This paper presents the design and control of an MRI-compatible 1-DOF needle driver robot and its precise position control using pneumatic actuation with long transmission lines. MRI provides superior image quality compared to other imaging modalities such as CT or ultrasound, but imposes severe limitations on the material and actuator choice (to prevent image distortion) due to its strong magnetic field. We are primarily interested in developing a pneumatically actuated breast biopsy robot with a large force bandwidth and precise targeting capability during radio-frequency ablation (RFA) of breast tumor, and exploring the possibility of using long pneumatic transmission lines from outside the MRI room to the device in the magnet to prevent any image distortion whatsoever. This paper presents a model of the entire pneumatic system. The pneumatic lines are approximated by a first order system with time delay, because its dynamics are governed by the telegraph equation with varying coefficients and boundary conditions, which cannot be solved precisely. The slow response of long pneumatic lines and valve subsystems make position control challenging. This is further compounded by the presence of non-uniform friction in the device. Sliding mode control (SMC) was adopted, where friction was treated as an uncertainty term to drive the system onto the sliding surface. Three different controllers were designed, developed, and evaluated to achieve precise position control of the RFA probe. Experimental results revealed that all SMCs gave satisfactory performance with long transmission lines. We also performed several experiments with a 3-DOF fiber-optic force sensor attached to the needle driver to evaluate the performance of the device in the MRI under continuous imaging.
Inhibitory control dysfunction is regarded as a core feature in addicts. The major objective of this study was to explore the time course of response inhibition in chronic heroin addicts and provide the neurophysiological evidence of their inhibitory control dysfunction. The amplitudes and latencies of ERP components were studied in fourteen heroin addicts (mean duration of heroin use being (13.54+/-5.71) years (Mean+/-SD), average abstinence being ((4.67+/-6.44) months)) and fourteen matched healthy controls with a visual Go/Nogo task. Our results showed that heroin addicts demonstrated significantly larger Go-N2 amplitudes which results in a decreased N2 Go/Nogo effect, but no statistically significant differences were found between heroin addicts and controls in P3. The ERP data suggest that fronto-central areas of heroin addicts were impaired during the inhibition process (200-300 ms) and over-activated to targets. The impaired early process might reflect an abnormal conflict monitoring process in heroin addicts. These results consolidate the inhibitory control dysfunction hypothesis in chronic heroin users.
Magnetic Resonance Imaging (MRI) provides superior soft-tissue contrast in cancer diagnosis compared to other imaging modalities. However, the strong magnetic field inside the MRI bore along with limited scanner bore size poses significant challenges. Since current approaches in breast biopsy using MR images is primarily a blind targeting approach, it is necessary to develop a MRI-compatible robot that can avoid multiple needle insertions into the breast tissue. This MRI-compatible robotic system could potentially lead to improvement in the targeting accuracy and reduce sampling errors. A master-slave surgical system has been developed comprising of a MRI-compatible slave robot which consists of one piezo motor and five pneumatic cylinders connected by long pneumatic transmission lines. The slave robot follows the configuration of the master robot, which provides an intuitive manipulation interface for the physician and operates inside the MRI bore to adjust the needle position and orientation and perform needle insertion task. Based on the MRI experiments using the slave robot, there was no significant distortion in the images and hence the slave robot can be safely operated inside the MRI with minimal loss in signal-to-noise ratio (SNR). Ex vivo and in vivo experiments have been conducted to evaluate the performance of the master-slave surgical system.
Magnetic resonance imaging (MRI) has been gaining popularity over standard imaging modalities like ultrasound and CT because of its ability to provide excellent soft-tissue contrast. However, due to the working principle of MRI, a number of conventional force sensors are not compatible. One popular solution is to develop a fiber-optic force sensor. However, the measurements along the principal axes of a number of these force sensors are highly cross-coupled. One of the objectives of this paper is to minimize this coupling effect. In addition, this paper describes the design of elastic frame structures that are obtained systematically using topology optimization techniques for maximizing sensor resolution and sensor bandwidth. Through the topology optimization approach, we ensure that the frames are linked from the input to output. The elastic frame structures are then fabricated using polymers materials, such as ABS and Delrin®, as they are ideal materials for use in MRI environment. However, the hysteresis effect seen in the displacement-load graph of plastic materials is known to affect the accuracy. Hence, this paper also proposes modeling and addressing this hysteretic effect using Prandtl-Ishlinskii play operators. Finally, experiments are conducted to evaluate the sensor’s performance, as well as its compatibility in MRI under continuous imaging.
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