CHARACTERIZATION OF AN ELECTROMAGNETIC LITHOTRIPTER USING TRANSIENT ACOUSTIC HOLOGRAPHY – Oleg A. Sapozhnikov

CHARACTERIZATION OF AN ELECTROMAGNETIC LITHOTRIPTER USING TRANSIENT ACOUSTIC HOLOGRAPHY – Oleg A. Sapozhnikov

In focused ultrasound surgery (FUS), an ultrasound source radiates pressure waves into the patient’s body to achieve a desired therapeutic effect. FUS has already gained regulatory approval in the U.S. for treating uterine fibroids and pain palliation for bone metastases; other applications – including prostate cancer, liver cancer, and neurosurgery – remain active topics for clinical trials and research. Because applications of FUS often involve high intensity levels, insufficient knowledge of the acoustic field in the patient could lead to damage of healthy tissue away from the targeted treatment site. In this sense, high-intensity ultrasound treatments could cause collateral effects much like radiotherapy treatments that use ionizing radiation. In radiotherapy, treatment planning is critical for delivery of an effective and safe treatment: Typically, CT or MRI is used to form a virtual patient and the treatment is planned by computer-aided design. Simulations are used to plan the geometric, radiological, and dosimetric aspects of the therapy using radiation transport simulations. Analogous to a radiation beam, ultrasound therapy uses an acoustic beam as a 3D “scalpel” to treat tumors or other tissues. Accordingly, there is motivation to establish standard procedures for FUS treatment planning that parallel those in radiotherapy [1, 2]. However, such efforts toward treatment planning first require very precise knowledge of the source transducer in order to accurately predict the acoustic beam structure inside the patient.

oleg1
Fig. 1 Acoustic holography to characterize an ultrasound source, with schematic illustration of the corresponding ultrasound field. A measured hologram in a plane can be used to reconstruct the entire wave field anywhere in 3D space.

Toward this end, it is instructive to recognize that ultrasound comprises pressure waves and thus possesses several basic features of wave physics that can be used in practice. One such feature is the potential to reproduce a 3D wave field from a 2D distribution of the wave amplitude and phase. This principle was made famous in optics by Dennis Gabor (Nobel Prize, 1971), who invented holography [3]. A similar approach is possible in acoustics [4 – 8] and is illustrated in Fig. 1 for a therapeutic ultrasound source. To measure an acoustic hologram, a hydrophone (i.e., a microphone used underwater) can be scanned across a plane in front of the transducer. Because these measurements in 2D capture the whole field, this measured hologram can be used to reconstruct the surface vibrations of the source transducer. In turn, once the vibrations of the source are known, the corresponding acoustic field can be computed in water or tissue or any other medium with known properties.

Besides ultrasound surgery, holography techniques can be applied to characterize ultrasound transducers used for other therapeutic and diagnostic ultrasound-based applications. In this work we have used it for the first time to characterize a shock wave lithotripter source. Shock wave lithotripters radiate high intensity pulses that are focused on a kidney stone. High pressure, short rise time, and path-dependent nonlinearity make characterization in water and extrapolation to tissue difficult.
The electromagnetic lithotripter characterized in this effort is a commercial model (Dornier Compact S, Dornier MedTech GmbH, Wessling, Germany) with a 6.5 mm focal width. A broadband hydrophone (a fiber optic probe hydrophone, model FOPH 2000, RP Acoustics; Leutenbach, Germany) was used to sequentially measure the field over a set of points in a plane in front of the source. Following the previously developed transient holography approach, the recorded pressure field was numerically back-propagated to the source surface (Fig. 2). The method provides an accurate boundary condition from which the field in tissue can be simulated.
oleg2
oleg3
Fig. 2 Characterization of an electro-magnetic shock wave lithotripter. Top: A photo of the lithotripter head. Bottom: Holographically reconstructed peak-to-peak pressure along the transducer face.

In addition, we use acoustic holography to characterize imaging probes, which generate short, transient pulses of ultrasound (Fig. 3). Accurate 3D field representations have been confirmed [9].

oleg3a
oleg3b
oleg 3c

Fig. 3 Characterization of a diagnostic imaging probe. Top: A photo of the HDI C5-2 probe, which was excited at a frequency of 2.3 MHz. Middle: Holographically reconstructed pattern of vibration velocities along the probe surface. Bottom: Corresponding phase distribution.

We believe that our research efforts on acoustic holography will make it possible in the near future for manufacturers to sell each medical ultrasound transducer with a “source hologram” as a part of its calibration. This practice will enable calculation of the 3D ultrasound and temperature fields produced by each source in situ, from which the “dose” delivered to a patient can be inferred with better accuracy than is currently achievable.

LITERATURE
1. White PJ, Andre B, McDannold N, Clement GT. A pre-treatment planning strategy for high-intensity focused ultrasound (HIFU) treatments. Proceedings 2008 IEEE International Ultrasonics Symposium, 2056-2058 (2008).
2. Pulkkinen A, Hynynen K. Computational aspects in high intensity ultrasonic surgery planning. Comput. Med. Imaging Graph. 34(1), 69-78 (2010).
3. Gabor D. A new microscopic principle. Nature 161, 777-778 (1948).
4. Maynard JD, Williams EG, and Lee Y. Nearfield acoustic holography: I. Theory of generalized holography and the development of NAH. J. Acoust. Soc. Am. 78, 1395-1413 (1985).
5. Schafer ME, Lewin PA. Transducer characterization using the angular spectrum method. J. Acoust. Soc. Am. 85(5), 2202-2214 (1989).
6. Sapozhnikov O, Pishchalnikov Y, Morozov A. Reconstruction of the normal velocity distribution on the surface of an ultrasonic transducer from the acoustic pressure measured on a reference surface. Acoustical Physics 49(3), 354–360 (2003).
7. Sapozhnikov OA, Ponomarev AE, Smagin MA. Transient acoustic holography for reconstructing the particle velocity of the surface of an acoustic transducer. Acoustical Physics 52(3), 324–330 (2006).
8. Kreider W, Yuldashev PV, Sapozhnikov OA, Farr N, Partanen A, Bailey MR, Khokhlova VA. Characterization of a multi-element clinical HIFU system using acoustic holography and nonlinear modeling. IEEE Transactions on Ultrasonics, Ferroelectrics, and Frequency Control 60(8), 1683-1698 (2013).
9. Kreider W, Maxwell AD, Yuldashev PV, Cunitz BW, Dunmire B, Sapozhnikov OA, Khokhlova VA. Holography and numerical projection methods for characterizing the three-dimensional acoustic fields of arrays in continuous-wave and transient regimes. J. Acoust. Soc. Am. 134(5), Pt 2, 4153 (2013).

 

 

Oleg A. Sapozhnikov1,2, Sergey A. Tsysar1, Wayne Kreider2, Guangyan Li3,
Vera A. Khokhlova1,2, and Michael R. Bailey2,4
1Physics Faculty, Moscow State University, Leninskie Gory, Moscow 119991, Russia
2Center for Industrial and Medical Ultrasound, Applied Physics Laboratory, University of Washington, 1013 NE 40th Street, Seattle WA 98105, USA
3Department of Anatomy and Cell Biology, Indiana University School of Medicine, 635 Barnhill Dr. MS 5055 Indianapolis, IN 462025120
4Department of Urology, University of Washington Medical Center, 1959 NE Pacific Street, Box 356510, Seattle, WA 98195, USA

 

Cervical Assessment with Quantitative Ultrasound – Timothy J Hall

The cervix, which is the opening into the uterus, is a remarkable organ. It is the only structure in the entire body that has diametrically opposed functions. The normal cervix stays stiff and closed throughout most of pregnancy while the baby develops and then completely softens and opens at just the right time so the full-grown baby can be born normally, through the vagina. This process of softening and opening involves remodeling, or breaking down, of the cervix’s collagen structure together with an increase in water, or hydration, of the cervix. When the process happens too soon, babies can be born prematurely, which can cause serious lifelong disability and even death. When it happens too late, mothers may need a cesarean delivery. [1,2]

Amazingly, even after 100 years of research, nobody understands how this happens. Specifically, it is unclear how the cervix knows when to soften, or what molecular signals initiate and control this process. As a result, obstetrical providers today evaluate cervical softness in exactly the same way as they did in the 1800s: they feel the cervix with their fingers and classify it as ‘soft’, ‘medium’ or ‘firm’. And, unsurprisingly, despite significant research effort, the preterm birth rate remains unacceptably high and more than 95% of preterm births are intractable to any available therapies.

The cervix is like a cylinder with a canal in the middle that goes up into the uterus. This is where the sperm travels to fertilize the egg, which then nests in the uterus. Cervical collagen is roughly arranged in 3 layers. There is a thin layer on the inner part that where collagen is mostly aligned along the cervical canal, and similarly a thin layer that runs along the outside of the cervix. Between these layers, in the middle of the cervix is a thicker layer of collagen that is circumferential, aligned like a belt around the canal. Researchers theorize that the inner and outer layers stabilize the cervix from tearing off as it shortens and dilates for childbirth, while the middle circumferential layer is most important for the strength and stiffness of the cervix to prevent it from opening prematurely, but nobody is certain. This information is critical to understanding the process of normal, and abnormal, cervical remodeling, and that is why recently there is growing interest in developing technology that can non-invasively and thoroughly assess the collagen in the cervix and measure its softness and hydration status. The most promising approaches use regular clinical ultrasound systems that have special processing strategies to evaluate these tissue properties.

One approach to assessing tissue softness uses ultrasound pressure to induce a shear wave, which moves outward like rings in water after a stone is dropped. The speed of the shear wave provides a measurement of tissue stiffness because these waves travel slower in softer tissue. This method is used clinically in simple tissues without layers of collagen, such as the liver for staging fibrosis. Cervical tissue is very complex because of the collagen layers, but, after many years of research, we finally have adapted this method for the cervix. The first thing we did was compare shear wave speeds in hysterectomy specimens (surgically removed uterus and cervix) between two groups of women. The first group was given a medicine that softens the cervix in preparation for induction of labor, a process called “ripening”. The second group was not treated. We found that the shear wave speeds were slower in the women who had the medicine, indicating that our method could detect the cervices that had been softened with the medicine.[3] We also found that the cervix was even more complex than we’d thought, that shear wave speeds are different in different parts of the cervix. Fortunately, we learned we could easily control for that by measuring the same place on every woman’s cervix. We confirmed that our measurements were accurate by performing second harmonic generation microscopy on the cervix samples in which we measured shear wave speeds. This is a sophisticated way of looking at the tiny collagen structure of a tissue. It told us that indeed, when the collagen structure was more organized, the shear wave speeds were faster, indicating stiffer tissue, and when the collagen started breaking down, the shear wave speeds were slower, indicating softer tissue.
The next step was to see if our methods worked outside of the laboratory. So we studied pregnant women who were undergoing cervical ripening in preparation for induction of labor. We took measurements from each woman before they got the ripening medicine, and then afterwards. We found that the shear wave speeds were slower after the cervix had been ripened, indicating the tissue had softened.[4] This told us that we could obtain useful information about the cervix in pregnant women.
We also evaluated attenuation, which is loss of ultrasound signal as the wave propagates, because attenuation should increase as tissue hydration increases. This is a very complicated measurement, but we found that if we carefully control the angle of the ultrasound beams relative to the underlying cervical structure, attenuation estimates are sensitive to the difference between ripened and unripened tissue in hysterectomy specimens. This suggests the potential for an additional parameter to quantify and monitor the status of the cervix during pregnancy, and we are currently analyzing attenuation in the pregnant women before and after they received the ripening medicine.

This technology is exciting because it could change clinical practice. On a very basic level, obstetrical providers would be able to talk in objective terms about a woman’s cervix instead of the subject “soft, medium, or firm” designation they currently use, which would improve provider communication and thus patient care. More importantly, it could provide a means to thoroughly study normal and abnormal cervical remodeling, and associate structural changes in the cervix with molecular changes, which is the only way to discover new interventions for preterm birth.

References
1. Feltovich H, Hall TJ, and Berghella V. Beyond cervical length: Emerging technologies for assessing the pregnant cervix. Am J Obst & Gyn, 207(5): 345-354, 2012.
2. Feltovich, H and Hall TJ. Quantitative Imaging of the Cervix: Setting the Bar. Ultrasound Obstet Gynecol. 42(2): 121-128, 2013.
3. Carlson LC, Feltovich H, Palmeri ML, Dahl JJ, Del Rio AM, Hall TJ, Estimation of shear wave speed in the human uterine cervix. Ultrasound Obstet Gynecol. 43( 4): 452–458, 2014.
4. Carlson LC, Romero ST, Palmeri ML, Munoz del Rio A, Esplin SM, Rotemberg VM, Hall TJ, Feltovich H. Changes in shear wave speed pre and post induction of labor: A feasibility study. Ultrasound Obstet Gynecol.published online ahead of print Sep.2014.

 

Unlocking the Mystery of the Cervix
Timothy J Hall, Helen Feltovich, Lindsey C. Carlson, Quinton W. Guerrero, Ivan M. Rosado-Mendez
University of Wisconsin, Madison, WI (tjhall@wisc.edu)

EVALUATING KIDNEY STONE SIZE IN CHILDREN USING THE POSTERIOR ACOUSTIC SHADOW – Barbrina Dunmire

Stone disease in the children is becoming more commonplace. Over the past 25 years the incidence has increased approximately 6-10% annually and is now 50 per 100,000 adolescents 1. The diagnosis of kidney stones in children, as in adults, relies primarily on diagnostic imaging. In adults, the most common imaging study performed in the United States for the initial diagnosis of kidney stones is a computed tomography (CT) scan, due to its superior sensitivity and specificity. This is not preferred for children as CT utilizes ionizing radiation and children have an increased sensitivity to radiation effects. In addition, stone formers often have recurrent stone episodes over their lifetime, which is especially relevant to younger stone formers. The repeated exposures of a CT scan could lead to an increased risks of secondary cancers2. As a result, ultrasound is often performed in children instead because there is no radiation associated with its use1. Ultrasound, however, is less sensitive and specific compared with CT, and is known to overestimate kidney stone size3-5, which is one of the primary determinants of how stones are managed.

We have identified a new technique to improve the accuracy of US stone sizing. Traditionally, a kidney stone will show up as a bright, or hyperechoic, object on US, and radiologists measure the longest linear dimension of the bright area to represent the stone size. We believe that the dark, or hypoechoic, acoustic shadow that appears behind a kidney stone provides additional information for predicting stone size. The resolution of the stone is affected by the distortion of the waves traveling through the intervening tissues; the resolution of the shadow is only affected by the local stone obstruction.

We screened 660 stone diagnoses over an 11 year period (2004 – 2014) at Seattle Children’s Hospital, a tertiary care referral center serving the greater Pacific Northwest. Over the study period, there were 37 patients presenting with an initial diagnosis of a kidney stone, and who had both a US and CT within three months of each other. Two reviewers retrospectively measured both the stone size and the shadow width from the ultrasound image. We compared the results to the stone size measured from the CT scan. A total of 48 stones were included in the study with an average size based on CT imaging of 7.85 mm. The shadow width was present in 88% of the cases, and, on average, was more accurate than measuring the stone itself. Measuring the stone width on ultrasound tended to overestimate the size of the stone by 1.2 ± 2.5 mm (reviewer 1) and 2.0 ± 1.7 mm (reviewer 2), while measuring the shadow width on ultrasound underestimated the size of the stone by -0.6 ± 2.5 mm (reviewer 1) and overestimated the stone size by 0.3 ± 1.2 mm (reviewer 2). In both cases, the shadow was a better predictor of stone size and, for reviewer 2, there was less variability in the data. Stone sizes based on CT are typically considered within 1 mm, with low variability.

Our technique is simple and can be easily adopted by pediatricians, radiologists, and urologists. It improves the accuracy of US and gives physicians more confidence that the reported size is more representative of the true stone size, without having to expose children to the radiation of a CT scan. This also allows the physician to make more accurate decisions about when to perform a surgery for a large stone or continue to observe a small stone that may pass on its own. The findings from this study may also potentially be applicable to stones in adult patients. We believe that with continued advancements in US, we can reduce the number of CT scans for both adults and children. The results in part highlight one of the drawbacks of ultrasound, which is user dependence; two users can have very different results. It is anticipated that future work on automated stone and shadow sizing can reduce this along with standardizing the method in which the shadow measurement is taken.

References
1. Tasian G and Copelovitch L. Evaluation and Management of Kidney Stones in Children. J Urol. 2014: Epub ahead of print
2. Pearce MS, Salotti JA, Little MP, et al. Radiation exposure from CT scans in childhood and subsequent risk of leukaemia and brain tumours: a retrospective cohort study. Lancet 2012; 380: 499-505.
3. Ray AA, Ghiculete D, Pace KT, Honey RJD. Limitations to ultrasound in the detection and measurement of urinary tract calculi. Urology 2010; 76(2):295-300.
4. Fowler KAB, Locken JA, Duchesne JH, Williamson MR. US for detecting renal calculi with nonehnanced CT as a reference standard. Radiology 2002; 222(1):109-113.
5. Dunmire B, Lee FC, Hsi RS, Cunitz BW, Paun M, Bailey MR, Sorensen MD, Harper JD. Tools to improve the accuracy of kidney stone sizing with ultrasound. Aug 2014; [Epub ahead of print].

 

Franklin C. Lee1 – franklee@uw.edu

Jonathan D. Harper 1 – jdharper@uw.edu
Thomas S. Lendvay1, 2 – Thomas.lendvay@seattlechildrens.org
Ziyue Liu3 – ziliu@iupui.edu
Barbrina Dunmire 4 – mrbean@uw.edu
Manjiri Dighe 5 – dighe@uw.edu
Michael Bailey – bailey@apl.washington.edu
Mathew D. Sorensen1, 6 – mathews@uw.edu

University of Washington
1 Department of Urology, Box 356510
5 Department of Radiology, Box 357115
1959 NE Pacific St, Seattle, WA 98195

2 Seattle Children’s Hospital
Urology, Developmental Pediatrics
4800 Sand Point WA NE, Seattle, WA 98105

3 Indiana University
Department of Biostatistics
410 W. Tenth St, Suite 3000, Indianapolis, IN 46202

4 University of Washington
Applied Physics Lab – Center for Industrial and Medical Ultrasound2
1013 NE 40th St, Seattle, WA 98105

6 Department of Veteran Affairs Medical Center
Division of Urology
1660 South Columbian Way, Seattle, WA 98108

Acoustic absorption of green roof samples commercially available in southern Brazil – Stephan Paul

Acoustic absorption of green roof samples commercially available in southern Brazil – Stephan Paul

Investigations into the benefits of green roofs have shown that such roofs provide many environmental benefits, such as thermal conditioning, air cleaning and rain water absorption. Analysing the way green roofs are usually constructed suggests that they may have also two interesting acoustical properties: sound insulation and sound absorption. The first property would provide protection of the house’s interior from environmental noise produced outside the house. Sound absorption, on the other hand, would reduce the environmental noise in the environment itself, by dissipating sound energy that is being irradiated on to the roof from environmental noise sources. Thus, sound absorption can help to reduce environmental noise in urban settings. Despite of being an interesting characteristic, information regarding acoustic properties of green roofs and their effects on the noise environment is still sparse. This work looked into the sound absorption of two types of green roofs commercially available in Brazil: the alveolar and the hexa system.

alveolar system

Fig 1: illustration of the alveolar system (left) and hexa system (right)

Sound absorption can be quantified by means of a sound absorption coefficient α, which ranges between 0 and 1 and is usually a function of frequency. Zero means that all incident energy is being reflected back into the environment and α = 1 means that all energy is being dissipated in the layers of the material, here the green roof. To find out how much sound energy the alveolar and the hexa system absorb standardized measurements were made in a reverberant chamber according to ISO-354 for different variations of both systems. The alveolar system used a thin layer of 2.5 cm of soil like substrate with and without grass and a 4 cm layer of substrate only. The hexa system was measured with layers of 4 and 6 cm of substrate without vegetation and 6 cm of substrate with a layer of vegetation of sedum. For all systems, high absorption coefficients (α > 0.7) were found for medium and high frequencies. This was expected due to the highly porous structure of the substrate. Nevertheless the alveolar system with grass, the alveolar system with 4 cm of substrate, the hexa with 6 cm of substrate and the hexa with sedum already provide high absorption for frequencies as low as 250 or 400 Hz. Thus, these green roofs systems are particularly interesting in urban settings, as traffic noise is usually low frequency noise and is hardly absorbed by smooth surfaces such as pavements or façades.

absorbtion coefficient

Fig 2: absorption coefficient of the alveolar samples (left) and hexa samples (rigth).

In the next step of this research is intended to make computational simulations of the noise reduction provided by the hexa and alveolar system in different noisy situations such as near airports or intense urban traffic.

 

Stephan Paul – stephan.paul@eac.ufsm.br

Undergrad
Program Acoustical Engineering
Fed. University of Santa Maria
Santa Maria, RS, Brazil

 

Ricardo Brum – ricardo.brum@eac.ufsm.br
Undergrad
Program Acoustical Engineering
Fed. University of Santa Maria
Santa Maria, RS, Brazil

 

Andrey Ricardo da Silva – andrey.rs@ufsc.br
Fed. University of Santa Catarina
Florianópolis, SC, Brazil
Tenile Rieger Piovesan – arqui.tp@gmail.com
Graduate program in Civil Engineering
Fed. University of Santa Maria
Santa Maria, RS, Brazil

 

4pPP3 – Traumatic brain injuries – Melissa Papesh

4pPP3 – Traumatic brain injuries – Melissa Papesh

Traumatic brain injuries from blast exposure have been called the “signature injury” of military conflicts in Iraq and Afghanistan. This is largely due to our enemies’ unprecedented reliance on explosive weaponry such as improvised explosive devices (IED) (Figure 1). Estimates indicate that approximately 19.5% of deployed military personnel have suffered traumatic brain injuries since 2001 (Rand Report, Invisible Wounds of War, 2008). With more than 2 million service members deployed to Iraq and Afghanistan, this means that over 400,000 American Veterans are currently living with the chronic effects of blast exposure.

Fig1_IED2007

Figure 1 caption: An armored military vehicle lies on its side after surviving a buried IED blast on April 15, 2007. The vehicle was hit by a deeply buried improvised explosive device while conducting operations just south of the Shiek Hamed village in Iraq. Photograph courtesy of the U.S. Army: http://www.army.mil/article/9708/general-lee-rides-again/

When a blast wave from a high-intensity explosive impacts the head, a wave of intense heat and pressure moves through the skull and brain. Delicate neural tissues are stretched and compressed, potentially leading to cell damage, cell death, hemorrhaging, and inflammation. All regions of the brain are at risk of damage, and the auditory system is no exception. In recent years, increasing numbers of young Veterans with blast exposure have sought help from VA audiologists for hearing-related problems such as poor speech understanding. However, standard tests of hearing sensitivity often show no signs of hearing loss. This this combination of factors often suggests damage to areas in the brain dealing with auditory signals.   The efforts of hearing health professionals to help these Veterans are hampered by a lack of information regarding the effects of blast exposure on auditory function. The purpose of this presentation is to present some early results of a study currently underway at the National Center for Rehabilitative Auditory Research (NCRAR) investigating the long term consequences of blast exposure on hearing. Discovering the types of auditory problems caused by blast exposure is a crucial step toward developing effective rehabilitation options for this population.

Study participants include Veterans who experienced high-intensity blast waves within the past twelve years. The majority of participants have experienced multiple blast episodes, with the most severe events occurring approximately eight years prior to enrolling in the study. Another group of participants of similar age and gender but with no blast exposure are also included to serve as comparisons to the blast-exposed group (controls). On questionnaires assessing hearing ability in different contexts, blast-exposed Veterans described having more difficulties in many listening situations compared control participants. Common challenging situations reported by blast-exposed Veterans involve understanding speech in background noise, understanding when multiple people are talking simultaneously, and recalling multiple spoken instructions. Further, blast-exposed Veterans are more likely to rate the overall quality of sounds such as music and voices more poorly than control participants, and often report that listening requires greater effort. Different tests of listening abilities found many areas of difficulty which probably help explain self-reports. First, blast-exposed Veterans often have poorer ability to distinguish timing cues than control participants. Hence, sounds may seem blurry or smeared over time. Second, the ability to process sounds presented to both ears is often poorer in blast-exposed Veterans. Normally, listeners are able to utilize small differences in the timing and level of sound arriving at the two ears to improve listening performance, especially in noisy listening environments. This ability is often degraded in blast-exposed Veterans. Third, blast-exposed Veterans are poorer at distinguishing changes in the pitch of sounds compared to control participants, even when the pitch change is large. Lastly, blast-exposed Veterans often have greater difficulty ignoring distracting information in order to focus on listening.   This leads to problems such as trouble conversing with others when the television is on or when conversing at restaurants or parties. Our study results show that these listening difficulties are often great enough to impact daily life, causing blast-exposed Veterans to avoid social situations that they once enjoyed.

Fig2_P300

Figure 2 caption: Average EEG responses from blast-exposed and control participant groups in response to a large change in tone pitch. The horizontal axis shows time since the pitch changed (which occurred at time 0 on this axis). The vertical axis shows the magnitude of the neural response of the brain. Notice that the peak of activity in the control group (blue star labeled ‘P300’)is considerably larger and occurs earlier in time compared to the blast-exposed group (red star labeled ‘P300’).

Self-assessment and behavioral performance measures are supported by numerous direct measures of auditory processing. Using a type of electroencephalography (EEG), we non-invasively measure the response of the brain to sound by assessing the timing and size of neural activity associated with sound perception and processing. These tests reveal that the brains of blast-exposed Veterans require more time to analyze sound and respond less actively to changes in sounds. For example, the average EEG responses of blast-exposed and control participants are shown in Figure 2. These waveforms reflect neural detection of a large change in the pitch of tones presented to participants. Notice that the peak marked ‘P300’ is larger and occurs earlier in time in control participants compared to blast-exposed Veterans. Similar effects are seen in response to more complex sounds, such as when participants are asked to identify target words among non-target filler words. Overall, these EEG results suggest degraded sound processing in the brains of blast-exposed Veterans compared to control participants.

In summary, our results strongly suggest that blast exposure can cause chronic problems in multiple areas of the brain where sound is processed. Blast exposure has the potential to damage auditory areas of the brain as well as cognitive regions, both of which likely contribute to hearing difficulties. Thus, though Veterans may have normal hearing sensitivity, blast exposure may cause problems processing complex sounds. These difficulties may persist for many years after blast exposure.

 

Melissa Papesh – Melissa.Papesh@va.gov

Frederick Gallun – Frederick.Gallun@va.gov

Robert Folmer – Robert.Folmer@va.gov

Michele Hutter – Michele.Hutter@va.gov

Heather Belding – Heather.Belding@va.gov

  1. Samantha Lewis – Michele.Lewis3@va.gov

National Center for Rehabilitative Auditory Research
Portland VA Medical Center
3710 SW US Veterans Hospital Road
Portland, OR 97239

Marjorie Leek – Marjorie.Leek@va.gov

Loma Linda VA Medical Center
11201 Benton St
Loma Linda, CA 92354

Popular version of paper “4pPP3. Effects of blast exposure on central auditory processing

Presented Thursday afternoon, October 30, 2014

168th ASA Meeting, Indianapolis

1aAB11 – A New Dimension to Bat Biosonar – Rolf Müller

1aAB11 – A New Dimension to Bat Biosonar – Rolf Müller

Sonar is a sensing modality that is found in engineering as well as in nature. Man-made sonar systems can be found in places that include the bows of nuclear submarines and the bumpers of passenger cars. Likewise, natural sonar systems can be found in toothed whales that can weigh over 50 tons as well as in tiny bats that weigh just a few grams. All these systems have in common that they emit ultrasonic waves and listen to the returning echoes for clues as to what may be going on in their environments.

Beyond these basic commonalities, man-made and biological sonar systems differ radically in their approach to emitting and receiving the ultrasonic waves. Human sonar engineers tend to favor large numbers of simple elements distributed over a wide area. For example, sonar engineers fit hundreds of emitting and receiving elements into the bow of a nuclear submarine and even automotive engineers often arrange a handful of elements along the bumper of a car. As small flying mammals, bats did not have the option of distributing a large number of sonar elements over wide areas. Instead, they were forced to take a radically different approach. This biological approach has led to sonar systems that are based on a small number of highly complex emitting and receiving elements. At the same time, they have achieved levels of performance that remain unmatched by their man-made peers.

Bat biosonar has only one emitting element, in some bat species this is the mouth and in other, nasally emitting species, the nose. In all bat species, the echoes are received through two receiving elements, i.e., the two ears. But where is the complexity that allows these three elements to vastly outperform naval sonars with hundreds of emitting and receiving elements?

Over the past few years, research on two groups (families) of bats with particularly sophisticated sonar systems has yielded clues to the existence of a new functional dimension in bat biosonar that could be a key factor behind the remaining performance gap between engineered sonar and biosonar. Horseshoe bats (Rhinolophidae) and Old World leaf-nosed bats (Hipposideridae) emit their biosonar pulses nasally and have elaborate baffle shapes (so-called “noseleaves”) that surround the nostrils and can be seen to act as miniature megaphones.
mueller_figure1
Figure 1. Noseleaves (“miniature megaphones”) and outer ears of Old World leaf-nosed bats.

Close-up studies of live bats have shown that the noseleaves and the outer ears of these species are both highly dynamic structures. The noseleaves of these bats, for example, have not only much greater geometric complexity than man-made megaphones, but most intriguingly their walls are dynamic: Each time the bat emits an ultrasonic wave packet through its nostrils, it can set the walls of its noseleaf in motion. Hence, the outgoing ultrasonic wave interacts with a changing surface geometry. On the reception side, certain horseshoe bats, for example, have been shown to change the shape of their outer ears within one tenth of second. This is about three times as fast as the proverbial blink of an eye. As for the noseleaf, these changes in shape can take place as the bat receives the ultrasonic echoes.

Figure 2 (video). Motions of the outer ear in an Old World leaf-nosed bats (landmarks added for tracking purposes).

While it is still not certain whether these dynamic features in the sonar system of bats have a function and help the animals to improve their sensory abilities, there is a growing body of evidence that suggests that these fast changes are more than just an oddity. The shape changes in the noseleaves and outer ears are the results of a highly specialized muscular machinery that is unlikely to have evolved without a significant functional advantage acting as a driving force. The resulting changes in shape are big enough to have an impact on the interaction between surface geometry and the passing ultrasonic waves and indeed acoustic impacts have been demonstrated using numerical as well as experimental methods. Finally, dynamic effects are wide-spread among bats with sophisticated sonar systems and are even found in unrelated species that are most likely to have acquired them in response to parallel evolutionary pressures.

 

Rolf Müller – rolf.mueller@vt.edu<mailto:rolf.mueller@vt.edu>
Anupam K. Gupta – anupamkg@vt.edu<mailto:anupamkg@vt.edu>
Yanqing Fu – fyq@vt.edu<mailto:@vt.edu>
Uzair Gillani – uzair@vt.edu<mailto:uzair@vt.edu>
Hongxiao Zhu – hongxiao@vt.edu<mailto:hongxiao@vt.edu>
Virginia Tech
1075 Life Science Circle
Blacksburg, VA 24061

Popular version of paper 1aAB11
Presented Monday morning, October 27, 2014
168th ASA Meeting, Indianapolis