Successful adaptive imaging requires accurate measurements of the aberration profile across the array surface. Two-dimensional spatial filters are used to obtain more accurate estimates of aberrating layers by suppressing wavefronts emanating from off-axis scatterers. Application of these filters to the rf signals of the individual elements rejects wavefronts arriving from angles other than the look direction of the array and results in an increase in element-to-element correlation. Spatial filtering reduced the amount of error in the measured aberration profiles and adaptive spatial filtering further improved the estimates. The improvements in aberration estimation obtained with these methods are verified using simulations and experiments in tissue-mimicking phantoms. The technique is applied to signals obtained from in vivo human thyroid.
Van VeenBDBuckleyKM. Beamforming: a versatile approach to spatial filtering, IEEE ASSP Mag5, 4–24 (1988).
2.
WangZLiJStoicaPNishidaTSheplakM.Constant-beamwidth and constant powerwidth wideband robust Capon beamformers for acoustic imaging, J Acoust Soc Am116, 1621–1631 (2004).
3.
WangZLiJWuR.Time-delay-and time-reversal-based robust Capon beamformers for ultrasound imaging, IEEE Trans Med Imag24, 1308–1322 (2005).
4.
ViolaFEllisMAWalkerWF. Ultrasound imaging with beamforming adapted to target, in Proc IEEE Ultrasonics Symp, pp. 128–131, IEEE cat. no. 06CH37777 (2006).
5.
FlaxWO'DonnellM.Phase-aberration correction using signals from point reflectors and diffuse scatterers: Basic principles, IEEE Trans Ultrason Ferroelect Freq Contr35, 758–767 (1988).
6.
NockLTraheyGESmithSW. Phase aberration correction in medical ultrasound using speckle brightness as a quality factor, J Acoust Soc Am85, 1819–1833 (1989).
7.
RigbyKWChalekCLHaiderBHImproved in vivo abdominal image quality using real-time estimation and correction of wavefront arrival time errors, in Proc IEEE Ultrasonics Symp, pp. 1645–1653, IEEE cat. no. 00CH37121 (2000).
8.
FinkM.Time reversal of ultrasonic fields — part I: Basic principles, IEEE Trans Ultrason Ferroelect Freq Contr39, 555–566 (1992).
9.
LiuD-LWaagRC. Correction of ultrasonic wavefront distortion using backpropagation and a reference waveform method for time-shift compensation, J Acoust Soc Am96, 649–660 (1994).
10.
GaussRCTraheyGE. Adaptive imaging in the thyroid using fundamental and harmonic echo data, in Proc IEEE Ultrasonics Symp, pp. 1515–1519, IEEE cat. no. 99CH37027 (1999).
11.
LiuDLBakerJAvon BehrenP.A clinical study of adaptive beamforming using time-delay adjustments on a 1-D array, in Proc IEEE Ultrasonics Symp, pp. 339–342, IEEE cat. no. 03CH37476 (2003).
12.
KrishnanSLiPCO'DonnellM.Adaptive compensation of phase and magnitude aberrations, IEEE Trans Ultrason Ferroelect Freq Contr43, 44–55 (1996).
LiP-CLiM-L.Adaptive imaging using the generalized coherence factor, IEEE Trans Ultrason Ferroelect Freq Contr50, 128–141 (2003).
15.
MannJAWalkerWF. Constrained adaptive beamforming: Point and contrast resolution, Proc SPIE, pp. 12–23, vol. 5035 (2003).
16.
WalkerWFTraheyGE. A fundamental limit on delay estimation using partially correlated speckle signals, IEEE Trans Ultrason Ferroelect Freq Contr42, 301–308 (1995).
17.
CarterGC. Coherence and time delay estimation, Proc IEEE75, 236–255 (1987).
18.
SelfridgeARKinoGSKhuri-YakubBT. A theory for the radiation pattern of a narrow-strip acoustic transducer, Applied Physics Letters37, 35–36 (1980).
19.
ProakisJGManolakisDG. Digital Signal Processing: Principles, Algorithms, and Applications, 3rd ed. (Prentice-Hall, Inc., Upper Saddle River, 1996).
20.
Van TreesHL. Optimum Array Processing: Part IV of Detection, Estimation, and Modulation Theory (John Wiley & Sons, Inc., New York, 2002).
21.
GonzalezRCWoodsRE. Digital Image Processing (Addison-Wesley Publishing Company, Inc., New York, 1992).
22.
JensenJA. Field: A program for simulating ultrasound systems, Med Biol Eng Comp, col 10th Nordic-Baltic Conference on Biomedical Imaging4, 351–353 (1996).
23.
DahlJJSooMSTraheyGE. Spatial and temporal aberrator stability for real-time adaptive imaging, IEEE Trans Ultrason Ferroelect Freq Contr52, 1504–1517 (2005).
24.
GaussRCTraheyGSooMS. Wavefront estimation in the human breast, in Proc SPIE, pp. 172–181, vol. 4325 (2001).
25.
NgGCWorrellSSFreiburgerPDTraheyGE. A comparative evaluation of several algorithms for phase aberration correction, IEEE Trans Ultrason Ferroelect Freq Contr41, 631–643 (1994).
26.
FernandezATDahlJJDumontDMTraheyGE. Array elevation requirements in phase aberration correction using an 8×128 1.75D array, in Proc SPIE, pp. 79–90, volume 4687 (2002).
27.
FernandezATTraheyGE. Two-dimensional phase aberration correction using an ultrasonic 1.75D array: Case study on breast microcalcifications, in Proc IEEE Ultrasonics Symp, pp. 348–353, IEEE cat. no. 03CH37476 (2003).
28.
HinkelmanLMMastTDMetlayLAWaagRC. The effect of abdominal wall morphology on ultrasonic pulse distortion. Part I. Measurements, J Acoust Soc Am104, 3635–3649 (1998).
29.
WaagRCAstheimerJP. Statistical estimation of ultrasonic propagation path parameters for aberration correction, IEEE Trans Ultrason Ferroelect Freq Contr52, 851–869 (2005).
30.
DahlJJMcAleaveySAPintonGFSooMSTraheyGE. Adaptive imaging on a diagnostic ultrasound scanner at quasi real-time rates, IEEE Trans Ultrason Ferroelect Freq Contr53, 1832–1843 (2006).
31.
JamesJF. A Student's Guide to Fourier Transforms: with Applications in Physics and Engineering (Cambridge University Press, Cambridge, 1995).
32.
HaykinSSteinhardtA.Adaptive Radar Detection and Estimation (John Wiley & Sons, Inc., New York, 1992).
