JP2012000389A - Magnetic resonance imaging apparatus and magnetic resonance imaging method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide technique to accurately acquire sensitivity map for real imaging data not depending on an imaging object part to acquire a high quality image.SOLUTION: Acquisition of navigation echo for displacement detection within a period of keeping position consistency, sensitivity map imaging to acquire data for sensitivity map making, and real imaging are carried out. The sensitivity map imaging and the real imaging are performed by displacing an excitement position by the displacement detected by the navigation echo. Then, image processing is applied by the sensitivity map formed by the data obtained within the period onto the reconstruction image obtained resulting from the real imaging.

Description

  The present invention relates to a magnetic resonance imaging technique. In particular, the present invention relates to an imaging technique when a multi-element coil is used as a receiving coil.

  A magnetic resonance imaging (MRI) apparatus measures a nuclear magnetic resonance (hereinafter referred to as “NMR”) signal from hydrogen, phosphorus or the like in a subject and visualizes a nuclear density distribution, a relaxation time distribution, and the like. This is called photographing. A multi-element coil (multi-coil) may be used as a receiving coil for detecting the NMR signal. A multi-coil is composed of a plurality of small RF coils with relatively high sensitivity. By synthesizing the signals received by each RF coil, a wide field of view can be obtained while maintaining the high sensitivity of the small RF coil. Can do.

  Although the multi-coil has high sensitivity, the spatial non-uniformity of sensitivity is large. Due to this non-uniformity of sensitivity, so-called shading occurs, in which the image corresponding to the low-sensitivity portion of the coil becomes dark. Therefore, in an inspection using a multi-coil, a multi-coil sensitivity distribution (sensitivity map) is acquired prior to image acquisition (main imaging) used for diagnosis, and shading correction is performed using this sensitivity map during image reconstruction. . Furthermore, the sensitivity map is used for the PARALLEL reconstruction process using the sensitivity difference of each element.

  A sensitivity map is calculated | required from the received signal of each small RF coil which comprises a multicoil. For example, the pixel value of each pixel of the phase image acquired by the multi-coil is divided by the pixel value of the corresponding pixel of the phase image acquired by a single element coil (hereinafter referred to as a single coil) consisting of one RF coil, and the sensitivity map (For example, see Non-Patent Document 1). The phase image for creating the sensitivity map is acquired by photographing the same part under the same photographing condition with each of the single coil and the multi-coil before the main photographing. Shooting for acquiring this phase image is called sensitivity map shooting.

Klaas P.M. Prussmann et al. “Coil Sensitivity Map for Sensitivity Encoding and Intensity Correction”, The proceedings of ISMRM 6th annual meeting, 1998, p2087.

  When the imaging target part is a part whose position fluctuates in time (fluctuating part), such as a part that is greatly affected by respiratory motion, when shooting sensitivity maps, when shooting with a single coil and when shooting with a multi-coil If the position and shape of the region to be imaged differ from each other, an accurate sensitivity map cannot be obtained.

  Further, normally, a single coil is a coil fixed in a gantry of an MRI apparatus, while a multi-coil is a coil attached to a subject. For this reason, when the imaging target part is a fluctuating part, the spatial arrangement of the multi-coil changes with the change of the imaging target part, and the position of the multi-coil with respect to the position of the single coil also changes. If the imaging target region fluctuates or deforms between the sensitivity map imaging and the actual imaging, inconsistency may occur between the reconstructed image and the sensitivity map.

  Furthermore, in the case of multi-slice imaging, position inconsistency may occur due to fluctuations in the imaging target region even within the main imaging. This reduces the quality of the reconstructed image.

  As described above, when the imaging target part is a variable part, there are various inconsistencies between the imaging position and the imaging target part position, the mismatch between the position of the single coil and the multi-coil, the mismatch between the positions of both coils and the imaging target part, etc. Inconsistent combinations occur. As a result, the quality of the sensitivity map and the reconstructed image itself is deteriorated, and the shading correction and the PARALLEL development are fraudulent, leading to the deterioration of the image quality.

  The present invention has been made in view of the above circumstances, and an object of the present invention is to provide a technique for obtaining a high-quality image by accurately obtaining a sensitivity map to be applied to data of actual imaging regardless of a region to be imaged. To do.

  The present invention performs navigation map acquisition and main imaging to acquire navigation echoes for displacement detection, data for sensitivity map creation, within a period in which position consistency can be obtained. Sensitivity map imaging and main imaging are performed by displacing the excitation position by the amount of displacement detected by the navigation echo. Then, image processing is performed on the reconstructed image obtained as a result of the main photographing with the sensitivity map generated from the data obtained during the same period.

  Specifically, pulse applying means for applying a high frequency pulse and a gradient magnetic field pulse to the subject, signal detecting means for detecting a nuclear magnetic resonance signal generated from the subject, the pulse applying means, and the signal detecting means A magnetic control unit that controls operations and executes imaging; and an image processing unit that reconstructs an image from a nuclear magnetic resonance signal detected by the signal detection unit and generates a display image to be displayed on a display device. A resonance imaging apparatus, wherein a displacement detection unit that detects a displacement of the subject and an imaging that changes a position of a predetermined imaging region according to the displacement detected by the displacement detection unit for each predetermined period Position change means, the signal detection means comprises a plurality of receiving coils having spatially different detection sensitivity distributions, and the measurement control means is configured to detect the displacement of the subject. The actual imaging of the imaging region after the change is executed while the displacement detected by the means is detected, and the image processing means adds the book to the image reconstructed from the nuclear magnetic resonance signal detected by the actual imaging. A sensitivity distribution of the plurality of receiving coils generated from sensitivity data that is a nuclear magnetic resonance signal acquired while the subject is at a displacement that substantially matches the displacement of the subject at the time of imaging is determined in advance. A magnetic resonance imaging apparatus characterized by performing image processing is provided.

  In addition, a signal including a pulse applying unit that applies a high-frequency pulse and a gradient magnetic field pulse to the subject, and a plurality of receiving coils that detect nuclear magnetic resonance signals generated from the subject and have spatially different detection sensitivity distributions. An image is reconstructed from a detection means, a measurement control means for controlling the operations of the pulse applying means and the signal detection means and executing imaging, and a nuclear magnetic resonance signal detected by the signal detection means, and displayed on a display device A magnetic resonance imaging method in a magnetic resonance imaging apparatus comprising: an image processing means for generating a display image to be detected, a displacement detection step for detecting a displacement of a subject for each predetermined period; and each time the displacement is detected The imaging position changing step for changing the position of the imaging area according to the detected displacement, and the change while the subject is at the detected displacement. An imaging step for executing a main imaging of a subsequent imaging area, an image reconstruction step for reconstructing an image from a nuclear magnetic resonance signal detected in the actual imaging, and the main imaging is performed on the reconstructed image. Image processing for performing predetermined image processing using sensitivity distributions of the plurality of receiving coils generated from nuclear magnetic resonance signals acquired while the subject is at a displacement that substantially matches the displacement of the subject And providing a magnetic resonance imaging method.

  According to the present invention, it is possible to obtain a high-quality image by accurately acquiring a sensitivity map to be applied to data of actual imaging regardless of the region to be imaged.

It is a block diagram of the MRI apparatus of 1st embodiment. (A) is explanatory drawing for demonstrating the imaging | photography sequence using the conventional multi-coil, (b) is a sensitivity map acquisition area, (c)-(e) is the position of an imaging | photography area | region and imaging | photography slice. FIG. 6 is an explanatory diagram for explaining the above. (A) is explanatory drawing for demonstrating the imaging | photography sequence which uses the conventional multi-coil and is a navigator echo, (b) is a sensitivity map acquisition area | region, (c)-(e) These are explanatory drawings for explaining the imaging region and the position of the imaging slice, respectively. (A) is a functional block diagram of the calculating part of 1st embodiment, (b) is a functional block diagram of the calculating part of 2nd embodiment. (A) is explanatory drawing for demonstrating the imaging | photography sequence of 1st embodiment, (b)-(d) is for demonstrating an imaging | photography area | region, a sensitivity map, and the position of an imaging | photography slice, respectively. It is explanatory drawing. (A) is explanatory drawing for demonstrating the imaging | photography sequence of the modification of 1st embodiment, (b), (c) each demonstrates an imaging | photography area | region, a sensitivity map, and the position of an imaging | photography slice. It is explanatory drawing for doing. It is explanatory drawing for demonstrating the sensitivity data acquisition timing and sensitivity map of 2nd embodiment. It is explanatory drawing for demonstrating the imaging | photography sequence of 2nd embodiment.

<< First Embodiment >>
Hereinafter, a first embodiment to which the present invention is applied will be described. Hereinafter, in all the drawings for explaining the embodiments of the present invention, those having the same function are denoted by the same reference numerals, and repeated explanation thereof is omitted.

  First, the MRI apparatus of this embodiment will be described. FIG. 1 is a block diagram of the MRI apparatus 100 of the present embodiment. The MRI apparatus shown in FIG. 1 is a typical MRI apparatus, and includes a magnet 102, a gradient magnetic field coil 103, an RF coil 104, an RF probe 105, a gradient magnetic field power source 106, an RF transmission unit 107, and a signal. A detection unit 108, a calculation unit 109, a sequencer 110, a display unit 111, an operation unit 112, and a storage unit 113 are provided.

  The magnet 102 generates a static magnetic field around the subject 101. The subject 101 is placed on the bed 114 and placed in this static magnetic field space.

  The gradient magnetic field coil 103 is constituted by gradient magnetic field coils in three directions of X, Y, and Z, and generates a gradient magnetic field in each direction in a static magnetic field space formed by the magnet 102 in response to a signal from the gradient magnetic field power supply 106. To do.

  The RF coil 104 is a transmission / reception coil. The RF coil 104 operates as a transmission coil that generates a high-frequency magnetic field in accordance with a signal from the RF transmission unit 107 and irradiates the subject 101, and a nuclear magnetic resonance signal generated by the subject 101. It operates as a receiving coil that receives (NMR signal; echo signal). The received echo signal is detected by the signal detection unit 108 and sent to the calculation unit 109. In the present embodiment, a single element coil (single coil) such as a birdcage coil is used as the RF coil 104. The RF coil 104 is operated as a receiving coil when used as a single coil when acquiring sensitivity data for creating a sensitivity map, which will be described later.

  The RF probe 105 receives a nuclear magnetic resonance signal (NMR signal; echo signal) generated by the subject 101. The received echo signal is detected by the signal detection unit 108 and sent to the calculation unit 109. In the present embodiment, a multi-element coil (multi-coil) including a plurality of RF coils is used for the RF probe 105. Note that which of the RF coil 104 and the RF probe 105 is used as a reception coil is determined by an instruction from the arithmetic unit 109 via the sequencer 110.

  The calculation unit 109 controls the overall operation of the MRI apparatus 100. A sequencer 110, a display unit 111, an operation unit 112, and a storage unit 114 are connected to the calculation unit 109. The calculation unit 109 causes the sequencer 110 to control the operation of each unit in accordance with a control time chart previously stored in the storage unit 114 and the instruction (imaging conditions) input from the user via the operation unit 112. Perform measurement. The control time chart is generally called a pulse sequence. In addition, the calculation unit 109 performs signal processing on the echo signal sent from the signal detection unit 108 to reconstruct an image. The obtained image is displayed on the display unit 111 and stored in the storage unit 113.

  The sequencer 110 operates the gradient magnetic field power source 106, the RF transmission unit 107, and the signal detection unit 108 in accordance with instructions from the calculation unit 109.

  At present, the imaging object of MRI is proton, which is the main constituent of the subject, as widely used clinically. The MRI apparatus 100 images the form or function of the human head, abdomen, extremities, etc. in a binary or ternary manner by imaging the spatial distribution of proton density and the spatial distribution of the relaxation phenomenon in the excited state. .

  The imaging procedure by the MRI apparatus 100 is as follows. First, the RF transmitter 107 is driven in accordance with the pulse sequence, and the subject 101 is irradiated with a high-frequency magnetic field pulse (RF pulse) from the RF coil 104. As a result, the echo signal generated from the subject 101 is given different phase encoding depending on the gradient magnetic field. As the number of phase encodings, values such as 128, 256, and 512 are usually selected per image. Each echo signal is normally detected as a time-series signal composed of 128, 256, 512, and 1024 sampling data. These data are two-dimensionally Fourier transformed to create one MR image.

  In the present embodiment, a multi-coil is used as the RF probe 105 as described above. In imaging using a multi-coil, multi-coil sensitivity distribution (sensitivity map) is used to perform shading correction and PARALLEL reconstruction processing on the reconstructed image, and finally generate a display image to be displayed on the display unit 111. Hereinafter, image processing performed on the reconstructed image using the sensitivity distribution is collectively referred to as correction.

  Prior to the description of the shooting sequence of the present embodiment, a conventional shooting sequence using a multi-coil will be described with reference to FIG. FIG. 2A is a diagram for explaining the flow of shooting (shooting sequence). Here, a multi-slice cine imaging of the heart will be described as an example. That is, the imaging target region is the heart 270, and a three-dimensional region is imaged by multi-slice imaging. At this time, in a plurality of breath holdings, one slice is photographed for each breath holding.

  As shown in this figure, in the conventional multi-slice cine imaging of the heart using a multi-coil, the sensitivity map of the entire imaging target area is obtained in advance, and the reconstructed image obtained in the actual imaging is corrected using it.

  First, prior to actual photographing, sensitivity map photographing (Map) 200 for obtaining sensitivity data for creating a sensitivity map is performed. FIG. 2B is a diagram for explaining the sensitivity map 201 obtained by the sensitivity map imaging (Map) 200, the sensitivity map acquisition region 250, and the heart 120 that is the imaging target region. The sensitivity map imaging (Map) 200 captures the sensitivity map acquisition region 250 using the single coil and the multi-coil as receiving coils under the same measurement conditions. The sensitivity map 201 is created from phase images obtained by reconstructing the respective echo signals. Note that the sensitivity map acquisition area 250 is generally a three-dimensional area including the entire imaging area in order to apply the created sensitivity map 201 to a reconstructed image obtained by the subsequent whole imaging.

  Note that it is desirable to perform the breathing 240 immediately before the sensitivity map photographing 200 and hold the breath between the sensitivity map photographing 200. Since there is no displacement or deformation due to respiratory motion during breath holding, it is possible to avoid fluctuations in the relative positions of the single coil and the multi-coil between the sensitivity map photographings 200.

  After the sensitivity map 201 is created, the controller 240 performs the adjustment 240 and performs the actual photographing every time the breath is held. As shown in the figure, main photographing 211, 221, and 231 are performed between the breath-holding units 210, 220, and 230, respectively. FIGS. 2C to 2E are diagrams for explaining the entire imaging region 260 and imaging slices in the main imaging 211, 221, and 231 respectively. In the figure, RL indicates the left-right direction of the subject, and HF indicates the head-foot (body axis) direction. The same applies hereinafter.

  As shown in these figures, in each of the main shootings 211, 221, and 231, each of the shootings is repeated for each slice, such as the first slice 216, the second slice 226, and the third slice 236, respectively. The photographing area 260 is photographed.

  The sensitivity map 201 is applied to each of the reconstructed images of the first slice 216, the second slice 226, and the third slice 236 obtained in each of the main photographing 211, 221, and 231 to perform correction and generate a display image. .

  Here, as shown in FIGS. 2C to 2E, if there is respiratory motion, the position of the imaging target portion 120 with respect to the coordinate system of the MRI apparatus 100 may be displaced, and a desired slice may not be imaged. This is because the imaging slice is determined based on the coordinate system of the MRI apparatus 100. In order to avoid this, there is a method of acquiring navigator echo and adjusting the shooting position for each main shooting.

  A method of adjusting the shooting position by navigator echo will be described with reference to FIG. As in FIG. 2, multi-slice cine imaging of the heart 120 will be described as an example. FIG. 3A is a diagram for explaining the flow of shooting (shooting sequence) in this case.

  First, prior to actual photographing, sensitivity map photographing (Map) 300 for obtaining sensitivity data for creating a sensitivity map is performed. The sensitivity map photographing (Map) 300 is the same as the example shown in FIG. FIG. 3B is a diagram for explaining a sensitivity map 301, a sensitivity map acquisition region 350, and an imaging target part (heart) 120 obtained by sensitivity map imaging (Map) 300.

  After the sensitivity map 301 is created, the breath is held every breath 340, navigator echoes are acquired and the main photographing is performed between the breaths, and a reconstructed image is obtained.

  At the time of the first breath holding 310, the navigator echo 312 is first acquired. From the acquired navigator echo 312, the fluctuation amount (displacement) of the imaging target part 120 at the time of breath holding 310 is detected (317). While controlling to change (318) the excitation position by the detected displacement, the main imaging 311 is performed, and a reconstructed image of the first slice 316 is obtained as shown in FIG.

  Next, breathing 340 is performed, navigator echo 322 is acquired during the second breath hold 320, and actual photographing 321 is performed. The main photographing 321 is performed while controlling to detect the displacement from the navigator echo 322 (327) and change the excitation position accordingly (328), as in the main photographing 311. As a result, a reconstructed image of the second slice 326 is obtained as shown in FIG.

  Then, the patient performs a breathing 340, acquires the navigator echo 332 during the third breath-holding 330, and performs the main photographing 331. The main photographing 331 is performed while controlling to detect the displacement from the navigator echo 332 (337) and to change the excitation position by that amount (328), as in the main photographing 311 and 321. As a result, a reconstructed image of the third slice 336 is obtained as shown in FIG.

  In this way, in multi-slice imaging, navigator echoes are acquired immediately before each main imaging and the excitation position is adjusted, so that the imaging target region can be accurately imaged even when there is respiratory motion. However, the mismatch of the position of the multi-coil (RF probe 105) and the mismatch of the position and shape of the imaging target part 120 between the acquisition of the sensitivity map 300 and the actual imaging 311, 321, and 331 are still not resolved.

  Therefore, in this embodiment, in order to avoid these inconsistencies, in addition to navigator echo acquisition, sensitivity map imaging is performed immediately before each main imaging, that is, while the body movement state is the same. In the case where the fluctuation of the body motion state is due to respiratory motion, in this embodiment, navigator echo acquisition, sensitivity map imaging, and main imaging are performed within one breath holding period.

  In order to realize this, the calculation unit 109 according to the present embodiment includes a measurement control unit 710, a displacement detection unit 720, an excitation position change unit 730, and a sensitivity map generation unit 740, as illustrated in FIG. And an image processing unit 750. The calculation unit 109 includes a CPU, a memory, and a storage device. The CPU loads the program stored in the storage device into the memory and executes the program, thereby realizing these functions.

  The measurement control unit 710 controls the operation of each unit of the MRI apparatus 100 according to the pulse sequence held in advance and the input imaging conditions, and executes predetermined imaging. In the present embodiment, navigator echo acquisition, sensitivity map imaging for acquiring sensitivity map creation data (sensitivity data), and main imaging (acquisition of echo signals that can reconstruct an image) are executed.

  The navigator echo is acquired in the presence of only the readout gradient magnetic field without applying phase encoding. A Fourier transform of the acquired echo becomes a projection image on the readout axis of the imaging region (FOV), and the displacement of the subject can be obtained from the edge of this projection image (a portion where the signal intensity changes suddenly). The displacement detection unit 720 obtains the displacement of the imaging target region from the acquired navigator echo using this method. The displacement is based on the position information held by the imaging region (FOV), based on the displacement from the center of the static magnetic field, that is, the coordinate value in each axis direction on the coordinate system of the MRI apparatus 100 with the center of the static magnetic field as the origin. Is calculated (detected).

  In order to change the imaging slice position in the coordinate system of the MRI apparatus 100, the excitation position changing unit 730 changes the amount of displacement of the imaging target portion detected by the displacement detection unit 720 and the excitation position at the time of subsequent imaging. The excitation position is changed by changing the irradiation frequency of the high frequency magnetic field generated according to the signal from the RF transmission unit 107. Therefore, the excitation position changing unit 730 uses the irradiation frequency for exciting the changed position as an imaging parameter used for subsequent imaging.

  In the case where the change or deformation of the imaging target region is due to respiratory motion, in this embodiment, navigator echoes are acquired immediately after each breath hold and before sensitivity map imaging and main imaging, and the excitation position is changed. Sensitivity map imaging and main imaging performed after navigator echo acquisition are executed at the changed excitation position.

  In the sensitivity map shooting of this embodiment, a predetermined pulse sequence is used, and shooting is performed using a single coil (RF coil 104) and a multi-coil (RF probe 105) as receiving coils under the same shooting conditions, and sensitivity data is obtained. get. The area from which the sensitivity data is acquired is determined by the changed excitation position. In the present embodiment, since the generated sensitivity map is applied only to a region to be measured in the subsequent main photographing, the sensitivity data may be acquired only from the region including the region.

  The sensitivity map generation unit 740 generates a sensitivity map from the acquired sensitivity data. The sensitivity map was obtained by operating the RF coil 104 (single coil) as a receiving coil and each pixel value of a phase image obtained by reconstructing an echo signal obtained using the RF probe 105 (multicoil) as a receiving coil. The echo signal is generated by dividing by each pixel value of the phase image obtained by reconstructing the echo signal.

  The image processing unit 750 reconstructs an image from the echo signal obtained by the actual photographing. Then, using the sensitivity map created from the sensitivity data acquired in the same body movement state, the reconstructed image is corrected and a display image is generated.

  Hereinafter, the operation of each unit of the calculation unit 109 during shooting according to the present embodiment will be described with a specific example. FIG. 5A is an explanatory diagram for explaining a flow (shooting sequence) of each shooting performed by the measurement control unit 710 of the present embodiment, and FIGS. 5B to 5D are views of the present embodiment. It is a figure for demonstrating the reconstructed image obtained by the main imaging | photography performed within an imaging | photography sequence. Note that, in the description of the imaging sequence of the present embodiment, the multi-slice cine imaging of the heart will be described as an example, as in the imaging sequences of FIGS. That is, the imaging target region 120 is a heart, and the fluctuation and deformation of the imaging target region are due to respiratory motion, and imaging for one slice is performed within one breath holding period.

  First, during the first breath hold 410 after the breathing 440, the measurement control unit 710 first acquires the navigator echo 412. Here, the displacement detector 720 calculates the displacement from the acquired navigator echo 412 (417). Further, the excitation position changing unit 730 changes the excitation position based on the calculated displacement (418), and updates the imaging parameter.

  Next, the measurement control unit 710 performs sensitivity map imaging 413 at the excitation position changed by the excitation position changing unit 730, and acquires sensitivity data. Thereby, sensitivity data of the first slice 416 is obtained. In addition, the measurement control unit 710 performs main imaging 411 of the excitation position changed by the excitation position changing unit 730. Thereby, an echo signal of the first slice 416 is obtained. Here, since the sensitivity map 414 generated from the sensitivity data obtained by the sensitivity map photographing 413 is applied only to the image of the first slice 416, the sensitivity data is acquired only for the range of the first slice 416.

  Next, after the breathing 440, the navigator echo 422 is also acquired between the second breath-holding 420 and changed to the excitation position determined based on the calculated displacement (427) (428). Then, sensitivity map imaging 423 and main imaging 421 for acquiring sensitivity data of the second slice 426 are performed at the changed excitation position.

  After the breathing 440, the navigator echo 432 is also acquired between the third breath-holding 430 and changed to the excitation position determined based on the calculated displacement (437) (438). Then, sensitivity map imaging 433 and main imaging 431 for acquiring sensitivity data of the third slice 436 are performed at the changed excitation position.

  The sensitivity map generation unit 740 generates sensitivity maps 414, 424, and 434 from the acquired sensitivity data at a predetermined timing after execution of the sensitivity map photographing 413, 423, and 433. In addition, the image processing unit 750 performs an image (first image) of the first slice 416 and an image of the second slice 426 from the echo signals obtained by the respective shooting at predetermined timing after execution of the main shootings 411, 421, and 431, respectively. The image (second image) and the image (third image) of the third slice 436 are reconstructed. Then, the image processing unit 750 corrects the reconstructed first image, second image, and third image with sensitivity maps 414, 424, and 434, respectively, and generates a display image.

  For example, the sensitivity map generation unit 740 generates the sensitivity maps 414, 424, and 434 immediately after the execution of the respective sensitivity map shootings 413, 423, and 433, and the image processing unit 750 immediately after the execution of the respective main shootings 411, 421, and 431. Reconstruct each image. However, it is not limited to this timing.

  Thus, according to the present embodiment, in the multi-slice cine imaging of the heart, the displacement is detected by the navigation echo for each breath hold and the excitation position is adjusted. Does not occur. In addition, since sensitivity map imaging and main imaging are performed during one breath-hold, there is no inconsistency in the position and shape of the single coil, multi-coil, and imaging target region.

  As described above, according to the present embodiment, navigator echo acquisition, sensitivity map imaging, and main imaging are performed between breath-holdings, that is, while the shape of the subject is constant. Sensitivity map imaging and main imaging are performed at the excitation position changed according to the displacement detected by the navigator echo. Therefore, an accurate echo signal of the imaging slice and sensitivity data necessary and sufficient for correction can be obtained in a period not affected by respiratory motion.

  Therefore, according to the present embodiment, it is possible to perform image processing such as shading correction and PARALLEL development on a reconstructed image acquired during one breath hold using a highly accurate and optimum sensitivity map. Therefore, it is possible to prevent the image quality from being deteriorated due to the mismatch of the sensitivity map, and a high-quality image can be obtained.

  In addition, inconsistency of the imaging slice position due to the position variation of the imaging target part for each breath hold is avoided by detecting the displacement by the navigator echo and adjusting the excitation position. Therefore, the image quality does not deteriorate even in multi-slice imaging.

  As described above, according to the present embodiment, it is possible to obtain a high-quality image regardless of whether the subject to be imaged is a part having a large influence of body movement or multi-slice imaging.

  In the above embodiment, in each breath holding period 410, 420, 430, the case where only one slice is taken as the main photographing 411, 421, 431 has been described as an example. A plurality of slices or 3D slab data may be acquired as long as it can be acquired within (usually about 15-20 sec).

  A shooting sequence in this case is shown in FIG. Here, an example in which the entire imaging region is divided into two slabs and measured. The flow of the shooting sequence is basically the same as in the above embodiment.

  That is, first, during the first breath hold 510, the measurement control unit 710 performs acquisition of the navigator echo 511, sensitivity map shooting 513, and main shooting 511. At this time, the displacement detection unit 720 detects the displacement of the imaging target region from the navigator echo 511 (517). Then, the excitation position changing unit 730 changes the excitation position according to the detected displacement (518). The measurement control unit 710 performs sensitivity map imaging 513 and main imaging 511 at the changed excitation position.

  In the sensitivity map shooting 513, sensitivity data is acquired for the area that matches the area shot in the subsequent main shooting 511. Here, in the subsequent main shooting, since shooting is performed for the first slab 516, sensitivity data is also acquired for the first slab 516. In the main photographing 511, photographing is performed for a plurality of slices for each slice (slice # 1, slice # 2, slice # 3) for the area corresponding to the first slab 516.

  Then, breathing 540 is performed, and the second breath holding 520 is entered. During the second breath hold 520, as with the first breath hold 510, the sensitivity map is captured at the excitation position (528) changed according to the acquisition of the navigator echo 521 and the displacement (527) detected by the navigator echo 521. 523 and actual photographing 521 are performed. Sensitivity data is acquired for the second slab 526, and in the main shooting 521, shooting is performed for a plurality of slices for each slice (slice # 4, slice # 5, slice # 6) for the second slab 526.

  Also in this modification, the sensitivity map generator 740 generates sensitivity maps 514 and 524 at a predetermined timing after each sensitivity map shooting 512 and 522. Further, the image processing unit 750 generates a reconstructed image of each slice at a predetermined timing after acquiring echo signals for each slice in the main photographing 511 and 521. In addition, the image processing unit 750 corrects each generated reconstructed image with each sensitivity map 514, 524 generated from the sensitivity data acquired within the breath holding period.

  According to this modification, the sensitivity data acquired for creating the sensitivity map increases from the 2D single slice to the 3D slab. Therefore, the data acquisition time becomes longer accordingly. However, since sensitivity map imaging uses a sequence with a low spatial resolution and a short TR, it can be sufficiently executed within the breath holding period together with the main imaging.

  For example, a typical example of sensitivity data acquisition conditions in sensitivity map shooting is an in-plane matrix of 32 × 32 and TR of about 3 ms. If the number of slices in one slab is 16, the acquisition time per slab data is about 32 × 16 × 3 = 1.5 sec.

  FIG. 6 shows an example in which the sensitivity data of one slab and the main imaging data are taken with one breath hold. However, the inside of the slab is further increased due to various factors such as the breath hold time and spatial resolution. The measurement pattern is not limited to this, such as dividing into a plurality of measurements.

<< Second Embodiment >>
Next, a second embodiment to which the present invention is applied will be described. In the first embodiment, sensitivity map shooting and main shooting are performed while the body movement state is kept constant, and sensitivity data and main shooting data are acquired. This prevents the position mismatch of the imaging target part and the multi-coil position mismatch during the sensitivity map imaging and the main imaging. In the present embodiment, a sensitivity map is acquired in advance in a plurality of body movement states, a sensitivity map with the least mismatch is adopted for each main photographing, and correction or the like is performed using the sensitivity map.

  Hereinafter, the present embodiment will be described focusing on the configuration different from the first embodiment.

  The configuration of the MRI apparatus 100 of this embodiment is basically the same as that of the first embodiment. As shown in FIG. 4B, the calculation unit 109 according to the present embodiment includes a measurement control unit 711, a displacement detection unit 720, an excitation position change unit 730, a sensitivity map generation unit 740, an image processing unit 751, and the like. Is provided. The calculation unit 109 of the present embodiment further includes a sensitivity map holding unit 760.

  The measurement control unit 711 is basically the same as the measurement control unit 710 of the first embodiment, and controls the operation of each unit of the MRI apparatus 100 according to the pulse sequence held in advance and the input imaging conditions, and performs predetermined imaging. Execute. In this embodiment, navigator echo acquisition, sensitivity map imaging for acquiring sensitivity map creation data (sensitivity data), and main imaging are executed. Acquisition of navigator echo and actual photographing are the same as in the first embodiment.

  The measurement control unit 711 according to the present embodiment performs sensitivity map imaging prior to navigator echo acquisition and main imaging. In this sensitivity map shooting, a plurality of sensitivity data corresponding to the body movement state is acquired. For example, when the region to be imaged is deformed and / or fluctuated due to periodic body movement, the sensitivity data of each time phase is acquired for at least one cycle.

  Note that the measurement control unit 711 acquires a navigator echo immediately before execution of sensitivity map shooting for each body movement state. Hereinafter, measurement for obtaining navigator echoes and sensitivity data for each predetermined body movement state is referred to as multi-phase sensitivity map imaging.

  For example, when the imaging target part is a part that fluctuates due to respiration, the measurement control unit 711 divides one respiratory cycle into a plurality of parts and sensitizes each timing at least for one respiratory cycle. Get the data. The respiratory waveform (displacement) is monitored by attaching a pressure sensor or the like to the subject. The measurement control unit 711 performs multiphase sensitivity map imaging based on an input from the pressure sensor.

  The displacement detector 720 calculates the displacement at that time from the acquired navigator echo. In addition, the sensitivity map generation unit 740 generates a sensitivity map from each acquired sensitivity data. And the sensitivity map holding | maintenance part 760 matches the detected displacement and a sensitivity map for every body movement state, and memorize | stores it in the memory | storage part 113 as sensitivity map data.

  FIG. 7 illustrates a case where, in multi-slice cine imaging of the heart, one respiratory cycle is divided into five (5 phases) and sensitivity data is acquired six times for each phase plus one time. In addition, the displacement (respiration displacement) of the heart which is the imaging target region due to the respiratory motion is indicated by 690.

  As shown in this figure, the measurement control unit 711 acquires navigator echoes and sensitivity data for each phase at the respective timings (t1, t2, t3, t4, t5, t6) divided into five. Then, the displacement detection unit 720 calculates the displacement of the phase from each navigator echo, and the sensitivity map creation unit calculates the sensitivity map of each phase (sensitivity map of the first phase (first sensitivity map) from each sensitivity data. ) 601, second sensitivity map 602, third sensitivity map 603, fourth sensitivity map 605, fifth sensitivity map 606, first phase sensitivity map (sixth sensitivity map) 606 ) Is generated. And the sensitivity map holding | maintenance part 760 matches a displacement and a sensitivity map for every phase, and memorize | stores it in the memory | storage part 113 as sensitivity map data.

  The number of sensitivity maps acquired in one breathing cycle, that is, the number of phases to be divided is not limited, but is determined according to the spatial resolution of the sensitivity map so that fluctuation due to respiration is reflected in the sensitivity map. Generally, the displacement due to respiration is about 20 mm. For example, when a 300 mm field of view (FOV) is acquired with 64 matrices, the spatial resolution is 4.7 mm. Therefore, when the displacement is about 20 mm, a sensitivity map of 5 phases or more may be acquired.

  The image processing unit 751 of the present embodiment selects a sensitivity map that is held in association with the displacement that is closest to the displacement detected by the displacement detection unit 720 immediately before the actual photographing from the sensitivity map data, and uses the sensitivity map. Correct the reconstructed image. That is, the reconstructed image is corrected using the sensitivity map created with the sensitivity data acquired at the respiration level closest to the respiration level at the time of the main photographing.

  Hereinafter, the operation of each unit of the calculation unit 109 during shooting according to the present embodiment will be described. FIG. 8 is an explanatory diagram for describing a photographing sequence of the present embodiment. Here again, an explanation will be given by taking multi-slice cine imaging of the heart as an example. That is, the imaging target part is a heart part whose position varies due to respiratory motion.

  First, the measurement control unit 711 performs multi-phase sensitivity map shooting 600. In the multi-phase sensitivity map photographing 600, navigator echoes and sensitivity data are acquired for each predetermined phase as described above. Here, one respiratory cycle is divided into five phases, and navigator echoes and sensitivity data are acquired 6 (5 + 1) times.

  The displacement detection unit 720 detects each displacement from the acquired navigator echo, and the sensitivity map generation unit 740 detects the first sensitivity map 601 and the second sensitivity map 602 from the acquired sensitivity data, respectively. A third sensitivity map 603, a fourth sensitivity map 605, a fifth sensitivity map 606, and a sixth sensitivity map 606 are generated. And the sensitivity map holding | maintenance part 760 matches and holds a displacement and a sensitivity map for every phase.

  Thereafter, for each breath 640, breath holding is performed, navigator echo acquisition and main photographing are performed.

  During the first breath hold 610 after the breathing 640, the measurement control unit 711 first acquires the navigator echo 612. Here, the displacement detector 720 detects a displacement from the acquired navigator echo 612 (617). Further, the excitation position changing unit 730 changes the excitation position based on the detected displacement (618) and updates the imaging parameter. Next, the measurement control unit 711 performs main imaging at the excitation position changed by the excitation position changing unit 730 to obtain an echo signal of the first slice.

  Next, after the breathing 640, the navigator echo 622 is acquired between the second breath-holding 620 as well, and the main imaging 621 is performed at the excitation position (628) changed based on the detected displacement (627). Run to get the echo signal of the second slice.

  The image processing unit 751 reconstructs an image (first image) of the first slice from the echo obtained by the main photographing 611. Then, the image processing unit 751 selects a sensitivity map held in association with the displacement closest to the displacement 617 detected from the navigator echo 612 from the sensitivity map data, and corrects the first image using the sensitivity map. Then, a display image is generated. Similarly, the second slice image (second image) is reconstructed from the echoes obtained by the main photographing 621. Then, a sensitivity map held in correspondence with the displacement closest to the displacement 627 detected from the navigator echo 622 is selected from the sensitivity map data, and the second image is corrected using the sensitivity map to generate a display image. To do.

  As described above, according to this embodiment, multiphase sensitivity data corresponding to respiratory displacement is acquired in advance, and a sensitivity map for each respiratory level is generated. Then, image processing such as shading correction and PARALLEL expansion is performed on the reconstructed image using the sensitivity map acquired at the respiration level closest to the respiration level at the time of performing the main photographing.

  Therefore, according to the present embodiment, the sensitivity map acquired at substantially the same respiration level as that at the time of main imaging is used for correction. And mismatch with the shape can be suppressed. In addition, the sensitivity map used for each correction is acquired at substantially the same multi-coil position as in the main photographing. That is, it is possible to suppress inconsistency of the multi-coil position itself between the sensitivity map photographing and the main photographing. Therefore, a highly accurate sensitivity map can be obtained for the reconstructed image.

  Therefore, according to this embodiment, it is possible to perform shading correction and PARALEL development on a reconstructed image acquired during one breath hold using an optimum sensitivity map. Therefore, it is possible to prevent the image quality from being deteriorated due to the mismatch of the sensitivity map, and a high-quality image can be obtained.

  Further, as in the first embodiment, the inconsistency of the imaging slice position due to the position fluctuation of the imaging target part for each breath hold is avoided by detecting the displacement by the navigator echo and adjusting the excitation position. Therefore, the image quality does not deteriorate even in multi-slice imaging.

  As described above, according to the present embodiment, as in the first embodiment, a high-quality image can be obtained regardless of whether the object to be imaged is a part having a large influence of body movement or multi-slice imaging.

  In the present embodiment, as in the first embodiment, the main photographing 611 and 621 may be configured to perform photographing of a plurality of slices.

  In each of the above embodiments, the sensitivity map may be created from the sensitivity data at any timing as long as the sensitivity data is acquired and before image processing.

  Further, in each of the above-described embodiments, the heart part that fluctuates and deforms due to respiratory motion is described as an example of the imaging target part, but the imaging target part is not limited to this. Any part where the position and shape of the subject change periodically due to body movements such as respiratory movement and pulsation, and can be suppressed to a movement that does not cause positional mismatch for a predetermined period of time. Good. Furthermore, in the present embodiment, the imaging target site may be a site where the position and shape of the subject change aperiodically. Of course, the region to be imaged may be a region that does not change due to body movement.

  In each of the above embodiments, the position (coordinate value) in the coordinate system of the MRI apparatus 100 is calculated from the navigator echo and used as the displacement (variation amount), but the displacement (variation amount) calculation method is not limited to this. I can't. For example, the navigator echo acquired first is a reference echo, and each subsequent navigator echo is a comparative echo. And you may comprise so that a cross correlation may be calculated between a reference | standard echo and a comparison echo, and a displacement may be calculated.

100: MRI apparatus, 101: subject, 102: magnet, 103: gradient coil, 104: RF coil, 105: RF probe, 106: gradient magnetic field power source, 107: RF transmitter, 108: signal detector, 109: Calculation unit, 110: measurement control unit, 111: display unit, 112: operation unit, 113: storage unit, 114: bed, 120: imaging target region, 200: imaging of sensitivity map, 201: sensitivity map, 210: first time Breath hold, 211: 1st real shot, 216: 1st slice, 220: 2nd breath hold, 221: 2nd real shot, 226: 2nd slice, 230: 3rd breath hold, 231: 3 Second main imaging, 236: third slice, 240: breathing, 250: sensitivity map acquisition area, 260: total imaging area, 270: imaging target region, 300: sensitivity map imaging, 31 : Breath holding, 311: Main shooting, 312: Navigator echo, 316: First slice, 317: Change amount detection, 318: Excitation position change, 320: Breath holding, 321: Main shooting, 322: Navigator echo, 326: First Two slices, 327: Change amount detection, 328: Excitation position change, 330: Breath hold, 331: Main imaging, 332: Navigator echo, 336: Third slice, 337: Change amount detection, 338: Excitation position change, 340: Breathing, 350: Sensitivity map acquisition area, 360: All imaging area, 410: Breath holding, 411: Main imaging, 412: Navigator echo, 413: Sensitivity map imaging, 416: First slice, 417: Variation detection, 418 : Excitation position change, 420: breath hold, 421: main shooting, 422: navigator echo, 423: sensitivity map shooting, 426: second scan Chair, 427: Change amount detection, 428: Excitation position change, 430: Breath hold, 431: Main shooting, 432: Navigator echo, 433: Sensitivity map shooting, 436: Third slice, 437: Change amount detection, 438: Excitation Position change, 440: Breathing, 460: Total imaging area, 510: Breath holding, 511: Main shooting, 512: Navigator echo, 513: Sensitivity map shooting, 514: Sensitivity map, 516: First slab, 517: Fluctuation amount Detection, 518: Excitation position change, 520: Breath hold, 521: Main shooting, 522: Navigator echo, 523: Sensitivity map shooting, 524: Sensitivity map, 526: Second slab, 527: Fluctuation detection, 528: Excitation position Change 540: Breathing 560: Total imaging area 600: Multi-phase sensitivity map shooting, 601: First sensitivity map, 602: Second sensitivity Degree map, 603: third sensitivity map, 604: fourth sensitivity map, 605: fifth sensitivity map, 606: sixth sensitivity map, 610: breath holding, 611: main shooting, 612: navigator echo, 617: fluctuation amount Calculation, 618: excitation position calculation, 620: breath holding, 621: main imaging, 622: navigator echo, 627: fluctuation amount calculation, 628: excitation position change, 640: breathing, 690: respiratory displacement, 710: measurement control unit 711: Measurement control unit, 720: Displacement detection unit, 730: Excitation position change unit, 740: Sensitivity map generation unit, 750: Image processing unit, 751: Image processing unit, 760: Sensitivity map holding unit

Claims (9)

A pulse applying means for applying a high frequency pulse and a gradient magnetic field pulse to the subject, a signal detecting means for detecting a nuclear magnetic resonance signal generated from the subject, and controlling the operations of the pulse applying means and the signal detecting means, A magnetic resonance imaging apparatus comprising: a measurement control unit that performs imaging; and an image processing unit that reconstructs an image from a nuclear magnetic resonance signal detected by the signal detection unit and generates a display image to be displayed on the display device. And
Displacement detection means for detecting the displacement of the subject for each predetermined period;
Photographing position changing means for changing the position of a preset photographing region in accordance with the displacement detected by the displacement detecting means,
The signal detection means includes a plurality of receiving coils having detection sensitivity distributions spatially different from each other,
The measurement control means includes
While the subject is in the displacement detected by the displacement detection means, perform the main imaging of the changed imaging area,
The image processing means includes
An image reconstructed from the nuclear magnetic resonance signal detected in the main imaging is a nuclear magnetic resonance signal acquired while the subject is in a displacement that substantially matches the displacement of the subject at the time of the main imaging execution. A magnetic resonance imaging apparatus that performs predetermined image processing using sensitivity distributions of the plurality of receiving coils generated from certain sensitivity data. The magnetic resonance imaging apparatus according to claim 1,
The magnetic resonance imaging apparatus according to claim 1, wherein the sensitivity data is acquired from an area including the changed imaging area immediately before execution of the main imaging. The magnetic resonance imaging apparatus according to claim 1,
The sensitivity distribution is created in advance from sensitivity data acquired for each displacement of the subject that can be detected by the displacement detection means, and is held for each displacement of the subject when the sensitivity data is acquired. Resonance imaging device. The magnetic resonance imaging apparatus according to any one of claims 1 to 3,
The magnetic resonance imaging apparatus, wherein the imaging region is a two-dimensional region. The magnetic resonance imaging apparatus according to any one of claims 1 to 3,
The magnetic resonance imaging apparatus, wherein the imaging region is a three-dimensional region. The magnetic resonance imaging apparatus according to any one of claims 1 to 5,
The displacement detection means detects the displacement for each breath hold of the subject. The magnetic resonance imaging apparatus according to any one of claims 1 to 6,
The displacement detection means detects a displacement of the subject by acquiring a navigator echo. The magnetic resonance imaging apparatus according to any one of claims 1 to 7,
The magnetic resonance imaging apparatus, wherein the imaging position changing unit changes an irradiation frequency of a high-frequency pulse applied by the pulse applying unit and changes a position of the imaging region. A signal applying means for applying a high-frequency pulse and a gradient magnetic field pulse to a subject, and a signal detecting means comprising a plurality of receiving coils having spatially different detection sensitivity distributions for detecting nuclear magnetic resonance signals generated from the subject. A measurement control means for controlling the operations of the pulse applying means and the signal detecting means to execute imaging, and a display for reconstructing an image from a nuclear magnetic resonance signal detected by the signal detecting means and displaying it on a display device An image processing means for generating an image, and a magnetic resonance imaging method in a magnetic resonance imaging apparatus comprising:
A displacement detecting step for detecting the displacement of the subject for each predetermined period;
An imaging position changing step for changing the position of the imaging area in accordance with the detected displacement each time the displacement is detected;
An imaging step of performing main imaging of the imaging area after the change while the subject is at the detected displacement;
An image reconstruction step of reconstructing an image from the nuclear magnetic resonance signal detected in the main imaging;
Sensitivity distribution of the plurality of receiving coils generated from nuclear magnetic resonance signals acquired while the subject is in a displacement that substantially matches the displacement of the subject at the time of performing the main imaging in the reconstructed image And an image processing step for performing predetermined image processing using a magnetic resonance imaging method.

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