JPH0654816A - Inspection method using nuclear magnetic resonance - Google Patents

Abstract

PURPOSE:To shorten the counting time of a measuring method for a diffusion coefficient distribution using nuclear magnetic resonance. CONSTITUTION:In a measuring method for an apparent diffusion coefficient distribution, a gradient echo E1 and a spin echo E2 by high frequency pulse 2 are measured by one sequence. As for an inclined magnetic field pulse for emphasizing a signal attenuation effect caused by a diffusion phenomenon, a bipolar inclined magnetic field pulse is used and by applying one pair of bipolar inclined magnetic field pulses Gd3, Gd4 to E1, and applying two pairs of bipolar inclined magnetic field pulses Gd1, Gd2, and Gd3, Gd4 to E2, two images for which the applied quantities of the inclined magnetic field pulse are different can be measured by one sequence and from these images, the apparent diffusion coefficient distribution is derived. In such a manner, the measuring time can be shortened to the time of a half of the conventional method.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an inspection method using nuclear magnetic resonance, and more particularly to a measuring method for reducing the measurement time of a diffusion coefficient distribution using nuclear magnetic resonance.

[0002]

2. Description of the Related Art Diffusion is Brownian motion of a molecule, and a diffusion coefficient D represents the ease of movement of a molecule. For example 40
It is about 0.0025 mm 2 / s for pure water at 0 ° C. and about 0.002 mm 2 / s for water in the living body. On the other hand, macroscopically blood flow in capillaries having a net-like microstructure is also considered to be pseudo diffusion, and the pseudo diffusion coefficient D ′ is the true diffusion coefficient D.
10 times the value. Among the methods for measuring diffusion coefficient using nuclear magnetic resonance, a method for distinguishing between them is also proposed, but a pseudo diffusion coefficient including the influence of both methods, ADC
(Aperant Diffusion Co-Efficient App
arent Diffusion Coeficients) is also effective for medical diagnosis. Now, during the measurement of the nuclear magnetic resonance signal, if the position of the nucleus fluctuates due to such a diffusion phenomenon, the signal intensity decreases, and this decreasing term is expressed by exp (-b.ADC).
Here, b is a gradient magnetic field factor representing the applied amount of the gradient magnetic field,
Ignoring the effect of the gradient magnetic field for imaging, b
It is given by ∝γ ² G ² τ ³ . G is the gradient magnetic field strength, τ is the time when diffusion can occur, and γ is the gyromagnetic ratio. When the normal imaging method as shown in FIG. 1 is used, since the gradient magnetic field strength is weak, the decrease amount of the nuclear magnetic resonance signal due to this diffusion phenomenon is very small and does not pose a problem, but as shown in FIG. When a strong gradient magnetic field is applied in the readout gradient magnetic field direction, b increases and the signal decrease amount increases.
When such a strong gradient magnetic field is applied on both sides of the 180 ° pulse, the effects of the first gradient magnetic field and the second gradient magnetic field are canceled in the stationary part, but they are not canceled in the large moving part. , The signal is greatly reduced under the influence of both gradient magnetic fields.

Conventionally, by using nuclear magnetic resonance, ADC distribution, A
When measuring DC (x, y, z), the day. Elle.
“Intra Voxel” by DL Bihan
Incoherent Motionon Imaginating Yousing Spin Echoes (Magnetic Resonance Inmedecine 19: 221-227 (199
91)) "(" Intravoxel Incoherent Motion Imaging
Using Spin Echos "(Magnetic Resonance in Medicine
19, pp221-227 (1991))) as shown in FIG.
In this imaging method, the gradient magnetic field factor b is changed to measure a plurality of images S ₀ (x, y, z) and S ₁ (x, y, z),

[0004]

[Equation 1] ADC (x, y, z) = {log (S ₀ (x, y, z) / S ₁ (x, y, z))} / (b ₁ -b ₀ ) From (Equation 1) , ADC (x, y, z). Where b
₁ and b ₀ are gradient magnetic field factors b in S ₀ (x, y, z) and S ₁ (x, y, z).

[0005]

SUMMARY OF THE INVENTION The above-mentioned prior art ADC
When obtaining (x, y, z), the time τ at which diffusion can occur
In order to accurately control the gradient magnetic field, the contribution of the gradient magnetic field for imaging other than the diffusion gradient magnetic field to the gradient magnetic field factor b is preferably as small as possible. However, since the intensity of the diffusion gradient magnetic field Gd has an upper limit, the application time must be lengthened in order to increase the influence of Gd, and the time for measuring one image is longer than that in normal imaging. Become. Further, in the above-mentioned conventional technique, since it is necessary to measure images of different b, there is a problem that the measurement time becomes longer. The present invention has been made in view of the above-mentioned drawbacks, and an object of the present invention is to solve the above-mentioned problems in the conventional technique and shorten the ADC distribution measurement time.

[0006]

The above object of the present invention is obtained from the above two echoes by generating a gradient echo and a spin echo having different gradient magnetic field factors b or two gradient echoes in one measurement. This is accomplished by using the image to determine the ADC distribution. That is, nuclear magnetic resonance provided with means for generating a static magnetic field, a gradient magnetic field, and a high-frequency magnetic field, a signal detecting means for detecting a nuclear magnetic resonance signal from an inspection target, and a computer for processing the detection signal of the signal detecting means. In the inspection method using nuclear magnetic resonance in the apparatus, a first step of measuring a first echo in which the influence of the bipolar gradient magnetic field pulse is small or zero, and the influence of the bipolar gradient magnetic field pulse is the above-mentioned first step. And a second step of measuring a second echo larger than the echo of. More specifically, the inspection method using nuclear magnetic resonance is the first method for measuring spin echoes generated by the first and second high-frequency pulses.
And a second step of measuring a gradient echo generated by the second high frequency pulse, the first step applying a first bipolar gradient magnetic field pulse between the first and second high frequency pulses. And a step of applying a second bipolar gradient magnetic field pulse during the measurement of the second high frequency pulse and the spin echo, the second step including the second step.
And a step of applying a second bipolar gradient magnetic field pulse between the high frequency pulse and the gradient echo measurement, wherein the second bipolar gradient magnetic field pulse can have a gradient magnetic field strength or a pulse width of zero. To do.

Furthermore, the inspection method using nuclear magnetic resonance is as follows:
It comprises a first step of measuring a gradient echo generated by the first high-frequency pulse and a second step of measuring a spin echo generated by the first and second high-frequency pulses, the first step being the first high-frequency wave. The method includes the step of applying a first bipolar gradient magnetic field pulse between the time of measuring the pulse and the gradient echo, and the second step includes the first and second steps.
The step of applying the first bipolar gradient magnetic field pulse between the high frequency pulses of 1 and the step of applying the second bipolar gradient magnetic field pulse between the second high frequency pulse and the time of measuring the spin echo. The bipolar gradient magnetic field pulse is characterized in that the gradient magnetic field strength or pulse width can be zero. In addition, the inspection method using nuclear magnetic resonance includes a first step of measuring a first gradient echo generated by a first high frequency pulse and a second step of measuring a second gradient echo generated by a second high frequency pulse. The first step includes the step of applying the first bipolar gradient magnetic field pulse during the measurement of the first high-frequency pulse and the first gradient echo, and the second step includes the second high-frequency pulse. The step of applying a second bipolar gradient magnetic field pulse between the pulse and the measurement of the second gradient echo, wherein the first bipolar gradient magnetic field pulse or the second bipolar gradient magnetic field pulse is a gradient magnetic field strength or a pulse width. Is characterized in that can be zero. Furthermore, in an inspection method using nuclear magnetic resonance for measuring diffusion coefficient distribution using two nuclear magnetic resonance images, a measuring method for obtaining two nuclear magnetic resonance images prior to measuring the diffusion coefficient distribution Signals due to factors other than the gradient magnetic field pulse for enhancing the diffusion phenomenon in the two nuclear magnetic resonance images by using the intensity ratio of the two signals obtained without applying the encoding gradient magnetic field and the gradient magnetic field pulse for enhancing the diffusion phenomenon It is characterized in that the difference in intensity is corrected and the diffusion coefficient distribution is obtained using the two corrected nuclear magnetic resonance images.

[0008]

The inspection method using nuclear magnetic resonance according to the present invention will be described below in the case of obtaining the ADC distribution by the measurement method shown in FIG. Echoes E ₁ and E ₂ in the figure are a spin echo and a gradient echo by the high frequency pulse 2, respectively. When the application direction of the static magnetic field is Z, the nuclear magnetization in the inspection target is initially oriented in the Z direction. When the first high-frequency pulse is applied in the X direction together with the slice gradient magnetic field Gs ₁ , a specific slice plane Z orthogonal to the Z direction is obtained.
A part of nuclear magnetization M ₁ (nuclear magnetization −1) in the vicinity of = Z ₀ is excited and a Y-direction component is generated. The flip angle α of the first high frequency pulse is not 90 °, and it is desirable that a part of the nuclear magnetization remains on the Z axis after the excitation. The phase of the excited nuclear magnetization M ₁ is dispersed by the read-out gradient magnetic field Gr ₁ , and then the signal is attenuated by the diffusion phenomenon by applying the gradient magnetic fields Gd ₁ and Gd ₂ . Gradient magnetic field G
d ₁ and Gd ₂ have the same pulse width and intensity, and the gradient magnetic field pulse has only the polarity reversed. These effects are canceled in the stationary part, but the intensity is applied when Gd ₁ and Gd ₂ are applied in the diffused part. The signals are attenuated because they sense different magnetic fields. Next, a high frequency pulse 2 is applied together with the slice gradient magnetic field Gs ₂ to rotate the excited nuclear magnetization M ₁ by β around the X axis. As a result, nuclear magnetization M ₃ (nuclear magnetization -3) is generated in the negative direction of the Y axis. At this time, a part M ₂ (nuclear magnetization −2) of the nuclear magnetization remaining on the Z axis is excited, and a new Y direction component is generated. After that, the gradient magnetic field Gd
Application of ₃ and Gd ₄ causes signal attenuation due to diffusion phenomenon. Gd ₃ and Gd ₄ are gradient magnetic field pulses having the same pulse width and intensity and only the polarities thereof are inverted, but they need not be the same as the gradient magnetic fields Gd ₁ and Gd ₂ .
The nuclear magnetization M ₃ is affected by all of the gradient magnetic fields Gd ₁ , Gd ₂ , Gd ₃ , and Gd _4, but the nuclear magnetization M ₂ is only affected by Gd ₃ and Gd ₄ . Then, the encoding gradient magnetic field Ge ₁ is applied to encode the phases of the nuclear magnetizations M ₃ and M ₂ .
Then, by applying a read-out gradient magnetic field Gr ₂ , the phases of the nuclear magnetizations M ₃ and M ₂ are dispersed. Gradient magnetic field Gr
Reference numeral ₂ is a gradient magnetic field pulse having the same pulse width and intensity as the gradient magnetic field Gr ₁ but with the polarity reversed. This pulse width is t ₁
And Next, the polarity of the read-out gradient magnetic field is reversed and G
Apply r ₃ . The gradient magnetic fields Gr ₃ are the gradient magnetic fields Gr ₁ and Gr _2.
Is a gradient magnetic field pulse having the same intensity and the same polarity as Gr ₁ . After Δt has elapsed after the application of the gradient magnetic field Gr _3, the nuclear magnetization M ₂ dispersed by the readout gradient magnetic field Gr ₂ is aligned in phase, and a gradient echo E ₂ is generated. When the time Δt further passes, the phases of the nuclear magnetization M ₃ dispersed by the readout gradient magnetic fields Gr ₁ and Gr ₂ are aligned, and the spin echo E ₁ is generated.

Ignoring the effects of the longitudinal relaxation time T ₁ , static magnetic field inhomogeneity, chemical shift, etc., the images S ₁ and S ₂ obtained from the _two echoes E ₁ and E ₂ are expressed as follows.

[0010]

[Equation 2] S ₁ = ρ ・ exp (-b ₁・ ADC (x, y, z)) (Equation 2)

[0011]

S ₂ = ρ · exp (-b ₂ · ADC (x, y, z)) (Equation 3) where ρ is spin density, and b ₁ and b ₂ are gradient magnetic fields Gd ₁ and Gd, respectively. ₂ , a gradient magnetic field factor due to Gd ₃ and Gd ₄ , and a gradient magnetic field factor due to the gradient magnetic fields Gd ₃ and Gd ₄ .
From the equations 2 and 3, the apparent diffusion coefficient distribution ADC (x,
y, z) is calculated by the following equation.

[0012]

[Equation 4] ADC (x, y, z) = {log (S ₁ / S ₂ )} / (b ₂ -b ₁ ) (Equation 4) By the way, the signal strength also depends on the relaxation time and the static magnetic field inhomogeneity. Decay. Further, since the difference in flip angle also affects the signal strength, it is desirable to set the measurement conditions so that these effects are equal when obtaining the diffusion coefficient distribution using two images as described above. . However, if such measurement conditions cannot be set, it is necessary to correct the difference in signal amount due to the flip angle, relaxation time, static magnetic field inhomogeneity, and the like. Therefore, in the above measuring method, the gradient echo e ₁ and the spin echo e ₂ are measured without applying the encode gradient magnetic field and the bipolar gradient magnetic field, and the right side of the equation 4 is {log (S ₁ · e ₂ / S ₂ / e ₁ )} / (b ₂ −
By substituting with b ₁ ), it is possible to correct the difference in the signal attenuation amount due to the above flip angle, relaxation time, static magnetic field inhomogeneity and the like. As mentioned above, according to the present invention 1
The apparent diffusion coefficient distribution can be obtained by performing the measurement once.

[0013]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 4 is a block diagram showing an example of an inspection apparatus using nuclear magnetic resonance. In FIG. 4, reference numeral 1 is a coil that generates a static magnetic field, 2 is a coil that generates a gradient magnetic field, and 3 is an inspection target. The inspection target is arranged in the coils 1 and 2. The sequencer 4 sends a command to the gradient magnetic field power supply 5 and the high frequency oscillator 6 to apply the gradient magnetic field and the high frequency magnetic field. The high frequency magnetic field is applied to the inspection target 3 by the high frequency transmitter 9 via the high frequency modulator 7 and the high frequency amplifier 8. The signal generated from the inspection object is received by the receiver 10, and the amplifier 1
1 through the phase detector 12 and the AD converter 13 to the CPU 1
4 and the signal processing is performed there, and then the display device 1
It is displayed in 5. If necessary, the storage medium 16 can also store signals and measurement conditions. Now, FIG. 3 is a measuring method showing an embodiment of the present invention. In addition, FIG. 5, FIG.
FIG. 7 shows the behavior of nuclear magnetization when the measurement method of FIG. 3 is executed. Hereinafter, embodiments of the present invention will be described in time series with reference to FIGS. 3, 5, 6, and 7. Echoes E ₁ and E _{2 in} FIG. 3 are a spin echo and a gradient echo by the high frequency pulse 2, respectively. In the following description, the application direction of the static magnetic field is Z and the application direction of the high frequency pulse is X.

(Time t ₀ ) (FIG. 5A): The nuclear magnetization M ₀ in the inspection object is initially oriented in the Z direction. (Time t ₁ ) (FIG. 5B): Slice gradient magnetic field Gs ₁
When a high frequency pulse 1 is applied together with it, a part of nuclear magnetization M _{1 in the} vicinity of a specific slice plane Z = Z ₀ orthogonal to the Z direction
(Nuclear magnetization -1) is excited and a Y-direction component is generated. (Time t ₂ ) (FIG. 5C): The phase of nuclear magnetization M ₁ is dispersed by the readout gradient magnetic field Gr ₁ . (Time t ₃ ) (FIG. 5 (d)): Two gradient magnetic field pulses Gd with the same product of the pulse width and the absolute value of the intensity and the polarity being inverted.
₁ and Gd ₂ are applied. Although the stationary site effects of Gd _1, Gd ₂ is canceled, the site that occurs in the diffusion Gd _1, G
When d ₂ is applied, magnetic fields with different strengths are felt, so that the signal is attenuated. (Time t ₄ ) (FIG. 6E): By applying the high frequency pulse 2 together with the slice gradient magnetic field Gs ₂ , the excited nuclear magnetization M ₁ is rotated by β around the X axis. As a result, nuclear magnetization M ₃ (nuclear magnetization -3) occurs in the negative direction on the Y axis. At this time, a part M of the nuclear magnetization remaining on the Z axis
₂ (nuclear magnetization-2) is excited, and a new Y-direction component is generated. (Time t ₅ ) (FIG. 6 (f)): Two gradient magnetic field pulses Gd with the same product of the pulse width and the absolute value of the intensity and the polarity being inverted.
₃ and Gd ₄ are applied. Nuclear magnetization M ₃ has gradient magnetic fields Gd ₁ and Gd
₂ , Gd ₃ and Gd ₄ are all affected, but the nuclear magnetization M ₂ is only affected by Gd ₃ and Gd ₄ . (Time t ₆₎ (Fig. 6 (g)): encoding gradient Ge ₁
Is applied to encode the phases of the nuclear magnetizations M ₃ and M ₂ .

(Time t ₇ ) (FIG. 6 (h)) By applying the read-out gradient magnetic field Gr ₂ , the nuclear magnetizations M ₃ and M ₂ are applied.
Disperse the phase of. The gradient magnetic field Gr ₂ is a gradient magnetic field pulse whose pulse width and intensity are the same as those of the gradient magnetic field Gr _1, and only the polarity is inverted. This pulse width is Δt. (Time t ₈₎ (Fig. 7 (i)): inverting the polarity of the readout gradient magnetic field, applying a Gr _3. The gradient magnetic field Gr ₃ is a gradient magnetic field pulse having the same intensity as the gradient magnetic fields Gr ₁ and Gr ₂ and the same polarity as Gr ₁ . (Time t ₉ ) (FIG. 7 (j)): Readout gradient magnetic field G when Δt has elapsed after the start of application of the gradient magnetic field Gr _3.
The phases of the nuclear magnetization M ₂ dispersed by r ₂ are aligned and a gradient echo E ₂ is generated. (Time t ₁₀₎ (Fig. 7 (k)): If more time Δt has elapsed, aligned phase of the readout gradient magnetic field Gr _1, Gr ₂ nuclear magnetization M ₃ which is dispersed by a spin echo E ₁ is generated.

Ignoring the effects of the longitudinal relaxation time T ₁ , static magnetic field inhomogeneity, chemical shift, etc., the images S ₁ and S ₂ obtained from the _two echoes E ₁ and E ₂ are expressed as follows.

[0017]

[Equation 5] S ₁ = ρ ・ exp (-b ₁・ ADC (x, y, z)) (Equation 5)

[0018]

[Equation 6] S ₂ = ρ · exp (-b ₂ · ADC (x, y, z)) (Equation 6) where ρ is spin density, and b ₁ and b ₂ are gradient magnetic fields Gd ₁ and Gd, respectively. ₂ , a gradient magnetic field factor due to Gd ₃ and Gd ₄ , and a gradient magnetic field factor due to the gradient magnetic fields Gd ₃ and Gd ₄ .
From Equations 5 and 6, the apparent diffusion coefficient distribution ADC (x,
y, z) is calculated by the following equation.

[0019]

[Equation 7] ADC (x, y, z) = {log (S ₁ / S ₂ )} / (b ₂ -b ₁ ) (Equation 7) The gradient magnetic field factor must have a sufficiently small effect of the gradient magnetic field used for imaging. For example, it is proportional to the cube of the application time of the gradient magnetic field for enhancing the diffusion coefficient and the square of the gradient magnetic field strength. Therefore, G
If d ₃ and Gd ₄ are equal to Gd ₁ and Gd ₂ ,

[0020]

[Formula 8] b ₁ = 8 · b ₂ (Formula 8). This is an example of how to select the gradient magnetic field factor, and Gd ₃ and Gd ₄ do not necessarily have to be equal to Gd ₁ and Gd ₂ . However, the product of the pulse width of Gd ₁ and Gd ₂ and the gradient magnetic field strength must not be zero. On the contrary, the product of the pulse widths of Gd ₃ and Gd ₄ and the gradient magnetic field strength may be zero. That is, it suffices if b ₁ ≠ b ₂ . In order that the nuclear magnetization M ₁ does not become 0, the flip angle α of the high frequency pulse 1 should not be 0 ° or a multiple of 180 °. Also the nuclear magnetization M
_In order that ₂ does not become 0, it is desirable that a part of the nuclear magnetization remains on the Z axis after the application of the high frequency pulse 1, so the flip angle α of the high frequency pulse 1 is not a multiple of 90 °, and It is necessary that the flip angle β of the pulse 2 is not 0 ° or a multiple of 180 °. As described above, according to the embodiment of the present invention shown in FIG. 3, it is possible to measure the apparent diffusion coefficient distribution in half the measurement time of the normal measurement. Now, FIG. 8 is a measuring method showing another embodiment of the present invention. Further, FIGS. 9, 10, and 11 show the behavior of nuclear magnetization when the measurement method of FIG. 8 is executed.
Hereinafter, an embodiment of the present invention will be described in chronological order with reference to FIGS. 6, 9, 10, and 11. Echoes E ₁ and E _{2 in} FIG. 8 are a gradient echo and a spin echo by the high frequency pulse 1, respectively. In the following description, the application direction of the static magnetic field is Z and the application direction of the high frequency pulse is X. Further, in this example, the case of measuring an image of a slice plane perpendicular to the Z axis will be described.

(Time t ₀ ) (FIG. 9A): The nuclear magnetization M ₀ in the inspection object is initially oriented in the Z direction. (Time t ₁ ) (FIG. 9B): Slice gradient magnetic field Gs ₁
When a high frequency pulse 1 is applied together with it, a part of nuclear magnetization M _{1 in the} vicinity of a specific slice plane Z = Z ₀ orthogonal to the Z direction
(Nuclear magnetization -1) is excited and a Y-direction component is generated. (Time t ₂ ) (FIG. 9C): Encoding gradient magnetic field Ge ₁
Is applied to encode the phase of the nuclear magnetization M ₁ . (Time t ₃ ) (FIG. 9 (d)): Two gradient magnetic field pulses Gd with the same product of the pulse width and the absolute value of the intensity and the polarity being inverted
₁ and Gd ₂ are applied. Although the stationary site effects of Gd _1, Gd ₂ is canceled, the site that occurs in the diffusion Gd _1, G
When d ₂ is applied, magnetic fields with different strengths are felt, so that the signal is attenuated. (Time t ₄₎ (Fig. 10 (e)): the nuclear magnetization M ₁ phase is dispersed by the readout gradient magnetic field Gr _1. This pulse width is Δt. (Time t ₅₎ (FIG. 10 (f)): by inverting the polarity of Gr ₁ applies a readout gradient magnetic field Gr _2. Gr ₁ and Gr ₂
Are equal in intensity. (Time t ₆₎ (Fig. 10 (g)): After the application start of the Gr _2, delta
When t has elapsed, the phases of the nuclear magnetization M ₁ dispersed by the readout gradient magnetic field Gr ₁ are aligned and a gradient echo E ₁ is generated. (Time t ₇₎ (FIG. 10 (h)): a slice gradient magnetic field Gs ₂
By applying the high frequency pulse 2 together with the nuclear magnetization M
Rotate ₁ around the X axis by β. At this time, the component of the nuclear magnetization M ₁ that falls on the XY plane is defined as the nuclear magnetization M ₄ (nuclear magnetization-4).
And

(Time t ₈ ) (FIG. 11 (i)): Two gradient magnetic field pulses Gd ₃ and Gd ₄ having the same product of the pulse width and the absolute value of the intensity and having the inverted polarities are applied. The nuclear magnetization M ₄ is affected by the gradient magnetic fields Gd ₁ and Gd ₂ , but the nuclear magnetization M ₁ is G
It is affected by all of d ₁ , Gd ₂ , Gd ₃ , and Gd ₄ . (Time t ₉₎ (Fig. 11 (j)): applying a readout gradient magnetic field Gr _3. Gr ₂ and Gr ₃ have the same intensity. (Time t ₁₀₎ (FIG. 11 (k)): After the start the gradient magnetic field Gr ₃ applied, at the expiration of Delta] t, matching the phase of the readout gradient magnetic field Gr ₂ nuclear magnetization M ₄ dispersed by a spin echo E ₂ Occurs. The method of obtaining ADC (x, y, z) using the gradient echo E ₁ and the spin echo E ₂ is the same as the above method. However, the method of selecting the gradient magnetic field factors b ₁ and b ₂ is slightly different, and the product of the pulse width of Gd ₁ and Gd ₂ and the gradient magnetic field strength must not be zero. The product of the pulse width of Gd ₃ and Gd ₄ and the gradient magnetic field strength may be 0. That is,
It is sufficient if b ₁ ≠ b ₂ . In order that the nuclear magnetization M ₁ does not become 0, the flip angle α of the high frequency pulse 1 is 0 ° or 18
Must not be a multiple of 0 °. When the flip angle α of the high frequency pulse 1 is an odd multiple of 90 °, the nuclear magnetization M ₁ becomes maximum. Further, in order that the nuclear magnetization M ₄ does not become 0, the flip angle β of the high frequency pulse 2 should not be an odd multiple of 90 °. When the flip angle α of the high frequency pulse 1 is an odd multiple of 90 ° and the flip angle α of the high frequency pulse 2 is an odd multiple of 180 °, the nuclear magnetization M ₄ becomes maximum. As described above, according to the other embodiment of the present invention shown in FIG. 8, it is possible to measure the apparent diffusion coefficient distribution in half the measurement time of the normal measurement. Now, FIG. 12 is a measuring method showing another embodiment of the present invention. Further, FIGS. 13, 14, 15, and 16 are shown in FIG.
It shows the behavior of nuclear magnetization when the measurement method of No. 2 is executed. Hereinafter, FIG. 12, FIG. 13, FIG. 14, FIG.
The embodiment of the present invention will be described in time series with reference to.

Echoes E ₁ and E _{2 in} FIG. 12 are a gradient echo by the high frequency pulse 1 and a gradient echo by the high frequency pulse 2, respectively. In the following description, the application direction of the static magnetic field is Z and the application direction of the high frequency pulse is X. Further, in this example, the case of measuring an image of a slice plane perpendicular to the Z axis will be described. (Time t ₀ ) (FIG. 13A): Nuclear magnetization M ₀ in the inspection target
Initially faces the Z direction. (Time t ₁ ) (FIG. 13B): Slice gradient magnetic field Gs ₁
When a high frequency pulse 1 is applied together with it, a part of nuclear magnetization M _{1 in the} vicinity of a specific slice plane Z = Z ₀ orthogonal to the Z direction
(Nuclear magnetization -1) is excited and a Y-direction component is generated. (Time t ₂ ) (FIG. 13C): Encoding gradient magnetic field G
The phase of the nuclear magnetization M ₁ is encoded by applying e ₁ . (Time t ₃ ) (FIG. 13 (d)): Two gradient magnetic field pulses G in which the products of the pulse width and the absolute value of the intensity are equal and the polarities are inverted.
Apply d ₁ and Gd ₂ . Although the stationary site effects of Gd _1, Gd ₂ are canceled, Gd ₁ is at the site that occurs in the diffusion,
When Gd ₂ is applied, a magnetic field with different strength is felt, so that the signal is attenuated. (Time t ₄ ) (FIG. 14E): The phase of the nuclear magnetization M ₁ is dispersed by the readout gradient magnetic field Gr ₁ . This pulse width is Δt. (Time t ₅ ) (FIG. 14 (f)): The polarity of Gr ₁ is reversed and the readout gradient magnetic field Gr ₂ is applied. Gr ₁ and Gr ₂
Are equal in intensity. (Time t ₆₎ (Fig. 14 (g)): After the application start of the Gr _2, delta
When t has elapsed, the phases of the nuclear magnetization M ₁ dispersed by the readout gradient magnetic field Gr ₁ are aligned and a gradient echo E ₁ is generated.

(Time t ₇ ) (FIG. 14 (h)): Gradient magnetic fields Ge ₂ and Gr ₃ for dephasing are applied, and nuclear magnetization M ₁ is applied.
To saturate. (Time t ₈₎ (Fig. 15 (i)): a slice gradient magnetic field Gs ₂
By applying the high frequency pulse 2 together with this, a part of the nuclear magnetization M ₅ (nuclear magnetization −5) remaining on the Z axis is excited, and a new Y-direction component is generated. (Time t ₉ ) (FIG. 15 (j)): Encoding gradient magnetic field G
The phase of nuclear magnetization M ₅ is encoded by applying e ₃ . (Time t ₁₀ ) (FIG. 15 (k)): Two gradient magnetic field pulses G in which the products of the pulse width and the absolute value of the intensity are equal and the polarities are inverted.
Apply d ₃ and Gd ₄ . Gd ₃ and Gd ₄ must not be equal to the above-mentioned gradient magnetic fields Gd ₁ and Gd ₂ . The nuclear magnetization M ₁ is affected by the gradient magnetic fields Gd ₁ and Gd ₂ , but the nuclear magnetization M ₅ is Gd ₃ ,
It is affected by Gd ₄ . (Time t ₁₁ ) (FIG. 15 (l)): The phase of the nuclear magnetization M ₅ is dispersed by applying the readout gradient magnetic field Gr ₄ . This pulse width is Δt. (Time t ₁₂₎ (FIG. 16 (m)): applying a readout gradient magnetic field Gr ₅ inverts the polarity of the readout gradient magnetic field. Gr ₅ and Gr ₄ have the same intensity. (Time t ₁₃₎ (FIG. 16 (n)): After the start gradient field Gr ₅ applied at a lapse of Delta] t, matching the phase of the readout gradient magnetic field Gr ₄ nuclear magnetization M ₅ dispersed by, gradient echo E ₂ Occurs. ADC using _two gradient echoes E ₁ and E ₂
The method of obtaining (x, y, z) is the same as the above method. However, the selection method of the gradient magnetic field factors b ₁ and b ₂ is slightly different, and Gd ₃ and Gd ₄ must not be equal to Gd ₁ and Gd ₂ . The product of the pulse width of Gd ₁ and Gd ₂ and the gradient magnetic field strength may be 0. The product of the pulse width of Gd ₃ , Gd ₄ and the gradient magnetic field strength may be 0, but Gd ₁ , Gd ₂ , G
For all d ₃ and Gd ₄ , the product of pulse width and gradient magnetic field strength must not be zero. That is, it suffices if b ₁ ≠ b ₂ .

In order that the nuclear magnetization M ₁ does not become 0, the flip angle α of the high frequency pulse 1 must not be 0 ° or a multiple of 180 °. Further, in order that the nuclear magnetization M ₅ does not become 0, the flip angle β of the high frequency pulse 2 should not be 0 ° or a multiple of 180 °. High frequency pulse 1
When the flip angle α of is an odd multiple of 90 °, the nuclear magnetization M ₁ becomes maximum. At this time, however, no nuclear magnetization remains on the Z axis and the nuclear magnetization M 1
_{Since 2} becomes almost 0, the flip angle α of the high frequency pulse 1 must not be an odd multiple of 90 °. When the flip angle β of the high frequency pulse 2 is 90 °, the nuclear magnetization M ₂ becomes maximum. Now, if the gradient magnetic field factor is large, the intensity of the gradient echo also becomes small and the S / N becomes worse. Therefore, of the gradient echoes E ₁ and E ₂ , the flip angle of the high-frequency pulse is set to a value close to 90 ° when measuring the echo having the larger gradient magnetic field factor. The flip angle of the high-frequency pulse may be small at the time of echo measurement in which the gradient magnetic field factor is small. In the above embodiment, the gradient magnetic field for dephasing is applied to saturate the nuclear magnetization M ₁ at time t ₇ , but this should not be affected by the nuclear magnetization M ₁ when measuring the nuclear magnetization M _2. This is because We will now describe another way to achieve this goal. There is known a method of removing artifacts caused by incompleteness of the high frequency pulse by integrating the collected signals while controlling the transmission phase and the reception phase of the high frequency pulse. In this regard, Gee. Evolution of New Broadband Decoupling Sequence (Journal of G.Bodenhausen)
Magnetic Resonance 53, 313-340 (1977)) ("Evaluation of New Broadband Deco
upling Sequence "(Journal of Magnetic Resonance, 5
3, pp313-340 (1977))). This method can also be applied to achieve the above-mentioned object. In the above embodiment, it is assumed that the integration is performed at least 4 times. When integrating four times or more, it is desirable that the number of integrations be a multiple of four. Here, the case where the transmission phase and the reception phase of the high frequency pulse at the time of measuring the gradient echo E ₁ are fixed at 0 ° and the phase control is performed at the time of measuring the gradient echo E ₂ will be described. Further, the transmission phase and the reception phase are the same phase, and this is θ. An example of the phase control method at this time is shown below.

The number of times of integration is 4n + 1 (n = 0, 1, 2)
...), θ = 0 ° When the number of integrations is 4n + 2 (n = 0, 1, 2, ...), θ =
90 ° When the number of times of integration is 4n + 3 (n = 0, 1, 2, ...), θ =
180 ° When the number of times of integration is 4n + 4 (n = 0, 1, 2, ...), θ =
When 270 ° and 0 ° correspond to the Y axis and 90 ° to the X axis, nuclear magnetization M ₂
The component of the nuclear magnetization M ₁ mixed in the measurement signal of is the Y component My, the X component Mx, -My, and -M.
x, and by adding these, the component of the nuclear magnetization M ₁ can be removed without affecting the nuclear magnetization M ₅ . As described above, according to the other embodiment of the present invention shown in FIG. 12, it is possible to measure the apparent diffusion coefficient distribution in half the measurement time of the normal measurement. Now, in Equations 5 and 6, only signal attenuation due to the influence of the diffusion gradient magnetic field is considered, but in reality, the signal intensity is attenuated due to relaxation time, static magnetic field inhomogeneity, and the like. Further, since the difference in flip angle also affects the signal strength, it is desirable to set the measurement conditions so that these effects are equal when the diffusion coefficient distribution is obtained using two images. However, in the three embodiments described above, two echoes generated by high-frequency pulses with different flip angles are used, and it is difficult to equalize the effects of relaxation time, static magnetic field inhomogeneity, and the like. Therefore, it is necessary to correct the difference in signal amount due to factors other than the diffusion gradient magnetic field before obtaining the diffusion count distribution. Therefore, the intensity of the diffusion gradient magnetic field is set to 0 in each measuring method of the above-mentioned embodiment.
As a signal measurement. Since the two signals obtained by the above measurement have an intensity ratio due to factors other than the diffusion gradient magnetic field, the above correction can be performed by using this intensity ratio. When measuring the correction signal, it is not necessary to apply an encode gradient magnetic field to form an image, and it is sufficient to know the value of each echo peak. When two echo peaks corresponding to the two images S ₁ and S ₂ of the equation 7 are measured by the above method and designated as e ₁ and e ₂ , respectively, correction of the difference in signal amount due to factors other than the diffusion gradient magnetic field is This is achieved by using Equation 9 instead of Equation 7.

[0027]

[Equation 9] ADC (x, y, z) = {log (S ₁ · e ₂ / S ₂ / e ₁ )} / (b ₂ -b ₁ ) (Equation 9) As described above, the correction signal Need not be imaged, and the echo peak can be measured during the adjustment prescan before image measurement, so the time required for correction can be almost ignored.

[0028]

As described above in detail, according to the present invention, a gradient echo and a spin echo having different gradient magnetic field factors b or two gradient echoes are generated in one measurement, and the two echoes are generated. Since the ADC distribution is obtained using the obtained image, it is possible to measure the apparent diffusion coefficient distribution in half the time of the conventional method.

[Brief description of drawings]

FIG. 1 is a diagram showing an example of an imaging method using nuclear magnetic resonance.

FIG. 2 is a diagram showing a method of measuring an apparent diffusion coefficient distribution by a conventional method.

FIG. 3 is a diagram showing a method of measuring an apparent diffusion coefficient distribution according to the embodiment of the present invention.

FIG. 4 is a configuration diagram of an inspection apparatus using nuclear magnetic resonance used in an example of the present invention.

FIG. 5 is a diagram showing the behavior of nuclear magnetization according to an example of the present invention.

FIG. 6 is a diagram showing the behavior of nuclear magnetization according to the example of the present invention.

FIG. 7 is a diagram showing the behavior of nuclear magnetization according to the example of the present invention.

FIG. 8 is a diagram showing a method of measuring an apparent diffusion coefficient distribution according to another embodiment of the present invention.

FIG. 9 is a diagram showing the behavior of nuclear magnetization according to another embodiment of the present invention.

FIG. 10 is a diagram showing the behavior of nuclear magnetization according to another embodiment of the present invention.

FIG. 11 is a diagram showing the behavior of nuclear magnetization according to another embodiment of the present invention.

FIG. 12 is a diagram showing a method for measuring an apparent diffusion coefficient distribution according to another embodiment of the present invention.

FIG. 13 is a diagram showing the behavior of nuclear magnetization according to another embodiment of the present invention.

FIG. 14 is a diagram showing the behavior of nuclear magnetization according to another embodiment of the present invention.

FIG. 15 is a diagram showing the behavior of nuclear magnetization according to another embodiment of the present invention.

FIG. 16 is a diagram showing the behavior of nuclear magnetization according to another embodiment of the present invention.

[Explanation of symbols]

1 ... Static magnetic field generating coil, 2 ... Gradient magnetic field generating coil, 3 ...
Inspection object, 4 ... Sequencer, 5 ... Gradient magnetic field power supply, 6 ... High frequency oscillator, 7 ... High frequency modulator, 8 ... High frequency amplifier, 9
... High-frequency transmitter, 10 ... Receiver, 11 ... Amplifier, 12 ...
Phase detector, 13 ... AD converter, 14 ... CPU, 15 ...
Display device, 16 ... Storage medium.

Claims (22)

[Claims] 1. A static magnetic field, a gradient magnetic field, and a high-frequency magnetic field generating means, a signal detecting means for detecting a nuclear magnetic resonance signal from an inspection target, and a computer for processing a detection signal of the signal detecting means. In an inspection method using nuclear magnetic resonance in a nuclear magnetic resonance apparatus, the first step of measuring a first echo where the influence of a bipolar gradient magnetic field pulse is small or zero, and the influence of the bipolar gradient magnetic field pulse are A second step of measuring a second echo larger than the first echo, the inspection method using nuclear magnetic resonance. 2. The inspection method using nuclear magnetic resonance according to claim 1, wherein the first step of measuring spin echoes generated by the first and second high frequency pulses and the second high frequency pulse are generated. Second measurement of gradient echo
Between the step of applying the first bipolar gradient magnetic field pulse between the first and second high frequency pulses, and the step of measuring the second high frequency pulse and the spin echo. A step of applying a second bipolar gradient magnetic field pulse to the second step.
The step of applying the second bipolar gradient magnetic field pulse between the high frequency pulse and the gradient echo measurement, and the second bipolar gradient magnetic field pulse may have a gradient magnetic field strength or a pulse width of zero. An inspection method using nuclear magnetic resonance. 3. The inspection method using nuclear magnetic resonance according to claim 2, wherein the first slice selective gradient magnetic field is applied to the inspection object while selectively acting on spins of a specific slice plane. The first high frequency pulse is applied to excite a part of the nuclear magnetization (hereinafter, nuclear magnetization-1), and the first bipolar gradient magnetic field is applied to the nuclear magnetization depending on the degree of the diffusion phenomenon. 1 is then attenuated, and then a second high-frequency pulse that selectively acts on a specific slice plane is applied while applying a second slice-selective gradient magnetic field, and the nuclear magnetization-
1 part (hereinafter, nuclear magnetization-3) is inverted, and at the same time, part of the nuclear magnetization that is not excited by the first high frequency pulse (hereinafter, nuclear magnetization-2) is excited, The nuclear magnetization-2 and the nuclear magnetization-3 are attenuated according to the degree of the diffusion phenomenon by applying a polar gradient magnetic field, and the encoding gradient magnetic field is applied by changing the intensity or the application time each time to apply the encoding magnetic field-2 and the nuclear magnetization. Changing the phase of the chemical formula-3, detecting the gradient echo of the nuclear magnetization-2 as the first signal while applying the readout gradient magnetic field, and performing a Fourier transform process to obtain a first image, and Detecting a spin echo of the nuclear magnetization-3 as a second signal while applying a read-out gradient magnetic field, and performing a Fourier transform process to obtain a second image,
The inspection method using nuclear magnetic resonance wherein the bipolar gradient magnetic field pulse 2 can have a gradient magnetic field strength or a pulse width of zero. 4. The inspection method using nuclear magnetic resonance according to claim 3, wherein at least one pulse of the first high-frequency pulse or the second high-frequency pulse has a flip angle of 0.
An inspection method using nuclear magnetic resonance, which is not a multiple of 90 ° or 90 °. 5. The inspection method using nuclear magnetic resonance according to claim 3, wherein the first bipolar gradient magnetic field pulse and the second bipolar gradient magnetic field pulse are products of pulse width and absolute value of intensity. Is composed of a combination of two gradient magnetic field pulses having the same polarity but different polarities, an inspection method using nuclear magnetic resonance. 6. An inspection method using nuclear magnetic resonance according to claim 1, wherein a first step of measuring a gradient echo generated by the first high frequency pulse and a spin generated by the first and second high frequency pulses. A second step of measuring an echo, the first step including a step of applying a first bipolar gradient magnetic field pulse during the measurement of the first high frequency pulse and the gradient echo; The step of applying the first bipolar gradient magnetic field pulse between the first and second high frequency pulses, and the second bipolar gradient between the measurement of the second high frequency pulse and the spin echo. A nuclear magnetic resonance method characterized in that the first bipolar gradient magnetic field pulse includes a step of applying a magnetic field pulse, and the gradient magnetic field strength or pulse width can be zero. Inspection method was used. 7. The inspection method using nuclear magnetic resonance according to claim 6, wherein the first slice selective gradient magnetic field is applied to the inspection object while selectively acting on spins in a specific slice plane. A first high-frequency pulse is applied to excite a part of the nuclear magnetization (hereinafter, nuclear magnetization-1), and a first encoding gradient magnetic field is applied while changing the intensity or the application time each time, so that the nuclear magnetization-1 The phase is changed, the first bipolar gradient magnetic field is applied to attenuate the nuclear magnetization -1 according to the degree of the diffusion phenomenon, and the first readout gradient magnetic field is applied to apply the nuclear magnetization -1 of the nuclear magnetization -1. Gradient echo first
And a second image which is selectively applied to a specific slice plane while applying a second slice selection gradient magnetic field. A high frequency pulse is applied to invert a part of the nuclear magnetization-1 (hereinafter, nuclear magnetization-4), and the second bipolar gradient magnetic field is applied to the nuclear magnetization-4 depending on the degree of diffusion phenomenon. Is detected, the spin echo of the nuclear magnetization-4 is detected as a second signal while applying a second readout gradient magnetic field, and a second image is obtained by performing a Fourier transform process. The inspection method using nuclear magnetic resonance, wherein the first bipolar gradient magnetic field pulse can have a gradient magnetic field strength or a pulse width of zero. 8. The inspection method using nuclear magnetic resonance according to claim 7, wherein the flip angle of the first high-frequency pulse is 90 °.
Alternatively, an inspection method using nuclear magnetic resonance, which is an odd multiple thereof. 9. The inspection method using nuclear magnetic resonance according to claim 7, wherein the flip angle of the second high-frequency pulse is 180.
An inspection method using nuclear magnetic resonance, which is characterized in that it is ° or an odd multiple thereof. 10. The inspection method using nuclear magnetic resonance according to claim 7, wherein the first bipolar gradient magnetic field pulse and the second bipolar gradient magnetic field pulse are products of a pulse width and an absolute value of intensity. Is composed of a combination of two gradient magnetic field pulses having the same polarity but different polarities, an inspection method using nuclear magnetic resonance. 11. An inspection method using nuclear magnetic resonance according to claim 1, wherein a first step of measuring a first gradient echo generated by the first high frequency pulse and a second step of generating the second high frequency pulse. And a second step of measuring a second gradient echo, the first step applying a first bipolar gradient magnetic field pulse during the measurement of the first high frequency pulse and the first gradient echo. The second step includes a step of applying a second bipolar gradient magnetic field pulse during the measurement of the second high frequency pulse and the second gradient echo, and the first bipolar gradient magnetic field pulse Alternatively, the magnetic field intensity of the second bipolar gradient magnetic field pulse can be zero or the pulse width can be zero. Method. 12. The inspection method using nuclear magnetic resonance according to claim 11, wherein the diffusion coefficient of the inspection target is obtained from the first gradient echo and the second gradient echo. Inspection method using. 13. The inspection method using nuclear magnetic resonance according to claim 11, wherein a first slice selective gradient magnetic field is applied to the inspection object while selectively acting on spins of a specific slice plane. A high frequency pulse of 1 is applied to excite a part of the nuclear magnetization (hereinafter, nuclear magnetization-1), and the first encoding gradient magnetic field is applied while changing the intensity or the application time each time, and the phase of the nuclear magnetization-1. And a first bipolar gradient magnetic field is applied to vary the nuclear magnetization depending on the degree of the diffusion phenomenon.
1 is attenuated, a radial echo of nuclear magnetization-1 is detected as a first signal while applying a first readout gradient magnetic field, and a Fourier transform process is performed to obtain a first image. A part of nuclear magnetization not excited by the first high-frequency pulse by applying a second high-frequency pulse that selectively acts on a specific slice plane while applying a second slice-selective gradient magnetic field (hereinafter , Nuclear magnetization-5)
Are excited and a second bipolar gradient magnetic field is applied to attenuate the nuclear magnetization-5 according to the degree of the diffusion phenomenon.
The gradient echo of the nuclear magnetization-5 is detected as the second signal while applying the read-out gradient magnetic field, and a second image is obtained by performing a Fourier transform process. The first bipolar gradient magnetic field The inspection method using nuclear magnetic resonance, wherein the pulse or the second bipolar gradient magnetic field pulse can have a gradient magnetic field strength or a pulse width of zero. 14. The inspection method using nuclear magnetic resonance according to claim 11 or 13, wherein the product of the absolute value of the pulse width and intensity of the first bipolar gradient magnetic field pulse is the second value. An inspection method using nuclear magnetic resonance characterized in that the product of the absolute value of the pulse width and the intensity of the bipolar gradient magnetic field pulse is not equal. 15. The inspection method using nuclear magnetic resonance according to claim 13, wherein at least one pulse of the first high-frequency pulse or the second high-frequency pulse has a flip angle of 0.
An inspection method using nuclear magnetic resonance, which is not a multiple of 90 ° or 90 °. 16. The inspection method using nuclear magnetic resonance according to claim 13, wherein the first bipolar gradient magnetic field pulse and the second bipolar gradient magnetic field pulse are products of pulse width and absolute value of intensity. Is composed of a combination of two gradient magnetic field pulses having the same polarity but different polarities, an inspection method using nuclear magnetic resonance. 17. The inspection method using nuclear magnetic resonance according to claim 13, wherein a step of obtaining a first image is performed between the step of obtaining the first image and the step of obtaining the second image. An inspection method using nuclear magnetic resonance comprising a step of applying a gradient magnetic field pulse for saturating the nuclear magnetization excited by. 18. The inspection method using nuclear magnetic resonance according to claim 13, wherein when the number of times of integration is a multiple of 4, the first method is used.
In the step of obtaining the image, the transmission phase and the reception phase of the first high-frequency pulse are set to 0 °, and in the step of obtaining the second image, the transmission phase and the reception phase of the second high-frequency pulse are integrated by the integration. An inspection method using nuclear magnetic resonance, characterized in that the inspection method is changed by 90 ° according to the number of times. 19. The examination method using nuclear magnetic resonance according to claim 13, wherein the gradient magnetic field of the bipolar gradient magnetic field pulse is included in the step of obtaining the first image and the step of obtaining the second image. In the step of high intensity, the flip angle of the high frequency pulse is set to a value close to 90 °, and in the step of low gradient magnetic field intensity of the bipolar gradient magnetic field pulse, the flip angle of the high frequency pulse is set to a value close to 0 °. An inspection method using nuclear magnetic resonance. 20. The inspection method using nuclear magnetic resonance according to claim 1, 2, or 6, wherein a diffusion coefficient of an inspection target is obtained from the spin echo and the gradient echo. An inspection method using nuclear magnetic resonance. 21. An inspection method using nuclear magnetic resonance according to any one of claims 3, 7, and 13, wherein the inspection object is examined from the first image and the second image. An inspection method using nuclear magnetic resonance, characterized by obtaining a diffusion coefficient distribution. 22. An inspection method using nuclear magnetic resonance for measuring diffusion coefficient distribution using two nuclear magnetic resonance images,
Prior to the measurement of the diffusion coefficient distribution, the intensity ratio of two signals obtained without applying the encode gradient magnetic field and the gradient magnetic field pulse for enhancing the diffusion phenomenon in the measuring method for obtaining the two nuclear magnetic resonance images is used. , The difference in signal intensity due to factors other than the gradient magnetic field pulse that emphasizes the diffusion phenomenon in the two nuclear magnetic resonance images is corrected, and the corrected 2
An inspection method using nuclear magnetic resonance, characterized in that a diffusion coefficient distribution is obtained by using one nuclear magnetic resonance image.