JPS63143050A - Method for calculating chemical shift spectrum - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

[Detailed Description of the Invention] [Field of Application in Children's Business] This invention relates to magnetic resonance (N
MR) This relates to a method for determining a chemical shift spectrum.

[Prior Art] Figure 3 is a waveform diagram showing a conventional method for obtaining a chemical shift spectrum, as disclosed in, for example, Japanese Patent Application Laid-Open No. 61-35339. The gradient magnetic field and the radio frequency magnetic field pulse applied to , @ is the received magnetic resonance signal.

FIG. 4 and FIG. 5 are explanatory diagrams each explaining the conventional method of obtaining a chemical shift spectrum, and (6) is an explanatory diagram for explaining the conventional method of obtaining a chemical shift spectrum.
(60) indicates the sensitivity region of the surface coil (6), and the inside of this dotted line is the surface coil (6). 6) is an area that can be received.

Now start the pulse sequence shown in FIG.

When a high frequency magnetic field pulse (c) is applied from a large transmitting coil (not shown) under a gradient magnetic field Gxm (the x direction is taken in the depth direction as shown in Fig. 4), the fourth Only the spins of the slice within the dotted line indicated by the arrow (62) in the figure are excited. On the other hand, the sensitivity area of the surface coil (6) is shown by the dotted line (60), and the arrow (62)
The common area between the dotted line (60) and the dotted line (60) will be received as a magnetic resonance signal (a). The SN ratio of the received signal is improved by repeating reception at Tr intervals and adding the average. Note that in order to acquire a magnetic resonance signal from a slice at a different position, the carrier frequency of the high-frequency magnetic field Q1) may be changed by Δf, as is known. As a result, as shown in FIG. 5, by installing the surface coil (6) on the surface of the subject (to), it is possible to obtain magnetic resonance signals having resolution in the depth direction within the selected volume.

For example, if the applied static magnetic field strength is 1.5T (Tesla),
By selecting the carrier frequency of the high-frequency magnetic field to be approximately 25 MHg, the magnetic resonance signal of phosphorus can be measured, and by Fourier transform processing, a chemical shift spectrum of phosphorus with depth resolution can be obtained.

For example, in FIG. 5, the area sliced in the depth direction (61a
), (61b), (61c), (6xa), (exe
) and (axf) spectra can be obtained separately.

[Problem that the invention seeks to solve]

The conventional method of reducing the chemical shift spectrum is as described above, but as shown in Figure 3, the problem is that the delay time T from exciting the locus-frequency magnetic field pulse until signal acquisition is long. there were. This is because the application time of the gradient magnetic field ω and the high-frequency magnetic field pulse Q1) is relatively long.

For example, under the application of the first gradient magnetic field GK, the pulse width of the applied high-frequency magnetic field pulse Qυ could not be made less than 1 m5ec.

As a result, the influence of relaxation time could not be ignored, and waveform distortion of the chemical shift spectrum became a problem.

This invention was made to solve the above-mentioned problems, and aims to provide a method for obtaining an accurate chemical shift spectrum that is less affected by relaxation time.

[Failure to solve the problem]

The method for obtaining a chemical spectrum according to the present invention includes: a first step of applying a static magnetic field to a subject; a second step of temporarily applying a high-frequency magnetic field pulse that excites the subject;
After completion of the second step, a third step of temporarily applying a first gradient magnetic field tilted in a first direction passing through at least the specific volume portion of the subject, a fourth step of receiving a magnetic resonance signal, and a fourth step of receiving a magnetic resonance signal; The first step is to change the magnetic field strength.
A fifth step of repeating the steps from step to fourth step, and a sixth step of Fourier transforming the magnetic resonance signal with respect to at least the first gradient magnetic field strength and time.

[Effect]

The method of obtaining a chemical shift spectrum in this invention is to measure the specimen using a high-frequency magnetic field pulse with a predetermined frequency proportional to the static magnetic field, whereas conventional methods change the frequency and separately acquire spectra in the depth direction. The whole section is excited, and the phase is modulated by the first gradient magnetic field G to separately obtain, for example, a spectrum in the depth direction.

Therefore, the method according to the present invention is completely different from the conventional method.In the method of the present invention, the high frequency magnetic field pulse and the gradient magnetic field are narrower than the conventional method. is obtained, and as a result, the delay time can be shortened and the influence of relaxation time is reduced.

〔Example〕

An embodiment of the present invention will be described below with reference to the drawings. Fig. 1 is a block diagram showing an apparatus for obtaining a chemical shift spectrum according to an embodiment of the present invention.

The above device is Medical Informatics Vol. 5 No. 3 P, 241-P, 252
(1985). In the figure, (1) is a magnet that generates a static magnetic field (strength BO), (2) is a sequence control device,
(3) supplies sequence data to the sequence controller @ (2) and also supplies the sequence controller [! a computer that inputs and processes the received signal input via f t2);
4) is a high frequency transmitter that transmits high frequency waves according to the modulation signal from the sequence control device @ (2); (5) is a transmitting coil that is driven by the high frequency transmitter (4) and outputs a predetermined high frequency magnetic field; (6) is a reception surface coil 1) which receives a magnetic resonance signal (reception signal) from the subject (to).

Surface coil (6) installed on the surface of the subject as a receiving coil
), it is possible to localize the measurement area of the object and improve reception sensitivity. (7) is a high frequency receiver that outputs the received signal from the surface coil (6) to the sequence control device (2). (8) is a gradient magnetic field power supply, and the first direction (X), the second direction (G), and the third direction (Z), which are orthogonal to each other, correspond to the first direction (X), the second direction (G), and the third direction (Z). Second and third gradient magnetic field power supplies (
It consists of 8a), (8b), and (sc). (9) is a gradient magnetic field coil that is driven by the gradient magnetic field power supply (8) and generates a gradient magnetic field as appropriate in the +T*z direction.

The controller is a console for inputting desired data to the computer (3), and qυ is a high frequency transmitter (4) and transmitting coil (5).
(6) is an impedance matching device inserted between the surface coil (6) and the high frequency receiver (7).

The device in the above embodiment includes a magnet (1), a transmitting coil (
5) Insert a human body (to be tested) into the receiving coil (6) and gradient magnetic field coil (9), apply a static magnetic field and a gradient magnetic field to the subject Q3, and generate nuclear spins inside the subject. Appropriately apply a high-frequency magnetic field pulse (hereinafter referred to as high-frequency pulse) to defeat 900 and receive the desired magnetic signal. It has an opening diameter of 60 to 100 am.

In addition, the sequence control device (2) irradiates high-frequency pulses to a subject such as a human body, performs sampling and averaging of received signals emitted from the subject, controls gradient magnetic fields, etc. Since the device (2) is programmable, the measurement sequences of these received signals can be arbitrarily recombined. Usually, this measurement sequence is assembled in the computer (3) and sent as data to the sequence control device f (2). Sequence control device (2
) decodes this data or command and transmits it to the high frequency transmitter (4).
It outputs necessary signals to the gradient magnetic field power source (8) and samples the received signal, that is, the NMR signal input from the subject (to) via the receiving coil (6). Therefore, during measurement of the received signal, the computer (3) can operate completely independently.

The high frequency transmitter (4) power amplifies the oscillator output that oscillates at the resonant frequency according to the modulation signal from the sequence control device (2) after 7th harmonic, and sends it to the transmitting coil (5) via the impedance matching device αυ. send. On the other hand, the receiving coil (6
), the received signal obtained from the impedance matching filter (2
) is input to the high frequency receiver 5 (7). When acquiring local high-resolution chemical shift spectra using this cross-coil method where transmission and reception are performed using separate coils (5) and (6), the above-mentioned surface coil (small loop coil) is used as the receiving coil. use

In the high frequency receptiongg (7), a phase sensitive detector (Phase 5 sensitive detector) is used.
), the received signal is quadrature-phase detected, and two signals with a bandwidth of about 1 KHz are sent to the sequence controller (2).
After being sent to , it is converted into digital gold by an AD converter. In the frequency band handled by the high frequency system, the magnetic field strength is 1. !
In the case of phosphorus at 5T (Tesla), it is 25MHz. Furthermore, a 12 to 15 bit AD converter is used.

Next, a method for obtaining a chemical shift spectrum using the apparatus having the above configuration will be explained.

FIG. 2 is a waveform chart showing a method for obtaining a chemical shift spectrum according to one embodiment of the present invention.

As the receiving coil, a surface coil (6) is used as in FIG. 4, but its sensitivity region is a region up to a depth of approximately A, where A is the diameter of the coil.

′First, a high-frequency pulse 0]) is temporarily applied under the application of a static magnetic field. This pulse 6υ uses an approximate 9d:l pulse (square wave) to maximize the signal strength. At this time, since no gradient magnetic field is applied, the spins of the entire human head are uniformly excited, for example in FIG. 4. Next, brush 1 direction (X
A first gradient magnetic field pulse Gx (7) tilted in the direction: axial direction passing through the center of the surface coil, ie depth direction) is applied, after which a magnetic resonance signal (2) is received. The above process is 0
8. Repeat by changing the intensity arithmetic to obtain N signals. If this is s(t, ox), then 8(t+Gx)=fp(ω,x)e""e"fox("
)"°"dωSe Now, let Gx(τ)dτ=Gxt0 (integration is performed for the application time of the GX pulse.

)s(t, Gx)=fp(ω,x)ej(″””ra”
"1lkclse Therefore, s(t,k)=Afp(ωrx>e""+k")thing・t
m ・Song (1) However, A: constant, k==γG, t
.

Here, ρ(ωSX) represents the chemical shift spectral density of the spin at the coordinate X.

From equation (1), ρ(ωoz)=Js(t,k)e−'(= +kx)d
Get tIdk.

That is, by two-dimensional Fourier transformation of S(t+k), the depth
The chemical shift spectrum ρ(ω, x) at is determined.

That is, spectra can be obtained separately in the depth direction.

For example, in FIG. 5, spins within the sensitivity region of the surface coil are received, and spectra of regions (61a) to (61f) are separately acquired.

In the case of the above embodiment, the high-frequency pulse c (p) and the gradient magnetic field pulse (1) may have a narrower pulse width than the conventional one. For example, the high-frequency pulse G can acquire a signal in about 0.1 m5 ec, and as a result, the delay time can be greatly shortened, and the waveform distortion of the chemical shift spectrum is reduced compared to the conventional method.

In the above embodiment, a circular loop surface coil is used, but the receiving coil may be a coil having another shape, such as a rectangular rectangular coil, a square coil, or an IJ round gap type coil.

In addition, the first gradient magnetic field pulse in the X direction was applied in order to decompose the chemical shift spectrum only in the first direction (X direction), but in the second direction (y direction) and the third direction (both directions are the same). The spectrum can be further resolved in the second or third direction by simultaneously applying gradient magnetic field pulses that are tilted in at least one of the two directions and repeatedly changing them arithmetic. That is, "(t
*')x tGy *Gt)=fffl'("I"
171 z)'3 ”te jγQx+kawa o, 0y for 1
゛Y°t.

Use the fact that the song is "d (a'm'd7") in e jr' z.

In this case, by using a surface coil that is long in the y direction and short in the Separated spectra can also be obtained.

That is, in the two directions, the sensitivity area is narrowed in advance using surface coils.

〔Effect of the invention〕

As described above, according to the present invention, the first step is to apply a static magnetic field to the subject, the second step is to temporarily apply a high frequency magnetic field pulse to excite the subject, and after the second step, at least the subject is The first through a specific volume of the sample.
a third step of temporarily applying a first gradient magnetic field tilted in the direction; a fourth step of receiving a magnetic resonance signal; and a fifth step of repeating the first to fourth steps by changing at least the first gradient magnetic field strength. The chemical shift spectrum was obtained by subjecting the magnetic resonance signal to at least the first strong gradient magnetic field Ei and the 2@6 steps of Fourier transform, so the delay time was shortened and the influence of the relaxation time was reduced. This has the effect of accurately obtaining a spatially resolved chemical shift spectrum.

[Brief explanation of the drawing]

FIG. 1 is a block configuration diagram showing an apparatus for determining a chemical shift spectrum according to an embodiment of the present invention, FIG. 2 is a waveform diagram showing a method for determining a chemical shift spectrum according to an embodiment of Jin's invention, and FIG. The figure is a waveform diagram illustrating a conventional method for determining a chemical shift spectrum, and the numbered diagram and FIG. 5 are explanatory diagrams each illustrating a conventional method for determining a chemical shift spectrum. (1)...Magnet, (2)...Sequence control device,
(31...computer, (4)...high frequency receiver, (5
)...Transmission coil, (6)...Surface coil, (7)
... High frequency receiver, (8) ... Gradient magnetic field power supply, (9
)...Gradient magnetic field coil, (c)...Test, (@)
...Specific volume part. In addition, in the figures, the same symbols indicate the same or corresponding parts.

Claims (9)

[Claims] (1) A first step of applying a static magnetic field to the subject; a second step of temporarily applying a high-frequency magnetic field pulse that excites the subject; after the second step, the field passes through at least a specific volume of the subject; A third step of temporarily applying a first gradient magnetic field tilted in the first direction, a fourth step of receiving a magnetic resonance signal, and repeating the first to fourth steps by changing at least the first gradient magnetic field strength. Fifth
and a sixth step of Fourier transforming the magnetic resonance signal with respect to at least the first gradient magnetic field strength and time. (2) The chemical composition according to claim 1, wherein in the fourth step, the magnetic resonance signal is received by a surface coil having a plane substantially parallel to a plane forming a specific volume of the subject. How to find the shift spectrum. (3) The surface coil is approximately circular, and the specific volume to be determined is located at a distance from the plane of the surface coil to the distance of the diameter of the surface coil, and the center is located at the center of the surface coil. A method for determining a chemical shift spectrum according to claim 2, which lies on a line passing through the line. (4) The method for determining a chemical shift spectrum according to claim 2 or 3, wherein the first gradient magnetic field is applied in an axial direction passing through the center of the surface coil. (5) In the third step, the second direction is perpendicular to the first direction.
The method for determining a chemical shift spectrum according to any one of claims 1 to 4, wherein a second gradient magnetic field that is tilted in a direction is applied and the intensity of the second gradient magnetic field is changed in the fifth step. (6) The shape of the surface coil plane is long in the second direction and short in the third direction perpendicular to the first and second directions, according to any one of claims 1 to 5. How to find the chemical shift spectrum of. (7) In the third step, a third gradient magnetic field tilted in a third direction perpendicular to the first direction and the second direction is applied, and a fifth gradient magnetic field is applied.
The method for determining a chemical shift spectrum according to any one of claims 1 to 5, wherein the third gradient magnetic field strength is changed in steps. (8) The high frequency magnetic field pulse in the second step is an approximate 90° pulse.
A method for determining a chemical shift spectrum as described in any of the paragraphs. (9) The method for determining a chemical shift spectrum according to claim 8, wherein the high-frequency magnetic field pulse in the second step is an approximate 90° square wave pulse.