Motion compensated magnetic resonance imaging of an active sun beetle using an in situ treadmill.

Magnetic resonance imaging is inherently non-invasive, and thus an ideal technique for probing living biological matter. The low sensitivity and prolonged data acquisition time, coupled with stringent magnetic field homogeneity requirements and spatial constraints inside the magnet, make the technique under-utilised for the study of live and freely moving model organisms. We introduce a new method for performing MRI of a live insect that is moving on a treadmill. The tethered insect, positioned on a treadmill inside an RF volume coil, provides a controlled environment for studying the organism, and maintains the spatial consistency for an MRI excitation slice, thereby limiting any residual motion artifacts within the slice or MRI field-of-view, and thus making the problem manageable with motion correction techniques available in clinical MRI research. We address the particular case of semi-periodic abdominal motion of the insect, and its effect on MRI reconstruction. An MR compatible optical imaging system has been integrated with the high-field magnet, in conjunction with a computer vision algorithm for extracting the real-time motion information, with the added advantage of phenotypic characterisation of the behaving organism. The motion information, with a prospective triggering system, has been used for the acquisition of spatially consistent k-space lines, thereby reducing artifacts due to the gross body motion of the walking insect.