JP2006320527A - Magnetic resonance imaging system - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an MRI system where deterioration of an image quality, degrading of detection ability of a breathing cycle etc. can be prevented even when an area for obtaining an NMR signal for monitoring breathing movement etc. is overlapped with an imaging area. <P>SOLUTION: Imaging operation for obtaining the NMR signal in order about a plurality of slices of an imaging range 301 and monitoring operation for exciting a prescribed excitation area 204 and detecting the NMR signal are repeated alternately. When a part of the imaging range 301 is overlapped with the excitation area 204 for monitoring, a slice which is not overlapped with the excitation area 204 is selected as an imaging slice just before the monitoring operation and that just after the monitoring operation. Thus, continuous excitation of the overlapped area by the imaging operation and the monitoring operation is avoided, so that modulation of the NMR signal due to the continuous excitation is prevented. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a magnetic resonance imaging (hereinafter referred to as MRI) apparatus that performs imaging while monitoring respiratory motion.

  There is a method of performing imaging while detecting respiratory motion in order to prevent artifacts due to respiratory motion when capturing an image of a subject in an MRI apparatus. In this imaging method, a nuclear magnetic resonance (NMR) signal acquisition operation for image creation and an NMR signal acquisition operation for respiratory motion monitoring are repeated as one set. When the position of the diaphragm is detected from the acquired NMR signal for respiratory motion monitoring and the diaphragm position is within a predetermined allowable range, the NMR signal for image creation acquired in the same set is used for image reconstruction. use. In addition, when imaging a site with heartbeat body movement such as a coronary artery, an operation for acquiring an NMR signal for image creation and an operation for acquiring an NMR signal for respiratory monitoring are performed in synchronization with an electrocardiogram waveform. It is possible to acquire an image from which both the physical body movement and the respiratory body movement are removed.

In Patent Document 1, in an imaging method for acquiring an NMR signal for image creation and an NMR signal for respiratory motion monitoring in synchronization with a heartbeat cycle, the timing for changing phase encoding information is optimized based on the heartbeat cycle and the respiratory cycle. It has been disclosed that the imaging time can be shortened by making it easier.
JP-A-9-106864

  The excitation region 204 for acquiring the NMR signal for respiratory motion monitoring needs to be set so as to include the moving range of the diaphragm due to respiration as shown in FIG. Therefore, the excitation region 204 includes a part of the liver and lung adjacent to the diaphragm. When the imaging region 701 is the entire liver, the entire lung, the entire chest, or the like, a part of the imaging region 701 is excited for monitoring. Regions 204 overlap. The portion where the imaging region 701 and the monitor excitation region 204 overlap is excited twice in a short time by the respiratory motion monitor NMR signal acquisition and the image creation NMR signal acquisition operation. Excited state is different. Therefore, when the respiratory motion monitor NMR signal acquisition and the image creation NMR signal acquisition are performed in this order, the monitor excitation region 204 that receives two excitations in a short time exhibits an NMR signal intensity different from that of the surrounding region. The image quality of the reconstructed image may deteriorate. On the other hand, when the acquisition of the NMR signal for image creation and the acquisition of the NMR signal for respiratory motion monitoring are performed in this order, the NMR signal acquired in the monitoring excitation region 204 is affected by two excitations. The detection accuracy may be reduced. In the technique described in Patent Document 1, it is not considered at all that the excitation region 204 for monitoring receives two excitations.

  An object of the present invention is to provide an MRI apparatus capable of preventing deterioration in image quality and deterioration in detection ability such as a respiratory cycle even when a region where an NMR signal is acquired for a respiratory motion monitor or the like overlaps with an imaging region Is to provide.

  In order to achieve the above object, according to the present invention, the following MRI apparatus is provided. That is, a static magnetic field generation unit that generates a static magnetic field, a gradient magnetic field generation unit that generates a gradient magnetic field, a high frequency magnetic field generation unit that generates a high frequency magnetic field, and a signal detection unit that detects a nuclear magnetic resonance signal generated from a subject And a control unit that controls the gradient magnetic field generation unit, the high-frequency magnetic field generation unit, and the signal detection unit to execute a predetermined pulse sequence, and the pulse sequence includes a plurality of slices within a predetermined imaging range. A first signal acquisition operation for acquiring nuclear magnetic resonance signals in order, and a second signal acquisition operation for detecting a nuclear magnetic resonance signal by exciting a predetermined excitation region of the subject for a purpose different from the first signal acquisition operation Are repeated alternately. The control unit includes an imaging order determination unit that determines the slice imaging order of the imaging range in the first signal acquisition operation. When a part of the imaging range overlaps with the excitation region of the second signal acquisition operation, the imaging order determination unit determines the excitation region of the second signal acquisition operation as an imaging slice in the temporal vicinity during the second signal acquisition operation. Select slices that do not overlap. Thereby, since it is avoided that the overlapping region is continuously excited by the first and second signal acquisition operations, the modulation of the NMR signal due to the continuous excitation can be prevented.

  The first signal acquisition operation described above is an operation of acquiring nuclear magnetic resonance signals in order for three or more k slices in one operation, and the imaging order determination unit overlaps the excitation region of the second signal acquisition operation. By determining the slices to be imaged in the imaging order so as to be imaged at any one of the second to (k-1) th, it is possible to avoid continuous excitation.

  The second signal acquisition operation described above can use an operation of acquiring a signal from the excitation region in order to monitor body movement.

The imaging order determination unit described above can be configured to determine the imaging order by the following processes (1) to (4), for example.
(1) Find a slice region that overlaps the excitation region of the second signal acquisition operation,
(2) From the total number of slices n in the imaging range, obtain the number of slices a in which the first signal acquisition operation acquires a signal in one operation and the number of repetition operations b required for signal acquisition of all slices,
(3) By selecting a slice from the first slice of the first to n-th slices every b in order, the provisional slice imaging order for imaging in the first first signal acquisition operation is determined, The first signal acquisition operation for the first time by shifting the position of each slice in the slice imaging order by the number of slices corresponding to the distance g between the overlapping slice region obtained in the processing of (1) and the center of all slices. Determine the true slice imaging order for imaging with
(4) The slice imaging order to be imaged in the second to b-th first signal acquisition operations is determined by shifting the true slice imaging order obtained in (3) one by one in order.

  It is also possible to adopt a configuration in which a screen showing the slice imaging order determined by the imaging order determining unit is displayed on the display.

Embodiments of the present invention will be described below with reference to the drawings.
First, the configuration of the MRI apparatus according to the first embodiment will be described with reference to FIG. The MRI apparatus according to the first embodiment includes a static magnetic field generator 101 that generates a static magnetic field in an imaging space, a subject 102 such as a patient, a bed 103 for placement in the imaging space, and a high-frequency magnetic field (RF ) A pulse is applied to the subject 102 to generate a high-frequency magnetic field (RF) coil 104 for detecting a nuclear magnetic resonance (NMR) signal, and gradient magnetic fields in the X, Y, and Z directions in the imaging space, respectively. Gradient magnetic field generating coils 105, 106, and 107 are provided.

  The RF coil 104 is connected to a high frequency power supply 108 that supplies a high frequency current for generating an RF pulse and an amplifier 114 that amplifies the received NMR signal. A modulator 113 and an oscillator 112 that oscillates a high frequency signal are connected to the high frequency power source 108. A receiver 115 for A / D converting and detecting the amplified signal is connected to the amplifier 114. The NMR signal detected by the receiver 115 is transferred to the computer 118. The computer 118 stores the NMR signal received from the receiver 115 and the connected storage medium 117 when the built-in CPU reads and executes the image reconstruction program stored in the storage medium 117. Image reconstruction is performed with reference to data such as shooting conditions. The reconstructed image is displayed on a display 119 connected to the computer. Further, gradient magnetic field power sources 109, 110, and 111 for supplying current are connected to the gradient magnetic field generating coils 105, 106, and 107, respectively.

  The gradient magnetic field power supplies 109, 110, 111, the oscillator 112, the high frequency power supply 108, the amplifier 114, and the receiver 115 are connected to a sequencer 116 that controls these operations. The computer 118 reads and executes a pulse sequence creation program stored in advance in the storage medium 117 to create an imaging pulse sequence that operates each unit at a predetermined timing in order to realize a desired imaging method. It passes to 116. In addition, a spatio-temporal map creation unit 118a is arranged in the computer 118, and creates a spatio-temporal map that determines the slice order for imaging in the imaging pulse sequence. The operation of the spatiotemporal map creation unit 118a will be described in detail later.

  In accordance with the imaging pulse sequence received from the computer 118, the sequencer 116 outputs a control signal to each unit and operates at a predetermined timing, thereby realizing a pulse sequence. As specific imaging conditions serving as parameters of the pulse sequence, conditions set in advance and conditions accepted from the operator by the input unit 121 are used. The sequencer 116 is connected to an electrocardiograph 120 attached to a patient who is the subject 102, receives an output signal thereof, and can perform a pulse sequence in synchronization with a cardiac cycle.

  The operation of each unit when executing the pulse sequence will be briefly described. The computer 118 creates an imaging pulse sequence according to the imaging conditions specified by the operator via the input unit 121, and passes it to the sequencer 116. The sequencer 116 transmits a control signal to the gradient magnetic field power sources 109 to 111 and causes the gradient magnetic field coils 105 to 107 to generate a gradient magnetic field in a desired direction in the imaging space. At the same time, a command is transmitted to the oscillator 112 and the modulator 113 to generate a predetermined high-frequency magnetic field waveform, and a current signal having this waveform is generated by the high-frequency power source 108 and sent to the high-frequency magnetic field coil 104. As a result, the high frequency magnetic field coil 104 generates an RF pulse and applies it to the subject 102. The NMR signal generated from the subject 102 is received by the high-frequency magnetic field coil 104, amplified by the amplifier 114, and A / D converted and detected by the receiver 115. In addition, when synchronizing with a cardiac cycle, application of a gradient magnetic field and application of an RF pulse are performed in synchronization with a signal from the electrocardiograph 120. The detected NMR signal is processed by the computer 118, detection of the diaphragm position and image reconstruction are performed, and the result of image reconstruction and the like is displayed on the display 119.

  FIG. 2A shows a time chart of the imaging pulse sequence of the present embodiment. In order to prevent artifacts due to respiratory body movements, this imaging pulse sequence includes an NMR signal acquisition operation for respiratory cycle monitoring (hereinafter referred to as a navigation sequence) 201 and an NMR signal acquisition operation for image creation (hereinafter referred to as an imaging sequence). ) 202 as a set in this order and repeated in the cycle Tw. Note that the imaging pulse sequence of FIG. 2A does not perform electrocardiographic synchronization.

  The excitation region (hereinafter referred to as “navigation excitation region”) 204 of the navigation sequence 201 is a region including the diaphragm 206 shown in FIG. 3, and the position of the diaphragm 206 is detected by acquiring the NMR signal in this region. On the other hand, the imaging region 301 of the imaging sequence 202 is the entire chest, and a part thereof overlaps with the navigation excitation region 204. In the imaging region 301, n slices are set in the body axis direction. The imaging sequence 202 acquires an NMR signal that fills all k spaces necessary for image reconstruction for a plurality of (a) slices predetermined in one cycle Tw by a high-speed imaging method. Therefore, image reconstruction can be performed for a slice in the imaging sequence 202 of one cycle.

  However, the computer 118 detects the position of the diaphragm 206 in the excitation region 204 from the NMR signal acquired in the navigation sequence 201, and when the detected position of the diaphragm 206 is out of the predetermined gate window 207, When the NMR signal acquired in the imaging sequence 202 of the cycle Tw is discarded and not used for image reconstruction of the a slice imaged in the cycle Tw, and the position of the diaphragm 206 is located in the gate window 207 Only use the acquired NMR signal for image reconstruction. Therefore, the imaging pulse sequence of FIG. 2A is repeatedly performed until NMR signals can be acquired for all slices in a state where the diaphragm 206 is positioned within the gate window 207.

  Note that a desired imaging method can be used as the imaging method of the navigation sequence 201 and the imaging sequence 202, but it is desirable to set the cycle Tw to 1 second or less in consideration of the respiratory cycle (around 5 seconds). For this reason, as the imaging method of the imaging sequence 202, a high-speed imaging method capable of imaging a slice of a number a per second is used. For example, an ecoplanar imaging method, a high-speed gradient echo method, or the like can be used. When the ecoplanar imaging method is used, the gradient magnetic field power sources 109 to 111 that can invert the supply current to the gradient coils 105 to 107 at high speed are used. Note that, here, a description will be given of a configuration for acquiring an NMR signal that fills all k spaces necessary for image reconstruction for a slice in the imaging sequence 202 of one cycle, but the present invention is not limited to this. It is also possible to acquire an NMR signal for a part of k space for each of a slices in one cycle, and take an image so as to fill the k space in several cycles.

  In such an imaging pulse sequence, since the imaging region 301 partially overlaps with the navigation excitation region 204, slices overlapping with the navigation excitation region 204 among the first to nth slices of the imaging region 301 are continuous. If excited twice, the image quality may deteriorate or the accuracy of the navigating NMR signal may decrease. Therefore, in the present embodiment, the spatio-temporal map creation unit (imaging order determination unit) 118a provided in the computer 118 creates in advance a spatio-temporal map in which the order of slices to be imaged is determined as shown in FIG. By executing the imaging pulse sequence according to this space-time map, the influence of the two excitations is eliminated.

  The space-time map in FIG. 4A will be specifically described. This space-time map shows the excitation position (excitation region 204) of the navigation sequence 201 and the excitation timing thereof, and the imaging slice plane of the imaging sequence 202 and the excitation timing thereof by solid lines. In FIG. 4A, the vertical axis 310 shown at the left end is a spatial coordinate axis indicating the body axis direction of the subject 102, and the slice plane to be excited and the navigation are the same as the vertical axis 310 shown in FIG. The position of the excitation region 204 is shown. On the other hand, the horizontal axis of FIG. 4A is a time axis. In FIG. 4A, the total number of slices n = 15 in the imaging region 301 and four slices that overlap with the excitation region 204 of the navigation sequence are four slices from the seventh slice to the tenth slice, and one imaging sequence 201. In the example shown in FIG.

  In the present embodiment, as shown in FIG. 4A, imaging (excitation) of the slice plane (seventh to tenth slices) that overlaps with the navigation excitation area 204 immediately before and after the navigation sequence 201 is avoided. A space-time map has been created. That is, immediately before and immediately after the navigation sequence 201, a slice plane (first to sixth or 11th to 15th slices) that does not overlap the navigation excitation area 204 is always imaged, and the slice that overlaps the navigation excitation area 204 The plane is imaged at a timing away from the navigation sequence 201 by an imaging time of one slice or more. This prevents the same area from being excited twice consecutively by the navigation sequence 201 and the imaging sequence 202, thereby preventing image quality degradation of the image acquired by the imaging sequence 202 and degradation of the navigation signal accuracy. Can do.

  As a comparative example, FIG. 4B shows a spatio-temporal map when the first to tenth slices are sequentially imaged as a general technique. In the spatio-temporal map of FIG. 4B, the tenth slice overlapping with the excitation region 204 is imaged immediately before the navigation sequence 201, so the accuracy of the navigation signal acquired in the immediately following navigation sequence 201 is captured. There is a possibility of decline.

  As described above, in the imaging method of the MRI apparatus of the present embodiment, when receiving an imaging instruction, the spatiotemporal map creation unit 118a creates a spatiotemporal map in advance so as not to excite the same region twice consecutively. To do. The imaging procedure by the computer 118 is as shown in the flowchart of FIG. First, when the computer 118 of the MRI apparatus receives an instruction for imaging for performing respiratory motion monitoring from the user via the input unit 121, in step 501, a screen for prompting input of imaging conditions is displayed on the display 119. The position of the excitation region 204 and the input of the imaging region 301 and the number of slices Sn of the navigation sequence 201 are received via the input unit 121. For example, the number of slices Sn is input as numerical data, and the setting of the imaging region 301 is accepted by performing alignment on the subject image using the subject image for positioning. Similarly, the navigation excitation area 204 is received by receiving a position designation on the object image for positioning. At the same time, the setting of imaging conditions such as the type of imaging method to be applied (gradient echo method or eco-planar imaging method, etc.), the RF pulse repetition time TR, and the number of acquired echoes is also accepted.

  In the next step 502, the computer 118 displays a screen prompting the user to make a selection on the display 119, and a spatio-temporal map in which the slice imaging order is optimized so as to avoid two consecutive excitations (FIG. 4 (a)). 4 or according to the general slice order shown in FIG. 4B, or accepts the user's selection. If the user selects imaging on the spatio-temporal map with the slice imaging order adjusted as shown in FIG. In step 503, the spatiotemporal map creation unit 118a in the computer 118 creates a spatiotemporal map. Although the spatiotemporal map creation unit 118a can be provided separately from the computer 118, in this embodiment, the CPU in the computer 118 reads the spatiotemporal map creation program stored in the memory in the computer 118. Is executed as the spatiotemporal map calculation unit 118a, and a spatiotemporal map as shown in FIG. 4A is created.

  The spatiotemporal map creation operation in step 503 will be described more specifically with reference to the flowchart of FIG. First, the vertical axis (spatial coordinate axis 310) of the spatiotemporal map of FIG. 4A is determined (step 601). The spatial coordinate axis 310, which is the vertical axis, consists of two components. The first is the number of slices Sn in the imaging sequence 202 and its range, and the second is the position of the excitation region 204 in the navigation sequence 201. These are obtained using the information received in step 502 of FIG. That is, the number Sm of slices overlapping the navigation excitation area 204 and its position are determined from the number of slices Sn and the position thereof and the position of the excitation area 204 of the navigation sequence 202. As described above, the spatial coordinate axis of the spatiotemporal map is determined (step 601).

Next, a time axis that is a horizontal axis is determined (step 602). For this purpose, first, it is necessary to derive the execution cycle Tw of the navigation sequence 201, the number of slices a captured by the imaging sequence 202 within one cycle Tw, and the number of repetitions b until the acquisition of the total number of slices Sn is completed. There is. In general, since the respiratory cycle is around 5 seconds, it is desirable to execute the navigation sequence 201 at a frequency of 500 ms to 1 second in order to improve the imaging efficiency and to accurately detect the respiratory cycle. The period Tw can be expressed by Tn + Ts × a. Here, Tn is the time required to execute the navigation sequence 201, and Ts is the imaging time Ts per slice in the imaging sequence 202. The time Tn and the time Ts are obtained by substituting the imaging conditions input in step 501 such as the type of imaging method to be applied, the RF pulse repetition time TR, the number of acquired echoes, and the like into predetermined mathematical expressions. Using the obtained time Tn and time Ts, a combination of integers a and b satisfying the following expression is obtained. Thereby, it is possible to calculate the number of slices a and the number of repetitions b until the acquisition of the total number of slices Sn is completed.
0.5 <Tn + Ts × a <1.0 and Sn / a = b
However, the unit of Tn and Ts is second. Note that depending on the set value of the total number of slices Sn, the value of Sn / a = b may not be an integer. In this case, the number of repetitions b is rounded up to the integer.

  As described above, the horizontal axis (time axis) of the spatiotemporal map in FIG. A spatio-temporal map is created using the determined spatial coordinate axis and time axis. As described above, the purpose of creating the spatio-temporal map is not to capture the slice plane overlapping the navigation excitation area 204 in the imaging sequence 202 immediately before and immediately after the navigation sequence 201. Is to optimize the acquisition order. Hereinafter, a data processing method for realizing the optimization will be described by comparing the flowchart of FIG. 6 with the excitation target slice position on the space-time map of FIG.

  First, as shown in FIG. 7A, an Sm slice thickness region is set around the center position of the first slice S1 and the nth slice Sn, and this is set as a temporary navigation excitation region 704. As the value of Sm, the number Sm of slices overlapping the navigation excitation area 204 obtained in step 601 is used. Next, the first slice to be photographed in the photographing sequence 202 is set as the first slice S1, and thereafter, a slice is selected in turn for every repetition number b obtained in step 602, and this is the navigation sequence. In 201, the image is temporarily set as a slice to be sequentially imaged. Thereby, a temporary space-time map is created for one cycle Tw (step 603). Thus, for example, if Sn = 15, Sm = 4, a = 5, and b = 3, the first, fourth, seventh, tenth, and thirteenth slices are temporary slices as shown in FIG. Selected.

  Next, a distance g between the temporary navigation excitation area 704 determined in step 603 and the true navigation excitation area 204 determined in step 601 is calculated (step 604, FIG. 7A).

  While maintaining the positional relationship between the temporary excitation region 704 and the temporary slice in the temporary space-time map set in step 603, the entire temporary excitation region 704 and the temporary slice are spatially maintained as shown in FIG. The temporary navigation excitation area 704 is made to coincide with the true navigation excitation area 204 by moving the distance g in the coordinate axis direction (step 605). For example, when the distance g is one slice thickness, the matched slice positions are the second, fifth, eighth, eleventh, and fourteenth slices as shown in FIG. 7B. As a result, a spatiotemporal map having the first repetition count is created. When the distance g is large and the first slice or the last slice after the movement exceeds the range of the slices S1 to Sn, for example, g is a slice thickness of 3, and the slice positions after matching are the fourth, seventh, In the case of the tenth, thirteenth, and sixteenth slices, for a slice exceeding Sn = 15, subtracting Sn from the slice position (16-Sn) is calculated, and the slice position after the subtraction (first slice) Select.

  Next, using the spatio-temporal map for the first iteration, the second and subsequent C-th time maps are added to each slice position to create a spatio-temporal map for the C-th iteration (step 1). 606). For example, when the first slice is the second, fifth, eighth, eleventh, and fourteenth slices as shown in FIG. 7B, the second and third slices are shown in FIG. As shown in (b), the third, sixth, ninth, twelfth and fifteenth slices and the fourth, seventh, tenth, thirteenth and sixteenth slices are obtained. For slice positions exceeding the total number of slices Sn, as in step 605, Sn is subtracted to be the position after subtraction. As described above, a spatio-temporal map up to the number of repetitions b is created.

  In step 505 of FIG. 5, the computer 118 passes the slice position and timing of the spatiotemporal map created in step 606 to the sequencer 116 and causes the imaging pulse sequence to be executed. The computer 118 detects the position of the diaphragm of the navigation imaging region 204 from the acquired NMR signal of the navigation sequence 201, and when the position of the diaphragm is within the predetermined gate window 207 as shown in FIG. Uses the NMR signal acquired by the imaging sequence 202 acquired at the period Tw for image reconstruction, and discards the NMR signal when it is out of the gate window 207. The imaging pulse sequence is repeatedly executed according to the spatiotemporal map until NMR signals for image reconstruction of all slices can be acquired. At this time, the computer 118 shows an image indicating the imaging slice position and the slice imaging order in the subject as shown in FIG. 8, and notifies the user that the imaging is performed in the optimized slice order.

  Thus, by not photographing the slice plane including the navigation excitation area 204 immediately before and after the navigation sequence 201, either the reconstructed image or the navigation signal is affected by two consecutive excitations. Can be prevented. Therefore, it is possible to obtain a reconstructed image in which artifacts due to twice excitation are prevented, and to perform respiratory motion monitoring with high accuracy.

  On the other hand, in step 502 of the flow of FIG. 5, when the user does not desire an imaging method that optimizes the imaging slice order in step 502, the process proceeds to step 504 and follows the slice order as shown in FIG. A spatio-temporal map in a general slice imaging order in which imaging is performed is created, and in step 505, imaging is performed along that map.

  If the size of the distance g is not an integral part of one slice in step 604, the fractional processing of less than one slice in step 605 may be moved up by one slice, for example, or it may correspond to a fraction. The imaging region 301 may be moved by the thickness of For example, when the temporary slice position is the first, fourth, seventh, tenth, and thirteenth slices as shown in FIG. 7A, and the distance g is 0.5 slices, The slice position is changed from the 1.5th slice to the 13.5th slice, and this is moved up and determined as the second, fifth, eighth, eleventh and fourteenth slices as shown in FIG. 7B. Can do.

Next, the MRI apparatus of the second embodiment will be described.
In the first embodiment described above, respiratory motion monitoring is performed without performing electrocardiogram synchronization. In the second embodiment, it is obtained from the electrocardiograph 120 as shown in FIG. The navigation sequence 201 and the imaging sequence 202 are performed after a delay time Td in synchronization with the R wave 203 of the signal. As described in the first embodiment, since the cycle Tw of the navigation sequence 201 is set to 1 second or less, a general heartbeat cycle can be obtained by appropriately setting the delay time Td from the R wave. The navigation sequence 201 and the imaging sequence 202 can be executed in synchronization with 1 second. Thereby, not only respiratory body motion but also artifacts caused by heartbeat body motion can be removed, which is suitable for imaging of coronary arteries and the like.

  Note that when the user desires imaging at a specific cardiac time phase, such as when the imaging sequence 202 is performed only during the diastole, without performing the imaging sequence 202 during the systole, the imaging time Ts per slice. The number of imaging slices a is set so that Ts × a obtained by multiplying the number of imaging slices a falls within a specific cardiac phase section. Since other configurations are the same as those in the first embodiment, description thereof will be omitted.

  In the first and second embodiments, the navigation sequence 201 and the imaging sequence 202 are repeated as a set in this order. However, the imaging sequence 202 and the navigation sequence 201 are performed in this order. It is also possible.

  In the first and second embodiments, the spatiotemporal map creation unit 118a is spatiotemporal so as to avoid imaging of slices that overlap the navigation excitation area 204 both immediately before and immediately after the navigation sequence 201. Although an example of creating a map has been described, the present invention is not limited to this configuration. For example, when there is a time between the imaging sequence 202 and the immediately following navigation sequence 201 or the immediately preceding navigation sequence 201, as in the case where the imaging sequence 202 is not performed during the systole, For a slice that is imaged continuously with the navigation sequence 201 performed with a gap, a space-time map may be created so as to allow imaging of the slice including the navigation excitation region 204. In this case, it is because the influence of continuous excitation is reduced by elapse of time such as systole.

  In the embodiment described above, the case where the excitation region 204 is set to the position of the diaphragm has been described. However, the navigation sequence 201 that acquires NMR signals using the region including the body fat of the chest and abdomen as the excitation region 204 is described. The present invention can also be used. In the above-described embodiment, the navigation sequence 201 is a sequence for monitoring respiratory motion. However, instead of the navigation sequence 201, the navigation sequence 201 is limited to the respiratory motion monitor as long as it is a sequence that excites a predetermined region 204. The present invention can be applied. For example, a pre-saturation sequence that suppresses NMR signals from blood in a thick blood vessel or cerebrospinal fluid can be used instead of the navigation sequence. In this case, the frequency of the pre-saturation sequence is determined based on the blood relaxation time T1. The determination of the slice order and the like can be determined by the same processing as in the first embodiment. As described above, according to the present invention, the imaging sequence and other sequences can be used together, and can be applied to imaging in which NMR signals are acquired in both sequences, and the S / N reduction of NMR signals acquired in both sequences can be reduced. The effect to prevent can be acquired.

1 is a block diagram showing the overall configuration of an MRI apparatus according to a first embodiment. (A) is explanatory drawing which shows the relationship between the timing of the navigation sequence 201 and the imaging sequence 202 of 1st Embodiment, and the change of a diaphragm, (b) is R wave of the electrocardiogram of 2nd Embodiment. FIG. 5 is an explanatory diagram showing timings of a navigation sequence 201 and an imaging sequence 202 when synchronized with 203. Explanatory drawing which shows the positional relationship of the navigation excitation area | region and the imaging area 301 in 1st Embodiment. (A) is explanatory drawing which shows the spatio-temporal map of the optimized slice order produced in 1st Embodiment, (b) is explanatory drawing which showed the general imaging method imaged in slice order in the spatio-temporal map . 3 is a flowchart illustrating an imaging procedure according to the first embodiment. The flowchart which shows the creation procedure of the spatiotemporal map of step 503 of FIG. 5 of 1st Embodiment in detail. (A)-(c) is explanatory drawing which shows the preparation procedure of the spatiotemporal map of 1st Embodiment. Explanatory drawing which shows the content of the screen which shows a user that the imaging procedure is optimized in 1st Embodiment. Explanatory drawing which shows the relationship between the excitation area | region 204 and the imaging slice 205 in the case of performing the conventional respiratory motion monitor.

Explanation of symbols

DESCRIPTION OF SYMBOLS 101 ... Static magnetic field generator, 102 ... Subject, 103 ... Bed, 104 ... High frequency magnetic field coil (RF coil), 105 ... X direction gradient magnetic field coil, 106 ... Y direction Gradient magnetic field coil, 107 ... Z direction gradient magnetic field coil, 108 ... High frequency magnetic field power supply, 109 ... X direction gradient magnetic field coil, 110 ... Y direction gradient magnetic field coil, 111 ... Z direction gradient magnetic field Coil, 112 ... Oscillator, 113 ... Modulator, 114 ... Amplifier, 115 ... Receiver, 116 ... Control device, 117 ... Storage medium, 118 ... Computer, 118a -Spatio-temporal map creation part (imaging order determination part) 119 ... Display, 120 ... Electrocardiograph, 121 ... Input part.

Claims (5)

A static magnetic field generating unit for generating a static magnetic field, a gradient magnetic field generating unit for generating a gradient magnetic field, a high frequency magnetic field generating unit for generating a high frequency magnetic field, a signal detecting unit for detecting a nuclear magnetic resonance signal generated from a subject, A control unit that controls the gradient magnetic field generation unit, the high-frequency magnetic field generation unit, and the signal detection unit to execute a predetermined pulse sequence;
The pulse sequence includes a first signal acquisition operation for sequentially acquiring nuclear magnetic resonance signals for a plurality of slices within a predetermined imaging range, and a predetermined excitation region of the subject for a purpose different from the first signal acquisition operation. A second signal acquisition operation of exciting and detecting the nuclear magnetic resonance signal alternately and repeatedly,
The control unit includes an imaging order determination unit that determines a slice imaging order of the imaging range in the first signal acquisition operation, and the imaging order determination unit includes a part of the imaging range in which the second signal acquisition operation is performed. When overlapping with the excitation region, a magnetic resonance imaging apparatus selecting a slice that does not overlap with the excitation region of the second signal acquisition operation as an imaging slice in the temporal vicinity at the time of the second signal acquisition operation .   2. The magnetic resonance imaging apparatus according to claim 1, wherein the first signal acquisition operation is an operation of sequentially acquiring nuclear magnetic resonance signals for three or more k slices in one operation, and the imaging order determination unit The magnetic resonance imaging apparatus is characterized in that the imaging order is determined so that a slice overlapping with the excitation region in the second signal acquisition operation is imaged at any one of the second to (k−1) th.   3. The magnetic resonance imaging apparatus according to claim 1, wherein the second signal acquisition operation is an operation of acquiring a signal from the excitation region in order to monitor body movement. 4. The magnetic resonance imaging apparatus according to any one of claims 1 to 3, wherein the imaging order determination unit includes:
(1) A process of obtaining a slice region overlapping with the excitation region of the second signal acquisition operation;
(2) A process of obtaining the number of slices a in which the first signal acquisition operation acquires a signal in one operation and the number of repetition operations b required for acquiring signals of all slices from the total number of slices n in the imaging range. ,
(3) By selecting a slice from the first slice of the first to n-th slices every b in order, the provisional slice imaging order for imaging in the first first signal acquisition operation is determined, The first signal acquisition operation for the first time by shifting the position of each slice in the slice imaging order by the number of slices corresponding to the distance g between the overlapping slice region obtained in the processing of (1) and the center of all slices. Processing for determining the true slice imaging order for imaging with
(4) The processing of determining the slice imaging order for imaging in the second to b-th first signal acquisition operations is performed by shifting the true slice imaging order obtained in (3) one by one in order. A magnetic resonance imaging apparatus. 5. The magnetic resonance imaging apparatus according to claim 1, wherein a screen showing a slice imaging order determined by the imaging order determining unit is displayed on a display. 6.

Images