenaufnahme, die mangels Genauigkeit oder Quantifizierbarkeit in ihrer Aussagekraft
beschränkt sind, zu einem verbesserten klinischen Gesamtbild ergänzen.

In dieser Arbeit wurde zum Zwecke einer solchen nicht-invasiven und quantitativen Zustandsüberwachung ein akustisches Messverfahren entwickelt. Dieses basiert auf einer Idealisierung des Oberschenkels mit Hüftprothesenschaft als Mehrschichtsystem und einer analytischen Modellierung dessen akustischen Reflexionsverhaltens in Zeit- und Frequenzbereich.

Mithilfe verschiedener daraus abgeleiteter Schritte der Signalverarbeitung, die das Empfangssignal des Schallwandlers aus einer Puls-Echo-Messung wechselnd in Zeit- und Frequenzbereich untersuchen, können automatisiert relevante Kennwerte ermittelt werden, die Hinweise auf den biologischen und biomechanischen Zustand der Hüftprothese geben. Dazu zählen Schichtdicken und Dämpfungskonstanten von äußerem Weichgewebe und Knochen, aber auch die Dicke des potenziell auftretenden Weichgewebe-Bereichs zwischen Knochen und Implantat sowie Schallkennimpedanzen von Knochen und dieser Zwischenschicht.

Mittels eines eigens entwickelten Simulationstools für die eindimensionale und frequenzabhängige Schallausbreitung im Mehrschichtsystemen sowie unter Nutzung speziell ausgewählter und selbst hergestellter Ersatzmaterialien wurden die erarbeitete physikalische Modellierung und die Signalverarbeitungsalgorithmik in Simulation und Experiment erprobt. Ein Vergleich zwischen Theorie, Simulation und Experiment zeigt eine sehr gute Übereinstimmung. Systematische Abweichungen aus früheren Arbeiten konnten durch die gänzlich neu erarbeitete physikalische Beschreibung der Situation ausgeräumt werden. Für alle beschriebenen quantitativen Kennwerte konnten gut mit Referenz-Werten übereinstimmende Ergebnisse im anwendungsnahen Bereich erzielt werden. Erste Untersuchungen zur Robustheit und Sensitivität des Algorithmus ergänzen die experimentellen Ergebnisse.

Zuletzt wurde in einer ersten Vergleichsmessung am menschlichem Oberschenkel mithilfe eines konventionellen Sonographie-Geräts aufgezeigt, dass das entwickelte akustische Verfahren zur Mehrschichtsystemcharakterisierung das Potenzial für eine Zustandsbewertung von Hüftprothesen hat.

Mehr als 10 Prozent der 250.000 pro Jahr in Deutschland implantierten Hüftprothesen lockern sich bereits in der ersten 10 Jahren nach der Operation wieder, was für die Patienten häufig schmerzhafte und komplikationsreiche Revisionsoperationen zur Folge hat. Bei einer Lockerung entwickelt sich zwischen Knochen und Implantat ein dünner Weichgewebe-Spalt. Dessen Dicke lässt Rückschlüsse auf den Grad der Lockerung zu und seine Materialeigenschaften geben Hinweise auf die Lockerungsursache, die rein mechanisch bedingt oder durch bakterielle Infektion ausgelöst sein kann. Klinisch übliche Diagnosetechniken wie die Projektionsradiographie (klassische Röntgenaufnahme) versagen jedoch bei der verlässlichen Erkennung einer Lockerung im Frühstadium sowie der Differenzierung deren Ursache.
Um diesem Problem zu begegnen, haben wir ein Ultraschallmessverfahren zur lokalen und quantitativen Charakterisierung der Knochen-Implantat-Grenzschicht entwickelt. Ein analytisches Modell für die Reflexion von Schallwellen in einem Dreischichtsystem wurde mit einer neuartigen Datenverarbeitungsmethodik kombiniert, um den Anforderungen der spezifischen medizinischen Anwendung gerecht zu werden. Durch nichtlinearen Fit der theoretischen Vorhersage des Modells an die tatsächliche Signalform der reflektierten Schallwellen im Frequenzbereich kann die Dicke der Zwischenschicht bestimmt werden und Vorhersagen über ihre physikalischen Eigenschaften sind möglich. Dadurch lassen sich dann potenziell Informationen zu Grad und Ursache der Lockerung gewinnen.
Der vorgestellte Ansatz wurde bereits erfolgreich auf idealisierte Testsysteme und ein Knochen-Implantat-System zur Dickenbestimmung im Bereich von ca. 200 µm bis 2 mm angewendet.

Der Vortrag wird sich auf den physikalischen Hintergrund und die Schlüsselkonzepte des Verfahrens sowie auf repräsentative Experimente konzentrieren, aber auch das zukünftige Potenzial der Technologie in der medizinischen Anwendung aufzeigen.

Loosening of an artificial hip joint is a frequent complication in orthopedics and trauma surgery. Due to a lack of accuracy, conventional diagnostic methods such as projection radiography cannot reliably diagnose loosening in its early stages or detect whether it is associated with the formation of a biofilm in the bone-implant interface.

In this work, we developed an ultrasonic measurement procedure for quantifying the thickness of the layer between bone and prosthesis as a correlate to loosening. In principle, it also allows for the material characterization of the interface. An analytical model for the reflection of sound waves in a three-layer system was combined with a new data processing method to face the challenges of the specific medical application. By non-linear fitting the theoretical prediction of the model to the actual shape of the reflected sound waves in frequency domain, the thickness of the interlayer can be determined and predictions about its physical properties are possible. The presented approach was successfully applied to idealized test systems and a bone-implant system for thickness determination in the range of approx. 200 µm to 2 mm [1].

The talk will focus on the physical background and the key concepts of the procedure as well as on representative experiments, but also highlight its future potential in medical application.

[1] J. Lützelberger et al., Sensors 23, 5942 (2023)

Particularly in medical technology, biotechnology or the pharmaceutical sector, very small quantities of fluids often have to be transported or dosed. Noninvasive measuring methods for flow rate or volume flow measurement that work without direct contact to the fluid and thus meeting the high hygiene standards of these industries hardly exist. Sensors available on the market are either not suitable for precise measurement of the smallest flow rates in the microliter range or are very expensive. For this field of applications, a retrofittable ultrasound-based flow sensor was developed in cooperation with the company ibidi GmbH, which can be integrated into an existing system consisting of very thin tubes or cannulas or capillaries as well as thin flexible tubes.

The loosening of an artificial joint is a frequent and critical complication in orthopedics and trauma surgery. Due to a lack of accuracy, conventional diagnostic methods such as projection radiography cannot reliably diagnose loosening in its early stages or detect whether it is associated with the formation of a biofilm at the bone–implant interface. In this work, we present a non-invasive ultrasound-based interferometric measurement procedure for quantifying the thickness of the layer between bone and prosthesis as a correlate to loosening. In principle, it also allows for the material characterization of the interface. A well-known analytical model for the superposition of sound waves reflected in a three-layer system was combined with a new method in data processing to be suitable for medical application at the bone–implant interface. By non-linear fitting of the theoretical prediction of the model to the actual shape of the reflected sound waves in the frequency domain, the thickness of the interlayer can be determined and predictions about its physical properties are possible. With respect to determining the layer’s thickness, the presented approach was successfully applied to idealized test systems and a bone–implant system in the range of approx. 200 µm to 2 mm. After further optimization and adaptation, as well as further experimental tests, the procedure offers great potential to significantly improve the diagnosis of prosthesis loosening at an early stage and may also be applicable to detecting the formation of a biofilm.

Due to increasingly ageing populations and a rising demand on quality of life hip replacement became one of the most common operations in orthopedics and trauma surgery over the last decades and even continues to gain importance. However, in more than 10 percent of cases, loosening of the implanted prosthesis occurs within the first 15 years after surgical implantation. As a result, the prosthesis usually has to be completely replaced in a complex operation which often leads to complications. The later the prosthesis loosening is detected, the more difficult the initial situation for a successful and complication-free prosthesis replacement is. In addition to early diagnosis, it is essential to distinguish between purely mechanical (aseptic) loosening and loosening caused by bacterial infection (septic). Due to a lack of accuracy, conventional diagnostic methods such as projection radiography cannot reliably diagnose loosening in its early stages or detect whether it is associated with the formation of a biofilm in the bone-implant interface.

In this work, we developed a non-invasive ultrasound-based measurement procedure for quantifying the thickness of the layer between the bone and the stem of a hip prosthesis as a correlate to loosening. In principle, it also allows for material characterization of the interface.

The introduced method is based on a well-known analytical model of the reflection of sound waves in a three-layer system being mainly used for characterizing the thickness of thin lubricant films. For the desired medical application of characterizing the bone-implant interface which comes along with rough surfaces, inhomogeneous materials and the impossiblity of reference measurements, we adapted and extended this model and developed suitable data processing algorithms for analyzing the interface.

With respect to determining the layer thickness, the procedure was experimentally validated at different idealized test systems and a more realistic bone-implant system within in the range of approx. 200 µm to 2 mm. Consequently, our procedure is able to quantify the thickness of thin interlayers even at rough, porous and inhomogeneous materials and without a reference measurement.

After further optimization and adaptation, as well as further experimental tests, the procedure offers great potential to significantly improve the diagnosis of prosthesis loosening at an early stage and may also bei applicable to detect the formation of a biofilm.