Needle Placement in MRI Systems

Robotic needle manipulators have been developed for assisted interventions in open-bore MRI [16,17], which uses split magnets that leave room for large remote manipulators to be used. Compared to closed-bore MRI, open-bore MRI operate at lower magnetic fields (1.5 versus 3.0 Teslas) and has significantly lower resolution. Image quality of open-bore MRI is not detailed enough or suitable for accurately treating a tumor on the order of 5 mm [18]. 

Closed-bore MRI manipulation requires actuators with excellent MRI compatibility because of their proximity to the image center. Piezoelectric motors have been reported to cause image distortion in closed-bore MRI [19]. Piezoelectric motors are also relatively slow, complex and expensive. Manipulators using pneumatics have had limited success in conjunction with closed-bore MRI [20, 21]. The main drawbacks to this approach are control issues due to the imprecision and compliance of pneumatics. Recent advances have been made using pneumatic stepper motors to eliminate these effects [22]. However, pneumatic systems, using continuous cylinders or step motors, tend to be complex and expensive. 

Compared to other actuation alternatives, DBAs have a huge potential for closed-bore MRI manipulation. They have excellent MRI compatibility, offer good performance and are simple and low cost. The binary manipulator system presented in the next section is an illustration of a potential future practical MRI manipulator using DBAs. 

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