MR conditional prostate intervention systems and actuations review

Magnetic resonance imaging (MRI) has the ability to provide high-resolution images of soft tissues without the use of radiation. So much research has been focused on the development of actuators and robotic devices that can be used in the MRI environment so “real-time” images can be obtained during surgeries. With real-time guidance from MRI, robots can perform surgical procedures with high accuracy and through less invasive routes. This technique can also significantly reduce the operation time and simplify pre-surgical procedures. Therefore, research on robot-assisted MRI-guided prostate intervention has attracted a great deal of interest, and several successful clinical trials have been published in recent years, pointing to the great potential of this technology. However, the development of MRI-guided robots is still in the primary stage, and collaboration between researchers and commercial suppliers is still needed to improve such robot systems. This review presents an overview of MRI-guided prostate intervention devices and actuators. Additionally, the expected technical challenges and future advances in this field are discussed

Cycloidal Stepper Motor: A Systematic Approach for Designing a Nonmagnetic Rotary Actuator

Magnetic resonance imaging (MRI) has the ability to provide high-quality images of soft tissues and obtain the positions of surgical tools and target tissues, which is extremely useful in minimally invasive surgery. Hence, there is a significant need for surgical robots capable of working in the MRI environment, but designing MR-conditional actuators is one of the biggest obstacles to developing such robots. This article provides a novel approach to building pneumatic motors. A gear set design inspired by the curtate hypocycloid is applied for the motion of the rotor. The motor's operating principle and mechanical design, including rotor and housing, are presented. The relationship between different transmission ratios and motors is explored, showing that motors with more chambers and higher resolution can be obtained based on this hypocycloid. A physical prototype is made by three-dimensional printing and laser cutting, and the experimental data show that the presented motor can achieve a maximum speed of 2000 r/min and a torque of 11 mN·m

Design of a Square Rotor Driven Pneumatic Stepper Actuator for MR-Guided Therapy

Magnetic resonance (MR) imaging has been widely used in the diagnostics and treatment of soft tissues due to its ability to acquire high-resolution images with outstanding contrast. Therefore, MR-guided therapy and its supporting equipment, including MR-conditional sensors and actuators, have been developed rapidly. In this article, a nonmagnetic pneumatic stepper motor was developed. The working principle was analyzed, and the theoretical static output torque was expressed mathematically. The driven part of the proposed design is a polygon rotor derived from the Wankel engine. Besides, the outline of the inner wall of the housing was investigated. Experiments were conducted with the motor functioning at different speeds under different air pressures; by controlling the air in each chamber sequentially, the rotor can rotate continuously in dual directions with a torque of up to 38 mN·m and a maximum speed of 400 r/min. The MR test showed that no image artifact was found

Development of a Compact Piezoworm Actuator For Mr Guided Medical Procedures

In this research, a novel piezoelectric actuator was developed to operate safely inside the magnetic resonance imaging (MRI) machine. The actuator based on novel design that generates linear and rotary motion simultaneously for higher needle insertion accuracy. One of the research main objectives is to aid in the selection of suitable materials for actuators used in this challenging environment. Usually only nonmagnetic materials are used in this extremely high magnetic environment. These materials are classified as MRI compatible materials and are selected to avoid hazardous conditions and image quality degradation. But unfortunately many inert materials to the magnetic field do not possess desirable mechanical properties in terms of hardness, stiffness and strength and much of the available data for MRI compatible materials are scattered throughout the literature and often too device specific . Furthermore, the fact that significant heating is experienced by some of these devices due to the scanner’s variable magnetic fields makes it difficult to draw general conclusions to support the choice of suitable material and typically these choices are based on a trial-and-error with extensive time required for prototype development and MRI testing of such devices. This research provides a quantitative comparison of several engineering materials in the MRI environment and comparison to theoretical behavior which should aid designers/engineers to estimate the MRI compatible material performance before the expensive step of construction and testing. This work focuses specifically on the effects in the MRI due to the material susceptibility, namely forces, torques, image artifacts and induced heating

Sunram 7: An MR Safe Robotic System for Breast Biopsy

In breast cancer patients, some nodules are only visible on MRI, thus, requiring MRI-guidance to perform the biopsy. MRI interventions are cumbersome due to the magnetic field and the constrained working space. An MR safe robotic system actuated by pneumatic stepper motors may enable these procedures, improving both accuracy and image-guided navigation. A compact multipurpose pneumatic stepper motor has been designed with outer dimensions $(45 \times 40\times 15)\mathbf{mm}^{\mathbf{3}}$. This is configurable as a linear, rotational or curved stepper motor with a customizable step size and radius of curvature. Five copies of these motors actuate the Sunram 7 biopsy robot, of which the moving part (without protruding racks and tubes) measures $(130 \times 65\times 55)\mathbf{mm}^{\mathbf{3}}$. After manually choosing the target location and angle of approach, the needle is robotically inserted into the breast and the integrated pneumatic biopsy gun is fired to sample tissue from the lesion. The maximum torque of the presented motor is 0.61 N m at 6 bar which can be achieved using 13-teeth polycarbonate gears. Using 17-teeth gears for higher accuracy and a more convenient working pressure of 2 bar the maximum torque is 0.28 N m. The accuracy in free air of the Sunram 7 robot is 1.69mm and 1.72mm in X and Z-direction respectively, with a resulting 2-D error of 2.54 mm. The workspace volume is 4.1 L. When targeting 10 mm-sized lesions in phantoms under MRI guidance, Sunram 7 achieved a success rate of 68%. The minimum interval between two successive biopsies was 5:47 minutes. The presented multipurpose stepper motor has distinct advantages over previous designs in terms of robustness, customizability, printability and ease of integration in MR safe robotics. The Sunram 7 is able to perform accurate MRI-guided biopsies in a large workspace volume while reducing the intervention time when compared to the gold standard (i.e., MRI-guided free-hand biopsy)