"Phased" array coil

[Dave Higgins]

Can anyone tell my why phased array coils are so named?
Why "phased"?

Dave

[Dave Higgins]

Wikipedia has an opinion on this:

In wave theory, a phased array is a group of antennas in which the relative phases of the respective signals feeding the antennas are varied in such a way that the effective radiation pattern of the array is reinforced in a desired direction and suppressed in undesired directions.

So the term originates from development of radio wave transmission.

How does this apply to MRI signal reception then? Haacke et al (p857):

In order to obtain optimal SNR from a phased array coil, it is necessary to make sure that the noise from coil to coil is largely uncorrelated. In order to achieve this ... there should be minimal electromagnetic interaction between the coils to make sure that sample noise is not correlated.

So like for transmission, it's about the shape and arrangement of the coil elements. And it's not simple. Again from Haacke et al (p858):

Methods for determining the optimal arrangement and number of coils in a phased array are still a subject of research. This is because there are several competing factors to be considered in the design of each coil.