Electromagnetic sensing for real-time tracking for surgery

Abstract

Disclosed is an on-chip tracking sensor for an electromagnetic tracking system, that includes an on-chip sensor coil formed by stacking a plurality of metal layers, in the CMOS technology, and an ultra-low noise Analog Front End (AFE) operably coupled to the on-chip tracking sensor coil. The AFE comprises an instrumentation amplifier with an input referred noise (IRN) less than a predefined value to match up with a pre-defined resistance of the on-chip sensor coil, and a programmable gate amplifier (PGA) serially connected to the instrumentation amplifier for increasing signal strength of an output voltage of the Instrumentation amplifier.

Description

[0001] Title

[0002] Electromagnetic sensing for real-time tracking for surgery

[0003] Field

[0004] The present disclosure relates to electromagnetic tracking, and more specifically to an on-chip magnetic sensor and amplifier for electromagnetic tracking.

[0005] In recent years, significant advances in medicine have been made with the goal of reducing patient morbidity through innovations in endoscopic, optical imaging, laparoscopic, and robotic technology. However, most contemporary methods require the use of X-Ray fluoroscopy to achieve accurate localisation during realtime imaging procedures (such as endoscopy, bronchoscopy, and colonoscopy) and navigation during high precision surgery. These procedures take time and expose both the patient and the diagnostic team to high levels of ionizing radiation. The electromagnetic tracking (EMT) system is a breakthrough in reducing ionizing radiation.

[0006] Electromagnetic tracking (EMT) is a critical technology for tracking and navigation in image-guided interventions, when there is no line of sight to the target. Clinical applications which currently exploit EMT for virtual navigation include bronchoscopy, neurosurgery and ear, nose and throat surgery. In general, an EMT system relies on two main components: a field generator, which generates a spatially dependent magnetic field, and a magnetic sensor, which, by field measurement, can determine its relative position and orientation with respect to the field generator. One of the two components is fixed, while the other needs to be tracked.

[0007] An EMT system is typically based on Faraday’s law to induce a voltage in a search coil. The EM tracking generally operates with magnetic fields from multiple sources that are spatially varying functions. The flux at a given point is detected, which may be resolved to a 5 degrees of freedom (DOF) position and orientation. Once the flux has been measured, the position and orientation of the sensor can be determined by using a non-linear least squares algorithm such as the Levenberg-Marquardt (LM) method. For convergence of the algorithm, the number of magnetic sources should be greater than or equal to the degrees of freedom, i.e., n > 5. However, the dimensions of existing inductive sensor coils put a constraint on the mechanical design of the instrument and spatial resolution of the sensor. The sensor must be rigid (non-flexible) typically for 10 mm. Otherwise, there is a risk of a sensor breakage due to the instrument bending. Moreover, the induced voltage from the sensor transmitted through the long cable, which introduces additional noise and decreases the accuracy of the system.

[0008] In the clinical setting without visual line-of-sight, electromagnetic tracking is the gold standard for instrument tracking and navigation. While clinical platforms for interventional bronchoscopy, colonoscopy, ENT surgery, and neurosurgical navigation are available, the limited flexibility and high costs of electromagnetic tracking (EMT) systems for research investigations preclude a better understanding of the technology's characteristics and limitations. Typical discrete sensors used for electromagnetic tracking cost around 10-30 EUR per unit at present depending on volume of production. The geometric constraints of current rigid-tip sensors also impose limits on the mechanical flexibility of the instrument’s tip. There is also a mechanical constraint on the usable wire width for existing discrete inductor sensors which mean that further miniaturisation is very challenging.

[0009] In view of the above, there is a need for an on-chip sensor solution for electromagnetic navigation that provides cost-effectiveness, improved signal integrity, and sensor miniaturisation.

[0010] According to the invention there is provided, as set out in the appended claims, an on-chip tracking sensor for an electromagnetic tracking system, manufactured in the CMOS technology. The on-chip tracking sensor includes an on-chip sensor coil formed by stacking a plurality of metal layers of different widths, in the CMOS technology; and an ultra-low noise Analog Front End (AFE) operably coupled to the on-chip tracking sensor coil, wherein the AFE comprises: a low-noise instrumentation amplifier with an input referred noise (IRN) less than a predefined value to match up with a pre-defined high resistance of the on-chip sensor coil.

[0011] In an embodiment of the present invention, the AFE further comprises a programmable gain amplifier (PGA) serially connected to the low-noise instrumentation amplifier for increasing signal strength of an output voltage sensed by the on-chip sensor coil.

[0012] In an embodiment of the present invention, the low noise instrumentation amplifier is a Capacitive coupled chopper instrumentation amplifier (CCIA).

[0013] In an embodiment of the present invention, the AFE is an Analog to Digital Converter (ADC).

[0014] In an embodiment of the present invention, the on-chip sensor coil is one of: a single layer, a multi-layer stacked, and a multi-layer unstacked inductor.

[0015] In an embodiment of the present invention, the on-chip sensor coil includes one or more layers of metal tracks with varied or same width and number of turns on each layer.

[0016] In an embodiment of the present invention, the on-chip sensor coil has a high sensitivity to time-varying magnetic fields typical of those used in electromagnetic navigation systems. In an embodiment of the present invention, the on-chip sensor coil has high- permeability material deposited or added in proximity to the on-chip coil to increase the coil’s sensitivity by increasing the flux linkage through the centre of the on-chip sensor coil.

[0017] In an embodiment of the present invention, the on-chip sensor coil includes one or more layers of wide and thick metals at a top portion and one or more layers of thin metals at a bottom portion, with varied width and number of turns on each layer.

[0018] In an embodiment of the present invention, the on-chip tracking sensor has high- permeability material deposited or added in proximity to the on-chip coil to increase the coil’s sensitivity by increasing the flux linkage through the centre of the on-chip sensor coil.

[0019] In an embodiment of the present invention, the CCIA architecture includes a current reuse input operational amplifier that includes a pair of differential inputs, wherein each differential input terminal includes a low leakage thick oxide gate device biased independently with a pseudo resistor of order of Giga ohms.

[0020] In an embodiment of the present invention, the IRN of the CCIA architecture is proportional to noise gains of pmos and nmos of differential input pairs, and inversely proportional to transconductance of pmos and nmos terminals of differential input pairs, and wherein the noise gain of a differential input pair is proportional to corresponding input, feedback and gate parasitic capacitances.

[0021] In an embodiment of the present invention, the CCIA architecture makes it possible to optimize the gate parasitic capacitance (Cgs ) of each input pair separately, which further reduces noise gains (? ). Without the dual loop architecture, the differential pair's input terminal will have gate parasitic capacitance from nmos and poms, which will increase noise gain, which is not the case in our scenario. In the proposed architecture, nmos and pmos are biased and coupled to Cin independently. To optimize noise gain, the parasitic gate capacitance of each nmos and pmos can be tuned relative to its Cin.

[0022] In an embodiment of the present invention, the DC offset voltage from the sensor coil is filtered out by a high pass filter formed by an input capacitance Cin and bias pseudo resistor of corresponding differential input.

[0023] In another aspect of the present invention, there is provided an Electromagnetic Tracking (EMT) system for image guided surgery of a patient. The EMT system includes the on-chip tracking sensor used around or inside a patient’s body. The EMT system further includes a multi-channel sinusoidal magnetic field generator placed under or beside the patient in the operating volume of the on-chip tracking sensor, for generating time-varying AC magnetic fields which vary throughout the operating volume, wherein the on-chip tracking sensor generates a filtered and amplified voltage, an instrumentation amplifier for amplifying an output voltage of the on-chip tracking sensor, a data acquisition unit for digitising an output voltage of the instrumentation amplifier, and a computing device for converting the digitised output voltage to a position and orientation of the on-chip tracking sensor.

[0024] In an embodiment of the present invention, the on-chip tracking sensor provides either a continuous or discontinuous digital or analogue output voltages or currents using either a wired or wireless connection between any two or more of the following stages; the instrumentation amplifier, the data acquisition unit, or the computing device.

[0025] In an embodiment of the present invention, the sinusoidal magnetic field generator generates at least six and no more than twelve transmit frequencies with steps of 100 Hz and 4kHz between 100 Hz and 100 kHz.

[0026] Various embodiments of the present invention provide an on-chip (sensor and analog front end) solution to EMT system that significantly reduces the overall sensor size and enhances performance. The sensor is in form of a multi-layer inductor with high magnetic field sensitivity and SNR, and that contains multiple turns on different layers which results in benefits in improved sensitivity and SNR. The design of the sensor is fully compatible with the standard CMOS process with ultra-thick metal (UTM) to minimise the resistivity of the inductor. This approach does not require any complex differential structures. The on-chip sensor has extremely small size which is beneficial for biomedical in-vivo applications. The chip sensor achieves improved sensitivity by the usage of top (thick) metals multilayer inductor with varied width and number of turns on each layer without the need of stacking the metals which brings more parasitic capacitance. The tracking sensor has been optimized to efficiently capture the magnetic field, so it maximises area within the constraints available and has a relatively small resistance due to the number and width of turns optimization. The on-chip tracking sensor has a rectangular shape which enables to capture more magnetic flux. Also, the long, rectangular design provides an ease of use at the tip of flexible medical catheters or needle-tips. In the present approach, different metal widths and spacing are used to find a trade-off between the sensitivity and resistivity of the coil. The prior art sensors are mainly focused on increasing inductance and reducing parasitic parameters of the inductor within a small volume. The on-chip tracking sensor of the present invention provides relatively small resistance despite the large area due to the optimized width, the number of turns and the number of layers used.

[0027] Adding extra contacts to the metal layers increases the parasitic capacitance of the coil. The present on-chip tracking sensor uses wide and thick metals to resistance , but the number of turns is high enough to obtain good sensitivity to the magnetic field. The on-chip tracking sensor has reduced cost, high scalability, improved signal integrity, and reduced size. The on-chip tracking sensor may also be augmented by the addition of high permeability magnetic material in proximity to the on-chip inductor. High permeability material in proximity to the on-chip inductor can help increase the flux linkage through on-chip inductor, thus increasing the sensitivity of the tracking sensor. Further, the on-silicon sensing addresses the need for low-cost, scalable production costs by leveraging the scalability of on-chip CMOS technology processes. The on-chip sensor flexibility is also significantly improved as the geometry can be optimised to the specific application.

[0028] There is also provided a computer program comprising program instructions for causing a computer program to carry out the above method which may be embodied on a record medium, carrier signal or read-only memory.

[0029] Brief Description of the Drawings

[0030] The invention will be more clearly understood from the following description of an embodiment thereof, given by way of example only, with reference to the accompanying drawings, in which:-

[0031] FIG.1 illustrates a conventional EMT system that includes a signal generator circuit for providing a reference sine wave for each emitter coil channel;

[0032] FIG.2A illustrates a die micrograph of a tracking sensor chip, in accordance with an embodiment of the present invention;

[0033] FIG.2B illustrates the installation of the tracking sensor chip in a tool within the patient’s body, in accordance with an embodiment of the present invention;

[0034] FIG.3 illustrates a circuit-level diagram of the tracking sensor chip, in accordance with an embodiment of the present invention;

[0035] FIGs.4A-4C illustrate the sensor coil of the tracking sensor chip, in accordance with an embodiment of the present invention;

[0036] FIG.5A and 5B illustrate the CCIA architecture of the AFE of the tracking sensor chip, in accordance with an embodiment of the present invention; FIGs. 6-8 illustrate the IRN, measured gain, and the measured linearity of the tracking sensor chip respectively, in accordance with an embodiment of the present invention;

[0037] FIG.9 illustrates an accuracy test set-up of the tracking sensor chip using a grid of Lego Duplo blocks, in accordance with an embodiment of the present invention;

[0038] FIG.10 illustrates a plot showing the grid of tests points used to determine the accuracy of the tracking sensor chip; FIGs. 1 1 A-11 D illustrate the accuracy test results of the accuracy test setup, in accordance with an embodiment of the present invention;

[0039] FIG. 12 illustrates the spectrum response showing the eight magnetic tones generated between 20-34 kHz in steps of 2 kHz;

[0040] FIG.13 illustrates the magnetic field generated by the 8 transmitter coils was measured at five grids of 81 points for two sensor orientations;

[0041] FIG.14 illustrates cumulative distribution function of the position error calculated at test points; and

[0042] FIG.15 illustrates the accuracy of resolved sensor position calculated from 810 test points.

[0043] Detailed Description of the Drawings

[0044] FIG.1 illustrates a conventional EMT system 100 that includes a signal generator circuit for providing a reference sine wave for each emitter coil channel. The signal is amplified and transmitted through the field generator coil array. A tracking sensor coil produces an induced alternating voltage due to the field generator. The sensed signal is amplified and sampled. The resulting samples are demodulated and processed through the position and orientation algorithm to yield a position and orientation vector or the tracking sensor coil.

[0045] FIG.2A illustrates a die micrograph of a tracking sensor chip 200 that integrates the functions of the tracking sensor coil, sensor amplifier and data acquisition on a single miniaturised chip, in accordance with an embodiment of the present invention. The tracking sensor chip 200 is manufactured using CMOS technology, and consists of an on-chip tracking sensor coil 202 and a Low Noise Analog Front End (AFE) 204.

[0046] FIG.2B illustrates the installation of the tracking sensor chip 200 in a patient’s body. The tracking sensor chip 200 may be installed in the patient’s body for electromagnetic navigation during image guided surgery, endoscopy, robotic surgery, and the like. The tracking sensor chip 200 may be hereinafter also referred to as an on-chip magnetic sensor and amplifier. The tracking sensor chip 200 may be embedded within to a long flexible device (i.e. catheter) that is inserted into the patient. The tracking sensor chip 200 may be connected to an external electronics unit 206 that includes an 8-channel sinusoidal magnetic field generator 207 which in this embodiment contains 8 transmitting channels, an instrumentation amplifier 208, and a data acquisition card 209. The external electronics unit 206 is communicatively coupled to a computing device 208 through wired or wireless means.

[0047] The 8-channel sinusoidal magnetic field generator 207 is shown to be placed below the patient which generates a multi-tone magnetic field which varies throughout the operating volume. The eight transmitter coils of the sinusoidal magnetic field generator 207 generate time-varying AC magnetic fields. When placed in the working volume of the field generator, the tracking sensor chip 200 receives a time-varying voltage signal, which is a superposition of voltages caused by each emitter coil's time-varying magnetic field.

[0048] The magnetic field of the magnetic field generator 207 varies with distance. The tracking sensor chip 200 may move significantly (up to 50 cm depending on the clinical case), which varies the magnetic field greatly, and so does the voltage induced by the sensor coil of the chip 200. As a result, the sensor coil is required to be with a high Dynamic Range (DR). In one scenario, the magnetic field generated by the magnetic field generator may be around 150nT and the sensor coil 202 of the chip 200 may generate an induced sensor voltage whose amplitude is very low, on the order of microvolts (nV), and must be filtered and amplified before sampling. The AFE 204 includes an on-chip ultra-low noise amplifier circuit for preparing the output of the sensor coil 202 for sampling.

[0049] The instrumentation amplifier 208 amplifies the signal from the tracking sensor chip 200, the data acquisition card 209 digitises the amplified signal, and the computing device 210 converts the measured voltage to position and orientation through software such as Python. It is to be noted that both the tracked sensor signal and the emitter (transmitter) current sense signal are superpositions of eight frequency components, each of which is induced by a transmitter board. The magnitude and phase of each frequency component can be measured using synchronous demodulation in software. It should be noted that synchronous demodulation schemes are also possible using time-based rather than frequency based approaches. Each frequency component's magnitude and phase information are fed into the position and orientation algorithm. In an example, the sinusoidal magnetic field generator 207 generates eight transmit frequencies with steps of 2 kHz between 20 and 34 kHz and a drive current of approximately 100mA in each emitter / transmitter coil. The data may be sampled by the AFE 204 at 200 kHz and 10000 samples may be used per pose estimate, yielding a 20 Hz update rate.

[0050] FIG.3 illustrates one circuit-level diagram of the tracking sensor chip 200 in accordance with an embodiment of the present invention. The tracking sensor chip 200 includes an on-chip sensor coil 202, a Capacitive coupled chopper instrumentation amplifier (CCIA) 204, and a programmable gate amplifier (PGA) 206. The CCIA 204, and the PGA 206 constitutes the AFE 204. The on-chip sensor coil 202 has been explained in detail with reference to FIGs.4A-4C. The CCIA 204 has been explained in detail with reference to FIGs. 5A and 5B. The PGA 206 can be implemented using any amplifier architecture, which uses programmable gain to increase signal strength as input voltage ranges from few pV to 1 mV.

[0051] FIG.4A illustrates a 3-D structure of the on-chip sensor coil 202. FIG.4B illustrates stacking of multiple metal layers in the on-chip sensor coil 202 using CMOS technology. FIG.4C illustrates a cross-sectional view of the on-chip sensor coil 202 in accordance with an embodiment of the present invention. The on-chip sensor 202 may be implemented as a multi-layer low-resistance inductor, and is of rectangular shape. The on-chip sensor 202 achieves improved sensitivity by the usage of thick metals at top and thin metals at bottom with varied width and number of turns on each layer without the need of stacking the metals which brings more parasitic capacitance. The wide and thick metals are used at top to minimise resistance, but the number of turns is high enough to obtain good sensitivity to the magnetic field. The multilayer stacking improves sensor coil sensitivity by increasing the area of metal traces as well as the amount of field captured by increasing the effective cross-sectional area within a given region. The on-chip sensor 202 uses Metal Layers M8, M9 and M10 arranged in stacked fashion, implemented to maximize sensitivity and minimize resistance in a given area. This method allows to capture more flux by increasing the effective cross- sectional area without increasing the area of the inductor on a die. Due to the rectangular shape and bigger area (1200 pm x 450 pm), the on-chip sensor 202 can capture more magnetic fields.

[0052] Referring back to FIGs.2 and 3, the on-chip sensor 202 has a resistance of 1 .3kQ, corresponding to noise 4.6 nV / Hz based on the structure illustrated in FIGs.4A- 4C. Therefore, the input referred noise (IRN) of the AFE 204 must not exceed this value and a target of IRN less than 2nV / ^Hz is desired to meet the system accuracy requirements. To meet the challenging IRN specifications, the AFE 204 includes a new CCIA architecture 304. This current reuse topology doubles the effective input-referred transconductance without increasing the bias current allowing a new state-of-the-art to be achieved. FIG.5A illustrates the CCIA architecture 304 in detail, in accordance with an embodiment of the present invention. The CCIA architecture 304 includes a current reuse input operational amplifier 502. FIG.5B illustrates the transistor level implementation of the current reuse input operational amplifier 502. As shown in FIG.5B, the current reuse input operational amplifier 502 is biased with pseudo resistors Rpd. The meeting the challenging IRN specification requires that all noise sources must be minimized. Large biasing pseudo resistors (Rpd>1 G) were implemented (FIG. 5B) to reduce noise. The 65nm CMOS process has non-zero gate currents which cause beta noise and can also cause large offsets with the GQ bias resistors. This problem is reduced by employing low gate leakage thick oxide gate devices (M1 -M4) as differential inputs biased separately with pseudo resistors. The ac coupling and dual loop topology allows these thick gate oxide devices (M1 -M4) to be operated from a 1 .2V supply. A disadvantage of the thick oxide input devices is the larger gate capacitance (Cgs) Large CCIA input capacitors (Cin) will be required to reduce the noise gain(q) penalty caused by the input pair's parasitic capacitance (Cgs) The CCIA architecture 304 makes it possible to optimize the parasitic capacitance (Cgs) of each input pair separately, which further reduces noise gains?;) (q) the need for a large input capacitor (Cin)

[0053] Referring to FIG.5A, the optimized IRN of the CCIA architecture 304 can be expressed as where qnand qp are the noise gain of nmos and pmos, k is the Boltzmann constant, T is temperature in kelvin, gmpand gmnare transconductance of pmos and nmos of differential input pairs,, Cin, Cfb and Cgsare input, feedback and gate parasitic capacitance. Upon optimising the trade-off between increasing the gm / Idratio of input pairs and the increasing of ?] due to increasing Cgsleads to gm / Id~ 20 (where gm is transconductance of transistor and Id is drain current) for the final design and a drain current of 1 mA with Cin set to 1 1 .6pF.

[0054] The offsets can be a limitation in CCIAs but for this work, as the induced voltage in the sensor is of the order of pV, so any DC offset from the sensors (order of nV) would not saturate the system and will be filtered out by the high pass filter formed by the input capacitance Cin and bias pseudo resistor RPd (with high pass corner <10Hz) . The input voltage of order of pV, causes a pA order current while chopping, removing the need for input impedance optimization technique. Since this sensor is designed for use inside the human body, temperature can be considered relatively stable as constant around (37°C). The DC input impedance of the chopper-stabilized CCIA when modulated with a 500kHz chopping frequency is >100kQ. Additional drawbacks with chopper amplifiers is a ripple at the output caused by the up-modulated OTA offset and flicker noise which can be eliminated at the output by connecting the first and second OTA stages with a DC-blocking impedance. To ensure stable DC biasing, a large pseudo resistor Rpd is placed at the second OTA stage's inputs.

[0055] Thus, referring to FIGs.2A and 2B, the sensor coil 202 and the AFE 204 may be fabricated in a 65nm CMOS technology. The total power drawn from a 1 .2V supply may be 5.6mW, the area may be 0.9mm2and IRN measured may be 1 .2 nV / Hz. The measured value of the sensitivity and resistance of the sensor coil 202 were 2.04e-04 V / Hz / T and 1.3kQ respectively. FIG.6 illustrates the IRN of the tracking sensor 202 with respect to the frequency of operation. FIG.7 illustrates the measured gain (with high pass corner) of the tracking sensor 202 with respect to the frequency of operation. FIG.8 illustrates measured linearity of the tracking sensor 202 with respect to the frequency.

[0056] FIG.9 illustrates an accuracy test set up which includes a grid of Lego Duplo blocks used to precisely move the tracking sensor 200 in known increments for accuracy analysis. The sensor 200 under test is attached to the blocks as shown. The eight coil field generator array is shown along with the power amplifier and sensor interface necessary to measure the received signal. Eight transmit frequencies have been used with steps of 2 kHz between 20 and 34 kHz and a drive current of approximately 100mA is used in each coil of the planar magnetic field generator. Data has been sampled at 200 kHz and 10000 samples have been used per pose estimate, yielding a 20 Hz update rate.

[0057] The accuracy of the tracking sensor chip 200 may be determined by recording a grid of measurements and comparing to the true mechanical positions of the sensor holder. The Lego Duplo blocks have been used to gather the grid of measurements. 243 test points were recorded in a 9 x 9 x 3 grid at intervals of 15.9 mm on each layer and 38.4mm between layers. The tests are repeated with two different sensor orientations giving a total of 486 test points. The position error is defined as the error between the measured grid of points and its ideal grid when both grids are aligned using Horns Absolute Orientation algorithm. At each test point, the data is averaged for 2 seconds with the sensor sampled at 20Hz.

[0058] FIG.10 illustrates a plot showing the grid of tests points used to determine the accuracy of the system. The relative position of the planar field generator coils is also shown.

[0059] The nominal accuracy of the system has resulted in approximately 2mm and 1 degree for position and orientation estimates respectively. Table I illustrates the results for the accuracy measurements, the mean, RMS and standard deviation of the errors.

[0060] FIG.1 1 A illustrates the position accuracy across the recorded test points plotted against distance from the centre of the field generator. FIG.1 1 B illustrates the angular accuracy across the recorded test points plotted against distance from the centre of the field generator. FIG.1 1 C illustrates the cumulative distribution function showing the statistical spread of the recorded positions. FIG.1 1 D illustrates the position noise or jitter of the sensor, as the sensor moves away from the field generator, noise increases as the SNR decreases.

[0061] FIG. 12 illustrates the spectrum response showing the eight magnetic tones generated between 20-34 kHz in steps of 2 kHz. The constant sinusoidal current in each field generator coil is shown on the top spectrum, while the corresponding sensor spectrum is shown on the bottom spectrum. The sensor spectrum varies with position and orientation relative to the field generator.

[0062] The embodiments in the invention described with reference to the drawings comprise a computer apparatus and / or processes performed in a computer apparatus. However, the invention also extends to computer programs, particularly computer programs stored on or in a carrier adapted to bring the invention into practice. The program may be in the form of source code, object code, or a code intermediate source and object code, such as in partially compiled form or in any other form suitable for use in the implementation of the method according to the invention. The carrier may comprise a storage medium such as ROM, e.g. a memory stick or hard disk. The carrier may be an electrical or optical signal which may be transmitted via an electrical or an optical cable or by radio or other means.

[0063] In the specification the terms "comprise, comprises, comprised and comprising" or any variation thereof and the terms include, includes, included and including" or any variation thereof are considered to be totally interchangeable, and they should all be afforded the widest possible interpretation and vice versa.

[0064] The invention is not limited to the embodiments hereinbefore described but may be varied in both construction and detail.

Claims

Claims:

1. An on-chip tracking sensor for an electromagnetic tracking system, manufactured in CMOS technology, comprising: an on-chip sensor coil formed by stacking a plurality of metal layers of different widths, in the CMOS technology; and an ultra-low noise Analog Front End (AFE) operably coupled to the on-chip tracking sensor coil, wherein the AFE comprises: a low-noise instrumentation amplifier with an input referred noise (IRN) less than a predefined value to match up with a pre-defined high resistance of the on-chip sensor coil.

2. The on-chip tracking sensor as claimed in claim 1 , wherein the AFE further comprises: a programmable gain amplifier (PGA) serially connected to the low-noise instrumentation amplifier for increasing signal strength of an output voltage sensed by the on-chip sensor coil.

3. The on-chip tracking sensor as claimed in claim 1 , wherein the low noise instrumentation amplifier is a Capacitive coupled chopper instrumentation amplifier.

4. The on-chip tracking sensor as claimed in claim 1 , wherein the AFE is an Analog to Digital Converter (ADC).

5. The on-chip tracking sensor as claimed in claim 1 , wherein the on-chip sensor coil is one of: a single layer, a multi-layer stacked, and a multi-layer unstacked inductor.

6. The on-chip tracking sensor as claimed in claim 1 , wherein the on-chip sensor coil includes one or more layers of metal tracks with varied or same width and number of turns on each layer.

7. The on-chip tracking sensor as claimed in claim 1 , wherein the on-chip sensor coil has a high sensitivity to time-varying magnetic fields typical of those used in electromagnetic navigation systems.

8. The on-chip tracking sensor as claimed in claim 1 , wherein the on-chip sensor coil has high-permeability material deposited or added in proximity to the on-chip coil to increase the coil’s sensitivity by increasing the flux linkage through the centre of the on-chip sensor coil.

9. An Electromagnetic Tracking (EMT) system for image guided medical interventions of a patient, comprising: the on-chip tracking sensor as claimed in claim 1 a multi-channel sinusoidal magnetic field generator placed in the operating volume of the on-chip tracking sensor, for generating timevarying AC or pulsed DC magnetic fields which vary throughout the operating volume, wherein the on-chip tracking sensor generates a filtered and amplified voltage; an instrumentation amplifier for amplifying an output voltage of the on-chip tracking sensor; a data acquisition unit for digitising an output voltage of the instrumentation amplifier; and a computing device for converting the digitised output voltage to a position and orientation of the on-chip tracking sensor.

10. The EMT system as claimed in claim 9, wherein the on-chip tracking sensor provides connection between any two or more of the following stages; the instrumentation amplifier, the data acquisition unit, or the computing device.

11. The EMT system as claimed in claim 9, wherein the sinusoidal magnetic field generator generates at least six and no more than twelve transmit frequencies with steps of between 100 Hz and 4 kHz between 1 and 100 kHz.

Images