publications

2023

1. SE

   Quantifying gender gaps in seismology authorship

   Ermert, L. A., Koroni, M., and Korta Martiartu, N.

   Solid Earth 2023

   Bib HTML

   @article{Inverts2023,
     author = {Ermert, L. A. and Koroni, M. and Korta Martiartu, N.},
     title = {Quantifying gender gaps in seismology authorship},
     journal = {Solid Earth},
     volume = {14},
     year = {2023},
     number = {5},
     pages = {485--498},
     html = {https://se.copernicus.org/articles/14/485/2023/},
     doi = {10.5194/se-14-485-2023},
     bibtex_show = {true},
     abbr = {SE}
   }

2. Commun Med

   First-in-human diagnostic study of hepatic steatosis with computed ultrasound tomography in echo mode

   Stähli, Patrick, Becchetti, Chiara, Korta Martiartu, N., Berzigotti, Annalisa, Frenz, Martin, and Jaeger, Michael

   Communications Medicine (Springer Nature) 2023

   Abs Bib HTML PDF

   Background:Non-alcoholic fatty liver disease is rapidly emerging as the leading global cause of chronic liver disease. Efficient disease management requires low-cost, non-invasive techniques for diagnosing hepatic steatosis accurately. Here, we propose quantifying liver speed of sound (SoS) with computed ultrasound tomography in echo mode (CUTE), a recently developed ultrasound imaging modality adapted to clinical pulse-echo systems. CUTE reconstructs the spatial distribution of SoS by measuring local echo phase shifts when probing tissue at varying steering angles in transmission and reception. Methods:In this first-in-human phase II diagnostic study, we evaluated the liver of 22 healthy volunteers and 22 steatotic patients. We used conventional B-mode ultrasound images and controlled attenuation parameter (CAP) to diagnose the presence (CAP≥ 280 dB/m) or absence (CAP < 248 dB/m) of steatosis in the liver. A fully integrated convex-probe CUTE implementation was developed on the ultrasound system to estimate liver SoS. We investigated its diagnostic value via the receiver operating characteristic (ROC) analysis and correlation to CAP measurements. Results:We show that liver CUTE-SoS estimates correlate strongly (r = −0.84, p = 8.27e−13) with CAP values and have 90.9% (95% confidence interval: 84–100%) sensitivity and 95.5% (81–100%) specificity for differentiating between normal and steatotic livers (area under the ROC curve: 0.93–1.0). Conclusions:Our results demonstrate that liver CUTE-SoS is a promising quantitative biomarker for diagnosing liver steatosis. This is a necessary first step towards establishing CUTE as a new quantitative add-on to diagnostic ultrasound that can potentially be as versatile as conventional ultrasound imaging.

   @article{NatureCUTE2023,
     author = {St{\"a}hli, Patrick and Becchetti, Chiara and Korta Martiartu, N. and Berzigotti, Annalisa and Frenz, Martin and Jaeger, Michael},
     title = {{First-in-human diagnostic study of hepatic steatosis with computed ultrasound tomography in echo mode}},
     year = {2023},
     volume = {3},
     number = {1},
     pages = {176},
     journal = {Communications Medicine (Springer Nature)},
     doi = {10.1038/s43856-023-00409-3},
     note = {First three authors have contributed equally.},
     bibtex_show = {true},
     abbr = {Commun Med},
     selected = {true},
     html = {https://doi.org/10.1038/s43856-023-00409-3},
     pdf = {CUTEinvivo_2023.pdf}
   }

3. Diagnostics

   Impact of Breathing Phase, Liver Segment, and Prandial State on Ultrasound Shear Wave Speed, Shear Wave Dispersion, and Attenuation Imaging of the Liver in Healthy Volunteers

   Paverd, Catherine, Kupfer, Sivert, Kirchner, Iara Nascimento, Nambiar, Sherin, Martin, Alexander, Korta Martiartu, Naiara, Frauenfelder, Thomas, Rominger, Marga B., and Ruby, Lisa

   Diagnostics 2023

   Abs Bib

   Objectives: Measurement location and patient state can impact noninvasive liver assessment and change clinical staging in ultrasound examinations. Research into differences exists for Shear Wave Speed (SWS) and Attenuation Imaging (ATI), but not for Shear Wave Dispersion (SWD). The aim of this study is to assess the effect of breathing phase, liver lobe, and prandial state on SWS, SWD, and ATI ultrasound measurements. Methods: Two experienced examiners performed SWS, SWD, and ATI measurements in 20 healthy volunteers using a Canon Aplio i800 system. Measurements were taken in the recommended condition (right lobe, following expiration, fasting state), as well as (a) following inspiration, (b) in the left lobe, and (c) in a nonfasting state. Results: SWS and SWD measurements were strongly correlated (r = 0.805, p < 0.001). Mean SWS was 1.34 ± 0.13 m/s in the recommended measurement position and did not change significantly under any condition. Mean SWD was 10.81 ± 2.05 m/s/kHz in the standard condition and significantly increased to 12.18 ± 1.41 m/s/kHz in the left lobe. Individual SWD measurements in the left lobe also had the highest average coefficient of variation (19.68%). No significant differences were found for ATI. Conclusion: Breathing and prandial state did not significantly affect SWS, SWD, and ATI values. SWS and SWD measurements were strongly correlated. SWD measurements in the left lobe showed a higher individual measurement variability. Interobserver agreement was moderate to good.

   @article{Catherine2023,
     author = {Paverd, Catherine and Kupfer, Sivert and Kirchner, Iara Nascimento and Nambiar, Sherin and Martin, Alexander and Korta Martiartu, Naiara and Frauenfelder, Thomas and Rominger, Marga B. and Ruby, Lisa},
     title = {Impact of Breathing Phase, Liver Segment, and Prandial State on Ultrasound Shear Wave Speed, Shear Wave Dispersion, and Attenuation Imaging of the Liver in Healthy Volunteers},
     journal = {Diagnostics},
     volume = {13},
     year = {2023},
     number = {5},
     article-number = {989},
     url = {https://www.mdpi.com/2075-4418/13/5/989},
     pubmedid = {36900133},
     issn = {2075-4418},
     doi = {10.3390/diagnostics13050989},
     bibtex_show = {true},
     abbr = {Diagnostics}
   }

4. IEEE-TMI

   Windowed Radon Transform for Robust Speed-of-Sound Imaging with Pulse-Echo Ultrasound

   Beuret, Samuel, Hériard-Dubreuil, Baptiste, Korta Martiartu, N., Jaeger, Michael, and Thiran, Jean-Philippe

   IEEE Transactions on Medical Imaging 2023

   Bib HTML

   @article{SamuelEPFL2023,
     author = {Beuret, Samuel and H\'eriard-Dubreuil, Baptiste and Korta Martiartu, N. and Jaeger, Michael and Thiran, Jean-Philippe},
     journal = {IEEE Transactions on Medical Imaging},
     title = {Windowed Radon Transform for Robust Speed-of-Sound Imaging with Pulse-Echo Ultrasound},
     year = {2023},
     volume = {},
     number = {},
     pages = {1-1},
     doi = {10.1109/TMI.2023.3343918},
     bibtex_show = {true},
     abbr = {IEEE-TMI},
     html = {https://ieeexplore.ieee.org/abstract/document/10363357}
   }

5. Sensors

   Excluding Echo Shift Noise in Real-Time Pulse-Echo Speed-of-Sound Imaging

   Salemi Yolgunlu, Parisa, Korta Martiartu, N., Gerber, Urs Richard, Frenz, Martin, and Jaeger, Michael

   Sensors 2023

   Bib HTML

   @article{Parisa2023,
     author = {Salemi Yolgunlu, Parisa and Korta Martiartu, N. and Gerber, Urs Richard and Frenz, Martin and Jaeger, Michael},
     title = {Excluding Echo Shift Noise in Real-Time Pulse-Echo Speed-of-Sound Imaging},
     journal = {Sensors},
     volume = {23},
     year = {2023},
     number = {12},
     article-number = {5598},
     issn = {1424-8220},
     doi = {10.3390/s23125598},
     bibtex_show = {true},
     abbr = {Sensors},
     html = {https://doi.org/10.3390/s23125598}
   }

2022

1. IUS

   Towards Attenuation Imaging with Computed Ultrasound Tomography in Echo Mode (CUTE)

   Korta Martiartu, Naiara, Salemi Yolgunlu, Parisa, Stähli, Patrick, Frenz, Martin, and Jaeger, Michael

   In 2022 IEEE International Ultrasonics Symposium (IUS) 2022

   Bib HTML PDF

   @inproceedings{KortaMartiartu2022,
     author = {Korta Martiartu, Naiara and Salemi Yolgunlu, Parisa and Stähli, Patrick and Frenz, Martin and Jaeger, Michael},
     booktitle = {2022 IEEE International Ultrasonics Symposium (IUS)},
     title = {Towards Attenuation Imaging with Computed Ultrasound Tomography in Echo Mode (CUTE)},
     year = {2022},
     pages = {1-4},
     doi = {10.1109/IUS54386.2022.9958131},
     html = {https://ieeexplore.ieee.org/abstract/document/9958131},
     bibtex_show = {true},
     abbr = {IUS},
     pdf = {CUTE_Att_IUS2022.pdf}
   }

2. PMB

   Pulse-echo speed-of-sound imaging using convex probes

   Jaeger, Michael, Stähli, Patrick, Korta Martiartu, Naiara, Yolgunlu, Parisa Salemi, Frappart, Thomas, Fraschini, Christophe, and Frenz, Martin

   Physics in Medicine & Biology 2022

   Abs Bib HTML PDF

   Computed ultrasound tomography in echo mode (CUTE) is a new ultrasound (US)-based medical imaging modality with promise for diagnosing various types of disease based on the tissue’s speed of sound (SoS). It is developed for conventional pulse-echo US using handheld probes and can thus be implemented in state-of-the-art medical US systems. One promising application is the quantification of the liver fat fraction in fatty liver disease. So far, CUTE was using linear array probes where the imaging depth is comparable to the aperture size. For liver imaging, however, convex probes are preferred since they provide a larger penetration depth and a wider view angle allowing to capture a large area of the liver. With the goal of liver imaging in mind, we adapt CUTE to convex probes, with a special focus on discussing strategies that make use of the convex geometry in order to make our implementation computationally efficient. We then demonstrate in an abdominal imaging phantom that accurate quantitative SoS using convex probes is feasible, in spite of the smaller aperture size in relation to the image area compared to linear arrays. A preliminary in vivo result of liver imaging confirms this outcome, but also indicates that deep quantitative imaging in the real liver can be more challenging, probably due to the increased complexity of the tissue compared to phantoms.

   @article{Jaeger22,
     author = {Jaeger, Michael and St{\"a}hli, Patrick and Korta Martiartu, Naiara and Yolgunlu, Parisa Salemi and Frappart, Thomas and Fraschini, Christophe and Frenz, Martin},
     title = {{Pulse-echo speed-of-sound imaging using convex probes}},
     year = {2022},
     doi = {10.1088/1361-6560/ac96c6},
     html = {http://iopscience.iop.org/article/10.1088/1361-6560/ac96c6},
     journal = {Physics in Medicine \& Biology},
     bibtex_show = {true},
     abbr = {PMB},
     pdf = {Jaegeretal2022.pdf}
   }

3. IEEE-TUFFC

   Toward speed-of-sound anisotropy quantification in muscle with pulse-echo ultrasound

   Korta Martiartu, Naiara, Simute, Saule, Jaeger, Michael, Frauenfelder, Thomas, and Rominger, Marga B.

   IEEE Transactions on Ultrasonics, Ferroelectrics, and Frequency Control 2022

   Abs Bib HTML PDF

   The velocity of ultrasound longitudinal waves (speed of sound) is emerging as a valuable biomarker for a wide range of diseases, including musculoskeletal disorders. Muscles are fiber-rich tissues that exhibit anisotropic behavior, meaning that velocities vary with the wave-propagation direction. Therefore, quantifying anisotropy is essential to improve velocity estimates while providing a new metric related to muscle composition and architecture. For the first time, this work presents a method to estimate speed-of-sound anisotropy in transversely isotropic tissues using pulse-echo ultrasound. We assume elliptical anisotropy and consider an experimental setup with a flat reflector parallel to the linear probe, with the muscle in between. This setup allows us to measure first-arrival reflection traveltimes using multistatic operation. Unknown muscle parameters are the orientation angle of the anisotropy symmetry axis and the velocities along and across this axis. We derive analytical expressions for the nonlinear relationship between traveltimes and anisotropy parameters, including reflector inclinations. These equations are exact for homogeneous media and are useful to estimate the effective average anisotropy in muscles. To analyze the structure of this forward problem, we formulate the inversion statistically using the Bayesian framework. We demonstrate that anisotropy parameters can be uniquely constrained by combining traveltimes from different reflector inclinations. Numerical results from wide-ranging acquisition and anisotropy properties show that uncertainties in velocity estimates are substantially lower than expected velocity differences in the muscle. Thus, our approach could provide meaningful muscle anisotropy estimates in future clinical applications.

   @article{KortaMartiartu2023,
     author = {Korta Martiartu, Naiara and Simute, Saule and Jaeger, Michael and Frauenfelder, Thomas and Rominger, Marga B.},
     journal = {IEEE Transactions on Ultrasonics, Ferroelectrics, and Frequency Control},
     title = {Toward speed-of-sound anisotropy quantification in muscle with pulse-echo ultrasound},
     year = {2022},
     volume = {69},
     number = {8},
     html = {https://ieeexplore.ieee.org/document/9817393},
     pages = {2499-2511},
     selected = {true},
     bibtex_show = {true},
     abbr = {IEEE-TUFFC},
     pdf = {TUFFC3189184_final.pdf},
     doi = {10.1109/TUFFC.2022.3189184}
   }

4. Git

   naiarako/UltrasoundAnisotropy: v1.0.0

   Korta Martiartu, N.

   2022

   Bib HTML

   @misc{https://doi.org/10.5281/zenodo.6635691,
     doi = {10.5281/ZENODO.6635691},
     html = {https://zenodo.org/record/6635691},
     author = {Korta Martiartu, N.},
     title = {naiarako/UltrasoundAnisotropy: v1.0.0},
     publisher = {Zenodo},
     year = {2022},
     copyright = {Open Access},
     bibtex_show = {true},
     abbr = {Git}
   }

2021

1. QIMS

   Speed of sound and shear wave speed for calf soft tissue composition and nonlinearity assessment

   Korta Martiartu, N., Nakhostin, Dominik, Ruby, Lisa, Frauenfelder, Thomas, Rominger, Marga B., and Sanabria, Sergio J

   Quantitative Imaging in Medicine and Surgery 2021

   Abs Bib HTML PDF

   Background: The purpose of this study was threefold: (I) to study the correlation of speed-of-sound (SoS) and shear-wave-speed (SWS) ultrasound (US) in the gastrocnemius muscle, (II) to use reproducible tissue compression to characterize tissue nonlinearity effects, and (III) to compare the potential of SoS and SWS for tissue composition assessment. Methods: Twenty gastrocnemius muscles of 10 healthy young subjects (age range, 23–34 years, two females and eight males) were prospectively examined with both clinical SWS (GE Logiq E9, in m/s) and a prototype system that measures SoS (in m/s). A reflector was positioned opposite the US probe as a timing reference for SoS, with the muscle in between. Reproducible tissue compression was applied by reducing probe-reflector distance in 5 mm steps. The Ogden hyperelastic model and the acoustoelastic theory were used to characterize SoS and SWS variations with tissue compression and extract novel metrics related to tissue nonlinearity. The body fat percentage (BF%) of the subjects was estimated using bioelectrical impedance analysis. Results: A weak negative correlation was observed between SWS and SoS (r=−0.28, P=0.002). SWS showed an increasing trend with increasing tissue compression (P=0.10) while SoS values decayed nonlinearly (P<0.001). The acoustoelastic modeling showed a weak correlation for SWS (r=−0.36, P<0.001) but a very strong correlation for SoS (r=0.86, P<0.001), which was used to extract the SoS acoustoelastic parameter. SWS showed higher variability between both calves [intraclass correlation coefficient (ICC) =0.62, P=0.08] than SoS (ICC =0.91, P<0.001). Correlations with BF% were strong and positive for SWS (r=0.60, P<0.001), moderate and negative for SoS (r=−0.43, P=0.05), and moderate positive for SoS acoustoelastic parameter (r=0.48, P=0.03). Conclusions: SWS and SoS provide independent information about tissue elastic properties. SWS correlated stronger with BF% than SoS, but measurements were less reliable. SoS enabled the extraction of novel metrics related to tissue nonlinearity with potential complementary information.

   @article{Korta_nonlinearity,
     author = {Korta Martiartu, N. and Nakhostin, Dominik and Ruby, Lisa and Frauenfelder, Thomas and Rominger, Marga B. and Sanabria, Sergio J},
     title = {Speed of sound and shear wave speed for calf soft tissue composition and nonlinearity assessment},
     journal = {Quantitative Imaging in Medicine and Surgery},
     volume = {0},
     number = {0},
     year = {2021},
     issn = {2223-4306},
     doi = {10.21037/qims-20-1321},
     html = {https://qims.amegroups.com/article/view/71291},
     bibtex_show = {true},
     abbr = {QIMS},
     pdf = {qims-11-09-4149.pdf}
   }

2. UMB

   Sources of Variability in Shear Wave Speed and Dispersion Quantification with Ultrasound Elastography: A Phantom Study

   Korta Martiartu, N., Nambiar, Sherin, Nascimento Kirchner, Iara, Paverd, Catherine, Cester, Davide, Frauenfelder, Thomas, Ruby, Lisa, and Rominger, Marga B.

   Ultrasound in Medicine & Biology 2021

   Abs Bib HTML PDF

   There is a growing interest in quantifying shear-wave dispersion (SWD) with ultrasound shear-wave elastography (SWE). Recent studies suggest that SWD complements shear-wave speed (SWS) in diffuse liver disease diagnosis. To accurately interpret these metrics in clinical practice, we analyzed the impact of operator-dependent acquisition parameters on SWD and SWS measurements. Considered parameters were the acquisition depth, lateral position and size of the region of interest (ROI), as well as the size of the SWE acquisition box. Measurements were performed using the Canon Aplio i800 system (Canon Medical Systems, Otawara, Tochigi, Japan) and four homogeneous elasticity phantoms with certified stiffness values ranging from 3.7 to 44 kPa. In general, SWD exhibited two to three times greater variability than SWS. The acquisition depth was the main variance-contributing factor for both SWS and SWD, which decayed significantly with depth. The lateral ROI position contributed as much as the acquisition depth to the total variance in SWD. Locations close to the initial shear-wave excitation pulse were more robust to biases because of inaccurate probe?phantom coupling. The size of the ROI and acquisition box did not introduce significant variations. These results suggest that future guidelines on multiparametric elastography should account for the depth- and lateral-dependent variability of measurements.

   @article{Korta_dispersion,
     title = {Sources of Variability in Shear Wave Speed and Dispersion Quantification with Ultrasound Elastography: A Phantom Study},
     journal = {Ultrasound in Medicine \& Biology},
     year = {2021},
     issn = {0301-5629},
     doi = {https://doi.org/10.1016/j.ultrasmedbio.2021.08.013},
     html = {https://www.sciencedirect.com/science/article/pii/S0301562921003689},
     author = {Korta Martiartu, N. and Nambiar, Sherin and {Nascimento Kirchner}, Iara and Paverd, Catherine and Cester, Davide and Frauenfelder, Thomas and Ruby, Lisa and Rominger, Marga B.},
     pdf = {KortaMartiartuetal2021_UMB.pdf},
     bibtex_show = {true},
     abbr = {UMB}
   }

2020

1. IEEE-TUFFC

   3D Wave-Equation-Based Finite-Frequency Tomography for Ultrasound Computed Tomography

   Korta Martiartu, N., Boehm, C., and Fichtner, A.

   IEEE Transactions on Ultrasonics, Ferroelectrics, and Frequency Control 2020

   Abs Bib HTML PDF

   Ultrasound computed tomography (USCT) has great potential for 3-D quantitative imaging of acoustic breast tissue properties. Typical devices include high-frequency transducers, which makes tomography techniques based on numerical wave propagation simulations computationally challenging, especially in 3-D. Therefore, despite the finite-frequency nature of ultrasonic waves, ray-theoretical approaches to transmission tomography are still widely used. This article introduces a finite-frequency traveltime tomography to medical ultrasound. In addition to being computationally tractable for 3-D imaging at high frequencies, the method has two main advantages: 1) it correctly accounts for the frequency dependence and volumetric sensitivity of traveltime measurements, which are related to off-ray-path scattering and diffraction. 2) It naturally enables out-of-plane imaging and the construction of 3-D images from 2-D slice-by-slice acquisition systems. Our method rests on the availability of calibration data in water, used to linearize the forward problem and to provide analytical expressions of cross correlation traveltime sensitivity. As a consequence of the finite-frequency content, sensitivity is distributed in multiple Fresnel volumes, thereby providing out-of-plane sensitivity. To improve computational efficiency, we develop a memory-efficient implementation by encoding the Jacobian operator with a 1-D parameterization, which allows us to extend the method to large-scale domains. We validate our tomographic approach using laboratory measurements collected with a 2-D setup of transducers and using a cylindrically symmetric phantom. We then demonstrate its applicability for 3-D reconstructions by simulating a slice-by-slice acquisition system using the same data set.

   @article{Korta2020,
     author = {Korta Martiartu, N. and {Boehm}, C. and {Fichtner}, A.},
     journal = {IEEE Transactions on Ultrasonics, Ferroelectrics, and Frequency Control},
     title = {3D Wave-Equation-Based Finite-Frequency Tomography for Ultrasound Computed Tomography},
     year = {2020},
     volume = {},
     number = {},
     pages = {1-1},
     keywords = {Ultrasound computed tomography (USCT);finite-frequency tomography;Born approximation;adjoint technique;breast imaging;resolution analysis;point-spread function;traveltime},
     doi = {10.1109/TUFFC.2020.2972327},
     issn = {1525-8955},
     month = {},
     selected = {true},
     bibtex_show = {true},
     abbr = {IEEE-TUFFC},
     html = {https://ieeexplore.ieee.org/abstract/document/8986678},
     pdf = {Manuscript_FF_IEEE.pdf}
   }

2019

1. ETHZ

   Tomography across scales: Knowledge transfer from seismology to imaging breast tissue with ultrasound

   Korta Martiartu, Naiara

   2019

   Abs Bib HTML

   Wave propagation is extensively used to understand the internal structure of media that are not accessible to direct observations. Seismology and medical ultrasound imaging are good examples of this. The former uses observations of seismic waves at the Earth’s surface to increase our knowledge about its interior. This is crucial, for instance, to improve our understanding about the Earth’s dynamics and evolution. Medical ultrasound, on the other hand, uses observations of acoustic waves, emitted and recorded at the surface of human bodies, to visualize internal body structures. This has become an essential screening tool, useful for diagnostic examination. This thesis presents an interdisciplinary work between seismology and medical ultrasound. In particular, we focus on transferring knowledge from seismic tomography to Ultrasound Computer Tomography (USCT), an emerging technology that holds great potential for early-stage breast cancer diagnosis. Here, the human breast is surrounded by transducers that collect transmitted and reflected ultrasound signals. This information is then used to obtain 3D quantitative images of acoustic tissue properties, which enable non-invasive tissue characterization and improve the specificity of standard imaging modalities. Current challenges in USCT mostly consist in providing a diagnostic tool with high accuracy (comparable to magnetic resonance imaging) and affordable computational and acquisition cost for clinical practice, the target being a maximum time of 15 minutes per patient. Despite the vastly different scale, seismic and medical ultrasound tomography share fundamental similarities that allow us to address these challenges from the stand point of the seismologist. We first introduce finite-frequency traveltime tomography to medical ultrasound. In addition to being computationally tractable for 3D imaging at high frequencies, the method has two main advantages: (1) It correctly accounts for the frequency dependence and volumetric sensitivity of traveltime measurements, which are related to off-ray-path scattering and diffraction. (2) It naturally enables out-of-plane imaging and the construction of 3D images from 2D slice-by-slice acquisition systems. Our method rests on the availability of calibration data measured in water, used to linearize the forward problem and to provide analytical expressions of cross-correlation traveltime sensitivity. We present a memory-efficient implementation suitable for arbitrarily large-scale domains, and we discuss its extension to amplitude tomography. To adapt existing acquisition systems to new imaging techniques, we then introduce optimal experimental design methods. These provide a systematic and quantitative framework to (1) evaluate the quality of different designs in terms of uncertainties in the estimated tissue parameters and (2) optimize the configuration with respect to predefined design parameters, for example the position of transducers on the scanning device. Our first application presents a cost-effective 3D configuration of transducers optimized for transmission tomography. This is useful to analyze appropriate quality measures for USCT experiments and explore computationally tractable optimization approaches. The multi-modality capability of USCT, however, requires careful designs that simultaneously provide accurate images for both transmission (e.g., velocity) and reflection (reflectivity) information. We therefore extend the formulation to jointly optimize the experiment for transmission and reflection data. Here we focus on image reconstruction methods with linear(ized) observable-parameter relationship, for which quality measures are analytically given and independent of breast properties. This is crucial for optimizing USCT devices prior to any data acquisition. Methods investigated within this thesis are validated using experimental data. These contributions represent innovative solutions for USCT and ultimately serve to foster the knowledge and technology transfer between seismology and medical imaging, which may benefit imaging methods on all scales.

   @phdthesis{Hedgehog_thesis,
     author = {Korta Martiartu, Naiara},
     title = {Tomography across scales: Knowledge transfer from seismology to imaging breast tissue with ultrasound},
     school = {{Eidgen\"ossische Technische Hochschule}},
     address = {{Z\"urich, Schweiz}},
     year = {2019},
     month = oct,
     doi = https://doi.org/10.3929/ethz-b-000416172,
     abbr = {ETHZ},
     selected = {true},
     bibtex_show = {true},
     html = {https://www.research-collection.ethz.ch/handle/20.500.11850/416172}
   }

2. JASA

   Optimal experimental design for joint reflection- transmission ultrasound breast imaging: From ray- to wave-based methods

   Korta Martiartu, N., Boehm, Christian, Hapla, Vaclav, Maurer, Hansruedi, Jovanović Balic, Ivana, and Fichtner, Andreas

   The Journal of the Acoustical Society of America 2019

   Abs Bib HTML PDF

   Ultrasound computed tomography (USCT) is an emerging modality to image the acoustic properties of the breast tissue for cancer diagnosis. With the need of improving the diagnostic accuracy of USCT, while maintaining the cost low, recent research is mainly focused on improving (1) the reconstruction methods and (2) the acquisition systems. D-optimal sequential experimental design (D-SOED) offers a method to integrate these aspects into a common systematic framework. The transducer configuration is optimized to minimize the uncertainties in the estimated model parameters, and to reduce the time to solution by identifying redundancies in the data. This work presents a formulation to jointly optimize the experiment for transmission and reflection data and, in particular, to estimate the speed of sound and reflectivity of the tissue using either ray-based or wave-based imaging methods. Uncertainties in the parameters can be quantified by extracting properties of the posterior covariance operator, which is analytically computed by linearizing the forward problem with respect to the prior knowledge about parameters. D-SOED is first introduced by an illustrative toy example, and then applied to real data. This shows that the time to solution can be substantially reduced, without altering the final image, by selecting the most informative measurements.

   @article{Korta_optimaldesign,
     author = {Korta Martiartu, N. and Boehm, Christian and Hapla, Vaclav and Maurer, Hansruedi and {Jovanovi{\'c} Balic}, Ivana and Fichtner, Andreas},
     title = {Optimal experimental design for joint reflection- transmission ultrasound breast imaging: From ray- to wave-based methods},
     journal = {The Journal of the Acoustical Society of America},
     volume = {146},
     number = {2},
     pages = {1252-1264},
     year = {2019},
     doi = {10.1121/1.5122291},
     html = {https://doi.org/10.1121/1.5122291},
     bibtex_show = {true},
     abbr = {JASA},
     pdf = {KortaMartiartu_etal_2019.pdf}
   }

2018

1. SPIE

   Time-domain spectral-element ultrasound waveform tomography using a stochastic quasi-Newton method

   Boehm, Christian, Korta Martiartu, N., Vinard, Nicolas, Jovanović Balic, Ivana, and Fichtner, Andreas

   Proc.SPIE, Medical Imaging 2018: Ultrasonic Imaging and Tomography 2018

   Abs Bib HTML

   Waveform inversion for ultrasound computed tomography (USCT) is a promising imaging technique for breast cancer screening. However, the improved spatial resolution and the ability to constrain multiple parameters simultaneously demand substantial computational resources for the recurring simulations of the wave equation. Hence, it is crucial to use fast and accurate methods for numerical wave propagation, on the one hand, and to keep the number of required simulations as small as possible, on the other hand. We present an efficient strategy for acoustic waveform inversion that combines (i) a spectral-element continuous Galerkin method for solving the wave equation, (ii) conforming hexahedral mesh generation to discretize the scanning device, (iii) a randomized descent method based on mini-batches to reduce the computational cost for misfit and gradient computations, and (iv) a trust-region method using a quasi-Newton approximation of the Hessian to iteratively solve the inverse problem. This approach combines ideas and state-of-the-art methods from global-scale seismology, large-scale nonlinear optimization, and machine learning. Numerical examples for a synthetic phantom demonstrate the efficiency of the discretization, the effectiveness of the mini-batch approximation and the robustness of the trust-region method to reconstruct the acoustic properties of breast tissue with partial information.

   @article{Boehm2018,
     author = {Boehm, Christian and Korta Martiartu, N. and Vinard, Nicolas and {Jovanovi{\'c} Balic}, Ivana and Fichtner, Andreas},
     title = {Time-domain spectral-element ultrasound waveform tomography using a stochastic quasi-{N}ewton method},
     journal = {Proc.SPIE, Medical Imaging 2018: Ultrasonic Imaging and Tomography},
     volume = {10580},
     pages = {10580--10580--9},
     year = {2018},
     abbr = {SPIE},
     bibtex_show = {true},
     doi = {10.1117/12.2293299},
     html = {https://doi.org/10.1117/12.2293299}
   }

2017

1. AdvGeo

   Optimized Experimental Design in the Context of Seismic Full Waveform Inversion and Seismic Waveform Imaging

   Maurer, H., Nuber, A., Korta Martiartu, N., Reiser, F., Boehm, C., Manukyan, E., Schmelzbach, C., and Fichtner, A.

   Advances in Geophysics 2017

   Abs Bib HTML

   During the past few years, significant improvements have been achieved in high-resolution imaging with seismic data. In particular, seismic full waveform inversion (FWI) has been proven to be a very promising tool. However, this technique requires high-quality data, whose acquisition can be very expensive. Furthermore, FWI is computationally extremely demanding, which currently limits its application to large-scale data sets. Both problems can be alleviated with optimized experimental design (OED) techniques. Using tools from the linearized inversion theory, we outline how source–receiver patterns can be identified that are most suitable for FWI experiments. This is demonstrated by reviewing a laboratory-scale experiment devoted to breast cancer detection with ultrasound data, and with a surface seismic survey study that is concerned with elastic FWI for shallow subsurface structures. By means of a vertical seismic profiling design example, we also show that the OED technology can be adapted to wavefield imaging techniques. Besides identifying optimized source–receiver patterns, OED can be employed for extracting the most useful attributes from a seismic data set, which can reduce the computational costs. For that purpose, we discuss a frequency-domain crosshole FWI experiment, where we quantify the information content of different data representations and identify suitable spatial and temporal sampling strategies. In a second crosshole study, it is inspected that source and receiver components allow the relevant elastic subsurface properties to be resolved. Finally, we outline a more general framework of seismic observables, with which the sensitivity of selected model parameters can be maximized. This is demonstrated with an example of regional earth mantle tomography.

   @article{Maurer_2017,
     title = {Optimized Experimental Design in the Context of Seismic Full Waveform Inversion and Seismic Waveform Imaging},
     editor = {Nielsen, Lars},
     journal = {Advances in Geophysics},
     volume = {58},
     pages = {1 - 45},
     year = {2017},
     issn = {0065-2687},
     author = {Maurer, H. and Nuber, A. and Korta Martiartu, N. and Reiser, F. and Boehm, C. and Manukyan, E. and Schmelzbach, C. and Fichtner, A.},
     html = {https://www.sciencedirect.com/science/article/pii/S0065268717300018},
     doi = {https://doi.org/10.1016/bs.agph.2017.10.001},
     abbr = {AdvGeo},
     bibtex_show = {true}
   }

2011

1. JGR:Oceans

   Application of acoustic full waveform inversion to retrieve high-resolution temperature and salinity profiles from synthetic seismic data

   Kormann, J., Biescas, B., Korta Martiartu, N., Puente, J., and Sallarés, V.

   Journal of Geophysical Research: Oceans 2011

   Abs Bib HTML

   Recent works show that multichannel seismic (MCS) systems are able to provide detailed information on the oceans’ fine structure. The aim of this paper is to analyze whether 1-D full waveform inversion algorithms are suitable to recover the extremely weak acoustic impedance contrasts associated to the oceans’ fine structure, as well as their potential to image meso-scale objects such as meddies. We limited our analysis to synthetic, noise-free data, in order to identify some methodological issues related to this approach under idealistic conditions (e.g., 1-D wave propagation, noise-free data, known source wavelet). We first discuss the influence of the starting model in the context of the multi-scale strategy that we have implemented. Then we show that it is possible to retrieve not only sound speed but also salinity and temperature contrasts within reasonable bounds from the seismic data using Neural Network relationships trained with regional oceanographic data sets. Potentially, the vertical resolution of the obtained models, which depends on the maximum frequency inverted, is of the order of 5–10 m, whereas the root mean square error of the inverted properties is shown to be ∼0.5 m/s for sound speed, 0.1°C for temperature, and 0.06 for salinity. To conclude this study, we have inverted synthetic data simulated along an oceanographic transect acquired during the EU-funded Geophysical Oceanography (GO) project. The results demonstrate the applicability of the method for synthetic data, as well as its potential to define oceanographic features along 2-D transects at full ocean depth with excellent lateral resolution.

   @article{Kormann,
     author = {Kormann, J. and Biescas, B. and Korta Martiartu, N. and de la Puente, J. and Sallar{\'e}s, V.},
     title = {Application of acoustic full waveform inversion to retrieve high-resolution temperature and salinity profiles from synthetic seismic data},
     journal = {Journal of Geophysical Research: Oceans},
     volume = {116},
     number = {C11},
     year = {2011},
     abbr = {JGR:Oceans},
     bibtex_show = {true},
     html = {https://agupubs.onlinelibrary.wiley.com/doi/abs/10.1029/2011JC007216}
   }