Yuji Iwadate1, Kunihiro Miyoshi2, Hiroyuki Kabasawa3. 1. Global MR Applications and Workflow, GE Healthcare Japan, 4-7-127 Asahigaoka, Hino, Tokyo, 193-0825, Japan. Electronic address: yuji.iwadate@ge.com. 2. MR Engineering, GE Healthcare Japan, 4-7-127 Asahigaoka, Hino, Tokyo, 193-0825, Japan. 3. Global MR Applications and Workflow, GE Healthcare Japan, 4-7-127 Asahigaoka, Hino, Tokyo, 193-0825, Japan.
Abstract
PURPOSE: To develop and demonstrate the feasibility of a pencil-beam navigator using a gradient reversal technique for reducing signal contamination from undesired excitation for precise motion detection and correction. MATERIALS AND METHODS: The navigator echo was obtained using normal and reversed gradient waveforms sequentially in three-dimensional spoiled gradient-recalled echo imaging. These two signals were combined in the complex domain for generating the final navigator data, which were used for detecting the diaphragm motion to nullify the side lobe effects with the smallest radius from the beam center. The navigator signals were compared with and without the proposed technique in phantom and human scans. In addition, navigator-gated imaging was performed in the human scans. RESULTS: In a phantom experiment, the proposed technique diminished signals from a phantom placed outside the beam's area. In human scans, the proposed technique reduced undesired signals in the navigator data for all subjects. The resultant images had fewer motion-induced ghosts than the images from the conventional technique for 8 subjects out of 10. CONCLUSIONS: We have demonstrated that the gradient reversal technique reduced undesired signals in a pencil-beam navigator. This technique can be an alternative for free-breathing abdominal scan when the conventional navigator technique cannot detect the patient's respiratory motion precisely.
PURPOSE: To develop and demonstrate the feasibility of a pencil-beam navigator using a gradient reversal technique for reducing signal contamination from undesired excitation for precise motion detection and correction. MATERIALS AND METHODS: The navigator echo was obtained using normal and reversed gradient waveforms sequentially in three-dimensional spoiled gradient-recalled echo imaging. These two signals were combined in the complex domain for generating the final navigator data, which were used for detecting the diaphragm motion to nullify the side lobe effects with the smallest radius from the beam center. The navigator signals were compared with and without the proposed technique in phantom and human scans. In addition, navigator-gated imaging was performed in the human scans. RESULTS: In a phantom experiment, the proposed technique diminished signals from a phantom placed outside the beam's area. In human scans, the proposed technique reduced undesired signals in the navigator data for all subjects. The resultant images had fewer motion-induced ghosts than the images from the conventional technique for 8 subjects out of 10. CONCLUSIONS: We have demonstrated that the gradient reversal technique reduced undesired signals in a pencil-beam navigator. This technique can be an alternative for free-breathing abdominal scan when the conventional navigator technique cannot detect the patient's respiratory motion precisely.