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| 2. |
- Kvikliene, Adriana, et al.
(författare)
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Modelling of nonlinear effects and the response of ultrasound contrast micro bubbles : simulation and experiment
- 2004
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Ingår i: Ultrasonics. - : Elsevier BV. - 0041-624X .- 1874-9968. ; 42:01-Sep, s. 301-307
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Tidskriftsartikel (refereegranskat)abstract
- The propagation of diagnostic ultrasonic imaging pulses in tissue and their interaction with contrast micro bubbles is a very complex physical process, which we assumed to be separable into three stages: pulse propagation in tissue, the interaction of the pulse with the contrast bubble, and the propagation of the scattered echo. The model driven approach is used to gain better knowledge of the complex processes involved. A simplified way of field simulation is chosen due to the complexity of the task and the necessity to estimate comparative contributions of each component of the process. Simulations are targeted at myocardial perfusion estimation. A modified method for spatial superposition of attenuated waves enables simulations of low intensity pulse pressure fields from weakly focused transducers in a nonlinear, attenuating, and liquid-like biological medium. These assumptions enable the use of quasi-linear calculations of the acoustic field. The simulations of acoustic bubble response are carried out with the Rayleigh-Plesset equation with the addition of radiation damping. Theoretical simulations with synthesised and experimentally sampled pulses show that the interaction of the excitation pulses with the contrast bubbles is the main cause of nonlinear scattering, and a 2-3 dB increase of second harmonic amplitude depends on nonlinear distortions of the incident pulse. (C) 2004 Elsevier B.V. All rights reserved.
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| 4. |
- Ressner, Marcus, 1967-, et al.
(författare)
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Ultrasound contrast for perfusion studies
- 2005
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Ingår i: Nordic Baltic Conference Biomedical Engineering and Medical Physics,2005. - Umeå : IFMBE. ; , s. 107-
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Konferensbidrag (refereegranskat)
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| 6. |
- Ressner, Marcus, et al.
(författare)
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Ultrasound contrast response to variation of incident pulse length and polarity
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Annan publikation (övrigt vetenskapligt/konstnärligt)abstract
- Microbubbles are used as ultrasound contrast agents (UCA) in diagnostic ultrasound as they considerably enhance the backscattered signal and generate specific signal characteristics that can be used to isolate echoes that originate from the blood volume. Emerging new advanced contrast specific insonation techniques have shown to better discriminate the backscattered UCA-signal but has not gained clinical practice due to their complexity and the need for additional soft- and hardware, or due to the debated safety aspects regarding microbubble cavitation at mechanical index (MI >>0.4). In this study we investigate a simplified approach to improve the nonlinear signal contribution from UCA at low MI < 0.4 by utilizing the asymmetry between positive and negative peak pressures for pulse lengths ≤3.5 cycles. In vitro registrations of the transmitted pulse peak pressure asymmetry from a single element transducer were obtained with a needle hydrophone after a transducer excitation pulse with increasing length from 0.5 to 5 cycles. A computational model (Bubblesim) was used to investigate the response from a single microbubble after interaction with transmitted pulse with variations of length, shape and polarity. Our results show that small changes (quarters of a pulse cycle) will change the transmitted pulse shape and distribution of peak pressures and that this effect can be used to change the scattering behavior of UCA in simulations and in vitro. This effect will increase with decreasing pulse lengths <5 cycles. The best case scenario for differentiation of harmonic UCA response with polarity change at MI <0.4 and real time imaging can for transducer frequencies of 2-2.5 MHz be found for pulse lengths of 2.25 and 2.75 cycles in the acoustic pressure interval of 300-500 kPa.
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