JP2005237702A - Magnetic resonance imaging apparatus and data processing method of magnetic resonance imaging apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a magnetic resonance imaging apparatus and a data processing method of the magnetic resonance imaging apparatus, capable of more precisely estimating the distribution of sensitivity of an RF coil based on image data obtained by performing sensitivity pre-scanning, and capable of more effectively correcting the brightness of the image data obtained by the scanning. <P>SOLUTION: The magnetic resonance imaging apparatus 20 comprises a means of executing the scanning for preparing sensitivity mapping data of the RF coil 24, a means 44b of executing the region reduction for a signal region near a non-signal region of the image data obtained by the scanning, and a means 44 of preparing the sensitivity mapping data using the image data after the region reduction. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a magnetic resonance imaging apparatus that captures an image of a subject using a nuclear magnetic resonance signal and a data processing method of the magnetic resonance imaging apparatus, and in particular, the luminance of image data due to the sensitivity distribution of a receiving coil. The present invention relates to a magnetic resonance imaging apparatus for correcting non-uniformity and a data processing method of the magnetic resonance imaging apparatus.

  Conventionally, a magnetic resonance imaging (MRI) apparatus 1 as shown in FIG. 12 is used as a monitoring apparatus in a medical field (see, for example, Patent Document 1).

  The magnetic resonance imaging apparatus 1 includes an X axis in each of the gradient magnetic field coils 3x, 3y, and 3z of the gradient magnetic field coil unit 3 in an imaging region of a subject P set inside a cylindrical static magnetic field magnet 2 that forms a static magnetic field. Excites the spins in the subject P magnetically by forming a gradient magnetic field in the Y-axis and Z-axis directions and transmitting a radio frequency (RF) signal of Larmor frequency from an RF (Radio Frequency) coil 4 Is an apparatus for reconstructing an image of the subject P using a nuclear magnetic resonance (NMR) signal generated by the above-described process.

  That is, a static magnetic field is previously formed in the static magnetic field magnet 2 by the static magnetic field power source 5. Further, in response to a command from the input device 6, the sequence controller control means 7a gives a sequence, which is signal control information, to the sequence controller 8, and the sequence controller 8 is connected to each gradient magnetic field coil 3x, 3y, 3z according to the sequence. The transmitter 10 which gives a high frequency signal to the magnetic field power supply 9 and the RF coil 4 is controlled. For this reason, a gradient magnetic field is formed in the imaging region, and a high-frequency signal is transmitted to the subject P.

  At this time, the X-axis gradient magnetic field, the Y-axis gradient magnetic field, and the Z-axis gradient magnetic field formed by the gradient magnetic field coils 3x, 3y, and 3z are mainly a phase encoding (PE) gradient magnetic field, a readout (RO: readout). The gradient magnetic field is used as a gradient magnetic field and a slice encoding (SE) gradient magnetic field. For this reason, the X coordinate, Y coordinate, and Z coordinate, which are nuclear position information, are converted into the nuclear spin phase, frequency, and slice position, respectively, and the sequence is repeatedly executed while changing the phase encoding amount.

  Then, the NMR signal generated along with the excitation of the nuclear spin in the subject P is received by the RF coil 4 and given to the receiver 11 to be converted into digitized raw data. Further, the raw data is taken into the sequence controller control means 7a via the sequence controller 8, and the sequence controller control means 7a arranges the raw data in the K space (Fourier space) formed in the raw data database 7b. Then, the image reconstruction unit 7c performs Fourier transform on the raw data arranged in the K space, whereby reconstructed image data of the subject P is obtained and stored in the image data database 7d. Further, image data is appropriately given to the display device 7f by the image display means 7e and displayed.

  In such a magnetic resonance imaging apparatus 1, the RF coil 4 includes a whole body (WB) coil for transmission and a phased array coil (PAC) for reception in order to increase imaging speed. (For example, refer nonpatent literature 1). Since the phased array coil includes a plurality of surface coils, the imaging time can be shortened by receiving NMR signals simultaneously by each surface coil and collecting more raw data in a short time.

  Here, in the image diagnosis by the magnetic resonance imaging apparatus 1, it is desired that luminance unevenness does not occur in the finally obtained image data. However, when the RF coil 4 is composed of a phased array coil having a plurality of surface coils, due to the non-uniformity of the sensitivity of each surface coil constituting the RF coil 4, the raw signal is simply Fourier transformed together with the signal intensity of the NMR signal. Since nonuniformity also occurs in the signal intensity of the image data obtained by the reconstruction processing, luminance unevenness occurs in the image data.

Therefore, conventionally, a sensitivity pre-scan is executed prior to the main scan for generating an image of the subject P. The sensitivity pre-scan by acquiring image data from a phased-array coil and the WB coil, the signal strength S _PAC of the image data by the procedure of the flowchart shown in FIG. _13, the division value is the signal intensity ratio of S _WB (S _PAC / S _WB ), the sensitivity distribution of the phased array coil is estimated as three-dimensional sensitivity map data, and the luminance of the image data is corrected by the obtained three-dimensional sensitivity map data.

  First, the sensitivity pre-scan execution means 7g gives a sequence for sensitivity estimation to the sequence controller control means 7a, and the sensitivity pre-scan is executed. Then, the WB reconstruction image obtained by the WB coil and the PAC reconstruction image obtained by the phased array coil are stored in the WB reconstruction image database 7h and the PAC reconstruction image database 7i, respectively.

  Further, an estimated value of the sensitivity distribution of the phased array coil is obtained by the sensitivity distribution estimation means 7j based on the WB reconstruction image and the PAC reconstruction image.

  That is, in step S1, threshold processing is performed on the WB reconstructed image and the PAC reconstructed image by the threshold processing means 7k. That is, the area where the signal intensity of the WB reconstructed image and the PAC reconstructed image is less than or equal to the threshold value is masked, and WB absolute value image data and PAC absolute value image data are generated.

  Next, in step S2, the division processing means 7l divides the signal intensity of the PAC absolute value image data by the signal intensity of the WB absolute value image data, and obtains the obtained signal intensity ratio as an estimated value of the sensitivity distribution of the phased array coil. .

  Next, in step S3, normalization processing of the signal intensity ratio between the PAC absolute value image data and the WB absolute value image data is performed by the normalizing means 7m.

  Next, in step S4, in order to estimate the sensitivity distribution in the non-signal area inside and outside the subject, which is the data missing portion caused by the threshold process, the region growing process is performed by the interpolation means 7n, and the sensitivity distribution in the non-signal area is obtained. Is interpolated.

  Next, in step S5, various processes such as a fitting process and a smoothing process are performed by the smoothing processing means 7o, a sensitivity map is created as volume data in the entire three-dimensional region, and stored in the sensitivity map database 7p.

Further, the main scan execution means 7q gives an image acquisition sequence to the sequence controller control means 7a, and the main scan is executed. Then, image data is obtained by the image reconstruction process of the image reconstruction means 7c and stored in the image data database 7d. Further, the image data correction means 7r corrects the brightness of the image data stored in the image data database 7d using the sensitivity map stored in the sensitivity map database 7p, and the image data after the brightness correction is displayed by the image display means 7e. It is given to the device 7f and displayed.
Japanese Patent No. 3135592 Roemer PB, et al. The NMR Phased Array, MRM 16, 192-225 (1990)

  Generally, image data obtained by sensitivity pre-scanning or main scanning includes a no-signal area. This is because a region such as the lung exists in the subject that is the imaging region, and there is a non-signal region where no NMR signal is generated. Here, in general, a phenomenon occurs in which the signal intensity decreases in the signal region in the vicinity of the boundary between the non-signal region and the signal region in the subject. This affects the estimated value of the sensitivity distribution of the phased array coil.

  However, in the conventional magnetic resonance imaging apparatus 1, the method for interpolating the no-signal area when creating the sensitivity map of the phased array coil is only to perform the region growing process on the no-signal area regardless of inside or outside the subject. is there.

  Furthermore, since the sensitivity prescan using the phased array coil and the sensitivity prescan using the WB coil are performed separately, the shape of the subject P in the image data acquired using the phased array coil and the WB coil are used. There is a possibility that a deviation may occur between the shape of the subject P in the acquired image data.

  Further, not only the sensitivity distribution of each surface coil of the phased array coil but also nonuniformity in signal intensity occurs in the Z-axis direction of the apparatus coordinate system not only due to the arrangement characteristics.

  However, in the conventional magnetic resonance imaging apparatus 1, the WB reconstructed image data and the PAC reconstruction are simply not considered without considering the signal intensity non-uniformity due to the positional deviation of the image data in the sensitivity pre-scan and the arrangement characteristics of the surface coil. The sensitivity distribution of the phased array coil is estimated based on the signal intensity ratio between the PAC absolute value image data and the WB absolute value image data obtained by thresholding each signal intensity of the constituent image data, and the sensitivity map. Is generated.

  As a result, in the conventional magnetic resonance imaging apparatus 1, the accuracy of the sensitivity distribution of the phased array coil estimated by the sensitivity prescan is not sufficiently obtained, and the brightness of the reconstructed image obtained by the main scan is sufficiently accurate. There is a problem that it cannot be corrected.

  The present invention has been made to cope with such a conventional situation, and more accurately estimates the sensitivity distribution of the RF coil based on the image data obtained by performing the sensitivity pre-scan, and the obtained RF coil. It is an object of the present invention to provide a magnetic resonance imaging apparatus and a data processing method for the magnetic resonance imaging apparatus that can more appropriately correct the luminance of image data obtained by performing the main scan based on the sensitivity distribution.

  In order to achieve the above-described object, a magnetic resonance imaging apparatus according to the present invention provides, as described in claim 1, means for executing a scan for generating sensitivity map data of an RF coil, and obtained by the scan. Means for performing a reduction reduction on a signal area in the vicinity of the no-signal area of the obtained image data, and a means for generating sensitivity map data using the image data after the region reduction. is there.

  In order to achieve the above-mentioned object, the magnetic resonance imaging apparatus according to the present invention includes means for executing a scan for generating sensitivity map data of an RF coil, and the scan as described in claim 2. Means for generating sensitivity map data using the image data obtained by the above, and means for correcting the sensitivity map data by weighting in the slice direction.

  In order to achieve the above object, the magnetic resonance imaging apparatus according to the present invention includes means for executing a scan for generating sensitivity map data of an RF coil, and the scan, as described in claim 3. Means for performing a reduction reduction on a signal area in the vicinity of the no-signal area of the image data obtained by the above, a means for generating sensitivity map data using the image data after the region reduction, and the sensitivity map data in the slice direction And a means for correcting by weighting.

  In addition, the data processing method of the magnetic resonance imaging apparatus according to the present invention is obtained by scanning for generating sensitivity map data of the RF coil as described in claim 7 in order to achieve the above-described object. The method includes a step of performing region reduction on a signal region in the vicinity of a non-signal region of image data, and a step of generating sensitivity map data using the image data after the region reduction.

  In addition, the data processing method of the magnetic resonance imaging apparatus according to the present invention is obtained by scanning for generating the sensitivity map data of the RF coil as described in claim 8 in order to achieve the above-described object. A method comprising: generating sensitivity map data using image data; and correcting by weighting the sensitivity map data in a slice direction.

  In addition, the data processing method of the magnetic resonance imaging apparatus according to the present invention is obtained by scanning for generating sensitivity map data of the RF coil as described in claim 9 in order to achieve the above-described object. A step of performing region reduction on a signal region in the vicinity of a no-signal region of image data, a step of generating sensitivity map data using the image data after the region reduction, and weighting the sensitivity map data in the slice direction And a step of correcting by the above.

  In the magnetic resonance imaging apparatus and the data processing method of the magnetic resonance imaging apparatus according to the present invention, the sensitivity distribution of the RF coil is estimated more accurately based on the image data obtained by performing the sensitivity prescan. Based on the sensitivity distribution of the RF coil, the brightness of the image data obtained by performing the main scan can be corrected more favorably.

  Embodiments of a magnetic resonance imaging apparatus and a data processing method of the magnetic resonance imaging apparatus according to the present invention will be described with reference to the accompanying drawings.

  FIG. 1 is a functional block diagram showing an embodiment of a magnetic resonance imaging apparatus according to the present invention.

  The magnetic resonance imaging apparatus 20 does not show a cylindrical static magnetic field magnet 21 that forms a static magnetic field, and a shim coil 22, a gradient magnetic field coil unit 23, and an RF coil 24 provided inside the static magnetic field magnet 21. It is built in the gantry.

  In addition, the magnetic resonance imaging apparatus 20 includes a control system 25. The control system 25 includes a static magnetic field power supply 26, a gradient magnetic field power supply 27, a shim coil power supply 28, a transmitter 29, a receiver 30, a sequence controller 31, and a computer 32. The gradient magnetic field power source 27 of the control system 25 includes an X-axis gradient magnetic field power source 27x, a Y-axis gradient magnetic field power source 27y, and a Z-axis gradient magnetic field power source 27z. The computer 32 includes an arithmetic device and a storage device (not shown), and an input device 33 and a display device 34 are provided.

  The static magnetic field magnet 21 is connected to a static magnetic field power supply 26 and has a function of forming a static magnetic field in the imaging region by a current supplied from the static magnetic field power supply 26. A cylindrical shim coil 22 is coaxially provided inside the static magnetic field magnet 21. The shim coil 22 is connected to the shim coil power supply 28, and is configured such that a current is supplied from the shim coil power supply 28 to the shim coil 22 to make the static magnetic field uniform.

  The gradient magnetic field coil unit 23 includes an X-axis gradient magnetic field coil 23 x, a Y-axis gradient magnetic field coil 23 y, and a Z-axis gradient magnetic field coil 23 z, and is formed in a cylindrical shape inside the static magnetic field magnet 21. A bed 35 is provided inside the gradient magnetic field coil unit 23 as an imaging region, and the subject P is set on the bed 35. The RF coil 24 may not be built in the gantry but may be provided near the bed 35 or the subject P.

  The gradient magnetic field coil unit 23 is connected to a gradient magnetic field power supply 27. The X axis gradient magnetic field coil 23x, the Y axis gradient magnetic field coil 23y, and the Z axis gradient magnetic field coil 23z of the gradient magnetic field coil unit 23 are respectively an X axis gradient magnetic field power source 27x, a Y axis gradient magnetic field power source 27y, and a Z axis. It is connected to the gradient magnetic field power supply 27z.

  The X-axis gradient magnetic field power source 27x, the Y-axis gradient magnetic field power source 27y, and the Z-axis gradient magnetic field power source 27z are supplied with currents supplied to the X-axis gradient magnetic field coil 23x, the Y-axis gradient magnetic field coil 23y, and the Z-axis gradient magnetic field coil 23z, respectively. In the imaging region, a gradient magnetic field Gx in the X-axis direction, a gradient magnetic field Gy in the Y-axis direction, and a gradient magnetic field Gz in the Z-axis direction can be formed, respectively.

  The RF coil 24 is connected to the transmitter 29 and the receiver 30. The RF coil 24 receives the high frequency signal from the transmitter 29 and transmits it to the subject P, and receives the NMR signal generated by the excitation by the high frequency signal of the nuclear spin inside the subject P and receives it to the receiver 30. Has the function to give.

  FIG. 2 is a detailed configuration diagram of the RF coil 24 and the receiver 30 shown in FIG.

  The RF coil 24 includes, for example, a WB coil 24a for high-frequency signal transmission and a phased array coil 24b for NMR signal reception. The phased array coil 24b includes a plurality of surface coils 24c, while the receiver 30 includes a plurality of reception system circuits 30a. Further, each surface coil 24c is individually connected to each reception system circuit 30a of the receiver 30, and the WB coil is connected to the transmitter 29 and the reception system circuit 30a.

  FIG. 3 is a schematic cross-sectional view showing an arrangement example of the WB coil 24a and the phased array coil 24b shown in FIG.

  For example, the surface coils 24c of the phased array coil 24b are arranged symmetrically around the Z axis that is around the cross section L including the specific region of interest of the subject P. Further, a WB coil 24a is provided outside the phased array coil 24b. The RF coil 24 transmits a high-frequency signal to the subject P by the WB coil 24a, while the surface coil 24c of the WB coil 24a or the phased array coil 24b transmits an NMR signal from the cross section L including the specific region of interest in multiple channels. Is received and provided to each receiving system circuit 30a of each receiver 30.

  On the other hand, the sequence controller 31 of the control system 25 is connected to the gradient magnetic field power source 27, the transmitter 29, and the receiver 30. The sequence controller 31 has control information necessary for driving the gradient magnetic field power supply 27, the transmitter 29, and the receiver 30, for example, operation control information such as the intensity, application time, and application timing of the pulse current to be applied to the gradient magnetic field power supply 27. And the gradient magnetic field power source 27, the transmitter 29, and the receiver 30 are driven according to the stored predetermined sequence to drive the X-axis gradient magnetic field Gx, the Y-axis gradient magnetic field Gy, and the Z-axis gradient magnetic field. It has the function of generating Gz and high frequency signals.

  In addition, the sequence controller 31 is configured to receive raw data, which is a digitized NMR signal, from the receiver 30 and to supply the raw data to the computer 32.

  For this reason, the transmitter 29 is provided with a function of supplying a high frequency signal to the RF coil 24 based on the control information received from the sequence controller 31, while the receiver 30 is required for the NMR signal received from the RF coil 24. A function for generating raw data that is a digitized NMR signal and a function for giving the generated raw data to the sequence controller 31 by performing the signal processing and A / D conversion are provided.

  In addition, the computer 32 reads and executes a program to thereby execute sensitivity pre-scan execution means 36, main scan execution means 37, sequence controller control means 38, raw data database 39, image reconstruction means 40, image data database. 41, PAC reconstruction image database 42, WB reconstruction image database 43, sensitivity distribution estimation means 44, sensitivity map database 45, image data correction means 46, and image display means 47. However, the computer 32 may be configured by providing a specific circuit regardless of the program.

  The sensitivity pre-scan execution means 36 has a function for generating a sequence (sensitivity estimation sequence) for executing sensitivity pre-scan for obtaining three-dimensional sensitivity map data, which is the sensitivity distribution of the phased array coil 24b, and the generated sensitivity. It has a function of executing a sensitivity pre-scan by giving an estimation sequence to the sequence controller control means 38.

  The main scan execution unit 37 has a function of executing the main scan by giving various sequences to the sequence controller control unit 38 when executing the main scan for acquiring the image data.

  The sequence controller control unit 36 gives the sequence controller 31 a required sequence among the sequences received from the sensitivity pre-scan execution unit 36 and the main scan execution unit 37 based on information from the input device 33 or other components. Therefore, it has a function to execute sensitivity pre-scan or main scan. The sequence controller control means 38 receives the raw data of the surface coils 24c of the WB coil 24a and the phased array coil 24b collected from the sequence controller 31 by executing the sensitivity pre-scan or the main scan, and forms it in the raw data database 39. Has a function of arranging in the K space (Fourier space).

  Therefore, the raw data database 39 stores the raw data for each of the WB coil 24a and the surface coil 24c generated in the receiver 30. That is, raw data is arranged in the K space formed in the raw data database 39.

  The image reconstruction unit 40 performs image reconstruction processing such as Fourier transform (FT) on the raw data arranged in the K space of the raw data database 39 by executing the main scan, thereby obtaining the image data of the subject P. A function of reconstructing, and a function of writing the reconstructed image data into the image data database 41.

  Further, the image reconstruction unit 40 uses a technique equivalent to the reconstruction process for the raw data obtained by executing the main scan on the raw data arranged in the K space of the raw data database 39 by executing the sensitivity pre-scan. A function for generating a PAC reconstructed image and a WB reconstructed image from the image data of the subject P obtained by the phased array coil 24b and the WB coil 24a by performing the reconstruction process, and the generated PAC reconstructed image and WB A function of writing the reconstructed images in the PAC reconstructed image database 42 and the WB reconstructed image database 43, respectively.

  The sensitivity distribution estimation means 44 uses the PAC reconstructed image and the WB reconstructed image stored in the PAC reconstructed image database 42 and the WB reconstructed image database 43, respectively, to obtain the three-dimensional sensitivity map data of the phased array coil 24b. A function to create, and a function to write the created three-dimensional sensitivity map data to the sensitivity map database 45. That is, the sensitivity distribution estimation unit 44 functions as a unit that generates sensitivity map data of the RF coil 24.

  For this reason, the sensitivity distribution estimation unit 44 includes a threshold processing unit 44a, a region reduction unit 44b, a division processing unit 44c, a normalization unit 44d, a data flattening unit 44e, an in-subject region interpolation unit 44f, and an out-subject region interpolation unit 44g. , Slice direction weighting means 44h and smoothing processing means 44i.

  The threshold processing unit 44a has a function of performing threshold processing on the PAC reconstructed image and the WB reconstructed image, that is, a portion in which each signal intensity of the PAC reconstructed image and the WB reconstructed image is equal to or less than a preset threshold. It has a function of masking data.

  The region reduction means 44b reduces the area after threshold processing of the PAC reconstructed image and WB reconstructed image used for sensitivity distribution estimation by the region reduction process, and obtains a portion having a small signal intensity in the vicinity of the mask area as three-dimensional sensitivity map data. It has a function of excluding it from data for creation.

  The division processing means 44c divides the PAC absolute value image, which is the signal absolute value of the PAC reconstructed image after the threshold processing and the region reduction process, by the WB absolute value image, which is the signal absolute value of the WB reconstructed image, thereby dividing the PAC absolute value image. It has a function of obtaining a signal intensity ratio between a value image and a WB absolute value image as three-dimensional sensitivity map data.

  The normalizing means 44d has a function of performing normalization processing on the three-dimensional sensitivity map data.

  The data flattening means 44e performs a data flattening process on the three-dimensional sensitivity map data using a conversion function, while using an inverse conversion function on the three-dimensional sensitivity map data after the data flattening process. It has a function of obtaining three-dimensional sensitivity map data before the flattening process. That is, the data flattening means 44e has a function of once converting the three-dimensional sensitivity map data into a flattened distribution suitable for linear interpolation, and returning the three-dimensional sensitivity map data after the linear interpolation processing to the original distribution. . Therefore, an arbitrary function can be used as a conversion function according to the purpose.

  The in-subject region interpolation unit 44f has a function of performing linear interpolation processing on the non-signal region in the subject P of the three-dimensional sensitivity map data.

  The non-subject region interpolation unit 44g has a function of performing interpolation by performing a region growing process on a non-signal region outside the subject P of the three-dimensional sensitivity map data.

  The slice direction weighting unit 44h has a function of weighting the three-dimensional sensitivity map data in the slice direction.

  The smoothing processing means 44i has a function of applying a smoothing filter to the three-dimensional sensitivity map data.

  The image data correction means 46 obtains 3D sensitivity map data according to image data acquisition conditions such as imaging conditions, data collection conditions, and image reconstruction conditions in the main scan from the 3D sensitivity map data stored in the sensitivity map database 45. It has a function of cutting out and extracting, and a function of correcting the luminance of the image data stored in the image data database 41 by executing the main scan using the extracted three-dimensional sensitivity map data.

  The image display means 47 has a function of giving the image data stored in the image data database 41 to the display device 34 for display.

  The magnetic resonance imaging apparatus 20 having the above-described configuration includes, as a whole, means for executing a scan such as a main scan and a sensitivity prescan, and a signal in the vicinity of a no-signal area of image data acquired in the sensitivity prescan. It functions as means for performing region reduction on a region, means for generating sensitivity map data using image data acquired in sensitivity pre-scanning, and means for correcting by weighting the sensitivity map data in the slice direction.

  Next, the operation of the magnetic resonance imaging apparatus 20 will be described.

  FIG. 4 is a flowchart showing a procedure when a tomographic image of the subject P is picked up by the magnetic resonance imaging apparatus 20 shown in FIG. 1, and the reference numerals with numerals in the figure indicate the steps of the flowchart.

  First, in step S10, the sensitivity pre-scan execution means 36 gives a sensitivity estimation sequence to the sequence controller control means 7a, and prior to the main scan for acquiring image data, the sensitivity map data of the phased array coil 24b is obtained. A sensitivity prescan to obtain is performed.

  That is, the subject P is set on the bed 35 in advance, and a current is supplied from the static magnetic field power source 26 to the static magnetic field magnet 21 to form a static magnetic field in the imaging region. Further, a current is supplied from the shim coil power supply 28 to the shim coil 22, and the static magnetic field formed in the imaging region is made uniform.

  Next, an operation command is given from the input device 33 to the sequence controller control means 38. Therefore, the sequence controller control means 38 gives the sequence for sensitivity estimation to the sequence controller 31. The sequence controller 31 drives the gradient magnetic field power source 27, the transmitter 29, and the receiver 30 in accordance with the sensitivity estimation sequence to thereby set an X-axis gradient magnetic field Gx and Y-axis gradient magnetic fields Gy, Z in the imaging region where the subject P is set. An axial gradient magnetic field Gz is formed and a high frequency signal is generated.

  At this time, the X-axis gradient magnetic field Gx, the Y-axis gradient magnetic field Gy, and the Z-axis gradient magnetic field Gz formed by the gradient coil are mainly a phase encode (PE) gradient magnetic field, a read (RO) gradient magnetic field, and a slice encode ( Used as a gradient magnetic field for SE). For this reason, regularity appears in the spin rotation direction of the nuclei inside the subject P, and the X and Y coordinates, which are two-dimensional position information in the slice formed in the Z-axis direction by the SE gradient magnetic field, are PE The phase change amount and the frequency change amount of the spin of the nucleus inside the subject P are respectively converted by the gradient magnetic field for RO and the gradient magnetic field for RO.

  A high frequency signal is given from the transmitter 29 to the WB coil 24a of the RF coil 24 in accordance with the sensitivity estimation sequence, and the high frequency signal is transmitted from the WB coil 24a to the subject P. Furthermore, NMR signals generated by nuclear magnetic resonance of the nuclei contained in the slice corresponding to the frequency of the high-frequency signal inside the subject P are generated by the WB coil 24a of the RF coil 24 and the surface coils 24c of the phased array coil 24b. It is received on the channel and given to each receiver 30.

  Each receiver 30 receives NMR signals from the surface coils 24c of the WB coil 24a and the phased array coil 24b, and executes various signal processing such as pre-amplification, intermediate frequency conversion, phase detection, low-frequency amplification, and filtering. . Further, each receiver 30 A / D converts the NMR signal to generate raw data which is an NMR signal of digital data. The receiver 30 gives the generated raw data to the sequence controller 31.

  The sequence controller 31 gives the raw data received from the receiver 30 to the sequence controller control means 38, and the sequence controller control means 38 places the raw data in the K space formed in the raw data database 39. Furthermore, the image reconstruction means 40 performs Fourier transform (FT) on the raw data obtained by using the WB coil 24a and the phased array coil 24b, respectively, thereby performing WB reconstruction that is three-dimensional image data of the subject P. A composition image and a PAC reconstruction image are generated and written in the WB reconstruction image database 43 and the PAC reconstruction image database 42, respectively.

  At this time, the reconstruction processing method of the raw data collected by the sensitivity pre-scan is the same method as the reconstruction processing method in the main scan. As a reconstruction processing method using the phased array coil 24b in this scan, Sum of Square processing (SoS processing) that takes the square root of the square sum of the image data obtained by each surface coil 24c, or each surface coil 24c is used. There is a reconstruction processing method that takes the sum of the absolute values of the signal intensities of the obtained image data.

  Next, in step S11, the sensitivity distribution estimation unit 44 uses the WB reconstructed image and the PAC reconstructed image in each slice stored in the WB reconstructed image database 43 and the PAC reconstructed image database 42 to obtain a three-dimensional image. Generate sensitivity map data.

  FIG. 5 is a flowchart showing a detailed procedure when the sensitivity map data is generated by the magnetic resonance imaging apparatus 20 shown in FIG. 1, and the reference numerals with numerals in the figure indicate each step of the flowchart.

  First, in step S20, the threshold processing unit 44a performs threshold processing on the PAC reconstructed image and the WB reconstructed image, and the signal strengths of the PAC reconstructed image and the WB reconstructed image are set to be equal to or less than preset threshold values, respectively. The data of the part to be masked. For this reason, the PAC reconstructed image and the WB reconstructed image in the region where the signal intensity is equal to or less than the threshold value, such as the lung field or the external region of the subject, are excluded from the data for creating the three-dimensional sensitivity map data. The

  Next, in step S21, the region reduction unit 44b reduces the region after threshold processing of the PAC reconstruction image and WB reconstruction image used for sensitivity distribution estimation by the region reduction processing, and the signal intensity in the vicinity of the mask region is small. Are excluded from the data for creating the three-dimensional sensitivity map data.

  FIG. 6 is a diagram showing an embodiment of the region reduction process by the magnetic resonance imaging apparatus 20 shown in FIG.

  The PAC reconstruction image and WB reconstruction image before the region reduction have a non-signal area D1 and a signal area D2 masked by threshold processing as shown in FIG. 6A. However, in general, the signal region D2 in the vicinity of the no-signal region D1 has a phenomenon that the signal intensity decreases. In addition, since the sensitivity prescan using the phased array coil 24b and the sensitivity prescan using the WB coil 24a are performed separately, if the position of the internal organ of the subject P is displaced, the PAC reconstruction is performed as it is. When the signal intensity ratio between the image and the WB reconstructed image is taken, the signal intensity in the signal region D2 in the vicinity of the non-signal region D1 becomes discontinuous.

  Therefore, as shown in FIG. 6B, the signal region D2 is reduced by replacing the portion D2 'in the vicinity of the non-signal region D1 in the signal region D2 with the non-signal region. As a result, the signal area D2 in which the signal intensity near the no-signal area D1 in each of the PAC reconstructed image and the WB reconstructed image is reduced is excluded from the data for creating the three-dimensional sensitivity map data.

  Next, in step S22, the division processing unit 44c converts the PAC absolute value image, which is the signal absolute value of the PAC reconstructed image in each slice after the threshold processing and the region reduction process, to the WB absolute value, which is the signal absolute value of the WB reconstructed image. By dividing by the value image, a signal intensity ratio between the PAC absolute value image and the WB absolute value image is obtained as three-dimensional sensitivity map data.

  Next, in step S23, normalization processing of the three-dimensional sensitivity map data obtained as a signal intensity ratio between the PAC absolute value image and the WB absolute value image is performed by the normalizing means 44d for each slice.

  Next, in step S24, the data flattening process using the conversion function is performed by the data flattening means 44e on the normalized three-dimensional sensitivity map data, and the three-dimensional sensitivity map data is flattened suitable for linear interpolation. Is converted to correct data. For example, the fitting of the three-dimensional sensitivity map data is performed by an arbitrary function such as an n-order function, an exponential function, or a logarithmic function, and processing for reducing local data undulations that affect linear interpolation is performed. The

  Next, in step S25, the in-subject region interpolation unit 44f performs linear interpolation processing on the non-signal region inside the subject P in the three-dimensional sensitivity map data after the data flattening processing.

  FIG. 7 is a diagram showing an example of linear interpolation for the non-signal region in the subject P of the three-dimensional sensitivity map data by the magnetic resonance imaging apparatus 20 shown in FIG.

  FIG. 7A is a diagram illustrating an example of 3D sensitivity map data viewed from the slice direction, and FIG. 7B is a diagram illustrating an example of 3D sensitivity map data viewed from the PE direction. The three-dimensional sensitivity map data after the normalization process and the data flattening process has a no-signal area D1 and a signal area D2. The non-signal region D1 includes a non-signal region D1a inside the subject P and a non-signal region D1b outside the subject P.

  Then, the intra-subject region interpolation means 44f linearly connects the signal intensity values in the signal region D2 of the cross section in the RO direction, for example, with respect to the non-signal region D1a inside the subject P as shown by the arrow in FIG. To perform linear interpolation. As a result, the non-signal area D1a inside the subject P is replaced with the signal area D2.

  The linear interpolation can be performed not only in the RO direction but also in any direction such as the PE direction and the SL direction.

  Next, in step S26, the data flattening means 44e converts the three-dimensional sensitivity map data after the linear interpolation into a state before the data flattening by an inverse conversion function.

  Next, in step S27, the non-subject region interpolation means 44g performs interpolation by applying a region growing process to the non-signal region outside the subject P of the three-dimensional sensitivity map data.

  FIG. 8 is an explanatory diagram showing an example of a region growing method for the non-signal region outside the subject P of the three-dimensional sensitivity map data by the magnetic resonance imaging apparatus 20 shown in FIG.

  FIG. 8A is a diagram for explaining a region growing method by the 26-point method, and FIG. 8B is a diagram for explaining a region growing method by the 6-point method.

  Region growing is a process of replacing a non-signal area with a value of a signal area as it is. For example, as shown in FIG. 8A, the region growing by the 26-point method is a signal region in which the signal intensity at the midpoint A of the grid is equal to or higher than a threshold value, while 26 grid points adjacent to the midpoint A are present. In the case where each signal intensity is equal to or less than a threshold value and is a no-signal area, the 26 grid points in the no-signal area are replaced with the signal intensity at the midpoint A.

  In addition, as shown in FIG. 8B, the region growing by the 6-point method is a signal region where the signal intensity at the midpoint A of the grid is equal to or higher than a threshold value, and on the other hand, 6 grid points adjacent to the midpoint A In the case where each signal intensity is equal to or less than the threshold value and is in the no-signal area, the six grid points in the no-signal area are replaced with the signal intensity at the midpoint A.

  FIG. 9 is a diagram showing an example of region growing for the non-signal region outside the subject P of the three-dimensional sensitivity map data by the magnetic resonance imaging apparatus 20 shown in FIG.

  The three-dimensional sensitivity map data after the linear interpolation has a non-signal region D1 outside the subject P and a signal region D2 inside the subject P as shown in FIG. As a result of the region growing on the non-signal region D1 outside the subject P, the non-signal region D1 outside the subject P is replaced with the signal region D2 and interpolated as shown in FIG. 9B. All the regions become the signal region D2. Then, three-dimensional sensitivity map data is created over the entire area of each slice.

  On the other hand, depending on the channel arrangement of the phased array coil 24b, the sensitivity distribution of the phased array coil 24b may not be uniform in the Z-axis direction (slice direction) of the apparatus coordinate system.

  Therefore, in step S28, the slice direction weighting means 44h corrects the three-dimensional sensitivity map data by weighting it in the slice direction. The slice direction weighting unit 44h can perform weighting in the slice direction by obtaining the reciprocal Y of the correction coefficient by, for example, the equation (1) and multiplying the three-dimensional sensitivity map data by the correction coefficient 1 / Y.

[Equation 1]
Y = 1 if Z <B (1)
Y = A × (Z−B) ² +1 if Z ≧ B
However,
Z: Slice position in the Z direction A: Coefficient B: Offset amount.

  FIG. 10 is a diagram plotting the correction coefficient 1 / Y when the magnetic resonance imaging apparatus 20 shown in FIG. 1 weights the three-dimensional sensitivity map data in the slice direction.

  In FIG. 10, the vertical axis represents the correction coefficient 1 / Y, and the horizontal axis represents the slice position Z in the Z direction. The solid line in FIG. 10 is a curve showing the correction coefficient 1 / Y when the coefficient A = −20 and the offset amount B = 0 in the equation (1).

  That is, when the slice position Z in the Z direction is smaller than a predetermined offset amount B = 0, the correction coefficient 1 / Y is set to 1 and the three-dimensional sensitivity map data is not corrected.

  On the other hand, when the slice position Z in the Z direction is greater than or equal to a predetermined offset amount B = 0, the correction coefficient 1 / Y is calculated by a calculation formula that is functionalized using a quadratic expression, and the obtained correction Correction is performed by multiplying the three-dimensional sensitivity map data by the coefficient 1 / Y.

  However, the calculation formula of the reciprocal Y of the correction coefficient can be approximated by using an arbitrary function without depending on the quadratic expression.

  Next, in step S29, the smoothing processing means 44i applies a 3D smoothing filter having a required intensity as appropriate to the three-dimensional sensitivity map data. As a result, it is possible to accurately generate final three-dimensional sensitivity map data that has no locally extremely large portion and has improved continuity in any of the RO direction, the PE direction, and the SL direction.

  In step S30, the three-dimensional sensitivity map data generated by the sensitivity distribution estimation means 44 is written and stored in the sensitivity map database 45.

  Next, in step S12 of FIG. 4, the main scan execution unit 37 gives an image acquisition sequence to the sequence controller control unit 38, and the main scan is executed. Then, raw data is collected and image data is obtained by image reconstruction processing of the image reconstruction means 40.

  Next, in step S13, the luminance of the image data obtained in the main scan is corrected by the three-dimensional sensitivity map data. For this reason, the image data correction means 46 corresponds to the corresponding three-dimensional sensitivity map data from the sensitivity map database 45 in accordance with various conditions such as the imaging sectional direction in the main scan, imaging conditions such as spatial resolution, data collection conditions, and image reconstruction conditions. Cut out.

  Then, the image data correction unit 46 corrects the luminance of the image data using the cut-out three-dimensional sensitivity map data. At this time, the three-dimensional sensitivity map data cut out as necessary may be normalized.

  As a result, the influence of the nonuniformity of the signal intensity due to the variation in sensitivity of the phased array coil 24b is suppressed, and image data with improved luminance can be obtained.

  According to the magnetic resonance imaging apparatus 20 as described above, the sensitivity distribution of the phased array coil 24b is estimated more accurately based on the image data obtained by performing the sensitivity pre-scan, and the obtained phased array coil 24b Based on the sensitivity distribution, the luminance of the image data obtained by performing the main scan can be corrected more favorably.

  In the case where the brightness correction method of image data by the conventional magnetic resonance imaging apparatus 1 cannot sufficiently correct the brightness of the image data, for example, the non-signal area such as the lung is included in the imaging area of the sensitivity prescan. In this case, the shape of the subject P photographed by the phased array coil 24b and the shape of the subject P photographed by the WB coil 24a at the time of the sensitivity pre-scan imaging so that the shape of the internal organs can be changed regardless of the intention of the subject P. According to the magnetic resonance imaging apparatus 20, even if the signal intensity is nonuniform in the Z-axis direction of the apparatus coordinate system due to the arrangement characteristics of each channel of the phased array coil 24b, The luminance of the image data can be corrected well.

  11 shows a tomographic image of the subject P after luminance correction obtained by the magnetic resonance imaging apparatus 20 shown in FIG. 1 and a tomographic image of the subject P after luminance correction obtained by the conventional magnetic resonance imaging apparatus 1. It is the figure compared.

  FIG. 11A is a tomographic image of the subject P after luminance correction obtained by the magnetic resonance imaging apparatus 20 shown in FIG. 1, and FIG. 11B is obtained by the conventional magnetic resonance imaging apparatus 20. 6 is a tomographic image of the subject P after luminance correction.

  According to FIG. 11B, as a result of a deviation between the shape of the subject P photographed by the phased array coil 24b and the shape of the subject P photographed by the WB coil 24a during the sensitivity pre-scan imaging, the image data It can be seen that the luminance is not sufficiently corrected.

  On the other hand, according to FIG. 11A, the shape of the subject P photographed by the phased array coil 24b and the shape of the subject P photographed by the WB coil 24a are obtained by the region reduction of the WB reconstruction image and the PAC reconstruction image. Even if a deviation occurs, it is possible to accurately generate the three-dimensional sensitivity map data with improved continuity, so that it can be confirmed that the luminance of the image data can be sufficiently corrected.

  In the magnetic resonance imaging apparatus 20 described above, a part of the data processing may be omitted, and a part of the components may be omitted accordingly. Further, a single coil may be used instead of the phased array coil 24b.

1 is a functional block diagram showing an embodiment of a magnetic resonance imaging apparatus according to the present invention. FIG. 2 is a detailed configuration diagram of an RF coil and a receiver shown in FIG. 1. The cross-sectional schematic diagram which shows the example of arrangement | positioning of the WB coil and phased array coil which are shown in FIG. The flowchart which shows the procedure at the time of imaging the tomographic image of a subject with the magnetic resonance imaging apparatus shown in FIG. The flowchart which shows the detailed procedure at the time of producing | generating a sensitivity map data with the magnetic resonance imaging apparatus shown in FIG. The figure which shows the Example of the region reduction process by the magnetic resonance imaging apparatus shown in FIG. The figure which shows the Example of the linear interpolation with respect to the no-signal area | region inside the subject of the three-dimensional sensitivity map data by the magnetic resonance imaging apparatus shown in FIG. FIG. 3 is an explanatory diagram illustrating an example of a region growing method for a non-signal region outside a subject of 3D sensitivity map data by the magnetic resonance imaging apparatus illustrated in FIG. 1. The figure which shows the Example of the region growing with respect to the no-signal area | region outside the subject of the three-dimensional sensitivity map data by the magnetic resonance imaging apparatus shown in FIG. The figure which plotted the correction coefficient at the time of performing weighting to the slice direction of three-dimensional sensitivity map data by the magnetic resonance imaging apparatus shown in FIG. FIG. 2 is a diagram comparing a tomographic image of a subject after luminance correction obtained by the magnetic resonance imaging apparatus shown in FIG. 1 and a tomographic image of the subject after luminance correction obtained by a conventional magnetic resonance imaging apparatus. The functional block diagram of the conventional magnetic resonance imaging apparatus. 10 is a flowchart showing a procedure for creating a sensitivity map by the magnetic resonance imaging apparatus shown in FIG.

Explanation of symbols

20 Magnetic Resonance Imaging Device 21 Magnet for Static Magnetic Field 22 Shim Coil 23 Gradient Magnetic Field Coil Unit 24 RF Coil 24a WB Coil 24b Phased Array Coil 24c Surface Coil 25 Control System 26 Static Magnetic Field Power Supply 27 Gradient Magnetic Field Power Supply 28 Shim Coil Power Supply 29 Transmitter 30 Receiver 30a Reception system circuit 31 Sequence controller 32 Computer 33 Input device 34 Display device 35 Bed 36 Sensitivity prescan execution means 37 Main scan execution means 38 Sequence controller control means 39 Raw data database 40 Image reconstruction means 41 Image data database 42 PAC reconstruction Image database 43 WB reconstruction image database 44 Sensitivity distribution estimation means 44a Threshold processing means 44b Region reduction means 44c Division processing means 44d Normalization means 4 e Data flattening means 44f subject region interpolation means 44g subject extracellular region interpolation means 44h slice direction weighting means 44i smoothing processing unit 45 sensitivity map database 46 the image data correction unit 47 the image displaying unit

Claims (9)

Means for executing a scan for generating sensitivity map data of the RF coil; means for performing a region reduction on a signal region in the vicinity of a non-signal region of the image data obtained by the scan; and the image after the region reduction. And a means for generating sensitivity map data using the data. Means for executing a scan for generating sensitivity map data of the RF coil, means for generating sensitivity map data using image data obtained by the scan, and weighting the sensitivity map data in the slice direction A magnetic resonance imaging apparatus comprising: means for correcting. Means for executing a scan for generating sensitivity map data of the RF coil; means for performing a region reduction on a signal region in the vicinity of a non-signal region of the image data obtained by the scan; and the image after the region reduction. A magnetic resonance imaging apparatus comprising: means for generating sensitivity map data using data; and means for correcting the sensitivity map data by weighting in the slice direction. The magnetic resonance imaging apparatus according to claim 1, wherein a no-signal area in the subject of the sensitivity map data is linearly interpolated. 4. The magnetic resonance imaging apparatus according to claim 1, wherein a non-signal region outside the subject of the sensitivity map data is region grown. 4. The magnetic resonance imaging apparatus according to claim 1, wherein a smoothing filter is applied to the sensitivity map data. A step of performing region reduction on a signal region in the vicinity of a non-signal region of image data obtained by scanning for generating sensitivity map data of the RF coil, and sensitivity map data using the image data after region reduction. A data processing method for a magnetic resonance imaging apparatus. Generating sensitivity map data using image data obtained by scanning for generating sensitivity map data of the RF coil, and correcting by weighting the sensitivity map data in the slice direction. A data processing method for a magnetic resonance imaging apparatus. A step of performing region reduction on a signal region in the vicinity of a non-signal region of image data obtained by scanning for generating sensitivity map data of the RF coil, and sensitivity map data using the image data after region reduction. A data processing method for a magnetic resonance imaging apparatus, comprising: generating and correcting the sensitivity map data by weighting in the slice direction.

Images