Tetsuji Tsukamoto

Adaptive 4D MR imaging using navigator-based respiratory signal for MRI-guided therapy.

For real‐time 3D visualization of respiratory organ motion for MRI‐guided therapy, a new adaptive 4D MR imaging method based on navigator echo and multiple gating windows was developed. This method was designed to acquire a time series of volumetric 3D images of a cyclically moving organ, enabling therapy to be guided by synchronizing the 4D image with the actual organ motion in real time. The proposed method was implemented in an open‐configuration 0.5T clinical MR scanner. To evaluate the feasibility and determine optimal imaging conditions, studies were conducted with a phantom, volunteers, and a patient. In the phantom study the root mean square (RMS) position error in the 4D image of the cyclically moving phantom was 1.9 mm and the imaging time was ≈10 min when the 4D image had six frames. In the patient study, 4D images were successfully acquired under clinical conditions and a liver tumor was discriminated in the series of frames. The image quality was affected by the relations among the encoding direction, the slice orientation, and the direction of motion of the target organ. In conclusion, this study has shown that the proposed method is feasible and capable of providing a real‐time dynamic 3D atlas for surgical navigation with sufficient accuracy and image quality. Magn Reson Med 59:1051–1061, 2008.

Integration of Projection Profile Matching into Clinical MR Scanner System for Real-Time Organ Tracking and Image Registration

We propose integrating projection profile matching into a 1.5 Tesla clinical magnetic resonance (MR) scanner system to track a target organ in real-time for MRI guided therapy. As soon as a scanner acquires echoes, MR echo data are transferred immediately from the scanner to an “on-the-fly” processing computer that executes projection profile matching, image reconstruction, image registration and motion correction, The system provides respiratory motion information about a target organ with a frame rate of up to 10 Hz and delay time of 200 ms. We report measurements of a phantom and a volunteer to evaluate the delay and the accuracy of the motion measurement with respect to the true motion, and feasibility. The study compares projection profile matching-based measurement and a “golden-standard” obtained by tracking a phantom with a video camera. The error was 1.5 mm with a delay of 200 ms. We tracked the moving liver of a volunteer, and two studies demonstrates that the system can be applied to clinical use.

Simultaneous Endoscopy and MRI Acquisition

An endoscope has been used to perform procedures with a laparoscope or thoracoscope in conventional operating rooms. One of the problems linked to endoscopic surgery is its narrow field of view and an inability to view the clinical target beneath the surface. Therefore, we propose an integrated environment where surgery can be performed with a magnetic resonance (MR)-compatible flexible endoscope in an MR scanner, and have developed a visualization system to navigate the endoscope for image-guided surgical procedures. In this system, MR images were used for the image guidance. An MR-compatible electromagnetic tracking sensor was used to track the endoscope tip. Augmented reality was achieved by fusion of the volume of interest and the real-time endoscope camera view. Real-time MR imaging helps to guide the needle to the target position accurately for the delivery of appropriate therapies. It might also improve the safety and efficacy of various percutaneous techniques such as radiofrequency and microwave liver tumor ablation.