2aAB1 – Most animals hear acoustic flow instead of pressure; we should too

Department of Mechanical Engineering
Binghamton University
State University of New York
Binghamton, NY 13902 USA

Popular version of paper 2aAB1
Presented Tuesday morning May 14, 2019. 8:35-8:55 am
177th ASA Meeting, Louisville, KY

The sound we hear consists of tiny, rapid changes in the pressure of air as it fluctuates about the steady atmospheric pressure. Our ears detect these minute pressure fluctuations because they produce time-varying forces on our eardrums. Many animals hear sound using pressure-sensitive eardrums such as ours. However, most animals that hear sound (including countless insects) don’t have eardrums at all. Instead, they listen by detecting the tiny motion of air molecules as they flow back and forth when sound propagates.

The motion of air molecules in a sound wave is illustrated the video below. The moving dots in this video depict motion of gas molecules due to the back and forth motion of a piston shown at the left. The sound wave is a propagating fluctuation in the density (and pressure) of the molecules. Note that a wave propagates to the right while the motion of each molecule (such as the larger moving dot in the center of the image) consists of back and forth motion. Small animals sense this back and forth motion by sensing the deflection of thin hairs that are driven by viscous forces in the fluctuating acoustic medium.

It is likely that the early inventors of acoustic sensors fashioned microphones to operate based on sensing pressure because they knew that is how humans hear sound. As a result, all microphones have possessed a thin pressure-sensing diaphragm (or ribbon) that functions much like our eardrums. The fact that most animals don’t hear this way suggests that there may be significant benefits to considering alternate designs. In this study, we explore technologies for achieving precise detection of sound using a mechanical structure that is driven by viscous forces associated with the fluctuating velocity of the medium. In one example, we have shown this to result in a directional microphone with flat frequency response from 1 Hz to 50 kHz (Zhou, Jian, and Ronald N. Miles. “Sensing fluctuating airflow with spider silk.” Proceedings of the National Academy of Sciences 114.46 (2017): 12120-12125.).

Nature shows that there are many ways to fashion a thin, lightweight structure that can respond to minute changes in airflow as occur in a sound field. A first step in designing an acoustic flow sensor is to understand the effects of the viscosity of the air on such a structure as air flows in a sound field; viscosity is known to be essential in the acoustic flow-sensing ears of small animals. Our mathematical model predicts that the sound-induced motion of a very thin beam can be dominated by viscous forces when its width becomes on the order of five microns. Such a structure can be readily made using modern microfabrication methods.

In order to create a microphone, once an extremely thin and compliant structure is designed that can respond to acoustic flow-induced viscous forces, one must develop a means of converting its motion into an electronic signal. We have described one method of accomplishing this using capacitive transduction (Miles, Ronald N. “A Compliant Capacitive Sensor for Acoustics: Avoiding Electrostatic Forces at High Bias Voltages.” IEEE Sensors Journal 18.14 (2018): 5691-5698).

Acknowledgement: This research is supported by a grant from NIH National Institute on Deafness and other Communication Disorders (1R01DC017720-01).

1aBAb2 – In saline flooded Lung exists superior acoustic conditions for treatment of lung cancer using therapeutic ultrasound

Dr. rer. nat. Frank Wolfram
Chirurgie II / Lung Cancer Centre
SRH Wald-Klinikum Gera
Straße des Friedens 122
07548 Gera
Tel: 0365 82-83151
E-Mail: Frank.Wolfram@WKG.SRH.de

Presented Monday morning 10:40, May 13, 2019
177^thASA Meeting, Louisville, KY

Lung Lung is known as a total acoustic absorber which in turn makes the use therapeutic ultrasound for local lung tumour treatment unsuitable.

By replacing pulmonary gas with saline, acoustic transmission can be achieved. Such One Lung Filling (OLF) has been studied intensively showing no cardio pulmonary deficiencies and is an accepted procedure in pneumology for clearance from proteinosis or silica dust.

Our aim is to combine OLF and therapeutic ultrasound where the cancerous lung is flooded while the contralateral side maintains ventilated. During stable OLF, central lung cancer tissue could be treated non-invasively using therapeutic ultrasound (HIFU). In order to understand ultrasound interaction in such flooded condition, the acoustic conditions were investigated and their impact on the lung cancer ablation process discussed.

For this study preclinical ex and in-vivo models have been used. Determination of acoustic parameter was performed using a broad band immersion technique. Lung cancers and flooded lung show a speed of sound and impedance as known solid tissue, whilst flooded lung show a significant lower attenuation. HIFU induces in adeno carcinoma temperatures above the ablative threshold (80°C), whilst the same acoustic dose in flooded lung only a non-lethal temperature rise (43°C) causes. Sonographic examinations revealed complete visibility of lung cancer and lung metastases.

During OLF atypical, but superior acoustic conditions for application of therapeutic ultrasound exists. Sonography is an excellent guiding modality providing a 100% tumor demarcation. The HIFU interacts with the malignant tissue leaving healthy lung parenchyma unaffected.

These findings suggest valuable benefits for future clinical implementation. Most lung cancer are inoperable at diagnosis due to poor lung function or advanced stage, the parenchyma sparing property of Lung HIFU could help to reduce tumor load while preserving lung function without toxicity. Additionally, the repeatability of therapeutic ultrasound can provide iterative treatment in case of recurrence or new metastasis.

1pBA4 – Dedicated signal processing for lung ultrasound imaging: Can we see what we hear?

Libertario Demi – libertario.demi@unitn.it

Department of Information Engineering and Computer Science
University of Trento, Italy

Popular version of paper 1pBA4
Presented Monday morning, May 13, 2019
177^thASA Meeting, Louisville, KY

Lung diseases have a large impact worldwide. Chronic Obstructive Pulmonary Diseases (COPD) and lower respiratory infections are respectively the third and fourth leading cause of death in the world, and are responsible for six million deaths per year [1]. Pneumonia, an inflammatory condition of the lung, is the leading cause of death in children under five years of age and responsible for approximately 1 million deaths per year. The economical burden is also significant. Considering only COPD, in the United States of America, the sum of indirect and direct healthcare costs is estimated to be in the order of 50 billion dollars [2].

Cost effective and largely available solutions for the diagnosis and monitoring of lung diseases would be of tremendous help, and this is exactly the role that could be played by ultrasound (US) technologies.

Compared to the current standard, i.e., X-ray based imaging technologies like a CT-scan, US tech is in fact safe, transportable, and cost-effective. Firstly, being an ionizing-radiation-free modality, US is a diagnostic option especially relevant to children, pregnant women and patients subjected to repeated investigations. Secondly, US devices are easily transportable to patient’s site, also in remote and rural areas, and developing countries. Thirdly, devices and examinations are significantly cheaper as compared to CT or MRI, making US tech accessible to a much broader range of facilities, thus reaching more patients.

However, this large potential is today underused. The examination of the lung is in fact performed with US equipment conceptually unsuitable to this task. Standard US scanners and probes have been designed to visualize body parts (hart, liver, mother’s womb, the abdomen) for which the speed of sound can be assumed to be constant. This is clearly not the case for the lung, due to presence of air. As a consequence, it is impossible to correctly visualize the anatomy of the lung beyond its surface and, in most conditions, the only usable products of standard US equipment are images that display “signs”.

These signs are called imaging artifacts, i.e., objects that are present in the image but which are not physically present in the lung (see example in the Figures). These artifacts, for most of which we still do not know why exactly they appear in the images, carry diagnostic information and are currently used in the clinics, but can obviously only lead to qualitative and subjective analysis.

Example of standard ultrasound images with different artifacts: A-line artifacts, left, are generally associated with a healthy lung, while B-lines, on the right, correlate with different pathological conditions of the lung. The arrows on top indicate the location of the lung surface in the image, visualized as a bright horizontal line. Beyond this depth the capability of these images to provide an anatomical description of the lung is lost.

Moreover, their appearance in the image largely depends on the user and on the equipment. Clearly, there is much more that we can do. Can we correctly (see) visualize what we (hear) receive from the lung after insonification? Can we re-conceive US tech in order to adapt it to the specific properties of the lung?

Can we develop an ultrasound-based method which can support, in real time, the clinician in the diagnosis of the many different pathologies affecting the lung? In this talk, trying to answer to these questions, recently developed imaging modalities and signal processing techniques dedicated to the analysis of the lung response to ultrasound will be introduced and discussed. In particular, in-vitro and clinical data will be presented which show how the study of the ultrasound spectral features [3] could lead to a quantitative ultrasound method dedicated to the lung.

[1] Global Health Estimates 2016: Deaths by Cause, Age, Sex, by Country and by Region, 2000-2016. Geneva, World Health Organization; 2018.

[2] The clinical and economic burden of chronic obstructive pulmonary disease in the USA, A.J. Guarascio et al. Clinicoecon Outcomes Res, 2013.

[3] Determination of a potential quantitative measure of the state of the lung using lung ultrasound spectroscopy. L. Demi et al. Scientific Reports, 2017.