JP2011229654A - Magnetic resonance imaging apparatus, blood flow dynamic analysis method, and program - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a perfusion image usable for diagnosis even if a change in a signal strength due to a contrast medium is small.SOLUTION: An average signal strength change profile Smean is obtained on the basis of signal strength change profiles S1(x, y) to Sn(x, y). Then, a base line BL and a peak value (minimum value) Smin are obtained, and a standard deviation SDbase is further obtained. Then, a statistical amount Z is calculated by using the peak value Smin of signal strength, a signal strength SDbase indicated by the base line BL and the standard deviation SDbase. The statistical amount Z is compared to a threshold value Z0, and when the value of the statistical amount is smaller than the threshold value Z0, the signal strength change profiles S1(x, y) to Sn(x, y) are smoothed.

Description

  The present invention relates to a magnetic resonance imaging apparatus, a blood flow dynamic analysis method, and a program for imaging a subject using a contrast agent.

  Conventionally, a magnetic resonance imaging apparatus is known in which a contrast medium is injected into a subject to obtain a perfusion image of the brain (see Patent Document 1).

JP 2010-022667 A

  In imaging using a contrast agent, even if the SNR (Signal to Noise Ratio) of the magnetic resonance signal is sufficiently high, if the change in signal intensity due to the contrast agent is small, a perfusion image suitable for diagnosis may not be obtained. is there. Therefore, it is desired to obtain a perfusion image that can be used for diagnosis even if the change in signal intensity due to the contrast agent is small.

A magnetic resonance imaging apparatus that collects magnetic resonance signals from a scan region set in a predetermined region of a subject into which a contrast agent has been injected,
First profile creating means for creating a first signal intensity change profile representing a time change in signal intensity of the magnetic resonance signal for each position in the scan region;
Correction means for correcting the first signal intensity change profile based on a fluctuation amount of the signal intensity of the magnetic resonance signal;
A magnetic resonance imaging apparatus.

A blood flow dynamic analysis method for analyzing blood flow dynamics of a predetermined region based on a magnetic resonance signal of a scan region set in a predetermined region of a subject into which a contrast agent is injected,
A first profile creating step for creating a first signal intensity change profile representing a time change of the signal intensity of the magnetic resonance signal for each position in the scan region;
A correction step of correcting the first signal intensity change profile based on a fluctuation amount of the signal intensity of the magnetic resonance signal;
This is a method for analyzing blood flow dynamics.

A program for obtaining an image of the predetermined part based on a magnetic resonance signal of a scan region set in a predetermined part of a subject into which a contrast agent has been injected,
A first profile creation process for creating a first signal intensity change profile representing a time change in signal intensity of the magnetic resonance signal for each position in the scan region;
A correction process for correcting the first signal intensity change profile based on a fluctuation amount of the signal intensity of the magnetic resonance signal;
Is a program for causing a computer to execute.

  Since the first signal intensity change profile is corrected based on the fluctuation amount of the signal intensity of the magnetic resonance signal, it is possible to obtain a perfusion image that can be used for diagnosis even if the signal intensity change due to the contrast agent is small. Become.

1 is a schematic view of a magnetic resonance imaging apparatus 1 according to an embodiment of the present invention. 2 is a diagram showing a processing flow of the MRI apparatus 100. FIG. It is an example of the set slice. It is explanatory drawing of the dynamic image of an intensity | strength image. It is a figure which shows the time change of the signal strength in slice SLg. It is a figure which shows roughly the signal intensity change profile of each position (x, y) obtained for each slice SL1-SLn. It is explanatory drawing when calculating | requiring average signal intensity change profile Smean. It is a figure which shows baseline BL of average signal strength change profile Smean, and minimum value Smin of signal strength. Signal intensity variation profile Sg _(x i, _{y j)} is an explanatory view of a procedure for smoothing a.

  Hereinafter, embodiments for carrying out the invention will be described in detail with reference to the drawings, but the present invention is not limited to the following embodiments.

FIG. 1 is a schematic diagram of a magnetic resonance imaging apparatus 1 according to an embodiment of the present invention.
Magnetic Resonance Imaging (MRI)
The Resonance Imaging apparatus 100) includes a magnetic field generator 2, a table 3, a cradle 4, a contrast medium injector 5, a receiving coil 6, and the like.

  The magnetic field generator 2 includes a bore 21 in which the subject 14 is accommodated, a superconducting coil 22, a gradient coil 23, and a transmission coil 24. The superconducting coil 22 applies a static magnetic field B0, the gradient coil 23 applies a gradient magnetic field, and the transmission coil 24 transmits an RF pulse. In place of the superconducting coil 22, a permanent magnet may be used.

  The cradle 4 is configured to be movable from the table 3 to the bore 21. The subject 14 is transported to the bore 21 by the cradle 4.

The contrast agent injection device 5 injects a contrast agent into the subject 14.
The receiving coil 6 is attached to the head 14 a of the subject 14. The receiving coil 5 receives a magnetic resonance signal from the head 14a.

  The MRI apparatus 100 further includes a sequencer 7, a transmitter 8, a gradient magnetic field power supply 9, a receiver 10, a central processing device 11, an input device 12, and a display device 13.

  Under the control of the central processing unit 11, the sequencer 7 sends information for executing the pulse sequence to the transmitter 8 and the gradient magnetic field power supply 9. Specifically, under the control of the central processing unit 11, the sequencer 7 sends RF pulse information (center frequency, bandwidth, etc.) to the transmitter 8, and gradient magnetic field information (gradient magnetic field strength, etc.). The gradient magnetic field power supply 9 is sent.

  The transmitter 8 outputs a drive signal for driving the RF coil 24 based on the information sent from the sequencer 7.

  The gradient magnetic field power supply 9 outputs a drive signal for driving the gradient coil 23 based on the information sent from the sequencer 7.

  The receiver 10 processes the magnetic resonance signal received by the receiving coil 6 and transmits it to the central processing unit 11.

  The central processing unit 11 implements various operations of the MRI apparatus 100 such as transmitting necessary information to the sequencer 7 and the display device 13 and reconstructing an image based on a signal received from the receiver 10. The operation of each unit of the MRI apparatus 100 is controlled. The central processing unit 11 is configured by, for example, a computer. The central processing unit 11 includes intensity image creation means 111 to perfusion image creation means 121.

  The intensity image creating unit 111 creates an intensity image representing the signal intensity of the magnetic resonance signal collected from the subject 14.

The first profile creating unit 112 has signal intensity change profiles S1 (x ₁ , y ₁ ) to Sn (x _z ) representing the time change of the signal intensity of the magnetic resonance signal for each position in the scan region of the subject 14. , Y _z ) (see FIG. 6 described later).

The second profile creation means 113 is based on the signal intensity change profiles S1 (x ₁ , y ₁ ) to Sn (x _z , _yz ) created by the first profile creation means 112 and the average signal intensity change profile Smean. (See FIG. 7 described later).

  Based on the average signal intensity change profile Smean created by the second profile creation means 113, the baseline calculation means 114 creates a baseline BL (see FIG. 8) representing the signal intensity before the contrast agent reaches the scan region. calculate.

  The detection means 115 detects the peak value of the signal intensity from the average signal intensity change profile Smean.

The standard deviation calculation means 116 calculates a standard deviation SDbase representing the signal intensity variation.
The correcting unit 117 corrects the signal intensity change profiles S1 (x ₁ , y ₁ ) to Sn (x _z , _yz ) based on the fluctuation amount ΔS (see FIG. 8). The correction unit 117 includes an index calculation unit 118, a determination unit 119, and a smoothing unit 120.

  The index calculation means 118 calculates a statistic Z (see equation (1)) as an index for determining whether the variation ΔS is small or large.

  The determination unit 119 determines whether the fluctuation amount ΔS is small or large based on the value of the statistic Z.

The smoothing means 120 smoothes the signal intensity change profiles S1 (x ₁ , y ₁ ) to Sn (x _z , _yz ).
The perfusion image creation means 121 creates a perfusion image.

  The central processing unit 11 is an example of the intensity image creation unit 111 to the perfusion image creation unit 121, and functions as these units by executing a predetermined program.

  The input device 12 inputs various commands to the central processing unit 11 according to the operation of the operator 15. The display device 13 displays various information.

  The MRI apparatus 100 is configured as described above. Next, the operation of the MRI apparatus 100 will be described.

FIG. 2 is a diagram showing a processing flow of the MRI apparatus 100.
In step ST1, imaging of the head 14a of the subject 14 is performed using a contrast agent. The operator 15 sets a slice in the scan area (head 14a) of the subject 14 before imaging.

FIG. 3 is an example of a set slice.
In the present embodiment, slices SL1 to SLn are set. Each slice is set by the operator 15 inputting information such as the slice position, the number of slices, and the slice thickness. The number of slices SL1 to SLn is, for example, twelve.

  After setting the slices SL1 to SLn, a contrast medium is injected into the subject 14, and a scan is executed. In the present embodiment, a scan for obtaining an MRI image of PWI (Perfusion Weighted Imaging) (for example, EPI (Echo Planar Imaging) scan) is executed. The magnetic resonance signals collected by the scan are subjected to processing such as A / D (Analog / Digital) conversion by the receiver 10 and transmitted to the central processing unit 11.

  In the central processing unit 11, the intensity image creating means 111 (see FIG. 1) creates a dynamic image of an intensity image representing the signal intensity of the magnetic resonance signal based on the signal received from the receiver 10 (see FIG. 4). .

FIG. 4 is an explanatory diagram of a dynamic image of an intensity image.
4A is a diagram showing n slices SL1 to SLn set on the head 14a of the subject 14, and FIG. 4B is a time series of intensity images in the slices SL1 to SLn according to the collection order. FIG.

In the present embodiment, since m intensity images are obtained for each slice, n × m intensity images are obtained in total. In FIG. 4B, partial intensity images of the slice SLg are indicated by codes CI ₁ , CI _α−1 , CI _α , CI _{α + 1} , CI _m .

FIG. 4C is a diagram illustrating _m intensity images CI _{1 to} CI m in the slice SLg among the slices SL1 to SLn.

The intensity images CI _{1 to} CI _m are arranged in the direction of the time axis t, and the positions of the pixels of the intensity images CI _{1 to} CI _m are represented by the x axis and the y axis. The signal intensity represented by each pixel of the intensity images CI _{1 to} CI _m is represented by “D _k (x, y)” (where k = _{1 to m} ). In FIG. 4C, representatively, the signal strength (eg, D ₁ ) at the positions (x _i , y _j−1 ), (x _i , y _j ), and (x _i , y _{j + 1} ) of the slice SLg. (X _i , y _j-1 )) is shown.

Further, the first profile creating means 112 (see FIG. 1) changes the signal intensity representing the time change of the signal intensity for each position (x, y) of the slice SLg based on the intensity images CI _{1 to} CI _m. A profile is created (see FIG. 5).

FIG. 5 is a diagram showing a time change of the signal intensity in the slice SLg.
The upper side of FIG. 5, there is shown m pieces of intensity image CI ₁ ~CI _m in the slice SLg, the lower side of FIG. 5, an example is schematically the signal intensity variation profile representing the time variation of the signal strength Is shown in

In FIG. 5, representatively, the signal intensity change profile Sg (x _i , y _{j + 1} ) at the positions (x _i , y _{j + 1} ), (x _i , y _j ), and (x _i , y _j−1 ) of the slice SLg. ), Sg (x _i , y _j ), and Sg (x _i , y _j−1 ) are schematically shown. The horizontal axis of the signal intensity change profile is time t, and the vertical axis represents the signal intensity. The first profile creating means 112 also creates a signal intensity change profile at another position (x, y) of the slice SLg, and also for each slice (x, y) for other slices other than the slice SLg. Create a signal strength change profile. Therefore, a signal intensity change profile at each position (x, y) is obtained for each slice SL1 to SLn (see FIG. 6).

  FIG. 6 is a diagram schematically showing a signal intensity change profile at each position (x, y) obtained for each slice SL1 to SLn.

In FIG. 6, for convenience of explanation, only the following five signal intensity change profiles are shown.
(1) Signal intensity change profile S1 (x ₁ , y ₁ ) at position (x ₁ , y ₁ ) of slice SL1
(2) Signal strength change profile Sg (x _i , y _{j + 1} ) at position (x _i , y _{j + 1} ) of slice SLg
(3) Signal strength change profile Sg (x _i , y _j ) at position (x _i , y _j ) of slice SLg
(4) Signal intensity change profile Sg (x _i , y _j-1 ) at position (x _i , y _j-1 ) of slice SLg
(5) Signal intensity change profile Sg (x _z , y _z ) at position (x _z , y _z ) of slice SLn

  However, the first profile creation means 112 actually determines the signal intensity change profile at each position (x, y) of the slices SL1 to SLn. After obtaining the signal intensity change profile, the process proceeds to step ST2.

In step ST2, the second profile creating means 113 (see FIG. 1) is based on the plurality of signal intensity change profiles S1 (x ₁ , y ₁ ) to Sn (x _z , _yz ) created in step ST1. An average signal intensity change profile Smean representing a time change of the average value of the signal intensity is obtained (see FIG. 7).

FIG. 7 is an explanatory diagram for obtaining the average signal intensity change profile Smean.
FIG. 7 shows a plurality of signal intensity change profiles S1 (x ₁ , y ₁ ) to Sn (x _z , y _z ) created in step ST1 in order from the top, with the signal at the bottom. The average signal intensity change profile Smean obtained based on the intensity change profiles S1 (x ₁ , y ₁ ) to Sn (x _z , _yz ) is shown. However, for convenience of explanation, the signal intensity change profiles S1 (x ₁ , y ₁ ), Sg (x _i , y _j ) are used for the signal intensity change profiles S1 (x ₁ , y ₁ ) to Sn (x _z , y _z ). ), And only Sn (x _z , y _z ) are shown.

The signal intensity DX _k (k = _{1 to} m) of the average signal intensity change profile Smean is the signal intensity change profile S1 (x ₁ , y ₁ ) to Sn (x _z , y _z ) created in step ST1. It is obtained as an average value of the intensity D _k (x, y). For example, the signal intensity DX ₁ of the average signal intensity change profile Smean is the signal intensity D ₁ (x ₁ , y ₁ ) to D of the signal intensity change profiles S1 (x ₁ , y ₁ ) to Sn (x _z , _yz ). _It is calculated | required as an average value of ₁ ( _xz , _yz ). The signal intensity DX _α of the average signal intensity change profile Smean is equal to the signal intensity D _α (x ₁ , y ₁ ) to D of the signal intensity change profiles S1 (x ₁ , y ₁ ) to Sn (x _z , y _z ). _It is obtained as an average value of _α (x _z , y _z ). Therefore, the average signal intensity change profile Smean represents the time change of the signal intensity in the entire scan region including the slices SL1 to SLn. The average signal intensity change profile Smean is obtained in order to determine whether the fluctuation amount of the signal intensity of the magnetic resonance signal is small or large in step ST6 described later. After obtaining the average signal intensity change profile Smean, the process proceeds to step ST3.

  In step ST3, the baseline calculation means 114 (see FIG. 1) calculates the baseline BL of the average signal intensity change profile Smean. Further, the detection means 115 (see FIG. 1) detects the peak value (minimum value) Smin of the signal strength from the average signal strength change profile Smean (see FIG. 8).

  FIG. 8 is a diagram showing the baseline BL and the minimum signal strength value Smin of the average signal strength change profile Smean.

  The baseline BL is a line that means the signal intensity before the contrast agent reaches the scan region. When the contrast agent reaches the scan region, the signal intensity tends to decrease rapidly. Therefore, the time ts at which the signal intensity starts to decrease rapidly can be considered as the arrival time of the contrast agent. Therefore, the baseline BL can be calculated as an average value of the signal intensities DX1 to DXs at the times t1 to ts, for example. However, since the value of the signal strength DX1 at time t1 is extremely larger than the signal strength at other times, it is considered that it is not suitable as the signal strength used for calculating the baseline BL. Therefore, in this embodiment, the value of the signal strength DX1 at time t1 is excluded from the signal strength used to calculate the baseline BL, and the baseline BL is signal strength between time t2 and ts (section R). Calculated as an average value of DX2 to DXs.

  After calculating the baseline BL and detecting the peak value Smin of the signal intensity, the process proceeds to step ST4.

  In step ST4, the standard deviation calculation means 116 (see FIG. 1) calculates a standard deviation SDbase representing the signal intensity variation between times t2 and ts. After calculating the standard deviation SDbase, the process proceeds to step ST5.

ここで、Ｓmin：信号強度のピーク値
Ｓbase：ベースラインＢＬが表す信号強度
ＳＤbase：標準偏差 In step ST5, the index calculation means 118 (see FIG. 1) calculates an index for determining whether the fluctuation amount ΔS is small or large. This index is used when determining whether or not the fluctuation amount ΔS is small or large in step ST6 described later. The index calculation means 118 calculates a statistic Z represented by the following formula (1) as this index.

Where Smin: peak value of signal strength
Sbase: Signal strength represented by the baseline BL SDbase: Standard deviation

After calculating the statistic Z, the process proceeds to step ST6.
In step ST6, the determination unit 119 (see FIG. 1) determines whether the variation ΔS is small or large based on the value of the statistic Z. The following describes how this determination is made.

When the value of the statistic Z is large, the ratio of the fluctuation amount ΔS and the standard deviation SDbase is large, so that the fluctuation amount ΔS is considered to be statistically significant with respect to the change in the signal strength in the section R. In this case, since it is considered that the change in signal intensity due to the contrast agent is sufficiently large, the determination unit 119 determines that the fluctuation amount ΔS is large. On the other hand, when the value of the statistic Z is small, the ratio between the fluctuation amount ΔS and the standard deviation SDbase is small, so that the fluctuation amount ΔS is not statistically significant with respect to the change in the signal strength in the section R. . In this case, since the change in the signal intensity due to the contrast agent is considered to be small, the determination unit 119 determines that the fluctuation amount ΔS is small. In the present embodiment, a threshold value Z0 serving as a reference for determining whether or not the value of the statistic Z is large is set in advance, and the determination unit 119 compares the statistic Z with the threshold Z0. If the statistical amount Z is larger than the threshold value Z0, it is determined that the variation amount ΔS is large. On the other hand, if the statistical amount Z is smaller than the threshold value Z0, it is determined that the variation amount ΔS is small. The value of the threshold value Z0 is, for example, about 3 to 6. If it is determined that the variation ΔS is large, the process proceeds to step ST8. In step ST8, the perfusion image creation means 121 (see FIG. 1) uses the signal intensity change profiles S1 (x ₁ , y ₁ ) to Sn (x _z , y _z ) created in step ST1 to create a perfusion image ( For example, a CBF (Cerebral Blood Flow) image, a CBV (Cerebral Blood Volume) image, and an MTT (Mean Transit Time) image) are created, and the flow ends.

However, if it is determined that the fluctuation amount ΔS is small, if a perfusion image is created using the signal intensity change profiles S1 (x ₁ , y ₁ ) to Sn (x _z , y _z ) as they are, it is useful for diagnosis. There is a possibility that a suitable perfusion image cannot be obtained. Therefore, in this embodiment, when it is determined that the fluctuation amount ΔS is small, the process proceeds to step ST7.

In step ST7, the smoothing means 120 (see FIG. 1) smoothes the signal intensity change profiles S1 (x ₁ , y ₁ ) to Sn (x _z , _yz ) created in step ST1. The smoothing procedure will be described below. In the description of the smoothing procedure, the signal intensity change profile Sg (x _i , y) is representatively selected from the signal intensity change profiles S1 (x ₁ , y ₁ ) to Sn (x _z , y _z ). _j )), and the procedure for smoothing the signal intensity change profile Sg (x _i , y _j ) will be described.

FIG. 9 is an explanatory diagram of a procedure for smoothing the signal intensity change profile Sg (x _i , y _j ).

9 (a), (b), and (c) show spatially adjacent signal intensity change profiles Sg (x _i , y _{j + 1} ), Sg (x _i , y _j ), and Sg (x _i , y _j-1 ).

In the present embodiment, these three signal intensity change profiles Sg (x _i , y _{j + 1} ), Sg (x _i , y _j ), and Sg (x _i , y _j−1 ) are used to change the signal intensity. Smooth the profile Sg (x _i , y _j ). The procedure for smoothing will be described below.

The smoothing unit 120 first performs temporal smoothing on the signal intensity change profile Sg (x _i , y _{j + 1} ) shown in FIG. 9A (see FIG. 9D).

FIG. 9D shows a signal intensity change profile Tg (x _i , y _{j + 1} ) obtained by temporally smoothing the signal intensity change profile Sg (x _i , y _{j + 1} ) shown in FIG. It is a figure which shows an outline.

In the present embodiment, temporal smoothing is performed by obtaining a moving average of n points arranged in the time axis direction with respect to the signal intensity change profile Sg (x _i , y _{j + 1} ). Here, n = 3, but it may be n = 5, for example. For convenience of explanation, only “E _α (x _i , y _{j + 1} )” and “E _α (x _i , y _{j + 1} )” are shown in FIG. 9D as the signal strength after temporal smoothing. However, in practice, the signal strength after temporal smoothing is required at each time point on the time axis.

The signal strength E _α (x _i , y _{j + 1} ) is _{equal to} the signal strength D _α-1 (x _i , y _{j + 1} ), D _α (x _i , y _{j + 1} ), and D _{α + 1} (x _i , y _{j + 1} ) as an average value. Signal intensities other than the signal intensity E _α (x _i , y _{j + 1} ) are also calculated by a moving average of three points arranged in the time axis direction. For example, the signal intensity E _{α + 1} (x _i , y _{j + 1} ) is _{equal to} the signal intensity D _α (x _i , y _j ), D _{α + 1} (x _i , y _j ), and D _{α + 2} (x _i , y in FIG. 9A). y _j ) is obtained as an average value.

FIG. 9D shows a signal intensity change profile Tg (x _i , y _{j + 1} ) when the signal intensity change profile Sg (x _i , y _{j + 1} ) shown in FIG. 9A is temporally smoothed. . However, the signal intensity change profiles Sg (x _i , y _j ) and Sg (x _i , y _j−1 ) shown in FIGS. Temporal smoothing is performed with a moving average. FIGS. 9E and 9F show the signal intensity change profiles Sg (x _i , y _j ) and Sg (x _i , y _j−1 ) shown in FIGS. 9B and 9C in terms of time. The signal intensity change profiles Tg (x _i , y _j ) and Tg (x _i , y _j−1 ) obtained by smoothing are shown.

After temporal smoothing is performed, next, the signal strength change profiles Tg (x _i , y _{j + 1} ), Tg (x _i , y _j ), and Tg (x _i , y _j−1 ) after temporal smoothing are performed. ) Is subjected to spatial smoothing (see FIG. 9G).

FIG. 9G shows a signal intensity change profile Pg (x _i , y _j ) obtained by spatial smoothing.

In this embodiment, by obtaining a spatial moving average of three signal intensity change profiles Tg (x _i , y _{j + 1} ), Tg (x _i , y _j ), and Tg (x _i , y _j-1 ). Performing spatial smoothing. For convenience of explanation, only “F _α (x _i , y _j )” and “F _{α + 1} (x _i , y _j )” are shown in FIG. 9G as the signal strength after spatial smoothing. However, in reality, the signal strength after spatial smoothing is required at each time point on the time axis.

The signal strengths F _α (x _i , y _j ) are the signal strengths E _α (x _i , y _{j + 1} ), E _α (x _i , y _j ), FIGS. And E _α (x _i , y _j−1 ) as an average value. Signal intensities other than the signal intensity F _α (x _i , y _{j + 1} ) are also obtained as an average value of the signal intensities in FIGS. 9 (d), (e), and (f). For example, the signal strength F _{α + 1} (x _i , y _{j + 1} ) is equal to the signal strength E _{α + 1} (x _i , y _{j + 1} ), E _{α + 1} (x _i , y _j ) of FIGS. ), And E _{α + 1} (x _i , y _j−1 ) as an average value.

As described above, the signal strength change profile Sg (x _i , y _j ) is smoothed by performing temporal smoothing and spatial smoothing. FIG. 9 shows a procedure for smoothing the signal intensity change profile Sg (x _i , y _j ). However, the smoothing means 120 performs temporal smoothing and spatialization for each of the signal intensity change profiles S1 (x ₁ , y ₁ ) to Sn (x _z , y _z ) created in step ST1 in the same procedure. Smoothing is performed. After performing smoothing, it progresses to step ST8.

  In step ST8, the perfusion image creation means 121 (see FIG. 1) creates a perfusion image using the signal intensity change profile obtained by the smoothing in step ST7, and ends the flow.

  In the present embodiment, before creating a perfusion image, an average signal intensity change profile Smean is created to determine whether or not the signal intensity variation ΔS is large. When it is determined that the fluctuation amount ΔS is small, the signal intensity change profile is smoothed, and a perfusion image is created using the signal intensity change profile obtained by the smoothing. Therefore, it is possible to obtain a perfusion image suitable for diagnosis even when the change in signal intensity due to the contrast agent is small.

In the present embodiment, the signal strength of the average signal strength change profile Smean is obtained as an average value of the signal strengths of the signal strength change profiles S1 (x ₁ , y ₁ ) to Sn (x _z , _yz ) (FIG. 7). However, since there is no contrast agent outside the subject 14, the signal intensity change profiles outside the subject 14 (for example, S1 (x ₁ , y ₁ ), Sn (x _z , _yz )) are contrast-enhanced. It does not represent fluctuations in signal intensity due to the agent. Therefore, when the average signal intensity change profile Smean is created, the signal intensity change profile outside the subject 14 is excluded from the signal intensity change profiles S1 (x ₁ , y ₁ ) to Sn (x _z , _yz ). The average signal intensity change profile Smean may be created using only the signal intensity change profile inside the subject 14.

In the present embodiment, the signal intensity change profiles S1 (x ₁ , y ₁ ) to Sn (x _z , _yz ) are corrected by smoothing. However, the signal intensity change profiles S1 (x ₁ , y ₁ ) to Sn (x _z , y _z ) may be corrected by another method different from smoothing.

  In the present embodiment, the average signal intensity profile Smean is a downward convex profile, and the fluctuation amount ΔS is obtained as a difference between the baseline BL and the minimum value Smin (see FIG. 8). However, depending on the measurement method, the profile may be convex upward. In this case, the maximum value of the signal intensity may be detected as a peak value, and the difference between the baseline BL and the maximum value may be calculated as the fluctuation amount ΔS.

  In this embodiment, in step ST4, the standard deviation SDbase is calculated as an index representing the variation in signal intensity. However, an index X different from the standard deviation SDbase may be calculated as long as it represents the variation in signal strength. In this case, the statistic Z can be calculated by replacing the standard deviation SDbase with another index X in Equation (1).

  In the present embodiment, it is determined whether the variation ΔS is small or large using the statistic Z (see Expression (1)). However, it may be determined whether the variation ΔS is small or large using an index different from the statistic Z.

  When it is determined in step ST6 that the fluctuation amount ΔS is small, the operator 15 may be notified by a pop-up window or the like that the change in the signal intensity due to the contrast agent is small.

DESCRIPTION OF SYMBOLS 100 MRI apparatus 2 Magnetic field generator 3 Table 4 Cradle 5 Contrast agent injection apparatus 6 Reception coil 7 Sequencer 8 Transmitter 9 Gradient magnetic field power supply 10 Receiver 11 Central processing unit 12 Input device 13 Display apparatus 14 Subject 14a Head 15 Operator 21 Bore 22 Superconducting coil 23 Gradient coil 24 Transmitting coil 111 Strength image creation means 112 First profile creation means 113 Second profile creation means 114 Baseline calculation means 115 Detection means 116 Standard deviation calculation means 117 Correction means 118 Index calculation means 119 Judging means 120 Smoothing means 121 Perfusion image creating means

Claims (15)

A magnetic resonance imaging apparatus that collects magnetic resonance signals from a scan region set in a predetermined region of a subject into which a contrast agent has been injected,
First profile creating means for creating a first signal intensity change profile representing a time change in signal intensity of the magnetic resonance signal for each position in the scan region;
Correction means for correcting the first signal intensity change profile based on a fluctuation amount of the signal intensity of the magnetic resonance signal;
A magnetic resonance imaging apparatus. The correction means includes
The magnetic resonance imaging apparatus according to claim 1, wherein it is determined whether the fluctuation amount is small or large, and the first signal intensity change profile is corrected based on the determination result. The correction means includes
The magnetic resonance imaging apparatus according to claim 2, further comprising an index calculating unit that calculates an index for determining whether the variation amount is small or large. Second profile creation means for creating a second signal strength change profile based on a plurality of first signal strength change profiles created by the first profile creation means;
Baseline calculation means for calculating a baseline representing the signal intensity before the contrast agent reaches the scan region based on the second signal intensity change profile;
Detecting means for detecting a peak value of the signal intensity from the second signal intensity change profile;
The amount of variation is
The magnetic resonance imaging apparatus according to claim 3, wherein the magnetic resonance imaging apparatus is an absolute value of a difference between a signal intensity represented by the baseline and a peak value of the signal intensity detected by the detection unit. The second signal strength change profile is:
The magnetic resonance imaging apparatus according to claim 4, wherein the magnetic resonance imaging apparatus represents a time change of an average value of signal intensities of the plurality of first signal intensity change profiles. The second profile creation means includes:
Among the plurality of first signal intensity change profiles, two or more first signal intensity change profiles representing a time change in signal intensity inside the subject are identified, and the two or more first signal intensity change profiles are identified. The magnetic resonance imaging apparatus according to claim 4, wherein the second signal intensity change profile is created based on a signal intensity change profile. The second signal strength change profile is:
The magnetic resonance imaging apparatus according to claim 6, wherein the magnetic resonance imaging apparatus represents a time change of an average value of signal intensities of the two or more first signal intensity change profiles.   The magnetic resonance imaging apparatus according to claim 4, wherein the peak value is a minimum value or a maximum value of signal intensity. The correction means includes
Based on the second signal intensity change profile, there is means for calculating a variation in signal intensity before the contrast agent reaches the scan region,
The index calculating means includes
9. The magnetic resonance imaging apparatus according to claim 4, wherein the index is calculated based on the amount of variation and variation in the signal intensity. The variation in signal strength is
The magnetic resonance imaging apparatus according to claim 9, wherein the contrast agent is a standard deviation of signal intensity before the contrast agent reaches the scan region. The correction means includes
11. The magnetic resonance imaging apparatus according to claim 1, further comprising a smoothing unit configured to smooth the first signal intensity change profile when it is determined that the fluctuation amount is small. The smoothing means includes
The magnetic resonance imaging apparatus according to claim 11, wherein the first signal intensity change profile is smoothed by temporal smoothing and spatial smoothing.   The magnetic resonance imaging apparatus according to claim 1, further comprising an intensity image creating unit that creates an intensity image representing a signal intensity of the magnetic resonance signal. A blood flow dynamics analysis method for analyzing blood flow dynamics of a predetermined region based on a magnetic resonance signal of a scan region set in a predetermined region of a subject into which a contrast agent is injected,
A first profile creating step for creating a first signal intensity change profile representing a time change of the signal intensity of the magnetic resonance signal for each position in the scan region;
A correction step of correcting the first signal intensity change profile based on a fluctuation amount of the signal intensity of the magnetic resonance signal;
A method for analyzing blood flow dynamics. A program for obtaining an image of the predetermined part based on a magnetic resonance signal of a scan region set in a predetermined part of a subject into which a contrast agent has been injected,
A first profile creation process for creating a first signal intensity change profile representing a time change in signal intensity of the magnetic resonance signal for each position in the scan region;
A correction process for correcting the first signal intensity change profile based on a fluctuation amount of the signal intensity of the magnetic resonance signal;
A program to make a computer execute.

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