2D and 3D reconstructions in acousto-electric tomography

We propose and test stable algorithms for the reconstruction of the internal conductivity of a biological object using acousto-electric measurements. Namely, the conventional impedance tomography scheme is supplemented by scanning the object with acoustic waves that slightly perturb the conductivity and cause the change in the electric potential measured on the boundary of the object. These perturbations of the potential are then used as the data for the reconstruction of the conductivity. The present method does not rely on "perfectly focused" acoustic beams. Instead, more realistic propagating spherical fronts are utilized, and then the measurements that would correspond to perfect focusing are synthesized. In other words, we use \emph{synthetic focusing}. Numerical experiments with simulated data show that our techniques produce high quality images, both in 2D and 3D, and that they remain accurate in the presence of high-level noise in the data. Local uniqueness and stability for the problem also hold

Nonlinear ultrasound image modeling: Development of a complete end-to-end model for qualitative and quantitative analysis of medical ultrasound

Finite amplitude sound propagation undergoes nonlinear distortion due to continuous path interaction with the propagation medium. This distortion tends to defocus the beam causing significant lateral and contrast resolution degradation. Fundamental understanding of this interaction requires development of computational models that accurately predict the nonlinear interaction - development of media-borne harmonics - as well as produce an ultrasound image - introduction of transducer effects, interface transitions, and innovative image processing to extract harmonics. Most computational models of ultrasound propagation assume axial symmetry for computational expediency. Two notable exceptions are the K-Z-K and NLP models. A new endto- end model, NUPROP, is introduced that also incorporates non-axially symmetric geometries and simplified transducer responses to accurately predict ultrasound RF signals for image reconstruction. Nonlinearities are modeled using either the Fubini solution or Burgers\u27 Equation coupled with angular spectrum propagation or Lommel formulation, appropriately masked by the transducer frequency response. Comparative analyses are performed on NUPROP results with high correlation with the literature. Parameter sensitivity analyses are performed to determine harmonic signal characteristics as a function of propagation distance. A-line and B-scan images are produced

Transcranial Ultrasound Holograms for the Blood-Brain Barrier Opening

[ES] El tratamiento de enfermedades neurológicas está muy limitado por la ineficiente penetración de los fármacos en el tejido cerebral dañado debido a la barrera hematoencefálica (BHE), lo que imposibilita mejorar la salud del paciente. La BHE es un mecanismo de protección natural para evitar la difusión de agentes potencialmente peligrosas para el sistema nervioso central. No obstante, la BHE se puede inhibir mediante ultrasonidos focalizados e inyección de microburbujas de forma segura, localizada y transitoria, una tecnología empleada mundialmente. La principal ventaja es su carácter no invasivo, siendo así muy atractiva y cómoda para el paciente. Normalmente, la zona cerebral enferma se trata en su parte central empleando un único foco. Sin embargo, enfermedades como el Alzheimer o el Parkinson requieren un tratamiento sobre estructuras de geometría compleja y tamaño elevado, situadas en ambos hemisferios cerebrales. Por tanto, la tecnología actual está muy limitada al no cumplir dichos requisitos. Esta tesis doctoral tiene como objetivo el desarrollo de una técnica novedosa, basada en hologramas acústicos, para resolver las limitaciones presentes en los tratamientos neurológicos empleando ultrasonidos. Se estudian las lentes acústicas holográficas impresas en 3D, que acopladas a un transductor mono-elemento, permiten el control preciso del frente de onda ultrasónico tanto para (1) compensar las distorsiones que sufre el haz hasta alcanzar el cerebro, como (2) focalizarlo simultáneamente en regiones múltiples y de geometría compleja o formando de vórtices acústicos, proporcionando así efectividad en tiempo y coste. Por ello, la investigación desarrollada en esta tesis abre un camino prometedor en el campo de la biomedicina que permitirá mejorar los tratamientos neurológicos, además de aplicaciones en neuroestimulación o ablación térmica del tejido.[CA] El tractament de malalties neurològiques està molt limitat per la ineficient penetració del fàrmac en el teixit cerebral danyat a causa de la barrera hematoencefàlica (BHE), i així no és possible una millora de salut del pacient. La BHE és un mecanisme de protecció natural per a evitar la difusió d'agents potencialment perillosos per al Sistema Nervios Central. No obstant això, aquesta barrera es pot inhibir mitjancant una tecnologia emprada mundialment basada en ultrasons focalitzats i injeccio de microbombolles. El principal avantatge és el seu caràcter no invasiu, sent així molt atractiva i còmoda per al pacient, i permet obrir la BHE de manera segura, localitzada i transitòria. Normalment, la zona cerebral malalta es tracta en la seua part central, emprant un unic focus. No obstant això, malalties com l'Alzheimer o el Parkinson requereixen un tractament al llarg d'estructures de geometria complexa i grandària elevada, situades en tots dos hemisferis cerebrals. Per tant, la tecnologia actual està fortament limitada al no complir amb aquests requeriments. Aquesta tesi doctoral està enfocada a investigar i desenvolupar una tècnica nova, basada en hologrames acústics, per a solucionar les limitacions presents en els tractaments neurològics. Una lent acústica holograca de baix cost impresa en 3D acoblada a un transductor d'element simple permet el control precs del front d'ona ultrasònic punt per a (1) compensar les distorsions que pateix el feix en el seu camí cap al cervell, i (2) focalització simultània del feix en regions multiples i de geometria complexa, proporcionant aix un tractament efectiu en temps i cost. Per això, la investigació desenvolupada en aquesta tesi demostra la possibilitat de realitzar qualsevol tractament neurològic, a més d'aplicacions en la neuroestimulació o l'ablació tèrmica dins del camp biomèdic.[EN] Treatments for neurological diseases are strongly limited by the inefficient penetration of therapeutic drugs into the diseased brain due to the blood-brain barrier (BBB), and therefore no health improvement can be achieved. In fact, the BBB is a protection mechanism of the human body to avoid the diffusion of potentially dangerous agents into the central nervous system. Nevertheless, this barrier can be successfully inhibited by using a worldwide spread technology based on microbubble-enhanced focused ultrasound. Its main advantage is its non-invasive nature, thus defining a patient-friendly clinical procedure that allows to disrupt the BBB in a safe, local and transient manner. Conventionally, the diseased brain structure has been targeted in its center, with a single focus. However, Alzheimer's or Parkinson's Diseases do require that ultrasound is delivered to entire, complex-geometry and large-volume structures located at both hemispheres of the brain. Therefore, current technology presents several limitations as it does not fulfill these requirements. This doctoral thesis aims to develop a novel technique based on using focused ultrasound acoustic holograms to solve the existing limitations to treat neurological diseases. In this dissertation, we study 3D-printed holographic acoustic lenses coupled to a single-element transducer that allow to accurately control the acoustic wavefront to both (1) compensate distortions suffered by the beam in its path to the brain, and (2) simultaneous focusing in multiple and complex-geometry structures or acoustic vortex generation, providing a time- and cost- efficient procedure. Therefore, the research carried out throughout this thesis opens a promising path in the biomedical field to improve the treatment for neurological diseases, neurostimulation or tissue ablation applications.Acknowledgments to the Spanish institution Generalitat Valenciana, which funding grant allowed me to develop this doctoral thesis, and as well funded my research stay at Columbia University. The development of the entire thesis was supported through grant Nª. ACIF/2017/045. Particularly, the research carried out in Chapter 3 and Chapter 4 was possible thanks to and supported through grant BEFPI/2019/075. Action co-financied by the Agència Valenciana de la Innovació through grant INNVAL10/19/016 and by the European Union through the Programa Operativo del Fondo Europeo de Desarrollo Regional (FEDER) of the Comunitat Valenciana 2014-2020 (IDIFEDER/2018/022).Jiménez Gambín, S. (2021). Transcranial Ultrasound Holograms for the Blood-Brain Barrier Opening [Tesis doctoral]. Universitat Politècnica de València. https://doi.org/10.4995/Thesis/10251/171373TESI

Holograms to Focus Arbitrary Ultrasonic Fields through the Skull

[EN] We report 3D-printed acoustic holographic lenses for the formation of ultrasonic fields of complex spatial distribution inside the skull. Using holographic lenses, we experimentally, numerically and theoretically produce acoustic beams whose spatial distribution matches target structures of the central nervous system. In particular, we produce three types of targets of increasing complexity. First, a set of points are selected at the center of both right and left human hippocampi. Experiments using a skull phantom and 3D printed acoustic holographic lenses show that the corresponding bi-focal lens simultaneously focuses acoustic energy at the target foci, with good agreement between theory and simulations. Second, an arbitrary curve is set as the target inside the skull phantom. Using time-reversal methods the holographic beam bends following the target path, in a similar way as self-bending beams do in free space. Finally, the right human hippocampus is selected as a target volume. The focus of the corresponding holographic lens overlaps with the target volume in excellent agreement between theory in free-media, and experiments and simulations including the skull phantom. The precise control of focused ultrasound into the central nervous system is mainly limited due to the strong phase aberrations produced by refraction and attenuation of the skull. Using the present method, the ultrasonic beam can be focused not only at a single point but overlapping one or various target structures simultaneously using low-cost 3D-printed acoustic holographic lens. The results open new paths to spread incoming biomedical ultrasound applications including blood-brain barrier opening and neuromodulation.This work is supported by the Spanish Ministry of Economy and Innovation (MINECO) through Project No. TEC2016-80976-R. N.J. and S.J. acknowledge financial support from Generalitat Valenciana through Grants No. APOSTD/2017/042, No. ACIF/2017/045, and No. GV/2018/11. F.C. acknowledges financial support from Agencia Valenciana de la Innovacio through Grant No. INNCON00/18/9 and European Regional Development Fund (Grant No. IDIFEDER/2018/022).Jiménez-Gambín, S.; Jimenez, N.; Benlloch Baviera, JM.; Camarena Femenia, F. (2019). Holograms to Focus Arbitrary Ultrasonic Fields through the Skull. Physical Review Applied. 12(1):014016-1-014016-14. https://doi.org/10.1103/PhysRevApplied.12.014016S014016-1014016-14121GABOR, D. (1948). A New Microscopic Principle. Nature, 161(4098), 777-778. doi:10.1038/161777a0Microscopy by reconstructed wave-fronts. (1949). Proceedings of the Royal Society of London. Series A. Mathematical and Physical Sciences, 197(1051), 454-487. doi:10.1098/rspa.1949.0075Leith, E. N., & Upatnieks, J. (1962). Reconstructed Wavefronts and Communication Theory*. Journal of the Optical Society of America, 52(10), 1123. doi:10.1364/josa.52.001123Ni, X., Kildishev, A. V., & Shalaev, V. M. (2013). Metasurface holograms for visible light. Nature Communications, 4(1). doi:10.1038/ncomms3807Huang, L., Chen, X., Mühlenbernd, H., Zhang, H., Chen, S., Bai, B., … Zhang, S. (2013). Three-dimensional optical holography using a plasmonic metasurface. Nature Communications, 4(1). doi:10.1038/ncomms3808Ma, G., & Sheng, P. (2016). Acoustic metamaterials: From local resonances to broad horizons. Science Advances, 2(2), e1501595. doi:10.1126/sciadv.1501595Cummer, S. A., Christensen, J., & Alù, A. (2016). Controlling sound with acoustic metamaterials. Nature Reviews Materials, 1(3). doi:10.1038/natrevmats.2016.1Liu, Z. (2000). Locally Resonant Sonic Materials. Science, 289(5485), 1734-1736. doi:10.1126/science.289.5485.1734Fang, N., Xi, D., Xu, J., Ambati, M., Srituravanich, W., Sun, C., & Zhang, X. (2006). Ultrasonic metamaterials with negative modulus. Nature Materials, 5(6), 452-456. doi:10.1038/nmat1644Yang, M., Ma, G., Yang, Z., & Sheng, P. (2013). Coupled Membranes with Doubly Negative Mass Density and Bulk Modulus. Physical Review Letters, 110(13). doi:10.1103/physrevlett.110.134301Li, Y., Liang, B., Gu, Z., Zou, X., & Cheng, J. (2013). Reflected wavefront manipulation based on ultrathin planar acoustic metasurfaces. Scientific Reports, 3(1). doi:10.1038/srep02546Xie, Y., Wang, W., Chen, H., Konneker, A., Popa, B.-I., & Cummer, S. A. (2014). Wavefront modulation and subwavelength diffractive acoustics with an acoustic metasurface. Nature Communications, 5(1). doi:10.1038/ncomms6553Jiménez, N., Cox, T. J., Romero-García, V., & Groby, J.-P. (2017). Metadiffusers: Deep-subwavelength sound diffusers. Scientific Reports, 7(1). doi:10.1038/s41598-017-05710-5Jiménez, N., Romero-García, V., Pagneux, V., & Groby, J.-P. (2017). Rainbow-trapping absorbers: Broadband, perfect and asymmetric sound absorption by subwavelength panels for transmission problems. Scientific Reports, 7(1). doi:10.1038/s41598-017-13706-4Qi, S., Li, Y., & Assouar, B. (2017). Acoustic Focusing and Energy Confinement Based on Multilateral Metasurfaces. Physical Review Applied, 7(5). doi:10.1103/physrevapplied.7.054006Bok, E., Park, J. J., Choi, H., Han, C. K., Wright, O. B., & Lee, S. H. (2018). Metasurface for Water-to-Air Sound Transmission. Physical Review Letters, 120(4). doi:10.1103/physrevlett.120.044302Li, Y., Jiang, X., Liang, B., Cheng, J., & Zhang, L. (2015). Metascreen-Based Acoustic Passive Phased Array. Physical Review Applied, 4(2). doi:10.1103/physrevapplied.4.024003Li, Y., & Assouar, M. B. (2015). Three-dimensional collimated self-accelerating beam through acoustic metascreen. Scientific Reports, 5(1). doi:10.1038/srep17612Kaina, N., Lemoult, F., Fink, M., & Lerosey, G. (2015). Negative refractive index and acoustic superlens from multiple scattering in single negative metamaterials. Nature, 525(7567), 77-81. doi:10.1038/nature14678Li, J., Fok, L., Yin, X., Bartal, G., & Zhang, X. (2009). Experimental demonstration of an acoustic magnifying hyperlens. Nature Materials, 8(12), 931-934. doi:10.1038/nmat2561Melde, K., Mark, A. G., Qiu, T., & Fischer, P. (2016). Holograms for acoustics. Nature, 537(7621), 518-522. doi:10.1038/nature19755Xie, Y., Shen, C., Wang, W., Li, J., Suo, D., Popa, B.-I., … Cummer, S. A. (2016). Acoustic Holographic Rendering with Two-dimensional Metamaterial-based Passive Phased Array. Scientific Reports, 6(1). doi:10.1038/srep35437Zhu, Y., Hu, J., Fan, X., Yang, J., Liang, B., Zhu, X., & Cheng, J. (2018). Fine manipulation of sound via lossy metamaterials with independent and arbitrary reflection amplitude and phase. Nature Communications, 9(1). doi:10.1038/s41467-018-04103-0Memoli, G., Caleap, M., Asakawa, M., Sahoo, D. R., Drinkwater, B. W., & Subramanian, S. (2017). Metamaterial bricks and quantization of meta-surfaces. Nature Communications, 8(1). doi:10.1038/ncomms14608Brown, M. D., Cox, B. T., & Treeby, B. E. (2017). Design of multi-frequency acoustic kinoforms. Applied Physics Letters, 111(24), 244101. doi:10.1063/1.5004040Hertzberg, Y., & Navon, G. (2011). Bypassing absorbing objects in focused ultrasound using computer generated holographic technique. Medical Physics, 38(12), 6407-6415. doi:10.1118/1.3651464Zhang, P., Li, T., Zhu, J., Zhu, X., Yang, S., Wang, Y., … Zhang, X. (2014). Generation of acoustic self-bending and bottle beams by phase engineering. Nature Communications, 5(1). doi:10.1038/ncomms5316Marzo, A., Seah, S. A., Drinkwater, B. W., Sahoo, D. R., Long, B., & Subramanian, S. (2015). Holographic acoustic elements for manipulation of levitated objects. Nature Communications, 6(1). doi:10.1038/ncomms9661Ter Haar, >Gail, & Coussios, C. (2007). High intensity focused ultrasound: Physical principles and devices. International Journal of Hyperthermia, 23(2), 89-104. doi:10.1080/02656730601186138Gélat, P., ter Haar, G., & Saffari, N. (2014). A comparison of methods for focusing the field of a HIFU array transducer through human ribs. Physics in Medicine and Biology, 59(12), 3139-3171. doi:10.1088/0031-9155/59/12/3139Fry, F. J., & Barger, J. E. (1978). Acoustical properties of the human skull. The Journal of the Acoustical Society of America, 63(5), 1576-1590. doi:10.1121/1.381852Thomas, J.-L., & Fink, M. A. (1996). Ultrasonic beam focusing through tissue inhomogeneities with a time reversal mirror: application to transskull therapy. IEEE Transactions on Ultrasonics, Ferroelectrics and Frequency Control, 43(6), 1122-1129. doi:10.1109/58.542055Hynynen, K., & Jolesz, F. A. (1998). Demonstration of Potential Noninvasive Ultrasound Brain Therapy Through an Intact Skull. Ultrasound in Medicine & Biology, 24(2), 275-283. doi:10.1016/s0301-5629(97)00269-xSun, J., & Hynynen, K. (1998). Focusing of therapeutic ultrasound through a human skull: A numerical study. The Journal of the Acoustical Society of America, 104(3), 1705-1715. doi:10.1121/1.424383Aubry, J.-F., Tanter, M., Pernot, M., Thomas, J.-L., & Fink, M. (2003). Experimental demonstration of noninvasive transskull adaptive focusing based on prior computed tomography scans. The Journal of the Acoustical Society of America, 113(1), 84-93. doi:10.1121/1.1529663Tanter, M., Thomas, J.-L., & Fink, M. (1998). Focusing and steering through absorbing and aberrating layers: Application to ultrasonic propagation through the skull. The Journal of the Acoustical Society of America, 103(5), 2403-2410. doi:10.1121/1.422759Hertzberg, Y., Volovick, A., Zur, Y., Medan, Y., Vitek, S., & Navon, G. (2010). Ultrasound focusing using magnetic resonance acoustic radiation force imaging: Application to ultrasound transcranial therapy. Medical Physics, 37(6Part1), 2934-2942. doi:10.1118/1.3395553Jolesz, F. A. (Ed.). (2014). Intraoperative Imaging and Image-Guided Therapy. doi:10.1007/978-1-4614-7657-3Shen, C., Xu, J., Fang, N. X., & Jing, Y. (2014). Anisotropic Complementary Acoustic Metamaterial for Canceling out Aberrating Layers. Physical Review X, 4(4). doi:10.1103/physrevx.4.041033Maimbourg, G., Houdouin, A., Deffieux, T., Tanter, M., & Aubry, J.-F. (2018). 3D-printed adaptive acoustic lens as a disruptive technology for transcranial ultrasound therapy using single-element transducers. Physics in Medicine & Biology, 63(2), 025026. doi:10.1088/1361-6560/aaa037Ferri, M., Bravo, J. M., Redondo, J., & Sánchez-Pérez, J. V. (2019). Enhanced Numerical Method for the Design of 3-D-Printed Holographic Acoustic Lenses for Aberration Correction of Single-Element Transcranial Focused Ultrasound. Ultrasound in Medicine & Biology, 45(3), 867-884. doi:10.1016/j.ultrasmedbio.2018.10.022Hynynen, K., McDannold, N., Vykhodtseva, N., & Jolesz, F. A. (2001). Noninvasive MR Imaging–guided Focal Opening of the Blood-Brain Barrier in Rabbits. Radiology, 220(3), 640-646. doi:10.1148/radiol.2202001804Tyler, W. J., Tufail, Y., Finsterwald, M., Tauchmann, M. L., Olson, E. J., & Majestic, C. (2008). Remote Excitation of Neuronal Circuits Using Low-Intensity, Low-Frequency Ultrasound. PLoS ONE, 3(10), e3511. doi:10.1371/journal.pone.0003511Schneider, U., Pedroni, E., & Lomax, A. (1996). The calibration of CT Hounsfield units for radiotherapy treatment planning. Physics in Medicine and Biology, 41(1), 111-124. doi:10.1088/0031-9155/41/1/009Mast, T. D. (2000). Empirical relationships between acoustic parameters in human soft tissues. Acoustics Research Letters Online, 1(2), 37-42. doi:10.1121/1.1336896Mazziotta, J. C., Toga, A. W., Evans, A., Fox, P., & Lancaster, J. (1995). A Probabilistic Atlas of the Human Brain: Theory and Rationale for Its Development. NeuroImage, 2(2), 89-101. doi:10.1006/nimg.1995.1012Yushkevich, P. A., Piven, J., Hazlett, H. C., Smith, R. G., Ho, S., Gee, J. C., & Gerig, G. (2006). User-guided 3D active contour segmentation of anatomical structures: Significantly improved efficiency and reliability. NeuroImage, 31(3), 1116-1128. doi:10.1016/j.neuroimage.2006.01.015Treeby, B. E., & Cox, B. T. (2010). Modeling power law absorption and dispersion for acoustic propagation using the fractional Laplacian. The Journal of the Acoustical Society of America, 127(5), 2741-2748. doi:10.1121/1.3377056Treeby, B. E., Jaros, J., Rendell, A. P., & Cox, B. T. (2012). Modeling nonlinear ultrasound propagation in heterogeneous media with power law absorption using a k-space pseudospectral method. The Journal of the Acoustical Society of America, 131(6), 4324-4336. doi:10.1121/1.4712021Jiménez, N., Camarena, F., Redondo, J., Sánchez-Morcillo, V., Hou, Y., & Konofagou, E. E. (2016). Time-Domain Simulation of Ultrasound Propagation in a Tissue-Like Medium Based on the Resolution of the Nonlinear Acoustic Constitutive Relations. Acta Acustica united with Acustica, 102(5), 876-892. doi:10.3813/aaa.919002Jiménez, N., Romero-García, V., Pagneux, V., & Groby, J.-P. (2017). Quasiperfect absorption by subwavelength acoustic panels in transmission using accumulation of resonances due to slow sound. Physical Review B, 95(1). doi:10.1103/physrevb.95.014205Tsang, P. W. M., & Poon, T.-C. (2013). Novel method for converting digital Fresnel hologram to phase-only hologram based on bidirectional error diffusion. Optics Express, 21(20), 23680. doi:10.1364/oe.21.023680Lirette, R., & Mobley, J. (2017). Focal zone characteristics of stepped Fresnel and axicon acoustic lenses. doi:10.1121/2.0000703Gatto, M., Memoli, G., Shaw, A., Sadhoo, N., Gelat, P., & Harris, R. A. (2012). Three-Dimensional Printing (3DP) of neonatal head phantom for ultrasound: Thermocouple embedding and simulation of bone. Medical Engineering & Physics, 34(7), 929-937. doi:10.1016/j.medengphy.2011.10.012Robertson, J., Martin, E., Cox, B., & Treeby, B. E. (2017). Sensitivity of simulated transcranial ultrasound fields to acoustic medium property maps. Physics in Medicine and Biology, 62(7), 2559-2580. doi:10.1088/1361-6560/aa5e98Hill, C. R., Bamber, J. C., & ter Haar, G. R. (Eds.). (2004). Physical Principles of Medical Ultrasonics. doi:10.1002/0470093978O’Neil, H. T. (1949). Theory of Focusing Radiators. The Journal of the Acoustical Society of America, 21(5), 516-526. doi:10.1121/1.1906542Chen, D.-C., Zhu, X.-F., Wei, Q., Wu, D.-J., & Liu, X.-J. (2018). Broadband acoustic focusing by Airy-like beams based on acoustic metasurfaces. Journal of Applied Physics, 123(4), 044503. doi:10.1063/1.501070

Simulation study on acousto-optics sensing of focused ultrasound

Abstract. The acousto-optics (AO) technique can provide a good contrast with high penetration depth (up to 5 cm) and can be potentially utilized in real time monitoring of the focused ultrasound (FUS) therapies. This work presents the AO simulation study on the interaction of light and FUS in the single-layer brain (SLB) medium and four-layer brain (FLB) medium. FUS pressure distribution at 0.5 MHz and 0.9 MHz frequency was simulated on k-Wave toolbox and the AO Monte Carlo (MC) algorithm was developed on MATLAB to simulate the AO effect in both mediums. The result for the SLB for both ultrasound (US) frequencies suggests that the modulation depth (MD) is high in the region of US focus with a magnitude of 2%-3% and <1% at 0.5 MHz and 0.9 MHz, respectively. Moreover, the MD decreases to 5 orders of magnitude at the source region. In the FLB, the MD decreased to 4–4.5 orders at the source and was present in the skull and US focus region with a magnitude of <1% at both US frequencies. These results suggest that AO can be utilized in sensing FUS effects on brain tissue and the AO signal-to-noise ratio (SNR) depends not only on the MD but also on the level of light intensity interacting with the US pressure

Potenciales ventajas del método pseudoespectral en auralizaciones

Auralization is a term introduced to describe the recreation of the experience of acoustic phenomena a listener would perceive in a specific soundfield. Sound propagation in a soundfield can be simulated with geometric based models or wave based models. Each one offers particular advantages and disadvantages. For wave based models, the finite element method, the boundary element method or the finite difference method are widely mentioned. They are characterized for achieving very precise results for individual frequencies applied to small and moderately sized rooms. Geometric methods lead to the ray tracing method or the image source method. These methods achieve good results for high frequencies and are efficient in large rooms and complex structures, but are not able to represent in a simple manner specific wave phenomena such as diffraction. Commercial software used to produce auralizations is usually based on a hybrid model combining ray tracing and image sources. This paper proposes an exploration on possible advantages and challenges on the use of the k-space pseudospectral method for wave based auralizations.El término auralización se refiere a la recreación en los oídos de un oyente de la sensación que percibiría en un espacio acústico determinado. La propagación del sonido en un espacio acústico puede simularse mediante procesos basados en el modelo geométrico o en el modelo ondulatorio. Cada uno ofrece ventajas y dificultades particulares. Entre los modelos basados en ondas pueden mencionarse principalmente el método de elementos finitos, el de contornos finitos o el de diferencias finitas. Se caracterizan por lograr resultados muy precisos para frecuencias únicas aplicadas a recintos de tamaño pequeño o medio. Por otro lado, los modelos geométricos dan lugar al método del trazado de rayos o al método de las fuentes imagen. Estos métodos logran buenos resultados en frecuencias altas y resultan eficientes en salas de gran tamaño con estructuras complejas, pero no pueden dar cuenta en forma sencilla de fenómenos específicamente ondulatorios como la difracción. Los programas comerciales utilizados para obtener auralizaciones suelen utilizar un modelo híbrido combinando el trazado de rayos y las fuentes imagen. El presente trabajo tiene la intención de iniciar una exploración sobre las posibles ventajas y desafíos del uso del método pseudoespectral del espacio k para obtener auralizaciones basadas en el modelo ondulatorio

Optics and Fluid Dynamics Department annual progress report for 2001

research within three scientific programmes: (1) laser systems and optical materials, (2) optical diagnostics and information processing and (3) plasma and fluid dynamics. The department has core competences in: optical sensors, optical materials, optical storage, biooptics, numerical modelling and information processing, non-linear dynamics and fusion plasma physics. The research is supported by several EU programmes, including EURATOM, by Danish research councils and by industry. A summary of the activities in 2001 is presented. ISBN 87-550-2993-0 (Internet