JPH05115453A - Magnetic resonance spectroscopy system - Google Patents

Abstract

PURPOSE:To execute a chemical shift measurement with high accuracy by collecting MRSI data related to a proton of the same matrix as MRSI of other nuclides such as 31P, 19F, 13C, etc., detecting a peak of water existing in large quantities in a living body, and utilizing it as an internal standard of a chemical shift. CONSTITUTION:A pulse sequence of a magnetic resonance spectroscopic imaging (MRSI) method based on a spin echo obtained by combining one-dimensional slice face selection and two-dimensional phase encoding is executed by a sequencer 11 to obtain spectrum data of a proton in each voxel. Subsequently, by executing a prescribed pulse sequence, MRSI data of 31P is obtained. Next, by a computer system 12, deviation data of static magnetic field intensity from scheduled static magnetic field intensity in each voxel is calculated from a water peak frequency in a spectrum of each voxel, and based thereon, a shift of a chemical shift is corrected with respect to the MRSI data of each voxel.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION The present invention relates to magnetic resonance (MR: magn).
The present invention relates to a magnetic resonance spectroscopy apparatus that obtains an MR spectrum as functional information of a living body by utilizing the phenomenon of etic resonance).

[0002]

2. Description of the Related Art As a technique for utilizing the magnetic resonance phenomenon, there is a magnetic resonance spectroscopy apparatus for obtaining functional information of a living body.

In this type of apparatus, particularly when MRSI (MR spectroscopic imaging) method is used to obtain spectra from a plurality of voxels of a subject at the same time, a static magnetic field deviation (predetermined intensity of static magnetic field strength) in the imaging region is obtained. Deviation), the peak position of the spectrum of each voxel deviates from the axis of chemical shift for each voxel. FIG. 8 shows a case where the head is an imaging target. For example, in MRSI for ³¹ P in which the peak position of PCr is conventionally set to 0 ppm, the peak position is different for each voxel. ing.

Since the peak position of the spectrum is different for each voxel described above, the operator is required to use a substance as a reference for chemical shift for each voxel (as described above, ³¹
In MRSI for P, it is customarily PCr. ) 0pp on the axis of chemical shift at the peak position
m must be set.

In addition to the above-mentioned setting of the chemical shift axis by the operator, as shown in FIG. 8, a sample of an external standard substance (for example, in the case of ³¹ P, HMPT (hexamethyl p
(hosphoroustriamide) etc. may be photographed at the same time and the spectrum may be used as a reference. But with this method,
If there is a static magnetic field deviation between the place where the sample of the external standard substance is placed and the region of interest of the living body, there is a problem that an accurate chemical shift cannot be measured.

[0006]

As described above, the method using an external standard substance sample is effective only when there is no inhomogeneity of the static magnetic field, and such a condition can be satisfied by ordinary large-diameter magnetic resonance. It is impossible and unrealistic with a device.

Further, for example, in the case where there is always a large peak of PCr, such as a normal muscle spectrum of ³¹ P, the operator can set the position of 0 ppm for each voxel as described above. Since the peak of PCr cannot be measured in the liver, this method cannot be applied.
Also in the brain and the like, the tumor part generally has a low density of phosphatized parts and may have a poor S / N, and thus it can be said that it is not practical. Furthermore, in the case of an in vitro analytical spectrometer, a reference substance may be mixed in a sample, but such a thing cannot be done in a living body, which is not practical. Then, the objective of this invention is providing the magnetic resonance spectroscopy apparatus which can perform a chemical shift measurement with high precision.

[0008]

In order to solve the above-mentioned problems and to achieve the object, the present invention has the following means. That is, the invention according to claim 1 is a data collecting means for obtaining a data group for generating an MR spectroscopic image of hydrogen nuclei existing in a specific region of a subject,

Calculation means for calculating deviation data of the static magnetic field strength in each voxel from the expected static magnetic field strength from the water peak frequency in the spectrum of each voxel defined for the specific region, and each voxel based on the deviation data of each voxel. A magnetic resonance spectroscopy apparatus including: a correction unit that corrects a shift of a chemical shift with respect to the MR spectrum data.

According to a second aspect of the invention, in the apparatus according to the first aspect, a holding means for holding in advance the chemical shift data and the frequency data of the specific compound is provided, and the chemical shift image of the specific compound is provided. It is characterized by automatically creating.

[0011]

According to the inventions of claims 1 and 2, ³¹ P,
MRSI data on protons in the same matrix as MRSI of other nuclides such as ¹⁹ F and ¹³ C are collected, a large amount of water peaks existing in the living body are detected, and this is used as an internal standard for chemical shift. Therefore, the axis of the chemical shift can be accurately set even when there is inhomogeneity in the static magnetic field or when it is difficult to recognize the peak of the substance to be used as a reference.

[0012]

DESCRIPTION OF THE PREFERRED EMBODIMENTS A magnetic resonance imaging apparatus according to the present invention will be described below with reference to the drawings. That is, as shown in FIG. 1, the apparatus is a permanent magnet, a normal conducting magnet, or a superconducting magnet, or a combination thereof, as a magnet assembly capable of accommodating a subject P therein. 1. A static magnetic field magnet (a static magnetic field correcting shim coil may be added) 1 and X, Y, Z axes for generating a gradient magnetic field for providing position information of a magnetic resonance signal inducing portion. Of the gradient magnetic field generating coil 2 and the magnetic resonance signal (MR
It has a gantry 4 which is internally provided with an RF coil 3 which is a transmission / reception system for detecting a signal), for example, a transmission coil and a reception coil. Also, a surface coil or the like used for local high-sensitivity reception is provided as necessary. In the subject introducing space of the gantry 4, the coil 1,
A magnetic field for generating a magnetic resonance phenomenon is generated by 2 and 3. In addition, a bed 5 for advancing / retreating inside the gantry 4 is installed in the vicinity of the gantry 4 while the subject P is placed thereon.

On the other hand, the present apparatus includes a transmitter 6 for controlling RF pulse transmission and a receiver 7 for controlling induction MR signal reception.
Are provided, which provide a transmission signal to the RF coil 3 and collect the induced MR signal.

Further, the present apparatus includes gradient magnetic field power supplies 8, 9 and 10 for controlling respective excitations of the X, Y and Z axis gradient magnetic field generating coils 2, and pulse sequence and spectroscopy generation for slice image generation. A sequencer 11 capable of performing a pulse sequence for a computer, a computer system 12 for controlling these and performing signal processing of a detection signal, and a display 1 for displaying a reconstructed image and the like.
Have three.

In the present embodiment, the sequencer 11 and the computer system 12 activate the pulse sequence according to the MRSI method shown in FIG. 2 or 4. Then, the collected data is processed by the computer system 12. In the example described below, a ³¹ P MRS is used.
Taking I as an example, M of other nuclides such as ¹⁹ F and ¹³ C
It goes without saying that it can also be applied to RSI. Note that ³¹
When MRSI of the head of P is performed, for example, 1.5T to 2
Voxel size 30mm ³ using T magnetic resonance apparatus A certain amount of data can be obtained with a scan time of about 30 minutes.

First, 3D-MRS of 8 × 8 matrix
A case of obtaining a ³¹ P spectrum by Method I will be described. That is, the pulse sequence shown in FIG. 2 is executed by the sequencer 11. Here, a slicing gradient magnetic field is applied along the z-axis direction, a first phase-encoding gradient magnetic field is applied along the X-axis direction, and a second phase-encoding gradient magnetic field is applied along the Y-axis direction. And collect proton MR spectroscopic image data.

The pulse sequence shown in FIG. 2 is a pulse sequence of the MRSI method based on spin echo in which one-dimensional slice plane selection and two-dimensional phase encoding are combined. By executing this sequence, spectrum data of protons in each voxel as shown in FIG. 3 is obtained.

For each voxel ^{From the 1} H spectrum, the peak of water is picked up by a known method, the water frequency of the Kth voxel is ω _Hk , and the difference Δω _Hk = ω _Hk −ω _Ho from the center frequency ω _Ho is calculated for each voxel. To do. Δω _Hk
Therefore, the deviation ΔB _k of the static magnetic field strength of each voxel is obtained by the following formula. ΔB _k = Δω _Hk / γ _H (γ _H : gyromagnetic ratio of water)

Next, a pulse sequence as shown in FIG. 4 is executed. This pulse sequence has a ³¹ P MRSI
3 shows a pulse sequence for collecting data. In this case, the number of matrices (generally 8 × 8 or 16 × 16) in ³¹ P MRSI data is ¹ H M
Match the number of matrices in the RSI data (generally, the voxel size in the MRSI data of ³¹ P has already been determined. ¹ H MRSI
It will determine the number of data matrices. ), And both voxels correspond spatially one-to-one.
Specifically, the areas of the gradient magnetic field pulses of the first and second phase encodes Ge1 and Ge2 of the MRSI of ³¹ P are ¹ HMR
In comparison with SI, ³¹ P ^It may be set to the reciprocal multiple of the ratio of the gyromagnetic ratio to ¹ H. For example, the gyromagnetic ratio of ³¹ P is ¹ H
Therefore, in the ³¹ P pulse sequence, the intensity of the gradient magnetic field pulse is 1 / 0.405 = 2.4.
8 times.

By executing the pulse sequence shown in FIG. 4, the ³¹ P MRSI data shown in FIG. 5 is obtained. This data shows that if there is no inhomogeneity of the static magnetic field, the reference material (for example, the peak of PCr in the case of ³¹ P is customarily the peak of PCr) is γ _PCr , and ω is _It should appear at the point of _Po = γ _PCr × Bo = γ _PCr (ω _Ho / γ _H ), but at voxel K, there is a deviation of ΔB _k from the static magnetic field Bo, so Δω _Pk = γ _PCr × Δ
Shift by B _k .

This ΔB _k is shown in FIGS. 2 and 3. Since it is measured by ¹ H MRSI, it is possible to calculate how much PCr deviates from the center frequency ω _Po (Δω _Pk ) for each voxel.

When displaying the spectrum of each voxel,
The point of ω _Po + Δω _Pk is displayed as 0 ppm on the chemical shift axis. Also, when the chemical shift is measured by displaying a cursor or the like, the calculation is performed based on this point (see FIG. 6). In addition, the frequency range in which the specific compound exists is held in the computer system 12. For example, α-ATP is as shown in FIG.
It exists in the range of ω _{A and} ω _B.

When creating the distribution image of α-ATP, the chemical shift image can be automatically created by integrating the points from ω _A to ω _B of each voxel and displaying the gray scale. it can. In the past, the operator had to specify the range to be integrated by ROI or the like.

The method of the above-described embodiment can be similarly applied to the local spectroscopy such as the ISIS method, which is the same as that of voxelt which takes spectra of other nuclides. ^{The 1} H spectrum is collected, the local magnetic field strength is obtained, and the axis of chemical shift such as ³¹ P is calibrated. The present invention is not limited to the above-mentioned embodiments, but various modifications can be made without departing from the scope of the present invention.

[0025]

As described above, the invention according to claim 1 is a data collecting means for obtaining a data group for generating an MR spectroscopic image of hydrogen nuclei existing in a specific region of an object,

Calculation means for calculating deviation data of the static magnetic field strength of each voxel from the expected static magnetic field strength from the water peak frequency in the spectrum of each voxel defined for the specific region, and each voxel based on the deviation data of each voxel. A magnetic resonance spectroscopy apparatus including: a correction unit that corrects a shift of a chemical shift with respect to the MR spectrum data.

The invention according to claim 2 is the apparatus according to claim 1, further comprising: holding means for holding in advance the chemical shift data and frequency data of the specific compound, and the chemical compound of the specific compound. The feature is that a shift image is automatically created.

Therefore, according to the inventions of claims 1 and 2, MRSI data on protons of the same matrix as MRSI of other nuclides such as ³¹ P, ¹⁹ F and ¹³ C is collected,
Since a large amount of water peaks in the living body are detected and used as an internal standard for chemical shift, it is difficult to recognize the peak of a substance to be used as a reference when there is inhomogeneity in the static magnetic field. Even if there is, the axis of chemical shift can be set accurately. Therefore, according to the present invention, it is possible to provide a magnetic resonance spectroscopy apparatus capable of highly accurately performing chemical shift measurement.

[Brief description of drawings]

FIG. 1 is a diagram showing a configuration of an embodiment of a magnetic resonance imaging apparatus according to the present invention.

FIG. 2 is a diagram showing a first example of a pulse sequence for MRSI in the present invention.

FIG. 3 is a diagram schematically showing spectrum data by MRSI of FIG.

FIG. 4 is a diagram showing a second example of a pulse sequence for MRSI in the present invention.

FIG. 5 is a diagram schematically showing spectrum data by MRSI of FIG.

FIG. 6 is a diagram showing a chemical shift axis used for measuring a chemical shift in the present invention.

FIG. 7 is a diagram showing data of specific compounds stored in the computer system according to the present invention.

FIG. 8 is a diagram showing a problem of the conventional technique.

[Explanation of symbols]

1 ... Static magnetic field magnet, 2 ... Gradient magnetic field coil, 3 ... RF coil, 4 ... Gantry, 5 ... Bed, 6 ... Transmitter, 7 ... Receiver, 8, 9, 10 ... Gradient magnetic field power supply, 11 ... Sequencer,
12 ... Computer system, 13 ... Display.

Claims (2)

[Claims] 1. A data collecting means for obtaining a data group for generating an MR spectroscopic image of hydrogen nuclei existing in a specific region of an object, and a water peak in a spectrum of each voxel defined for the specific region. Calculation means for calculating the deviation data of the static magnetic field strength in each voxel from the expected static magnetic field strength from the frequency of, and the MR of each voxel based on the deviation data of each voxel.
A magnetic resonance spectroscopy apparatus comprising: a correction unit that corrects a shift in chemical shift with respect to spectrum data. 2. A chemical shift image for the specific compound is automatically created by including a holding unit that holds the chemical shift data and the frequency data of the specific compound in advance. Magnetic Resonance Spectroscopy System.