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| 2. |
- Jansson, Tomas, et al.
(författare)
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Frequency dependence of speckle in continuous-wave ultrasound with implications for blood perfusion measurements.
- 2002
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Ingår i: IEEE Transactions on Ultrasonics, Ferroelectrics and Frequency Control. - 0885-3010. ; 49:6, s. 715-725
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Tidskriftsartikel (refereegranskat)abstract
- Speckle in continuous wave (CW) Doppler has previously been found to cause large variations in detected Doppler power in blood perfusion measurements, where a large number of blood vessels are present in the sample volume. This artifact can be suppressed by using a number of simultaneously transmitted frequencies and averaging the detected signals. To optimize the strategy, statistical properties of speckle in CW ultrasound need to be known. This paper presents analysis of the frequency separation necessary to obtain independent values of the received power for CW ultrasound using a simplified mathematical model for insonation of a static, lossless, statistically homogeneous, weakly scattering medium. Specifically, the autocovariance function for received power is derived, which functionally is the square of the (deterministic) autocorrelation function of the effective sample volumes produced by the transducer pair for varying frequencies, at least if a delta correlated medium is assumed. A marginal broadening of the modeled autocovariance functions is expected for insonation of blood. The theory is applicable to any transducer aperture, but has been experimentally verified here with 5-MHz, 6.35-mm circular transducers using an agar phantom containing small, randomly dispersed glass particles. A similar experimental verification of a transducer used in multiple-frequency blood perfusion measurements shows that the model proposed in this paper is plausible for explaining the decorrelation between different channels in such a measurement.
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| 3. |
- 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. |
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| 5. |
- 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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