Position determination of a body part in a magnetic resonance imaging system and determination of a specific absorption rate of a body part in a magnetic resonance imaging system

Abstract

The invention relates to a method for determining the position of a body part in a magnetic resonance imaging (MRI) system, the method comprising the following steps: positioning the body part on a body part cushion on a patient table (4) of the MRI system; determining a magnetic stray field with a magnetic field sensor (2) arranged in or on the body part cushion to thus determine position data; transmitting the position data to an evaluation unit by means of a transmission means; determining the position of the body part in the MRI system based on the position data and the fact that the body part is positioned on the body part cushion, by means of the evaluation unit. The invention further relates to a corresponding method for determining a specific absorption rate of a body part in a MRI system, a body part cushion, and a MRI system.

Description

[0001] Regardless of the grammatical gender of a particular term, persons with male, female or other gender identities are included.

[0002] The invention relates to a method for determining the position of a body part in a magnetic resonance imaging system, a body part pillow, in particular a head pillow, a method for determining a specific absorption rate of a body part in a magnetic resonance imaging system and a magnetic resonance imaging system.

[0003] In magnetic resonance imaging (MRI) examinations, a specific absorption rate (SAR) is typically determined. It is particularly important that the average SAR over a given time interval remains below a threshold value to prevent harm to patients, especially from excessive heating. Generally, a distinction is made between head SAR, whole-body SAR, and exposed partial-body SAR. To determine these, it is necessary to know the patient's position within the whole-body coil, for example, to differentiate between a head scan and a foot scan. Furthermore, the patient's orientation on the examination table is important, especially whether they are in the feet-first supine position (FFS) or head-first supine position (HFS).Particularly in the case of an FFS examination, the patient usually lies in an arbitrary and therefore unknown position on the examination table, and the specific examination region cannot be easily determined.

[0004] In the case of FFS examinations, the state of the art therefore often assumes a worst-case position where the highest SAR would occur. Thus, a maximum SAR is assumed, which, while safe, may severely limit the quality of the examination (image quality / measurement time / number of slices).

[0005] It would be desirable, however, to know or be able to determine the position of an exposed body part, especially the head position, on the patient table relative to the magnetic resonance imaging (MRI) system or relative to the center of the MRI system's magnet. Information about the head position would be particularly important to rule out overheating of the brain tissue.

[0006] In principle, it would be conceivable to determine body position using a 3D camera. However, such a solution is quite complex and expensive. Furthermore, not every magnetic resonance imaging (MRI) system is equipped with a suitable 3D camera or designed for such use. Moreover, the data provided by a 3D camera could present the additional problem of proper evaluation and interpretation of the camera data, which could be difficult to resolve. Therefore, it would be desirable to find a solution that allows for the most precise determination of head position, preferably one that is more cost-effective and / or accurate than a solution using a 3D camera.

[0007] It is therefore an object of the present invention to provide a means for determining the position of a body part, in particular the head, in a magnetic resonance imaging system or on the patient table of a magnetic resonance imaging system. Furthermore, it is an object to provide a means for determining the specific absorption rate of a body part, in particular the head, in a magnetic resonance imaging system or on the patient table of a magnetic resonance imaging system.

[0008] This problem is solved by a method according to claim 1, a method according to claim 6, a body part cushion according to claim 7, and a medical imaging system according to claim 15. Further features and advantages will become apparent from the dependent claims, the description, and the accompanying figures.

[0009] According to a first aspect of the invention, a method for determining the position of a body part, in particular a head, of a subject in a magnetic resonance imaging system is provided. The method comprises the following steps: - Positioning the body part on a body part cushion, the body part cushion being arranged in particular on a patient table of the magnetic resonance imaging system; - Determining a magnetic field, in particular a stray field, with a magnetic field sensor arranged in or on the body part cushion in order to determine position data, wherein the magnetic field sensor in particular comprises a 3D Hall sensor; - Transmitting the position data to an evaluation device using a transmission device; - Determining the position of the body part in the magnetic resonance imaging system using position data based on the body part being placed on the body part cushion, by the evaluation device.

[0010] Advantageously, the method according to the invention enables relatively simple and cost-effective position detection. In particular, a position determined in this way can be used to determine a specific absorption rate of the body part. Specifically, position determination can thus also be made possible during an examination with the patient feet-first on the patient table ("feet-first supine" position - FFS), i.e., in which a patient is moved feet-first on the patient table into the examination tunnel of the magnetic resonance imaging system ("feet-first supine" position - FFS). This invention can also be advantageous during an examination with the head-first ("head-first supine" position - HFS). While HFS often involves fixed positions for the head coils, this solution does not require the head to be positioned according to these prescribed positions.Compared to position determination using a 3D camera, this method can advantageously reduce costs. Higher accuracy can also be achieved in some cases. In particular, the method according to the invention is typically less dependent on a patient's appearance, especially head hair / head covering, as well as their weight and size, compared to determination using camera data.

[0011] The determination of the body part's position specifically concerns its relative position within the magnetic resonance imaging (MRI) system, particularly relative to the magnetic center of the MRI system. The body part can be any body part, especially one that is already positioned on a cushion for the examination. Specifically, the body part is a part of a subject. The subject can be a living being, especially a human or an animal.

[0012] The body part chosen can be the head. Precise position tracking of the head is particularly advantageous because, due to its relatively low mass (e.g., compared to the typically much heavier torso), it is more susceptible to overheating. Alternatively, another body part could be used, such as a knee or elbow.

[0013] The term "body part cushion" generally refers to a cushion-like object suitable for supporting a body part. Unless explicitly excluded, the term "body part cushion" can also encompass the term "head pillow." In particular, within the scope of this invention, when referring to a "body part cushion," the more specific term "head pillow" can be used as a variant, and when referring to a body part, the more specific term "head" can be used as a variant. The subject's body part is supported on the cushion. Preferably, the body part cushion is arranged on a patient table of the magnetic resonance imaging (MRI) system. In particular, the entire subject can be supported on the patient table, with the body part being indirectly supported on the patient table via the body part cushion.The body part cushion can be used, in particular, to provide greater comfort and / or to support a specific position or orientation of the subject's body part. In a simple example, the subject may lie flat on their back, with the body part, in this case a head, resting on the body part cushion, in this case a head pillow. Alternatively, the subject may be positioned, for example, on their stomach. In this case, the subject's face may be positioned towards the body part cushion or head pillow. The head pillow may include a cutout, particularly a hole, for the face. Alternatively, the body part cushion may, for example, be a knee support.

[0014] Position data is determined using a magnetic field sensor in or on the body part cushion based on a magnetic field, particularly a stray field. The magnetic field sensor can be attached to the outside of the body part cushion (e.g., on the side). The magnetic field sensor can also be at least partially integrated into the body part cushion. A stray magnetic field can be understood to be, in particular, the magnetic field outside the examination tunnel or outside the main magnet of the magnetic resonance imaging (MRI) system. The stray field can be, in particular, the stray field of the B0 magnetic field of the MRI system or of the main magnet of the MRI system, or encompass it. While the magnetic field within the main magnet is largely homogeneous, this magnetic field decreases outside the main magnet. Generally, the magnetic field is weaker the further away from the examination tunnel is.Using information about the magnetic field profile outside the examination tunnel, the position of the magnetic field sensor can be deduced in conjunction with the measured stray field. The position of the magnetic field sensor, and thus the position of the body part cushion, and consequently the position of the body part, can therefore be correlated with the measured magnetic field. Preferably, the position (and, if applicable, the orientation) of the magnetic field sensor on the body part cushion is known or predefined and is taken into account during position determination. Preferably, the relative positioning of the body part on the body part cushion is also known or predetermined and is taken into account during position determination. Optionally, it may be possible to use multiple magnetic field sensors on and / or in the body part cushion. Multiple magnetic field sensors can, for example, provide additional position information (e.g.,(an orientation) can be determined. The position of the majority of magnetic field sensors relative to the body part cushion, for example relative to a geometric center point of the body part cushion, can be precisely defined.

[0015] The position data can, for example, include the measurement data from the magnetic field sensor. For instance, the position data can be magnetic stray field measurement data. The magnetic field sensor can be a three-dimensional (3D) magnetic field sensor, in particular a 3D Hall sensor. A three-dimensional magnetic field sensor is, in particular, a magnetic field sensor that can detect a magnetic field strength for each of three spatial directions. For example, three Hall elements can be provided, each capable of determining a magnetic field strength in one spatial direction. The position data can, for instance, include the magnetic field strength in three spatial directions. Optionally, the position data can be at least partially processed by the magnetic field sensor and / or before being transmitted to the evaluation device. For example, the measurement data from the magnetic field sensor can be compressed, summarized, or calculated into a different value.

[0016] The position data is transmitted to an evaluation unit via a transmission device. This transmission device may, for example, comprise a communication device, in particular a transmitter, to which body part pads are attached, and a receiver that communicates with the evaluation unit. Optionally, the transmission device may include a cable connection, in particular between the communication device and the receiver. Optionally, wireless transmission between the communication device and the receiver may be provided. The evaluation unit may, in particular, be a control unit of the magnetic resonance imaging system or part of a control unit of the magnetic resonance imaging system. The evaluation unit may include a computer unit for evaluating the position data or for determining the position.

[0017] The positional data is used to determine the position of the body part within the magnetic resonance imaging (MRI) system, particularly by the evaluation unit. For example, it may be possible to determine a z-position from the magnitude of the measured stray field. Alternatively, a relative position to the main magnet of the MRI system, such as relative to the center of the main magnet, may be determined. It may also be possible to use the patient table's movement to determine the current position of the body part and / or its position at a specific time. For example, the subject or patient may be placed on the patient table and body part cushion outside the examination tunnel, and the position of the body part is determined using the magnetic stray field.In the next step, the patient table is moved into the examination tunnel with the body part being examined, and the distance moved is also measured. Based on the initial position and the distance moved, the position within the examination tunnel can then be determined. Optionally, measurements of the subject, particularly height or length, can be used to determine the position. This allows for a particularly precise determination of the body part's position. Compared to positioning with a 3D camera, for example, this can provide a solution that is significantly more cost-effective and offers greater accuracy. Furthermore, limitations on accuracy caused by a patient's weight and size can be reduced.

[0018] According to one embodiment, the position data is transmitted wirelessly, in particular via radio transmission, and / or via cable to the evaluation unit. Transmission via cable can, for example, be provided galvanically using coiled cables. In the case of wireless transmission, the position data can be transmitted from the body part cushion to a receiver on the evaluation unit by a communication device, in particular comprising a transmitter. Particularly in the case of wireless transmission, an energy storage device can be provided, which is configured to supply power to the magnetic field sensor and / or the communication device. The magnetic resonance imaging system can be configured to activate a safety mode if no signals are received from the evaluation unit or the receiver of the evaluation unit.In safety mode, the magnetic resonance imaging (MRI) system can operate by assuming the maximum possible SAR (Static Area Rate) in the body part, regardless of the actual position of the body part. This can be particularly advantageous with wireless transmission, allowing the system to react to signal loss, for example, due to a depleted power supply. Wired transmission has the advantage of eliminating the need for a power supply in the pillow. The magnetic field sensor, for instance, can be powered via the wiring.

[0019] According to one embodiment, the position data is transmitted optically, in particular using infrared light, to the evaluation device. Optical transmission represents a particularly advantageous method of wireless transmission. When this invention refers to "optical" or "light," it generally includes light in a broader sense, including infrared and UV light, unless otherwise specified. The use of infrared light is particularly preferred. While radio transmission often requires a rather expensive radio license, this license is generally not needed for optical transmission. Furthermore, interference with other radio transmissions can be ruled out. Another advantage is that no cable is required, which could potentially be an obstruction.Furthermore, optical transmission, for example using a light-emitting diode (LED), can be advantageously achieved with relatively low energy consumption. For example, the communication device can comprise a light source or light transmitter, in particular an infrared light transmitter (IR transmitter). The IR transmitter can, in particular, comprise an IR LED and an LED driver with a microcontroller. For example, the LED driver can be switched ON or OFF via an I / O pin of a microcontroller. The light transmitter or light source can, for example, be arranged and / or fixed at the edge of the body part cushion. Preferably, the light transmitter or light source is positioned on the body part cushion in such a way that a receiver, in particular an IR receiver, attached to a part of the magnetic resonance imaging system, in particular the MR scanner of the magnetic resonance imaging system, can receive the optically transmitted position data.

[0020] According to one embodiment, the position data is transmitted using light pulses, in particular based on pulse width modulation (PWM). For example, the microcontroller can be configured to translate the position data into a sequence of PWM pulses. This sequence of PWM pulses can then be emitted by the IR LED. The sequence of PWM pulses can conform to a defined protocol (e.g., IR-Link, TOS-Link, or similar). Advantageously, light pulses enable a particularly simple and reliable transmission method.

[0021] According to one embodiment, the body part position is determined by determining the position of the body part based on at least one offset relative to the position of the magnetic field sensor, wherein the value of the at least one offset is set, in particular, depending on the body size of the subject. The at least one offset can include an offset originating from a defined point, for example, the center point, of the body part cushion and / or a defined lying position on the body part cushion. The at least one offset can also include an offset between the defined point of the body part cushion and a position of the body part defined by the body part cushion and / or a center point of the body part.For example, it may be possible to first determine the position of the magnetic field sensor based on the position data, then to determine the position of the body part cushion from that, and then again to determine the position of the body part. For example, the position of the magnetic field sensor can be determined directly based on the measured field, particularly the stray field. It may be possible, for example, to determine the position of the body part cushion and the position of the body part in a single step, for example, using a common offset. The position may, in particular, include a z-position in each case. Optionally, it may be possible to determine essentially only the z-position. The z-position is the position that typically corresponds to the longitudinal direction of the patient table and / or a direction of movement of the patient table into the examination tunnel of the magnetic resonance imaging system.Accordingly, the z-position is a position measured in a z-direction. The offset can be a z-offset or an offset in the z-direction. For example, a first z-offset can be a fixed offset between the position of the magnetic field sensor and a defined point, particularly the center, of the body part cushion. A second z-offset can be used to determine the position of the body part, particularly the head position, from the position of the magnetic field sensor. Optionally, the first and second offsets can be combined into a single offset for the determination. In a simpler version, the second offset, or the combined offset, can be a fixed offset. The fixed offset can be used for all patients, for example. However, this could introduce a certain degree of error if the body part sizes differ.This error can be prevented or at least reduced by taking the patient's size into account during the determination process. One approach would be to use a body part size, such as head size, directly to determine the offset. However, this is often initially unknown and would therefore have to be measured, which could increase the time required and potentially introduce measurement errors. Fortunately, a patient's height is usually recorded in their medical record. The body part size, particularly head size, can then be derived from the body part size. This can preferably be done using known proportional body ratios. For example, an offset, especially for the head, can be determined using a linear function of the body size. This linear function could, for instance, have the form Z-offset = body size × A + B.B can specify a fixed offset that is independent of body size, and A can be a fixed factor by which the body size is multiplied. For example, A can be in the range of 1 / 7 to 1 / 9, preferably 1 / 7 to 1 / 8.5. For example, assuming body size = head size × 7.5, the parameter A can have the value A = (1 / 7.5). The offset can be determined based on age. In particular, an adapted determination can be provided for children.

[0022] According to one embodiment, the position of at least one additional body part is determined based on the position of the body part and, optionally, also based on the subject's height. For example, known proportions can be used to determine the distances between the body part and the additional body part, and thus the position of the at least one additional body part. For example, the body part could be the head, and the at least one additional body part could be the heart and / or the popliteal fossa.

[0023] According to one embodiment, the transmission of position data during a magnetic resonance imaging (MRI) scan is interrupted by the MRI system, in particular by switching off a transmitter for transmitting the position data. Accordingly, it may be provided that the position is not determined during the actual MRI scan, especially to avoid interference and / or because the body part cushion is within the homogeneous magnetic field in the examination tunnel, and thus a current, accurate position determination might not even be possible. Optionally, it may be provided that position data is determined and transmitted again after the MRI scan. This can, for example, serve for verification purposes.

[0024] According to a further aspect of the invention, a method for determining the position of a body part, in particular a head, of a subject in a magnetic resonance imaging system is provided, wherein the body part is arranged on a body part cushion on a patient table of the magnetic resonance imaging system. The method comprises the following steps: - Determining a magnetic field, in particular a stray field, with a magnetic field sensor arranged in or on the body part cushion in order to determine position data, wherein the magnetic field sensor in particular comprises a 3D Hall sensor; - Transmitting the position data to an evaluation device using a transmission device; - Determining the position of the body part in the magnetic resonance imaging system using position data based on the body part being placed on the body part cushion, by the evaluation device.

[0025] Another aspect of the invention is a method for determining a specific absorption rate of a body part of a subject in a magnetic resonance imaging system, comprising the following steps: - Performing a method according to one of the preceding claims to determine a position of the body part; - Determining the specific absorption rate of the body part based on an expected field distribution during a measurement of the magnetic resonance imaging system and the determined position of the body part.

[0026] All the advantages and features of the position determination method can be analogously applied to the method for determining the Specific Absorption Rate (SAR), and vice versa. Advantageously, the specific absorption rate of the body part, particularly the SAR of the head, can thus be determined. This eliminates the need to assume a worst-case scenario, especially during FFS measurements. This allows for improved measurement performance. For example, faster measurements are possible. Instead of HFS measurements, where position is determined via the head coil, FSS measurements can be used, which can be advantageous for claustrophobic patients, for instance. Furthermore, the number of SAR threshold exceedance alerts can potentially be reduced, enabling higher patient throughput.Even with a tabletop attachment that is freely movable on the patient's bed, where both the FFS and HFS positions are unknown, meaning that only worst-case SAR values ​​could previously be calculated, this disadvantage can also be overcome with the method according to the invention. The specific absorption rate can generally be understood as the rate of absorption of electric fields in a material, specifically in the material of the body part. The specific absorption rate can be understood in particular as absorbed power per unit mass. Absorption typically leads to a heating of the absorbing area. For example, a distinction can be made between head SAR, whole-body SAR, and exposed partial-body SAR. To determine the SAR, it is necessary to know the position of the respective body part whose SAR is to be determined.By determining the position of the body part and, if necessary, at least one other body part, the SAR can be reliably determined. The expected field distribution for determining the SAR can be obtained, for example, from a measurement protocol of the magnetic resonance imaging (MRI) system, particularly if it is automated. By determining the SAR based on the position of the body part, improved measurement performance can be achieved because a rough worst-case estimate is no longer necessary.

[0027] Another aspect of the invention is a body part pillow, in particular a head pillow, for positioning a body part, especially the head, during a magnetic resonance imaging (MRI) scan. The body part pillow comprises a magnetic field sensor, in particular a 3D Hall sensor, for detecting the local magnetic field as position data. The body part pillow also includes a communication device for transmitting the position data to a receiver. All advantages and features of the method for determining position and the method for determining a specific absorption rate can be applied analogously to the body part pillow, and vice versa. The communication device can, for example, include an interface with a cable connection and / or a transmitter for sending the position data. In a simple embodiment, the communication device can essentially consist of the transmitter.The transmitter can be designed to cooperate with a corresponding receiver, in particular a receiver of an evaluation device, or to wirelessly transmit the position data to the receiver. For example, the transmitter can be a radio transmitter. For example, the transmitter can be based on the emission of light signals. In particular, the transmitter can include an LED. For example, the transmitter can be an infrared light transmitter (IR transmitter). The transmitter can, for example, include a light source, in particular an LED, especially an IR LED, and a light source driver, in particular an LED driver. The body part cushion can include a magnetic field sensor component, wherein the magnetic field sensor component comprises the magnetic field sensor. For example, the magnetic field sensor component can include a circuit board, wherein the circuit board includes the magnetic field sensor, in particular in the form of a 3D Hall sensor, as an integrated component.The magnetic field sensor component can include a microcontroller configured to control the acquisition of position data and to transmit the position data to the communication device, in particular the sensor. The microcontroller can be integrated into the circuit board. The microcontroller can be configured to control or switch the light source driver. For example, the light source driver can be switched ON or OFF via an I / O pin of the microcontroller.

[0028] According to one embodiment, the body part pillow is designed to receive control signals, particularly from the evaluation unit. For example, a control signal can be to switch to a sleep mode. For example, a control signal can include an "ON" command or an "OFF" command. The body part pillow can be designed to receive the control signal at a different frequency, particularly a light frequency, than the frequency used to transmit the position data. For example, the frequency of the control signals can be lower than the frequency used for the position data.

[0029] According to one embodiment, the body part cushion includes an energy storage device and / or is designed to be equipped with one. The energy storage device can be, for example, a battery, an accumulator, or a capacitor. The body part cushion can optionally be designed so that the energy storage device is galvanically rechargeable. For example, corresponding mating contacts can be provided in a head-pillow docking station for charging the energy storage device. Optionally, the body part cushion can include a display device, for example, comprising at least one LED, designed to indicate the charge level of the energy storage device. For example, the display device can be designed to indicate the charge level by means of a color code. For example, a color code can include a red indicator for "energy storage empty" and a green indicator for "energy storage sufficiently full."

[0030] According to one embodiment, the communication device is designed to also transmit information about the state of charge of the energy storage device. For example, a status indicator can be provided on the receiver side, which is designed to indicate a sufficient state of charge and / or an insufficient state of charge.

[0031] According to one embodiment, the body part cushion comprises at least one solar cell and is designed to draw energy from the at least one solar cell for operating the magnetic field sensor and / or the communication device, in particular to charge an energy storage device for supplying the magnetic field sensor and / or the communication device. Advantageously, automatic charging can thus be particularly simple. The solar cell(s) can, for example, be attached to at least one side, optionally to several sides, of the body part cushion. For example, the solar cells can be charged via ambient light. Additionally or alternatively, the at least one solar cell can be designed to be supplied with energy via a dedicated light source.Optionally, at least one solar cell can be designed to be charged at a different light frequency than the light frequency at which the position data is optically transmitted and / or at which the body part cushion is designed to optically receive control signals. For example, at least one solar cell can be a silicon solar cell, in particular a non-magnetic silicon solar cell.

[0032] According to one embodiment, the communication device comprises a light source, in particular an infrared light source, especially an IR LED, and is configured to optically transmit the position data to the evaluation device via the light source. The light source can be part of a transmitter, in particular an IR LED, part of an IR transmitter. The communication device can include a light source driver, in particular an LED driver. The body part pad can include a microcontroller configured to control the light source driver. For example, the light source driver can be configured to be switched ON or OFF via an I / O pin of the microcontroller. The light source can, for example, be arranged and / or fixed at the edge of the body part pad.Preferably, the light source is positioned on the body part cushion in such a way that a receiver, in particular an IR receiver, attached to a part of the magnetic resonance imaging system, in particular the MR scanner of the magnetic resonance imaging system, can receive the optically transmitted position data.

[0033] According to one embodiment, the communication device is configured to transmit position data by means of light pulses, in particular based on pulse width modulation (PWM). The microcontroller can be configured to translate the position data into a sequence of PWM pulses. The microcontroller can be configured to output the sequence of PWM pulses to a light source driver, in particular an LED driver of the communication device. The light source, in particular the LED, and especially the IR LED, can be configured to emit the sequence of PWM pulses, in particular controlled by the light source driver.

[0034] According to one embodiment, the body part cushion includes an RF shield designed to shield the communication device in such a way as to suppress measurement artifacts of the magnetic resonance imaging system caused by the communication device. Measurement artifacts can, in particular, include image artifacts. The RF shield is preferably MR-compatible. For example, the RF shield can include a Faraday cage. The Faraday cage can, in particular, be made of carbon and / or copper. For example, the Faraday cage can include at least one opening and / or at least one transparent window and / or at least one grid. The at least one window can, in particular, be arranged in front of the transmitter and / or in front of the at least one solar cell. The transparent window can, in particular, be transparent to the frequency of the light signals for transmitting the position data.The translucent window can be, in particular, a glass window, optionally an ITO-coated glass window. The grille can be, for example, a copper grille. For example, the opening and / or the window can have a diameter of less than 15 mm, preferably less than 10 mm. For example, the opening and / or the window can have a diameter of more than 1 mm, preferably more than 3 mm.

[0035] According to one embodiment, the body part cushion is designed such that the positioning of the body part is restricted with regard to its orientation relative to the magnetic resonance imaging system. For example, the body part cushion may be designed such that it can only be used in FFS positioning.

[0036] According to one embodiment, the body part cushion includes a reed switch and is configured to control the power supply to the magnetic field sensor and / or the communication device via the reed switch, such that the power supply is activated depending on a magnetic field at the location of the body part cushion. Reed switches typically include contacts that are actuated or closed by a magnetic field. For example, the magnetic field sensor can be configured to become active only when it comes into proximity with the magnetic field, particularly a stray field, or when the magnetic field is active. This can be a simple way to automatically save energy when the body part cushion is not currently in use.

[0037] Another aspect of the invention is a receiver for receiving and forwarding position data of a body part pillow as described herein. All advantages and features of the method for determining position, the method for determining a specific absorption rate, and the body part pillow can be transferred analogously to the receiver and vice versa. The receiver can include a light sensor for receiving the position data. The receiver can include a power light source, in particular an LED, for illuminating at least one solar cell of the body part pillow with light. The receiver can include a coil connector for a coil slot of the magnetic resonance imaging system and be configured to be connected to a coil slot of the magnetic resonance imaging system. The coil slot can in particular include a coil socket.The receiver can be attached to, or attachable to, a patient table or inside an examination tunnel of the magnetic resonance imaging (MRI) system. The receiver can include a light source, in particular an LED, for illuminating at least one solar cell. The receiver can include RF shielding designed to suppress measurement artifacts of the MRI system caused by the receiver. The receiver can also be configured to transmit control signals, in particular from a data processing unit.

[0038] Another aspect of the invention is a magnetic resonance imaging (MRI) system comprising a body part pillow as described herein, a receiver for receiving and forwarding the position data of the body part pillow, and an evaluation unit configured to receive the position data from the receiver and thereby determine the position of the body part in the MRI system. In particular, the receiver is configured to forward received position data to the evaluation unit. The MRI system is specifically configured to determine position data using a method as described herein and / or a specific absorption rate using a method as described herein.All the advantages and features of the positioning method, the specific absorption rate determination method, the body part pillow, and the receiver can be applied analogously to the magnetic resonance imaging system, and vice versa. The receiver may include a microcontroller for controlling the receiver. The receiver may also include a signal amplifier for amplifying the incoming signal, particularly the positional data.

[0039] According to one embodiment, the body part cushion comprises a light source, in particular an infrared light source, and is configured to optically transmit the position data to the receiver, the receiver comprising a light sensor for receiving the position data. In particular, the body part cushion can include a communication device with the light source. The light source can be an LED, in particular an IR LED. The communication device can generally be configured according to a communication device as described herein, for example, with regard to the aspect of the body part cushion or the method. The light source and the receiver can be positioned and / or positionable such that the receiver can receive the optically transmitted position data from the light source. In particular, the light source and the receiver are preferably positioned such that direct optical signal transmission is possible.If the communication device is configured to transmit position data by means of light pulses, the receiver can be configured to receive corresponding light pulses. For example, the communication device and the receiver can be configured based on a common protocol for transmitting the position data. The receiver can comprise a photodiode, in particular an IR photodiode (infrared photodiode), and / or a phototransistor, in particular an IR phototransistor. The receiver can include a microcontroller configured to translate light signals, in particular PWM signals, from the light source back into position data.

[0040] According to one embodiment, the receiver is further configured to send control signals to the body part pillow, and the body part pillow is configured to receive the control signals. In particular, a control unit of the magnetic resonance imaging system and / or the evaluation unit can be configured to generate the control signals. The magnetic resonance imaging system can be configured to transmit the control signal at a different frequency, in particular a different light frequency, than the frequency used to transmit the position data. For example, the frequency of the control signals can be lower than the frequency used for the position data.

[0041] According to one embodiment, the receiver comprises a coil connector for a coil slot of the magnetic resonance imaging (MRI) system and is configured to be connected to a coil slot of the MRI system. Accordingly, the MRI system comprises at least one coil slot, preferably several coil slots. The coil slot can, in particular, comprise a coil socket, or several coil slots can, in particular, each comprise at least one coil socket. The use of a coil slot can advantageously enable the position data to be received reliably and without interference, while simultaneously requiring only minimal modifications to an existing MRI system or an existing MRI system design, by utilizing an already existing or planned coil slot.This allows, for example, the avoidance or minimization of additional costs. The coil connector can be a wireless coil connector, for instance. The receiver can be designed to identify itself as a special coil without RX and TX channels. This can enable particularly easy integration into an existing system architecture, for example, by using an internal identification method for the coils of the magnetic resonance imaging (MRI) system. In particular, the interface properties of the receiver can be designed analogously to the interface properties of the coils of the MRI system. A microcontroller of the receiver can be connected to and / or connectable to the same I2C bus as the coils of the MRI system. The receiver can be designed to transmit received position data via I2C, analogous to the signals received by the coils, for example, to an LC hub or...to pass the scanner on. It may be provided that the coil connector is inserted into a predefined coil slot among several coil slots. The communication device can be positioned on the headrest to align with the receiver's defined coil slot, particularly in such a way as to facilitate signal transmission between the communication device and the receiver. This allows, in particular, for orientation and a defined elevation relative to the patient's bed and / or headrest. For example, it may be provided that the coil connector is inserted into a coil slot that is generally free during the current measurement. For example, in the case of a subject, especially a patient, in the FFS position, a slot can be used that would be intended for connecting a head coil in the case of the HFS position.It may be provided that a coil slot for the receiver is located centrally in the transverse direction of the patient table, and that the coil slot may be located, in particular, in an area near the entrance of the examination tunnel. A central coil slot can be particularly advantageous because direct transmission over the shortest possible path is possible, without the direction of signal transmission, especially optical signal transmission, being dependent on the z-position of the body part cushion. For example, the patient table may include a handle for manually moving the table. The receiver may be located on the handle, particularly centrally on the handle.

[0042] According to one embodiment, the receiver is attached to, integrated into, and / or attachable to a part of the magnetic resonance imaging (MRI) system, in particular the MRI scanner. Advantageously, an attached or integrated receiver simplifies the workflow by requiring only the placement of the body part cushion. Furthermore, by selecting a suitable attachment point, signal reception, especially for optical signals, can be made more reliable. Specifically, the receiver can be attached to a patient table or inside an examination tunnel of the MRI system. Preferably, the receiver is arranged, or can be arranged, centrally in the transverse direction of the patient table. A central arrangement can be particularly advantageous for optical signal transmission.In this case, the direction of signal transmission can be largely independent of the z-position of the body part cushion, especially the head cushion, if the transmitter is positioned centrally on the body part cushion. For example, the patient bed may include a handle for manually moving the bed. The receiver may be positioned on the handle, particularly centrally on the handle.

[0043] According to one embodiment, the communication device and the receiver are designed so that the position data can be transmitted to the evaluation unit via radio transmission and / or via cable. For example, the magnetic resonance imaging system can include a cable between the communication device and the receiver.

[0044] According to one embodiment, the body part cushion comprises at least one solar cell and is configured to supply power to the magnetic field sensor and / or the communication device via the at least one solar cell and / or to charge an energy storage device for the magnetic field sensor and / or the communication device. Optionally, the magnetic resonance imaging system, particularly at the receiver, comprises a power source, especially an LED, for illuminating the at least one solar cell with light. The power source can, for example, be a white light source, particularly a white LED. Alternatively, the power source can comprise a specific light frequency and / or light frequency bandwidth. For example, a green LED or an infrared LED can be provided as the power source.The light source is preferably matched to the frequency-dependent efficiency of the at least one solar cell, in particular such that the light source emits light at a frequency for which the at least one solar cell exhibits a particularly high efficiency. It may be provided that the frequency of the light source differs from the frequency used to transmit the position data. The magnetic resonance imaging system may be configured to switch on the light source as soon as a signal from the communication device indicates that the energy storage state of the communication device is low.

[0045] According to one embodiment, the body part cushion comprises an energy storage device, wherein the body part cushion is specifically designed such that the energy storage device is galvanically rechargeable, and wherein the magnetic resonance imaging system includes a charging station for the energy storage device of the body part cushion, in particular a galvanic charging station. For example, the body part cushion can include charging contacts, in particular contacts on a lower surface of the body part cushion. The charging station can include corresponding mating contacts. The charging station can be a docking station for the body part cushion.

[0046] According to one embodiment, the body part cushion and / or the receiver includes RF shielding configured to shield the communication device and / or the receiver in such a way as to suppress measurement artifacts of the magnetic resonance imaging system caused by the communication device. The RF shielding can be configured as described herein, particularly with regard to the body part cushion.

[0047] All embodiments described herein can be combined with one another, unless explicitly stated otherwise.

[0048] The following describes embodiments with reference to the attached figures. Fig. Figure 1 shows a flowchart of a method for determining the position of a body part of a subject in a magnetic resonance imaging system according to an embodiment of the invention. Fig. Figure 2 shows a flowchart of a method for determining a specific absorption rate of a body part of a subject in a magnetic resonance imaging system according to an embodiment of the invention, and Fig. Figure 3 shows a flowchart of a method for determining the position of a body part of a subject in a magnetic resonance imaging system according to a further embodiment of the invention. Fig. Figure 4 shows a sketched side view of a magnetic resonance imaging system according to an embodiment of the invention, and Fig. Figure 5 shows a sketched side view of a magnetic resonance imaging system according to a further embodiment of the invention.

[0049] Fig. Figure 1 shows a flowchart of a method for determining the position of a body part of a subject in a magnetic resonance imaging (MRI) system according to an embodiment of the invention. In a first step 101, the body part is positioned on a body part cushion which lies on a patient table 4 of the MRI system. The body part can, in particular, be a head, which is positioned on a head pillow. In a further step 102, a magnetic stray field is determined. For this purpose, a magnetic field sensor 2 is used, which is arranged in or on the body part cushion. For example, a 3D Hall sensor can be used. The measurement data of the magnetic stray field are subsequently processed as position data. The position data can be raw measured data of the stray field or already adjusted or processed data based on the raw data.Typically, the magnetic stray field is measured outside an examination tunnel 8 of the magnetic resonance imaging system. This utilizes the fact that the field strength of the stray field depends on the relative position to the examination tunnel 8. In a further step 103, the position data is transmitted to an evaluation unit. A transmission medium is used for this purpose. For example, the transmission medium can be a radio transmitter in conjunction with a radio receiver. Alternatively or additionally, the transmission medium can be a cable transmission, i.e., the position data can be transmitted via cable. It can be particularly advantageous to transmit the data optically, especially with infrared light, to the evaluation unit. For such optical data transmission of the position data, light pulses based on pulse width modulation can be used, for example. The light pulses orThe light for optical transmission can be generated by a suitable LED and received by a light detector on the evaluation unit. In a further step, the evaluation unit determines the position of the body part, for example, the head, within the magnetic resonance imaging system based on the positional data. This assumes that the body part is properly positioned on the body part support cushion, allowing the position of the cushion, and thus the position of the body part, to be inferred from the sensor position. The position of the body part can be determined, in particular, by its offset relative to the position of the magnetic field sensor. It is especially advantageous to calculate this offset as a function of the size of the subject whose body part is being measured. The subject could be, for example, a human or an animal.Alternatively, a general offset can be used, or the offset can be determined by directly measuring the body part. By including body height in the calculation, known relationships to body proportions can be used to estimate the size of the body part without having to measure it directly. Body height is typically recorded in a patient's medical record anyway. For example, in the case of a head resting on a pillow, it might be possible to implement a Head_in_Pillow_Z_Offset as a linear function of the patient's height, e.g., using the formula... Head_in_pillow_Z_Offset = Body size × A + B with the two scalars A and B, where B specifies a fixed z-offset that is independent of body size, and the head size is estimated from body size based on A. For example, A can be derived from common average values ​​according to the relationship Body size=body size×7.5=>A=(1 / 7.5).

[0050] It can optionally be further provided to determine the position of at least one additional body part based on the position of the body part, and optionally also based on the subject's height. Standard principles for body proportions can also be used for this purpose.

[0051] Fig. Figure 2 shows a flowchart of a method for determining the specific absorption rate of a body part of a subject in a magnetic resonance imaging (MRI) system according to an embodiment of the invention. In a first step 201, the body part is positioned on a body part cushion, which lies on a patient table 4 of the MRI system. The body part can, in particular, be a head, which is positioned on a head cushion 3. In a further step 202, a magnetic stray field is determined. For this purpose, a magnetic field sensor 2, in particular a 3D Hall sensor, is used, which is arranged in or on the body part cushion. The measurement data of the magnetic stray field are subsequently processed as position data. In a further step 203, the position data are transmitted to an evaluation device by means of a transmission means.In a further step 204, the evaluation unit determines the position of the body part, for example the head, in the magnetic resonance imaging system based on the positional data. Steps 201-204 can be compared in particular to steps 101-104 of the procedure with reference to... Fig. The procedure described in section 1 corresponds to the method described in section 205. In a further step, the specific absorption rate (SAR) of the body part is determined based on an expected field distribution during a measurement of the magnetic resonance imaging system and the determined position of the body part. Conventional position-dependent calculation methods can be used to determine the SAR. Crucially, within the scope of the invention, the method of position determination used for determining the SAR is of particular importance.

[0052] Fig. Figure 3 shows a flowchart of a method for determining the position of a body part of a subject in a magnetic resonance imaging (MRI) system according to a further embodiment of the invention. In a first step 311, a pillow 3 and a receiver with an IR connector are stored in a storage location, for example, in a cabinet. The pillow 3 has a magnetic field sensor 2, in particular a 3D Hall sensor. In a further step 312, the pillow 3 is placed on a patient table 4 of an MRI system, and the receiver is connected to a designated coil slot 22 of the MRI system by means of a coil connector 21. The head of a subject, in particular a patient, is placed on the pillow 3 while the subject is prepared for a MRI scan on the patient table 4.While the pillow 3 is placed on the patient table 4 and thus within the magnetic stray field of the magnetic resonance imaging system, a (preferably optical) transmitter (and optionally a magnetic field sensor 2) of the pillow 3 is automatically switched on via a reed switch. The receiver is automatically activated by the power supply via the coil slot 22. In a further step 313, the magnetic field sensor 2 of the pillow 3 determines the magnetic stray field at its position as position data and transmits this data, particularly at regular intervals (e.g., every few seconds), to the receiver. The transmission of the position data can preferably be optical. The receiver then forwards the data, in particular, to an evaluation device. This step 313 described here can be carried out analogously to steps 102-104 of the [reference to be added]. Fig. The procedure described in section 1 is provided for. In a further step 314, a magnetic resonance imaging (MRI) scan is started. To start the MRI scan, the transmitter that transmits the position data is switched off. This can be done, for example, by a command sent to the pillow 3 (e.g., optically). In a further step 315, the MRI scan is terminated. Optionally, the transmitter can be reactivated in this step 315 to transmit further position data. In a further step 316, the pillow 3 and the receiver are returned to their storage location. In particular, the transmitter of the pillow 3 switches off again because the reed switch is no longer exposed to the stray magnetic field at the entrance of the examination tunnel 8.

[0053] Fig. Figure 4 shows a sketched side view of a magnetic resonance imaging (MRI) system according to an embodiment of the invention. In this embodiment, the body part pillow is a head pillow 3, and the body part is the head 5 of a patient. The patient lies on a patient table 4 of the MRI system in front of the examination tunnel 8 of the MRI system, and the head 5 rests on the head pillow 3. The head pillow 3 includes a magnetic field sensor 2 (for example, a 3D Hall sensor) for detecting the local magnetic field, in particular the stray field, as position data. Furthermore, a communication device 6 is provided on the body part pillow for transmitting the position data to a receiver. The communication device 6 can, for example, be or include an interface with a cable connection or a transmitter, in particular a radio transmitter or optical transmitter.The magnetic resonance imaging system further comprises a receiver for receiving and transmitting the position data of the pillow 3 and an evaluation unit designed to receive the position data from the receiver and thus determine the position of the body part in the magnetic resonance imaging system. The receiver and the evaluation unit are not shown here. The magnetic resonance imaging system is specifically designed to perform a procedure as described in one of the [references]. Fig. The procedure is described in sections 1-3. The example shown could, for instance, involve a knee examination. The position of the head is determined based on the position of the magnetic field sensor 2 via the location-dependent magnetic field. The distance between the magnetic field sensor 2 and the entrance of the examination tunnel 8 ("bore") is denoted by a. The distance between the isocenter 12 of the magnetic resonance imaging system and the tunnel entrance is denoted by b. The distance between the position of the patient's knee 11 in the initial position shown here and the isocenter is denoted by c. This distance corresponds to the distance the patient table 4 is moved to position the knee for measurement. d denotes the patient's height or length.If the sensor's position in its current state is calculated, the sensor's position Zpos (relative to the isocenter), and thus the head's position during the knee measurement, can be calculated, for example, using Zpos = (a + b - c). More precisely, Zpos determines the sensor position here. Optionally, the head's position can be determined using an offset v based on the sensor position, specifically in this example according to Zpos = (a + b - c - v). The offset can depend on the patient's height. An approach to calculate a relative position RelPos of the examination based on the patient's height could, for example, be RelPos = (Zpos / d). Based on the relative position, a specific absorption rate of individual body parts can be determined.

[0054] Fig. Figure 5 shows a sketched side view of a magnetic resonance imaging (MRI) system according to a further embodiment of the invention. In this embodiment, the body part pillow is a head pillow 3 and the body part is the head 5 of a patient. The patient lies on a patient table 4, which is located in front of the examination tunnel 8 of the MRI system, and the head 5 rests on the head pillow 3. The head pillow 3 includes a magnetic field sensor 2, in particular a 3D Hall sensor, for detecting the local magnetic field, especially stray field, as position data. Furthermore, a communication device 6 is provided for transmitting the position data to a receiver on the body part pillow. In this embodiment, the communication device 6 includes an IR LED as an optical transmitter with which the position data can be transmitted optically, in particular in the form of light pulses (for example, based on pulse width modulation).The beam path 7 of the optical signal transmission is shown schematically here. The position data is transmitted optically to a receiver 20, in particular an IR receiver. The receiver 20 is plugged into a coil slot 22 via a coil connector 21 and is connected to an evaluation unit (not shown here) of the magnetic resonance imaging system. The evaluation unit is designed to receive the position data from the receiver and thus determine the position of the body part in the magnetic resonance imaging system. The head position 15 is defined here based on a distance to the isocenter in the examination tunnel 8. The magnetic resonance imaging system is specifically designed to perform a procedure as described in one of the... Fig.The embodiment described in Figures 1-3 is to be carried out as follows. Based on the position of the body part, a specific absorption rate can be determined. In this embodiment, the pillow 3 comprises at least one solar cell 9 and is configured to obtain energy via the at least one solar cell 9 for the operation of the magnetic field sensor 2 and / or the communication device 6 with the IR LED. The magnetic resonance imaging system can include, in particular at the receiver 20, a power source, in particular an LED, for irradiating the solar cells 9 with light. The pillow 3 can optionally also have an energy storage device for supplying the magnetic field sensor 2 and / or the communication device 6. The energy storage device can, in particular, be rechargeable via the at least one solar cell 9. The communication device 6 can optionally be configured to also transmit information about the charge level of the energy storage device.Optionally, the pillow 3 can include a reed switch and be configured to control the power supply to the magnetic field sensor 2 and / or the communication device 6 via the reed switch, such that the power supply is activated depending on a magnetic field at the location of the pillow 3, in particular such that the power supply is activated when a magnetic field has a certain minimum strength. RF shielding can be provided for the communication device 6 and / or the receiver 20, which is configured to shield the communication device 6 and / or the receiver 20 in such a way as to suppress measurement artifacts of the magnetic resonance imaging system caused by the communication device 6 and / or the receiver 20.

Claims

[1] Method for determining the position of a body part, in particular a head, of a subject in a magnetic resonance imaging system, the method comprising the following steps: - Positioning the body part on a body part cushion, the body part cushion being arranged in particular on a patient table (4) of the magnetic resonance imaging system; - Determining a magnetic field, in particular a stray field, with a magnetic field sensor (2) arranged in or on the body part cushion in order to determine position data, wherein the magnetic field sensor (2) in particular comprises a 3D Hall sensor; - Transmitting the position data to an evaluation device using a transmission device; - Determining the position of the body part in the magnetic resonance imaging system using position data based on the body part being placed on the body part cushion, by the evaluation device. [2] Method according to claim 1, wherein the position data are transmitted optically, in particular with infrared light, to the evaluation device. [3] Method according to one of the preceding claims, wherein the position data are transmitted by means of light pulses, in particular based on pulse width modulation. [4] Method according to any one of the preceding claims, wherein the body part position is determined by determining the position of the body part based on at least one offset relative to the position of the magnetic field sensor (2), where the value of at least one offset is set depending on the body size of the subject. [5] Method according to one of the preceding claims, wherein the position of at least one additional body part is determined based on the position of the body part and optionally further based on the body size of the subject. [6] Method for determining a specific absorption rate of a body part, in particular a head, of a subject in a magnetic resonance imaging system, comprising the following steps: - Performing a method according to one of the preceding claims to determine a position of the body part; - Determining the specific absorption rate of the body part based on an expected field distribution during a measurement of the magnetic resonance imaging system and the determined position of the body part. [7] Body part pillows, in particular head pillows (3), for positioning a body part, in particular the head, during a magnetic resonance imaging measurement, wherein the body part cushion includes a magnetic field sensor (2) for detecting the local magnetic field as position data, wherein the body part cushion includes a communication device (6) for transmitting the position data to a receiver (20). [8] Body part cushion according to claim 7, wherein the body part cushion comprises at least one solar cell (9) and is designed to obtain energy via the at least one solar cell (9) for the operation of the magnetic field sensor (2) and / or the communication device (6), in particular to charge an energy storage device for supplying the magnetic field sensor (2) and / or the communication device (6). [9] Body part cushion according to claim 7 or 8, wherein the communication device (6) comprises a light source, in particular an infrared light source, and is designed to optically transmit the position data to the evaluation device by means of the light source. [10] Body part cushion according to one of claims 7 to 9, wherein the body part cushion comprises a reed switch and is configured to control a power supply to the magnetic field sensor (2) and / or the communication device (6) via the reed switch, such that the power supply is activated depending on a magnetic field at the location of the body part cushion. [11] Magnetic resonance imaging system comprising a body part cushion according to one of claims 7 to 10, a receiver (20) for receiving and forwarding the position data of the body part cushion, an evaluation device designed to receive position data from the receiver (20) and thus to determine the position of the body part in the magnetic resonance imaging system, wherein the magnetic resonance imaging system is in particular designed to determine position data using a method according to one of claims 1 to 5 and / or a specific absorption rate using a method according to claim 6. [12] Magnetic resonance imaging system according to claim 11, wherein the body part cushion includes a light source, in particular an infrared light source, and is designed to optically transmit the position data to the receiver (20), wherein the receiver (20) includes a light sensor for receiving the position data. [13] Magnetic resonance imaging system according to claim 11 or 12, wherein the receiver (20) comprises a coil connector (21) for a coil slot (22) of the magnetic resonance imaging system and is configured to be connected to a coil slot (22) of the magnetic resonance imaging system. [14] Magnetic resonance imaging system according to any one of claims 11 to 13, wherein the body part cushion includes at least one solar cell (9) and is designed to supply power to the magnetic field sensor (2) and / or the communication device (6) via the at least one solar cell (9) and / or to charge an energy storage device for the magnetic field sensor (2) and / or the communication device (6), wherein the magnetic resonance imaging system, in particular at the receiver (20), comprises a supply light source, in particular an LED, for irradiating the at least one solar cell (9) with light. [15] Magnetic resonance imaging system according to any one of claims 11 to 14, wherein the body part cushion and / or the receiver (20) comprises RF shielding configured to shield the communication device (6) and / or the receiver (20) in such a way as to suppress measurement artifacts of the magnetic resonance imaging system caused by the communication device (6) and / or the receiver (20).

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