Implantable Medical Device Configured for Detecting a Presence of an MRI Device

Abstract

An implantable medical device comprises a sensing device for sensing a magnetic field, and a processing device configured to detect a presence of an MRI device based on measurement values obtained from the sensing device. The processing device is configured to conclude that an MRI device is present if a multiplicity of measurement values indicates an increase of a strength of the magnetic field. Further, the sensing device is configured to conduct measurements at a specified frequency in between 1 Hz and 50 Hz, in particular at 4 Hz, and to provide measurement values at a predefined sampling rate.

Claims

1. An implantable medical device, comprising: a sensing device for sensing a magnetic field; and a processing device configured to detect a presence of an MRI device based on measurement values obtained from the sensing device; wherein the processing device is configured to conclude that an MRI device is present if a multiplicity of measurement values obtained from the sensing device indicates an increase of a strength of the magnetic field, wherein the sensing device is configured to conduct measurements at a specified frequency in between 1 Hz and 50 Hz, and to provide measurement values at a predefined sampling rate.

2. The implantable medical device of claim 1, wherein the processing device is configured to conclude that an MRI device is present if a multiplicity of consecutive measurement values indicate an increase of the strength of the magnetic field.

3. The implantable medical device of claim 1, wherein the processing device is configured to increment a counter value if a measurement value indicates an increase of the strength of the magnetic field.

4. The implantable medical device of claim 3, wherein the processing device is configured to increment the counter value if a measurement value indicates an increase of the strength of the magnetic field exceeding a predefined count threshold.

5. The implantable medical device of claim 3, wherein the processing device is configured to decrement the counter value if a measurement value indicates a decrease of the strength of the magnetic field, wherein the decrease of the magnetic field strength exceeds a predefined countdown threshold.

6. The implantable medical device of claim 3, wherein the processing device is configured to conclude that an MRI device is present if the counter value is increased for a predefined number of times or if the counter value reaches or exceeds a predefined detection threshold.

7. The implantable medical device of claim 6, wherein the processing device is configured to conclude that an MRI device is present if the counter value is increased for a predefined number of consecutive times or if the counter value reaches or exceeds a predefined detection threshold.

8. The implantable medical device of claim 3, wherein the processing device is configured to reset the counter value to a start value if the counter value is not increased in a predefined period of time.

9. The implantable medical device of claim 3, wherein the processing device is configured to reset the counter value to a start value if a measurement value indicates a decrease of the strength of the magnetic field by a value larger than a predefined reset threshold.

10. The implantable medical device of claim 3, wherein the processing device is configured to reset the counter value to a start value if a predefined number of consecutive measurement values each indicate a decrease of the strength of the magnetic field by a value larger than a predefined countdown threshold.

11. The implantable medical device of claim 1, wherein the processing device is configured to modify operation of the implantable medical device if it is concluded that an MRI device is present.

12. The implantable medical device of claim 5, wherein the processing device is configured to: modify operation of the implantable medical device if it is concluded than an MRI device is present, and terminate modification of operation of the implantable medical device if counter value is reset, or start a termination timer if counter value is reset, and terminate modification of operation of the implantable medical device when the termination timer reached a predefined time margin.

13. The implantable medical device of claim 1, wherein the processing device is configured to conclude that an MRI device is present if a at least a part of a curve associated with the multiplicity of consecutive measurement values corresponds to at least a part of a reference curve.

14. Method for operating an implantable medical device, comprising: sensing a magnetic field using a sensing device of the implantable medical device; and detecting a presence of an MRI device, using a processing device of the implantable medical device, based on measurement values obtained from the sensing device; concluding, by the processing device, that an MRI device is present if a multiplicity of measurement values obtained from the sensing device indicates an increase of a strength of the magnetic field, wherein the sensing device conducts measurements at a specified frequency in between 1 Hz and 50 Hz, and provides measurement values at a predefined sampling rate.

15. The implantable medical device of claim 1, wherein the specified frequency is 4 Hz.

16. The method of claim 14, wherein the specified frequency is 4 Hz.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0046] Various features and advantages of the present invention may be more readily understood with reference to the following detailed description and the embodiments shown in the drawings. Herein,

[0047] FIG. 1 shows a schematic illustration of an implantable medical device in a patient;

[0048] FIG. 2 shows a schematic drawing of an MRI device;

[0049] FIG. 3 shows a schematic drawing of an implantable medical device;

[0050] FIG. 4 shows graphs of measurement values output by a sensing device of the implantable medical device, and a counter value derived from the measurement values; and

[0051] FIG. 5 shows characteristic curves of a sensing device in the shape of a GMR sensor.

DETAILED DESCRIPTION

[0052] Subsequently, embodiments of the present invention shall be described in detail with reference to the drawings. In the drawings, like reference numerals shall designate functionally similar structural elements, if appropriate.

[0053] It is to be noted that the embodiments are not limiting for the present invention, but merely represent illustrative examples.

[0054] FIG. 1 shows a schematic illustration of an implantable medical device 1, for example, in the shape of a stimulation device, such as a pacing device or a defibrillation device. The implantable medical device 1 may, for example, comprise a generator 10 which, for example, as illustrated in FIG. 1, may be subcutaneously implanted into a patient, wherein an electrode 11 is connected to the generator 10 and extends from the generator 10 towards a region of interest, for example, the patient's heart, such that a therapy function may be provided at the region of interest, for example, in the patient's heart.

[0055] An implantable medical device 1 of this kind may, for example, be configured to provide a therapy function over a prolonged period of time, for example, a pacing function or a defibrillator function. The implantable medical device 1, for this, may be permanently implanted into a patient P and may function in a substantially autarkic manner, wherein a communication connection may be established with the implantable medical device 1 using an external device 2, for example, to program the implantable medical device 1 or to transfer, using, for example, telemetry, data from the implantable medical device 1 to the external device 2.

[0056] An external device 2 may communicate with the implantable medical device 1 using electromagnetic means, for example, by establishing an inductive coupling in between the implantable medical device 1 and the external device 2.

[0057] The external device 2 may alternatively be a permanent magnet which may be brought into the vicinity of the implantable medical device 1 in order to trigger an action of the implantable medical device 1, for example, for waking up the medical device 1.

[0058] If, as schematically illustrated in FIG. 2, a patient P shall undergo an MRI examination using an MRI device 3, the patient P, carrying an implantable medical device 1, is introduced into a bore 30 of the MRI device 3 by placing the patient P on a patient bed 31 and by continuously moving, using an electro-motoric drive of the patient bed 31, the patient P into the bore 30 in a movement direction V. When moving the patient P into the bore 30 of the MRI device 3, the patient P herein is brought into the range of a constant magnetic field M of the MRI device 3, the magnetic field M generally having a maximum magnetic field strength (corresponding to the magnetic flux density B and indicated usually in Tesla [T]) within the bore 30. Hence, when the patient P is moved into the bore 30 of the MRI device 3, the magnetic field strength of the magnetic field M at the location of the implantable medical device 1 will steadily increase.

[0059] Caused by a magnetic field M of an MRI device 3, electrical signals may be induced within an implantable medical device 1. Hence, it shall be detected if an implantable medical device 1 comes into the range of an MRI device 3, such that operation of the implantable medical device 1 can suitably be modified in order to avoid a disturbance of operation by the MRI device 3.

[0060] FIG. 3 illustrates an embodiment of a generator 10 of an implantable medical device 1, for example, in the shape of a stimulation device such as a pacemaker device or a defibrillator device. Included in a housing of the generator 10 is a processing device 101, implemented, e.g., by electronic circuitry on a circuit board, which serves to control operation of the generator 10 for transmission of electrical stimulation energy via the electrodes 11 connected to a connector block 100 of the generator 10, and for analyzing sense signals received, e.g., via the electrodes 11 to provide for a therapy aligned to an activity of, for example, the patient's heart.

[0061] The generator 10 further comprises an energy storage 102 in the shape of a battery, a sensing device 103, for example, in the shape of a GMR sensor for sensing magnetic fields, and a communication device 104 for establishing a communication connection, for example, to an external device 2, as illustrated in FIG. 1.

[0062] The sensing device 103 is connected to the processing device 101 and is configured to conduct measurements yielding measurement values indicative of a magnetic field strength at the location of the sensing device 103. The sensing device 103 may, for example, be configured to conduct measurements at a specified sampling rate, for example, at a rate in between 1 Hz and 50 Hz, for example, 4 Hz. The sensing device 103 provides (discrete) measurement values to the processing device 101, which are analyzed by the processing device 101 and are used for controlling operation of the implantable medical device 1.

[0063] Referring now to FIG. 4, when a patient P is moved into the bore 30 of an MRI device 3 by electromotively moving the patient's bed 31 in a movement direction V, the sensing device 103 outputs measurement values S over time. The measurement values S herein are provided at the specified sampling rate in digits, one digit corresponding to a voltage value of 1 mV as output by the sensing device 103 (left vertical axis in FIG. 4).

[0064] FIG. 4 in addition to the measurement values S shows corresponding change values S′ (corresponding to the discrete slope of the measurement values S) over time, the change values S′ indicating a change between an actual measurement value and the previous measurement value (right vertical axis in FIG. 4).

[0065] Based on the measurement values S and the change values S′ a counter value C is derived.

[0066] Herein, the counter value C initially is set to 0. If a measurement value S is obtained which corresponds to a change value S′ exceeding a specified initial margin, for example, 3 digits, the counter value is incremented from 0 to 1, wherein subsequently the counter value C is incremented by one each time the change value S′ associated with the actual measurement value S exceeds a predefined count threshold A1, corresponding, for example, to a value of 2 digits.

[0067] If it is found that a counter value C reaches, at time T1, a detection threshold A3, it is assumed that an MRI device 3 is present and hence a flag “MRI detected” may be set by the processing device 101. Accordingly, in a phase D following time T1 operation of the implantable medical device 1 may be modified in order to account for the presence of the magnetic field M of the MRI device 3 and to suitably adjust operation of the implantable medical device 1 in order to reduce a risk for disturbances caused by the magnetic field M of the MRI device 3.

[0068] Alternatively or in addition to comparing the counter value C to a detection threshold A3, the processing device 101 may be configured to determine whether the counter value C for a predefined number of consecutive times is incremented, indicating that the change value S′ for consecutive measurement values S repeatedly exceeds the count threshold A1. The predefined number of consecutive times may, for example, be set to 5. If, hence, the counter value C is consecutively incremented by 1 for five consecutive measurements, it is assumed that presumably the magnetic field steadily increases as the patient P is moved into an MRI device 3 and, hence, an MRI device 3 is present.

[0069] In the example of FIG. 4, at time T1 an MRI device 3 is assumed to be detected, and hence in phase D following time T1 a suitable indicator flag is set. The counter value C, due to the further increase of the magnetic field M and the corresponding rise of the measurement values S, continues to be incremented, until a plateau is reached, corresponding, for example, to a rest period in which the patient P rests in the bore 30 of the MRI device 3 and the patient bed 31 is at a standstill.

[0070] If the patient P is moved out of the bore 30, the magnetic field strength at the location of the implantable medical device 1 will decrease, which is detected and indicated by the measurement values S. If it is found that a change value S′ corresponding to a measurement value S indicates a decrease of the magnetic field strength by a margin exceeding a reset threshold A2, as it is the case at time T2 in FIG. 4, the counter value C is reset to 0. In addition, the “MRI detected” indicator flag is canceled, such that the phase D indicating a detected MRI device 3 lasts between time T1 and time T2, as illustrated in FIG. 4.

[0071] Alternatively or in addition, if it is found that the counter value C is not further incremented over a predefined period of time, for example, ranging from 1 minute to 20 minutes, the counter value C may also be reset to 0.

[0072] Referring now to FIG. 5, the sensing device 103, for example, implemented using two GMR sensors rotated by 90° to one another, has characteristic curves O1, O2, O3 which are nonlinear and are substantially independent of an angular orientation of the sensing device 103 (illustrated 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 digits, each digit corresponding to a voltage value of 1 mV. Herein, the digits are nonlinearly correlated to the magnetic field strength (magnetic flux density, measured in Tesla), as this is indicated by the characteristic curves O1, O2, O3.

[0073] If the sensing device 103 detects the presence of an MRI device 3 and correspondingly sets the “MRI detected” flag, the processing device 101 is configured to modify operation of the implantable medical device 1. For example, if the implantable medical device 1 is a stimulation device, for example, a pacemaker device, a therapy function can be modified, for example, by switching off a sensing function in order to provide a pacing action without a clocking by cardiac activity. If the implantable medical device 1 is, for example, a defibrillator device, a shock function may be switched off, in particular in order to avoid an erroneous shock while a patient P is within an MRI device 3, due to signals induced within the implantable medical device 1 by the magnetic field M of the MRI device 3.

[0074] An implantable medical device as concerned herein may in particular be a cardiac stimulation device such as a pacemaker device or a defibrillator device, but may also be a stimulation device, for example, for a neuro-stimulation. In addition, the implantable medical device may, for example, be a sensor device, such as an implantable pressure sensor or the like.

[0075] Because a magnetic field strength, for determining whether an MRI device is present, is analyzed over time by observing multiple (preferably consecutive) measurement values, a detection reliability for detecting an MRI device—in differentiation to another external device—may be improved. In this way the number of wrong detections of an MRI device may be substantially reduced, hence improving therapy for a patient and the patient's well-being.

[0076] A functionality as described herein may be implemented by a change in software of an implantable medical device, such that implementation may be easy and cost-effective without requiring a change in hardware.

[0077] It will be apparent to those skilled in the art that numerous modifications and variations of the described examples and embodiments are possible in light of the above teachings of the disclosure. The disclosed examples and embodiments are presented for purposes of illustration only. Other alternate embodiments may include some or all of the features disclosed herein. Therefore, it is the intent to cover all such modifications and alternate embodiments as may come within the true scope of this invention, which is to be given the full breadth thereof. Additionally, the disclosure of a range of values is a disclosure of every numerical value within that range, including the end points.

LIST OF REFERENCE NUMERALS

[0078] 1 Implantable medical device (pacemaker device) [0079] 10 Generator [0080] 100 Connector block [0081] 101 Processing device [0082] 102 Energy storage [0083] 103 Sensing device [0084] 104 Communication device [0085] 11 Electrode [0086] 2 External device [0087] 3 MRI device [0088] 30 Bore [0089] 31 Patient bed [0090] A1 Count threshold [0091] A2 Reset threshold [0092] A3 Detection threshold [0093] C Counter value [0094] D Phase [0095] M Magnetic field (magnetic flux density) [0096] O1, O2, O3 Characteristic curve (sensor output) [0097] P Patient [0098] S Measurement values (in digits) [0099] S′ Slope [0100] V Moving direction