Avanto mr system

All images were scanned using a 1.5T Siemens Avanto MR system (Siemens, Munich, Germany) equipped with an eight-channel phased-front coil dedicated to the abdomen. In order to reduce gastrointestinal motion artifacts, the patients were instructed to abstain from water and food for 4 h before the scan. The imaging sequences included coronal fast imaging, employing the steady-state acquisition (FIESTA) sequence, axial fat-suppression T2WI, axial DWI, and axial in-phase and out-of-phase T1-weighted imaging (T1WI). DWI was collected by echo-planar imaging (EPI), with b values of 0 and 800. The respiratory trigger technique was used for T2WI and DWI, and the end-expiratory breath-holding method was used for FIESTA and T1WI scans to reduce respiratory motion artifacts. Table 1 lists the detailed image acquisition parameters.

Experiments were performed in a 1.5 T whole-body MR scanner (Siemens Avanto MR system; Siemens AG, Erlangen, Germany) equipped with a 12-channel head coil (Fig. 6A). The subjects’ heads were fixed with foam in order to limit head motion. Functional images were acquired with the following parameters: single-shot gradient-echo EPI sequence; 30 contiguous axial slices; slice thickness = 4 mm; TR = 3.3 s; TE = 60 ms; flip angle = 90°; FOV = 256 × 256 mm²; matrix = 64 × 64 (i.e., nomimal voxel size = 4 × 4 × 4 mm³). Four dummy scans were performed at the beginning of each functional measurement in order to achieve magnetization steady state. For each protocol, a total of 240 brain volumes (i.e., 120 at rest and 120 during contractions) were acquired in a single run lasting ∼13 min. The MR acquisition was synchronized to the stimulation procedure using the Powerlab system. All fMRI experiments were performed on the same day with identical positioning of the stimulation electrodes and the MRI coil. The three protocols were separated by a 15-min recovery period in order to minimize potential fatigue effects^{24 (link)}. At the end of the three protocols, 3D T₁-weighted anatomical images were obtained.