Directional synthetic aperture flow imaging

A method for flow estimation using synthetic aperture imaging and focusing along the flow direction is presented. The method can find the correct velocity magnitude For any flow angle, and full color flow images can be measured using only 32 to 128 pulse emissions. The approach uses spherical wave emissions with a number of defocused elements and a linear frequency-modulated pulse (chirp) to improve the signal-to-noise ratio. The received signals are dynamically focused along the flow direction and these signals are used in a cross-correlation estimator for finding the velocity magnitude. The flow angle is manually determined from the B-mode image. The approach can be used for both tissue and blood velocity determination. The approach was investigated using both simulations and a flow system with a laminar flow. The flow profile was measured with a commercial 7.5 MHz linear array transducer. A plastic tube with an internal diameter of 17 mm was used with an EcoWatt 1 pump generating a laminar, stationary flow. The velocity profile was measured for flow angles of 90 and 60 degrees. The RASMUS research scanner was used for acquiring radio frequency (RF) data from 128 elements of the array, using 8 emissions with 11 elements in each emission. A 20-/spl mu/s chirp was used during emission. The RF data were subsequently beamformed off-line and stationary echo canceling was performed. The 60-degree flow with a peak velocity of 0.15 m/s was determined using 16 groups of 8 emissions, and the relative standard deviation was 0.36% (0.65 mm/s). Using the same setup for purely transverse flow gave a standard deviation of 1.2% (2.1 mm/s). Variation of the different parameters revealed the sensitivity to number of lines, angle deviations, length of correlation interval, and sampling interval. An in vivo image of the carotid artery and jugular vein of a healthy 29-year-old volunteer was acquired. A full color flow image using only 128 emissions could be made with a high-velocity precision.

[1]  L. Rabiner,et al.  A computer program for designing optimum FIR linear phase digital filters , 1973 .

[2]  J. Jensen,et al.  In-vivo synthetic aperture flow imaging in medical ultrasound , 2003, IEEE Transactions on Ultrasonics, Ferroelectrics and Frequency Control.

[3]  J. Jensen,et al.  An effective coded excitation scheme based on a predistorted FM signal and an optimized digital filter , 1999, 1999 IEEE Ultrasonics Symposium. Proceedings. International Symposium (Cat. No.99CH37027).

[4]  M. Fox.  Multiple crossed-beam ultrasound Doppler velocimetry , 1978 .

[5]  Jorgen Jensen.  Velocity vector estimation in synthetic aperture flow and B-mode imaging , 2004, 2004 2nd IEEE International Symposium on Biomedical Imaging: Nano to Macro (IEEE Cat No. 04EX821).

[6]  G.E. Trahey,et al.  Synthetic elevation beamforming and image acquisition capabilities using an 8 /spl times/ 128 1.75D array , 2003, IEEE Transactions on Ultrasonics, Ferroelectrics and Frequency Control.

[7]  J. Jensen,et al.  A new method for estimation of velocity vectors , 1998, IEEE Transactions on Ultrasonics, Ferroelectrics and Frequency Control.

[8]  M.E. Aderson,et al.  Multi-dimensional velocity estimation with ultrasound using spatial quadrature , 1998, IEEE Transactions on Ultrasonics, Ferroelectrics and Frequency Control.

[9]  J. Jensen,et al.  Estimation of blood velocity vectors using transverse ultrasound beam focusing and cross-correlation , 1999, 1999 IEEE Ultrasonics Symposium. Proceedings. International Symposium (Cat. No.99CH37027).

[10]  Jørgen Arendt Jensen,et al.  Experimental ultrasound system for real-time synthetic imaging , 1999, 1999 IEEE Ultrasonics Symposium. Proceedings. International Symposium (Cat. No.99CH37027).

[11]  S. I. Nikolov,et al.  Velocity estimation using synthetic aperture imaging [blood flow] , 2001, 2001 IEEE Ultrasonics Symposium. Proceedings. An International Symposium (Cat. No.01CH37263).

[12]  J. Arendt Jensen,et al.  A method for real-time three-dimensional vector velocity imaging , 2003 .

[13]  O. Bonnefous.  Statistical analysis and time correlation processes applied to velocity measurement (blood flow) , 1989, Proceedings., IEEE Ultrasonics Symposium,.

[14]  G. Trahey,et al.  Angle Independent Ultrasonic Detection of Blood Flow , 1987, IEEE Transactions on Biomedical Engineering.

[15]  V. Newhouse,et al.  Ultrasound Doppler Probing of Flows Transverse with Respect to Beam Axis , 1987, IEEE Transactions on Biomedical Engineering.

[16]  C. Kasai,et al.  Real-Time Two-Dimensional Blood Flow Imaging Using an Autocorrelation Technique , 1985, IEEE 1985 Ultrasonics Symposium.

[17]  J. Jensen.  Estimation of Blood Velocities Using Ultrasound: A Signal Processing Approach , 1996 .

[18]  J. Jensen,et al.  Calculation of pressure fields from arbitrarily shaped, apodized, and excited ultrasound transducers , 1992, IEEE Transactions on Ultrasonics, Ferroelectrics and Frequency Control.

[19]  J. Jensen,et al.  Velocity estimation using synthetic aperture imaging , 2001 .

[20]  J. A. Jensen,et al.  Recursive ultrasound imaging , 1999, 1999 IEEE Ultrasonics Symposium. Proceedings. International Symposium (Cat. No.99CH37027).

[21]  M. O'Donnell,et al.  Synthetic aperture imaging for small scale systems , 1995, IEEE Transactions on Ultrasonics, Ferroelectrics and Frequency Control.

[22]  O. Bonnefous,et al.  Time Domain Formulation of Pulse-Doppler Ultrasound and Blood Velocity Estimation by Cross Correlation , 1986, Ultrasonic imaging.

[23]  J. Jensen,et al.  Multielement synthetic transmit aperture imaging using temporal encoding , 2003, IEEE Transactions on Medical Imaging.

[24]  J. Jensen,et al.  Directional velocity estimation using focusing along the flow direction. I: theory and simulation , 2003, IEEE Transactions on Ultrasonics, Ferroelectrics and Frequency Control.

[25]  J A Jensen,et al.  A new estimator for vector velocity estimation. , 2001, IEEE transactions on ultrasonics, ferroelectrics, and frequency control.

[26]  J. Jensen,et al.  A new estimator for vector velocity estimation [medical ultrasonics] , 2001, IEEE Transactions on Ultrasonics, Ferroelectrics and Frequency Control.