| 1. |
- Andersson, Carl, 1992, et al.
(författare)
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Acoustic Levitation from Superposition of Spherical Harmonics Expansions of Elementary Sources: Analysis of Dependency on Wavenumber and Order
- 2019
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Ingår i: IEEE International Ultrasonics Symposium, IUS. - 1948-5719 .- 1948-5727. ; 2019-October, s. 920-923
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Konferensbidrag (refereegranskat)abstract
- Acoustic levitation of spherical objects in mid-air is a technique that is gaining traction in various human computer interaction applications such as data visualization or interactive displays. The commonly used hardware platforms are phased ultrasonic transducer arrays, used to levitate small spheres of polystyrene. Previous works have used angular spectrum decomposition of the incident sound field to derive the radiation force exerted on an arbitrary sphere. We show an alternate formulation more suited to sound fields from transducer arrays, based on direct spherical harmonics expansions of the sound fields from the individual transducer elements in the array. Finally we investigate how the truncation order of the spherical harmonics expansion influence the calculated force, for varying sphere sizes.
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| 2. |
- Andersson, Carl, 1992, et al.
(författare)
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Creation of Large Quiet Zones in the Presence of Acoustical Levitation Traps
- 2021
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Ingår i: IEEE International Ultrasonics Symposium, IUS. - 1948-5719 .- 1948-5727.
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Konferensbidrag (refereegranskat)abstract
- We propose a method to generate an acoustical levitation trap at the same time as suppressing the sound in a multi-wavelength region of space. The method uses a spherical basis expansion of the sound field in the quiet zone, calculated by translating individual source expansions of elements in a transducer array. We show that it is possible to control the size of the quiet zone with the truncation order of the expansion, and explain the trade-off between field suppression in the quiet zone and stiffness loss of the levitation trap. Measurements of a generated sound field show the existence of a region of lower sound pressure. Simulations demonstrate a contrast up to 50 dB and sizes up to 60 mm for a 256 element array.
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| 3. |
- Andersson, Carl, 1992, et al.
(författare)
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Reducing Spiraling in Transducer Array Based Acoustic Levitation
- 2020
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Ingår i: IEEE International Ultrasonics Symposium, IUS. - 1948-5719 .- 1948-5727. ; 2020-September
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Konferensbidrag (refereegranskat)abstract
- Ultrasonic transducer array based levitation can be applied for non-contact manipulation of small objects. The technique can sometimes suffer from instability issues in the form of uncontrolled oscillatory movement that builds up until the levitating object moves out of the levitation trap region and drops. We propose an additional condition to the established description of the levitation trap, and describe how the condition is used in numerical optimization of a cost function to obtain the phases and amplitudes of the elements in the array. The proposed condition successfully reduces the rotational components in the force field responsible for the uncontrolled increase in kinetic energy of the levitating object.
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| 4. |
- Erlöv, Tobias, et al.
(författare)
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Improved Tracking Performance in High Frame Rate Imaging Using Iterative Phase Tracking
- 2019
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Ingår i: 2019 IEEE International Ultrasonics Symposium (IUS). - 1948-5719 .- 1948-5727. - 9781728145969 - 9781728145976 ; 2019, s. 2158-2161
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Konferensbidrag (refereegranskat)abstract
- High frame rate ultrasound imaging is necessary to enable tracking of rapid dynamic events such as the carotid pulse wave velocity. Several studies have shown that it is feasible to use motion tracking methods that are applied on standard ultrasound frame rates also on very high frame rates. However, few studies have addressed the issue of accumulated tracking errors over vast numbers of frames during Lagrangian tracking. These could stem from e.g. limited signal-to-noise ratio often resulting from the use of plane wave imaging. One recently proposed solution was to combine motion tracking with an iterative tracking scheme. The purpose of this study has been to evaluate if the iterative tracking scheme could be exploited to increase the robustness of a phase-based tracking method in high frame rate plane wave imaging to track the carotid artery wall diameter. The results showed the iterative tracking scheme to give increased robustness with significantly (p<0.0003) less differences in measured lumen diameters between adjacent lines. Thus, this study enforces the suggestion to use the iterative tracking scheme during Lagrangian tracking in high frame rate imaging.
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| 5. |
- Evertsson, Maria, et al.
(författare)
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Extending imaging range in magnetomotive ultrasound with tailored magnetic nanoparticles
- 2020
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Ingår i: IUS 2020 - International Ultrasonics Symposium, Proceedings. - 1948-5727 .- 1948-5719. - 9781728154480 ; 2020-September
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Konferensbidrag (refereegranskat)abstract
- In magnetomotive ultrasound (MMUS), magnetic nanoparticles (MNPs) are used as a contrast agent. A time-varying magnetic field displaces the MNPs which in turn move their closest surrounding - a motion detected with ultrasound. A limiting factor for MMUS is the magnetic force magnitude decay with depth, which restricts the imaging area. Several attempts to extend the imaging depth have been suggested, such as magnetic field generator configuration or choice of MNP core materials. In this study we present a new approach by modifying the design of the contrast agent using a commercially available nanoparticle with a nano-flower shaped iron oxide core (synomag®-D, micromod, Germany). In order to evaluate the performance of this particle, a conventional particle (perimag®, micromod, Germany), was used for comparison. Using an electromagnet with a cone shaped iron core as a field generator, the induced MMUS displacement of the two MNP varieties where analyzed when altering the magnetic field strength and magnetic field frequency. Further, by using a more clinically relevant magnetic field setup, the depth where the synomag MNPs could produce significant MMUS displacement, was evaluated. The synomag MNPs produced a 1.8 times larger displacement than the perimag MNPs. At 52mm, MMUS displacement was still detectable using synomag MNPs. This indicates that the particle design plays an important role in MMUS imaging. Moreover, this study also confirms that MMUS imaging at clinically relevant depths is possible.
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| 6. |
- Evertsson, Maria, et al.
(författare)
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Revolving permanent magnet causes rotating particle motion that makes new detection schemes possible in magnetomotive ultrasound
- 2019
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Ingår i: 2019 IEEE International Ultrasonics Symposium, IUS 2019. - 1948-5727 .- 1948-5719. - 9781728145976 - 9781728145969 ; 2019-October, s. 2373-2375
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Konferensbidrag (refereegranskat)abstract
- Magnetomotive ultrasound, MMUS, can reveal the presence of a magnetic contrast agent by applying an external magnetic field. If the interaction between the agent and the field is strong enough, a movement that can be detected by ultrasound is induced in the surrounding tissue, thereby inferring the contrast agent distribution. Electromagnets have been used to generate the necessary magnetic field, but due to their size, weight, and propensity to heat up, they are impractical to work with. Furthermore, the resulting magnetic force is directed mainly along the symmetry axis of such magnets, and thus the resulting movement is primarily a one-dimensional oscillation. We suggest the use of a rotating permanent magnet that generates a two-dimensional particle motion, and that this makes new detection schemes for MMUS possible. A prototype probe, containing a rotating neodymium magnet, was used to move a metallic sphere embedded in tissue-mimicking material. Cine loops recorded any in-plane movement with the magnetic probe placed in two different positions. A two-dimensional movement was demonstrated, using both our previously developed MMUS algorithm as well as a phase-based motion tracking algorithm. The conventional 1D MMUS processing detected the axial component in both magnetic probe positions, whereas the two-dimensional motion tracking algorithm estimated a rotational motion from the same measurements. The added dimension of motion could engender possibilities to more precise signal processing and thus improve robustness of magnetomotive motion detection. Moreover, the incorporation of a permanent magnet makes for a more practical device, as compared to using electromagnets.
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| 7. |
- Khodaverdi, Azin, et al.
(författare)
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The feasibility of using center frequency spectra in photoacoustic imaging for tissue characterization
- 2023
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Ingår i: IUS 2023 - IEEE International Ultrasonics Symposium, Proceedings. - 1948-5727 .- 1948-5719. - 9798350346459
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Konferensbidrag (refereegranskat)abstract
- In photoacoustic imaging, the amplitude of the photoacoustic signal is used for mapping the spatial distribution of a chromophore in the body and few studies have focused on the potential of using frequency content of the photoacoustic data. This study investigates the feasibility of using the photoacoustic center frequency spectrum in differentiating microspheres of various sizes and colors in phantoms. The microspheres with colors of green and blue, and the same size showed different center frequency spectrum shapes while keeping the offset (mean frequency) approximately the same. In addition, smaller microspheres showed higher center frequency offset, while larger microspheres showed smaller offset, suggesting the potential to use the center frequency spectrum for differentiating chromophores of various optical properties in the body.
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| 8. |
- Kranemann, Tim C., et al.
(författare)
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The magnetic force generation in magnetomotive ultrasound imaging
- 2020
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Ingår i: IUS 2020 - International Ultrasonics Symposium, Proceedings. - 1948-5727 .- 1948-5719. - 9781728154480 ; 2020-September
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Konferensbidrag (refereegranskat)abstract
- In magnetomotive ultrasound imaging, the tissue displacement due to a magnetic force on embedded magnetic nanoparticles is measured. It was previously shown that the nanoparticle contrast agent exhibits a non-linear magnetization characteristic, which is also reflected in the magnetomotive force. However, this non-linearity was rarely taken into account for the application. Here, the implications of the assumption of a linear and a nonlinear static magnetization characteristic were contrasted by analytic calculations. The calculations were restricted to the typical scenario of an excitation with a magnetic field generator fed with a single current consisting of only a sinusoidal and a DC component. Due to this waveform of the excitation current, the description of the force was carried out with the coefficients of a Fourier series. It was evident that nonlinear saturation of the particles is the preferred operating point for the application, as forces relative to particle concentration are maximized. Further, the excitation current can be chosen with or without a DC component to excite a force of approximately the same magnitude at the single or double frequency of the excitation current. The calculations thus contribute to the profound understanding of the magnetomotive force. The calculations can further be used to match magnetic fields and nanoparticles. Future work is expected to include the dynamic magnetization properties of the contrast agent.
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| 9. |
- Meirza, Benjamin, et al.
(författare)
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Construction of an ultrasound phantom with micrometer-sized wall-less vessels
- 2019
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Ingår i: 2019 IEEE International Ultrasonics Symposium, IUS 2019. - 1948-5719 .- 1948-5727. - 9781728145976 - 9781728145969 ; 2019-October, s. 1209-1211
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Konferensbidrag (refereegranskat)abstract
- The development of new ultrasound imaging technologies that aim to resolve objects smaller than the conventional ultrasounds diffraction limit calls for new types of phantoms to evaluate these technologies. When it comes to vascular flow phantoms, this becomes challenging due to the difficulty of manufacturing phantoms with vessels smaller than 1 mm in diameter. Here we describe a novel manufacturing method to construct phantoms with micro-vessels with a size down to 88 μm using oil-based clear ballistic gel (Clear Ballistics, Greenville, SC, USA) as surrounding material. Clear ballistic gel is a long-term stable tissue-mimicking material with speed of sound around 1470 m/s.
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| 10. |
- Petäjä, Artturi, et al.
(författare)
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Ultrasonic measurement of the longitudinal motion of the arterial wall - a novel parameter for improved analysis of the motion at late systole
- 2023
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Ingår i: IUS 2023 - IEEE International Ultrasonics Symposium, Proceedings. - 1948-5727 .- 1948-5719. - 9798350346459
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Konferensbidrag (refereegranskat)abstract
- Increasing interest and research is directed towards longitudinal arterial wall motion (LMov) identified by ultrasonography, most often of the common carotid artery (CCA). LMov comprises of both antegrade and retrograde motion phases that create motion patterns specific to an individual. Preliminary data from several independent groups strongly suggest correlation between LMov parameters and cardiovascular health status. One LMov phase of special interest is the main retrograde phase (B) in systole which encompasses a smaller antegrade motion (X) in late systole. This phase has been challenging to quantify given the small magnitude of X. Here we propose a novel parameter ratio for improved analysis of X and thus of the longitudinal motion in late systole.
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