What is parallel beam forming?

Parallel beam forming can be performed in both reception and transmission (Demi et al., 2013). It speeds up the rate of data acquisition (Hoskins et al., 2010), which can be used to increase the frame rate, field of view, more frame averaging to reduce noise, or reduce acquisition time (particularly important for 3D imaging).

Parallel beam forming in reception used to be very popular, however, the fact that one wide beam or plane wave is sent from which multiple receive lines are acquired means that the overall pressure fluctuations are not of sufficient size to generate harmonics. This makes this method incompatible with tissue harmonic imaging, which is considered essential to modern day imaging.

One possible exception is small animal imaging with microconvex probes. Due to the higher frequencies required and the fact that the patients’ small body sizes often will not provide sufficient depth for harmonics to be generated, many manufacturers still use fundamental imaging. In this situation, parallel beam forming in reception would have utility.

For most imaging, however, parallel beam forming in transmission is more effective. This involves the emission of narrow beams in parallel, which means that the pressure fluctuations are sufficient to generate harmonics. The downside, however, is that each beam can only use a portion of the transducer’s bandwidth, resulting in lower axial resolution with this technique.

References:

Demi, L., Viti, J., Kusters, L., et al. (2013). Implementation of Parallel Transmit Beamforming Using Orthogonal Frequency Division Multiplexing – Achieveable Resolution and Interbeam Interference. IEEE Transactions on Ultrasonics, Ferroelectrics, and Frequency Control: 60(11).

Hoskins, P., Martin, K., Thrush, A. (2010). Diagnostic Ultrasound Physics & Equipment. Cambridge University Press.