Fat quantification using an interleaved bipolar acquisition

Abstract

To demonstrate a new multigradient echo bipolar acquisition sequence for fat quantification. A multiecho bipolar acquisition is used such that the even echoes have opposite polarity to the odd echoes. In addition, the readout gradients alternate their polarities every other phase-encode line. Each echo, therefore, consists of phase-encode lines with both positive and negative polarities. Phase-encodes acquired with the same polarity are grouped together, and parallel imaging reconstruction is used to obtain two full k-space maps with opposite readout polarities at all the echoes. By complex averaging, the inconsistent phase errors between odd and even echoes are removed and water/fat separation techniques used with conventional unipolar sequences can be performed. Phantoms and in vivo experiments demonstrated accurate fat fraction and increased signal to noise ratio efficiency compared with the established unipolar acquisition. Artefacts due to phase and magnitude errors of bipolar acquisition were eliminated in all experiments. The interleaved bipolar sequence is an efficient technique for fat quantification. It demonstrated accurate fat measurements in a shorter scan time compared with the standard unipolar sequence.