Fourier domain beamforming for transverse-oscillations

Transverse Oscillations (TO) is the name given to a technique able to produce ultrasound images with oscillations in both axial and lateral directions. Such images have shown their potential for improving motion estimation. In this paper we present an alternative to Time Domain Transverse Oscillations (TDTO) beamforming. Conventional approaches to TO use Fraunhoffer approximation to design their beamformer, which is not respected for broadband signals. We propose to proceed to a Fourier Transform of the raw Rf signals before apodization in order to separate the contribution of each frequency band and adapt the apodization function to each frequency. This method is refered to as Fourier Domain Transverse Oscillations (FDTO) beamforming. FDTO is validated by simulations on PSFs obtained with FDTO and TDTO. Their comparison shows higher normalized cross-correlation with FDTO than TDTO for expected transverse oscillations wavelength between 1 and 2.5 mm in our configuration. FDTO is also validated on a speckle phantom. Visually FDTO PSFs, PSFs and specke images 2D spectra have lost the diagonal orientation of their pattern.