The Geometry Factor as a Cramr-Rao Bound for Magnitude and Phase
Pineda A, Lew C, Bammer R
The geometry factor in SENSE imaging provides a measure of the noise amplification of the unaliasing process. It gives the ratio of the noise of the reconstructed complex image obtained from the full acquisition over that of the accelerated acquisition. We recast SENSE in terms of the magnitude and phase. Assuming a sensitivity matrix with no errors, we compute the Cramr-Rao bound (CRB) to show numerically that the geometry factor is a normalized CRB for both magnitude and phase. Hence, the minimum variance of the magnitude and phase of the reconstructed images are minimized when the geometry factor is minimized.