Significant progress has been made in the development of magnetic micromanipulation for minimally invasive surgery. The development of systems to localize millimeter-sized robots during magnetic manipulation without line-of-sight detection remains, however, a challenging task. In this study, we focused on the development of a tracking system aiming to fill this gap. A robot which consists of a cylindrical magnet of 1 mm diameter is localized using a 2D array of 3D magnetoresistive sensors. The system, also called magnetic field camera, provides tracking of the robot with a refresh rate of 2 Hz. The developed tracking algorithm reaches a mean absolute error for the position and the orientation of, respectively 0.56 mm and 5.13° in 2D. This system can be added to existing magnetic manipulation systems allowing closed loop control of the navigation. The performances of the magnetic field camera are not affected by an exposure to strong magnetic fields. Exposures up to 3 T have been validated. Increasing the integrability of the magnetic field camera into magnetic manipulation systems. The presented tracking system makes it possible to target applications such as minimally invasive eye surgery or drug delivery. The high spatial and magnetic resolutions allow the tracking of magnetic particles, down to 200 μm diameter, when placed close to the surface. The system could also be suitable for the localization of small objects for 2D biomanipulation.

This letter demonstrates the use of an field-programmable gate array and commercially available Hall effect magnetic field sensors to create a magnetic field camera offering high-speed capability for ac measurements. The achieved performance of the presented camera reaches 7 kHz of sampling rate over an array of 7 × 7 sensors, covering an area of 56 mm × 56 mm (31.36 cm ² ), synchronously sampled with a recording capability of up to 10 hours on X -, Y -, and Z -axes. The sensors exhibit a dynamic range of ± 266 mT, and a typical rms noise of 140 µT (peak-to-peak noise of 1 mT). Through its synchronous sampling capability and 7 kHz sampling rate, this camera fills a gap observed in the field of magnetic field cameras, in which mainly dc applications were addressed up to now. This opens the way to new metrological possibilities in several domains, ranging from industrial and physics applications to biomedical engineering.

This paper describes a 3D electromagnetic tracking (EMT) system, based on quasi-static magnetic fields and a sub-millimeter 3D magnetometer, providing complete localization – both spatial and angular positions – during surgical procedures. By integrating miniaturized sensors into surgical tools, such as deep brain stimulation (DBS) electrodes, this tracking system offers complementary or alternative solutions for X-ray imaging. Each spatial position in the measurement volume (MV) is uniquely encoded by a vector of four magnetic field amplitudes using the multilateration principle. The orientation is derived from the three orthogonal components associated with this vector. The field generator (FG) was manufactured on printed circuit boards ensuring high reproducibility and accurate magnetic fields. Position localization was evaluated using a custom magnetic field camera placed at various positions in the MV while the orientation was evaluating using a stereotactic system used in DBS surgery. Finally, DBS implantations were simulated to conclude on the validity of the tracking system for DBS surgery. The system achieved spatial and angular errors of 1.72 mm and 0.89° within a MV of 15 x 15 x 15 cm3 located at 18 cm from the FG and an update rate of the position of 0.4 Hz. Better performances – mean spatial and angular errors of 0.87 mm and 0.52° – were achieved when simulating DBS implantations. With its large distance to the FG, this quasi-static EMT system is particularly well-suited for DBS surgery, offering regular feedback to neurosurgeons. The tracking system could also be adapted to other functional neurosurgeries.

This paper demonstrates a new type of magnetic sensor using a perpendicular spin transfer torque magnetic tunnel junction. The sensing element has a cylindrical shape of 50 nanometers in diameter and is to our knowledge among the smallest magnetic sensor ever reported. This paper describes the principle of operation of the sensing element and the associated signal processing electronics, which delivers a signal proportional to the external magnetic field. Experimental results are detailed and compared to state-of-the-art commercially available integrated magnetic sensors as well as published magnetoresistive sensors based on magnetic tunnel junctions with comparable size. The measured sensitivity of the developed sensor is 1.28 V/T, and its dynamic range reaches 80 mT. The measured noise level is 21.8 μT/√Hz. Two different operating principles of the proposed sensor are described and compared, one based on a time-to-digital converter and one based on a pulse-width-modulated signal. Both methods require only standard microelectronics components, which are suitable for a monolithic integration of the sensing element with its conditioning electronics. Subsequent improvements of the sensing element as well as conditioning electronics are required to further lower the noise level. The sensing element and its conditioning electronics are compatible with fabrication processes already used in magnetic random-access memory fabrication. This opens the way to mass production and addresses various markets such as consumer electronics, automotive, industrial sensing, physics experiments or medical devices.

This paper presents a tracking system using magnetometers, possibly integrable in a deep brain stimulation (DBS) electrode. DBS is a treatment for movement disorders where the position of the implant is of prime importance. Positioning challenges during the surgery could be addressed thanks to a magnetic tracking. The system proposed in this paper, complementary to existing procedures, has been designed to bridge preoperative clinical imaging with DBS surgery, allowing the surgeon to increase his/her control on the implantation trajectory. Here the magnetic source required for tracking consists of three coils, and is experimentally mapped. This mapping has been performed with an in-house three-dimensional magnetic camera. The system demonstrates how magnetometers integrated directly at the tip of a DBS electrode, might improve treatment by monitoring the position during and after the surgery. The three-dimensional operation without line of sight has been demonstrated using a reference obtained with magnetic resonance imaging (MRI) of a simplified brain model. We observed experimentally a mean absolute error of 1.35 mm and an Euclidean error of 3.07 mm. Several areas of improvement to target errors below 1 mm are also discussed.