JP5269499B2 - Magnetic resonance imaging apparatus, SAR calculation apparatus, method of operating magnetic resonance imaging apparatus, and SAR calculation method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To appropriately calculate the upper limit value of SAR relative to a body part to be actually irradiated with an RF pulse in an MRI system. <P>SOLUTION: A partial body weight estimating part 144 acquires irradiation range information which indicates the range of a body part to be irradiated with the RF pulse when imaging is performed from a three-dimensional image including an imaging region reconfigured in pre-scanning, and estimates the partial body weight of the body part, on the basis of the acquired irradiation range information. Then, an SAR calculating part 145 calculates the upper limit value of the SAR in the body part relative to the body part to be irradiated with the RF pulse, on the basis of the partial body weight estimated by the partial body weight estimating part 144. <P>COPYRIGHT: (C)2009,JPO&amp;INPIT

Description

  The present invention relates to a magnetic resonance imaging apparatus, a SAR calculation apparatus, and a magnetic resonance apparatus that reconstruct an image by detecting a magnetic resonance signal emitted from a part of a subject by irradiating a part of the subject with an RF (Radio Frequency) pulse. The present invention relates to an operation method of an imaging apparatus and a SAR calculation method, and more particularly, to a calculation of a SAR value that is a safety standard when irradiating an RF pulse.

  2. Description of the Related Art Conventionally, a magnetic resonance imaging apparatus is an apparatus that captures an image of a subject using a magnetic resonance phenomenon. An RF (Radio Frequency) is applied to a subject placed in a static magnetic field to cause the magnetic resonance phenomenon. Irradiate a pulse. In general, it is known that the body temperature of a living body rises when irradiated with an RF pulse. However, in the case of a human body, there is a possibility that a disorder occurs when the body temperature rises once. Therefore, from the viewpoint of safety, the intensity of the RF pulse irradiated to the subject is regulated by law.

  Usually, as an evaluation value for evaluating the safety of such an RF pulse, SAR (Specific Absorption Rate) indicating the amount of energy absorbed in a unit mass of tissue per unit time is used. The Ministry of Health, Labor and Welfare Examination Practice Communication and IEC (International Electrotechnical Commission) standards define the upper limit of the SAR used in the magnetic resonance imaging apparatus in order to regulate the strength of the RF pulse.

  However, in recent years, there has been an increase in photography that increases the SAR for various reasons, and the legal upper limit of the SAR has become strict from the viewpoint of safety. Therefore, in order to create a safe and effective magnetic resonance imaging apparatus, it is necessary to more strictly calculate the upper limit value of the SAR.

  In order to calculate the SAR value strictly, it is necessary to grasp to what part of the subject the RF pulse is irradiated and how much size and weight the irradiated part has. For example, in Patent Document 1, a method of estimating the partial weight of a body part including the imaging part based on the input body weight, height, and imaging part of the subject and calculating the upper limit value of the SAR from the estimated partial weight. Is disclosed.

JP 2006-95278 A

  However, in the conventional technique described in Patent Document 1, since the partial weight is estimated based on the input weight, height, and imaging part, how much RF pulse is actually irradiated to which part of the subject. The size and weight of the irradiated part cannot be grasped, and the upper limit value of the SAR cannot be calculated appropriately.

  This problem will be specifically described with reference to FIG. FIG. 7 is a diagram for explaining a problem in the conventional technique. For example, as shown in the figure, when imaging the subject's head, the subject is inserted deeper into the transmission coil in the state (b) than in the state (a). Therefore, the range of the body part that is actually irradiated with the RF pulse is larger in (b) than in (a), and the partial body weight to be used for calculating the SAR should be larger in (b) than in (a). It is. However, in the conventional technique, when the imaging region is the same, the partial weight is estimated to be the same, and therefore, the upper limit value of the SAR regarding the body part to which the RF pulse is actually irradiated cannot be appropriately calculated.

  The present invention has been made to solve the above-described problems caused by the prior art, and is a magnetic resonance imaging apparatus capable of appropriately calculating the upper limit value of the SAR regarding the body part to which the RF pulse is actually irradiated, It is an object of the present invention to provide an SAR calculation apparatus, an operation method of a magnetic resonance imaging apparatus, and an SAR calculation method.

  In order to solve the above-described problems and achieve the object, a magnetic resonance imaging apparatus according to an embodiment of the present invention detects a magnetic resonance signal emitted from a subject by irradiating the subject with an RF pulse. An imaging region reconstructed in advance by a signal detection unit, an image reconstruction unit that reconstructs an image of the subject based on the magnetic resonance signal detected by the signal detection unit, and the image reconstruction unit Is acquired from an image including the body part SAR irradiated with the RF pulse at the time of photographing, and the body part SAR related to the body part irradiated with the RF pulse is acquired based on the acquired irradiation range information. A SAR calculation unit that calculates an upper limit value.

  Further, the SAR calculation apparatus according to another aspect of the present invention is an irradiation indicating a range of a body part irradiated with the RF pulse at the time of imaging from an image including an imaging region reconstructed in advance by a magnetic resonance imaging apparatus. An irradiation range acquisition unit that acquires range information, and an upper limit value calculation unit that calculates an upper limit value of the body part SAR related to the body part irradiated with the RF pulse based on the irradiation range information acquired by the irradiation range acquisition unit And comprising.

  According to another aspect of the present invention, the magnetic resonance imaging apparatus is operated by activating a signal detection unit that detects a magnetic resonance signal emitted from the subject by irradiating the subject with an RF pulse. An image reconstruction unit that reconstructs an image of the subject is activated based on the magnetic resonance signal detected by the signal detection unit, and includes an imaging region reconstructed in advance by the image reconstruction unit The irradiation range information indicating the range of the body part irradiated with the RF pulse from the captured image is acquired, and based on the acquired irradiation range information, the upper limit value of the body part SAR regarding the body part irradiated with the RF pulse The SAR calculation unit for calculating

  Further, the SAR calculation method according to another aspect of the present invention is an irradiation that indicates a range of a body part irradiated with the RF pulse at the time of imaging from an image including an imaging region reconstructed in advance by a magnetic resonance imaging apparatus. Obtaining range information, and calculating an upper limit value of the body part SAR relating to the body part irradiated with the RF pulse based on the obtained irradiation range information.

  According to the present invention, there is an effect that it is possible to appropriately calculate the upper limit value of the SAR regarding the body part that is actually irradiated with the RF pulse.

  Exemplary embodiments of a magnetic resonance imaging apparatus, a SAR calculation apparatus, a method for operating a magnetic resonance imaging apparatus, and a SAR calculation method according to the present invention will be described below in detail with reference to the accompanying drawings. In the following, the magnetic resonance imaging apparatus is referred to as an “MRI (Magnetic Resonance Imaging) apparatus”, and the magnetic resonance signal emitted from the subject when irradiated with an RF pulse is referred to as an “MR signal”.

  First, the configuration of the MRI apparatus according to the present embodiment will be described with reference to FIG. FIG. 1 is an explanatory diagram for explaining the configuration of the MRI apparatus according to the present embodiment. As shown in the figure, this MRI apparatus includes a static magnetic field magnet 1, a gradient magnetic field coil 2, an RF coil 3, a static magnetic field power supply 4, a gradient magnetic field power supply 5, a transmitter 6, and a receiver 7. , A sequence control device 8, a power measuring device 9, and a console device 100.

The static magnetic field magnet 1 is a magnet formed in a cylindrical shape, and generates a static magnetic field H ₀ in a space inside the cylinder in which the subject P is arranged by a current supplied from a static magnetic field power supply 4. The gradient magnetic field coils 2 are three pairs of coils disposed inside the static magnetic field magnet 1, and three directions of x, y, and z are placed inside the static magnetic field magnet 1 by current supplied from the gradient magnetic field power supply 5. A gradient magnetic field is generated along

  The RF coil 3 is a receiving coil disposed so as to face the subject P within the opening of the static magnetic field magnet 1, irradiates the subject P with an RF pulse transmitted from the transmitter 6, and is excited. To receive the MR signal emitted from the hydrogen nucleus of the subject P. The static magnetic field power source 4 is a power source that supplies current to the static magnetic field magnet 1, and the gradient magnetic field power source 5 is a power source that supplies current to the gradient magnetic field coil 2 based on an instruction from the sequence control device 8.

  The transmitter 6 is a device that transmits an RF pulse to the RF coil 3 via a power measuring device 9 described later based on an instruction from the sequence control device 8. The receiver 7 detects the MR signal received by the RF coil 3, and transmits raw data obtained by digitizing the detected MR signal to the sequence control device 8.

  The sequence control device 8 is a device that scans the subject P by driving the gradient magnetic field power source 5, the transmitter 6, and the receiver 7 based on the sequence information transmitted from the console device 100. Here, the sequence information refers to the strength of the power supplied from the gradient magnetic field power supply 5 to the gradient magnetic field coil 2 and the timing of supplying the power, and the strength of the RF pulse transmitted from the transmitter 6 to the RF coil 3 and the RF pulse. This is information defining a procedure for performing scanning, such as timing and timing at which the receiver 7 detects an MR signal. Then, when the raw data is transmitted from the receiver 7 as a result of scanning the subject P, the sequence control device 8 collects the raw data and transmits it to the console device 100.

  The power measuring device 9 is a device that measures the high frequency output of the RF pulse transmitted from the transmitter 6 to the RF coil 3. The power measuring device 9 measures the high frequency output of the RF pulse in the pre-scan, and transmits information indicating the measured high frequency output to the console device 100.

  The console device 100 controls the entire MRI apparatus based on an operation from an operator, converts raw data transmitted from the sequence control device 8 into k-space data, and reconstructs an image from the k-space data. Device. The console apparatus 100 also calculates the SAR value when the subject P is irradiated with the RF pulse.

  Although not shown here, this MRI apparatus is provided with a gantry for supporting the static magnetic field magnet 1, the gradient magnetic field coil 2, the RF coil 3, and the like, and a top plate for placing the subject P. It also has a bed for supporting the top board.

  Next, the configuration of the console device 100 shown in FIG. 1 will be described with reference to FIG. FIG. 2 is a functional block diagram showing a configuration of console device 100 shown in FIG. As shown in the figure, the console device 100 includes an input unit 110, a display unit 120, a storage unit 130, and a control unit 140.

  The input unit 110 is an input unit for accepting various inputs by an operator, and is realized by a pointing device such as a mouse or a trackball, a keyboard, or the like, and accepts various operations by cooperating with the display unit 120 described later. A user interface is provided to the operator.

  The display unit 120 is an output unit for displaying various information such as a captured image, and is realized by a monitor device such as a CRT (Cathode Ray Tube) display or a liquid crystal display. The display unit 120 displays various messages for the operator, a reconstructed image of the subject reconstructed by the image reconstructing unit 143 described below, and the like under the control of the main control unit 141 described later.

  The storage unit 130 is a storage unit that stores various types of information, and includes an image storage unit 131 and a partial weight definition information storage unit 132. The image storage unit 131 is a storage unit that stores a reconstructed image of a subject reconstructed by an image reconstructing unit 143 described later.

  The partial weight definition information storage unit 132 is a storage unit that stores partial weight definition information in which a partial weight is defined for each part. FIG. 3 is a diagram illustrating an example of partial weight definition information stored in the partial weight definition information storage unit 132. Specifically, as shown in the figure, the partial body weight definition information storage unit 132 associates the site of the subject, the height [cm], the body weight [kg], and the partial body weight W [kg]. Information is stored as partial weight definition information.

  Among these, values indicating predetermined ranges are respectively set for the height and the weight. The partial weight W is set with a calculation formula for calculating the partial weight based on the range of the body part to which the RF pulse is actually irradiated. Here, the range of the body part irradiated with the RF pulse is indicated by irradiation range information including a plurality of parameters defined in advance according to the feature of the shape.

FIG. 4 is a diagram for explaining irradiation range information regarding the head. For example, as shown in the figure, it is assumed that four types of parameters are defined as irradiation range information relating to the head, that is, the lateral width x, depth y, height z, and lateral width u of the chin portion. In this case, as shown in FIG. 3, the partial weight W of the head in the partial weight definition information includes, for example, f ₁ (x, y, z, u), f ₂ (x, y, z, u), f ₃ (x, y, z, u), f ₄ (x, y, z, u), f ₅ (x, y, z, u), f ₆ (x, y, z, u), etc. x , Y, z, and u are used to set a calculation formula for calculating the partial weight based on four types of parameters.

Similarly, for example, when three types of parameters of abdominal width x, depth y, and height z are defined as irradiation range information regarding the abdomen, as shown in FIG. For example, g ₁ (x, y, z), g ₂ (x, y, z), g ₃ (x, y, z), g ₄ (x, y, z), g A calculation formula for calculating the partial weight W is set based on three types of parameters x, y, z such as ₅ (x, y, z) and g ₆ (x, y, z).

Here, f ₁ (x, y, z, u) to f ₆ (x, y, z, u) and g ₁ (x, y, z) to g ₆ (x, y) set to the partial weight W are set. , Z) and the like are defined by modeling each part based on statistical information on the subject or information on the subject photographed in the past according to height and weight.

  The control unit 140 is a processing unit that has a control program such as an OS (Operating System), a program that defines various processing procedures, and an internal memory for storing necessary data, and executes various processes using these. A main control unit 141, a sequence control unit 142, an image reconstruction unit 143, a partial weight estimation unit 144, and a SAR calculation unit 145.

  The main control unit 141 is a processing unit that receives various instructions and various requests from the operator via the input unit 110 and controls the operation of each functional unit based on the received instructions and requests. Specifically, when receiving an imaging instruction (pre-scan (preliminary scan) or main-scan instruction) from the operator, the main control unit 141 generates sequence information based on the specified imaging conditions. And transmitted to the sequence control unit 142. This sequence information is transmitted to the sequence control device 8 via the sequence control unit 142 and is used when photographing is performed by the sequence control device 8.

  In addition, when accepting an imaging instruction from the operator, the main control unit 141 simultaneously accepts input of weight, height, imaging region, imaging condition, and operation mode. Here, for example, the chest, abdomen, lower abdomen, and thighs are input as the imaging region, and the imaging conditions include the type of pulse sequence (including the number of RF pulses), the number of multi-slices, and the slice thickness Etc. are entered. As the operation mode, a normal operation mode, a primary level management operation mode, or a secondary level management operation mode is input.

  The items input here are used when the partial weight of the body part is estimated by the partial weight estimation unit 144 described later, and when the SAR value and the upper limit value of various SARs are calculated by the SAR calculation unit 145, respectively. .

  In addition, when receiving a pre-scan instruction from the operator, the main control unit 141 generates sequence information so that shooting is performed by a flip-angle FE method in which the SAR value can be ignored, and the generated sequence Information is transmitted to the sequence control unit 142. Since the purpose of the pre-scan is to grasp the range of the body part irradiated with the RF pulse, the main control unit 141 seems to perform imaging with an FOV (Field of View) large enough to confirm the sensitivity region. Generate sequence information.

  When the pre-scan is actually performed, the main control unit 141 displays the high-frequency output transmitted from the power measuring device 9 when the pre-scan is performed and the state where the subject is not placed on the top board. By calculating the difference from the high frequency output measured in advance, the high frequency output value absorbed by the subject is detected. The high-frequency output value detected here is used when the SAR calculation unit 145 described later calculates the SAR values of various SARs.

  The sequence control unit 142 is a processing unit that controls transmission / reception of data exchanged with the sequence control device 8. Specifically, when the sequence information is transmitted from the main control unit 141, the sequence control unit 142 transmits the sequence information to the sequence control device 8. When the raw data is transmitted from the sequence control device 8, the sequence control unit 142 delivers the transmitted raw data to the image reconstruction unit 143 described later.

  The image reconstruction unit 143 is a processing unit that reconstructs an image based on the raw data delivered from the sequence control unit 142. Specifically, the image reconstruction unit 143 converts raw data delivered from the sequence control unit 142 into k-space data under the control of the main control unit 141, and performs Fourier transform on the k-space data. A three-dimensional image is reconstructed by performing predetermined image reconstruction processing such as processing.

  In the pre-scan, the image reconstruction unit 143 reconstructs a three-dimensional image of the body part that is actually irradiated with the RF pulse. FIG. 5 is a diagram illustrating an example of a three-dimensional image of a body part irradiated with an RF pulse. (A) and (b) shown in the figure show three-dimensional images of the head of the subject pre-scanned in the states (a) and (b) shown in FIG. 7, respectively.

As shown in FIGS. 5A and 5B, in the pre-scan, a three-dimensional image of a body part actually irradiated with an RF pulse is reproduced even if the subject's weight, height, and imaging region are the same. Composed. Therefore, for example, as shown in FIG. 5C, when pre-scanning is performed on an infant with a small physique, a three-dimensional image of a body part smaller than that of an adult is reconstructed.

  The three-dimensional image reconstructed by the pre-scan in this way is used when the partial weight of the body part is estimated by the partial weight estimation unit 144 described later. The three-dimensional image reconstructed by the pre-scan does not have to be dedicated for one shooting, and is shared with a map image for shimming or parallel imaging in order to shorten the shooting time. Is desirable.

  The partial body weight estimation unit 144 is a processing unit that estimates a partial body weight of a body part irradiated with an RF pulse during imaging. Specifically, the partial body weight estimation unit 144 is configured to display a three-dimensional image including the imaging region reconstructed by the pre-scan under the control of the main control unit 141 after the pre-scan is performed. Read from 131 and acquire irradiation range information indicating the range of the body part irradiated with the RF pulse at the time of photographing from the read three-dimensional image.

  For example, it is assumed that the imaging region received from the operator by the main control unit 141 is the head. In this case, the partial weight estimation unit 144 calculates the horizontal width x, depth y, height z, and horizontal width u of the chin portion as irradiation range information about the head from the three-dimensional image reconstructed by the prescan. Obtain (see FIG. 4).

  When the irradiation range information is acquired, the partial weight estimation unit 144 reads, from the partial weight definition information storage unit 132, partial weight definition information related to the imaging region received from the operator by the main control unit 141. Then, the partial body weight estimation unit 144 estimates the partial body weight of the body part irradiated with the RF pulse based on the read part weight definition information and the irradiation range information acquired from the three-dimensional image.

  For example, it is assumed that the imaging region received from the operator by the main control unit 141 is the head, and that the height received by the main control unit 141 is 150 [cm] and the weight is 50 [kg]. Assume that the partial weight definition information stored in the weight definition information storage unit 132 is as shown in FIG.

In that case, the partial weight estimation unit 144 reads the partial weight information definition information with the partial weight W = f ₅ (x, y, z, u) from the partial weight definition information storage unit 132, and x, y, z, u The partial weight W is calculated by substituting the lateral width x, depth y, height z, and lateral width u of the chin portion obtained from the three-dimensional image into the parameters.

  In this manner, the partial weight estimation unit 144 acquires irradiation range information indicating the range of the body part that is actually irradiated with the RF pulse from the three-dimensional image reconstructed by the prescan, and the acquired irradiation range information Since the partial weight of the body part is calculated based on the above, the partial weight can be estimated with high accuracy.

  Here, although the case where the partial weight estimation unit 144 calculates the partial weight using a predefined calculation formula has been described, for example, the number of voxels of a three-dimensional image reconstructed by pre-scanning is counted. By measuring the area and volume of the body part, the measured volume and the mass per unit volume determined in advance for each part (if the part is the same, the tissues constituting the part are also substantially the same. The partial weight of the body part may be calculated based on the above. Thereby, compared with the case where the partial weight W is calculated based on the partial length of a site | part, a partial weight can be calculated more correctly.

  The SAR calculation unit 145 is a processing unit that calculates SAR values and upper limit values of various SARs. Specifically, the SAR calculation unit 145 calculates SAR values and upper limit values of various SARs based on IEC 60601-2-33 2nd Edition, which is a safety standard for MRI apparatuses. Here, the SAR value is a high frequency output per unit mass absorbed by the subject, and the unit is [W / kg].

  In IEC 60601-2-33 2nd Edition, SAR is classified into whole body SAR, head SAR, local SAR, and body part SAR according to the region to be imaged. The whole body SAR is used for photographing the whole body, the head SAR is used for photographing the head, and the local SAR is used for photographing a small area of the body using a transmission / reception surface coil. Is the average value. The body part SAR is an item incorporated from the IEC standard second edition, and is an average value over the weight of the body part exposed to the transmitting high-frequency coil.

  The upper limit value of each SAR is defined for each predetermined operation mode, and the normal operation mode, the first level management operation mode, and the second level management operation mode are defined as the operation mode. .

For example, in the normal operation mode, the upper limit of the whole body SAR is 2 W / kg, the upper limit of the head SAR is 3.2 W / kg, the upper limit of the local SAR is 10 W / kg for the head and trunk, and 20 W / kg for the extremities. kg, the upper limit of the body part SAR is
10-8 × (partial body weight / body weight of photographing object) [W / kg] (1)
It is defined as

  The upper limit values of these SARs are defined for the purpose of suppressing the temperature rise of the trunk and the crystalline lens having a small cooling effect due to blood flow to 1 ° C. or less by heating with high frequency.

  On the other hand, when a high frequency is applied to the whole body, the SAR value of each SAR is obtained by dividing the high frequency output value absorbed by the subject by the body weight of the subject, When the high frequency is applied only to the head, the head weight is estimated from the standard data on the human body and the high frequency output value is divided by the head weight to obtain the SAR value of the head SAR.

  In accordance with the above standard, the SAR calculation unit 145 determines the upper limit value for the whole body SAR according to the operation mode received from the operator by the main control unit 141. The SAR calculation unit 145 also includes the weight of the subject and the number of RF pulses received by the main control unit 141, the high-frequency output value (high-frequency output value absorbed by the subject) detected by the main control unit 141, and Is used to calculate the SAR value of the whole body SAR.

  Further, the SAR calculation unit 145 determines an upper limit value for the head SAR and the local SAR according to the operation mode received from the operator by the main control unit 141. In addition, the SAR calculation unit 145 is determined for each body weight, height, and imaging region (for example, chest, abdomen, lower abdomen, thigh, etc.) received from the operator by the main control unit 141, for example. The SAR values of the head SAR and the local SAR are calculated using the standard data of the partial weight of the human body (stored in the storage unit 130 and the like) and the high-frequency output value detected by the main control unit 141. Here, the head weight or the like is a substantially constant value for adults and is relatively easy to estimate, but it is difficult to estimate the body part SAR value only by weight information.

  Therefore, the SAR calculation unit 145 operates the partial body weight SAR and the partial body weight estimated by the partial body weight estimation unit 144 and the main control unit 141 according to the operation mode received from the operator by the main control unit 141. Using the weight of the subject received from the person, the upper limit value is calculated using a calculation formula defined for each operation mode (for example, formula (1) for the normal operation mode). In addition, the SAR calculation unit 145 calculates the SAR value of the body part SAR using the partial weight estimated by the partial weight estimation unit 144 and the high-frequency output value detected by the main control unit 141.

  Note that the SAR value calculated here is calculated based on the standard data or the partial weight estimated by the partial weight estimation unit 144, and therefore it is expected that there is an error in each. Therefore, it is necessary to set the upper limit value of each SAR low on the safe side in consideration of the error.

  Then, when the SAR calculation unit 145 calculates the SAR value and the upper limit value of each SAR, for each type of SAR, the SAR calculation unit 145 determines whether or not the calculated SAR value exceeds the upper limit value. The main control unit 141 is instructed to display a photographing prohibition message on the display unit 120. On the other hand, if the SAR value does not exceed the upper limit value, the SAR calculation unit 145 instructs the main control unit 141 to display the photographing prohibition message on the display unit 120. Accordingly, the operator can determine whether to perform the main scan or reset the imaging conditions.

  Next, a processing procedure of SAR calculation by the console apparatus 100 according to the present embodiment will be described with reference to FIG. FIG. 6 is a flowchart illustrating a SAR calculation processing procedure by the console apparatus 100. Here, a case where the SAR value and the upper limit value of the body part SAR are calculated will be described.

  As shown in the figure, in this console device 100, first, the main control unit 141 accepts input of weight, height, imaging region, imaging conditions, and operation mode (step S101), and the sequence control unit 142 performs a sequence. A pre-scan is performed by transmitting information (step S102).

  Further, the main control unit 141 includes a high-frequency output transmitted from the power measuring instrument 9 when the pre-scan is performed, and a high-frequency output measured in advance in a state where the subject is not placed on the top board. The high frequency output value absorbed by the subject is detected by calculating the difference between the two (step S103).

  Subsequently, the image reconstruction unit 143 reconstructs a three-dimensional image from the raw data collected by the prescan (step S104), and then the partial weight estimation unit 144 is reconstructed by the image reconstruction unit 143. The irradiation range information indicating the range of the body part irradiated with the RF pulse at the time of photographing is acquired from the acquired image (step S105), and the partial body weight of the body part is estimated based on the acquired irradiation range information (step S106). .

  Thereafter, the SAR calculation unit 145 calculates the upper limit value of the body part SAR based on the partial weight estimated by the partial weight estimation unit 144, the high-frequency output value detected by the main control unit 141, and the like (step S107). Further, the SAR value of the body part SAR is calculated (step S108).

  Here, when the calculated SAR value exceeds the upper limit value (step S109, Yes), the main control unit 141 displays a shooting prohibition message on the display unit 120 (step S110), and the shooting condition is set by the operator. Wait for it to change. When accepting the change of the imaging condition from the operator (step S111, Yes), the main control unit 141 returns to step S108, calculates the body part SAR again, and steps until the calculated SAR value becomes equal to or less than the upper limit value. The processes of S110 and S111 are repeated.

  When the calculated SAR value is equal to or lower than the upper limit (step S109, No), the main control unit 141 displays a photographing permission message on the display unit 120 (step S112), and performs an actual scan from the operator. Wait for instructions. When receiving an instruction for a main scan from the operator (step S113, Yes), the main control unit 141 performs the main scan by transmitting sequence information to the sequence control unit 142 (step S114).

  When the main scan is performed in this way, the image reconstruction unit 143 reconstructs a three-dimensional image from the raw data collected by the main scan (step S115), thereby ending a series of processing related to photographing.

  In step S107, after calculating the upper limit value of the SAR, the main control unit 141 notifies the operator of the calculated upper limit value (for example, displaying the calculated upper limit value on the display unit 120). Again, an input of shooting conditions may be received from the operator.

  As described above, in this embodiment, the partial weight estimation unit 144 has an irradiation range indicating the range of the body part irradiated with the RF pulse from the three-dimensional image including the imaging part reconstructed in the prescan. Information is acquired, and the partial body weight of the body part is estimated based on the acquired irradiation range information. And since the SAR calculation part 145 calculates the body part SAR regarding the body part irradiated with the RF pulse based on the partial body weight estimated by the partial weight estimation part 144, the body part actually irradiated with the RF pulse The upper limit value of the SAR can be appropriately calculated.

  In addition, each component of each apparatus illustrated in the present embodiment is functionally conceptual and does not necessarily need to be physically configured as illustrated. In other words, the specific form of distribution / integration of each device is not limited to that shown in the figure, and all or a part thereof may be functionally or physically distributed or arbitrarily distributed in arbitrary units according to various loads or usage conditions. Can be integrated and configured.

  As described above, the magnetic resonance imaging apparatus, the SAR calculation apparatus, the operation method of the magnetic resonance imaging apparatus, and the SAR calculation method according to the present invention are useful for calculating a SAR value that is a safety standard when irradiating an RF pulse. Especially, it is suitable when calculating the body part SAR.

It is explanatory drawing for demonstrating the structure of the MRI apparatus which concerns on a present Example. It is a functional block diagram which shows the structure of the console apparatus shown in FIG. It is a figure which shows an example of the partial weight definition information memorize | stored by the partial weight definition information storage part. It is a figure for demonstrating the irradiation range information regarding a head. It is a figure which shows an example of the three-dimensional image of the body part irradiated with RF pulse. It is a flowchart which shows the process sequence of SAR calculation by a console apparatus. It is a figure for demonstrating the problem in the prior art.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Static magnetic field magnet 2 Gradient magnetic field coil 3 RF coil 4 Static magnetic field power supply 5 Gradient magnetic field power supply 6 Transmitter 7 Receiver 8 Sequence control apparatus 9 Power measuring device 100 Console apparatus 110 Input part 120 Display part 130 Storage part 131 Image storage part 132 Partial weight definition information storage unit 140 Control unit 141 Main control unit 142 Sequence control unit 143 Image reconstruction unit 144 Partial weight estimation unit 145 SAR calculation unit

Claims (8)

A signal detection unit that detects a magnetic resonance signal emitted from the subject by irradiating the subject with an RF pulse;
An image reconstruction unit that reconstructs an image of the subject based on the magnetic resonance signal detected by the signal detection unit;
Obtaining irradiation range information indicating the range of the body part irradiated with the RF pulse at the time of imaging from an image including the imaging region reconstructed in advance by the image reconstruction unit, and based on the acquired irradiation range information A SAR calculation unit for calculating an upper limit value of the body part SAR regarding the body part irradiated with the RF pulse;
A magnetic resonance imaging apparatus comprising: A partial weight estimation unit for estimating a partial weight of the body part based on the irradiation range information;
The magnetic resonance imaging apparatus according to claim 1, wherein the SAR calculation unit calculates an upper limit value of the body part SAR based on the partial body weight estimated by the partial body weight estimation unit. An imaging region reception unit that receives input of imaging region information indicating the imaging region;
A partial weight definition information storage unit that stores partial weight definition information in which the partial weight is defined according to the irradiation range information for each part; and
The partial weight estimation unit includes partial weight definition information related to the imaging part indicated by the imaging part information received by the imaging part reception unit in the partial weight definition information stored in the partial weight definition information storage unit. 3. The magnetic resonance imaging apparatus according to claim 2, wherein the partial body weight of the body part irradiated with the RF pulse is estimated based on the body weight definition information read out and the irradiation range information acquired from the image.   The magnetic resonance imaging apparatus according to claim 3, wherein the partial weight definition information storage unit stores the partial weight definition information defined based on statistical information about the subject.   The magnetic resonance imaging apparatus according to claim 3, wherein the partial body weight definition information storage unit stores the partial body weight definition information defined based on information on a subject imaged in the past. An irradiation range acquisition unit for acquiring irradiation range information indicating a range of a body part irradiated with the RF pulse at the time of imaging from an image including an imaging region reconstructed in advance by a magnetic resonance imaging apparatus;
Based on the irradiation range information acquired by the irradiation range acquisition unit, an upper limit value calculation unit that calculates an upper limit value of the body part SAR regarding the body part irradiated with the RF pulse;
A SAR calculation device comprising: A signal detection unit that detects a magnetic resonance signal emitted from the subject by irradiating the subject with an RF pulse operates,
Based on the magnetic resonance signal detected by the signal detection unit, an image reconstruction unit that reconstructs the image of the subject operates,
Obtaining irradiation range information indicating the range of the body part irradiated with the RF pulse at the time of imaging from an image including the imaging region reconstructed in advance by the image reconstruction unit, and based on the acquired irradiation range information , A SAR calculation unit for calculating an upper limit value of the body part SAR regarding the body part irradiated with the RF pulse is operated.
A method of operating a magnetic resonance imaging apparatus. Obtaining irradiation range information indicating a range of a body part irradiated with the RF pulse at the time of imaging from an image including an imaging region reconstructed in advance by a magnetic resonance imaging apparatus,
Based on the acquired irradiation range information, an upper limit value of the body part SAR regarding the body part irradiated with the RF pulse is calculated.
A SAR calculation method.

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