Prospective self-gating for simultaneous compensation of cardiac and respiratory motion.

Segmented cardiac acquisitions generally require the use of an electrocardiogram (ECG) in combination with a breathhold or a respiratory navigator placed on the diaphragm. These techniques necessitate patient cooperation and increase the complexity of cardiac imaging. The ECG signal may be distorted inside the magnet by interferences from radiofrequency and gradient action. Breathhold acquisition limits the total scan time, while navigators on the diaphragm might not fully reflect respiratory-induced motion of the heart. To overcome some of these problems, several self-gating (SG) or "wireless" techniques have recently been presented. All of these approaches, however, are based on either cardiac triggering or respiratory gating, or the data are processed retrospectively, reducing the efficiency of data acquisition. In this work a prospective SG approach for free-breathing imaging is presented that requires neither ECG gating nor respiratory navigation. The motion data used for cardiac triggering and respiratory gating are extracted from the repeatedly acquired k-space center. Based on computer simulations and in vivo data of the heart, it is shown that cardiac as well as respiratory motion can be accurately extracted in real time. Using the method proposed, the scan efficiency could be significantly increased while preserving image quality relative to retrospective SG approaches.