Triaxial MRI-Compatible Fiber-optic Force Sensor

Abstract

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.

MRI-VisAct: a Bowden-cable-driven MRI-compatible series viscoelastic actuator

“…As a consequence, only the bending torques along the direction of the shaft can result in significant deflections of the compliant element, as shown in Figure 4. This way, cross-coupling of forces and moments on the sensor, a parasitic effect suffered by many optical force sensors developed for MR environment (Tan et al 2011), can be largely avoided. By adjusting their geometric parameters, the bending stiffness of the leaf springs are designed to be compliant enough to result in large enough deflections that can be measured with sufficient resolution to estimate interaction torques with high fidelity, and large enough to render targeted torque levels and to achieve desired motion/torque control bandwidths from the device.…”

A novel MRI compatible soft tissue indentor and fibre Bragg grating force sensor

“…This is sufficient for application to (non- Other researchers have developed more complex tri-axial force sensor systems (e.g. [14,31,32,45]) for MRI. However the uniaxial force measurements presented here ensured a simple and compact indentor design and are sufficient for comparison to inverse FEA as the same resultant uniaxial force can easily be generated as an output.…”

Towards the Development of a Master-Slave Surgical System for Breast Biopsy under Continuous MRI

“…Fig. 1 shows the needle (which is a substitute for a biopsy needle) attached to the fiber-optic force sensor [16]. The parallel mechanism uses three pneumatic cylinders as both structural components and actuators and provides two needle rotational DOFs and one translational DOF.…”

“…To further ensure needle rotation elimination, the plastic fixing tube is attached to the outside of the fixture, into which the fixing pin is press-fitted and it mates with the customized groove on the needle. The needle driver attaches to the parallel mechanism at its fixture through a previously developed MRI-compatible fiber-optic force sensor [16] that is used to sense the needle insertion force. This force sensor is mounted on the mobile platform of the parallel mechanism, as shown in Fig.…”