JPH0316854B2 - - Google Patents

Description

Detailed Description of the Invention (Field of Industrial Application) The present invention relates to a nuclear magnetic resonance imaging device (hereinafter referred to as NMR), and particularly relates to a nuclear magnetic resonance imaging device (hereinafter referred to as NMR), and in _particular ,
This invention relates to improvements in means for obtaining calculation images of T ₂ and proton density ρ.

(Prior art) Longitudinal relaxation time T ₁ , which is considered to be medically useful, has been measured from images measured by NMR imaging devices.
There is a technique to obtain an image related to the value (T ₁ image) and an image related to the transverse relaxation time T ₂ value (T ₂ image).

(Problems to be Solved by the Invention) However, the T ₁ image and the T ₂ image have been obtained using different methods as follows.

For example, the T ₁ image is calculated as follows. Inversion recovery method (hereinafter abbreviated as IR method) as shown in Figure 9
The IRSE method, which is a combination of the
The saturation recovery method (Saturation
One original image is obtained using the SRSE method, which is a combination of Recovery (hereinafter abbreviated as SR method) and SE method, and calculations are performed using these two images and an approximation formula for signal strength.

As shown in Figure 10, the SRSE method is a pulse sequence in which an echo signal is obtained by applying a 90° pulse and then a 180° pulse, and the time from the 90° pulse to the center of the echo signal is Ts, 90°. The time from pulse application to application of a 90° pulse in the next view is defined as Tr.

In addition, the IRSE method has a 10th phase as shown in Figure 9.
This is a pulse sequence in which a 180° pulse for inversion recovery is applied before each 90° pulse in the SRSE method shown in the figure. The time Td, the time from the 90° pulse to the center of the echo signal Ts, the inversion
The time from application of a 180° pulse for recovery to application of a 180° pulse for the next view is defined as Tr.

The theoretical formula for signal strength in the _SRSE method is I _SR = Io・exp(−Ts/T ₂ ) {1−2・exp(−Tr/T ₁
+Ts/2T ₁ )+exp(-Tr/T ₁ )} Also, the theoretical formula I for signal strength in the IRSE method is I _IR = Io・exp(-Ts/T ₂ ){1-2・exp(-Td/ T ₁
)+2・exp(−Tr/T ₁ +Ts/2T ₁ )−exp(−Tr/T ₁ )}.

For this theoretical formula, here, as Tr≫T ₁ ,
If exp(−Tr/T ₁ )=0, I _SR ≒Io・exp(−Ts/T ₂ ) I _IR ≒Io・exp(−Ts/T ₂ ) {1−2・exp(−Td/ T ₁
)} Therefore, I _IR /I _SR =1-2·exp(-Td/T ₁ ) T ₁ =Td/ln {2I _SR /(I _SR −I _IR )} The T ₁ value is determined from this formula.

When obtaining a T ₂ image, for example, multiple echoes can be obtained using the CPMG method described on pages 570 to 576 of the June 1984 issue of the publication "Image Information (M)" (Vol. 16 No. 11). T ₁ and ρ are removed from the data and the T ₂ value is determined by the least squares method.

In addition, in the CP method, which allows multiple echo data to be taken out continuously in one data collection to obtain the _T2 value, if the length of the applied pulse is incomplete, the error will increase as the echoes are acquired. However, the pulse sequence called CPMG method solved this problem by applying a ₁₈₀ ° pulse after a 90° pulse as shown in Figure 7. n
This is a pulse sequence that is applied repeatedly to generate n echoes.

Conventional methods using such techniques have the following drawbacks.

(1) The T ₁ image and the T ₂ image are obtained separately, and the calculation images of T ₁ , T ₂ , and ρ cannot be obtained at the same time.

(2) Exact values cannot be determined because approximate formulas are used.

(3) Due to the condition of Tr≫T ₁ , Tr must be made long, and the total scan time is long.

(4) The scan parameters of the original image are not optimized, and the best calculated image cannot be found under the given conditions.

(5) There is a systematic error due to the influence of the slice shape.

(6) There is a systematic error due to pulse error.

In view of these points, an object of the present invention is to provide NMR imaging in which highly accurate T ₁ , T ₂ , and ρ calculation images can be obtained simultaneously from a plurality of original images obtained in a short time using an NMR imaging device. The goal is to provide equipment.

(Means for solving the problem) In order to achieve such an objective, the present invention devises a new pulse sequence for computational images in a nuclear magnetic resonance imaging device, and combines the IRnSE method and SRmSE method.
_IRnSE method and _SRmSE
Each scan parameter in the method is characterized in that it is selected so that the evaluation function of the T ₁ , T ₂ , and ρ calculation images in the range of interest is the best.

(Example) The present invention will be explained in detail below using the drawings. FIG. 1 is a diagram showing the configuration of essential parts of an embodiment of an NMR imaging device according to the present invention. In the figure, 1 is a magnet assembly, inside which a space (hole) is provided for inserting an object, and a main magnet that surrounds this space and applies a uniform static magnetic field Ho to the object. a magnetic field coil 2, and a gradient magnetic field coil 3 for generating a gradient magnetic field (consisting of an x gradient magnetic field coil, a y gradient magnetic field coil, and a z gradient magnetic field coil configured to be able to individually generate gradient magnetic fields) ), an RF transmitting coil 4 that provides a high-frequency pulse to excite the spins of atomic nuclei within the object, a receiving coil 5 that detects NMR signals from the object, and the like are arranged.

The main magnetic field coil is connected to the static magnetic field control circuit 15, Gx,
Gy, Gz each gradient magnetic field coil is gradient magnetic field control circuit 1
4, the RF transmitting coil is connected to the power amplifier 18, and the NMR signal receiving coil is connected to the preamplifier 19.
are connected to each other.

13 is a controller that controls the sequence of generation of gradient magnetic fields and high-frequency magnetic fields.
Performs necessary control to capture the NMR signal into the waveform memory 21.

17 is a gate modulation circuit, and 16 is a high frequency oscillator that generates a high frequency signal. Gate modulation circuit 17
appropriately modulates the high frequency signal output from the high frequency oscillator 16 using a control signal from the controller 13 to generate a high frequency pulse with a predetermined phase. This high frequency pulse is applied to the RF transmitting coil 4 through the RF power amplifier 18.

19 is a preamplifier that amplifies the NMR signal obtained from the detection coil 5; 20 is a phase circuit that phase-detects the NMR signal by referring to the output signal of the high-frequency oscillator; and 21 is a waveform that stores the phase-detected waveform signal from the preamplifier. A memory that includes an A/D converter.

11 is a computer that receives the signal from the waveform memory 21 and performs predetermined signal processing to obtain a tomographic image;
12 is a display device such as a television monitor that displays the obtained tomographic image.

Reference numeral 30 denotes an operation console, which is connected to the computer 11 and is input means for inputting various information necessary for this apparatus.

Next, the procedure for creating a calculated image in such a configuration will be explained.

Here, three images obtained using the IR3SE method,
From a total of 7 images, 4 images obtained using the SR4SE method,
A case where T ₁ , T ₂ , and ρ images are post-calculated will be explained as an example.

In addition, the IR3SE method, as shown in Figure 2,
This is a pulse sequence similar to the IRSE method, but in one view, a 180° ₍₂₎ pulse is repeatedly applied three times to obtain three echo signals. The FR4SE method is similar to the SR4SE method, as shown in Figure 3, and is a multi-echo method in which 180° ₍₂₎ pulses are applied four times to obtain four echo signals per view. .

(1) Pulse Sequence The pulse sequences shown in FIGS. 2 and 3 will be explained in more detail as follows.

Interval T _s1 between the 90° pulse and the center of the first echo signal, T _s2 between the centers of each echo signal after the first echo signal, interval Td between the 180° ₍₁₎ pulse and the 90° pulse, repeat time Each Tr can be selected arbitrarily.

These time managements are performed by the controller 13, and the time settings can be performed using the console 30.

180° ₍₁₎ pulse is a 180° pulse for spin reversal,
180° ₍₂₎ is a 180° pulse for spin echo, and both are 90° _-45 to reduce pulse error.
Composite pulses of 270° _-45 and 90° _-45 are used.

The number of 180° pulses for each view is determined by the IR3SE method.
Both SR4SE methods have even numbers.

Note that the suffix value attached to the frequency of the composite pulse represents the phase difference with the 90° excitation pulse, and these pulses are non-selective pulses.

The excitation 90° pulse is a selection pulse and is Gaussian modulated.

Application of such a 90° pulse to a 180° pulse is performed as follows. That is, under the control of the controller 13, the gate modulation circuit 1
A predetermined 90° pulse or 180° pulse signal obtained through 7 is applied to the RF transmitting coil 4 via the power amplifier 18 to generate an RF magnetic field to be applied to the object.

On the other hand, the gradient magnetic field is as follows.
The gradient magnetic field Gx in the x direction is a projection gradient, and a is a spoiler for eliminating noise outside the slice plane due to the 180° pulse.

The z-direction gradient magnetic field Gz is a slice gradient, the y-direction gradient magnetic field Gy is a warp gradient, and b is a spoiler for eliminating artifacts due to 180° pulse errors. Further, c is a spoiler for removing correlation between views.

Application of each gradient magnetic field is controlled by a controller 13.

Each echo signal generated by the above pulse sequence is detected by the receiving coil 5.
The spin echo signal detected by the receiving coil is
The signal is stored in a waveform memory 21 via a preamplifier 19 and a phase detection circuit 20.

(2) Regarding the signal strength formula The signal strength formula for the IR3SE method is Io=C _IR3 (T ₁ /Tr) [1-2exp (-Td/T ₁ ) + 2exp
(-Tr/T ₁ +Ts ₁ /T ₁ +3Ts ₂ /2T ₁ ) -2exp (-Tr/T ₁ +Ts ₁ /T ₁ +Ts ₂ /2T ₁ ) +2exp
(−Tr/T ₁ +Ts ₁ /2T ₁ ) −exp(−Tr/T ₁ )]・ρ, the first echo is Io・exp(−Ts ₁ /T ₂ ) and the second echo is Io・exp (−Ts ₁ /T ₂ −Ts ₂ /T ₂ ) The third echo is Io·exp(−Ts ₁ /T ₂ −2Ts ₂ /T ₂ ).

The signal strength formula for the SR4SE method is Io=C _SR4 (T ₁ /Tr)・[1−2exp(−Tr/T ₁ +Ts ₁
/T ₁ +5s ₂ /2T ₁ ) +2exp(-Tr/T ₁ +Ts ₁ /T ₁ +3Ts ₂ /2T ₁ )-2exp(-Tr/T ₁ +Ts ₁
/T ₁ +Ts ₂ /2T ₁ ) +2exp(-Tr/T ₁ +Ts ₁ +2T ₁ )-exp(-Tr/T ₁
)]・ρ, the first echo is Io・exp(−Ts ₁ /T ₂ ), the second echo is Io・exp(−Ts ₁ /T ₂ −Ts ₂ /T ₂ ), and the third echo is Io・exp(−Ts ₁ /T ₂ −2Ts ₂ /T ₂ ) The fourth echo is Io・exp(−Ts ₁ /T ₂ −3Ts ₂ /T ₂ ).

Here, C _IR3 and C _SR4 are functions representing the influence of the slice shape, and are determined as follows.

The signal strength formula that does not include the effect of slice shape is
Let Fn(Tr, Ts, T ₁ , T ₂ , ρ).

(b) When the angle at which the magnetization falls due to a 90° pulse is α°, the signal strength is equal to the pulse sequence of 1.
If it is composed of 90° pulses and an odd number of 180° pulses, sind/1 + COSα・exp(−Tr/T ₁ )・Fn
(Tr, Ts, T ₁ , T ₂ , ρ)…(1).

(b) If a Gaussian 90° pulse is used,
α at a point at distance Z from the center of the slice is α=(π/2)exp(−Z ² ) (2).

(c) By integrating equation (1) with respect to Z using equation (2), the signal strength including the influence of the slice shape can be found,
The following formula is obtained.

Fn(Tr, Ts, T ₁ , T ₂ , ρ)∫Sin{(π/
2) exp(−Z ² )}/1+COS {(π/2) exp(−Z ² )
}exp(−Tr/T ₁ )dZ...(3) Since the integral of equation (3) is a function only of (T ₁ /Tr), this value is written as Codd(T ₁ /Tr).

(d) Since Codd is a function only of T ₁ /Tr, Codd can be found by numerical integration within the necessary range of T ₁ /Tr, and from this value Codd can be found as a polynomial of T ₁ /Tr.

From the above, the signal strength equation Fs (Tr, Ts, T ₁ , T ₂ , ρ) including the influence of slice shape is Fn
and Codd, a coefficient representing the influence of slice shape.
It is found as the product of

Fs(Tr, Ts, T ₁ , T ₂ , ρ) = Fn(Tr, Ts, T ₁
, T ₂ , ρ) Codd (T ₁ /Tr) where Codd is, for example, 0.2<T ₁ /Tr<
In the case of 10.0, Codd=8.1537E−6(T ₁ /Tr) ⁶ −2.95086E−4(T ₁ /Tr) ⁵ −4.27675E−3(T ₁ /Tr) ⁴ −3.17902E−2(T ₁ /Tr) ³ +1.29262E-1 (T ₁ /Tr) ² -2.8554E-1 (T ₁ /Tr) +1.0557 Pulse sequence consists of one 90° pulse and an even number of 180° pulses In this case, if the signal strength formula that does not include the influence of the slice shape is Fn, the signal strength when the angle at which the magnetization falls is α° is Sinα/1−COSα・exp(−Tr/T ₁ )・Fn...(4), which can be calculated in the same way as the above case.

For example, if we use a Gaussian 90° pulse,
When 0.2<T ₁ /T ₂ <10.0, the coefficient Ceven representing the influence of slice shape is Ceven=−2.4203E−5(T ₁ /Tr) ⁵ +5.6861E−4(T ₁ /Tr) ⁴ −3.6523E− 3(T ₁ /Tr) ³ −1.0071E−2(T ₁ /Tr) ² +3.2162E−1(T ₁ /Tr) +0.9178.

By using the signal strength equation that includes the influence of the slice shape determined here, systematic errors due to the slice shape can be removed.

The above is a calculation using a Gaussian 90° pulse, but even if other 90° pulses are used, if the angle α at which the magnetization falls due to the 90° pulse at a point at a distance Z from the center of the slice is found, the same calculation can be performed. Can calculate.

(3) Regarding systematic errors due to 90° pulse error When a 90° pulse becomes a β° pulse due to RF pulse non-uniformity, etc., the obtained signal strength can be calculated using equation (1) or ( It can be found by integrating equation 4) with respect to Z using equation (5).

α＝β・exp(−Z ² ) …(5) If the coefficient representing this influence is C〓, then Codd,
Similar to Cever, C〓 is a function only of (T ₁ /Tr), and its shape is determined by the evenness of the number of 180° pulses.

The 180° pulse numbers of IR3SE and SR4SE are both numbers, so if the Tr is made equal, the C of IR3SE and SR4SE is
matches. Therefore, the effect of 90° pulse error is multiplied by C〓 for all images,
The only effect on the calculated values of T ₁ , T ₂ and ρ is that C〓 is applied to the ρ value.

From the above, if the transistors of IR3SE and SR4SE are made equal, systematic errors due to 90° pulse errors in T ₁ and T ₂ values can be removed.

Other effects of making Tr equal are as follows. The coefficient Ceven, which represents the influence of slice shape, is also the same between IR3SE and SR4SE, so
Systematic errors due to slice shape are still reflected in the ρ value.
It only takes Ceven. Therefore, if it is not necessary to accurately determine the ρ value, a normal signal strength equation that does not include the influence of the slice shape may be used. It is also effective when the slice shape is unknown.

(4) Optimization of scan parameters The scan parameters that provide the best evaluation functions for T ₁ , T ₂ , and ρ calculated images of the human body are calculated using the law of error propagation. The signal strength formula (2) above is used as the signal strength formula.

Here, the theoretical formula for signal strength and the required T ₁ ,
A method for determining scan parameters that optimize the evaluation function of a calculated image from T ₂ and ρ values will be explained. Here, the sum of standard deviations normalized as an evaluation function, that is, σ _T1 /T ₁ +σ _T2 /T ₂ +σ〓/ρ, where σ _T1 , σ _T2 , σ〓 are the standard deviations of T ₁ , T ₂ , ρ Use.

The scan parameters of the seven images are 〓 ₁ , 〓
₂ , ..., 〓 ₇ , If the signal strength formula is F ₁ , F ₂ ...F ₇ , then T ₁ calculated from the image by the least squares method,
The covariance matrix V _T1T2 〓 of the values of T ₂ and ρ is V _T1T2 , 〓 = (A ^T V ^-1 ₁₂₃ A) ^-1 However, V ₁₂₃ is the covariance matrix of the original image, and the variance σ ² of the original image is , average value n, sampling time
As Ta, it is expressed as σ ² ∝n ^-1 Ta ^-1 , and A
teeth, becomes.

Therefore, the variance of the values of T ₁ , T ₂ , and ρ is
V _T1T2 is found as the diagonal element of 〓.

From the above, the evaluation functions of the calculated image are 〓 ₁ , 〓 ₂ ,
..., 〓 ₇ , Ta ₁ , Ta ₂ , ..., Ta ₇ , n ₁ , n ₂ , ...,
It is found as a function of n ₇ .

Based on this principle, appropriate scan parameters are determined by the following procedure.

Define the theoretical formula for signal strength.

Based on the theoretical formula, the range of T ₁ , T ₂ , and ρ to be measured, and the variance of the original image, the evaluation function of the calculated image is determined as a function of the scan parameter.

In the above, since the evaluation function of the calculated image has been determined as a multivariable function of the scan parameters, the scan parameters that give the best evaluation function are determined by a method (such as the simplex method) that finds the extreme values of the multivariable function.

An example of the scan parameters obtained in this manner is as follows. Note that the Tr in the IR3SE method and the SR4SE method is made equal.

When scanning with a total scan time of 600 seconds, in the IR3SE method, Tr = 2.36 seconds Td = 0.579 seconds Ts ₁ = 0.02 seconds Ts ₂ = 0.02 seconds Average number of times (AVE) = 1 In the SR4SE method, Tr = 2.36 seconds Tr ₁ = 0.02 seconds Ts ₂ = 0.079 seconds Average number of scans (AVE) = 1 In addition, when scanning in 300 seconds, the total scan time is Tr = 1.18 seconds Td = 0.414 seconds Ts ₁ = 0.02 seconds Ts ₂ = 0.02 seconds Average number of times (AVE) = 1 In the SR4SE method, Tr = 1.18 seconds Ts ₁ = 0.02 seconds Ts ₂ = 0.074 seconds Average number of times (AVE) = 1 (5) Imaging is performed using the scan parameters in (4) above. That is, in the IR3SE method, echo signals are measured by scanning with the above parameters over predetermined views (the number of views is, for example, 127) that are different from each other of the warp gradient (gradient magnetic field Gy). The measured echo signals are divided into first, second, and third echo signal groups, and each is reconstructed into two-dimensional images using the computer 11 to obtain three original images.

Next, in the SR4SE method, scanning is performed using the above parameters over predetermined views (the number of views is 127, for example) that differ from each other in the warp gradient (gradient magnetic field Gy), and echo signals are similarly measured and stored in the waveform memory 21. The obtained data is divided into first, second, third and fourth echo signal groups and similarly reconstructed into two-dimensional images using the computer 11 to obtain four original images.

(6) Using the seven original images obtained in (5) above, calculate T ₁ , T ₂ , and ρ images (calculated images) using the nonlinear least squares method.
(obtained by calculation on the computer 11).

In the above method, the gradient magnetic fields Gx, Gy, Gz
The relationship between slice, projection, and warp is arbitrary.

By the above procedure, calculation images of T ₁ , T ₂ , and ρ can be obtained accurately and simultaneously.

Figures 4 to 6 show solid line results using a phantom in which a NiCl ₂ aqueous solution and heavy water were appropriately mixed. Values determined by analytical methods (measured T ₁ ,
T ₂ , ρ) and the value calculated from the calculated image (calculated
T ₁ , T ₂ , ρ) agreed within the measurement error, demonstrating highly accurate calculation.

(Other Examples) Note that the present invention is not limited to the above-mentioned embodiments, but can be implemented as follows.

(1) As a pulse sequence, in the example, the interval from the 90° pulse to the first echo signal is Ts ₁ ,
The interval between each echo signal after the first echo signal was defined as Ts ₂ , which is defined as the interval from the 90° pulse to the first echo signal,
The interval from the first echo signal to the second echo signal is Ts ₁ , the interval from the second echo signal to the third echo signal, and the interval from the third echo signal to the fourth echo signal.
The interval to the echo signal is Ts ₂ , the interval from the (2n-2)th echo signal to the (2n-1)th echo signal, and the interval from the (2n-1)th echo signal to the 2nth echo signal ( However, n≧
Let 3) be Tsn. In this case, the 180° pulse error can be removed by using an even number of echoes.

Furthermore, the interval between each echo signal may be completely arbitrary.

(2) 90° pulse with Gaussian modulation, composite
The 180° pulse is not limited to the embodiment, and other 90° pulses and 180° pulses may be used, and calculated images can be obtained in the same way.

(3) In the example, seven images were obtained from imaging using the IR3SE method and the SR4SE method, and based on these, T ₁ , T ₂ ,
Although we have shown the case where each calculation image of ρ is obtained, the method is not limited to this, and in general, the IRnSE method and
(n+m) images may be obtained from imaging using the SRmSE method, and each calculation image of T ₁ , T ₂ , and ρ may be obtained based on these images.

(Effects of the Invention) As explained above, the present invention has the following effects.

Since no approximation formula is used, accurate values can be obtained.

By using the scan parameter that minimizes the variance of the calculated image, the best calculated image can be found in a predetermined imaging time.

By combining the IRnSE method and the SRmSE method and making the number of 180° pulses an even number, the standard deviation of the calculated image can be reduced. Figure 7 shows
The figure shows the sum of normalized standard deviations at representative points of the human body's T ₁ and T ₂ values for various pulse sequence combinations. As is clear from this graph, both the IRnSE method and the SRmSE method
It can be seen that when the number of 180° pulses is even, the standard deviation is small. In other words, it can be seen that the IR3SE method and SR4SE method are better than the IR4SE method and SR4SE method.

Since multi-echo is used, the number of images used for calculation can be increased without increasing the imaging time. As a result, high-quality calculated images can be obtained in a short imaging time. As seen in Figure 7, the imaging time for the combination of the IR3SE and SR4SE methods is half the time of the black dots, but the imaging time for the combination of the SRSEE and SR2SE methods and the IRSE and SR2SE methods It can be seen that the sum of normalized standard deviations is smaller than in the case of the combination with , and a high-quality calculated image can be obtained.

By using multi-echo, T ₁ , T ₂
The dispersion can be reduced over a wide range of .
FIG. 8 is a diagram showing the sum of normalized standard deviations for T ₁ and T ₂ values.

By making the evenness of the 180° pulse numbers and Tr equal in the IRnSE method and the SRmSE method, systematic errors in the T ₁ and T ₂ values due to the 90° pulse error can be removed.

Systematic errors due to the slice shape can be removed by using a signal strength equation that includes the influence of the slice shape.

Composite pulse to 180° ₍₂₎ pulse
By using 90° _-45 270° ₄₅ and 90° _-45 and setting the interval between each echo signal so that two adjacent echo signals are equal, the 180° pulse error is removed with an even echo signal. be able to.

[Brief explanation of the drawing]

Fig. 1 is a diagram showing the main part configuration of an embodiment of the NMR imaging device according to the present invention, Fig. 2 is a diagram showing a pulse sequence of the IR3SE method, Fig. 3 is a diagram showing a pulse sequence of the SR4SE method, and Fig. 4 is a diagram showing a pulse sequence of the SR4SE method. Figures to Figure 6 are
Regarding the values of T ₁ , T ₂ , and ρ, the values determined by the analytical method and the values determined by the calculated image according to the present invention are _compared . , a diagram showing the sum of normalized standard deviations at representative points of T ₂ values. Figure 8 shows T ₁ , in various pulse sequence combinations.
Figures 9 to 11, which relate to the sum of normalized standard deviations for _T2 values, are diagrams showing examples of conventional pulse sequences. DESCRIPTION OF SYMBOLS 1... Magnet assembly, 2... Main magnetic field coil, 3... Gradient magnetic field coil, 4... RF transmitting coil, 5... Receiving coil, 11... Computer, 12... Display, 13... Controller ,1
4... Gradient magnetic field control circuit, 15... Static magnetic field control circuit, 16... High frequency oscillator, 17... Gate modulation circuit, 18... Power amplifier, 19... Preamplifier, 20... Phase detection circuit, 21... Waveform memory, 30...operation console.

Claims (1)

[Scope of Claims] 1. A nuclear magnetic resonance imaging apparatus that applies high-frequency pulses and a magnetic field to an object to generate nuclear magnetic resonance signals, and uses these signals to obtain an image of the tissue of the object, comprising the following steps: Time (T ₁ , T ₂ ) or proton density (ρ)
1. A nuclear magnetic resonance imaging apparatus characterized by comprising a control/calculation means having the following functions (a) to (c) for obtaining a calculated image regarding at least one of the following: Note (a) IRnSE method (n is an integer) that provides the best evaluation function for T ₁ , T ₂ , and ρ calculation images in the range of interest.
The scan parameters of the SRmSE method (m is an integer) are determined by the following procedure. Define the theoretical formula for signal strength. Based on the theoretical formula, the range of T ₁ , T ₂ , and ρ to be measured and the variance of the original image, the evaluation function of the calculated image is determined as a multivariable function of the scan parameter. Using a method for finding the extrema of a multivariate function, scan parameters are found for which the evaluation function obtained in the above process is the best. (b) Imaging is performed using the scan parameters determined in (b) above using a pulse sequence using the IRnSE method and the SRmSE method. (c) Calculate T ₁ , T ₂ , and ρ images from (n+m) images obtained from imaging using the IRnSE method and the SRmSE method. 2. The control/calculation means uses the IRnSE method and
2. The nuclear magnetic resonance imaging apparatus according to claim 1, wherein the 180° pulse is applied an even number of times in a pulse sequence in both the SRmSE method and the SRmSE method. 3. The control/calculation means uses the IRnSE method and
In both SRmSE methods, the number of 180° pulses is made equal in the pulse sequence, and the repetition time Tr of both is made equal.
2. The nuclear magnetic resonance imaging apparatus according to claim 1, further comprising a function of controlling the values to be equal. 4 The control/calculation means uses the IR3SE method and the SR4SE method.
2. The nuclear magnetic resonance imaging apparatus according to claim 1, wherein the nuclear magnetic resonance imaging apparatus is configured to perform imaging using a method to obtain seven images, and calculate T ₁ , T ₂ , and ρ images from these seven images. 5 The control/calculation means uses the IR3SE method and the SR4SE method.
According to claim 1, the system is configured such that seven images are obtained by imaging according to the method, and T ₁ , T ₂ , and ρ images are calculated from these seven images, and the following values are used as scan parameters. The nuclear magnetic resonance imaging device described. Note: In the IR3SE method, the time T _r from the first 180° pulse application to the next 180° pulse application is 2.36 seconds, and the time T _d from the first 180° pulse application to the next 90° pulse application is 0.58 seconds. seconds, the time T _s1 from the application of the 90° pulse to the center of the first echo signal generated thereafter is 0.02
seconds, the time from the center of the first echo signal to the center of the second echo signal, and from the center of the second echo signal to the center of the third echo signal, respectively.
Scan a predetermined number of views with T _s2 set to 0.02 seconds. In the SR4SE method, the time T _r from the first 90° pulse application to the first 90° pulse application of the next view is 2.36 seconds, and the time T r from the first 90° pulse application to the center of the first echo signal generated thereafter is 2.36 seconds. time T _s1
Scanning is performed for a predetermined number of views, with the time interval T _s2 between the centers of each echo signal after the first echo signal being 0.079 seconds. The seven images to be obtained are obtained by averaging the IR3SE method and the SR4SE method in a 1:1 ratio. 6 The control/calculation means uses the IR3SE method and the SR4SE method.
According to claim 1, the system is configured such that seven images are obtained by imaging according to the method, and T ₁ , T ₂ , and ρ images are calculated from these seven images, and the following values are used as scan parameters. The nuclear magnetic resonance imaging device described. Note: In the IR3SE method, the time T _r from the first 180° pulse application to the next 180° pulse application is 1.18 seconds, and the time T _d from the first 180° pulse application to the next 90° pulse application is 0.41 seconds. seconds, the time T _s1 from the application of the 90° pulse to the center of the first echo signal generated thereafter is 0.02
seconds, the time from the center of the first echo signal to the center of the second echo signal, and from the center of the second echo signal to the center of the third echo signal, respectively.
Scan a predetermined number of views with T _s2 set to 0.02 seconds. In the SR4SE method, the time T _r from the first 90° pulse application to the first 90° pulse application of the next view is 1.18 seconds, and the time T r from the first 90° pulse application to the center of the first echo signal generated thereafter is 1.18 seconds. time T _s1
0.02 seconds, and the time interval T _s2 between the centers of each echo signal after the first echo signal is 0.074 seconds, and a predetermined number of views are scanned. The seven images to be obtained are obtained by averaging the IR3SE method and the SR4SE method in a 1:1 ratio.