JP2001187039A - Mri device and flow-quantifying method in asl imaging - Google Patents

Abstract

PROBLEM TO BE SOLVED: To collect data in a short period of time, and easily and precisely quantify the flow (tissue blood stream) of an imaging slab by simply applying a simple process for a small operation amount to the collected data. SOLUTION: This MRI device is equipped with image data obtaining means (S4, 5, 12 and 13), and scale value operating means (S1 to 3, 6 to 11), and a flow obtaining means (S14). The image data obtaining means (S4, 5, 12 and 13) perform a scanning based on an ASL method to a photographed region, and obtain the image data of the photographed region based on the ASL method. The scale value operating means (S1 to 3, 6 to 11) operate a scale value. The flow obtaining means (S14) quantitatively obtains the flow by multiplying the image data by the scale value for each picture element. The scanning is performed one time each for a control mode and a tag mode, and the image data is satisfied by one sheet of the ALS image data.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for perfusion without administering a contrast agent to a subject.
on: ASL (Artificial Spin Labeli) capable of providing images of tissue blood flow or blood vessels
The present invention relates to an MRI (magnetic resonance imaging) apparatus capable of quantifying a flow by a simple method in imaging based on the ng) method and a flow quantification method in ASL imaging.

[0002] The ASL method referred to in the present invention refers to the entire spin labeling method in a broad sense.

[0003]

2. Description of the Related Art In magnetic resonance imaging, nuclear spins of a subject placed in a static magnetic field are magnetically excited by a high frequency signal of a Larmor frequency, and FI generated by the excitation is excited.
This is a method of obtaining an image from a D (free induction attenuation) signal or an echo signal.

As one category of the magnetic resonance imaging, a spin labeling method for evaluating tissue perfusion, that is, an ASL method is known. In the ASL method, a blood vessel image and microcirculation of a subject are administered without administering a contrast agent to the subject, that is, in a non-invasive state.
This is a technique for providing a perfusion (tissue blood flow) image or the like reflecting (perfusion), and in recent years, research on this technique has been actively conducted. In particular, clinical applications have begun, especially for the head.

The ASL method is based on "continuous A"
SL (CASL) method ”and“ dynamic ASL
(DASL) method. The CASL method is a method of applying a large continuous diabiatic RF, and the spin state in a blood vessel is labeled (magnetized) at a certain point in time.
Then, the signal change after the labeled bolus of blood reaches the imaging slab (observation surface) is imaged. On the other hand, the DASL method is a pulse-like diabatic.
This is a method of applying RF, in which magnetization in a blood vessel is constantly changed, and imaging of a tissue that is continuously receiving a magnetized blood flow is performed to evaluate the perfusion of the tissue. This DASL can be relatively easily implemented even in a clinical MRI apparatus.

The DASL method includes a STAR (Signal)
Targeting with Alternatin
g Radio frequency) method and FAIR
(Flow Sensitive Alternati
ng Inversion Recovery) method. In addition, EPIST has been added to the improved STAR method.
AR (echo planar MR imaging)
and signal targeting wit
h alternating radiofrequency
ncy) method.

In this ASL imaging, generally, two images of a control mode and a label (tag) mode are generated. Image data obtained in each of the tag mode and the control mode is subjected to a difference calculation for each pixel between the images. As a result, information on blood flowing into the imaging slab, that is, an ASL image representing perfusion is obtained.

[0008] Attempts to quantify the flow (tissue blood flow) by such ASL imaging are known. The following describes this attempt.

[0009] The flow F is generally derived from the Bloch equation (for example, "MRM 35: 540-
546 (1996), C.I. Scwarzwauer e
tal ”). The longitudinal relaxation Blo when there is a flow F
The ch equation is

(Equation 1)

Therefore, an image is obtained in each of the tag mode and the control mode, and the flow F is calculated. That is, by measuring the _{M 0} and T1 for each pixel, the blood T1
(= T1 _a : subscript a means artery) is solved assuming that it is the same as T1 of the organization.

(Equation 2) Is reported.

[0011]

However, calculating the flow F based on the above equation (c) has a problem that a very complicated and large amount of calculation is required as a practical problem. Especially, itself measuring the M ₀ and T1 for each pixel, since the measurement data is large, the amount of calculation is enormous, calculation time becomes longer.

In order to satisfy the expression (c), as a precondition, the spin of water in the arterial blood flow carried to the tissue is immediately transferred into the tissue and becomes the T1 value of the tissue. It is necessary to change. However, in practice, such a condition is not completely satisfied during the time from the labeling of the upstream arterial blood flow to the start of data collection (TI time (actually, about 1 to 2 sec)). This is because there are many water spins remaining in the capillary bed. For this reason, even if a large amount of time and a large amount of calculation are used to calculate the T1 map image, it includes a measurement error due to the precondition being not completely satisfied as described above. Even if it is assumed that the measurement is accurate, there may be a situation where a situation different from the actual flow state occurs, and the error increases on the contrary.

Further, since a large number of image data are used, misregistration due to body movement occurs, and from this point, it is pointed out that measurement accuracy is deteriorated due to mixing of errors.

As described above, there are various problems in applying the conventional method of quantifying a flow (tissue blood flow) to actual clinical practice. Had been requested. In particular, when applied to patients with general acute phase infarction and the like, it is necessary that the flow can be quantified in a short time and easily.

The present invention has been made in view of the above-mentioned situation of the prior art, and data acquisition from an imaging slab based on ASL imaging can be minimized. Can simply and accurately quantify the flow of the imaging slab (tissue blood flow)
It is an object of the present invention to provide an RI apparatus and a quantification method.

[0016]

First, terms used in the present invention will be clarified.

The “flow” is often obtained by placing an imaging slab on the brain.
It refers to "bral blood flow", but since it is an amount applicable to organs other than the head, it is used in the meaning of tissue blood flow and generalized to flow F [ml / 100cc / m
in]. "Quantification of flow" refers to obtaining flow quantification information (blood flow and the like) for each pixel, and includes a mode in which a blood flow image is presented as a flow image.

According to the present invention, in principle, a single sheet of A is obtained non-invasively based on the ASL method without using a contrast agent.
By performing simple scaling on the SL image, quantified information of the flow (tissue blood flow) can be obtained. The scale value (scaling value) used for this scaling is calculated in advance, or is calculated each time from the image value of the reference phantom.

Hereinafter, (1): model analysis of ASL imaging, (2): determinants of MRI signal intensity, and (3): a simple flow calculation method according to the present invention based on the items (1) and (2). Will be described in order of principle.

(1) Model Analysis of ASL Imaging (1.1) Model of ASL Imaging (Part 1) (1.1.1) Bloch Equation Including Flow In general, the longitudinal magnetization density of the tissue where the flow F exists M is
Bloch equation mentioned above

(Equation 3) It is. Assuming that the inversion time is TI,

## EQU4 ## 1 / T1 _app = 1 / T1 + F / λ (2) is solved in the tag mode and the control mode, respectively, to calculate the flow F.

(1.1.2) Calculation of Flow F by FAIR Method FAIR (Flow Sensitive Alter)
NATING INVERSION RECOVER
In the y) method, ignoring contributions due to the transverse relaxation time T2, flip angle FA, gain, etc., the longitudinal relaxation time T1 between blood and tissue is the same, and the longitudinal magnetization immediately before receiving an IR (inversion recovery) pulse is Assume that you are recovering. This allows
In the control mode, a state is created in which blood of spins whose longitudinal magnetization is saturated continues to flow, while in the tag mode, blood of inverted spins continues to flow.

[0022] In this state, ignoring the delay time t _d to reach the slice plane tagged spins (when not ignore this, the section below TI becomes "TI-t _d"), the control mode and each signal intensity _{S cont} and _{S ta g} image s in the tag mode, the proportional coefficient as a,

(Equation 5) Can be expressed as

Here, two types of ASL, ΔS and ASLR,
A method of calculating the flow F from the value will be described.

(1.1.2.1) Derivation of Flow F from ΔS M ₀ and T 1 are measured for each pixel, and T 1 (= T 1) of blood is measured.
Assume that a) is the same as T1 of the tissue.

[0025]

(Equation 6)

(Equation 7) Approximation using

(Equation 8) It is represented by From this equation, it can be seen that ΔS and flow F are in a proportional relationship. Therefore, when this is solved, the flow F
Is

(Equation 9) Is calculated by This analytical expression is generally reported.

(1.1.2.2) Derivation of Flow F from ASLR

(Equation 10) It is expressed as Therefore, when this is solved for flow F,

[Equation 11] Is obtained. That is, when determining the flow F from the ASLR, as can be seen from this equation, the contribution of the reception gain included in the proportionality coefficient A and the proton density of the tissue at the time of saturation is offset.

(1.2) Model of ASL Imaging (Part 2) (1.2.1) Derivation of Model from Fick's Principle In ASL imaging, a stationary tissue is offset by a difference between generated signals in the control mode and the tag mode. Only the signal of the blood flow component labeled in the upstream part remains. For this reason,

(Equation 12) think of.

As shown below, according to Fick's principle, in a unit voxel, the difference between the inflow of the longitudinal magnetization component of blood from arterial blood and the outflow due to veins and relaxation during a short time dt:

(Equation 13) And

That is,

[Equation 14] Here, assuming that "water is a diffusible tracer and is uniformly and instantaneously diffused in any tissue to form a uniform compartment" (see FIG. 1 for the compartment model), the venous blood and the vertical Since the magnetization density is in an equilibrium state,

ΔM (t) = λMv (t) (12) Substituting equation (12) into equation (11),

(Equation 16) Becomes

(1.2.2) General Solution in Pulsed ASL Method Here, the longitudinal magnetization M _a (t) in arterial blood is defined in consideration of a delay until blood flows into the imaging slab,
By using Pulsed ASL method, trace within the organization
Derivation of r-concentration change characteristics (Paper “MRM40: 383
-396 (1998) ".

A) Longitudinal magnetization in arterial blood: M _a (t) Longitudinal magnetization in arterial blood M _a (t) is as follows: τ: time width of tag, t _d : arrival time of labeled blood to an imaging slab. , As shown in FIG.

[Equation 17] Can be expressed as

B) Longitudinal magnetization in tissue: ΔM (t) As shown in FIG.

(Equation 18) It is expressed as

However,

[Equation 19] It is.

Here, when k approaches 0, Q _p (t)
Approaches 1 and can be ignored.

For example, assuming a 1.5 Tesla MRI apparatus,

(Equation 20) Becomes t _d can be neglected if the distance between the tag slab and the imaging slab is set sufficiently and small (t _d = 0).
Often.

For this reason, approximately,

(Equation 21) It is represented by

(2) Determining Factors of MRI Signal Strength In general, the MRI signal: S changes according to the Bloch equation. When this MRI signal S is expressed by a function that takes into account the contribution of parameters,

(Equation 22) Is determined by

[0038]

[Outside 1] It is.

[0039] Looking considered the paragraphs above, A ₁ term is the subject dependent terms, A ₂ term is independent of the device, a term which is determined by the imaging parameters, A ₃ term is determined by the mechanical device Term. If A ₁ wherein the same organization, the same value without depending on the subject, A ₂ term becomes equal if the same parameters.

[0040] In contrast, since the A ₃ term is the device-specific factors, it is necessary to correct. Fortunately, in the case of MR imaging, if the value of the reception gain is known, the converted signal intensity corresponding to the raw signal intensity emitted from the human body can be easily calculated. In addition, the influence due to the device-specific variation is usually small, and even if there is a certain degree of variation, by simultaneously imaging the reference phantom, it is possible to correct a signal change due to the device variation from the image signal. Can be.

(3) Principle of a Simple Flow Calculation Method According to the Present Invention (3.1) Principle (3.1.1) Relationship between ASL Signal and Flow The biggest feature of ASL imaging is that other contrast agents are administered. In contrast to this method, the arterial blood directly below the blood flow inlet to the imaging slab is directly labeled. In other words, perfusion imaging can be performed in which signal value fluctuations due to individual differences in parts that are not technical or are not measured, such as fluctuations in signal values due to the contrast agent administration method and lung function, can be minimized. It is in.

This means that, as a model, as described above, the input function to the tissue compartment of arterial blood: M
_a (t) can be approximated by a rectangular function.

Based on the ASL method, signal values S _cont and S _tag ASL image values (difference values) ΔS between the control mode and the tag mode in which the same slab is imaged by the same device using the same apparatus.
Is

## _EQU23 ## ΔS = S _cont −S _tag . In this image value ΔS, the flow: F is a dominant factor. Therefore, the flow F based on arterial blood flow
Are set to be dominant, and signal values S _cont and S _tag in the control mode and the tag mode are collected.

In the ASL imaging, strictly speaking, the flow F also depends on the T1 value of the tissue or blood flow. However, the flow F is derived in the above-described model analysis (in particular, see the model analysis based on Fick's principle), or , Thesis "MRM4
0: 383-396 (1998) ", the ASL image value ΔS and the flow F can be considered to be approximately uniform and proportional. Therefore, if the proportionality constant is A,

ΔS = A · F (23) It can be expressed by a simple equation.

(3.1.2) Factors for Determining Proportional Coefficient A In an actual MRI signal, imaging parameters: M ₀ , T 1, T 2, F described in the above general theory (see section (2))
A, T _recovery , RGN, and V contribute. this,

(Equation 25) It expresses.

By the way, referring to the Bloch equation, the ASL image has a scale value except for a large blood vessel.

(Equation 26) Is constant, it can be considered that it is almost proportional to the flow F. Therefore, parameters for obtaining the scale value K will be considered.

(A) M ₀ , TI The tissue image value (proton density image) M ₀ and the inversion time TI at the time of saturation are originally different values for each tissue, that is, for each pixel. TI If the static magnetic field of 1.5 Tesla, a value of approximately 700 msec 900 msec, in white matter with gray matter, _{M 0} takes a value near 1. According to the ASL model,
The value of “M ₀ · exp (−TI / T1)” is white matter: ex
p (-1200/700) = 0.180, gray matter: ex
p (−1200/900) = 0.2636, which is almost twice as large.

However, in practice, in order for T1 of blood to completely assimilate with T1 of tissue water, the reversal time TI after labeling is insufficient if TI = 1500 msec or so, and the capillary of the imaging slab is insufficient. Still have a blood component, which maintains the T1 of the blood. For this reason, the organization for each of the _"M 0 · exp (-TI / T
1) The difference should not be as great as the theoretical value.

When T1 is actually measured as in the conventional method, it is necessary to calculate the T1 value for each pixel from a plurality of images in which the inversion time TI is changed each time. Due to the influence of noise and the fact that T1 of the inflowing blood flow is not always assimilated to T1 of the tissue, calculation errors cannot be avoided.

(B) T2, FA It is desirable that the tissue T2 value and the flip angle FA are the same in the control mode and the tag mode. It is desirable to minimize the influence of these parameters. When using an FE-based pulse sequence, it is particularly preferable to shorten the echo time TE.

Regarding the flip angle for imaging, in the case of the high-speed FE method, it is better not to use a flip angle that is too deep in order to suppress signal value fluctuation in k-space.
On the other hand, in the high-speed SE method and the SE-based EPI method, the flip angle is 9
There is no problem if it is set to 0 °.

(C) Inversion ratio α By using an adiabatic pulse as the RF pulse and setting the RF power slightly higher, the influence of the non-uniformity of the RF magnetic field can be reduced, and the spin is completely reversed. You. That is, the inversion ratio (i
nversion rate) α can be regarded as α = 1. Even if α <1 is set, basically
There is no difference between organizations.

(D) Reception gain In the case of MR imaging, the reception gain can be changed for each measurement, so that it is necessary to obtain it for each patient. However, the reception gain may be fixed, or the reception gain may be converted to the input conversion signal strength to the RF coil every time.

On the other hand, instead of ΔS, ASLR = ΔS /
If S _cont is used, the effects of M ₀ and the reception gain are cancelled.

Further, in the present invention, the above-described flow calculation method can be performed in consideration of “the arrival time t _{d of the} labeled blood to the imaging slab”.

[0056] Although the arrival time t _d is not a serious problem in the normal brain, the case of the cases where there is a blockage or constriction of blood vessels, often can not ignore this. In such a case, the above (1)
When T1 attenuation correction is performed on the measured signal strength ΔS shown in equation 8),

[Equation 27]

That is, in the signal intensity ΔS _cor after correcting the T1 attenuation, “A · 2αM _0a ” can be regarded as a constant with respect to the difference in tissue, so that the arrival time t _d is expressed as a parameter as shown in FIG. and, a straight line that rises from _{t d.}

[0058] In this case, if a flow F be different arrival time t _d is constant, the slope is seen to be a constant. Therefore, when the inclination is obtained, the arrival time t
_The flow F can be calculated without depending on _d . The slope can be calculated by measuring at least two points that satisfy t _d ≦ TI ≦ t _d + τ.

Specifically, t_d<TI₁, TI₂<T_d
2 points (TI ₁, ΔS₁), (T
I₂, ΔS₂) To the slope G of the curve of the signal value ΔS_radTo
Ask. That is,

[Equation 28] Becomes here,

[Number 29] and put the _{K 4 = λ / (A ·} 2αM 0a),

The flow F can be calculated from F = K ₄ · G _rad .

In summary, the measured values (TI ₁ , ΔS
₁ ), (TI ₂ , ΔS ₂ )

(Equation 31) Thus, the flow F can be calculated.

[0061] Here, T1 = T1 _a of blood is about 1200
〜1500 ms. Further, selection of TI is as shown in FIG. 14, smaller than the arrival time t _d is added the time width τ of tagging the minimum value of the arrival time t _d, which may take larger and than the upper limit value to obtain a maximum value value You need to choose. As a result, TI ₁ = 700 to 900 ms, TI ₂ = 12
A range of 00 to 1500 ms is considered appropriate. However, this range varies depending on the positional relationship between the imaging slice and tagging.
It is desirable to optimize each time. Note that if time permits, a more accurate gradient G _rad may be obtained by performing linear approximation from three or more measured values.

The principle described above is applied to CBF (cereb
The following is a summary of a case where the present invention is applied to a simple flow calculation of ral (flow).

In ASL imaging, when calculating a difference between a control mode image and a tag mode image collected from an imaging slab to obtain a difference image, the signal intensity of the difference image and the flow of the imaging slab are approximately proportional to each other. is there. Therefore, in the present invention, a flow is quantitatively calculated by basically performing simple scaling from one ASL image collected at one kind of inversion time TI.

That is, assuming that the conversion scale values of the flow F with respect to ΔS or ASLR are K ₁ , K ₂ , and K ₄ , as shown in FIG.

(Equation 32) Or, as shown in FIG.

The flow F can be calculated by performing the simple scaling of F = G _rad × K ₄ .

The scale value used for this scaling can be obtained by various methods. This method includes: a) a method of calculating from ΔS (= Scont−Stag), b) a method of calculating from ASLR (= ΔS / Scont), c) a method of calculating from blood signals of large vessels, or d) TI. There is a method of calculating from the gradient G _rad of the curve of ΔS with respect to. Calculation method of the scale value K ₁ of the first a) further, ai) a method of calculating from the reference set in the stationary reference phantom or normal tissue (method for correcting the reception gain), or, aii) calculated from the flow phantom (Method of not correcting the reception gain). Furthermore, method of calculating scale values K ₄ of the fourth d) further method of calculating the reference set to di) static reference phantom or normal tissue, or divided into a method of calculating from dii) flow phantom.

In general, except for the portion of the large blood vessel, the Bl
From the Och equation, the scale value K for ΔS:

(Equation 34) If the scale value K is constant, the ASL image is almost proportional to the flow F. Fortunately, T1 is in the range of about 800 to 900 msec in gray matter and white matter,
_{0 is} also a value near 1.

For example, the flow F of the normal part of the thalamus as a gray matter is expressed as F =
It is about 80 to 100 [ml / 100 cc / min]. For this reason, the scale value K may be determined so that the value of the flow F becomes such. The unit of the flow F obtained by the Bloch equation is a reversal time TI of [mse
c], [ml / 1cc / msec]
Becomes Therefore, the value of this flow F is set to 1000 × 1
If 00 × 60 = 600000 times, [ml / 100
cc / min].

The reference (reference part) of the ASL imaging when calculating the flow is, for example, gray.
For the matter, an ROI may be set so as not to include a blood vessel (particularly, a vein), and a signal value in the ROI may be calculated. For example, the reference may be on the thalamus.
If the left and right thalamus units are normal, the average value of the left and right ROIs may be calculated.

The signal value of this reference is expressed as S (thal
amus), the proportional coefficient K is

(Equation 35) Required by

In the case where a variation occurs when a tissue in the body is taken as a reference, a phantom having a flow may be used and the reference may be set in the phantom.

Since the reception gain can vary, it is desirable to calculate it for each patient. However, if the reception gain data is measured by a plurality of normal persons and the average value is obtained, even if the reception gain is fixed, As long as the imaging parameters do not change, measurement can be performed using the reception gain.

Further, the stationary phantom is scanned at the same time, and a reference signal is calculated from the phantom part, or gray m in the image of the subject is calculated.
When an ROI is set for a relatively uniform tissue such as atter and a reference signal is calculated by averaging the image values, the ASL image value S _cont before the difference is used to correct the fluctuation of the image value due to the reception gain and other factors. be able to.

The above-described principle of the present invention has been described based on the analysis result when the ASL imaging is performed by the FAIR method, but the principle described above is based on the EPISTAR method and the ASIR method.
Of course, the present invention can be applied to any method such as the TER method, its modification method, and the method using a continuous wave.

The specific configuration of the present invention is as follows. For an MRI apparatus, an ASL (Artificial
An imaging unit that performs a scan based on a Spin Labeling method to obtain image data of the imaging region based on the ASL method, and applies a scale value to the image data obtained by the imaging unit to apply a tissue blood in the imaging region. Flow quantifying means for quantitatively determining a flow composed of a flow.

In one embodiment of the flow quantification method in ASL imaging, an AS
L (Artificial Spin Labeling)
Performing a magnetic resonance scan based on the ASL method, obtaining image data of the imaging region based on the ASL method from data obtained by the scan, and quantifying a flow of tissue blood flow in the imaging region. And a step of quantitatively obtaining the flow by applying a scale value to the image data.

In another aspect of the flow quantification method in ASL imaging, an AS
L (Artificial Spin Labeling)
Performing a magnetic resonance scan based on the ASL method, obtaining image data of the imaging region based on the ASL method from data obtained by the scan, and quantifying a flow of tissue blood flow in the imaging region. Determining a scale value for the image data, and quantitatively determining the flow by applying the scale value to the image data. In the determining the scale value, the reference flow referred to with respect to the subject is performed. Is characterized in that the scale value is determined so as to match a known flow.

Specific structures and features according to other aspects of the present invention will become apparent from the following embodiments of the present invention and the accompanying drawings.

[0078]

Embodiments of the present invention will be described below with reference to the accompanying drawings.

(First Embodiment) An MRI apparatus according to a first embodiment will be described with reference to FIGS. This MR
The I apparatus calculates the scale value by the a) + i) term of the above-described approach, that is, corrects the reception gain from the stationary reference phantom, and scales the reception gain and the ASL image of the reference taken on the normal tissue. A value is obtained, and scaling is performed using this scale value.

FIG. 4 shows a schematic configuration of the MRI apparatus.
This device configuration can be commonly used in each embodiment described later.

The MRI apparatus comprises a bed on which the subject P is placed, a static magnetic field generator for generating a static magnetic field, a gradient magnetic field generator for adding positional information to the static magnetic field, and a transceiver for transmitting and receiving high-frequency signals. And a control / calculation unit that controls the entire system and reconstructs images.

The static magnetic field generating section includes, for example, a superconducting magnet 1 and a static magnetic field power supply 2 for supplying a current to the magnet 1, and has a cylindrical opening (diagnostic space) into which the subject P is loosely inserted. the axial direction (Z axis direction) to generate a static magnetic field H _0.
Note that a shim coil 14 is provided in this magnet portion. The shim coil 14 is supplied with a current for homogenizing a static magnetic field from a shim coil power supply 15 under the control of a controller described later. The couch part can retreatably insert the top plate on which the subject P is placed into the opening of the magnet 1.

The gradient magnetic field generator has a gradient magnetic field coil unit 3 incorporated in the magnet 1. The gradient magnetic field coil unit 3 includes three sets (types) of x, y, and z coils 3x to 3z for generating gradient magnetic fields in X, Y, and Z axis directions orthogonal to each other. The gradient magnetic field further includes x,
A gradient magnetic field power supply 4 for supplying a current to the y, z coils 3x to 3z is provided. The gradient magnetic field power supply 4 supplies a pulse current for generating a gradient magnetic field to the x, y, and z coils 3x to 3z under the control of a sequencer 5 described later.

The x, y, and z coils 3x from the gradient magnetic field power supply 4
By controlling the pulse current supplied to ~ 3z,
The gradient magnetic fields in the X, Y, and Z directions, which are three axes as physical axes, are synthesized, and the slice-direction gradient magnetic field Gs as a logical axis is synthesized.
Each direction of the phase encoding direction gradient magnetic field Ge and the reading direction (frequency encoding direction) gradient magnetic field Gr can be arbitrarily set or changed. Slice direction, phase encoding direction, and gradient magnetic fields in the readout direction are superimposed on the static magnetic field H _0.

The transmitting / receiving section includes an RF coil 7 disposed near the subject P in the imaging space in the magnet 1,
And a transmitter 8T and a receiver 8R, which are connected to each other. The transmitter 8T and the receiver 8R are connected to a sequencer 5 described later.
Supplies RF current pulses of a Larmor frequency for causing a magnetic resonance (MR) phenomenon to the RF coil 7 under the control of the RF coil 7, and receives a high-frequency MR signal received by the RF coil 7 to generate various signals. Processing is performed to form a corresponding digital signal.

The control / arithmetic unit includes a sequencer (also called a sequence controller) 5, a host computer 6, an arithmetic unit 10, a storage unit 11, and a display unit 1.
2 and an input device 13. Among them, the host computer 6 accepts the information instructed by the operator according to the stored software procedure, instructs the sequencer 5 on the scan sequence information based on this information, and also includes the sequencer 5 as well as the arithmetic unit 10 and the storage unit. 11 and a function of controlling the operation of the entire apparatus including the display 12.

The sequencer 5 has a CPU and a memory, stores the pulse sequence information sent from the host computer 6, and operates the gradient magnetic field power supply 4, the transmitter 8T, and the receiver 8R in accordance with the information. Control. In addition, the sequencer 5 temporarily inputs the digital data of the MR signal from the receiver 8R, and transfers the data to the arithmetic unit 10 that performs the reconstruction processing.

Here, the pulse sequence information is all information necessary for operating the gradient magnetic field power supply 4, the transmitter 8R, and the receiver 8T in accordance with a series of pulse sequences, for example, x, y, z coils. Information about the intensity of the pulse current applied to 3x to 3z, the application time, the application timing, and the like are included.

The ASL imaging method of this embodiment can use any method such as the STAR method, the EPIATAR method, and the FAIR method. Further, the pulse sequence that can be adopted by these methods may be any pulse sequence as long as it is for high-speed imaging in which the magnitude of longitudinal magnetization is emphasized. For example, fast FE method, fast SE
Method, EPI (Echo Planar Imagin)
g) Method, FASE (High-speed Asymmetric Metric SE)
And the hybrid EPI method.

The arithmetic unit 10 reads the input raw data, arranges the raw data in the Fourier space (also called k-space or frequency space) of the image, averages the data, and inter-tags data in the tag mode and the control mode. , The threshold processing of data, the absolute value processing of complex data, and the reconstruction processing of reconstructing raw data into real space data (for example, two-dimensional or three-dimensional Fourier transform processing) are performed in an appropriate order. It has become. . When three-dimensional imaging is performed, the arithmetic unit 10
In order to generate two-dimensional image data from three-dimensional image data, MIP (maximum intensity projection) processing or the like can be performed.

The storage unit 11 can store not only raw data and reconstructed image data but also image data subjected to arithmetic processing. The display 12 displays an image. Further, the operator can input necessary information such as desired scan conditions, scan sequence, and image processing method to the host computer 6 via the input device 13.

Next, the operation of this embodiment will be described.

Now, it is assumed that ASL imaging for obtaining a flow image of a blood vessel image of a head artery is performed using the EPISTAR method as the ASL method. The pulse sequence used here is, for example, a sequence of a high-speed FE method using an IR pulse.

For this reason, at the time of scanning, for example, FIG.
As shown in (a) and (b), a tag slab by applying a tag IR (inversion) pulse to the artery inflow side and an MT (magnetization tran) to the artery outflow side are applied to the imaging slab which is the imaging region.
sfer) A control slab by applying a control IR pulse for the purpose of canceling the effect is selectively set. Then, a scan using a first pulse sequence including a pulse train including a tag IR pulse to be selectively applied to a tag slab and an imaging pulse train to be selectively applied to an imaging slab (hereinafter, referred to as a scan)
"Tag (label) scan"), and a second pulse sequence consisting of a pulse train including a control IR pulse selectively applied to the control slab and an imaging pulse train selectively applied to the imaging slab. Scans (hereinafter referred to as “control scans”) are performed in chronological order in an appropriate order. An imaging mode in which tag scanning is performed is called a tag mode, and an imaging mode in which control scanning is performed is called a control mode.

In the following description, an image based on the echo data collected by the control scan will be referred to as a “control image”, and that obtained by the tag scan will be referred to as a “tag image”, as necessary.

When the scanning in both modes is performed and the echo data is collected in this manner, the arithmetic unit 10 causes the real-space image data S _tag and S _tag in each mode to be acquired.
_cont (see FIGS. 5C and 5D).
Then, the reconstructed image data S _tag and S _tag
cont is subjected to the post-processing of flow quantification thereafter.

This flow quantification process is, as described above,
Still obtains a reception gain _{G 1} from (also possible with or tissue) reference phantom ref1, ASL image Δ of the reference ref2 taken this reception gain _{G 1} in normal tissues
Scale value K from S _measured (ref2)
_1cor , and this scale value _K1cor is used for scaling.

As for the stationary reference phantom ref1, for example, the CBF (gray) of the normal part of gray matter
Is empirically known to be about 80 to 100 [ml / 100 cc / min], so that a proportional coefficient that can be applied uniformly, that is, a scale value K
_{One cor} is determined.

Further, regarding the reference ref2,
The ROI is set to a gray matter (for example, the thalamus). At this time, blood vessels (particularly veins) are not included in the ROI. If the thalamus is normal left and right, RO
Set I and measure their average.

The procedure of the quantification process will be described in detail below.

Now,

[Outside 2] It can be expressed as. Note that the above-described image values and image measurement values are real space images obtained by reconstructing echo data.

In this MRI apparatus, as schematically shown in FIG. 6, an image and data are prepared (step 1), and a gain, a scale value, and a flow are sequentially calculated from the prepared image and data (step 1). 2). Here, the scale value is calculated based on the item ai) in the above-described approach for the scale value calculation, and scaling is performed.

The first process 1 will be described.

In advance, a static reference phantom ref
1 (see FIG. 7), the image value S _{cont / cor} (re
f1) is statistically calculated and stored in the storage unit 11 (step S1 in FIG. 6). The reference phantom ref1 is a phantom whose T1 is close to blood (1200 to 1500 msec when the static magnetic field is 1.5T). This operation is performed by the operation unit 10 or the host computer 6
However, the host computer 6 may receive the data calculated by a device other than the MRI apparatus via the input device 13 and store the data in the storage unit 11.

[0105] In order to calculate the reception gain G _1, instead of the static reference phantom ref1, it is also possible to use a head structure itself.

In addition, the gray matter of the head is determined in advance.
Gray ma when ref is the reference ref2
The known flow F (ref2) of ter is stored in the storage unit 11 (step S2).

Then, with the stationary reference phantom ref1 placed near the subject's head, ASL imaging, that is, control scan and tag scan are performed once in an appropriate order (see FIG. 7). The control scan and the tag scan are executed by operating the gradient magnetic field power supply 4, the transmitter 8T, and the receiver 8R under the control of the sequencer 5. The echo data received by the RF coil 7 and processed by the receiver 8R is reconstructed by the arithmetic unit 10 and generated as image values in each mode.

Therefore, each time the flow quantification for each subject or the flow quantification for the same subject (that is, each measurement), a control scan and a tag scan are simultaneously performed on the subject and the reference phantom ref1, Data measurement and collection of each mode are performed.

[0109] Of these, the image measurement from the echo signal generated by the control scan S _{c
ont / measured} (ref1) is generated (step S3).

Further, from the echo data obtained by scanning in the control mode and the scan mode, the control image S _{cont / measured} (x,
y) and the tag image S _{tag / measured} (x,
y) is reconstructed (steps S4 and S5).

Further, the control image S
_{cont / measured} (x, y) and tag image S
_{From tag / measured} (x, y), the reference ref2 (RO
When placed I), the image measurement control scan and tag scan each for the reference _{ref2 S c ont / measured (ref2} ) and S
_{tag / measured} (ref2) is generated (steps S6 and S7).

Here, steps S1 to S7 are not limited to the processing order described above, but may be processed in an appropriate order.

When the preparation is completed, the calculation of the gain, the scale value, and the flow is performed as post-processing by the operation unit 10.
Is executed by

[0114] in <gain _{G 1} of the operation> First, the process step of correcting the reception gain _{G 1} is executed. Here, the reception gain G1 is determined from the data stored or generated in steps S1 and S3 described above.

[Equation 36] Is calculated (step S8). That is, for each measurement, the corrected reception gain G ₁ is determined.

It should be noted that the image values S of normal gray matter and white matter
_Since the individual difference of _{cont / cor} is small, if there is a known image value S _{cont / cor} , the reception gain G ₁ is corrected and calculated from the above equation (1a) for each measurement by using the value. Is also good. This makes it possible to omit the prior measurement using the stationary reference phantom ref1. Further, in each measurement, the reception gain G ₁
If it is known, the series of measurements and calculations in steps S1 to S3 may be omitted, and the known gain value may be directly used in the processing described later.

< _Calculation of Scale Value _K1cor >
Scale value (proportional coefficient) K with corrected reception gain
_{The process} for calculating 1 _cor is started.

First, the ASL image value ΔS _measured (ref2) for the reference ref2 is obtained from the data generated in steps S6 and S7 described above.

(37) Is calculated (step S9).

[0118] Further, [Delta] S for the reference ref2 using the reception gain _{G 1} corrected in Step S8
_cor (ref2)

(38) Is calculated (step S10).

Then, the scale value K 1 _cor is

[Equation 39] Is calculated (step S11).

This scale value K 1 _cor does not depend on the apparatus or the subject as long as the imaging parameters are the same.
_{One cor} may be calculated and their average may be calculated. Thus, if the imaging parameters are the same ASL imaging, the scale value K thus obtained is
_{One cor} can be commonly used.

<Operation of Flow F (x, y)> Next, a process for calculating the flow F (x, y) is started. In this processing step, first, in step S4 described above,
Generated image S in S5
_{cont / measured} (x, y) and S
ASL using _{tag / measured} (x, y)
The image ΔS _measured (x, y) is

(Equation 40) (Step S12).

[0122] Then, ASL image ΔS determined reception gain _{G 1} and now which has been corrected in step S8
_{From measured} (x, y), ASL image ΔS
_cor (x, y)

[Equation 41] Is calculated (step S13).

Thereafter, using the scale value _K1cor already obtained in step S11,

(Equation 42) The flow F (x, y) is calculated for each pixel from the equation (step S14).

In this way, the flow F (x, y) distributed two-dimensionally is obtained, and is displayed on the display 12 as information for quantifying the flow F.

As described above, the present embodiment focuses on the fact that the ASL image value ΔS and the flow F are approximately proportional to each other, and the scale value K _1cor which is a proportional coefficient _thereof.
Is calculated, and this scale value K _1cor is _converted to the ASL image ΔS
_The flow F (x, y) can be quantitatively calculated by simple scaling that is simply multiplied by _cor (x, y).

For this reason, since only one ASL image is required in principle, data collection for flow quantification can be minimized, and the scanning time and calculation load of ASL imaging are greatly reduced. be able to.

In addition, since only one ASL image is required in principle, a measurement error due to misregistration when a large number of images are used as in the related art can be almost certainly eliminated. In addition, since the flow F can be quantified by simple scaling using the ASL image, it is possible to suppress the mixing of a measurement error due to the creation of the T1 map as in the related art. Therefore, the flow (tissue blood flow) can be easily and accurately quantified.

In this quantification, the reception gain G
₁ is corrected, and scaling is performed using this gain. Therefore, even when the reception gain G ₁ fluctuates,
The flow F can be accurately quantified.

Since the scale value _K1cor is calculated using the corrected reception gain, it is not always necessary to obtain this scale value for each measurement, and the scale value of one value is used for a fixed number of measurements. They may be commonly used.

Further, in the case of the present embodiment, the reception gain is corrected, and the ASL image ΔS
Since scaling is performed on _cor (x, y), there is a unique merit that the process of calculating the scale value K 1 _{cor and} the _process of calculating the flow F (x, y) can be performed independently.

Further, from the aspect of numerical data obtained by flow quantification, it is possible to follow the condition of the same subject for each individual.

(Second Embodiment) An MRI apparatus according to a second embodiment will be described with reference to FIGS. In the following embodiments, the same or equivalent components as those of the above-described first embodiment will be denoted by the same reference numerals, and description thereof will be omitted or simplified.

In this MRI apparatus, the scale value is calculated according to the item aii) of the above-mentioned approaches, that is, the scale value is calculated from the ASL image of the reference flow phantom, and scaling is performed.

As shown in FIG. 8, the flow phantom 20 has a small cylindrical phantom body 21, a pump 23 connected to the phantom body 21 through a hose 22 so as to form a circulation path, And a flow rate controller 24 for controlling the discharge pressure of the fluid to control the flow rate.
The phantom body 21 includes a cylinder 21A disposed near the head HD of the subject, and a porous gel 21B packed in the cylinder. The fluid is circulated by the pump 23 through the phantom body 21 at a relatively slow speed.
As this fluid, T1 value of tissue blood 血液 1200 to 15
For example, an aqueous solution of copper sulfate having the same T1 value as that of 00 msec is used. The flow controller 24 controls the discharge pressure of the pump 23 so that the flow value of the fluid matches the flow on the order of the gray matter. That is, the flow value of the flow phantom 20 is known.

The phantom body 21 is placed near the head HD of the subject, and is always scanned simultaneously with the head. In each scan, the image value of the flow phantom 20 is also measured, a scale value is calculated so that the image value matches a known flow, and scaling based on this scale value is performed.

In order to perform flow quantification by scaling characterized as described above, the MRI apparatus shown in FIG.
As schematically shown in FIG. 1, images and data are prepared (step 1), and scaling, that is, a flow operation is performed from the prepared images and data (step 2).

The processing of the first step 1 will be described.

A known flow F (ref) using the flow phantom 20 as the reference phantom ref is stored in the storage unit 11 in advance (step S2 in FIG. 9).
1).

It is to be noted that a configuration not using the flow phantom 20 is also possible. In this case, for example, a pathologically normal gray matter of the subject's head is set as a reference, and a known statistical flow of the gray matter is used. Is stored in the storage unit 11 for reference (step S21).

Then, ASL imaging, that is, control scan and tag scan are executed once in an appropriate order while the reference phantom ref including the flow phantom 20 is placed near the head of the subject. This control scan and tag scan
As described above, this is executed by operating the gradient magnetic field power supply 4, the transmitter 8T, and the receiver 8R under the control of the sequencer 5. The echo data received by the RF coil 7 and processed by the receiver 8R is reconstructed by the arithmetic unit 10 and generated as image values in each mode.

Therefore, each time the flow quantification measurement is performed, the control scan and the tag scan are simultaneously performed on the subject and the reference phantom ref, and data measurement and collection in each mode are performed.

Of these, the control image S _{cont / measured} (x, y) of the head is obtained from the echo data obtained by scanning in the control mode and the scan mode.
And the tag image S _{tag / measured} (x, y) is reconstructed (steps S22, S23).

The control image S
_{cont / measured} (x, y) and tag image S
_{From the tag / measured} (x, y), when the ROI is placed on the reference phantom ref (FIG. 1)
0), image measurement values S _{cont / measured of} each of the control scan and the tag scan in the ROI.
(Ref) and S _{tag / measured} (ref)
Are generated respectively (steps S24 and S25).

Here, steps S21 to S25 are not limited to the processing order described above, but may be processed in an appropriate order.

When the preparation is completed, the operation of the scale value and the flow is executed by the arithmetic unit 10 as post-processing.

< _Calculation of Scale Value K _1measured > First, the scale value (proportional coefficient) K
_{The process} for calculating _1measured is entered.

From the data generated in steps S24 and S25, the ASL
Image value ΔS _measured (ref) is

[Equation 43] Is calculated (step S26).

Further, the scale value K is calculated using the flow F (ref) obtained in step S21.
_1measured ,

[Equation 44] Is calculated (step S27).

<Calculation of Flow F (x, y)> Next, a process for calculating the flow F (x, y) is started. In this processing step, first, the above-described step S2
2. Generated image S _{con in} S23
_{t / measured} (x, y) and S
ASL using _{tag / measured} (x, y)
The image ΔS _measured (x, y) is

[Equation 45] (Step S28).

Next, using the scale value K _1measured calculated in step S27,

[Equation 46] The flow F (x, y) is calculated for each pixel from the equation (step S29).

The flow F (x, y) distributed two-dimensionally is obtained in this way, and is displayed on the display 12 as information for quantifying the flow F.

In this embodiment, the flow F (x,
When calculating y), be sure to use the scale value K
Calculation of _1measured be performed simultaneously, it is required to use the scale values in the flow calculation. This is because the reception gain is not corrected.

As described above, the flow can be quantified. According to the present embodiment, the same operation and effect as those of the first embodiment can be obtained.

In particular, according to the present embodiment, the scale value K _{1m measured} is calculated every time the flow quantification is measured, and scaling is performed with this scale value K _1measured . For this reason, even if the reception gain or the like varies due to mechanical factors of the apparatus, the flow F (x, y) is corrected in a state in which these fluctuation factors are not directly corrected, but the fluctuations are corrected. You can ask.

In the present embodiment, when the scale value is calculated with the reception gain corrected for each measurement of the flow quantification or with the known reception gain, the scale value can be obtained once. The same scale value can be used even if the measurement changes. However, even in such a configuration, when the scale value may fluctuate over time or from device to device, as described in the above-described first embodiment, the scale value may be changed by the number of times that the unit can fluctuate. In each case, calibration for correcting the scale value with the reception gain may be performed.

Further, the flow phantom employed in this embodiment has a relatively small structure capable of simultaneously scanning with its main body placed beside the patient, but when the flow phantom is large, a certain size is required. For each measurement, separately from the subject, calculate the scale value corrected by the reception gain,
The scale value may be used for scaling.

(Third Embodiment) An MRI apparatus according to a third embodiment will be described with reference to FIG.

In this MRI apparatus, the calculation of the scale value is performed according to item b) of the above-described approach, and an ASLR (ASL signal to ASL signal) based on ASL imaging is used.
A scale value is calculated from the control signal ratio value, and scaling is performed. According to this scaling method, a control image and an ASL image are required, but in principle, there is a feature that correction of a reception gain and a reference phantom are not required.

In order to perform the flow quantification by the scaling characterized as described above, the MRI apparatus shown in FIG.
As schematically shown in FIG. 1, images and data are prepared (step 1), and scaling, that is, a flow operation is performed from the prepared images and data (step 2).

The first process 1 will be described.

In advance, for example, a pathologically normal gray matter of the head of the subject is used as a reference, and a known statistical flow of the gray matter is stored in the storage unit 11 for reference (FIG. 11, step S31). ).

Then, the ASL imaging, that is, the control scan and the tag scan are performed once on the head of the subject in an appropriate order. Therefore,
At each flow quantification measurement, a control scan and a tag scan are performed on the subject's head, and data measurement and collection in each mode are performed.

The control image S _{cont / measured} (x, y) of the head is obtained from the echo data obtained by scanning in the control mode and the scan mode.
And the tag image S _{tag / measured} (x, y) is reconstructed (steps S32 and S33).

Further, the control image S
_{cont / measured} (x, y) and tag image S
_{From tag / measured} (x, y), when the ROI is placed in the reference ref, the image measurement values S _{cont / measured} (ref) and S of the control scan and the tag scan in the ROI, respectively.
_{tag / measured} (ref) is generated (steps S34, S35).

Here, steps S31 to S35 are not limited to the processing order described above, but may be processed in an appropriate order.

When the preparation is completed, the operation of the scale value and the flow is executed by the arithmetic unit 10 as post-processing.

< _Calculation of Scale Value K _2measured > First, the scale value (proportional coefficient) K
_{The process} for calculating _2measured is started.

Based on the data generated in steps S34 and S35, the ASL
Image value ΔS _measured (ref) is

[Equation 47] Is calculated (step S36).

Next, the difference result ΔS
_measured (ref) and the control image S generated in step S34
AS using _{cont / measured} (ref)
LR (ref),

[Equation 48] (Step S37).

Next, using this ASLR (ref) and the flow F (ref) stored in step S31, the scale value K _2measured is _{calculated as follows} :

[Equation 49] Is calculated (step S38). Flow F (re
f) is F (graymatter) = 80 to 100
[Ml / 100 cc / min].

<Operation of Flow F (x, y)> Next, a process for calculating the flow F (x, y) is started. In this processing step, first, the above-described step S3
2, the generated image S _{con in} S33
_{t / measured} (x, y) and S
ASL using _{tag / measured} (x, y)
The image ΔS _measured (x, y) is

[Equation 50] (Step S39).

The control image S _{cont / measured} generated in step S32 is added to the calculation result.
Using (x, y),

(Equation 51) Is calculated (step S40).

Next, using the calculation result and the scale value K _{2mea measured} calculated in step S38,

(Equation 52) The flow F (x, y) is calculated for each pixel from the equation (step S41).

In this way, the flow F (x, y) distributed two-dimensionally is obtained and displayed on the display 12 as information for quantifying the flow F.

As described above, the scale value is calculated using the ASLR value, and the flow can be obtained by applying the scale value to the scaling. Therefore, this embodiment also has the same operation as that of each of the above embodiments. The effect is obtained.

In particular, as in the first and second embodiments, Δ
Unlike the case where S is used, by using the ASLR value, the reception gain correction processing is unnecessary in principle. For this reason, the scale value does not have to be calculated for each flow quantification measurement, and can be commonly calculated and used every certain number of measurements. That is, since the scale value calculation and the flow calculation can be executed independently, the flexibility of the post-processing of the flow quantification is increased, and the calculation process is simplified.

In the case where the scale value calculation and the flow calculation are performed independently as described above, when the reference ref is used in the tissue as described above, about several cases of the pathologically normal subject are used for the reference data. Can be collected, and a statistical average value of the scale value can be calculated from the data. With this configuration, as long as the imaging parameters do not change, scaling can be performed using the same scale value, and the calculation processing of the scale value can be omitted.

Further, in the third embodiment described above, instead of placing a reference on the head tissue portion, a second
The flow phantom described in the embodiment may also be used. In that case, the reference for the scale value calculation may be calculated in the flow phantom portion, and the scale value calculation may be performed as in the first embodiment. When a flow phantom is used, a statistical measurement for calculating a standard value of a scale value is not required, unlike a case where a reference is placed on a human body tissue portion.

However, when there is a flow phantom that can be scanned simultaneously with the patient every time the flow quantification is measured, it is not always necessary to employ the scale value calculation method using the ASLR value (third embodiment). Simpler processing is required if the scale value calculation method used (second embodiment) is employed.

(Fourth Embodiment) An MRI apparatus according to a fourth embodiment will be described with reference to FIGS.

In this MRI apparatus, the calculation of the scale value is handled by the item c) of the above-mentioned approach, that is, a blood vessel (especially a large blood vessel) reflected in a part of a slice image at the time of scanning is treated as a reference. A scale value is calculated using the blood vessel signal, and scaling is performed. Therefore, as described above, there is a feature that it is not necessary to prepare the experience value of the reference flow in advance.

Here, the principle of using the signal value of a large blood vessel will be described.

Now, suppose that all the space in a certain voxel is occupied by flowing blood: blood, and completely replaced by blood: blood tagged by a non-excited tag scan in the control within the inversion time TI. ,
The ASL image value ΔS _blood is

(Equation 53) Can be approximated. In a typical organization,

(Equation 54) Therefore, the flow F is

[Equation 55] Becomes

Here, TI used for ASL imaging
In the time zone on the order of 1200 to 1800 msec, it is difficult to completely assimilate the water component in the tagged blood with the tissue, and it is considered that the water component is in a transitional state leading to complete assimilation. Therefore, tissue and blood _{M 0} and T1
Have the same value. Under this assumption, (4
Substituting equation a) into equation (4c), the flow F becomes

[Equation 56] Approximately expressed as Unit TI [msec], F
When using the [ml / 100cc / min], scale value _{K 3} is a proportionality factor, taking into account the units,

[Equation 57] It is expressed as

[0185] As can be seen from this (4e) equation, the calculation for obtaining the scale value K _3, M _0, reception gain A, and inversion ratio α is not involved is canceled. Also, as for λ, the value in water: λ = 0.9-1 is adopted to further simplify the equation.

Therefore, the MRI apparatus of the present embodiment is similar to that of FIG.
As schematically shown in FIG. 2, an image and data are prepared (step 1), and scaling, that is, a flow operation is performed from the prepared image and data (step 2).

The process of the first step 1 will be described.

In advance, the scale value calculation parameter is
The inversion time TI and the inversion ratio α used for imaging are stored in the storage unit 11 (step S5 in FIG. 12).
1). The condition is that voxels in the blood vessel to be imaged are filled with the tagged blood within the inversion time TI.

[0189] ASL imaging, that is, control scan and tag scan, is performed once on the head of the subject in an appropriate order. Therefore,
At each flow quantification measurement, a control scan and a tag scan are performed on the subject's head, and data measurement and collection in each mode are performed.

Among them, the control image S _{cont / measured} (x, y) of the head is obtained from the echo data obtained by scanning in the control mode and the scan mode.
And the tag image S _{tag / measured} (x, y) is reconstructed (steps S52 and S53).

The control image S
_{cont / measured} (x, y) and tag image S
_From the data of _{tag / measured} (x, y), when the ROI is placed on a blood vessel (large blood vessel) forming a part of the image (see FIG. 13), each image measurement value of the control scan and the tag scan in the ROI S
_{cont / meas ured} (blood) and S
_{tag / measured} (blood) is generated respectively (steps S54 and S55).

Here, steps S51 to S55 are not limited to the processing order described above, but may be processed in an appropriate order.

When the preparation is completed, the operation of the scale value and the flow is executed by the arithmetic unit 10 as post-processing.

[0194] First <computation scale value _{K 3>,} enters the process for calculating the scale factor (proportional coefficient) _{K 3.}

From the data generated in steps S54 and S55, the ASL for large blood vessel: blood is obtained.
Image value ΔS _measured (blood) is

[Equation 58] Is calculated (step S56).

Further, the scale value K is calculated using the scale value calculation parameters TI and λ stored in step S51.
₃ is

[Equation 59] Is calculated (step S57).

<Calculation of Flow F (x, y)> Next, a process for calculating the flow F (x, y) is started. In this processing step, first, in step S5 described above.
2. Generated image S _{con in} S53
_{t / measured} (x, y) and S
ASL using _{tag / measured} (x, y)
The image ΔS _measured (x, y) is

[Equation 60] (Step S58).

[0198] Then, using the scale value _{K 3} that was calculated in step S57, the

[Equation 61] The flow F (x, y) for each pixel is calculated from the equation (step S59).

The flow F (x, y) distributed two-dimensionally is obtained in this way, and is displayed on the display 12 as information for quantifying the flow F.

As described above, the flow can be quantified, and the present embodiment can provide the same operation and effects as those of the first embodiment.

In particular, according to the present embodiment, the signal of the large blood vessel portion forming a part of the captured image is diverted, so that the process of empirically determining the reference flow in advance becomes unnecessary. At the same time, there is no need to correct the reception gain.

[0202] When treating a blood vessel as a reference, a large artery may be used. If such a large artery does not exist in a slice image, the ROI is applied to a large vein such as a sagittal sinus whose signal value is particularly large by the FAIR method. Just set it.

If the reception gain is corrected, it is not always necessary to calculate the scale value for each flow quantification, and a statistical average value can be used as the scale value.

(Fifth Embodiment) An MRI apparatus according to a fifth embodiment will be described with reference to FIGS.

In this MRI apparatus, as in the case of calculating the scale value K1 according to the _first embodiment, the ASL image of the reference set in the normal tissue by the term di) of the above-mentioned approaches, using the scale value K ₄ is calculated, the scaling is performed.

In this MRI apparatus, as schematically shown in FIG. 15, an image and data are prepared (step 1), and a scale value K ₄ and a flow F (x, y) are obtained from the prepared image and data. The calculations are performed in order (step 2).

[0207] The process of the first step 1 will be described.

In advance, for example, gray matte of the head
gray ma when r is a reference ref
The known flow F (ref) of the storage unit 1
1 (step S61). In addition, T1 of blood
T1 = T1a is stored in advance in the storage unit 11 as _a value (step S62).

[0209] Also, from the echo data by the executed control mode and the scan mode of the scan in TI = TI _1, the head of the control image S
_{Cont / measured1} (x, y) and tag image S _{tag / measured1} (x, y) are reconstructed (steps S63, S64). Similarly, TI = TI ₂
Control image S _{cont / measured2} (x, y) of the head from the echo data obtained by scanning in the control mode and the scan mode executed in
And tag image S _{tag / measured2} (x, y)
Is reconfigured (steps S65 and S66).

Further, from the control image S _{cont / measured1} (x, y) and the tag image S _{tag / measured1} (x, y) of the above-mentioned one set, a reference ref is provided to the gray matter of the head.
When the (ROI) is placed, the image measurement values S _{cont / measured1} (ref) and S of the control scan and the tag scan for the reference ref, respectively.
_{tag / measur} ed1 (ref) are respectively generated (step S67, S68). Similarly, the other set of control images S
_{From cont / measured2} (x, y) and tag image S _{tag / measured2} (x, y), reference ref (R
OI), the image measurement values S _{cont / measured2} (ref) and S of the control scan and the tag scan for the reference ref, respectively.
_{tag / measured2} (ref) is generated respectively (steps S69 and S70).

Here, steps S61 to S70 are not limited to the processing order described above, but may be processed in an appropriate order.

When the preparation is completed, the operation of the scale value and the flow is executed by the arithmetic unit 10 as post-processing.

[0213] First <computation of the scale values _{K 4>,} enters the process for calculating the scale factor (proportional coefficient) _{K 4.} From the data generated in steps S67 and S68, the ASL image value Δ
S _measured1 (ref)

(Equation 62) Is calculated (step S71). Similarly, from the generated data in steps S69 and S70, the ASL image value ΔS _mea for the reference ref.
_surred2 (ref)

[Equation 63] Is calculated (step S72).

Next, as described above, the two ASs
L image value ΔS _measured1 (ref) and ΔS
_measured2 (ref) is T1 attenuation correction with T1 = T1 _a, the image value ΔS
_{cor / measured1} (ref) and ΔS _{cor
/ Measured2} (ref) is obtained (steps S73, S74).

Next, using these correction values, the gradient G _rad of the ASL image value ΔS is calculated.

[Equation 64] Is calculated (step S75).

[0216] Next, the scale value _{K 4} is

[Equation 65] Is calculated (step S76).

<Operation of Flow F (x, y)> Next, a process for calculating the flow F (x, y) is started. In this processing step, first, the above-described step S6
3, generated image S _{con in} S64
_{t / measured1} (x, y) and S
_{Using tag / measured1} (x, y), AS
L image ΔS _measured1 (x, y) is

[Equation 66] (Step S77). Similarly,
The generated image S in steps S65 and S66 described above
_{cont / measured2} (x, y) and _{S t
ag / measured2} (x, y) using ASL
The image ΔS _{measure d2} (x, y) is

[Equation 67] (Step S78).

[0218] Then, using the T1 = T1 _a, T1 decay corrected one image value _{ΔS cor /} measured1
(X, y) is

[Equation 68] Is calculated (step S79). Similarly, T1 = T1
_The other image value ΔS that has been T1 attenuated using a
_{cor / measured2} (x, y)

[Equation 69] Is calculated (step S80).

Next, using these two T1 attenuation corrected image values, the gradient G _rad (x, y) is calculated.

[Equation 70] The calculation is performed (step S81).

[0220] Finally, already using the scale value _{K 4} which has been obtained in step S76, the flow F (x, y) and

[Equation 71] Is calculated for each pixel (step S82).

In this way, the flow F (x, y) distributed two-dimensionally is obtained and displayed on the display 12 as information for quantifying the flow F.

As described above, according to the present embodiment, with respect to the reference, the gradient G _rad (ref) of the ASL image value after correcting T1 with respect to TI is obtained.
_rad calculates a scale value _{K 4} is a proportionality coefficient from (ref), the scale value _{K 4,} similarly ASL image value Δ
The flow F (x, y) is obtained by simple scaling by multiplying the gradient G _rad (x, y) obtained with respect to S (x, y).
y) can be calculated quantitatively.

Therefore, also in this embodiment, the same operation and effect as those of the above-described embodiments can be obtained, and even if the arrival time of the arterial blood from the slice plane and the tagging plane is delayed, the data of at least two points can be obtained. Slope G of ΔS curve
_{By obtaining rad} , a more accurate flow F can be obtained without depending on such a delay.

By the way, in the above-described first to fifth embodiments, the case where the imaging part is the head is illustrated.
The imaging site can be applied to various sites such as a kidney, a liver, and a muscle blood flow.

Note that the present invention is not limited to the above-described exemplary embodiments, and those skilled in the art will understand, based on the contents of the appended claims, within the spirit and scope of the invention. Can be modified and changed into various modes, which also belong to the scope of the present invention.

[0226]

As described above, according to the present invention,
In ASL imaging, attention is paid to the fact that a flow composed of tissue blood flow in an imaging region and the signal intensity of an ALS image can be approximated as a proportional relationship, and an ASL (Artificial
A scan based on the spin labeling method is performed to obtain image data of an imaging region, and a scale value is applied to the image data to quantitatively obtain a flow composed of tissue blood flow in the imaging region. The flow can be accurately quantified by a simple quantification operation (scaling) in which a scale value is multiplied by the slope value of the curve of each pixel of the data or each pixel of the image data.

That is, unlike the conventional method, in principle, only one image data needs to be prepared, and its collection time is as short as necessary and the quantification operation is also smaller than that of the conventional method. And the amount of calculation is reduced, so that the flow can be quantified quickly, easily and accurately. For this reason, compared to conventional methods with a large amount of collected data and computational complexity, which are practically difficult to use, for patients with general acute infarction,
Especially effective.

By displaying this flow quantification as an image,
Clinically meaningful comparisons using image values,
Diagnostic methods can also be provided, such as tracking changes in flow values on a patient-by-patient basis or over time for the same patient.

[0229] Naturally, since a contrast agent is not required, noninvasiveness can be maintained, and there is no X-ray exposure, which is advantageous.

[Brief description of the drawings]

FIG. 1 is an explanatory diagram of a compartment model for explaining the principle of the present invention.

FIG. 2 is an explanatory diagram in model analysis for explaining the principle of the present invention.

FIG. 3 is an explanatory diagram illustrating a scaling principle according to one embodiment of the present invention.

FIG. 4 is a block diagram showing an example of an MRI apparatus according to the embodiment of the present invention.

FIG. 5 is a diagram schematically illustrating the principle of imaging by the ASL method.

FIG. 6 is a schematic explanatory diagram exemplifying a flow from generation of image data to a flow quantification calculation executed in the first embodiment.

FIG. 7 is a diagram illustrating a positional relationship between a slice of the head and a stationary phantom.

FIG. 8 is a schematic configuration diagram of a flow phantom according to a second embodiment.

FIG. 9 is a schematic explanatory view exemplifying a flow from generation of image data to a flow quantification calculation executed in the second embodiment.

FIG. 10 is a diagram illustrating a positional relationship between a slice of a head and a flow phantom.

FIG. 11 is a schematic explanatory diagram exemplifying a flow from generation of image data to a flow quantification calculation executed in a third embodiment.

FIG. 12 is a schematic explanatory diagram illustrating a flow from generation of image data to a flow quantification calculation executed in a fourth embodiment.

FIG. 13 is a view for explaining a positional relationship between a slice of a head and a reference (vein).

FIG. 14 is a view for explaining a scaling method based on an inclination of each pixel of an ASL image according to the fifth embodiment.

FIG. 15 is a schematic explanatory view exemplifying a flow from generation of image data to a flow quantification calculation executed in a fifth embodiment.

[Explanation of symbols]

 Reference Signs List 1 magnet 2 static magnetic field power supply 3 gradient magnetic field coil unit 4 gradient magnetic field power supply 5 sequencer 6 host computer 7 RF coil 8T transmitter 8R receiver 10 operation unit 11 storage unit 12 display 13 input device 20 flow phantom

Claims (27)

[Claims] An ASL (Arter) is provided in an imaging region of a subject.
ial SpinLabeling), and obtains image data of the imaging region based on the ASL method. A tissue blood in the imaging region by applying a scale value to the image data obtained by the imaging unit. An MRI apparatus comprising: flow quantification means for quantitatively determining a flow composed of a flow. 2. The MRI apparatus according to claim 1, wherein the imaging unit executes a scan in a control mode and a tag mode based on the ASL method to obtain image data in each mode. Generating means for generating, from the image data, image data of one of the imaging regions according to the ASL method.
I device. 3. The MRI apparatus according to claim 2, wherein the flow quantification unit includes a calculation unit that calculates the flow for each pixel by multiplying the one image data by the scale value. A featured MRI device. 4. The M according to claim 1, wherein
An MRI apparatus, comprising: a RI value calculation means for calculating the scale value. 5. The MRI apparatus according to claim 4, wherein the scale value calculating means is means for calculating the scale value in which at least an error of the apparatus or an error due to a change in reception gain with respect to the scan is corrected. An MRI apparatus characterized by the following. 6. The MRI apparatus according to claim 5, wherein the scale value calculating means is configured to obtain reference image data based on the ASL method of a reference referred to with respect to the subject, An MRI apparatus comprising: an arithmetic unit that calculates the scale value based on known information about the scan and reference image data of the reference. 7. The MRI apparatus according to claim 6, wherein the reference is a normal tissue or a flow phantom of the subject, and the known information is a known flow. 8. The MRI apparatus according to claim 7, wherein the reference image data based on the ASL method is difference data between image data collected by a tag mode scan and a control mode scan based on the ASL method. An MRI apparatus characterized by the following. 9. The MRI apparatus according to claim 8, wherein: a reception gain correction unit that corrects a reception gain for the reception signal at the time of the scan; Means for reflecting the reference image data obtained by the reference image data obtaining means. 10. The MRI apparatus according to claim 9, wherein said reception gain correction means is means accompanied by scanning using a reference phantom exhibiting a T1 value approximated to the T1 value of blood. apparatus. 11. The MRI apparatus according to claim 7, wherein the reference image data based on the ASL method is an ASLR (ASL si) based on image data acquired by scanning in a tag mode and a control mode based on the ASL method.
gnal to control signal ra
(Tio). 12. The MRI apparatus according to claim 6, wherein the reference is a blood vessel present in an image of an imaging region of the subject, the known information is an imaging parameter of the scan, and the ASL An MRI apparatus characterized in that the reference image data based on the method is difference data between image data acquired by scanning in the tag mode and the control mode based on the ASL method. 13. The MRI apparatus according to claim 6, wherein the reference image data acquisition unit executes a scan in a control mode and a tag mode based on the ASL method, and executes an image in each mode. An MRI apparatus, which is means for obtaining data, wherein the scan is configured to also serve as a scan executed by the imaging means. 14. The MRI apparatus according to claim 4, wherein the scale value calculation means is configured to operate together with the flow quantification means every time the flow quantification measurement is performed. A featured MRI device. 15. The MRI apparatus according to claim 9, wherein the scale value calculating means is configured to operate independently of the flow quantification means in time. A featured MRI device. 16. The MRI apparatus according to claim 15, wherein in the flow quantification measurement under the same imaging condition, the same scale value calculated by the scale value calculation means is used by the flow quantification means. An MRI apparatus comprising: 17. The MRI apparatus according to claim 1, wherein the imaging unit executes a scan in a control mode and a tag mode based on the ASL method to obtain image data in each mode, and a scan unit for both modes. Generating means for generating image data of at least two images of the imaging region based on the ASL method from the image data, wherein the flow quantifying means calculates a slope of a pixel value from the image data of at least two images. An MRI apparatus comprising: first calculating means for calculating for each pixel; and second calculating means for calculating the flow for each pixel by multiplying the slope of the pixel value for each pixel by the scale value. . 18. The MRI apparatus according to claim 17, wherein said first calculating means is means for calculating, for each pixel, a gradient of a pixel value after T1 correction with respect to a nuclear spin inversion time TI. MRI equipment. 19. The MRI apparatus according to claim 17, wherein the flow quantification unit obtains at least two image values based on the ASL method of a reference to the subject, and the flow quantification unit obtains at least two image values. An MRI apparatus comprising: means for calculating a slope of a pixel value subjected to the T1 correction; and means for calculating the scale value from the slope. 20. An ASL (Arte
performing a magnetic resonance scan based on a real spin labeling method, obtaining image data of the imaging region based on the ASL method from data obtained by the scan, and a flow including a tissue blood flow in the imaging region. A flow quantification method using ASL imaging, comprising: a step of obtaining a scale value for quantification; and a step of applying the scale value to the image data to quantitatively obtain the flow. 21. The flow quantification method according to claim 20, wherein the scan is a scan in both a control mode and a tag mode based on the ASL method, and the image data is generated from image data in both modes. A is characterized by being image data of one image in the imaging area.
Flow quantification method by SL imaging. 22. The flow quantification method according to claim 21, wherein the step of quantitatively determining the flow is a step of multiplying the one image data by the scale value and calculating the flow for each pixel. A flow quantification method by ASL imaging, characterized in that: 23. The flow quantification method according to claim 20, wherein the step of obtaining the scale value includes both image data obtained by scanning in a control mode and a tag mode based on the ASL method for a reference referred to with respect to the subject. A flow quantification method by ASL imaging, wherein a scale value is obtained by using difference data of the above or data comprising a ratio of the difference data to image data obtained by scanning in the control mode. 24. The flow quantification method according to claim 20, wherein the step of obtaining the image data includes executing a scan in a control mode and a tag mode based on the ASL method to obtain image data in each mode. While generating at least two ASL image data of the imaging region based on the ASL method from the image data of both modes, the step of determining the flow quantitatively includes calculating a slope of a pixel value from the at least two image data. A flow quantification method, wherein the flow is calculated for each pixel, and the flow is calculated for each pixel by multiplying the slope of each pixel of the pixel value by the scale value. 25. The flow quantification method according to claim 24, wherein the step of calculating the slope calculates a slope of a pixel value after T1 correction with respect to a nuclear spin inversion time TI for each pixel. Flow quantification method. 26. The flow quantification method according to claim 24, wherein the step of obtaining the scale value comprises: converting an image value of the reference to the subject according to an ASL method to at least two.
And obtaining said T1 for said at least two image values.
A flow quantification method comprising: calculating a slope of a corrected pixel value; and calculating the scale value from the slope. An ASL (Arte) is provided in an imaging region of a subject.
performing a magnetic resonance scan based on a real spin labeling method, obtaining image data of the imaging region based on the ASL method from data obtained by the scan, and a flow including a tissue blood flow in the imaging region. A step of obtaining a scale value for quantifying, and a step of applying the scale value to the image data to quantitatively determine the flow, wherein the step of obtaining the scale value is referred to with respect to the subject. A flow quantification method using ASL imaging, wherein the scale value is determined so that a reference flow matches a known flow.