2.3.1. Imaging system

A detailed description of the awake rat imaging system is published elsewhere (Stenroos et al., 2018). Notably, we used a quadrature transmit/receive volume coil (ID = 42 mm) that provided both high anatomical resolution and high signal-to-noise ratio for voxel-based BOLD phMRI. The design of the rat holder (Ekam Imaging, Boston, MA) stabilized the head in padded sidebars, minimizing discomfort caused by ear bars and other restraint systems that are commonly used to immobilize the head for awake animal imaging. Shown in Figure 1 is the mean ± SE for the movement (μm) in the x, y, and z axes over the 35 min scanning session for all rats in the study. The average displacement in any orthogonal direction over the entire scanning session did not exceed 65 μm. Rats with repeated motion exceeding 150 μm, i.e., greater than one half the in-plane dimensions of a voxel (ca 300 μm²) in any orthogonal direction were excluded from the study. Given the design of the head holder to minimize stress and discomfort with the least mechanical restriction, loss of subjects due to gross motion artifact was unavoidable.

Motion associated with awake imaging. Shown is the degree of motion recorded over the 35 min imaging protocol. The data are reported as the mean and standard error in micrometers for axis X, Y, and Z from all rats from each experimental condition.