- Meeting abstract
- Open Access
1105 MR imaging sequences and clinical validation of a technique for respiratory motion correction in XMR-guided cardiac catheterisations
© King et al; licensee BioMed Central Ltd. 2008
- Published: 22 October 2008
- Motion Model
- Respiratory Motion
- Sagittal Slice
- Augmented Reality System
- Diaphragm Position
We have previously developed an augmented reality system that provides an anatomical roadmap derived from MR imaging that is continually aligned to X-ray fluoroscopy images in the XMR hybrid imaging environment . We have used this system to guide cardiac catheterisation for more than 50 clinical cases. This system provides an accuracy of 2 mm, but respiratory motion introduces errors that are typically much greater than this. In this abstract, we describe a novel technique for correcting for respiratory motion using a patient-specific motion model derived from MR imaging. Validation was performed on four volunteer and three patient datasets.
Two MR imaging sequences are required to form the motion model: a 3-D high-resolution MRI for the anatomy and a dynamic near real-time scan to determine the respiratory motion. For the high-resolution dataset, a free breathing 3-D balanced TFE sequence is used, which is acquired at diastole during end-expiration. For the volunteers three additional high-resolution volumes were acquired at different respiratory positions for validation (typically, 120 slices, TR = 4.4 ms, TE = 2.2 ms, flip-angle = 90°, acquired voxel size 2.19 × 2.19 × 2.74 mm3, reconstructed to 1.37 × 1.37 × 1.37 mm3, 256 × 256 matrix). Two different dynamic scan sequences were applied, which use respiratory navigators immediately before and after acquisition:
- D TFEPI, typically, 20 slices, TR = 11.75 ms, TE = 5.84 ms, flip-angle = 20°, acquired voxel size 3.81 × 4.27 × 8.0 mm3, reconstructed to 2.22 × 2.22 × 4.0 mm3, 144 × 144 matrix, 100 dynamics;
2 sagittal slices
Multislice balanced TFE, typically, TR = 2.74 ms, TE = 1.37 ms, flip-angle = 60°, acquired voxel size 1.78 × 1.75 × 8.0 mm3, reconstructed to 1.09 × 1.09 × 8.0 mm3, 320 × 320 matrix, 100 dynamics. The 2 sagittal slice sequence was tested because in our experience the dominant cardiac respiratory motion parameters are the inferior-superior and anterior-posterior translations, the inferior-superior scaling, and the lateral axis rotation. All of these parameters can be more accurately estimated from high-resolution sagittal slices.
A heart model was constructed from the 3-D high-resolution scan and the motion model. In order to use this model within the augmented reality system, the diaphragm position is automatically determined from X-ray fluoroscopy images. The cardiac roadmap is then updated using the model. We gate the X-ray images at diastole by synchronising X-ray image acquisition with the electrocardiogram signal.
We have demonstrated the construction of a patient-specific cardiac respiratory motion model from MRI data and its application to an augmented reality system for guiding cardiac catheterisations. We anticipate that such models will have widespread applications that include roadmapping during MR-guided interventions and also MR image acquisition.