JP3161752B2 - Magnetic resonance diagnostic equipment - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for realizing a pre-processing function for automatically adjusting the applied intensity of a high-frequency magnetic field in a magnetic resonance diagnostic apparatus before imaging.

[0002]

2. Description of the Related Art The prior art closest to the present invention is an automatic adjustment method of a high-frequency magnetic field intensity adopted by our company. The applied intensity of the high-frequency magnetic field is adjusted so that the obtained signal is maximized. In the conventional method, the signal intensity is measured by changing the applied intensity in the minimum step desired to be set, and the corresponding data of the applied intensity and the signal amount within a predetermined range is obtained. Find a large applied intensity. However, since the measured data contains errors due to various factors, even if the measurement is performed in the minimum steps that require the setting, if the curve is clearly a quadratic function curve centered on the maximum signal amount May be bumpy. Therefore, a method of performing least square fitting with a quadratic function to search for a place where the signal amount should be maximum has been adopted.

However there is a problem that error becomes larger when shortening the repetition time T _R to take measurements and subsequent measurement of such a scheme.

[0004] Other conventional techniques for adjusting the applied strength of a high-frequency magnetic field are discussed, for example, in NMR Medicine, VOL7 (1987) P70, Abstracts of 9th Annual Meeting of the Magnetic Resonance Medical Society of Japan. In this method, a method is devised for obtaining signal data capable of accurately adjusting the applied intensity. There are two issues that need to be mentioned. The first point is that data having a large number of echoes is easier to adjust the change of the signal amount with respect to the applied intensity than data of the signal amount of the normal first echo. The second issue is
Measurement time interval T _R when measuring the signal amount for each applied intensity
In order to solve the problem that the measurement must be performed with a sufficiently long T _R in order to perform accurate adjustment because the applied intensity at which the signal amount becomes the maximum differs depending on the signal amount, the T _This is to propose a method in which the applied intensity at which the signal amount is maximized does not change even if _R is shortened.
A specific method is to change the applied intensity of the 180 ° pulse without changing the applied intensity of the 90 ° pulse in the high frequency magnetic field used. However, although not mentioned in the above document, this method is based on the premise that the applied intensity of the 90 ° pulse is accurately determined in advance. It seems that there is a problem of starting from the beginning. Moreover, applying the intensity of even a 90-degree pulse is believed that the problem that error becomes larger remains at still shorter T _R by nonuniform magnetic resonance even if it is set correctly.

[0005]

In the above prior art, when the repetition time T _R is shortened to shorten the measurement time, the error increases, and the applied intensity of the high frequency magnetic field cannot be adjusted with sufficient accuracy. was there.

An object of the present invention is to provide a method for stably adjusting the applied intensity of a high-frequency magnetic field with sufficient accuracy in a short measurement time.

[0007]

In order to achieve the above object, the number of measurement data is reduced and the applied intensity at which the signal amount increases is estimated. Also, in order to perform stable and accurate estimation even with a relatively short T _R , the first
The estimation is calculated based on the ratio between the signal amounts of the echo and the second echo.

[0008]

[Action] Reducing the number of measurement data, shorten the measurement time as a whole, taking data at the same tooth measurement time interval T _R is made. Further, T when _R a shorter signal of the first echo and the second echo are both smaller becomes yet applied intensity becomes the maximum signal amount changes toward lower both applied strength. However, the ratio between the signal amounts of the first echo and the second echo is T
Since canceling the impact _{of R} is shortened, application intensity ratio of the signal amount is maximum T _R is changed even shorter small. Therefore, the error is reduced due to the effect of T _R by estimating the applied intensity based on the ratio of signal amount.

[0009]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The configuration of a magnetic resonance diagnostic apparatus embodying the present invention will be described below with reference to FIG.

The inspection object 201 is a static magnetic field generator 202.
Is placed in a static magnetic field. Various operations for obtaining a tomogram of the inspection target 201 are performed by the sequence control device 206. The sequence control device 206 includes a gradient magnetic field generator 203, a high-frequency magnetic field generator 204, and the receiver 20.
5 is controlled. Here, the gradient magnetic field generator 203 causes a difference in the magnetic field depending on the location of the inspection target 201, and the high-frequency magnetic field generator 204 has a purpose of changing the direction of the magnetization oscillating at a frequency within a certain range in the inspection target 201. I am carrying it. Further, the receiving device 205 measures the electromagnetic waves emitted by the magnetization in the inspection target 201, and passes the measurement data to the processing device 207. The processing device 207 stores the measurement data, processes the data, and displays the result on the display device 208.

The present invention relates to a method for adjusting the applied intensity of the high-frequency magnetic field generated by the high-frequency magnetic field generator 204 in the magnetic resonance diagnostic apparatus having the above configuration. The general flow in the embodiment of the present invention will be described below together with the equipment used at that time.

First, the test object 201 is put into a magnetic resonance diagnostic apparatus. Based on a sequence describing the operation of each device for application adjustment, the sequence controller 206 issues a command to each device to operate it. In the first measurement, the high-frequency magnetic field generator 204 is operated with a preset applied intensity, and at the same time, the gradient magnetic field generator 204 is operated based on a signal measurement sequence, and an echo signal generated from the test object 201 is received by the receiver 207. To detect. The obtained signal data is sent to the processing device 207. After waiting a predetermined time interval T _R, then the echo signal in the same manner by changing the applied intensity preset step measured signaling data to the processing unit 207. The processing device 207 compares the measured data with the previous measurement data to determine the applied strength of the gradient magnetic field used for the next measurement, and passes the value to the sequence control device 206. Measuring the echo signals after waiting a predetermined time interval T _R as well. When the processing device 207 determines that the necessary data has been collected, the data measurement ends. Next, the processing device 207 estimates the applied intensity of the high-frequency magnetic field at which the signal amount becomes maximum based on the measured data. Based on the estimated value, an applied intensity serving as a reference for the high-frequency magnetic field is determined. When actually photographing the inspection target 201, the applied strength of the high-frequency magnetic field may be changed depending on various setting conditions for photographing. In this case, a value obtained by multiplying a reference applied intensity by a coefficient determined by imaging conditions is set as an applied intensity of a high-frequency magnetic field used for actual imaging.

The above is the general flow of the present invention.
In detail, what kind of sequence for adjusting the applied intensity, what kind of data is obtained, what kind of calculation is performed from the obtained data to determine the reference applied intensity, data to be measured The following describes the order in which the measurement is performed to reduce the number of.

The sequence for adjusting the applied intensity and the data obtained will be described below with reference to FIG.

FIG. 3 is a sequence diagram showing at what timing each device of the magnetic resonance diagnostic apparatus operates. The horizontal axis represents time, and the vertical axis represents the operating state of each device. RF 304 is a high-frequency magnetic field generator 204
X307, y30
6, z305 are gradient magnetic fields of the respective channels generated by the gradient magnetic field generator 203. A / D 308 represents receiving device 205. The FID signal 309 is a signal generated from the inspection target 201 and generates a first echo 310 and a second echo 311 as shown in FIG. When an echo is generated, the gate of the A / D 308 is turned on, and measurement is started. The data obtained is
This is signal data of the first echo 310 and the second echo 311. The echo signal is a signal having a peak value at the center, and only the peak value has significance in the subsequent processing. Therefore, the peak value of the echo signal is simply referred to as a signal amount. Signal amount is depends on the repetition time T _R of the case of measuring the applied intensity and repeated signal of a high frequency magnetic field.

In the measurement, the signal intensity of the first echo and the second echo is measured by changing the applied intensity of the high frequency magnetic field until necessary data is obtained. The high frequency magnetic field used in the sequence includes a 90 ° pulse 301 and a first 180 ° pulse 302.
And the second 180 ° pulse 303. 90 ° pulse 30
The waveforms of the 1 and 180 ° pulses are different. The waveform and intensity of the first 180 ° pulse 302 and the second 180 ° pulse 303 are the same. The high-frequency magnetic field to be changed for each measurement includes a first 180 ° pulse 302 and a second 180 ° pulse 30
3 must be changed at the same ratio, and the 90 ° pulse may be changed at the same ratio as the 180 ° pulse or may not be changed, so long as either is determined.

The corresponding data of the thus applied intensity obtained by the first echo signal of the corresponding data, and applying strength and signal of the second echo is dependent on the repetition time T _R. The amount required for subsequent calculations are balanced amount corresponding to the applied intensity independently of the possible T _R. Therefore, attention is paid to the ratio of the signal amounts of the first echo and the second echo, that is, (signal amount of the second echo) / (signal amount of the first echo). Data of the ratio of the applied intensity and the signal amount is to some extent canceled the effect of T _R, the error is small. Therefore, in the present embodiment, it is assumed that data of interest is data corresponding to the applied intensity and the signal amount ratio.
It should be noted that attention may be paid to other data. For example, the third echo even after measured, can either take the signal amount ratio of the n echo and the m echo, it is also possible to focus on only the signal of the n-th echo taking sufficiently long T _R.

Next, a calculation method for obtaining a reference applied intensity from the corresponding data of the applied intensity and the signal amount ratio will be described with reference to FIG.

The horizontal axis in FIG. 1 represents the applied intensity, and the vertical axis represents the signal amount ratio. The dashed line indicates the correspondence 108 that is not measured but should be the original, and the circled points represent the measured points.
The applied intensity at the peak point 106 which should be originally is the applied intensity 109 which should be originally obtained. Since the number of measurement points is small, it is not possible to accurately determine the originally required applied intensity 109, but it is possible to obtain an applied intensity close to that by the following method. Necessary measurement data are only three points: point A 101, point B 102, and point C 103. A point 101 is the maximum point among the measurement points. Values on both sides of point B 102, point C 103 and point A 101. The value at point B is lower than the value at point C 103. A straight line 107 connecting the points A and B is taken, and a point on the straight line is a point 104 having the same signal amount ratio as the point C 103.
Ask for. E point 1 which is the middle point between C point 103 and D point 104
05 is requested. The applied intensity 110 at the point E is close to the originally required applied intensity 109. By the above method, the applied strength of point E is 110
Is calculated, and it is set as an applied intensity which is a reference of the high-frequency magnetic field.

However, when the values on both sides of the point A are the same, it is assumed that the applied intensity at the point A is the reference applied intensity. Further, when there are two points where the signal ratio becomes maximum, it is assumed that the applied intensity at the midpoint is the reference applied intensity.

The method of estimating the reference applied intensity from the corresponding data of the applied intensity and the signal amount ratio is not limited to the above-described embodiment. Can be obtained by performing the same operation as above, or can be obtained by performing least square fitting with a quadratic function using all the obtained data, and includes the maximum value of the signal amount among the obtained data. It can also be obtained by fitting a quadratic function from three points.

Next, the order of data measurement to minimize the number of data measurement points will be described.

In the present embodiment, the data necessary for calculating the applied intensity as a reference for the high-frequency magnetic field from the corresponding data of the applied intensity and the signal ratio were three points centered on the maximum value in the data. In the special case where there are two maximum values, only those two points are sufficient. Therefore, it is possible to measure data while searching for necessary data, and to terminate the data measurement when searching is completed, so that data can be measured in such an order as to shorten the measurement time as a whole. The procedure will be described below with reference to the flowcharts of FIGS.

I in FIGS. 4 and 5 represents the applied intensity of the high-frequency magnetic field, and the subscript numbers represent the order. F (I) indicates the signal amount ratio at the applied intensity I.

_First , in step 401, the applied intensity is set to an initial value I1, and a signal is measured. In step 402, the next applied intensity I ₂ is set to a value increased by step S, and a signal is measured. In step 403, the signal quantity F when the applied intensity signal amount when the I ₂ F (I ₂₎ and the applied intensity I ₁ (I ₁₎
Is compared. When F (I ₂ ) and F (I ₁ ) are equal, the measurement is stopped. If F (I ₂ ) is larger than F (I ₁ ), the process proceeds to step 404, and the parameter n for counting the order is set to 3.

In step 405, the n-th applied intensity is set to n-
The signal is measured with the first applied intensity increased by step S. In step 406, the n-th signal amount F
(I _n ) is compared with the ( _n−1 ) -th signal amount F (I _n−1 ). F
If (I _n ) is less than or _equal to F (I _n-1 ), stop the measurement. If F (I _n ) is larger than F (I _n-1 ), the process proceeds to step 407, in which the count parameter n representing the order is increased by one, the process returns to step 405, and the measurement is continued until the condition of step 406 is satisfied.

If F (I ₂ ) is smaller than F (I ₁ ) in step 403, the process proceeds to step 501, where the third applied intensity I
_{3 is set} to an applied intensity reduced by the step S from the _first applied intensity I1. In step 502, the third signal amount F
(I ₃ ) is compared with the _first signal amount F (I ₁ ). F (I ₃ )
Is smaller than or equal to F (I ₁ ), the measurement is completed. If F (I ₃ ) is larger than F (I ₁ ), step 503 is executed.
To set the count parameter n representing the order to 4.
The n-th applied intensity I _n at step 504 from the (n-1) th applied intensity I _n-1 to the applied intensity reduced by a step S. In step 505, F (I _n ) is compared with F (I _n-1 ). When F (I _n ) is equal to or smaller than F (I _n-1 ), the measurement is stopped. When F (I _n ) is larger than F (I _n-1 ),
Proceeding to step 506, the count parameter n representing the order is incremented by one, and returning to step 504, step 50
The measurement is continued until the condition of 5 is satisfied.

As described above, there is a method of taking data to reduce the number of data points. However, since data is originally taken in large steps, if there is no concern about an increase in the number of data points, a certain range can be determined. The method of taking all the data of the given score may be used.

[0029]

According to the present invention, stable data can be obtained even if the repetition time T _R , which is a time interval for taking data point by point, is reduced to some extent, and the number of data points to be measured is reduced. Therefore, even if the measurement time as a whole is reduced, it is possible to stably adjust the applied intensity of the high-frequency magnetic field with sufficient accuracy.

[Brief description of the drawings]

FIG. 1 is a diagram showing a correspondence relationship between an applied intensity of a high-frequency magnetic field and a signal amount ratio in an embodiment of the present invention.

FIG. 2 is a configuration diagram of a magnetic resonance diagnostic apparatus.

FIG. 3 is a measurement sequence diagram used for adjusting an applied intensity.

FIG. 4 is a first half of a flowchart for changing the measurement order and reducing the number of measurement points.

FIG. 5 is a latter half of the above flowchart.

────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Yuji Enomoto 882 Ma, Katsuta-shi, Ibaraki Pref. Hitachi Measurement Engineering Co., Ltd. (56) References JP-A-3-57980 (JP, A) JP-A-63 -296738 (JP, A) Table 1-503361 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) A61B 5/055 JICST file (JOIS)

Claims (7)

(57) [Claims] 1. A high-frequency magnetic field having a predetermined applied intensity is marked on an object.
In addition, from the object to the applied high-frequency magnetic field
Diagnosis of the target object is possible by measuring the signal amount of
The magnetic resonance imaging apparatus that ability, high frequency magnetic field generator for applying a plurality of application intensity to the object
Means and a signal amount for each of the plurality of applied intensities applied
And the corresponding relationship between the applied intensity and the signal amount.
Calculating a plurality of corresponding data items, and calculating the calculated plurality of pairs.
From the response data, a first response data in which the signal amount indicates the maximum value.
Data, the second corresponding data having an applied intensity adjacent to the first corresponding data.
And the first corresponding data and the applied intensity
Adjacent third signal having a larger signal amount than the second corresponding data
Means for selecting the corresponding data, and the first corresponding data and
And the third correspondence data from the second correspondence data
The fourth corresponding data having the same signal amount as the signal amount of
Means for calculating, and the applied intensity of the fourth correspondence data
And the average of the applied intensities of the third corresponding data
Calculated as the reference applied intensity, which is the basis for adjusting the applied force.
Processing means comprising: means for applying to the object based on the calculated reference application intensity.
Control means for adjusting the applied intensity to be applied.
Magnetic resonance diagnostic device. 2. The magnetic resonance diagnostic apparatus according to claim 1,
The reference applied intensity is the applied intensity of the first corresponding data.
And the applied intensity of the third correspondence data.
A magnetic resonance diagnostic apparatus characterized by the above-mentioned. 3. The magnetic resonance diagnostic apparatus according to claim 1, wherein
The processing means comprises an X-axis indicating the applied intensity and a Y-axis indicating the signal amount.
The point indicated by the first corresponding data on the graph
On the straight line connecting the points indicated by the second correspondence data,
The fourth correspondence data is calculated so that there is a point to be executed.
Magnetic resonance imaging apparatus you wherein a. 4. The magnetic recording medium according to claim 1, wherein
In the sound diagnostic device, the processing device is configured to transmit corresponding data that maximizes the signal amount.
If there are two, the two
It is characterized by calculating the average value of the applied intensity of the corresponding data of
Magnetic resonance diagnostic apparatus. 5. The magnetic recording medium according to claim 1, wherein
In the sound diagnostic apparatus, the high-frequency magnetic field generating means may include the plurality of applied intensities, (1) when applying the plurality of applied intensities to the object,
(2) The signal amount measured by the sequentially applied applied intensity is increased.
The applied intensity of the last applied applied intensity
Applied until the signal value is lower than
Magnetic resonance diagnostic apparatus. 6. A magnetic recording medium according to claim 1, wherein
In the sound diagnostic device, the high-frequency magnetic field generators have different numbers of echoes.
A plurality of applied intensities corresponding to the first echo and the second echo
Applied to the object, and the receiving means applies the plurality of applied intensities to each of the plurality of applied intensities.
On the other hand, the first signal amount corresponding to the first echo and
Receiving a second signal quantity corresponding to the second echo, wherein the processing means comprises: the first signal quantity and the second signal quantity;
Calculate the signal amount ratio indicating the ratio of the applied intensity and the
Data indicating the corresponding relationship of the signal amount ratios
Characterized by calculating a plurality of data as corresponding data
Resonance diagnostic device. 7. A high-frequency magnetic field having a predetermined applied intensity is marked on an object.
In addition, from the object to the applied high-frequency magnetic field
Diagnosis of the target object is possible by measuring the signal amount of
A first echo and a second echo having different numbers of echoes , respectively.
High frequency multiple application strength degree is applied to the object in accordance with the
Magnetic field generating means, and for each of the plurality of applied strengths,
The first signal amount corresponding to one echo and the second echo
Receiving means for receiving a corresponding second signal amount, and a signal amount indicating a ratio of the first signal amount and the second signal amount
Calculate the ratio, and apply each of the applied intensity and the signal amount ratio.
A plurality of corresponding data indicating the corresponding relationship is calculated and calculated.
For adjusting the applied intensity based on multiple sets of corresponding data
Processing means for calculating a reference applied intensity to be applied to the object based on the calculated reference applied intensity.
Control means for adjusting the applied intensity to be applied.
Magnetic resonance diagnostic equipment.