Ole Marius Hoel Rindal

• Vrålstad, Anders Emil; Fosodeder, Peter; Deibele, Karin Ulrike; Nyrnes, Siri Ann; Rindal, Ole Marius Hoel & Skoura-Torvik, Vibeke [Show all 8 contributors for this article] (2026). Coherence Based Sound Speed Aberration Correction — with clinical validation in fetal ultrasound. IEEE Transactions on Medical Imaging. ISSN 0278-0062. doi: 10.1109/TMI.2026.3691415. Full text in Research Archive
• Måsøy, Svein-Erik; Dénarié, Bastien Emmanuel; Sørnes, Anders Rasmus; Holte, Espen; Grenne, Bjørnar Leangen & Espeland, Torvald [Show all 10 contributors for this article] (2024). Aberration correction in 3D transthoracic echocardiography. WFUMB Ultrasound Open. 2(2). doi: 10.1016/j.wfumbo.2024.100062. Full text in Research Archive
• Vrålstad, Anders Emil; Rindal, Ole Marius Hoel; Bjåstad, Tore Grüner & Måsøy, Svein-Erik (2024). Sound Speed and Virtual Source Correction in Synthetic Transmit Focusing. IEEE Open Journal of Ultrasonics, Ferroelectrics, and Frequency Control Society (OJUFFC). doi: 10.1109/OJUFFC.2024.3411578. Full text in Research Archive
• Vrålstad, Anders Emil; Kvalevåg, Magnus Dalen; Rindal, Ole Marius Hoel & Måsøy, Svein-Erik (2024). Universal REFoCUS Beamforming With Spatial Weighting. IEEE Open Journal of Ultrasonics, Ferroelectrics, and Frequency Control Society (OJUFFC). doi: 10.1109/OJUFFC.2024.3398595. Full text in Research Archive
• Vrålstad, Anders Emil; Fosodeder, Peter; Rindal, Ole Marius Hoel; Deibele, Karin Ulrike; Nyrnes, Siri Ann & Skoura-Torvik, Vibeke [Show all 8 contributors for this article] (2024). Coherence Based Sound Speed Aberration Correction -- with clinical validation in fetal ultrasound. arXiv. doi: 10.48550/arXiv.2411.16551. Full text in Research Archive
• Arnestad, Håvard; Rindal, Ole Marius Hoel; Austeng, Andreas & Näsholm, Sven Peter (2024). Robust Non-Parametric Estimation of Speckle Probability Densities and gCNR. IEEE Open Journal of Ultrasonics, Ferroelectrics, and Frequency Control Society (OJUFFC). 4, p. 89–99. doi: 10.1109/OJUFFC.2024.3445868. Full text in Research Archive Show summary

  In ultrasound imaging, speckle originates from a large amount of sub-resolution scatterers within the medium. In idealized cases, the speckle envelope statistics follow a Rayleigh distribution, but in practical pulse-echo imaging, the distribution depends on both the imaging system and the underlying tissue structure. Estimating envelope statistics is part of quantitative ultrasound workflows and is also important for image quality assessment as it relates to lesion and tissue detectability. A concrete example is the generalized contrast-to-noise ratio (gCNR), which is a functional of two pixel-value probability density functions (PDFs) from different speckle regions. Such speckle PDFs have, by convention, been estimated from data using histograms, but the accuracy of these estimates can be affected by the nontrivial selection and tuning of the binning parameters. However, the statistics literature widely advocates kernel density estimation (KDE) as a better alternative to histogram-based approaches. In this article, we propose applying a KDE-based method to estimate speckle PDFs in medical ultrasound imaging. The method is practically tuning-free and leverages the Box-Cox transformation to achieve best-in-class performance across a wide range of test cases, and is also robust in cases where gCNR estimation may otherwise fail, such as for skewed distributions that may arise with adaptive beamformers. Furthermore, this work highlights theoretical aspects related to the estimation of PDFs and derived quantities, including the gCNR.

• Kvalevåg, Magnus; Vrålstad, Anders Emil; Rindal, Ole Marius Hoel; Bjåstad, Tore Grüner; Dénarié, Bastien & Kristoffersen, Kjell [Show all 8 contributors for this article] (2023). vbeam: A Fast and Differentiable Beamformer for Optimizing Ultrasound Imaging. Proceedings - IEEE Ultrasonics Symposium. ISSN 1948-5719. doi: 10.1109/IUS51837.2023.10307255. Full text in Research Archive Show summary

  We present vbeam: a new open-source beamforming library that provides fast parallel beamforming computation on the CPU and GPU for modern imaging setups. It is auto-differentiable which allows for incorporating image optimization and machine learning (ML) into the beamformer, and vice versa. The library can be used from either Python or MATLAB and aims to be a beamforming research tool which can be used stand-alone or integrated with tools, such as USTB, Field II and MUST.

• Rindal, Ole Marius Hoel; Bjåstad, Tore Grüner; Espeland, Torvald; Berg, Erik Andreas Rye & Måsøy, Svein-Erik (2023). A Very Large Cardiac Channel Data Database (VLCD) Used to Evaluate Global Image Coherence (GIC) as an In Vivo Image Quality Metric. IEEE Transactions on Ultrasonics, Ferroelectrics and Frequency Control. ISSN 0885-3010. 70(10), p. 1295–1307. doi: 10.1109/TUFFC.2023.3308034. Full text in Research Archive Show summary

  Ultrasound image quality is of utmost importance for a clinician to reach a correct diagnosis. Conventionally, image quality is evaluated using metrics to determine the contrast and resolution. These metrics requires localization of specific regions and targets in the image such as a region of interest (ROI), a background region, and or, a point scatterer. Such objects can all be difficult to identify in in-vivo images, especially for automatic evaluation of image quality in large amounts of data. Using a matrix array probe, we have recorded a Very Large cardiac Channel data Database (VLCD) to evaluate coherence as an in-vivo image quality metric. The VLCD consists of 33 280 individual image frames from 538 recordings of 106 patients. We also introduce a Global Imag Coherence (GIC), an in-vivo image quality metric that does not require any identified ROI since it is defined as an average coherence value calculated from all the data pixels used to form the image, below a pre-selected range. The GIC is shown to be a quantitative metric for in-vivo image quality when applied to the VLCD. We demonstrate, on a subset of the dataset, that the GIC correlates well with the conventional metrics contrast ratio (CR) and the generalized contrast-to-noise ratio (gCNR)with R=0.74 (p0.9, p

• Måsøy, Svein-Erik; Dénarié, Bastien Emmanuel; Sørnes, Anders Rasmus; Holte, Espen; Grenne, Bjørnar Leangen & Espeland, Torvald [Show all 10 contributors for this article] (2023). Aberration correction in 2D echocardiography. Quantitative Imaging in Medicine and Surgery (QIMS). ISSN 2223-4292. 13(7), p. 4603–4617. doi: 10.21037/qims-22-895. Full text in Research Archive
• Heimark, Sondre; Eitzen, Ingrid; Vianello, Isabella; Bøtker-Rasmussen, Kasper; Mamen, Asgeir & Rindal, Ole Marius Hoel [Show all 9 contributors for this article] (2022). Blood Pressure Response and Pulse Arrival Time During Exercise Testing in Well-Trained Individuals. Frontiers in Physiology. 13. doi: 10.3389/fphys.2022.863855. Full text in Research Archive Show summary

  Introduction: There is a lack of data describing the blood pressure response (BPR) in well-trained individuals. In addition, continuous bio-signal measurements are increasingly investigated to overcome the limitations of intermittent cuff-based BP measurements during exercise testing. Thus, the present study aimed to assess the BPR in well-trained individuals during a cycle ergometer test with a particular focus on the systolic BP (SBP) and to investigate pulse arrival time (PAT) as a continuous surrogate for SBP during exercise testing. Materials and Methods: Eighteen well-trained male cyclists were included (32.4 ± 9.4 years; maximal oxygen uptake 63 ± 10 ml/min/kg) and performed a stepwise lactate threshold test with 5-minute stages, followed by a continuous test to voluntary exhaustion with 1-min increments when cycling on an ergometer. BP was measured with a standard automated exercise BP cuff. PAT was measured continuously with a non-invasive physiological measurements device (IsenseU) and metabolic consumption was measured continuously during both tests. Results: At lactate threshold (281 ± 56 W) and maximal intensity test (403 ± 61 W), SBP increased from resting values of 136 ± 9 mmHg to maximal values of 219 ± 21 mmHg and 231 ± 18 mmHg, respectively. Linear within-participant regression lines between PAT and SBP showed a mean r2 of 0.81 ± 17. Conclusion: In the present study focusing on the BPR in well-trained individuals, we observed a more exaggerated systolic BPR than in comparable recent studies. Future research should follow up on these findings to clarify the clinical implications of the high BPR in well-trained individuals. In addition, PAT showed strong intra-individual associations, indicating potential use as a surrogate SBP measurement during exercise testing.

• Heimark, Sondre; Bøtker-Rasmussen, Kasper; Rindal, Ole Marius Hoel; Seeberg, Trine Margrethe; Stepanov, Alexey & Boysen, Elin Sundby [Show all 10 contributors for this article] (2022). COMPARISON OF CONTINUOUS MEAN ARTERIAL PRESSURE BY A WEARABLE CUFF-LESS DEVICE AGAINST INTRA-ARTERIAL MEASUREMENTS. Journal of Hypertension. ISSN 0263-6352. 40(1), p. e107–e108. doi: 10.1097/01.hjh.0000836332.51137.4c. Full text in Research Archive
• Arnestad, Håvard; Austeng, Andreas; Näsholm, Sven Peter & Rindal, Ole Marius Hoel (2022). The Effect of Retrospective Transmit Focusing on Minimum Variance Beamforming. Proceedings - IEEE Ultrasonics Symposium. ISSN 1948-5719. doi: 10.1109/IUS54386.2022.9958050. Full text in Research Archive Show summary

  Minimum variance (MV) beamforming is a well-known adaptive beamforming approach. Retrospective transmit beamforming (RTB), on the other hand, is a technique implemented in some modern ultrasound scanners that strives to obtain two-way focus everywhere in the imaged region. However, it is not immediately clear how these methods should be combined in the image reconstruction pipeline. In this work, we suggest a general and efficient implementation for combining MV with RTB, and we study a few effects and synergetic benefits in comparison to multiple line acquisition processing and conventional delay-and-sum beamforming. Our finding is that RTB improves the resolution and robustness of MV beamforming outside the focal zone.

• Heimark, Sondre; Rindal, Ole Marius Hoel; Seeberg, Trine Margrethe; Stepanov, Alexey; Boysen, Elin Sundby & Bøtker-Rasmussen, Kasper [Show all 11 contributors for this article] (2021). Blood pressure altering method affects correlation with pulse arrival time. Blood Pressure Monitoring. ISSN 1359-5237. 27(2). doi: 10.1097/MBP.0000000000000577. Full text in Research Archive Show summary

  Objective: Pulse arrival time (PAT) is a potential main feature in cuff-less blood pressure (BP) monitoring. However, the precise relationship between BP parameters and PAT under varying conditions lacks a complete understanding. We hypothesize that simple test protocols fail to demonstrate the complex relationship between PAT and both SBP and DBP. Therefore, this study aimed to investigate the correlation between PAT and BP during two exercise modalities with differing BP responses using an unobtrusive wearable device. Methods: Seventy-five subjects, of which 43.7% had a prior diagnosis of hypertension, participated in an isometric and dynamic exercise test also including seated periods of rest prior to, in between and after. PAT was measured using a prototype wearable chest belt with a one-channel electrocardiogram and a photo-plethysmography sensor. Reference BP was measured auscultatory. Results: Mean individual correlation between PAT and SBP was −0.82 ± 0.14 in the full protocol, −0.79 ± 0.27 during isometric exercise and −0.77 ± 0.19 during dynamic exercise. Corresponding correlation between PAT and DBP was 0.25 ± 0.35, −0.74 ± 0.23 and 0.39 ± 0.41. Conclusion: The results confirm PAT as a potential main feature to track changes in SBP. The relationship between DBP and PAT varied between exercise modalities, with the sign of the correlation changing from negative to positive between type of exercise modality. Thus, we hypothesize that simple test protocols fail to demonstrate the complex relationship between PAT and BP with emphasis on DBP.

• Rodriguez-Molares, Alfonso; Rindal, Ole Marius Hoel; D´Hooge, Jan; Måsøy, Svein-Erik; Austeng, Andreas & Bell, Muyinatu A. Lediju [Show all 7 contributors for this article] (2020). The Generalized Contrast-to-Noise Ratio: A Formal Definition for Lesion Detectability. IEEE Transactions on Ultrasonics, Ferroelectrics and Frequency Control. ISSN 0885-3010. 67(4), p. 745–759. doi: 10.1109/TUFFC.2019.2956855. Full text in Research Archive Show summary

  In the last 30 years, the contrast-to-noise ratio (CNR) has been used to estimate the contrast and lesion detectability in ultrasound images. Recent studies have shown that the CNR cannot be used with modern beamformers, as dynamic range alterations can produce arbitrarily high CNR values with no real effect on the probability of lesion detection. We generalize the definition of CNR based on the overlap area between two probability density functions. This generalized CNR (gCNR) is robust against dynamic range alterations; it can be applied to all kind of images, units, or scales; it provides a quantitative measure for contrast; and it has a simple statistical interpretation, i.e., the success rate that can be expected from an ideal observer at the task of separating pixels. We test gCNR on several state-of-the-art imaging algorithms and, in addition, on a trivial compression of the dynamic range. We observe that CNR varies greatly between the state-of-the-art methods, with improvements larger than 100%. We observe that trivial compression leads to a CNR improvement of over 200%. The proposed index, however, yields the same value for compressed and uncompressed images. The tested methods showed mismatched performance in terms of lesion detectability, with variations in gCNR ranging from -0.08 to +0.29. This new metric fixes a methodological flaw in the way we study contrast and allows us to assess the relevance of new imaging algorithms.

• Rindal, Ole Marius Hoel; Rodriguez-Molares, Alfonso & Austeng, Andreas (2020). Resolution Measured as Separability Compared to Full Width Half Maximum for Adaptive Beamformers. Proceedings - IEEE Ultrasonics Symposium. ISSN 1948-5719. doi: 10.1109/IUS46767.2020.9251787. Full text in Research Archive Show summary

  Spatial resolution is defined as a system's ability to separate targets using some kind of criterion, such as the Rayleigh criterion. However, in practice, lateral resolution is often evaluated by measuring the Full Width Half Maximum (FWHM at -6dB) of the point spread function (PSF). We hypothesize that FWHM overestimates the system resolution for some adaptive beamformers, compared to using the Rayleigh criterion. Simulation results seem to confirm this hypothesis.

• Palmer, Cameron Lowell & Rindal, Ole Marius Hoel (2019). Wireless, Real-Time Plane-Wave Coherent Compounding on an iPhone: A Feasibility Study. IEEE Transactions on Ultrasonics, Ferroelectrics and Frequency Control. ISSN 0885-3010. 66(7), p. 1222–1231. doi: 10.1109/TUFFC.2019.2914555. Full text in Research Archive
• Tjønnås, Johannes; Seeberg, Trine Margrethe; Rindal, Ole Marius Hoel; Haugnes, Pål & Sandbakk, Øyvind (2019). Assessment of Basic Motions and Technique Identification in Classical Cross-Country Skiing. Frontiers in Psychology. 10. doi: 10.3389/fpsyg.2019.01260. Full text in Research Archive Show summary

  Cross-country skiing is a popular Olympic winter sport, which is also used extensively as a recreational activity. While cross-country skiing primarily is regarded as a demanding endurance activity it is also technically challenging, as it contains two main styles (classical and skating) and many sub-techniques within these styles. To further understand the physiological demands and technical challenges of cross-country skiing it is imperative to identify sub-techniques and basic motion features during training and competitions. Therefore, this paper presents features for identification and assessment of the basic motion patterns used during classical-style cross-country skiing. The main motivation for this work is to contribute to the development of a more detailed platform for comparing and communicating results from technique analysis methods, to prevent unambiguous definitions and to allow more precise discussions and quality assessments of an athlete's technical ability. To achieve this, our paper proposes formal motion components and classical style technique definitions as well as sub-technique classifiers. This structure is general and can be used directly for other cyclic activities with clearly defined and distinguishable sub-techniques, such as the skating style in cross country skiing. The motion component features suggested in our approach are arm synchronization, leg kick, leg kick direction, leg kick rotation, foot/ski orientation and energy like measures of the arm, and leg motion. By direct measurement, estimation, and the combination of these components, the traditional sub-techniques of diagonal stride, double poling, double poling kick, herringbone, as well as turning techniques can be identified. By assuming that the proposed definitions of the classical XC skiing sub-techniques are accepted, the presented classifier is proven to map measures from the motion component definitions to a unique representation of the sub-techniques. This formalization and structure may be used on new motion components, measurement principles, and classifiers, and therefore provides a framework for comparing different methodologies. Pilot data from a group of high-level cross-country skiers employing inertial measurement sensors placed on the athlete's arms and skis are used to demonstrate the approach. The results show how detailed sub-technique information can be coupled with physical, track, and environmental data to analyze the effects of specific motion patterns, to develop useful debriefing tools for coaches and athletes in training and competition settings, and to explore new research hypotheses.

• Rindal, Ole Marius Hoel; Rodriguez-Molares, Alfonso; Måsøy, Svein-Erik & Bjåstad, Tore Grüner (2019). Improved Lesion Detection Using Nonlocal Means Post-Processing. Proceedings - IEEE Ultrasonics Symposium. ISSN 1948-5719. 2019-October, p. 1013–1016. doi: 10.1109/ULTSYM.2019.8926303. Full text in Research Archive Show summary

  Software beamforming allows more flexible and complex algorithms, often referred to as adaptive beamforming techniques, that are blurring the boundaries between beamforming and image processing. Many adaptive beamforming algorithms claim to improve lesion detectability. Based on recent advances, we hypothesize that image processing techniques that reduce speckle variability yield better lesion detectability than state-of-the-art adaptive beamformers.This hypothesis is investigated on six algorithms: two image processing techniques, and four adaptive beamformers. As a target we use Field II simulations of a hypoechoic cyst with noise added to simulate different SNR conditions. Lesion detectability is estimated using the Generalized Contrast-to-Noise Ratio (GCNR). The results support our hypothesis.

• Rindal, Ole Marius Hoel; Austeng, Andreas; Fatemi, Ali & Rodriguez-Molares, Alfonso (2019). The Effect of Dynamic Range Alterations in the Estimation of Contrast. IEEE Transactions on Ultrasonics, Ferroelectrics and Frequency Control. ISSN 0885-3010. 66(7), p. 1198–1208. doi: 10.1109/TUFFC.2019.2911267. Full text in Research Archive
• Solli, Guro Strøm; Kocbach, Jan; Seeberg, Trine Margrethe; Tjønnås, Johannes; Rindal, Ole Marius Hoel & Haugnes, Pål [Show all 8 contributors for this article] (2018). Sex-based differences in speed, sub-technique selection, and kinematic patterns during low- and high-intensity training for classical cross-country skiing. PLOS ONE. 13(11). doi: 10.1371/journal.pone.0207195. Full text in Research Archive Show summary

  Objectives We investigated sex-based differences in speed, sub-technique selection, and kinematic patterns during low- (LIT) and high-intensity training (HIT) for classical cross-country (XC) skiing across varying terrain. Methods Six male and six female elite XC skiers with an approximately 15% differences in VO2max (men: 68.9±2.9 mL·min-1·kg-1, women: 60.1±3.3 mL·min-1·kg-1) were monitored using a multi-sensor system to collect time-synchronised data of heart rate, speed, and multiple tri-axial inertial measurements units while XC skiing on a 5-km competition track. Results Men skied 21% faster than women during HIT (5.9±0.3 m·s-1 vs. 4.9±0.2 m·s-1, P < .001), with the greatest difference (26%) while skiing on flat terrain, whereas skiing speed did not significantly differ between men and women during LIT. At similar instructed intensity and rating of perceived effort, women exhibited significantly higher relative heart rate (85±2% vs. 71±3% of maximum) and blood lactate levels (4.0±1.3 vs. 1.2±0.2 mmol/L) during LIT (all P < .001) than men, whereas physiological responses did generally not differ between the sexes during HIT. During both intensities and among both sexes, double poling (DP) was the sub-technique most used relative to distance, followed by miscellaneous sub-techniques (MISC), diagonal stride (DIA), kick double poling (DK) and herringbone (HRB). In relation to distance women used DIA more than men during LIT (22% vs. 17%, P = .009) and HIT (23% vs. 12%, P = .001), whereas men used MISC, including tucking and turning, more than women during LIT (39% vs. 25%, P = .017) and HIT (41% vs. 30%, P = .064). In particular, men used DP more than women while skiing the uphill sections during both LIT (24% vs. 11%, P = .015) and HIT (39% vs. 13%, P = .002). Conclusions Our findings provide novel insights into sex-based differences in speed, sub-technique selection, and kinematic patterns during LIT and HIT for classical skiing.

• Wiacek, Alycen; Rindal, Ole Marius Hoel; Falomo, Eniola; Myers, Kelly; Fabrega-Foster, Kelly & Harvey, Susan [Show all 7 contributors for this article] (2018). Robust Short-Lag Spatial Coherence Imaging of Breast Ultrasound Data: Initial Clinical Results. IEEE Transactions on Ultrasonics, Ferroelectrics and Frequency Control. ISSN 0885-3010. 66(3), p. 527–540. doi: 10.1109/TUFFC.2018.2883427. Full text in Research Archive
• Bernard, Olivier; Bradway, David; Hansen, Hendrik H.G.; Kruizinga, Pieter; Nair, Arun & Perdios, Dimitris [Show all 11 contributors for this article] (2018). The Ultrasound File Format (UFF) - First Draft. Proceedings - IEEE Ultrasonics Symposium. ISSN 1948-5719. 2018-January:8579642, p. 1–4. doi: 10.1109/ULTSYM.2018.8579642. Full text in Research Archive
• Rindal, Ole Marius Hoel; Seeberg, Trine Margrethe; Tjønnås, Johannes; Haugnes, Pål & Sandbakk, Øyvind (2018). Automatic Classification of Sub-Techniques in Classical Cross-Country Skiing Using a Machine Learning Algorithm on Micro-Sensor Data. Sensors. 18(1). doi: 10.3390/s18010075. Full text in Research Archive Show summary

  The automatic classification of sub-techniques in classical cross-country skiing provides unique possibilities for analyzing the biomechanical aspects of outdoor skiing. This is currently possible due to the miniaturization and flexibility of wearable inertial measurement units (IMUs) that allow researchers to bring the laboratory to the field. In this study, we aimed to optimize the accuracy of the automatic classification of classical cross-country skiing sub-techniques by using two IMUs attached to the skier’s arm and chest together with a machine learning algorithm. The novelty of our approach is the reliable detection of individual cycles using a gyroscope on the skier’s arm, while a neural network machine learning algorithm robustly classifies each cycle to a sub-technique using sensor data from an accelerometer on the chest. In this study, 24 datasets from 10 different participants were separated into the categories training-, validation- and test-data. Overall, we achieved a classification accuracy of 93.9% on the test-data. Furthermore, we illustrate how an accurate classification of sub-techniques can be combined with data from standard sports equipment including position, altitude, speed and heart rate measuring systems. Combining this information has the potential to provide novel insight into physiological and biomechanical aspects valuable to coaches, athletes and researchers

• Prieur, Fabrice Jean Gabriel; Rindal, Ole Marius Hoel & Austeng, Andreas (2018). Signal Coherence and Image Amplitude With the Filtered Delay Multiply and Sum Beamformer. IEEE Transactions on Ultrasonics, Ferroelectrics and Frequency Control. ISSN 0885-3010. 65(7), p. 1133–1140. doi: 10.1109/TUFFC.2018.2831789. Full text in Research Archive
• Rodriguez-Molares, Alfonso; Rindal, Ole Marius Hoel; D'Hooge, Jan R M; Måsøy, Svein-Erik; Austeng, Andreas & Torp, Hans (2018). The generalized contrast-to-noise ratio. Proceedings - IEEE Ultrasonics Symposium. ISSN 1948-5719. doi: 10.1109/ULTSYM.2018.8580101. Full text in Research Archive
• Wiacek, Alycen; Falomo, Eniola; Myers, Kelly; Rindal, Ole Marius Hoel; Fabrega-Foster, Kelly & Harvey, Susan [Show all 7 contributors for this article] (2018). Clinical Feasibility of Coherence-Based Beamforming to Distinguish Solid from Fluid Hypoechoic Breast Masses. Proceedings - IEEE Ultrasonics Symposium. ISSN 1948-5719. 2018-January. doi: 10.1109/ULTSYM.2018.8579846. Full text in Research Archive
• Prieur, Fabrice Jean Gabriel; Rindal, Ole Marius Hoel; Holm, Sverre & Austeng, Andreas (2017). Influence of the Delay-Multiply-And-Sum beamformer on the ultrasound image amplitude. Proceedings - IEEE Ultrasonics Symposium. ISSN 1948-5719. doi: 10.1109/ULTSYM.2017.8092637. Full text in Research Archive
• Seeberg, Trine Margrethe; Tjønnås, Johannes; Rindal, Ole Marius Hoel; Haugnes, Pål; Dalgard, Steffen Harald & Sandbakk, Øyvind (2017). A multi-sensor system for automatic analysis of classical cross-country skiing techniques. Sports Engineering. ISSN 1369-7072. 20(4), p. 313–327. doi: 10.1007/s12283-017-0252-z. Full text in Research Archive Show summary

  Commercial systems utilizing data from inertial measurement units (IMUs) to analyse movement patterns have not yet been adapted to monitor daily training in cross-country (XC) skiing. The main purposes of this study are to investigate: (1) the feasibility and potential of a multi-sensor system consisting of a heart rate sensor, global navigation satellite systems (GNSSs) data and seven IMUs placed at multiple locations on the body for outdoor XC skiing, and (2) the validity of employing hard decision rules based on the correlation between arms and legs for detecting sub-techniques in classical XC skiing. All sensor data were synchronously sampled and synchronized with GNSS data from a commercially available sports watch while XC skiing on varying tracks, from amateur skiers and world-class athletes. An algorithm based on the correlation of the angular velocity of arms and legs was developed to detect the three main classic sub-techniques, diagonal, double poling with a kick and double poling. Other sub-techniques were classified as miscellaneous (0–20%). The system is shown to work well outdoors on snow during different conditions, and the implemented algorithm was validated by video analyses to detect the three sub-techniques with a sensitivity of 99–100%. This study is the first to detect and link sub-techniques in XC skiing to GNSS data, thereby associating the detection and distribution of sub-techniques to different terrains. Such information gives insight into the technical and tactical aspects of skiers’ daily training and competitions, thereby providing a tool for coaches and athletes.

• Hverven, Stine Myhre; Rindal, Ole Marius Hoel; Rodriguez-Molares, Alfonso & Austeng, Andreas (2017). The influence of speckle statistics on contrast metrics in ultrasound imaging. Proceedings - IEEE Ultrasonics Symposium. ISSN 1948-5719. p. 1–4. doi: 10.1109/ULTSYM.2017.8091875. Full text in Research Archive Show summary

  Adaptive beamformers aim for improved resolution and contrast in the ultrasound images, and their performance is typically benchmarked using metrics such as contrast ratio (CR) and contrast-to-noise ratio (CNR). Using synthetic aperture Field II simulations, we show that certain beamformers alter speckle statistics and that this opens up for cherry picking of contrast metrics.

• Hverven, Stine Myhre; Rindal, Ole Marius Hoel; Hunter, Alan Joseph & Austeng, Andreas (2017). Point scatterer enhancement in ultrasound by wavelet coefficient shrinkage. Proceedings - IEEE Ultrasonics Symposium. ISSN 1948-5719. 2017, p. 1–4. doi: 10.1109/ULTSYM.2017.8092971. Full text in Research Archive Show summary

  Background speckle can often obscure objects of interest in an ultrasound image. The probability of detection and classification of point scatterers is highly affected by background speckle. The proposed algorithm uses a coherence-based wavelet coefficient shrinkage method. Point scatterers in the ultrasound image are enhanced by separating coherent point targets from incoherent background speckle. Results using Field II ultrasound simulations show how the algorithm retains the point scatterers and increases their conspicuity. The algorithm has potential to detect microcalcifications in breast tissue.

• Rindal, Ole Marius Hoel; Aakhus, Svend; Holm, Sverre & Austeng, Andreas (2017). Hypothesis of Improved Visualization of Microstructures in the Interventricular Septum with Ultrasound and Adaptive Beamforming. Ultrasound in Medicine and Biology. ISSN 0301-5629. 43(10), p. 2494–2499. doi: 10.1016/j.ultrasmedbio.2017.05.023. Full text in Research Archive
• Rodriguez-Molares, Alfonso; Rindal, Ole Marius Hoel; Bernard, Olivier; Nair, Arun; Bell, Muyinatu A. Lediju & Liebgott, Herve [Show all 8 contributors for this article] (2017). The UltraSound ToolBox. Proceedings - IEEE Ultrasonics Symposium. ISSN 1948-5719. doi: 10.1109/ULTSYM.2017.8092389. Full text in Research Archive Show summary

  We present the UltraSound ToolBox (USTB), a processing framework for ultrasound signals. USTB aims to facilitate the comparison of imaging techniques and the dissemination of research results. It fills the void of tools for algorithm sharing and verification, and enables a solid assessment of the correctness and relevance of new approaches. It also aims to boost research productivity by cutting down implementation time and code maintenance. USTB is a MATLAB toolbox for processing 2D and 3D ultrasound data, supporting both MATLAB and C++ implementations. Channel data from any origin, simulated and experimental, and using any kind of sequence, e.g. synthetic transmit aperture imaging (STAI) or coherent plane-wave compounding (CPWC), can be processed with USTB. Here we describe some of the elements of USTB such as: the ultrasound file format, the concept of the general beamformer, and the signal processing pipeline. We also show a minimal code example, and demonstrate that USTB can be used with the most used transmit sequences: STAI, CPWC, diverging wave imaging (DWI), focused imaging (FI), and retrospective transmit beamforming (RTB).

• Rindal, Ole Marius Hoel; Rodriguez-Molares, Alfonso & Austeng, Andreas (2017). The dark region artifact in adaptive ultrasound beamforming. Proceedings - IEEE Ultrasonics Symposium. ISSN 1948-5719. doi: 10.1109/ULTSYM.2017.8092255. Full text in Research Archive Show summary

  An undesired effect, the dark region artifact (DRA), has been under-communicated in our research community. The DRA appear next to acoustically strong targets for some of the many adaptive beamformers introduced in the literature. This study investigates the DRA for a collection of adaptive beamformers and shows that this effect originates because some of the methods fail to estimate which signals arise in the mainlobe and which originates from sidelobes. The DRA results in darker regions in the ultrasound images, indicating the wrong acoustical amplitude. Therefore, the measured contrast can falsely appear higher for adaptive beamformers affected by the DRA.

• Rindal, Ole Marius Hoel; Austeng, Andreas; Torp, Hans Garman; Holm, Sverre & Rodriguez-Molares, Alfonso (2016). The dynamic range of adaptive beamformers. Proceedings - IEEE Ultrasonics Symposium. ISSN 1948-5719. 2016-November. doi: 10.1109/ULTSYM.2016.7728717. Full text in Research Archive
• Rindal, Ole Marius Hoel & Austeng, Andreas (2016). Double Adaptive Plane-wave Imaging. Proceedings - IEEE Ultrasonics Symposium. ISSN 1948-5719. 2016-November. doi: 10.1109/ULTSYM.2016.7728906. Full text in Research Archive
• Palmer, Cameron Lowell; Rindal, Ole Marius Hoel; Holm, Sverre & Austeng, Andreas (2016). Realtime plane-wave software beamforming with an iPhone. Proceedings - IEEE Ultrasonics Symposium. ISSN 1948-5719. 2016-November, p. 1–4. doi: 10.1109/ULTSYM.2016.7728408. Full text in Research Archive
• Rindal, Ole Marius Hoel; Åsen, Jon Petter; Holm, Sverre & Austeng, Andreas (2014). Understanding contrast improvements from capon beamforming. Proceedings - IEEE Ultrasonics Symposium. ISSN 1948-5719. p. 1694–1697. doi: 10.1109/ULTSYM.2014.0420. Full text in Research Archive

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• Arnestad, Håvard; Näsholm, Sven Peter; Rindal, Ole Marius Hoel & Austeng, Andreas (2025). Low-Complexity Adaptive Beamforming for Acoustic Pulse-Echo Imaging. Full text in Research Archive
• Arnestad, Håvard; Rindal, Ole Marius Hoel; Austeng, Andreas & Näsholm, Sven Peter (2024). Estimation of probability densities in ultrasound imaging. Full text in Research Archive
• Rindal, Ole Marius Hoel; Fiorentini, Stefano; Avdal, Jørgen; Austeng, Andreas & Molares, Alfonso Rodriguez (2023). The Generalized Beamformer in the UltraSound ToolBox. Full text in Research Archive Show summary

  Access to channel data, and real-time processing of such, have left us a landscape filled with beamforming techniques often using specific wavefronts with specific reconstruction algorithms. This implies high costs for code maintenance and makes it difficult to compare different techniques. We demonstrate a generalized beamformer (GB) to reconstruct any transmit (tx) waveform from any probe into a defined grid of pixels. It covers linear and sector scans, both steered and stepped tx and even complex beamforming such as multiple line acquisition (MLA) and retrospective tx beamforming (RTB). Also, we show how the GB can be utilized to improve the channel data used for adaptive beamforming.

• Melteig, Elina & Rindal, Ole Marius Hoel (2023). Skiteknikk under lupen med sensordata og maskinlæring. Titan.uio.no. Full text in Research Archive
• Rindal, Ole Marius Hoel; Vrålstad, Anders Emil; Bjåstad, Tore Grüner; Sørnes, Anders Rasmus & Måsøy, Svein-Erik (2023). Improving Image Quality Degradation due to Blocked Array in Cardiac Ultrasound Imaging. Full text in Research Archive Show summary

  The footprint of a cardiac ultrasound (US) probe is designed to fit the size of the intercostal space between the ribs to avoid ribs blocking the US energy. Some patients will have an intercostal space narrower than the footprint, making array blockage inevitable. In some cases, the clinician may be forced to place the probe in a position subject to rib blockage to achieve the desired anatomical view. Firstly, we demonstrate that such rib blockages reduce the image quality and lead to depth-varying geometrical distortions, potentially tilting structures and reducing resolution. Secondly, we demonstrate that compensating for the blocked array in the retrospective transmit beamforming (RTB) corrects most of the unwanted effects and improves image quality.

• Rindal, Ole Marius Hoel (2023). Sonair introducing ADAR: 3D Acoustic Detection And Ranging in air. Full text in Research Archive
• Måsøy, Svein-Erik; Dénarié, Bastien Emmanuel; Sørnes, Anders; Holte, Espen; Grenne, Bjørnar Leangen & Espeland, Torvald [Show all 10 contributors for this article] (2023). Aberration correction in 3D echocardiography. Full text in Research Archive Show summary

  3D imaging is increasingly used in echocardiography. However, aberrations caused by sound speed variations in the body wall, degrades image quality, thereby compromising accurate diagnosis. Research into methods for compensating aberrations in pulse-echo imaging, referred to as aberration correction (AC), has been ongoing for more than 40 years. An AC algorithm has been developed and implemented to run real-time on a clinical ultrasound system for both 2D and 3D imaging. The algorithm estimates and corrects arrival time errors across all subapertures in a matrix array probe. A clinical trial has been carried out with the aim to evaluate the efficacy of our AC algorithm in improving image quality for 3D transthoracic echocardiography.

• Rindal, Ole Marius Hoel; Gløersen, Øyvind; Kvåle, Kaja Frøysaa; Tjønnås, Johannes & Liverud, Anders Erik (2023). Visualizing and Annotating Video and Microsensor Data from Cross-Country Skiing using the Autoactive Research Environment. Full text in Research Archive
• Rindal, Ole Marius Hoel; Gløersen, Øyvind & Tjønnås, Johannes (2023). Analyzing Micro Parameters of Diagonal Stride in Cross-country Skiing using Microsensors on Snow. Full text in Research Archive
• Gløersen, Øyvind; Rindal, Ole Marius Hoel & Tjønnås, Johannes (2023). Digital Skiguru – Quantifying “Ski Feeling” using Microsensors. Full text in Research Archive
• Näsholm, Sven Peter; Arnestad, Håvard; Austeng, Andreas & Rindal, Ole Marius Hoel (2023). Calculating the generalized contrast-to-noise ratio using kernel density estimation. Full text in Research Archive Show summary

  The histogram-based generalized contrast-to-noise ratio (gCNR) evaluates how well image regions with different intensity can be distinguished. The gCNR is defined as ‘one minus the overlap region’ of normalized histograms from two regions. Histogram-based gCNR depends on user parameters like bin size and bin offset, but there are also approaches to robustify the histogram calculation. Kernel density estimation (KDE) is a well-established alternative to histograms to estimate probability density functions (PDFs), and is generally considered to be more robust. We suggest replacing histograms with KDE in gCNR calculations.

• Kvalevåg, Magnus; Vrålstad, Anders Emil; Rindal, Ole Marius Hoel; Bjåstad, Tore Grüner; Dénarié, Bastien & Kristoffersen, Kjell [Show all 8 contributors for this article] (2023). vbeam: A Fast and Differentiable Beamformer for Optimizing Ultrasound Imaging. Full text in Research Archive
• Vrålstad, Anders Emil; Kvalevåg, Magnus; Rindal, Ole Marius Hoel & Måsøy, Svein-Erik (2023). Universal REFoCUS with Spatial Weighting. Full text in Research Archive Show summary

  The REFoCUS algorithm decomposes any arbitrary transmit wave into its Huygens-Fresnel components allowing Synthetic Transmit Aperture (STA) beamforming. The STA dataset is found by advancing the backscattered channel data by the applied transmit (Tx) delay and summing across Tx events. This simple advance-and-sum, also called adjoint inversion in frequency domain, has shown image quality similar to true STA beamforming for phased array sequences, but showed artifacts for sequences with walking aperture [1]. The artifacts were suppressed by regularizing the inversion at the cost of SNR [2]. Our time-domain implementation with pixel dependent apodization aims to generalize the REFoCUS method for all scan setups without introducing artifacts. The apodization is based on the directivity limitations of transducer elements, and it also works for 2D arrays using Sub-Aperture (SAP) technology.

• Måsøy, Svein-Erik; Dénarié, Bastien; Sørnes, Anders; Holte, Espen; Grenne, Bjørnar & Espeland, Torvald [Show all 10 contributors for this article] (2022). Aberration Correction in the Echo Lab - A Clinical Pilot. Full text in Research Archive
• Gereb, Gabor; Hansen, Roy Edgar; Lønmo, Tor Inge Birkenes; Näsholm, Sven Peter; Austeng, Andreas & Rindal, Ole Marius Hoel (2022). Improving Sonar Surveying of Subsea Cables and Pipelines with Adaptive Beamforming. Full text in Research Archive Show summary

  Background, Motivation and Objective Safe and efficient transportation of offshore energy requires well-maintained underwater infrastructure, no matter if the energy source is fossil, wind, sun, or wave. Subsea cables and pipelines can be efficiently surveyed using sonar systems mounted on surface or underwater vehicles. Adaptive array signal processing methods are increasingly explored to improve image quality and detection or estimation accuracy in specific survey scenarios. However, adaptive methods can be sensitive to the context they are used in. Therefore, choosing the right beamforming approach from the available candidates requires extensive testing in various scenarios, which is often not feasible out at sea. Statement of Contribution/Methods Realistic simulation of complex underwater scenarios has been previously demonstrated using the Field II Ultrasound Simulation Program in combination with the open access package UltraSound ToolBox (USTB). We use Field II to create digital twins of water column images from pipeline surveys, and then modify parameters such as the layout, depth, and SNR to extend the scope of testing. We add multiple realizations of random noise to the signal and then use USTB to beamform the data with different techniques. On the beamformed data we perform estimation of multiple parameters such as the position and size of the pipe and the seabed depth around it. Finally, using the known ground truth of the model, we compare the bias and variance of the estimations made using images reconstructed by different beamformers. Results/Discussion Following on the results of previous studies demonstrating the benefits of adaptive beamforming in sonar bathymetry, we present a benchmark study of adaptive beamforming techniques such as Low Complexity Adaptive (LCA) and Capon Minimum Variance (MVDR). Comparison with the Coherence Factor (CF) method is made as well. We use Delay-and-Sum (DAS) as a reference with various apodizations. We provide quantitative performance assessment based on the statistical distribution of the estimations with reference to the ground truth in different scenarios.

• Gereb, Gabor; Hansen, Roy Edgar; Austeng, Andreas; Lønmo, Tor Inge Birkenes; Näsholm, Sven Peter & Rindal, Ole Marius Hoel (2022). Ultrasound Beamformer Benchmarking Pipeline. Full text in Research Archive
• Rindal, Ole Marius Hoel; Näsholm, Sven Peter; Hansen, Roy Edgar & Austeng, Andreas (2022). Image Enhancement Using Capon Minimum Variance Adaptive Beamforming in Synthetic Aperture Sonar. Full text in Research Archive
• Rindal, Ole Marius Hoel; Näsholm, Sven Peter; Hansen, Roy Edgar & Austeng, Andreas (2022). Compensating Dynamic Range Alterations from Adaptive Beamforming using Histogram Matching. Full text in Research Archive
• Austeng, Andreas; Näsholm, Sven Peter; Hansen, Roy Edgar & Rindal, Ole Marius Hoel (2022). Spatial Aperture Coherence with Synthetic Transmit Focusing in SAS. Full text in Research Archive
• Vrålstad, Anders Emil; Rindal, Ole Marius Hoel; Bjåstad, Tore Grüner & Måsøy, Svein-Erik (2022). Sound Speed Correction for Virtual Source Retrospective Transmit Beamforming. Full text in Research Archive
• Austeng, Andreas; Arnestad, Håvard; Bjåstad, Tore Grüner; Måsøy, Svein-Erik & Rindal, Ole Marius Hoel (2022). Issues with Histogram Matching for Fair Evaluation of Image Quality Metrics. Full text in Research Archive
• Rindal, Ole Marius Hoel; Vrålstad, Anders Emil; Bjåstad, Tore Grüner; Austeng, Andreas & Måsøy, Svein-Erik (2022). Coherence from REFoCUS compared to Retrospective Transmit Beamforming. Full text in Research Archive
• Arnestad, Håvard; Austeng, Andreas; Näsholm, Sven Peter & Rindal, Ole Marius Hoel (2022). The Effect of Retrospective Transmit Focusing on Minimum Variance Beamforming. Full text in Research Archive
• Rindal, Ole Marius Hoel; Bjåstad, Tore Grüner; Espeland, Torvald; Berg, Erik Andreas Rye & Måsøy, Svein-Erik (2022). Global Image Coherence (GIC) – an in-vivo Image Quality Metric. Full text in Research Archive
• Rindal, Ole Marius Hoel (2022). Transition of advanced techniques from medical ultrasound to sonar imaging using the UltraSound ToolBox. Full text in Research Archive
• Eitzen, Ingrid; Heimark, Sondre; Seeberg, Trine Margrethe; Bøtker-Rasmussen, Kasper; Mamen, Asgeir & Waldum-Grevbo, Bård [Show all 9 contributors for this article] (2022). Well-trained individuals have an exaggerated blood pressure response during exercise testing. Full text in Research Archive
• Heimark, Sondre; Rindal, Ole Marius Hoel; Seeberg, Trine Margrethe; Stepanov, Alexey; Boysen, Elin Sundby & Bøtker-Rasmussen, Kasper [Show all 11 contributors for this article] (2021). Pulse Arrival Time Can Track Changes in Systolic Blood Pressure. Full text in Research Archive
• Rindal, Ole Marius Hoel (2021). Open source processing of ultrasound images with the USTB. CIUS blogg: Innovations in Ultrasound - From the Centre for Innovative Ultrasound Solutions. Full text in Research Archive
• Heimark, Sondre; Rindal, Ole Marius Hoel; Seeberg, Trine Margrethe; Stepanov, Alexey; Boysen, Elin Sundby & Bøtker-Rasmussen, Kasper [Show all 11 contributors for this article] (2021). PULSE ARRIVAL TIME CAN TRACK CHANGES IN SYSTOLIC BLOOD PRESSURE. Journal of Hypertension. ISSN 0263-6352. doi: 10.1097/01.hjh.0000745808.43316.c3. Full text in Research Archive
• Rindal, Ole Marius Hoel (2021). The UltraSound Toolbox : Open source processing of ultrasound images with the UltraSound ToolBox. CIUS Annual Report 2020. Full text in Research Archive
• Seeberg, Trine Margrethe; Kocbach, Jan; Noordhof, Dionne; Danielsen, Jørgen; Haugnes, Pål & Skovereng, Knut [Show all 10 contributors for this article] (2020). COMPARISON OF SUB-TECHNIQUE UTILIZATION, KINEMATICS AND PHYSIOLOGICAL RESPONSES BETWEEN LOW- AND HIGH-INTENSITY ROLLER SKI SKATING. Full text in Research Archive
• Berg-Hansen, Pål; Moen, Stine Marit; Jahren, Silje Ekroll; Klyve, Thomas; Meyer, Fredrik & Strisland, Frode [Show all 10 contributors for this article] (2020). Use of sensors in MS rehabilitation - a pilot study. Full text in Research Archive
• Rindal, Ole Marius Hoel (2020). Software Beamforming in Medical Ultrasound Imaging – A Blessing and a Curse. Full text in Research Archive
• VIANELLO, Isabella; Mamen, Asgeir; Heimark, Sondre; Sandbakk, Øyvind; Samani, Afshin & Rindal, Ole Marius Hoel [Show all 7 contributors for this article] (2020). BLOOD PRESSURE VARIATION AS INDICATOR OF AEROBIC PERFORMANCE. Full text in Research Archive
• Danielsen, Dag Inge & Rindal, Ole Marius Hoel (2020). Ultralyd-forbedringer gir også utfordringer. Titan.uio.no. Full text in Research Archive
• Tjønnås, Johannes; Seeberg, Trine Margrethe; Rindal, Ole Marius Hoel; Haugnes, Pål & Sandbakk, Øyvind (2019). Basic Motions and Technique Identification in Classical Cross-Country Skiing. Full text in Research Archive
• Benjaminsen, Christina; Seeberg, Trine Margrethe; Sandbakk, Øyvind; Tjønnås, Johannes & Rindal, Ole Marius Hoel (2018). Ski-eliten kvesser teknikken med sensorer på kroppen. Gemini. ISSN 0802-085X. Full text in Research Archive Show summary

  Norsk langrennssport går vitenskapelig til verks for å analysere hvordan våre gullhåp utnytter kreftene sine når de går på ski. Sensorbasert forskning skal gi løperne verdifulle treningstips og hjelpe dem med å finne det helt perfekte skipar.

• Seeberg, Trine Margrethe; Sandbakk, Øyvind; Tjønnås, Johannes; Rindal, Ole Marius Hoel & Benjaminsen, Christina (2018). Researchers are helping elite skiers to hone their performance. [Internet]. Gemini. Full text in Research Archive Show summary

  Norwegian cross-country skiing is applying science to analyse how its elite athletes exploit their strengths during training and competition. The aims of this sensor-based research are to give skiers valuable advice about training and help them find the perfect pair of skis.

• Seeberg, Trine Margrethe; Sandbakk, Øyvind; Tjønnås, Johannes; Rindal, Ole Marius Hoel & Kokkegård, Hanne (2018). Norges skiløbere kører suverænt på avanceret sensor-teknologi. Full text in Research Archive Show summary

  Ny teknologi kan gøre brugen af video overflødig, fordi målingerne er så præcise. Og sensorerne virker ude på løjperne - ikke kun i laboratoriet.

• Rindal, Ole Marius Hoel; Rodriguez-Molares, Alfonso & Austeng, Andreas (2018). A simple, artifact-free, virtual source model. Full text in Research Archive Show summary

  Retrospective beamforming is a synthetic technique that, by combination of several converging waves, reduces the number of transmission events without reduction of image quality. However, due to a discontinuity in the conventional spherical virtual source model, an artifact occurs at the focal depth where the virtual sources are located. We correct the artifact by modifying the spherical model by assuming plane wave propagation in a region around the focal depth. This hybrid model is simpler and lighter than the current accepted solution.

• Prieur, Fabrice Jean Gabriel; Rindal, Ole Marius Hoel; Holm, Sverre & Austeng, Andreas (2017). Influence of the Delay-Multiply-And-Sum beamformer on the ultrasound image amplitude. Full text in Research Archive
• Rindal, Ole Marius Hoel & Bell, Muyinatu A. Lediju (2017). Short Lag Spatial Coherence beamforming in ultrasound imaging. Full text in Research Archive
• Rindal, Ole Marius Hoel; Seeberg, Trine Margrethe; Tjønnås, Johannes; Haugnes, Pål; Dalgard, Steffen Harald & Sandbakk, Øyvind (2016). Analysis of sub-techniques in classical cross-country skiing by employing machine learning algorithms on micro sensor data. Full text in Research Archive
• Rindal, Ole Marius Hoel; Austeng, Andreas & Solberg, Anne H Schistad (2019). Software Beamforming in Medical Ultrasound Imaging - a blessing and a curse. Universitetet i Oslo. Full text in Research Archive Show summary

  Medical ultrasound (US) imaging is a non-invasive imaging modality. Smaller and cheaper US systems make US imaging available to more people, leading to a democratization of medical US imaging. The improvements of general processing hardware allow the reconstruction of US images to be done in software. These implementations are known as software beamforming and provide access to the US data earlier in the processing chain. Adaptive beamforming exploits the early access to the full US data with algorithms adapting the processing to the data. Adaptive beamforming claims improved image quality. The improved image will potentially result in an improved diagnosis. Adaptive beamformers have seen enormous popularity in the research community with exponential growth in the number of papers published. However, the complexity of the algorithms makes them hard to re-implement, making a thorough comparison of the algorithms difficult. The UltraSound ToolBox (USTB https://www.USTB.no) is an open source processing framework facilitating the comparison of imaging techniques and the dissemination of research results. The USTB, including the implementation of several state-of-the-art adaptive beamformers, has partly been developed in this thesis and used to produce most of the results presented. The results show that some of the contrast improvements reported in the literature turn out to be from secondary effects of adaptive processing. More specifically, we show that many state-of-the-art algorithms alter the dynamic range. These dynamic range alterations are invalidating the conventional contrast metrics. Said differently; many adaptive algorithms are so flexible that they instead of improving the image quality are merely optimizing the metrics used to evaluate the image quality. We suggest a dynamic range test, compromising data, and code, to assess whether an algorithm alters the dynamic range. A thorough review of the contrast metrics used in US imaging shows there is no consensus on the metrics used in the research literature. Therefore, our introduction of the generalized contrast to noise ratio (GCNR) is essential since this is a contrast metric immune to dynamic range alterations. The GCNR is a remedy for the curse of the metric breaking abilities of software beamforming. Software beamforming also has its blessings. The flexible implementations made possible by software beamforming does lead to improved image quality. The improved resolution of the minimum variance adaptive beamformer does lead to enhanced visualization of the interventricular septum in the human heart. The ability to do beamforming in software allows the implementation of the full reconstruction chain from raw data to the final rendered images on an iPhone. As well as the results presented in the published papers, this thesis does a thorough review of the software beamforming processing chain as implemented in the USTB.

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