Junichi Tokuda

MRI-Compatible Pneumatic Robot for Transperineal Prostate Needle Placement

Magnetic resonance imaging (MRI) can provide high-quality 3-D visualization of prostate and surrounding tissue, thus granting potential to be a superior medical imaging modality for guiding and monitoring prostatic interventions. However, the benefits cannot be readily harnessed for interventional procedures due to difficulties that surround the use of high-field (1.5T or greater) MRI. The inability to use conventional mechatronics and the confined physical space makes it extremely challenging to access the patient. We have designed a robotic assistant system that overcomes these difficulties and promises safe and reliable intraprostatic needle placement inside closed high-field MRI scanners. MRI compatibility of the robot has been evaluated under 3T MRI using standard prostate imaging sequences and average SNR loss is limited to 5%. Needle alignment accuracy of the robot under servo pneumatic control is better than 0.94 mm rms per axis. The complete system workflow has been evaluated in phantom studies with accurate visualization and targeting of five out of five 1 cm targets. The paper explains the robot mechanism and controller design, the system integration, and presents results of preliminary evaluation of the system.

OpenIGTLink: an open network protocol for image-guided therapy environment

With increasing research on system integration for image‐guided therapy (IGT), there has been a strong demand for standardized communication among devices and software to share data such as target positions, images and device status.

MRI signal intensity based B-spline nonrigid registration for pre- and intraoperative imaging during prostate brachytherapy

To apply an intensity‐based nonrigid registration algorithm to MRI‐guided prostate brachytherapy clinical data and to assess its accuracy.

Image registration for targeted MRI-guided transperineal prostate biopsy.

To develop and evaluate image registration methodology for automated re‐identification of tumor‐suspicious foci from preprocedural MR exams during MR‐guided transperineal prostate core biopsy.

Transperineal In-Bore 3-T MR Imaging–guided Prostate Biopsy: A Prospective Clinical Observational Study

PURPOSE To determine the detection rate, clinical relevance, Gleason grade, and location of prostate cancer ( PCa prostate cancer ) diagnosed with and the safety of an in-bore transperineal 3-T magnetic resonance (MR) imaging-guided prostate biopsy in a clinically heterogeneous patient population. MATERIALS AND METHODS This prospective retrospectively analyzed study was HIPAA compliant and institutional review board approved, and informed consent was obtained. Eighty-seven men (mean age, 66.2 years ± 6.9) underwent multiparametric endorectal prostate MR imaging at 3 T and transperineal MR imaging-guided biopsy. Three subgroups of patients with at least one lesion suspicious for cancer were included: men with no prior PCa prostate cancer diagnosis, men with PCa prostate cancer who were undergoing active surveillance, and men with treated PCa prostate cancer and suspected recurrence. Exclusion criteria were prior prostatectomy and/or contraindication to 3-T MR imaging. The transperineal MR imaging-guided biopsy was performed in a 70-cm wide-bore 3-T device. Overall patient biopsy outcomes, cancer detection rates, Gleason grade, and location for each subgroup were evaluated and statistically compared by using χ(2) and one-way analysis of variance followed by Tukey honestly significant difference post hoc comparisons. RESULTS Ninety biopsy procedures were performed with no serious adverse events, with a mean of 3.7 targets sampled per gland. Cancer was detected in 51 (56.7%) men: 48.1% (25 of 52) with no prior PCa prostate cancer , 61.5% (eight of 13) under active surveillance, and 72.0% (18 of 25) in whom recurrence was suspected. Gleason pattern 4 or higher was diagnosed in 78.1% (25 of 32) in the no prior PCa prostate cancer and active surveillance groups. Gleason scores were not assigned in the suspected recurrence group. MR targets located in the anterior prostate had the highest cancer yield (40 of 64, 62.5%) compared with those for the other parts of the prostate (P < .001). CONCLUSION In-bore 3-T transperineal MR imaging-guided biopsy, with a mean of 3.7 targets per gland, allowed detection of many clinically relevant cancers, many of which were located anteriorly.

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.

Needle Guiding Robot for MR-guided Microwave Thermotherapy of Liver Tumor using Motorized Remote-Center-of-Motion Constraint

Searching for optimal needle insertion path by intraoperative magnetic resonance imaging (MRI) is complex and time-consuming task in MR-guided microwave thermotherapy of liver tumor. This paper reports the semi-active needle-guiding robot for MR-guided therapy by which a surgeon can freely selects needle insertion path while maintaining the remote center of motion at the pre-defined tumor site. The robot consists of three-degree-of-freedom active XYZ base stage with ultrasonic motors and passive needle holder with unconstrained two-degree-of-freedom rotation measured by optical fiber sensor with aluminum die cast. Once the target point on the tumor is defined in volumetric MR images, the base stage keeps the remote-center-of-motion at the target point, while physician can interactively selects the orientation of the needle path with continuous single slice MR imaging. Experiments to test the accuracy of remote-center-of-motion indicated that the robot can keep the needle tip with an average error of 0.7 ∼ 0.3 mm in the compatibility test showed the robot can be safely used in MR axial plane, and 1.0-0.4 mm in the sagittal plane. Unlike related studies published elsewhere where the MR compatible robot autonomously brings the tools to predefined location, the proposed approach is fit to use in microwave thermotherapy of liver cancer.

Integration of the OpenIGTLink Network Protocol for image-guided therapy with the medical platform MeVisLab

OpenIGTLink is a new, open, simple and extensible network communication protocol for image‐guided therapy (IGT). The protocol provides a standardized mechanism to connect hardware and software by the transfer of coordinate transforms, images, and status messages. MeVisLab is a framework for the development of image processing algorithms and visualization and interaction methods, with a focus on medical imaging.

MRI-Compatible Manipulator With Remote-Center-of-Motion Control

To develop and assess a needle‐guiding manipulator for MRI‐guided therapy that allows a physician to freely select the needle insertion path while maintaining remote center of motion (RCM) at the tumor site.

Lung Motion and Volume Measurement by Dynamic 3D MRI Using a 128-Channel Receiver Coil

RATIONALE AND OBJECTIVES The authors present their initial experience using a 3-T whole-body scanner equipped with a 128-channel coil applied to lung motion assessment. Recent improvements in fast magnetic resonance imaging (MRI) technology have enabled several trials of free-breathing three-dimensional (3D) imaging of the lung. A large number of image frames necessarily increases the difficulty of image analysis and therefore warrants automatic image processing. However, the intensity homogeneities of images of prior dynamic 3D lung MRI studies have been insufficient to use such methods. In this study, initial data were obtained at 3 T with a 128-channel coil that demonstrate the feasibility of acquiring multiple sets of 3D pulmonary scans during free breathing and that have sufficient quality to be amenable to automatic segmentation. MATERIALS AND METHODS Dynamic 3D images of the lungs of two volunteers were acquired with acquisition times of 0.62 to 0.76 frames/s and an image matrix of 128 x 128, with 24 to 30 slice encodings. The volunteers were instructed to take shallow and deep breaths during the scans. The variation of lung volume was measured from the segmented images. RESULTS Dynamic 3D images were successfully acquired for both respiratory conditions for each subject. The images showed whole-lung motion, including lifting of the chest wall and the displacement of the diaphragm, with sufficient contrast to distinguish these structures from adjacent tissues. The average time to complete segmentation for one 3D image was 4.8 seconds. The tidal volume measured was consistent with known tidal volumes for healthy subjects performing deep-breathing maneuvers. The temporal resolution was insufficient to measure tidal volumes for shallow breathing. CONCLUSION This initial experience with a 3-T whole-body scanner and a 128-channel coil showed that the scanner and imaging protocol provided dynamic 3D images with spatial and temporal resolution sufficient to delineate the diaphragmatic domes and chest wall during active breathing. In addition, the intensity homogeneities and signal-to-noise ratio were adequate to perform automatic segmentation.