IMPLANTABLE MEDICAL DEVICE CONFIGURED TO DETECT THE PRESENCE OF MRI MACHINE - Patent application

Abstract

The implantable medical device (1) includes a sensing device (103) for sensing a magnetic field (M) and a processing device (101) configured to detect the presence of an MRI device (3) based on measurements (S) obtained from the sensing device (103). The processing device (101) is configured to conclude that an MRI device (3) is present when a plurality of measurements (S) indicate an increase in the strength of the magnetic field (M). Furthermore, the sensing device (103) is configured to take measurements at a specific frequency between 1 Hz and 50 Hz, particularly 4 Hz, and to provide measurements (S) at a predetermined sampling rate.

Description

[Technical field]

[0001] The present invention relates to an implantable medical device as defined in the preamble of claim 1 and to a method for operating an implantable medical device. [Background technology]

[0002] An implantable medical device is configured for implantation in a patient. An implantable medical device in this context may be, for example, a pacemaker device for providing pacing action of the patient's heart, or a defibrillator device, such as an implantable cardioverter defibrillator (ICD), for providing defibrillation, or a sensor device having sensing functionality, for example, for monitoring the patient's cardiac activity. An implantable medical device may also be a recording device, such as a loop recorder, or a transmitting device for transmitting a signal to a device external to the patient, or a data carrier, such as a patient identification device.

[0003] Such an implantable medical device includes a sensing device for sensing the magnetic field and a processing device configured to detect the presence of the MRI device based on measurements obtained from the sensing device.

[0004] An implantable medical device (e.g., a stimulator such as a pacemaker or defibrillator device) is generally configured to output electrical stimulation energy for therapeutic stimulation. The implantable medical device may also be configured to sense electrical signals associated with (e.g., cardiac activity) in order to trigger and clock the stimulation, among other things. When the implantable medical device is introduced into the magnetic field of an MRI device, electrical signals are induced in the leads and other conductive parts of the implantable medical device, and such electrical signals are believed to disrupt the operation of the medical device. For example, in the case of an implantable medical device in the form of a pacemaker or defibrillator device, disruption of the stimulation may cause erroneous stimulation and thus have a significant impact on the patient's treatment, which must be avoided.

[0005] There is therefore a need to detect whether a patient carrying an implantable medical device is in the vicinity of an MRI machine and, in this case, be able to alter the operation of the medical device to reduce the risk of malfunction of the implantable medical device.

[0006] Patent Document 1 discloses an implantable medical device including a power source, a sensing device, and / or a stimulating device. The MR detection unit can identify typical changes in MR of the implantable medical device on a patient bed of an MRI device based on the time-dependent changes in the measurements of at least two magnetic field sensors and the difference between the measurements of the at least two magnetic field sensors. Here, the presence of the MRI device is assumed if the measurements of the at least two magnetic field sensors exceed a threshold value.

[0007] US Patent No. 5,999,333 discloses an implantable medical device having a first magnetic field direction sensor disposed at a first location within a housing and configured to generate a signal representative of a first direction of a magnetic field at the first location, and a second magnetic field direction sensor disposed at a second location within the housing and configured to generate a signal representative of a second direction of the magnetic field at the second location. Based on the signals obtained via the first and second magnetic field direction sensors, the presence of an MRI device is concluded.

[0008] Typically, an implantable medical device is configured to electromagnetically interact with an external device, such as a programming or triggering device, that is placed outside the patient's body and can be brought into the vicinity of the implantable medical device. Electromagnetic interaction between the external device and the implantable medical device can establish communication between the implantable medical device and the external device, for example, to program the implantable medical device or to transfer data from the implantable medical device to the external device.

[0009] The implantable medical device must be configured to be able to distinguish between an external device that interacts with the implantable medical device and another magnetic device (in particular an MRI device) that may cause disruption of the operation of the implantable medical device and therefore needs to be detected so that the operation of the implantable medical device can be appropriately altered to reduce the risk of malfunction of the implantable medical device. [Prior art documents] [Patent documents]

[0010] [Patent Document 1] U.S. Pat. No. 9,364,663 [Patent Document 2] U.S. Pat. No. 9,981,124 Summary of the Invention [Problem to be solved by the invention]

[0011] It is an object of the present invention to provide an implantable medical device and a method of operating an implantable medical device that allows reliable detection of the presence of an MRI device in an easy to implement manner. [Means for solving the problem]

[0012] This object is achieved by an implantable medical device having the features of claim 1.

[0013] Thus, the processing unit of the implantable medical device is configured to conclude that an MRI device is present if the multiple measurements indicate an increase in magnetic field strength.

[0014] MRI machines use a strong, constant magnetic field, e.g., having a nominal field strength of greater than 1 T (e.g., 1.5 T, 3 T, or 7 T). By superimposing the constant magnetic field with a time-varying gradient magnetic field, a magnetic resonance effect is induced that can be detected using an RF detection coil to pick up signals within the patient's body to perform imaging of the patient.

[0015] Now, when a patient undergoes an MRI examination, the patient is typically placed on a patient bed of the MRI machine, and the body part to be examined is positioned inside the bore of the MRI machine by moving the patient bed into the bore of the MRI machine.

[0016] When a patient carrying an implantable medical device such as a cardiac stimulation device undergoes an MRI examination, the implantable medical device must be able to detect that the patient is approaching the MRI device so that the operation of the implantable medical device can be appropriately modified to reduce the risk of the MRI device (especially the strong magnetic field of the MRI device) affecting the operation of the implantable medical device. If it is detected that the patient is within the magnetic field of the MRI device, the sensing function of the implantable medical device, for example, for triggering or clocking a stimulation operation, can be turned off so that the device can be operated in a mode that does not use sensing of electrical activity in the region of interest (e.g., the patient's heart) (e.g., in the so-called VV0 mode of a pacemaker device) so that a therapy (e.g., a pacing operation) is performed without clocking based on an external sensing signal. Additionally or alternatively, a therapy function (e.g., a shock function of a defibrillator device) can be turned off so that a (false) shock during the MRI examination is avoided.

[0017] To detect whether a patient carrying an implantable medical device is in the vicinity of an MRI machine, measurements from a sensing device that detects a magnetic field are examined, and if a plurality of measurements obtained from the sensing device of the implantable medical device are found to indicate an increase in strength of the magnetic field, the patient may be placed on a patient bed of the MRI machine and moved into the bore of the MRI machine by moving the patient bed at a substantially constant speed.

[0018] When a patient is placed on the patient bed of an MRI machine and the patient bed is moved into the bore of the MRI machine, the magnetic field strength at the location of the implanted medical device steadily increases as the patient is moved into the MRI machine. This steady increase in magnetic field strength at the location of the implanted medical device can be observed by monitoring the sensing device measurements. When multiple time-offset measurements indicate an increase in magnetic field strength, it can be concluded that the patient is being moved into the MRI machine, which can appropriately alter the operation of the implanted medical device.

[0019] Thus, by observing measurements obtained from the sensing device and determining whether there is an increase in magnetic field strength indicative of a steady movement of the patient into the MRI device, a situation in which a patient moves into the MRI device can be distinguished from a situation in which an external device other than the MRI device (e.g., a programming device, etc.) is brought near the implanted medical device to interact with the implanted medical device. When a patient undergoes an MRI examination, the operation of the implanted medical device needs to be monitored to avoid malfunction. Instead, when an external device is brought near the implanted medical device, potentially communication with the external medical device is established or a specific function of the implanted medical device is triggered, for example, the external device provides a wake-up signal to the implanted medical device.

[0020] In one embodiment, the sensing device is configured to provide measurements at a predefined sampling rate. For example, the sensing device can be used to take measurements at a particular frequency (e.g., a frequency between 1 Hz and 50 Hz (e.g., 4 Hz)) such that the sensing device outputs (discrete) measurements at the predefined sampling rate. The measurements are input to a processing device which analyzes the measurements and if multiple measurements indicate a (steady) increase in magnetic field strength, the presence of an MRI device is concluded.

[0021] The sensing device may output measurements indicative of the magnetic field strength, where the measurements may be output as numerical values, each corresponding to a particular voltage value (e.g., 1 mV). Because the sensing device may have a non-linear characteristic curve, the voltage value may indicate a particular change in magnetic field strength in a non-linear manner (depending on the magnetic field strength).

[0022] In one embodiment, the processing device is configured to conclude that an MRI device is present if a number of successive measurements show an increase in the strength of the magnetic field, and thus, if an increase in the strength of the magnetic field is found for successive measurements, it is concluded that the patient is moved into the MRI device, and thus the MRI device is identified.

[0023] For example, if for several consecutive measurements, an increase in the strength of the magnetic field is detected for each measurement by more than a certain margin, a conclusion can be made about the presence of an MRI device. Thus, if for several consecutive measurements, the magnetic field strength increases by at least a certain margin for each measurement, it can be concluded that an MRI device is present, for example because the strength of the magnetic field is found to steadily increase due to the patient bed moving into the MRI device. Alternatively or in combination, the presence of an MRI device can be concluded if the magnetic field increases without significant decrease over a certain number of consecutive measurements.

[0024] In one embodiment, the processing device is configured to increment the counter value if the measurements indicate an increase in the strength of the magnetic field. Here, for example, the processing device may be configured to increment the counter value if the measurements indicate an increase in the strength of the magnetic field that exceeds a predefined count threshold. Thus, each time a measurement obtained from the sensing device indicates that the strength of the magnetic field has changed by a certain minimum margin corresponding to the count threshold, the counter value is incremented, and the counter value counts the number of times the measurements indicate a substantial increase in the magnetic field strength.

[0025] Here, the counter value may be incremented by 1 from an initial starting value (e.g., 0) if the measurement indicates an increase in magnetic field strength beyond a first margin. Then, for each increment, if a subsequent measurement indicates an increase in magnetic field strength beyond a second margin corresponding to the count threshold, the counter value is again incremented by 1 to indicate the number of measurement occasions that exceeded the count threshold. The first margin may be greater than the second margin. If the measurement values ​​are output numerically, the first margin may correspond to a value of, for example, 2 to 5 numerical values ​​(e.g., 3 numerical values) and the second margin corresponding to the count threshold may correspond to a value of, for example, 1 to 3 numerical values ​​(e.g., 2 numerical values).

[0026] Thus, the counter value is derived from the measurements: the counter value in each case is incremented by one (if applicable) for each measurement taken from the sensing device, regardless of the actual increase in magnetic field strength.

[0027] According to one embodiment of the invention, the processing device is configured to decrement the counter value if the measurements indicate a decrease in the strength of the magnetic field, the decrease exceeding a predefined countdown threshold, for example if the measurements are output as numbers, the countdown threshold may correspond to a decrease of two or three numbers.

[0028] According to one embodiment of the present invention, the counter value cannot fall below zero.

[0029] The counter can be decremented by one or more count values ​​(e.g., 2, 3, etc.) in one step. By selecting a higher decrement count value, the counter will be decremented faster. If the processing unit is configured to perform a particular action related to the counter decrement (e.g., pending detection of the presence of an MRI device or returning the implantable device from MRI mode to normal operation), setting a higher decrement value (i.e., after a small number of counter decrements) will trigger that action more quickly than if a smaller decrement value had been selected.

[0030] In one embodiment, the processing device is configured to conclude that an MRI device is present if the counter value is incremented a predetermined number of times (e.g., a predetermined consecutive number of times) (more than once, preferably more than twice). The predetermined number of times may, for example, have a value between 2 and 20 (e.g., 5). If the counter value is found to be steadily increasing a predetermined (consecutive) number of times, it is concluded that an MRI device is present since a steadily increasing magnetic field strength at the location of the implantable medical device has been found.

[0031] Additionally or alternatively, the processing device may be configured to conclude that an MRI device is present if the counter value reaches or exceeds a predefined detection threshold. Thus, even if the counter value is not found to steadily increase for a predefined (consecutive) number of times, a conclusion may be made about the presence of an MRI device if the counter value reaches or exceeds the detection threshold. Thus, if the counter value becomes comparable to or exceeds the detection threshold, it is assumed that an MRI device is present in any case.

[0032] In one embodiment, the processing device is configured to reset the counter value to a starting value (e.g., 0) if the counter value is not incremented within a predetermined period of time. The predetermined period of time can be, for example, in the range of 1 minute to 20 minutes (e.g., 10 minutes). Thus, if the counter value is found to no longer increase and this is observed for a suitable period of time, the counter value is reset as it is assumed that the implantable medical device is not or is no longer within range of the MRI device.

[0033] Alternatively or additionally, the processing device may be configured to reset the counter value to a starting value (e.g., 0) if the measurements indicate a decrease in the strength of the magnetic field by a value greater than a predefined reset threshold. If the magnetic field strength is found to decrease substantially, it may be assumed that the implantable medical device is not or is no longer within range of the MRI device. The counter value is therefore reset so that the detection procedure is started anew to detect the presence of the MRI device in case of an increase in the magnetic field strength.

[0034] In one embodiment of the invention, the processing device is configured to reset the counter value to a starting value when a predetermined number of consecutive measurements each indicate a decrease in the strength of the magnetic field, the counter value being reset if each of the measurements has decreased by a value greater than a predetermined countdown threshold.

[0035] Setting a predefined number of consecutive measurements for determining the resetting of the counter has the advantage that the exit of the MRI environment of the MRI device can be detected reliably. By exiting the MRI environment, the magnetic field strength of the patient (and the implanted medical device) is usually decreased at a controlled rate, which should be detected by the processing device. A single measurement of a decrease in the magnetic field followed by an increase, or a single measurement of one alternating decrease and increase, may not be sufficient to indicate an exit from the MRI environment in some cases. For example, such an event may be caused by a disturbance in the magnetic field measurement, or by an adjustment of the MRI patient table by a doctor or nurse. For example, the number of consecutive measurements may be set from 2 to 10 measurements. Especially when the number was set to three consecutive measurements, reliable results could be generated. The predefined countdown threshold may correspond to a drop of two or three values.

[0036] In one embodiment, the sensing device may be a GMR sensor (GMR stands for Giant Magnetoresistance) and is thus configured to measure the magnetic field strength and output a voltage value indicative of the magnetic field strength present at the location of the sensing device.

[0037] In one embodiment, the processing unit is configured to modify the operation of the implantable medical device if it is concluded that an MRI device is present. The modification of the operation can include, among others, switching off a sensing function of the implantable medical device, or switching off or modifying a therapeutic function. For example, in the case of a stimulator device such as a pacemaker device, the pacing function can be modified such that pacing is achieved without external triggering or clocking, e.g. corresponding to a so-called VV0 mode of the pacemaker device. In the case of a defibrillator device, the shock function can be turned off, e.g. such that the shock function cannot be used while the patient carrying the device is undergoing an MRI examination.

[0038] According to one embodiment of the invention, the processing unit is configured to terminate said modification of the operation of the implantable medical device when the counter value is reset, whereby the resetting of the counter value is associated with the exit of the MRI environment, such that the modification of the operation of the implantable device is no longer necessary and the implantable device can return to normal non-MRI mode.

[0039] According to one embodiment, the processing device is configured to start an end timer when the counter value is reset. The modification of the operation of the implantable medical device is terminated when the end timer reaches a predefined time margin. Application of the end timer is advantageous in situations where the counter value is reset before the patient has completely exited the MRI environment. In such a case, the modification of the operation of the implantable medical device is maintained after the reset of the counter value for a certain period of time as a patient safety measure. The period is defined by said time margin and can be set, for example, to 30, 60, 90, 120 seconds. In particular, setting the time margin to 60 seconds has produced reliable results. If during that period the counter value increases again and the presence of an MRI device is redetected, the modification of the operation of the implantable device may be maintained (i.e. not terminated after the expiration of the period). If the presence of an MRI device is not redetected during said period or until the end timer reaches the time margin, the modification of the operation of the implantable device is terminated and the implantable medical device returns to a normal non-MRI operating mode. Upon returning to the normal operating mode, the implantable medical device resumes application of the routine for detecting the presence of an MRI device according to the present invention. The end timer is set to its start value and is retriggered the next time the counter value is reset.

[0040] Alternatively, according to an embodiment of the present invention, the processing device is configured to conclude that an MRI device is present if at least a portion of the curve associated with the plurality of successive measurements corresponds to at least a portion of the reference curve. In the context of the present invention, a portion of a curve corresponds to a portion of a second curve if their shapes are somewhat similar. For example, a curve generated by a plurality of successive measurements obtained by a sensing device can be compared to a reference curve by calculating the difference in slope of portions of both curves and comparing the difference to a threshold value. If the difference is below a threshold value, the two portions of the curves may correspond to each other. If the difference is above a threshold value, there may be no correspondence between the sections of both curves. Alternatively, the portions of both curves may be compared by calculating the difference in the areas under the curves. If the difference is below a certain threshold value, the two portions of the curves may have a certain similarity and they correspond to each other. The reference curve can be stored in the implantable medical device during the manufacturing process and is accessible to the processing device. For example, the reference curve can be generated by a large number of measurements of the magnetic field strength of an object entering the MRI device on a patient table to generate a large number of test curves. The test curves are used to calculate an average curve that is stored as the reference curve. Alternatively, or in combination, the reference curve may be continuously adapted or updated with a newly generated curve associated with multiple successive measurements from the sensing device.

[0041] This object is also achieved by a method of operating an implantable medical device comprising the steps of sensing a magnetic field using a sensing device of the implantable medical device, and detecting the presence of an MRI machine using a processing device of the implantable medical device based on measurements obtained from the sensing device, where if the measurements indicate an increase in strength of the magnetic field then it is concluded by the processing device that an MRI machine is present.

[0042] The advantages and advantageous embodiments of the implantable medical device as described above apply equally to the method, and therefore reference is made thereto.

[0043] The various features and advantages of the present invention can be more readily understood by reference to the following detailed description and the embodiments illustrated in the drawings. [Brief description of the drawings]

[0044] [Figure 1] 1 shows a schematic diagram of an implantable medical device within a patient. [Diagram 2] 1 shows a schematic diagram of an MRI apparatus. [Diagram 3] 1 shows a schematic diagram of an implantable medical device. [Figure 4] 1 shows a graph of measurements output by a sensing device of an implantable medical device and counter values ​​derived from the measurements. [Diagram 5] 2 shows the characteristic curves of a sensing device in the form of a GMR sensor. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0045] Embodiments of the present invention will now be described in detail with reference to the figures, in which like reference numbers, where appropriate, indicate functionally similar structural elements.

[0046] It should be noted that the embodiments do not limit the present invention, but merely represent illustrative examples.

[0047] 1 shows a schematic diagram of an implantable medical device 1, for example in the form of a stimulator device, such as a pacing or defibrillator device. The implantable medical device 1 may for example include a generator 10 that may be subcutaneously implanted in a patient, for example as shown in FIG 1, with electrodes 11 connected to the generator 10 and extending from the generator 10 towards a region of interest (e.g. the patient's heart) so as to provide a therapeutic function in the region of interest (e.g. within the patient's heart).

[0048] Such an implantable medical device 1 may be configured to provide a therapeutic function (e.g., a pacing or defibrillator function) over an extended period of time. To this end, the implantable medical device 1 may be permanently implanted in the patient P and may function in a substantially autonomous manner, with a communications connection being established with the implantable medical device 1, for example, using an external device 2, for example, to program the implantable medical device 1 or to transfer data from the implantable medical device 1 to the external device 2, for example, using telemetry.

[0049] The external device 2 may communicate with the implantable medical device 1 using electromagnetic means, for example by establishing an inductive coupling between the implantable medical device 1 and the external device 2 .

[0050] Alternatively, the external device 2 may be a permanent magnet that can be brought close to the implantable medical device 1 to trigger an operation of the implantable medical device 1, for example to wake up the medical device 1.

[0051] As shown diagrammatically in Fig. 2, when a patient P undergoes an MRI examination using an MRI apparatus 3, the patient P carrying the implantable medical device 1 is introduced into the bore 30 of the MRI apparatus 3 by placing the patient P on the patient bed 31 and continuously moving the patient P into the bore 30 in a moving direction V using the motorized drive of the patient bed 31. When the patient P is moved into the bore 30 of the MRI apparatus 3, the patient P here is placed within the range of a constant magnetic field M of the MRI apparatus 3, which generally has a maximum magnetic field strength (corresponding to the magnetic flux density B, usually indicated in Tesla [T]) within the bore 30. Thus, as the patient P is moved into the bore 30 of the MRI apparatus 3, the magnetic field strength of the magnetic field M at the location of the implantable medical device 1 steadily increases.

[0052] Due to the magnetic field M of the MRI machine 3, electrical signals may be induced in the implantable medical device 1. Thus, when the implantable medical device 1 comes within range of the MRI machine 3, it can be detected and the operation of the implantable medical device 1 can be appropriately modified to avoid interference with the operation by the MRI machine 3.

[0053] 3 shows one embodiment of a generator 10 of an implantable medical device 1 in the form of a stimulator device, such as, for example, a pacemaker or defibrillator device. Contained within the housing of the generator 10 is a processing unit 101, implemented by electronic circuitry on a circuit board, which functions to control the operation of the generator 10, for example, to transmit electrical stimulation energy via electrodes 11 connected to a connector block 100 of the generator 10, and to analyze sensed signals received, for example, via the electrodes 11, to provide therapy tailored to the patient's cardiac activity.

[0054] The generator 10 further comprises an energy storage device 102 in the form of a battery, a sensing device 103, e.g. in the form of a GMR sensor for sensing a magnetic field, and a communication device 104, e.g. for establishing a communication connection to an external device 2, as shown in FIG.

[0055] Sensing device 103 is connected to processing device 101 and configured to make measurements that result in measurements indicative of the magnetic field strength at the location of sensing device 103. Sensing device 103 may be configured, for example, to make measurements at a particular sampling rate (e.g., a rate between 1 Hz and 50 Hz (e.g., 4 Hz)). Sensing device 103 provides (discrete) measurements to processing device 101 that are analyzed by processing device 101 and used to control the operation of implantable medical device 1.

[0056] 4, as a patient P is moved into the bore 30 of the MRI machine 3 by motorizing the patient's bed 31 in a moving direction V, the sensing device 103 outputs measurements S over time, where measurements S are provided numerically at a particular sampling rate, with one numerical value corresponding to a voltage value of 1 mV output by the sensing device 103 (left vertical axis of FIG. 4).

[0057] In addition to the measurement value S, FIG. 4 shows the corresponding change value S' (corresponding to the discrete slope of the measurement value S) over time, which indicates the change between the actual measurement value and the previous measurement value (right vertical axis of FIG. 4).

[0058] Based on the measurement value S and the change value S', a counter value C is derived, where the counter value C is initially set to 0. When a measurement value S is obtained that corresponds to a change value S' that exceeds a certain initial margin (e.g., 3 values), the counter value is incremented from 0 to 1, and thereafter the counter value C is incremented by 1 each time the value S' associated with the actual measurement value S exceeds a predefined count threshold A1, e.g., corresponding to a value of 2 values.

[0059] If the counter value C is found to reach the detection threshold A3 at time T1, the MRI device 3 is assumed to be present and therefore the flag "MRI detected" may be set by the processing device 101. Thus, in phase D following time T1, the operation of the implantable medical device 1 may be modified to take into account the presence of the magnetic field M of the MRI device 3 and to adjust the operation of the implantable medical device 1 appropriately in order to reduce the risk of disturbances caused by the magnetic field M of the MRI device 3.

[0060] Alternatively or in addition to comparing the counter value C with the detection threshold A3, the processing device 101 may be configured to determine whether the counter value C has been incremented a predetermined number of consecutive times, indicating that the change value S' for successive measurements S repeatedly exceeds the count threshold A1. The predetermined number of consecutive times may be set to, for example, 5 times. Thus, if the counter value C is incremented by 1 consecutively for 5 successive measurements, it is assumed that the patient P has been moved into the MRI device 3 and thus the magnetic field is probably steadily increasing since the MRI device 3 is present.

[0061] 4, it is assumed that at time T1 the MRI machine 3 is detected and therefore in the phase D following time T1 an appropriate indicator flag is set. With a further increase in the magnetic field M and a corresponding rise in the measurement value S, the counter value C continues to increment until it reaches a plateau which corresponds for example to a rest period when the patient P is at rest within the bore 30 of the MRI machine 3 and the patient bed 31 is stationary.

[0062] As patient P moves out of bore 30, the magnetic field strength at the location of implantable medical device 1 decreases, which is detected and indicated by measurement S. If the change value S' corresponding to measurement S is found to indicate a decrease in magnetic field strength by a margin exceeding reset threshold A2, as is the case at time T2 in FIG. 4, then counter value C is reset to 0. Also, the "MRI detected" indicator flag is cancelled such that phase D, indicative of a detected MRI device 3, persists between times T1 and T2, as shown in FIG. 4.

[0063] Alternatively or additionally, the counter value C may also be reset to 0 if it is found that the counter value C is not further incremented for a predetermined period of time (eg, in the range of 1 minute to 20 minutes).

[0064] 5, for example, a sensing device 103 implemented using two GMR sensors rotated 90° relative to one another has characteristic curves O1, O2, O3 that are non-linear and substantially independent of the angular orientation of the sensing device 103 (as shown by the fact that the characteristic curves O1, O2, O3 corresponding to different angular orientations of the sensing device 103 are substantially identical). The sensing device 103 outputs a numerical value, each corresponding to a voltage value of 1 mV, which is non-linearly correlated with the magnetic field strength (magnetic flux density measured in Tesla) as shown by the characteristic curves O1, O2, O3.

[0065] If the sensing device 103 detects the presence of the MRI device 3 and correspondingly sets an "MRI detected" flag, the processing device 101 is configured to modify the operation of the implantable medical device 1. For example, if the implantable medical device 1 is a stimulator device (e.g., a pacemaker device), the therapy function may be modified, for example, by turning off the sensing function, to provide a pacing operation without clocking by cardiac activity. If the implantable medical device 1 is, for example, a defibrillator device, the shock function, due to a signal induced in the implantable medical device by the magnetic field M of the MRI device 3, may be turned off, in particular to avoid erroneous shocks while the patient P is in the MRI device 3.

[0066] The implantable medical device concerned here may in particular be a cardiac stimulating device, such as a pacemaker or defibrillator device, but may also be, for example, a stimulator device for neurostimulation, etc. The implantable medical device may also be, for example, a sensor device, such as an implantable pressure sensor.

[0067] Since the magnetic field strength for determining whether an MRI device is present is analyzed over time by observing multiple (preferably consecutive) measurements, the detection reliability for detecting an MRI device can be improved in differentiation from other external devices. In this way, the number of false detections of MRI devices can be significantly reduced, thereby improving patient care and patient health.

[0068] The functionality described herein may be implemented through software modifications to the implantable medical device, making it easy and cost effective to implement without requiring hardware modifications. [Explanation of symbols]

[0069] 1. Implantable medical devices (pacemakers) 10 Generator 100 Connector Block 101 Processing equipment 102 Energy storage device 103 Sensing device 104 Communication equipment 11 electrodes 2 External device 3 MRI machine 30 Bore 31 Patient Beds A1 Count Threshold A2 Reset Threshold A3 Detection Threshold C Counter value D Phase M magnetic field (magnetic flux density) O1, O2, O3 characteristic curve (sensor output) P patient S (numerical) measurement S' gradient V direction of movement

Claims

1. a sensing device (103) for sensing a magnetic field (M); a processing device (101) configured to detect the presence of an MRI device (3) based on measurements (S) obtained from the sensing device (103), the processing device (101) being configured to conclude that an MRI device (3) is present if a plurality of measurements (S) obtained from the sensing device (103) indicate an increase in the strength of the magnetic field (M); An implantable medical device (1), comprising: the sensing device (103) is configured to take measurements at a specific sampling rate between 1 Hz and 50 Hz and provide measurements (S) at the specific sampling rate; the processing device (101) is configured to increment a counter value (C) if the measurement (S) indicates an increase in the strength of the magnetic field (M); The implantable medical device (1), characterized in that the processing unit (101) is configured to reset the counter value (C) to a starting value if the counter value (C) does not increase for a predetermined period of time.

2. The implantable medical device (1) of claim 1, characterized in that the processing device (101) is configured to conclude that an MRI device (3) is present if a number of consecutive measurements (S) show an increase in the strength of the magnetic field (M).

3. The implantable medical device (1) of claim 1 or 2, characterized in that the processing device (101) is configured to increment the counter value (C) when a measurement value (S) indicates an increase in the strength of the magnetic field (M) exceeding a predetermined count threshold (A1).

4. The implantable medical device (1) of any one of claims 1 to 3, characterized in that the processing device (101) is configured to decrement the counter value (C) when the measurement value (S) indicates a decrease in the strength of the magnetic field (M), the decrease in the strength of the magnetic field exceeding a predetermined countdown threshold.

5. The implantable medical device (1) of any one of claims 1 to 4, characterized in that the processing device (101) is configured to conclude that an MRI device (3) is present if the counter value (C) increases a predetermined number of times or if the counter value (C) reaches or exceeds a predetermined detection threshold (A3).

6. The implantable medical device (1) of claim 5, characterized in that the processing device (101) is configured to conclude that an MRI device (3) is present if the counter value (C) increases a predetermined number of consecutive times or if the counter value (C) reaches or exceeds a predetermined detection threshold (A3).

7. The implantable medical device (1) of any one of claims 1 to 6, characterized in that the processing device (101) is configured to reset the counter value (C) to a starting value when the measurement value (S) indicates a decrease in strength of the magnetic field (M) by a value greater than a predetermined reset threshold (A2).

8. The implantable medical device (1) of any one of claims 1 to 7, characterized in that the processing device (101) is configured to reset the counter value (C) to a starting value when a predetermined number of consecutive measurements (S) each indicate a decrease in strength of the magnetic field (M) by a value greater than a predetermined countdown threshold.

9. An implantable medical device (1) according to any one of claims 1 to 8, characterized in that the processing device (101) is configured to modify the operation of the implantable medical device (1) if it is concluded that an MRI device (3) is present.

10. The processing device (101) if the counter value (C) is reset, completing the change in operation of the implantable medical device (1); or The implantable medical device (1) of claim 9 with reference to any one of claims 4 to 7, configured to start an end timer when the counter value (C) is reset and to end the change in operation of the implantable medical device (1) when the end timer reaches a predetermined time margin.

11. The implantable medical device (1) of any one of claims 1 to 10, characterized in that the processing device (101) is configured to conclude that an MRI device (3) is present if at least a portion of a curve associated with a plurality of consecutive measurement values ​​(S) corresponds to at least a portion of a reference curve.

12. A method of operation performed by an implantable medical device (1), comprising: a sensing device (103) of the implantable medical device (1) sensing a magnetic field (M); a processing unit (101) of the implantable medical device (1) detecting the presence of an MRI device (3) based on measurements (S) obtained from the sensing unit (103); Including, If a plurality of measurements (S) obtained from the sensing device (103) indicate an increase in the strength of a magnetic field (M), the processing device (101) concludes that an MRI device (3) is present, said sensing device (103) taking measurements at a specific sampling rate between 1 Hz and 50 Hz and providing measurements (S) at said specific sampling rate; The processing device (101) increments a counter value (C) if the measurement value (S) indicates an increase in the strength of the magnetic field (M), The method of claim 1, wherein the processing unit (101) resets the counter value (C) to a starting value if the counter value (C) does not increase for a predetermined period of time.

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