Robotic System Development for Precision MRI-Guided Needle-Based Interventions

This dissertation describes the development of a methodology for implementing robotic systems for interventional procedures under intraoperative Magnetic Resonance Imaging (MRI) guidance. MRI is an ideal imaging modality for surgical guidance of diagnostic and therapeutic procedures, thanks to its ability to perform high resolution, real-time, and high soft tissue contrast imaging without ionizing radiation. However, the strong magnetic field and sensitivity to radio frequency signals, as well as tightly confined scanner bore render great challenges to developing robotic systems within MRI environment. Discussed are potential solutions to address engineering topics related to development of MRI-compatible electro-mechanical systems and modeling of steerable needle interventions. A robotic framework is developed based on a modular design approach, supporting varying MRI-guided interventional procedures, with stereotactic neurosurgery and prostate cancer therapy as two driving exemplary applications. A piezoelectrically actuated electro-mechanical system is designed to provide precise needle placement in the bore of the scanner under interactive MRI-guidance, while overcoming the challenges inherent to MRI-guided procedures. This work presents the development of the robotic system in the aspects of requirements definition, clinical work flow development, mechanism optimization, control system design and experimental evaluation. A steerable needle is beneficial for interventional procedures with its capability to produce curved path, avoiding anatomical obstacles or compensating for needle placement errors. Two kinds of steerable needles are discussed, i.e. asymmetric-tip needle and concentric-tube cannula. A novel Gaussian-based ContinUous Rotation and Variable-curvature (CURV) model is proposed to steer asymmetric-tip needle, which enables variable curvature of the needle trajectory with independent control of needle rotation and insertion. While concentric-tube cannula is suitable for clinical applications where a curved trajectory is needed without relying on tissue interaction force. This dissertation addresses fundamental challenges in developing and deploying MRI-compatible robotic systems, and enables the technologies for MRI-guided needle-based interventions. This study applied and evaluated these techniques to a system for prostate biopsy that is currently in clinical trials, developed a neurosurgery robot prototype for interstitial thermal therapy of brain cancer under MRI guidance, and demonstrated needle steering using both asymmetric tip and pre-bent concentric-tube cannula approaches on a testbed

SEED LOCALIZATION IN IMAGE-GUIDED PROSTATE BRACHYTHERAPY INTRAOPERATIVE DOSIMETRY SYSTEMS

Prostate cancer is the most common cancer among men in the United States. Many treatments are available, but prostate brachytherapy is acknowledged as a standard treatment for patients with localized cancer. Prostate brachytherapy is a minimally invasive surgery involving the permanent implantation of approximately 100 grain-sized radioactive seeds into the prostate. While effective, contemporary practice of brachytherapy is suboptimal because it spreads the stages of planning, implant, and dosimetry over several weeks. Although brachytherapy is now moving towards intraoperative treatment planning (ITP) which integrates all three stages into a single day in the operating room,the American Brachytherapy Society states, “the major current limitation of ITP is the inability to localize the seeds in relation to the prostate.” While the procedure is traditionally guided by transrectal ultrasound (TRUS), poor image quality prevents TRUS from accurately localizing seeds to compute dosimetry intraoperatively. Alternative methods exist, but are generally impractical to implement in clinics worldwide. The subject of this dissertation is the development of two intraoperative dosimetry systems to practically solve the problem of seed localization in ITP. The first system fuses TRUS with X-ray fluoroscopy using the ubiquitous non-isocentric mobile C-arm.The primary contributions of this dissertation include an automatic fiducial and seed segmentation algorithm for fluoroscopic images, as well as a next generation intraoperative dosimetry system based on a fiducial with seed-like markers. Results from over 30 patients prove that both contributions are significant for localizing seeds with high accuracy and demonstrate the capability of detecting cold spots. The second intraoperative dosimetry system is based on photoacoustic imaging, and uses the already implemented TRUS probe to detect ultrasonic waves converted from electromagnetic waves generated by a laser. The primary contributions of this dissertation therefore also include a prototype benchtop photoacoustic system and an improved clinical version usable in the operating room. Results from gelatin phantoms, an ex vivo dog prostate, and an in vivo dog study reveal that multiple seeds are clearly visible with high contrast using photoacoustic imaging at clinically safe laser energies.Together, both systems significantly progress the latest technologies to provide optimal care to patients through ITP

Treatment planning study of cyberKnife prostate SBRT (stereotactic body radiation therapy) using CT-based vs MRI-based prostate volumes

This study has been conducted for the purpose of investigating the systematic dose reduction of rectum and neurovascular bundles (NVBs) during treatment planning of the CyberKnifeTM prostate SBRT using CT-Based volumes versus MRI-based volumes. Three prostate cancer patients were Planned for the CyberKnifeTM prostate SBRT and they underwent computed tomography (CT) and magnetic resonance imaging (MRI) preplanning exams. The patients were positioned during both exams using an immobilizing device. A radiation oncologist and a radiologist delineated the prostate gland, intra-prostatic and peri-prostatic structures, and pelvic organs of interest in both CT and MRI images. The CT and MRI images were fused based on fuducial markers to accurately align the prostate. Radiation Therapy Oncology protocol RTOG 0938 was followed to meet the target volume (prostate plus margin) dose coverage requirement, and dose-volume constraints for organs at risk, including rectum, bladder, femoral heads, penile bulb, urethra, skin and NVBs. Radiation dose volume parameters were recorded for both volumes and compared. The preliminary result shows that the CT-based volumes were generally larger than MRI-based volumes of the prostate. Therefore, the CT-based volumes resulted in less accurate treatment planning and dose delivery to radiosensitive structures

Treatment planning and dosimetric verification of cyberknife prostate SBRT (stereotactic body radiation therapy) on an MR-based 3D prostate model imaging insert in a pelvis phantom

Purpose of this study was to validate a novel CyberKnife stereotactic body radiotherapy (SBRT) treatment planning on an MRI-based 3D prostate model insert in an anthropomorphic pelvis phantom using Gafchromic EBT3 films to perform dosimetric measurements. The methodology of this study is based on a pelvis phantom and a physical printed 3D model of the prostate with dominant intra-prostatic-lesion and surrounding organs at risk segmented from a patient MR images. Cyberknife prostate treatment planning was performed to have at least 95% the planning target volumes (PTV: prostate expanded with margins of 5 mm in all directions except 3 mm posteriorly) covered by 3625 cGy (725x5) and a simultaneous dose escalation to 4750 cGy on the dominant intra-prostatic-lesion. Plan dosimetry verification was performed using Gafchromic EBT3 films on a Stereotactic Dose Verification Phantom. First, film calibration was done on Gafchromic EBT3 films exposed to various doses of 0-2500 cGy based on a LINAC (Trilogy) and CyberKnife monthly quality assurance (QA) for machine output calibration. Second, absolute dose measurements were taken by using films within the dose range 0-2250 cGy. Third, Gafchromic EBT3 films were placed in coronal and sagittal planes on the standard “blue phantom” or Stereotactic Dose Verification Phantom (SDVP) on which one fraction of the treatment plan is delivered for verification measurements. Then, on the prostate-pelvis phantom, a dosimetry inserts were used with films through the DIL region. After the calibration, the accuracy of absolute dose measurements with EBT3 was verified to be ≤ 1% in the dose range of interest (500-1500 cGy). On the SDVP phantom, comparison of films vs. plan for the coronal plane yielded ≥ 99.7% passing rates while for sagittal plane yielded ≥ 95.3% passing rates under the gamma criteria of ≤ 2% in dose and ≤ 2mm in distance to agreement (DTA). This study demonstrated that it is feasible to plan and deliver a SBRT treatment to prostate with a simultaneous dose escalation to the dominant intra-prostatic lesion

Teleoperation of MRI-Compatible Robots with Hybrid Actuation and Haptic Feedback

Image guided surgery (IGS), which has been developing fast recently, benefits significantly from the superior accuracy of robots and magnetic resonance imaging (MRI) which is a great soft tissue imaging modality. Teleoperation is especially desired in the MRI because of the highly constrained space inside the closed-bore MRI and the lack of haptic feedback with the fully autonomous robotic systems. It also very well maintains the human in the loop that significantly enhances safety. This dissertation describes the development of teleoperation approaches and implementation on an example system for MRI with details of different key components. The dissertation firstly describes the general teleoperation architecture with modular software and hardware components. The MRI-compatible robot controller, driving technology as well as the robot navigation and control software are introduced. As a crucial step to determine the robot location inside the MRI, two methods of registration and tracking are discussed. The first method utilizes the existing Z shaped fiducial frame design but with a newly developed multi-image registration method which has higher accuracy with a smaller fiducial frame. The second method is a new fiducial design with a cylindrical shaped frame which is especially suitable for registration and tracking for needles. Alongside, a single-image based algorithm is developed to not only reach higher accuracy but also run faster. In addition, performance enhanced fiducial frame is also studied by integrating self-resonant coils. A surgical master-slave teleoperation system for the application of percutaneous interventional procedures under continuous MRI guidance is presented. The slave robot is a piezoelectric-actuated needle insertion robot with fiber optic force sensor integrated. The master robot is a pneumatic-driven haptic device which not only controls the position of the slave robot, but also renders the force associated with needle placement interventions to the surgeon. Both of master and slave robots mechanical design, kinematics, force sensing and feedback technologies are discussed. Force and position tracking results of the master-slave robot are demonstrated to validate the tracking performance of the integrated system. MRI compatibility is evaluated extensively. Teleoperated needle steering is also demonstrated under live MR imaging. A control system of a clinical grade MRI-compatible parallel 4-DOF surgical manipulator for minimally invasive in-bore prostate percutaneous interventions through the patient’s perineum is discussed in the end. The proposed manipulator takes advantage of four sliders actuated by piezoelectric motors and incremental rotary encoders, which are compatible with the MRI environment. Two generations of optical limit switches are designed to provide better safety features for real clinical use. The performance of both generations of the limit switch is tested. MRI guided accuracy and MRI-compatibility of whole robotic system is also evaluated. Two clinical prostate biopsy cases have been conducted with this assistive robot