Hasnine A. Haque

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.

Advanced computer assistance for magnetic resonance-guided microwave thermocoagulation of liver tumors.

RATIONALE AND OBJECTIVES The purpose of this study was to utilize computer assistance effectively for both easy and accurate magnetic resonance (MR) image-guided microwave thermocoagulation therapy of liver tumors. MATERIALS AND METHODS An open configuration MR scanner and a microwave coagulator at 2.45 GHz were used. Navigation software, a 3D Slicer, was customized to combine fluoroscopic MR images and preoperative MR images for the navigation. New functions to display MR temperature maps with simple parameter setting, and to record and display the coagulated areas by multiple microwave ablations in the 3-dimensional space (footprinting), were also introduced into the software. The VGA signal of the computer display was directly transferred to the surgeons monitor. RESULTS The customized software could be used for both accurate image navigation and convenient and easy temperature monitoring. Because repeated punctures and ablations are usually required in this procedure, the footprinting function made targeting of the tumors both easy and accurate and was quite effective in achieving the necessary and sufficient treatment. Furthermore, clear display on the surgeons monitor, which was obtained by direct transfer of the VGA signal, enabled precise image navigation. CONCLUSION The newly developed computer assistance was quite useful and helpful for this MR-guided procedure.

Preliminary clinical experiences of a motorized manipulator for magnetic resonance image-guided microwave coagulation therapy of liver tumors.

BACKGROUND In magnetic resonance (MR) image-guided microwave thermocoagulation of liver tumors, the choice of the optimal puncture route is an important and time-consuming process. To assist this process, we have developed a motorized MR-compatible manipulator. METHODS The manipulator consists of a passive end effecter with 2 degrees-of-freedom (DOF) rotation and active base stages with 3 ultrasonic motors. It automatically chases the preset target point with synergetic remote-center-of-motion (RCM) control. A mechanical torque limiter and an electrical shutdown switch were added for patient safety. RESULTS The manipulator was used for this procedure in 15 cases and successfully utilized to treat liver tumors in various locations. Thoracoscopic assistance was combined with the manipulator in 6 cases. No complications were experienced. CONCLUSIONS The manipulator was found to be very effective for assisting MR-guided microwave coagulation of liver tumors.

MRI-Guided Microwave Ablation

MRI-guided microwave ablation for liver tumors has been performed using near-real-time magnetic resonance (MR) images with a double-donut-type open-configuration MR scanner. A microwave coagulator was developed in Japan for hemostasis in hepatic resection under open surgery. Microwave ablation has already been established as one useful minimally invasive procedure for liver tumors. The microwave coagulator operated at 2.45 GHz utilizes dielectric heating similar to microwave ovens. For the ablation of liver tumors, an MR-compatible needle-type electrode was inserted through an MR-compatible puncture needle. The combination of MR image guidance and microwave ablation was quite feasible. During microwave ablation, clear MR images without interference and MR temperature maps could be observed and ablation could be performed without a ground pad. To increase the availability and efficacy of this treatment, various surgical instruments, such as adaptors for the optical tracking system to control image planes, an MR-compatible endoscopic system, navigation software, and a motorized manipulator, have been developed. In this chapter, the outline of this procedure and the advances in peripheral instruments are introduced.

Technical Developments for MR-Guided Microwave Thermocoagulation Therapy of Liver Tumors

We have started clinical studies of MR-guided thermocoagulation therapy of liver tumors. Through this therapy for two years, we have developed new instruments, such as a filter to reduce noise in MRI from the microwave coagulator, a new MR-compatible electrode for easy detection of the tip position and an MR-compatible endoscopic system for trans-diaphragmatic approach to liver tumors just below the diaphragm. Concerning software, a program was modified for the real-time display of MR temperature map with a scale bar. A navigation software, 3D Slicer was customized to add real-time image navigation capability. The re-sliced images in the two perpendicular planes complemented the limitations of real-time MR image, which is taken in 2-3 seconds. These technical developments play important roles for more accurate, safer and easier treatment.

A new function for accurate MR guided microwave ablation using vertically opened 0.5-T MR system

The purpose of our study is to evaluate the newly developed functions in microwave thermocoagulation therapy within a vertically oriented open MR system. The newly developed functions were to record the ablation areas in 3-dimensional space and accurate targeting the planned treatment volumes of liver tumor during procedure. Before using these functions, we could know the treatment volumes in the dynamic study of post operation. The evolved function facilitated intraoperative surgical margin evaluation and prompted additional surgical margin ablation in MR-guided microwave ablation for liver tumor. Our results demonstrate the feasibility of these functions in minimally invasive MR guided microwave thermocoagulation therapy in an open MR system.

Automated registration of 3D ultrasound and CT/MR images for liver

In clinical diagnosis of liver cancer or treatment using US image guided navigation often required correlation of suspicious region in US with the clinical findings on CT or MR images. We proposed a faster automated registration technique consists of two-steps registration framework which contains vessel structure-based coarse registration and gradient feature-based fine registration. Results were validated using 30 clinical image data-sets collected in standard clinical workflow of the patient undergoing liver cancer treatment. Registration success rate found to be 73%. Registration error were measured 3.88±1.38[mm] and 3.22±1.91[mm] for US-MR and US-CT cases respectively. Total computation time was determined as 40 sec. on GEs standard Advantage Workstation.

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.