| 1. |
- Persson, Magnus, et al.
(författare)
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A new non-invasive ultrasonic method for simultaneous measurements of longitudinal and radial arterial wall movements: first in vivo trial.
- 2003
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Ingår i: Clinical Physiology and Functional Imaging. - 1475-0961. ; 23:5, s. 247-251
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Tidskriftsartikel (refereegranskat)abstract
- During recent years, the radial movement of the arterial wall has been extensively studied, and measurements of the radial movement are now an important tool in cardiovascular research for characterizing the mechanical properties of the arterial wall. In contrast, the longitudinal movement of vessels has gained little or no attention as it has been presumed that this movement is negligible. With modern high-resolution ultrasound, it can, however, be seen that the intima-media complex of the arterial wall moves not only in the radial direction, but also in the longitudinal direction during pulse-wave propagation. This paper describes a new non-invasive ultrasonic method that is able to measure simultaneously two dimensionally arterial vessel wall movements. The method is demonstrated in a limited in vivo trial. Results from the in vivo trial show that, apart from the well-known radial movement, there is a distinct longitudinal movement in the human common carotid artery with, in this case, the intima-media complex moving substantially as compared with the region of the tunica adventitia. Two-dimensional evaluation of the vessel-wall movements, taking not only the radial movement, but also the longitudinal movement into account, may provide novel information of importance in the evaluation of vessel-wall function.
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| 2. |
- Persson, Magnus, et al.
(författare)
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Non-invasive measurement of arterial longitudinal movement
- 2002
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Ingår i: Proceedings of the IEEE Ultrasonics Symposium. - 1051-0117. ; 2, s. 1783-1786
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Konferensbidrag (refereegranskat)abstract
- In arterial vessel wall characterisation the longitudinal movements of vessels have gained little or no attention. It has been presumed that the arterial vessels move very little in the longitudinal direction. With modern high resolution ultrasound it can, however, be seen that arterial vessels move not only in the circumferential, but also in longitudinal direction. This paper describes a non-invasive, ultrasound based method which estimates the longitudinal and the circumferential movement, respectively. The method is demonstrated in a limited in vivo study of the common carotid artery. Results show that, apart from the well known circumferential movement, there is a distinct longitudinal movement.
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| 3. |
- Almqvist, Monica, et al.
(författare)
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Ultrasound field characterisation in air using light diffraction tomography
- 2004
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Ingår i: AMUM 2004: Advanced Metrology for Ultrasound in Medicine 2004. - : IOP Publishing. - 1742-6596 .- 1742-6588. ; 1, s. 150-154
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Konferensbidrag (refereegranskat)abstract
- The aim of this work was to show the applicability of light diffraction tomography on airborne ultrasound. Different air-coupled transducers in the frequency range 40 kHz - 2 MHz were measured to show the method's performance. A calibrated microphone and the pulse-echo method were used to evaluate the results. The absolute measurements agreed within the calibrated microphone's uncertainty range. Pulse waveforms and corresponding FFT-diagrams show the method's higher bandwidth compared to the microphone. Further, the method offers non-perturbing measurements with high spatial resolution, which was especially advantageous for measurements close to the transducer surfaces. The S/N-ratio was larger than or in the same range as that of the two comparing methods.
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| 4. |
- Cinthio, Magnus, et al.
(författare)
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Estimation of arterial pulse wave velocity with a new improved tissue Doppler method
- 2001
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Ingår i: 2001 Conference Proceedings of the 23rd Annual International Conference of the IEEE Engineering in Medicine and Biology Society. - 0780372115 ; , s. 188-191
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Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- The mechanical properties of the large arteries are important determinants in the circulation physiology. Quantities associated with vessel wall elasticity are of particular interest since they offer a possibility to separate diseased arteries from healthy. Pulse wave velocity (PWV) is a local measure of the arterial wall elasticity. This paper describes a new improved method for non-invasive local PWV estimation. The PWV estimation is based on arterial wall movements, which is detected by Tissue Doppler Imaging (TDI), a color Doppler optimized for low velocities. The TDI facility allows the artery to be measured at several positions simultaneously, which improves the PWV estimation considerably. The method is validated with respect to operator repeatability and operator reproducibility in a limited clinical study.
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| 5. |
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| 6. |
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| 7. |
- 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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| 8. |
- Jansson, Tomas, et al.
(författare)
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Movement artefact suppression in blood perfusion measurements using a multifrequency technique
- 2002
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Ingår i: Ultrasound in Medicine and Biology. - 0301-5629. ; 28:1, s. 69-79
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Tidskriftsartikel (refereegranskat)abstract
- The standard way of suppressing movement artefacts in Doppler measurements is by means of a high-pass filter. This is because artefacts usually are of high amplitude, but have low frequencies. The immediate drawback is, then, that low-velocity blood flow is also filtered out. In this paper, a method to reduce movement artefacts in blood perfusion measurements is proposed, using simultaneous transmission and reception of multiple frequencies in a continuous-wave Doppler system. It is shown that Doppler signals originating from blood may be considered uncorrelated for a large enough frequency separation between channels, and tissue movements are more correlated. By subtracting perfusion estimates obtained by time-domain processing, correlated signals can be suppressed. The subtraction algorithm is shown to produce a linear perfusion estimate, but with twice the standard deviation compared to an estimate obtained by simply averaging channels. Movement artefacts in both in vitro and in vivo models are shown to be reduced by the algorithm. Imbalance between channels does, however, cause the artefacts to be only partly reduced. The problem can be alleviated by filtering the signals prior to subtraction, but this results in a nonlinear estimate, especially for large time constants in the filter. Some amount of filtering can still be desirable to suppress partly correlated artefacts, even if identical time-domain processing units are implemented, as could be done digitally. (E-mail: tomas.jansson@elmat.lth.se)
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| 9. |
- Jansson, Tomas, et al.
(författare)
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Speckle in the Doppler signal - correlation of CW-Doppler signals from blood for varying transmit frequency
- 2002
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Ingår i: 2002 IEEE Ultrasonics Symposium. Proceedings (Cat. No.02CH37388). - 0780375823 ; , s. 1499-1502
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Konferensbidrag (refereegranskat)abstract
- Speckle is an unwanted noise in ultrasound images, and appears as returning echoes are coherently summed over the transducer surface. In Doppler applications, the total power of the received spectrum varies in a manner similar to speckle. This paper investigates the correlation of continuous-wave (CW) Doppler signals obtained from simultaneously transmitted carrier frequencies, when a slowly flowing blood stream is insonated. The covariance function of received Doppler power versus transmitted frequency is shown to agree well to a theoretical modelled function, as well as experiments made on static, independent scatterers, even though the present measurements have a larger variability. The speckle to noise ratio of the Doppler signal amplitude was found to be 1.87 (S.E. 0.04), compared to the theoretical number 1.91 valid for pulse-echo imaging. It was also found that average of spectral estimates from independent channels reduce the variability of such estimates
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