Effects of breathing motion on the spatial resolution in microscopic imaging techniques of rodents

Magnetic resonance microscopy is capable of producing high-resolution pulmonary images in live rodents by synchronizing the image acquisition across multiple breaths. The precision with which one can control motion will probably define the resolution limit that can be attained in such studies. This work was performed to evaluate how reliably the respiratory structures return to the same position from breath to breath each time data are acquired. Radio-opaque beads were surgically glued on the diaphragm of anesthetized, mechanically ventilated rats. Their range of motion (relative to a reference vertebral bead) was evaluated using digital micro-radiography with two specific biological pulse sequences: (1) ventilation synchronous acquisition, and (2) both ventilation synchronous and cardiac gated acquisition. The standard deviation of the displacement was on the order of, or less than 100 microns, which is comparable to the resolution limit for in vivo magnetic resonance imaging imposed by signal to noise constraints. With careful control of motion, its impact on resolution can be limited. This work provides the first quantitative measure of the motion imposed resolution limits for in vivo imaging.