A Prototype Manipulator for Magnetic Resonance-Guided Interventions Inside Standard Cylindrical Magnetic Resonance Imaging Scanners

Abstract

The aim of this work is to develop a remotely controlled manipulator to perform minimally invasive diagnostic and therapeutic interventions in the abdominal and thoracic cavities, with real-time magnetic resonance imaging (MRI) guidance inside clinical cylindrical MR scanners. The manipulator is composed of a three degree of freedom Cartesian motion system, which resides outside the gantry of the scanner, and serves as the holder and global positioner of a three degree of freedom arm which extends inside the gantry of the scanner At its distal end, the arm's end-effector can carry an interventional tool such as a biopsy needle, which can be advanced to a desired depth by means of a seventh degree of freedom. These seven degrees of freedom, provided by the entire assembly, offer extended manipulability to the device and a wide envelope of operation to the user, who can select a trajectory suitable for the procedure. The device is constructed of nonmagnetic and nonconductive fiberglass, and carbon fiber composite materials, to minimize artifacts and distortion on the MR images as well as eliminate effects on its operation from the high magnetic field and the fast switching magnetic field gradients used in MR imaging. A user interface was developed for man-in-the-loop control of the device using real-time MR images. The user interface fuses all sensor signals (MR and manipulator information) in a visualization, planning, and control command environment. Path planning is performed with graphical tools for setting the trajectory of insertion of the interventional tool using multislice and/or three dimensional MR images which are refreshed in real time. The device control is performed with an embedded computer which runs real-time control software. The manipulator compatibility with the MR environment and image-guided operation was tested on a 1.5 T MR scanner.

A General-Purpose MR-Compatible Robotic System

“…The limited space inside a cylindrical MR scanner was addressed by performing a series of studies to analyze the available space above the human volunteers in the supine and prone position [14], [18]. Multislice sets of transverse and sagittal MR images were collected, and the available space was extracted with edge detection processing.…”

“…On the basis of the above space analysis studies and the design criteria for a general-purpose robot with sufficient maneuverability, we used a kinematic configuration that incorporates three orthogonal DoF (X, Y, and Z) for global positioning of an arm that carries an end effector and three rotational DoF for setting the Euler angles of access to a target [14], [15]. The end effector has an additional linear DoF (Δ) for the insertion of an interventional tool such as biopsy needles or thermal ablators.…”

“…Therefore, we implemented an MR-image-based safety check software component [14], [17]. At the beginning of a session, a set of transverse slices are also acquired to extract the boundaries of the subject via an edge detection algorithm based on the Canny method [20] and generate a 3-D mask of the subject's volume.…”

“…The seventh linear (Δ) DoF used for insertion is actuated manually using a cable-driven mechanism and a hand-held actuation device. Because the step of inserting a probe is preferentially performed with the operator by the side of the subject, this option provided the simplest mechanism that performed effectively in all studies [14], [17], [19]. …”

“…Several examples of MR-compatible manipulators have been developed, including a system for brain biopsies [5], two systems for breast interventions [6]- [8], one system for general use with the special "double-donut" scanners [9], [10], an endoscope positioner [11], two systems for prostate procedures [10], [12], and two general-purpose devices for use with standard cylindrical MR scanners [13], [14]. We review the development of a general-purpose robotic system at the Washington University for performing minimally invasive interventions with real-time MR guidance [14]- [17].Our motivation for this work originates from the essential features of MRI that both compliment and improve current diagnostic and therapeutic IGIs that use X-ray fluoroscopy, computed tomography, or ultrasound. A major advantage of MRI is that it is minimally invasive, both for the patient and the medical staff.…”