Yücel Karabiyik

• Boukraa, Mohamed Aziz; Karabiyik, Yücel; Austeng, Andreas; Holm, Sverre & Näsholm, Sven Peter (2026). Proof of concept for full-waveform inversion in ultrasound time-harmonic shear-wave elastography. Physics in Medicine and Biology. ISSN 0031-9155. 71(10), p. 1–22. doi: 10.1088/1361-6560/ae6af4. Full text in Research Archive Show summary

  Objective. In ultrasound time-harmonic elastography, tissue elasticity is estimated from the ultrasound-measured shear-wave displacement fields, generated by an external vibrator. Commonly used techniques to map from the ultrasound pulse-echo data to tissue elasticity maps, such as the phase-gradient and local-frequency estimation methods, base their estimates on a set of displacement field data and do not involve direct numerical modeling of the underlying shear-wave propagation. In the current proof-of-concept study, the objective is to develop a Full-Waveform Inversion (FWI) approach to ultrasound-based time-harmonic elastography, providing a physics-driven framework for improved tissue elasticity estimation. Approach. FWI is a methodology commonly applied in geophysics. It relies on simulating the wave propagation and scattering in heterogeneous media to model the intricate relationship between the observed wavefield and the propagation medium properties. Our FWI-based tissue-harmonic elastography approach is based on minimizing a cross-correlation based objective function that quantifies phase mismatches between measured and simulated shear waves. Results. Experiments on synthetic phantom data obtained from the fractional Kelvin-Voigt wave model demonstrate that our approach accurately reconstructs the shear wave speed of the medium, even in the presence of significant noise, and without relying on pre-filtering steps such as directional filtering, which selects waves based on their propagation direction. An improvement of approximately 0.4 m.s -1 within the inclusion region, compared to an established method, is observed for a noisy wavefield with decreasing signal-to-noise ratio, ranging from 20 to -10 dB from top to bottom of the ultrasound image. In addition, the reconstructed shear-wave speed map achieved a 50% reduction in standard deviation. Significance. This work demonstrates the potential for enhanced elasticity mapping using FWI-based reconstruction in time-harmonic elastography with prospective impacts for future clinical applications.

• Maddali, Dharani Dhar; Solvin, Håvard Bjerkeseth; Lippert, Matthias; Karabiyik, Yücel; Dahle, Gry & Hjelmervik, Jon Mikkelsen [Show all 9 contributors for this article] (2024). Monte Carlo-based rendering of 3D echocardiography for mixed reality-guided atrial septal puncture positioning. Computer Assisted Surgery. 29(1). doi: 10.1080/24699322.2024.2403444. Full text in Research Archive Show summary

  Catheter-based intervention procedures contain complex maneuvers, and they are often performed using fluoroscopic guidance assisted by 2D and 3D echocardiography viewed on a flat screen that inherently limits depth perception. Emerging mixed reality (MR) technologies, combined with advanced rendering techniques, offer potential enhancement in depth perception and navigational support. The study aims to evaluate a MR-based guidance system for the atrial septal puncture (ASP) procedure utilizing a phantom anatomical model. A novel MR-based guidance system using a modified Monte Carlo-based rendering approach for 3D echocardiographic visualization was introduced and evaluated against standard clinical 3D echocardiographic display on a flat screen. The objective was to guide the ASP procedure by facilitating catheter placement and puncture across four specific atrial septum quadrants. To assess the system’s feasibility and performance, a user study involving four experienced interventional cardiologists was conducted using a phantom model. Results show that participants accurately punctured the designated quadrant in 14 out of 16 punctures using MR and 15 out of 16 punctures using the flat screen of the ultrasound machine. The geometric mean puncture time for MR was 31 s and 26 s for flat screen guidance. User experience ratings indicated MR-based guidance to be easier to navigate and locate tents of the atrial septum. The study demonstrates the feasibility of MR-guided atrial septal puncture. User experience data, particularly with respect to navigation, imply potential benefits for more complex procedures and educational purposes. The observed performance difference suggests an associated learning curve for optimal MR utilization.

• Ziksari, Mahsa Sotoodeh; Austeng, Andreas; Näsholm, Sven Peter; Cecconello, Elsa; Holm, Sverre & Karabiyik, Yücel (2024). Application of Spatial Autocorrelation in Experimental Time-Harmonic Elastography. IEEE International Symposium on Applications of Ferroelectrics (ISAF). ISSN 2375-0448. doi: 10.1109/UFFC-JS60046.2024.10793924. Full text in Research Archive
• Ziksari, Mahsa Sotoodeh; Austeng, Andreas; Näsholm, Sven Peter; Cecconello, Elsa; Holm, Sverre & Karabiyik, Yücel (2024). An Autocorrelation-Based Approach for Estimating Shear Wave Speed using 2D Velocity Vector. IEEE International Symposium on Applications of Ferroelectrics (ISAF). ISSN 2375-0448. doi: 10.1109/UFFC-JS60046.2024.10794020. Full text in Research Archive
• Karabiyik, Yücel; Avdal, Jørgen; Ekroll, Ingvild Kinn; Fiorentini, Stefano; Torp, Hans & Løvstakken, Lasse (2019). Data Adaptive 2-D Tracking Doppler for High-Resolution Spectral Estimation. IEEE Transactions on Ultrasonics, Ferroelectrics and Frequency Control. ISSN 0885-3010. 67(1). doi: 10.1109/TUFFC.2019.2937281. Full text in Research Archive Show summary

  Spectral broadening in pulsed-wave Doppler caused by the transit-time effect deteriorates the frequency resolution and may cause overestimation of maximum velocities in high-velocity blood flow regions and for large beam-to-flow angles. Data-adaptive spectral estimators have been shown to provide improved frequency resolution, especially for small ensemble lengths, but offer little or no improvement when the transit-time effect dominates. In this work, a method is presented that combines a data-adaptive spectral estimation method, the power spectral Capon, and 2-D tracking Doppler to enable improved frequency resolution for both high and low velocities. For each velocity, a time signal is extracted by tracking scatterers over time and space to decrease the transit-time effect, and power spectral Capon is used for spectral estimation. The method is evaluated using simulations, flow phantom recordings, and recordings from healthy and stenotic carotid arteries. Simulation results showed that the spectral width was decreased by 60% compared to 2-D tracking Doppler for velocities around 2.3 m/s using 12 time samples. The reduction was estimated to be 66% using the flow phantom results for 0.85-m/s mean velocity. A 5-dB SNR gain was observed from the in vivo results compared with Welch's method. Computer simulations confirm that in the presence of velocity gradients or out-of-plane motion, the proposed method can be used to reduce spectral broadening by requiring shorter observation windows.

• Karabiyik, Yücel; Ekroll, Ingvild Kinn; Eik-Nes, Sturla & Løvstakken, Lasse (2018). Quantitative Doppler analysis using conventional color flow imaging acquisitions. IEEE Transactions on Ultrasonics, Ferroelectrics and Frequency Control. ISSN 0885-3010. 65(5), p. 697–708. doi: 10.1109/TUFFC.2018.2808226. Full text in Research Archive
• Karabiyik, Yucel; Avdal, Jørgen; Ekroll, Ingvild Kinn; Torp, Hans & Løvstakken, Lasse (2016). Data adaptive 2-D tracking Doppler. Proceedings - IEEE Ultrasonics Symposium. ISSN 1948-5719. 2016-November. doi: 10.1109/ULTSYM.2016.7728713. Full text in Research Archive
• Kathpalia, Aditi; Karabiyik, Yücel; Eik-Nes, Sturla; Tegnander, Eva; Ekroll, Ingvild Kinn & Kiss, Gabriel [Show all 7 contributors for this article] (2016). Adaptive Spectral Envelope Estimation for Doppler Ultrasound. IEEE Transactions on Ultrasonics, Ferroelectrics and Frequency Control. ISSN 0885-3010. 63(11), p. 1825–1838. doi: 10.1109/TUFFC.2016.2587381. Full text in Research Archive
• Karabiyik, Yucel; Ekroll, Ingvild Kinn; Eik-Nes, Sturla; Avdal, Jørgen & Løvstakken, Lasse (2016). Adaptive Spectral Estimation Methods in Color Flow Imaging. IEEE Transactions on Ultrasonics, Ferroelectrics and Frequency Control. ISSN 0885-3010. 63(11), p. 1839–1851. doi: 10.1109/TUFFC.2016.2594838. Full text in Research Archive
• Kathpalia, Aditi; Karabiyik, Yucel; Simensen, Bente; Tegnander, Eva; Eik-Nes, Sturla & Torp, Hans [Show all 8 contributors for this article] (2015). A robust Doppler spectral envelope detection technique for automated blood flow measurements. Proceedings - IEEE Ultrasonics Symposium. ISSN 1948-5719. doi: 10.1109/ULTSYM.2015.0419. Full text in Research Archive

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• Alix, Corentin; Boulestreau, Romain; Ribot, Emeline; Couffinhal, Thierry; Karabiyik, Yücel & Salles, Sebastien Andre Roger (2026). In Vivo Detection of Guided Waves in the Carotid Wall Using a skin-Mounted Piezoelectric Patch and Ultrafast Ultrasound Imaging. Full text in Research Archive
• Boukraa, Mohamed Aziz; Karabiyik, Yücel; Austeng, Andreas; Holm, Sverre & Näsholm, Sven Peter (2026). Improved Full-Waveform Inversion in Time-Harmonic Elastography. Full text in Research Archive
• Han, Chaoran; Alix, Corentin; Näsholm, Sven Peter; Austeng, Andreas; Salles, Sébastien & Karabiyik, Yücel (2026). Transverse Oscillation-Based Velocity Estimation in Ultrasound Time-Harmonic Elastography. Full text in Research Archive
• Ziksari, Mahsa Sotoodeh; Alix, Corentin; Austeng, Andreas; Salles, Sebastien Andre Roger & Karabiyik, Yücel (2026). Directional clutter filter imaging for time harmonic elastography. Full text in Research Archive
• Boukraa, Mohamed Aziz; Karabiyik, Yücel; Austeng, Andreas & Näsholm, Sven Peter (2025). Full-Waveform Inversion in Ultrasound Time-Harmonic Shear-Wave Elastography. Full text in Research Archive
• Boukraa, Mohamed Aziz; Karabiyik, Yücel; Austeng, Andreas & Näsholm, Sven Peter (2025). Multifrequency Full-Waveform Inversion in Ultrasound Time-Harmonic Shear-Wave Elastography. Full text in Research Archive
• Han, Chaoran; Boukraa, Mohamed Aziz; Näsholm, Sven Peter; Austeng, Andreas; Ziksari, Mahsa Sotoodeh & Karabiyik, Yücel (2025). A Simulation Framework for Ultrasound Time Harmonic Elastography (THE). Full text in Research Archive
• Boukraa, Mohamed Aziz; Karabiyik, Yücel; Näsholm, Sven Peter & Austeng, Andreas (2025). Full waveform inversion in time harmonic shear wave elastography. Full text in Research Archive
• Han, Chaoran; Ziksari, Mahsa Sotoodeh; Näsholm, Sven Peter; Austeng, Andreas; Cecconello, Elsa & Boukraa, Mohamed Aziz [Show all 8 contributors for this article] (2025). Shear-wave speed estimation in time harmonic elastography. Full text in Research Archive
• Boukraa, Mohamed Aziz; Karabiyik, Yücel; Näsholm, Sven Peter & Austeng, Andreas (2025). Full waveform inversion for time harmonic shear wave elastography. Full text in Research Archive
• Ziksari, Mahsa Sotoodeh; Austeng, Andreas; Näsholm, Sven Peter; Cecconello, Elsa; Holm, Sverre & Karabiyik, Yücel (2024). Application of Spatial Autocorrelation in Experimental Time-Harmonic Elastography. Full text in Research Archive
• Ziksari, Mahsa Sotoodeh; Austeng, Andreas; Näsholm, Sven Peter; Cecconello, Elsa; Holm, Sverre & Karabiyik, Yücel (2024). An Autocorrelation-Based Approach for Estimating Shear Wave Speed Using 2D Velocity Vector. Full text in Research Archive
• Karabiyik, Yücel; Avdal, Jørgen; Ekroll, Ingvild Kinn; Torp, Hans & Løvstakken, Lasse (2018). Limiting spectral broadening in Pulsed Wave Doppler. Full text in Research Archive
• Karabiyik, Yücel; Prieur, Fabrice Jean Gabriel & Holm, Sverre (2018). Visualization of shear waves from time-harmonic ultrasound elastography. Full text in Research Archive
• Sjøbakk, Torill Anita Eidhammer; Haukaas, Tonje Husby; Bathen, Tone Frost; Moestue, Siver Andreas; Selnæs, Kirsten Margrete & Øen, Silje Kjærnes [Show all 27 contributors for this article] (2016). BILDER UTEN GRENSER. Full text in Research Archive Show summary

  Stand på Forskningstorget i Trondheim.

• Karabiyik, Yucel; Avdal, Jørgen; Ekroll, Ingvild Kinn; Torp, Hans & Løvstakken, Lasse (2016). Data Adaptive 2-D Tracking Doppler. Full text in Research Archive
• Karabiyik, Yücel; Avdal, Jørgen; Ekroll, Ingvild Kinn; Torp, Hans & Løvstakken, Lasse (2016). Data Adaptive 2-D Tracking Doppler. Full text in Research Archive
• Kathpalia, Aditi; Karabiyik, Yucel; Simensen, Bente; Tegnander, Eva; Eik-Nes, Sturla & Torp, Hans [Show all 8 contributors for this article] (2015). A robust Doppler spectral envelope detection technique for automated blood flow measurements. Full text in Research Archive
• Karabiyik, Yücel; Ekroll, Ingvild Kinn; Avdal, Jørgen; Torp, Hans & Løvstakken, Lasse (2015). Adaptive Spectral Estimation Methods in Color Flow Imaging. Full text in Research Archive
• Karabiyik, Yücel; Ekroll, Ingvild Kinn; Avdal, Jørgen; Torp, Hans & Løvstakken, Lasse (2015). Adaptive Spectral Estimation Methods in Color Flow Imaging. Full text in Research Archive
• Karabiyik, Yucel; Løvstakken, Lasse; Ekroll, Ingvild Kinn; Torp, Hans & Eik-Nes, Sturla (2017). Quantitative Doppler analysis using color flow imaging and adaptive signal processing. Norges teknisk-naturvitenskapelige universitet. ISSN 9788232625277. Full text in Research Archive Show summary

  Kvantitative Doppler-m˚alinger fra farge-Doppler ved bruk av adaptiv signalprosessering Medisinsk ultralyd er et viktig verktøy i obstetrikk for ˚a vurdere mors helse og fosterets utvikling gjennom svangerskapet. Doppler-ultralyd brukes for ˚a estimere blodstrømshastigheter og i svangerskap kan Dopplerm˚alinger fra blant annet navlesnoren avsløre risikosvangerskap. Ultralydskannere er relativt billige og svangerskapsultralyd er et vanlig tilbud til gravide i industrialiserte land, mens det i utviklingsland er mangel p˚a b˚ade ultralydskannere og kvalifiserte operatører. M˚alet gjennom doktorgradsarbeidet har vært ˚a utvikle Doppler-metoder som kan effektivisere arbeidsflyt og gi kvantitative Dopplerm˚alinger automatisk, spesielt for uerfarne operatører. Metodene skal være implementerbare ogs˚a p˚a billige, uvanserte skannere som ofte er aktuelle for utviklingsland. Farge-Doppler brukes i dag som en kvalitativ metode som visualiserer blodstrøm. I dette arbeidet har de kvantitative mulighetene til farge-Doppler blitt undersøkt, spesielt med tanke p˚a nøyaktighet og bilderate. N˚ar flere avbildningssekvenser brukes samtidig (duplex/triplex mode), synker bilderaten drastisk, noe som kan motvirkes ved ˚a avbilde et mindre omr˚ade og bruke mindre data til hastighetsestimering. For ˚a unng˚a triplex-sekvenser, ble det dermed først undersøkt om adaptiv spektralestimering kunne brukes til ˚a estimere middelhastigheten til blodstrømmen slik som i farge-Doppler. Det ble vist at dette kunne gjøres selv uten ˚a m˚atte filtrere bort vevssignalet først, noe som ga mer nøyaktige hastighetsestimat for de lavere blodstrømshastighetene som ellers ville blitt ødelagt av vevsfilteret ved bruk av farge-Doppler. For ˚a effektivisere arbeidsflyt og unng˚a duplex/triplex-sekvenser, er det deretter utviklet en metode som gir hastighetsspekter fra alle punkt i farge-Dopplerbildet ved hjelp av adaptiv spektralestimering og romlig midling. I tillegg ble det utviklet en metode for ˚a estimere envelopen til hastighetsspektrene for ˚a lettere finne maksimumshastigheter og relevante Dopplerindekser. Den siste metoden som er presentert i dette doktorgradsarbeidet prøver˚a minimere spredning i hastighetsspekteret for˚a unng˚a overestimering av maksimumshastigheter. Metoden gir hastighetsspekter av høy kvalitet basert p˚a f˚a datapunkt som er forenelig med farge-Doppler. En ultralydskanner med en kombinasjon av metodene som er presentert i denne avhandlingen, vil oppn˚a en forbedret farge-Doppler-metode med mulighet for kvantitative blodstrømsm˚alinger. Metoden vil være enkel ˚a ta i bruk og kan redusere variasjoner i m˚alinger og mellom operatører.

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