Resolving Ultrasound Contrast Microbubbles Using Minimum Variance Beamforming

Diamantis, Konstantinos; Anderson, Thomas; Butler, Mairéad; Villagomez-Hoyos, Carlos A.; Jensen, Jørgen Arendt; Sboros, Vassilis

doi:10.1109/tmi.2018.2859262

Cited by 34 publications

(19 citation statements)

References 38 publications

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“…There exist multiple definitions of resolution ranging from the −3dB Rayleigh resolution criteria (Rayleigh 1879), to the Sparrow resolution defined as where the saddle point between the two peaks first develops -thus being a measure on separability. A brief review shows that many authors tend to use the FWHM (-6 dB) (Liebgott et al 2016;Matrone, Savoia, and Magenes 2015), while others use some measure of separability (Camacho, Parrilla, and Fritsch 2009;Jensen and Austeng 2014) while some use both (Diamantis et al 2019). We will have a brief look at both.…”

Section: Resolutionmentioning

confidence: 99%

The Generalized Contrast-to-Noise Ratio: A Formal Definition for Lesion Detectability

Rodríguez-Molares

Rindal

D'hooge

et al. 2020

IEEE Trans. Ultrason., Ferroelect., Freq. Contr.

312

122

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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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Section: Resolutionmentioning

confidence: 99%

The Generalized Contrast-to-Noise Ratio: A Formal Definition for Lesion Detectability

Rodríguez-Molares

Rindal

D'hooge

et al. 2020

IEEE Trans. Ultrason., Ferroelect., Freq. Contr.

312

122

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“…This process can also be seen as an approximate estimation of the PSF. Note that it is accepted that the axial resolution is at best half the pulse length, 67 which in our case is 1 λ (514 μm), whereas the lateral resolution varies across the image depending on the beam width 67,68 and can be up to a few λ using the delay-and-sum beamfomers, 69 which are used here. The histogram of the MB echo size distribution from the sheep ovary is displayed in Figure 2.…”

Section: Methodsmentioning

confidence: 99%

“…Note that once 2 particles approach closer than a few wavelengths, they are likely to become larger in size before appearing as a merged particle in the image. 69…”

Section: Methodsmentioning

confidence: 99%

Super-Resolution Contrast-Enhanced Ultrasound Methodology for the Identification of In Vivo Vascular Dynamics in 2D

Kanoulas¹,

Butler²,

Rowley

et al. 2019

Invest Radiol

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Objectives The aim of this study was to provide an ultrasound-based super-resolution methodology that can be implemented using clinical 2-dimensional ultrasound equipment and standard contrast-enhanced ultrasound modes. In addition, the aim is to achieve this for true-to-life patient imaging conditions, including realistic examination times of a few minutes and adequate image penetration depths that can be used to scan entire organs without sacrificing current super-resolution ultrasound imaging performance. Methods Standard contrast-enhanced ultrasound was used along with bolus or infusion injections of SonoVue (Bracco, Geneva, Switzerland) microbubble (MB) suspensions. An image analysis methodology, translated from light microscopy algorithms, was developed for use with ultrasound contrast imaging video data. New features that are tailored for ultrasound contrast image data were developed for MB detection and segmentation, so that the algorithm can deal with single and overlapping MBs. The method was tested initially on synthetic data, then with a simple microvessel phantom, and then with in vivo ultrasound contrast video loops from sheep ovaries. Tracks detailing the vascular structure and corresponding velocity map of the sheep ovary were reconstructed. Images acquired from light microscopy, optical projection tomography, and optical coherence tomography were compared with the vasculature network that was revealed in the ultrasound contrast data. The final method was applied to clinical prostate data as a proof of principle. Results Features of the ovary identified in optical modalities mentioned previously were also identified in the ultrasound super-resolution density maps. Follicular areas, follicle wall, vessel diameter, and tissue dimensions were very similar. An approximately 8.5-fold resolution gain was demonstrated in vessel width, as vessels of width down to 60 μm were detected and verified (λ = 514 μm). Best agreement was found between ultrasound measurements and optical coherence tomography with 10% difference in the measured vessel widths, whereas ex vivo microscopy measurements were significantly lower by 43% on average. The results were mostly achieved using video loops of under 2-minute duration that included respiratory motion. A feasibility study on a human prostate showed good agreement between density and velocity ultrasound maps with the histological evaluation of the location of a tumor. Conclusions The feasibility of a 2-dimensional contrast-enhanced ultrasound-based super-resolution method was demonstrated using in vitro, synthetic and in vivo animal data. The method reduces the examination times to a few minutes using state-of-the-art ultrasound equipment and can provide super-resolution maps for an entire prostate with similar resolution to that achieved in other studies.

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“…We hypothesise that some adaptive beamforming algorithms may decrease the FWHM without increasing target separability. Some authors have included an analysis of separability when evaluating beamforming algorithms [1] [2] [3]. However, the consequences of using FWHM as a measure of resolution for adaptive beamformers could lead to the wrong conclusions.…”

Section: Introductionmentioning

confidence: 99%

Resolution Measured as Separability Compared to Full Width Half Maximum for Adaptive Beamformers

Rindal

Austeng

Rodríguez-Molares

2020

2020 IEEE International Ultrasonics Symposium (IUS)

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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.

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Resolving Ultrasound Contrast Microbubbles Using Minimum Variance Beamforming

Cited by 34 publications

References 38 publications

The Generalized Contrast-to-Noise Ratio: A Formal Definition for Lesion Detectability

The Generalized Contrast-to-Noise Ratio: A Formal Definition for Lesion Detectability

Super-Resolution Contrast-Enhanced Ultrasound Methodology for the Identification of In Vivo Vascular Dynamics in 2D

Resolution Measured as Separability Compared to Full Width Half Maximum for Adaptive Beamformers

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