Simultaneous 3D localization of multiple MR-visible markers in fully reconstructed MR images: proof-of-concept for subsecond position tracking

An inductively coupled ultra-thin, flexible, and passive RF resonator for MRI marking and guiding purposes: Clinical feasibility

PURPOSE

The purpose of this study is to develop a wireless, flexible, ultra-thin, and passive radiofrequency-based MRI resonant fiducial marker, and to validate its feasibility in a phantom model and several body regions.

METHODS

Standard microfabrication processing was used to fabricate the resonant marker. The proposed marker consists of two metal traces in the shape of a square with an edge length of 8 mm, with upper and lower traces connected to each other by a metalized via. A 3T MRI fiducial marking procedure was tested in phantom and ex vivo, and then the marker's performance was evaluated in an MRI experiment using humans. The radiofrequency safety was also tested using temperature sensors in the proximity of the resonator.

RESULTS

A flexible resonator with a thickness of 115 μm and a dimension of 8 × 8 mm was obtained. The experimental results in the phantom show that at low background flip angles (6-18°), the resonant marker enables precise and rapid visibility, with high marker-to-background contrast and signal-to-noise ratio improvement of greater than 10 in the vicinity of the marker. Temperature analysis showed a specific absorption ratio gain of 1.3. Clinical studies further showed a successful biopsy procedure using the fiducial marking functionality of our device.

CONCLUSIONS

The ultra-thin and flexible structure of this wireless flexible radiofrequency resonant marker offers effective and safe MR visualization with high feasibility for anatomic marking and guiding at various regions of the body. Magn Reson Med 80:361-370, 2018. © 2017 International Society for Magnetic Resonance in Medicine.

An MRI-powered and controlled actuator technology for tetherless robotic interventions

This paper presents a novel actuation technology for robotically assisted MRI-guided interventional procedures. In the proposed approach, the MRI scanner is used to deliver power, estimate actuator state and perform closed-loop control. The actuators themselves are compact, inexpensive and wireless. Using needle driving as an example application, actuation principles and force production capabilities are examined. Actuator stability and performance are analyzed for the two cases of state estimation at the input versus the output of the actuator transmission. Closed-loop needle position control is achieved by interleaving imaging pulse sequences to estimate needle position (transmission output estimation) and propulsion pulse sequences to drive the actuator. A prototype needle driving robot is used to validate the proposed approach in a clinical MRI scanner.