Abstract
Magnetic resonance‐guided percutaneous interventions with needles require fast pulse sequences with acquisition times less than 1 s to image the needle trajectory within moving organs. To guide the movement of a rigid instrument with high sampling rate, an magnetic resonance imaging method was developed that reduces the acquisition time down to a few hundred milliseconds by restricting the field of view to a small stripe around the instrument trajectory. To maintain the dynamic steady state, saturation pulses for outer volume suppression were inserted into additional repetition time‐intervals. These saturation intervals were combined with three sequence variants: a spoiled gradient echo sequence, an echo‐shifted steady state free precession and a balanced steady state free precession sequence. The magnetization dynamics were analyzed by means of numerical optimized simulations. Results were compared with phantom experiments and an average signal‐to‐suppression‐ratio of 15.5 could be achieved. With a field of view reduction of up to 12.5% an update rate of six images per second could be achieved. Finally, animal experiments demonstrated the fast and reliable needle tip visualization during percutaneous magnetic resonance‐guided interventions with the help of a robotic assistance system. Magn Reson Med, 2011. © 2011 Wiley‐Liss, Inc.