Patent Description:
Magnetic resonant imaging (MRI) scanners utilize magnetic fields, magnetic field gradients, and radio waves to generate a series of images of a patient. In order to focus on the relevant images, the MRI scanner may use a gating or trigger-mechanism. One such mechanism can be an electrocardiogram (ECG). An ECG signal includes a number of waves, segments, complexes, and intervals. In particular, the R-wave is often used to gate MRI image collection, storage, and/or transmission.

In an MRI environment, the gradients produced by the MRI scanner can induce a potential on the vascular system of the patient as their blood circulates, known as the magnetohydrodynamic (MHD) effect. The MHD effect can amplify or distort the T-wave of an ECG signal to the degree that an MRI gating mechanism may confuse the amplified or distorted T-wave for an R-wave. Thus, the MHD can lead to gating errors in MRI gated imaging. Accordingly, there is a need in the art for improved systems for gating MRI image collection based on ECG signals captured in an MRI environment.

United States patent application <CIT> discloses a device for synchronizing a magnetic resonance unit with the cardiac rhythm of a patient, comprising a number of electrodes for leading off electrocardiogram signals from the body of the patient and an evaluation unit for determining a characteristic trigger time within a cardiac rhythm period of the patient from the electrocardiogram signals. The device allows reliable determination of characteristic trigger times within the cardiac rhythm period of the patient even with elevated magnetic field strengths and which operates at least largely independently of external magnetic field by comparing electrocardiogram signals obtained before and after the introduction of the patient into the magnetic resonance unit, in order to determine an enlargement of at least one characteristic of the electrocardiogram signals due to the magnetic field.

European patent application <CIT> discloses a magnetic resonance tomography (MRT) apparatus for the examination of a body comprises parameter acquisition devices for the acquisition of cardiovascular parameters of the body and a control device in communication with the parameter acquisition devices for synchronizing the imaging, wherein the control device is adapted to analyze the data of at least two parameter acquisition devices and to output a control signal based on the analysis.

The journal article <NPL>, discloses that accurate synchronization between magnetic resonance imaging data acquisition and a subject's cardiac activity ("triggering") is essential for reducing image artifacts but conventional, contact-based methods for this task are limited by several factors, including preparation time, patient inconvenience, and susceptibility to signal degradation. It further discloses to evaluate the performance of a new contact-free triggering method developed with the aim to eventually replace conventional methods in non-cardiac imaging applications. The method's performance is evaluated in the context of <NUM> Tesla non-enhanced angiography of the lower extremities. This journal publication further discloses a basic algorithm capable of estimating in real-time the phase of the cardiac cycle from reflection photoplethysmography signals obtained from skin color variations of the forehead recorded with a video camera. Instead of finding the algorithm's parameters heuristically, they were optimized using videos of the forehead as well as electrocardiography and pulse oximetry signals that were recorded from eight healthy volunteers in and outside the scanner, with and without active radio frequency and gradient coils. Based on the video characteristics, synthetic signals were generated, and the "best available" values of an objective function were determined using mathematical optimization. The performance of the proposed method with optimized algorithm parameters was evaluated by applying it to the recorded videos and comparing the computed triggers to those of contact-based methods. Additionally, the method was evaluated by using its triggers for acquiring images from a healthy volunteer and comparing the result to images obtained using pulse oximetry triggering.

The present disclosure is directed generally to systems and methods for correcting an electrocardiogram (ECG) signal impacted by the magnetohydrodynamic (MHD) effect. The MHD effect occurs due to a patient undergoing magnetic resonant imaging (MRI). The systems and methods derive patient information (such as heart rate) from images captured by a camera, and use this patient information to calculate a T-wave correction factor. This T-wave correction factor is used to counteract the amplification or distortion of the T-wave due to the MHD effect. An MRI scanner may then use the corrected ECG signal for more accurate gated imaging.

The system includes an MRI scanner, an ECG monitor, an MRI-compatible camera, and an image processing unit (IPU). While the patient undergoes an MRI scan, the ECG monitor captures an ECG signal for the patient. At the same time, the camera captures a series of images of the patient. The series of images captured by the camera are provided to the IPU. The IPU processes the images to derive patient information to calculate a T-wave correction factor. The IPU then attenuates the amplitude (or otherwise compensates for the distortion) of the T-wave of the captured ECG signal based on the T-wave correction factor to generate a corrected ECG signal. This corrected ECG signal is then used by the MRI scanner for more accurate gated imaging, as the adjusted T-wave is no longer confused with an R-wave.

Generally, in one aspect, an MRI gating system is provided. The MRI gating system includes an ECG monitor. The ECG monitor is configured to capture an ECG signal of a patient.

The MRI gating system further includes a camera. The camera is configured to capture a series of patient images. According to an example, the camera is a high frame rate camera or a vital signs camera. According to a further example, the camera has a frame rate of at least <NUM>,<NUM> frames per second.

According to an example, the series of patient images capture a neck area of the patient.

The MRI gating system further includes an image processing unit. The image processing unit (IPU) is configured to determine a T-wave correction factor. The T-wave correction factor is determined based on the series of patient images. According to an example, the T-wave correction factor is further based on a patient heart rate derived from the series of patient images.

According to an example, the T-wave correction factor is further based on a diameter of a carotid artery. Further, the T-wave correction factor may be further based on a blood flow velocity in the carotid artery.

According to an example, the T-wave correction factor is further based on a magnetic field incident upon the patient. In this example, the magnetic field may be generated by the MRI scanner.

According to an example, the T-wave correction factor is further based on an angle between a magnetic field incident upon the patient and a direction of the blood flow in the carotid artery.

The IPU is further configured to generate a corrected ECG signal. The corrected ECG signal is generated based on the captured ECG signal and the T-wave correction factor.

The MRI gating system further includes an MRI scanner. The MRI scanner is configured to generate a gated MRI image set. The gated MRI image set is generated based on the corrected ECG signal. According to an example, the MRI scanner generates the gated MRI image set further based on one or more R-waves of the corrected ECG signal.

Generally, in another aspect, an MHD effect correction system for an ECG signal is provided. The MHD effect correction system includes a camera configured to capture a series of patient images. The MHD effect correction system further includes an image processing unit configured to (<NUM>) determine a T-wave correction factor based on the series of patient images and (<NUM>) generate a corrected ECG signal based on the ECG signal and the T-wave correction factor.

Generally, in another aspect, a method for correcting an ECG signal for an MHD effect is provided. The method includes capturing, via a camera, a series of patient images. The method further includes determining, via a processor, a T-wave correction factor based on the series of patient images. The method further includes generating, via the processor, a corrected ECG signal based on a captured ECG signal and the T-wave correction factor. According to an example, the method further includes capturing, via an ECG monitor, the captured ECG signal. According to an example, the method further includes generating, via a magnetic resonating image (MRI) scanner, a gated MRI image set based on the corrected ECG signal.

In various implementations, a processor or controller may be associated with one or more storage media (generically referred to herein as "memory," e.g., volatile and non-volatile computer memory such as RAM, PROM, EPROM, EEPROM, floppy disks, compact disks, optical disks, magnetic tape, SSD, etc.). In some implementations, the storage media may be encoded with one or more programs that, when executed on one or more processors and/or controllers, perform at least some of the functions discussed herein. Various storage media may be fixed within a processor or controller or may be transportable, such that the one or more programs stored thereon can be loaded into a processor or controller so as to implement various aspects as discussed herein. The terms "program" or "computer program" are used herein in a generic sense to refer to any type of computer code (e.g., software or microcode) that can be employed to program one or more processors or controllers.

These and other aspects of the various embodiments will be apparent from and elucidated with reference to the embodiment(s) described hereinafter.

Also, the drawings are not necessarily to scale, emphasis instead generally being placed upon illustrating the principles of the various embodiments.

The present disclosure is directed generally to systems and methods for correcting an electrocardiogram (ECG) impacted by the magnetohydrodynamic (MHD) effect. The MHD effect occurs due to a patient undergoing magnetic resonant imaging (MRI). The systems and methods derive patient information (such as heart rate) from images captured by a camera, and use this patient information to calculate a T-wave correction factor. This T-wave correction factor is used to counteract the amplification of the T-wave due to the MHD effect. An MRI scanner may then use the corrected ECG signal for more accurate gated imaging.

The system includes an MRI scanner, an ECG monitor, an MRI-compatible camera, and an image processing unit (IPU). While the patient undergoes an MRI scan, the ECG monitor captures an ECG signal for the patient. At the same time, the camera captures a series of images of the patient. The camera can be a high frame-rate camera or vital signs camera aimed at the neck area of the patient. More specifically, the camera can be aimed at one of the carotid arteries of the patient.

The series of images captured by the camera are provided to the image processing unit. The IPU processes the images to derive patient information to calculate the T-wave correction factor. The IPU can also receive aspects of the patient information from other sources. Prior to deriving the patient information, the image processing unit may stabilize and/or de-noise one or more of the patient images.

First, the IPU determines a heart rate of the patient based on the patient images. The heart rate is determined by analyzing the skin proximate to the carotid artery of the patient. The IPU can use the heart rate of the patient to determine the velocity of the blood flowing through the carotid artery. The IPU also receives and/or derives information regarding the diameter of the carotid artery.

The IPU also receives information regarding the magnetic field generated by the MRI scanner. Specifically, this information can include the magnitude of the magnetic field, as well as the angle between the magnetic field and the direction of blood flow. The magnetic field information can be provided by a sensor, or it can be provided to the IPU directly from the MRI scanner.

The IPU uses the aforementioned information to calculate a T-wave correction factor. The IPU then attenuates the amplitude of the T-wave of the captured ECG signal based on the T-wave correction factor to generate a corrected ECG signal. This corrected ECG signal is then used by the MRI scanner for more accurate gated imaging, as the adjusted T-wave is no longer confused with an R-wave.

<FIG> shows a system diagram for an MRI gating system <NUM>. The MRI gating system <NUM> generates a gated MRI image set <NUM> based on a corrected ECG signal <NUM>. The corrected ECG signal <NUM> is generated by IPU <NUM> based on patient images <NUM>, captured by camera <NUM>, and an ECG signal <NUM> captured by an ECG monitor <NUM>.

A patient <NUM> is inserted into the bore of an MRI scanner <NUM>. In some examples, the entire patient <NUM> enters the bore; in other examples, only the relevant portion of the patient (head, limb, etc.) enters the bore. The MRI scanner <NUM> uses magnetic fields, magnetic field gradients, and radio waves to generate a series of MRI images of the patient <NUM>.

While the patient <NUM> is inserted in the MRI scanner <NUM> and undergoing MRI scans, ECG monitor <NUM> captures ECG signals <NUM> corresponding to the patient <NUM>. The ECG signals <NUM> may be based on one or more leads connected to one or more electrodes placed on the patient <NUM>. The ECG monitor <NUM> may be positioned inside or outside of the MRI scanner <NUM>, depending on the application. As depicted in <FIG>, the ECG signal <NUM> conveyed from the ECG monitor <NUM> to the IPU <NUM> has an amplified T-wave due to the MHD effect.

Also, while the patient <NUM> undergoes MRI scanning, a camera <NUM>, positioned inside the MRI scanner <NUM>, captures a series of patient images <NUM>. The camera <NUM> may be a high frame rate camera, such as a camera with a frame rate of at least <NUM>,<NUM> frames per second. Alternatively, the camera <NUM> may be a vital signs camera. As shown in <FIG>, the camera <NUM> may be arranged to capture images <NUM> of the patient's neck area <NUM>, including one of the patient's carotid arteries <NUM>.

The MRI gating system <NUM> further includes an IPU <NUM>. The IPU <NUM> is in wired or wireless communication with the MRI scanner <NUM>, the ECG monitor <NUM>, and the camera <NUM>. The IPU receives patient images <NUM> from the camera <NUM>, ECG signals <NUM> from the ECG monitor <NUM>, and information regarding the magnetic field <NUM> from the MRI scanner <NUM>. Alternatively, the information regarding the magnetic field <NUM> may be captured and conveyed to the IPU <NUM> via a sensor positioned within the MRI scanner <NUM>. The combination of the IPU <NUM> and the camera <NUM> may be considered an MHD effect correction system <NUM>.

The primary purpose of the IPU <NUM> is to calculate the T-wave correction factor <NUM> for an ECG signal <NUM>. The T-wave correction factor <NUM> is applied to the ECG signal <NUM> to compensate for the amplified T-wave due to the MHD effect. An example T-wave correction algorithm <NUM> is shown as equation <NUM> below: <MAT>.

In equation <NUM>, U is the voltage induced by the MHD effect, |B| is the magnitude <NUM> of the magnetic field <NUM> incident upon the patient <NUM> during MRI scanning, |v| is the blood flow velocity <NUM> through the carotid artery <NUM> of the patient <NUM>, d is the diameter <NUM> of the carotid artery <NUM>, and q is the angle <NUM> between the lines of the magnetic field <NUM> and the blood flow direction <NUM> in the carotid artery <NUM>. In this example, U is the T-wave correction factor <NUM>. Further in this example, d is orthogonal to B and v. In other examples, U may be further processed to determine the T-wave correction factor <NUM>. The value of the T-wave correction factor <NUM> may then be subtracted from the T-wave of the ECG signal <NUM> to generate the corrected ECG signal <NUM>.

Upon receiving the series of patient images <NUM>, the IPU <NUM> may pre-process the images <NUM> using de-noising and/or frame stabilization algorithms <NUM>. Once the images <NUM> have been pre-processed, the IPU <NUM> further processes the images <NUM> to determine the heart rate <NUM> of the patient <NUM>. The patient heart rate <NUM> can be determined by analyzing the movement of the patient's skin around one of their carotid arteries <NUM> via the images <NUM> captured by a high frame rate camera <NUM>.

The IPU <NUM> can also use the patient heart rate <NUM> to determine the blood flow velocity <NUM>. Blood flow velocity <NUM> may be determined in a number of ways, such as factoring in the patient's blood pressure.

The diameter <NUM> of the carotid artery <NUM> may be provided to the IPU <NUM> by patient records or by a medical professional operating the MRI gating system <NUM>. In further examples, the diameter <NUM> of the carotid artery <NUM> can be derived from the patient images <NUM>.

The magnitude <NUM> of the magnetic field <NUM> incident upon the patient <NUM>, as well as the angle <NUM> between the magnetic field <NUM> and the blood flow direction <NUM> in the carotid artery, may be provided to the IPU <NUM> directly by the MRI scanner <NUM> or via a sensor within the MRI scanner <NUM>.

Once the IPU <NUM> has either received or determined all of the variables of equation <NUM>, the IPU <NUM> then determines the T-wave correction factor <NUM>. An example T-wave correction factor <NUM> may be less than or equal to <NUM> mV. In one example, the IPU <NUM> then determines the corrected ECG signal <NUM> by subtracting the T-wave correction factor <NUM> from the captured ECG signal <NUM>. In other examples, performs additional calculations with the T-wave correction factor <NUM> and the captured ECG signal <NUM> to generate the corrected ECG signal <NUM>. As shown in <FIG>, the corrected ECG signal <NUM> has a T-wave of a typical amplitude.

The corrected ECG signal <NUM> is then provided to the MRI scanner <NUM> for gated imaging. In gated imaging, the MRI scanner <NUM> continually generates MRI images, but only stores and/or transmits MRI images corresponding to a gating event or trigger. In one example, the MRI scanner <NUM> generates one or more gated images <NUM> based on the R-waves <NUM> of the corrected ECG signal <NUM>. Accordingly, each of the gated images <NUM> corresponds to an R-wave <NUM> of one cycle of the ECG signal <NUM>. Applying the T-wave correction factor <NUM> to the ECG signal <NUM> prevents the MRI scanner <NUM> from confusing the amplified T-waves with R-waves <NUM>, thus preventing gating and/or triggering errors.

In one example, the MRI scanner <NUM> provides the gated images <NUM> to a user interface <NUM> for display. The user interface <NUM> may be an aspect of the MRI scanner <NUM> itself, or it may be a component of a stand-alone device, such as a personal computer. The MRI scanner <NUM> may be in wired or wireless communication with the user interface <NUM>. In a further example, the gated images may be stored in a memory of the MRI scanner and/or a memory of a stand-alone device, such as a personal computer or a network server.

<FIG> shows an illustration of some aspects of the MRI gating system, including an MRI scanner <NUM>, camera <NUM>, and ECG monitor <NUM>. The patient <NUM> is inserted into the bore of the MRI scanner <NUM> along with the camera <NUM>. While the patient undergoes MRI scanning, the camera <NUM> captures a series of patient images <NUM> of the neck area <NUM> of the patient <NUM> (which may include one of the patient's carotid arteries <NUM>). Also during the MRI scan, the ECG monitor <NUM> captures an ECG signal <NUM>. As shown in <FIG>, this ECG signal <NUM> has an amplified T-wave during MRI scanning due to the MHD effect.

<FIG> shows a schematic of the IPU <NUM>. The IPU <NUM> includes a processor <NUM> for executing T-wave correction algorithm <NUM> (such as equation <NUM>), as well as the de-noising and/or frame stabilization algorithms. The IPU <NUM> further includes memory <NUM> for storing data received by the other components of the MRI gating system <NUM> and/or generated by the processor <NUM>. The IPU <NUM> further includes transceiver <NUM> for communicating (unidirectionally or bidirectionally) with camera <NUM>, ECG monitor <NUM>, and MRI scanner <NUM>.

Generally, in another aspect, and with reference to <FIG>, a method <NUM> for correcting an ECG signal for an MHD effect is provided. The method <NUM> includes capturing <NUM>, via a camera, a series of patient images. The method <NUM> further includes determining <NUM>, via a processor, a T-wave correction factor based on the series of patient images. The method <NUM> further includes generating <NUM>, via the processor, a corrected ECG signal based on a captured ECG signal and the T-wave correction factor. According to an example, the method <NUM> further includes capturing <NUM>, via an ECG monitor, the captured ECG signal. According to an example, the method <NUM> further includes generating <NUM>, via a magnetic resonating image (MRI) scanner, a gated MRI image set based on the corrected ECG signal.

The above-described examples of the described subject matter can be implemented in any of numerous ways. For example, some aspects may be implemented using hardware, software or a combination thereof. When any aspect is implemented at least in part in software, the software code can be executed on any suitable processor or collection of processors, whether provided in a single device or computer or distributed among multiple devices/computers.

The present disclosure may be implemented as a system, a method, and/or a computer program product at any possible technical detail level of integration.

Computer readable program instructions for carrying out operations of the present disclosure may be assembler instructions, instruction-set-architecture (ISA) instructions, machine instructions, machine dependent instructions, microcode, firmware instructions, state-setting data, configuration data for integrated circuitry, or either source code or object code written in any combination of one or more programming languages, including an object oriented programming language such as Smalltalk, C++, or the like, and procedural programming languages, such as the "C" programming language or similar programming languages. In some examples, electronic circuitry including, for example, programmable logic circuitry, field-programmable gate arrays (FPGA), or programmable logic arrays (PLA) may execute the computer readable program instructions by utilizing state information of the computer readable program instructions to personalize the electronic circuitry, in order to perform aspects of the present disclosure.

Aspects of the present disclosure are described herein with reference to flowchart illustrations and/or block diagrams of methods, apparatus (systems), and computer program products according to examples of the disclosure.

The computer readable program instructions may be provided to a processor of a, special purpose computer, or other programmable data processing apparatus to produce a machine, such that the instructions, which execute via the processor of the computer or other programmable data processing apparatus, create means for implementing the functions/acts specified in the flowchart and/or block diagram block or blocks. These computer readable program instructions may also be stored in a computer readable storage medium that can direct a computer, a programmable data processing apparatus, and/or other devices to function in a particular manner, such that the computer readable storage medium having instructions stored therein comprises an article of manufacture including instructions which implement aspects of the function/act specified in the flowchart and/or block diagram or blocks.

The flowchart and block diagrams in the Figures illustrate the architecture, functionality, and operation of possible implementations of systems, methods, and computer program products according to various examples of the present disclosure.

Other implementations are within the scope of the following claims and other claims to which the applicant may be entitled.

Claim 1:
A magnetohydrodynamic (MHD) effect correction system (<NUM>) for an electrocardiogram (ECG) signal (<NUM>), the system being characterized by comprising:
a camera (<NUM>) configured to capture a series of patient images (<NUM>); and
an image processing unit (<NUM>) configured to:
determine a T-wave correction factor (<NUM>) based on the series of patient images (<NUM>); and
generate a corrected ECG signal (<NUM>) based on the ECG signal (<NUM>) and the T-wave correction factor (<NUM>).