| 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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| 11. |
- Plessky, V., et al.
(författare)
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Bulk Acoustic Wave Transformer employing Periodically Polled array of Piezoelectric Rods
- 2016
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Ingår i: IEEE International Ultrasonics Symposium, IUS. - 1948-5719 .- 1948-5727. - 9781467398978 ; 2016-November, s. Art no 7728583-
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Konferensbidrag (refereegranskat)abstract
- Multilayer bulk acoustic wave transformer employing a periodical array of piezoelectric rods with alternating polarization is experimentally demonstrated for the first time. Voltage transformation coefficient in excess of 6 was measured at a frequency of 150kHz, providing thus a solid experimental verification of the recently proposed principle of operation. Finite element analysis is used to reveal the underlying device physics.
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| 12. |
- Sjostrand, Sandra, et al.
(författare)
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Contrast-enhanced magnetomotive ultrasound imaging (CE-MMUS) for colorectal cancer staging : Assessment of sensitivity and resolution to detect alterations in tissue stiffness
- 2019
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Ingår i: 2019 IEEE International Ultrasonics Symposium, IUS 2019. - 1948-5719 .- 1948-5727. - 9781728145976 - 9781728145969 ; 2019-October, s. 1077-1080
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Konferensbidrag (refereegranskat)abstract
- A key challenge in the treatment of colorectal cancer is identification of the sentinel draining lymph node. Magnetomotive ultrasound, MMUS, has identified lymph nodes in rat models: superparamagnetic iron oxide nanoparticles (SPIONs) accumulated in the lymph are forced to oscillate by an external magnetic field; the resulting axial displacement is recovered allowing structure delineation with potential to indicate alterations in tissue stiffness, but it is limited by small vibration amplitudes. We propose CE-MMUS using SPION loaded microbubbles (SPION-MBs) to enhance sensitivity, reduce toxicity, and offer additional diagnostic or perfusion information. Laser doppler vibrometry measurements was performed on SPION containing tissue mimicking material during magnetic excitation. These measurements show a vibration amplitude of 279 ± 113 μm in a material with Young's modulus of 24.3 ± 2.8 kPa, while the displacements were substantially larger, 426 ± 9 μm, in the softer material, with a Young's modulus of 9.6 ± 0.8 kPa. Magnetic field measurement data was used to calibrate finite element modelling of both MMUS and CE-MMUS. SPION-MBs were shown to be capable of inducing larger tissue displacements under a given magnetic field than SPIONs alone, leading to axial displacements of up to 2.3x larger. A doubling in tissue stiffness (as may occur in cancer) reduces the vibration amplitude. Thus, there is potential for CE-MMUS to achieve improved stiffness sensitivity. Our aim is to define the potential contribution of CE-MMUS in colorectal cancer diagnosis and surgical guidance.
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| 13. |
- Yanchev, Ventsislav Mitkov, 1976, et al.
(författare)
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COMSOL modeling of SAW Resonators
- 2016
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Ingår i: IEEE International Ultrasonics Symposium, IUS. - 1948-5719 .- 1948-5727. - 9781467398978 ; 2016-November, s. Art no 7728546-
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Konferensbidrag (refereegranskat)abstract
- Here we demonstrate some generic 2D and 3D routines for SAW analysis employing the commercial COMSOL Multiphysics platform for finite element analysis (FEA). More specifically, we consider the analysis and optimization of high performance LSAW resonators for RF filters. The LSAW nature - being well studied and sufficiently complicated - is chosen as a suitable example for analysis and the results are compared to state-of-the-art knowledge. We found very good agreement between the results of the analytical scheme proposed here and the state-of-art findings. Finally, we demonstrate a TC-SAW piston-mode device simulated using SiO2/128 degrees Y-X LiNbO3.
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| 14. |
- Yanchev, Ventsislav Mitkov, 1976, et al.
(författare)
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Design and fabrication of efficient piezo-MEMS voltage transformers
- 2017
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Ingår i: IEEE International Ultrasonics Symposium, IUS. - 1948-5719 .- 1948-5727. ; 0
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Konferensbidrag (refereegranskat)abstract
- RF Voltage transformers operating in one of the ISM frequency bands have recently been demanded in emerging low-power applications, such as wake-up radios in wireless networks, remotely triggered switches, stand-by units in home electronics, etc. S0 Lamb wave resonant (LWR) transformers have been first proposed. Later, SAW transformers designed as 'degenerated' CRF have been proposed. Here we demonstrate a tetherless design of efficient LWR transformer and discuss the abilities to boost the voltage gain.
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| 15. |
- Yanchev, Ventsislav Mitkov, 1976, et al.
(författare)
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Parametric study of the resonant TC-SAW piston-mode configurations
- 2017
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Ingår i: IEEE International Ultrasonics Symposium, IUS. - 1948-5719 .- 1948-5727. - 9781538633830
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Konferensbidrag (refereegranskat)abstract
- Recent trends in RF filter design has brought the necessity to design SAW resonators with boosted performance. Most importantly, improvements in both the resonators' quality factors (Q) and temperature coefficient of frequency (TCF) are needed. TC-SAW concept employing 128 Y-cut LiNbO3 has attracted considerable practical interest in this view. Some excellent works from Qorvo have demonstrated the viability of this technology. Here we present some more detailed theoretical and experimental studies on the scaling rules regarding the design of TC-SAW resonators with suppressed spurious transverse mode responses.
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| 16. |
- Yantchev, Ventsislav, et al.
(författare)
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A Four Parameter Microfluidic Tandem SAW-IS Bio-Sensor
- 2019
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Ingår i: IEEE International Ultrasonics Symposium, IUS. - 1948-5719 .- 1948-5727. ; 2019-October, s. 193-196
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Konferensbidrag (refereegranskat)abstract
- Surface Acoustic Resonance (SAR) biosensing has recently been proposed as a highly compact and robust alternative to the conventional SAW delay-line based biosensing. The device can also be presented as a one-port high frequency alternative to the QCM, employing SAW resonance. It enables simple one-port measurements at low powers, while offering robust integration with microfluidics and implementation in integrated sensor arrays. Here we discuss the SAR approach as a key enabling and demonstrate its integration with the impedance spectroscopy (IS) concept in a single microfluidic device. The IS is integrated within a SAW reflector formed as interdigitated electrode (IDE) capacitor. A test fixture with SAW and IS ports is designed and fabricated. Four sensitive parameters are deduced from the tandem sensor readout and employed in a proof of principle study of liposome layers and their interaction with Ca2+ ions.
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| 17. |
- Andersson, Roger, et al.
(författare)
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B-field energy dependent phase lag dispersion in magnetomotive ultrasound imaging
- 2015
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Ingår i: 2015 IEEE International Ultrasonics Symposium (IUS). - 1948-5719.
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Konferensbidrag (refereegranskat)abstract
- Magnetomotive ultrasound imaging is an emerging technique where superparamagnetic iron oxide nanoparticles can be used as an ultrasound contrast agent. A time-varying external magnetic field acts to move tissue embedded particles, and ultrasound is used to detect the resulting tissue movement. In experimental phantom studies we have observed a phase lag dispersion in the magnetomotive response in respect to applied time-varying magnetic field (B-field). We hypothesize that this dispersion is triggered by the strength of the applied B-field in combination with concentration of embedded nanoparticles in the region. The cohort response of the nanoparticles aligns as the magnetic field gets more energetic. Moreover, the tightening of the phase response indicate an asymptotic tapering towards a phase limit.
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| 18. |
- Evertsson, Maria, et al.
(författare)
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In vivo magnetomotive ultrasound imaging of rat lymph nodes - a pilot study
- 2015
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Ingår i: 2015 IEEE International Ultrasonics Symposium (IUS). - 1948-5719.
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Konferensbidrag (refereegranskat)abstract
- The drive to gain a better understanding of how diseases arise and how to provide ever-earlier detection are some of the key factors for the development of molecular imaging. Compared to other imaging modalities ultrasound has not received the same attention for molecular imaging mainly due to its limited contrast resolution, together with contrast agents confined to the intravascular space. To overcome these issues, new nano-sized contrast agents and new ultrasound imaging techniques e.g. photo acoustic imaging, have been developed. Another such imaging technique under development is magnetomotive ultrasound imaging (MMUS). We have previously developed a frequency and phase tracking algorithm which is able to detect superparamagnetic iron oxide nanoparticles (SPIO NPs) using MMUS, where our suggested first clinical application is to detect sentinel lymph nodes (SLNs) in breast cancer surgery. Recently we have shown detection of SPIO laden rat SLNs in situ. Here we present the feasibility of in vivo detection of SLNs in rats. The algorithm clearly pinpoints the NP laden SLN, even in presence of significant artefactual tissue movement. The magnetomotive displacement increased when a higher voltage was applied on the coil creating the magnetic field (e.g. 56.6% increasing the voltage from 20V to 50V). An uneven concentration distribution of NPs in the SLN was found. The maximum magnetomotive displacement difference between two different cross sections in one SLN was 9.76 times. The study also showed that for a higher concentration of NPs a lower magnetic coil excitation voltage could be used in order to create a magnetomotive displacement of a certain magnitude. The result from this in vivo study shows that the method has potential for future clinical use.
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| 19. |
- Gudmundson, Erik, et al.
(författare)
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Overcoming the Nyquist Limit in Blood Flow Velocity Estimation
- 2012
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Ingår i: 2012 IEEE International Ultrasonics Symposium (IUS'12), Proceedings of. - 1948-5719. ; , s. 1615-1618
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Konferensbidrag (refereegranskat)abstract
- Spectral Doppler ultrasound imaging typically consists of a spectrogram, showing the velocity distribution of the blood, and a brightness (B-) mode image allowing the operator to navigate. It is desirable to have both high spectral and velocity resolution, so that details in the blood flow can be traced, as well as a high B-mode frame rate to allow for tracking of movements and to adjust the position of the transducer. The blood flow signal is often sampled 1) using alternating transmissions for blood flow estimation and for B-mode imaging, or, 2) by acquiring a full Doppler spectrum and then parts of the B-mode image. The former has the disadvantage that it halves the sampling rate, making it likely that aliasing will occur when imaging fast moving blood or deeply positioned vessels; the latter that gaps appears in the spectrogram, and that if the frame rate of the B-mode images is slow, it will be difficult to track movements. Adaptive methods have been implemented to circumvent such problems, but even so, to get an acceptable frame rate of the B- mode images, the number of transmissions for Doppler estimation will be limited, restricting the spectral resolution. Alternatively, one may use an irregularly spaced emission pattern, but existing work on the topic is limited and generally suffers from poor resolution and spurious velocity components resulting from the irregular sampling pattern. In this paper, we examine the BIAA algorithm, showing that this approach allows for an accurate velocity estimate even from irregularly sampled measurements. Using an irregular emission pattern, with half the emissions used to form the B-mode image, the remaining emissions are found to yield accurate velocity estimates without reducing the maximally measurable velocity and without the spurious velocity components. Moreover, we show that the approach will allow for the same maximal velocity without aliasing as if all emissions would have been used for the velocity estimation.
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