Navigator‐based motion compensation for liver BOLD measurement with five‐echo SAGE EPI and breath‐hold task

Abstract

PurposeThe purpose of this work is to apply multi‐echo spin‐ and gradient‐echo (SAGE) echo‐planar imaging (EPI) combined with a navigator‐based (NAV) prospective motion compensation method for a quantitative liver blood oxygen level dependent (BOLD) measurement with a breath‐hold (BH) task.MethodsA five‐echo SAGE sequence was developed to quantitatively measure T2 and T2* to depict function with sufficient signal‐to‐noise ratio, spatial resolution and sensitivity to BOLD changes induced by the BH task. To account for respiratory motion, a navigator was employed in the form of a single gradient‐echo projection readout, located at the diaphragm along the inferior–superior direction. Prior to each transverse imaging slice of the spin‐echo EPI‐based readouts, navigator acquisition and fat suppression were incorporated. Motion data was obtained from the navigator and transmitted back to the sequence, allowing real‐time adjustments to slice positioning. Six healthy volunteers and three patients with liver carcinoma were included in this study. Quantitative T2 and T2* were calculated at each time point of the BH task. Parameters of t value from first‐level analysis using a general linear model and hepatovascular reactivity (HVR) of Echo1, T2 and T2* were calculated.ResultsThe motion caused by respiratory activity was successfully compensated using the navigator signal. The average changes of T2 and T2* during breath‐hold were about 1% and 0.7%, respectively. With the help of NAV prospective motion compensation whole liver t values could be obtained without motion artifacts. The quantified liver T2 (34.7 ± 0.7 ms) and T2* (29 ± 1.2 ms) values agreed with values from literature. In healthy volunteers, the distribution of statistical t value and HVR was homogeneous throughout the whole liver. In patients with liver carcinoma, the distribution of t value and HVR was inhomogeneous due to metastases or therapy.ConclusionsThis study demonstrates the feasibility of using a NAV prospective motion compensation technique in conjunction with five‐echo SAGE EPI for the quantitative measurement of liver BOLD with a BH task.