“Constant repetition time” imaging protocols for high resolution lung proton MR Imaging in mice

Purpose: The fundamental spatial resolution of in vivo MR lung imaging is limited by motion in thoracic cavity [1]. This problem is particularly evident in microscopic lung imaging of rodents because of their high cardiac (400-700 bpm) and breathing rate (100-150 breaths/min). To overcome these limitations several methods have been proposed, including scan-synchronous ventilation [2] and cardiac gating approach [3]. However, cardiac and ventilation triggered techniques do not allow predetermined and constant repetition time of the sequence, resulting in variable image contrast. In this study, we investigate the potential of two “constant repetition time” approaches based on retrospective self-gating (RSG) and signal averaging (SA) [4]. Associated imaging sequences were based on very short echo time for visualization of lung structures and parenchyma.