3D Cine Magnetic Resonance Imaging of Respiratory Motion in Mechanically Ventilated Mice and Rats

The pathophysiology of diaphragm dysfunction in mechanically ventilated patients has yet to be fully understood, and adequate animal models are required to accommodate further research. Mechanical ventilation settings, such as the level of positive end-expiratory pressure (PEEP), play a crucial role. The goal was to develop a method to image 3D thoracic movement during mechanical ventilation of mice and rats at different respiratory pressure settings. Rats (Wistar) and mice (C57BL/6) were anesthetized with a mix of ketamine, atropine, and dexmedetomidine. Anesthesia was maintained by continuous infusion through a peritoneal catheter. Next, a tracheostomy was performed to enable mechanical ventilation of the animals. Animals were placed in a 7T MR system while ventilated with an MR-compatible ventilator. 3D cine imaging of the thorax was conducted using a 3D gradient echo sequence with pseudo-spiral k-space filling. A navigator signal, generated by the slice selection rewinder gradient, was recorded every TR. Retrospective binning and reconstruction of the data in 12 respiratory cine time frames was performed using in-house developed software. We successfully visualized thoracic movement in 3D in both species during mechanical ventilation, enabling the investigation of changes in thorax geometry throughout the respiratory cycle at varying PEEP levels. We found that retrospective binning of respiratory frames was highly facilitated by the fixed respiration rate. The protocol presented here can be used to study cardiac and thoracic geometry and movement in mechanically ventilated mice and rats.