JPH02234743A - Csf photographing method - Google Patents

Abstract

PURPOSE:To prevent the occurrence of arch fact due to the flow of CSF and body movement and to photograph CSF angiorgraphy in a short time by a method wherein the pulse repeating time of a CE-FAST pulse sequence satisfies a specified condition, and the gradient waveform of the CE-FAST pulse sequence is deformed. CONSTITUTION:A sequence memory circuit 6 controls a gate demodulating circuit 8 according to a command from a calculator 7, and applies an RF pulse signal from an RF power amplifier 4 to an RF transmission coil. The sequence memory circuit 6 controls a gradient magnetic field drive circuit 3 by means of a sequence signal generated based on CE-FAST to feed a gradient magnetic field to three axes of an X-, a Y-, and a Z-axis. A pulse repeating time TR of a CE-FAST pulse sequence satisfies a formula of T2M < TR < T2CSF. Before or after an NMR signal is detected or approximately at the same time as a time when the NMR signal is detected, the gradient waveform of the CE-FAST pulse sequence is deformed, and the flow of CSF and a phase shift due to body movement are reduced to zero. In the formula, T2M is a lateral relaxation time of tissue except CSF, and T2CSF is the lateral relaxation time T2 of CSF.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention uses a nuclear magnetic resonance imaging system to measure cerebrospinal fluid (C).
Regarding the method of photographing SF), especially CEFAST (Co
ntruste Enhanced Fourie
r Acquired Steady-state
(Technique) It is concerned with improving image quality by making use of the characteristics of the pulse sequence and adding improvements thereto.

(Prior Art) A nuclear magnetic resonance imaging diagnostic apparatus includes a magnet section that includes a static magnetic field coil that creates a uniform static magnetic field and a gradient magnetic field coil that creates a magnetic field that has linear gradients in each of the x, y, and z directions. A transmitting/receiving unit that applies an RF pulse to a subject placed within a magnetic field formed by the subject, and controlling the operation of the transmitting/receiving unit and the magnet unit, which detects an NMR signal from the subject; It has a control image processing section that processes detected data and displays an image.

As a general method for imaging CSF using this nuclear magnetic resonance imaging system, in setting the imaging parameters of the SE method pulse sequence, the pulse repetition time TR and R
1on. The time TE from exciting the subject with the F pulse to generating the NMR signal is set longer. gTR
, a method of obtaining a T2-weighted image using the S'E method pulse sequence of TE is known. The basic form of the SE method pulse sequence is shown in FIG. In FIG. 7, the subject is excited with a 90° pulse, and a 180° pulse is further applied to generate an NMR signal as a spin echo signal after TE from the 90° pulse. Thereafter, the protons in the analyte are allowed to recover for a certain period of time, and after TR, the analyte is excited again with a 90° pulse.

In addition, in order to remove the influence of non-uniformity of the quiet magnetic field,
The interval between the 6 pulses and the 180° pulse is often equal to the interval between the 180° pulse and the echo signal. TR,T
The echo signal generated by the SE method pulse sequence of IongTR and TE in which E is set long is given by the following equation.

p fu/) e x p (1 TE/T 2)
=---- ■Here, ρ; prol·n density fm; change in signal intensity due to influence of flow (invention or problem to be solved) However, using the conventional SE method pulse sequence, CSF
When photographing a patient, it takes several minutes to several tens of minutes to perform one scan, placing a burden on the patient. Furthermore, since the scanning time is long, artifacts based on CSF flow, body movement, etc. occur on the image.

The present invention has been made in order to solve the problems of the conventional methods as described above, and provides a method for suppressing artifacts caused by CSF flow, body movement, etc., and for performing CSF angiography in a short time. The purpose is to provide.

(Means for Solving the Problems) In order to achieve the above object, the present invention uses a CEFAST pulse sequence, and the pulse repetition time TR of the CE-FAST pulse sequence satisfies T2M<T.
In addition to satisfying R < T 2 CSF, the gradient waveform of the CB-FAST pulse sequence is modified before or after detecting the NMR signal, or before and after detecting the NMR signal, so that the phase shift based on CSF flow, body movement, etc. is made zero. The structure is as follows.

However, in the formula, T2M is the transverse relaxation time T of tissues other than CSF.
2, T''2 CSF is the horizontal wire sum time T2 of the CSF.

<<Operation> The scan time of CB-FAST pulse sequence is 1
It is known that it is around 1 minute. Therefore, this CE-
Pulse repetition time TR of FAST pulse sequence
By setting to satisfy 72M<TR<72CSF, an NMR signal with enhanced CSF can be obtained, and by changing the gradient waveform of the CE-FAST pulse sequence, the CSF flow can be adjusted. ,
Phase shifts due to body movements etc. are canceled and artifacts can be suppressed.

(Example) Hereinafter, the present invention will be explained in detail with reference to the drawings.

FIG. 1 is a schematic diagram of a nuclear magnetic resonance imaging diagnostic apparatus implementing the present invention. In the figure, reference numeral 1 has a space into which a subject is inserted, a static magnetic field coil that surrounds this space and applies a constant static magnetic field to the subject, and a gradient magnetic field that generates a gradient magnetic field. This is a magnet assembly in which a coil, an RF transmitting coil that provides an RF pulse to excite nuclear spins within the subject, a receiving coil that detects an NMR signal from the subject, and the like are arranged.

The static magnetic field coil, gradient magnetic field coil, RF transmitting coil, and receiving coil each include a static magnetic field power supply 2, a gradient magnetic field drive circuit 3,
It is connected to an RF power amplifier 4 and a preamplifier 5.

The sequence storage circuit 6 operates the gate modulation circuit 8 (modulates the RF output signal of the RF oscillation circuit 9 at a predetermined timing) according to instructions from the computer 7, and applies an RF pulse signal from the RF power amplifier 4 to the RF transmitting coil. do. Further, the sequence storage circuit 6 operates the gradient magnetic field drive circuit 3 using a sequence signal based on CE-FAST to supply gradient magnetic fields to the three axes of x, y, and z, respectively.

A phase detector 10 detects the phase of the received signal output of the preamplifier 5 using the output of the RF oscillation circuit 9 as a reference signal. This power signal is converted into a digital signal by the AD converter 11 and input to the calculation@7. 12 is an operation console for inputting instructions and various setting values for realizing various pulse sequences to the computer 7; 13 is a display device for displaying images reconstructed by the computer 7;

In the above configuration, according to instructions from the computer 7, the sequence memory circuit 1i46 is not shown in FIG.
Generates a T-pulse sequence signal.

In FIG. 2, Gx is a gradient magnetic field applied to the X axis, which is referred to as the frequency encoding axis. The read gradient applied to the X-axis is for observing spin echo signals, and the dephase gradient is for providing phase information in the X-axis direction. Gy is a gradient magnetic field that applies a magnetic field with a different phase each time to the Y axis, which is called a phase encode axis. The warg gradient applied to the Y-axis is to give phase information in the Y-axis direction, and warp 2 is the same as warp 1.
By applying a magnetic field that is the same size and in the opposite direction, the total amount of warp is reduced to zero. GZ is Z called slice axis
This is a gradient magnetic field applied to the axis.

The slice gradient applied to the Z axis is for exciting only spins within a specific plane, and the reface gradient is for removing the phase difference generated during slicing. RF is a high frequency rotating magnetic field applied in a direction perpendicular to a static magnetic field, and is generally applied as an α° pulse.

The echo signal produced by the CE-FAST pulse sequence is given by the following equation.

・・・・・・■ Here E1=expP (-TR/TI)E2=exp
(-TR/T2) 1-EIE22 +cos (E22-E1)1 -
E 1 b= (1+cos α) E2 Figure 3 shows the ■ formula for CSF and tissues other than CSF (here,
G.R. EY MATTER. gray matter, WJ{ITE
MATTER. This is a plot of white matter). However, at 0.5T, T2CSF = 1000ms
ec, T2G. M. =101msec, T2WH=-9
The time is 2 msec. Here, T2CSF is CS
Transverse relaxation time T2 of F, 72G. H. is the horizontal relaxation time of gray matter ■2, T2W. H. is the white matter transverse relaxation time ■2.

From Fig. 3, the pulse repetition time TR is T 2N<T
By setting so that R < T 2 CSF is not satisfied, it can be confirmed that only CSF is a high signal and signals other than CSF are small.

Figure 4 shows the ■ formula for organizations other than CSP and CSF (here,
KIDNEY. kidney, liver)
This is a plot of . However, at 0.5T,
T2CSF = 1 0 0 0 msec, 1
2κID=58 msec. T2LIV =
43 msec. Here T2
CSF is the lateral summation time of CSF ■2, 72KID is the horizontal relaxation time of the kidney T2, and T2LIV is the horizontal relaxation time of the liver ■2.

From Figure 4, the pulse repetition time TR is 72M<TR
By setting to satisfy < T 2 CSF, it is confirmed that only CSF is a high signal and signals other than CSF are small.

Although FIG. 3 shows an example of gray matter and white matter, and FIG. 4 shows an example of kidney and liver, the inventor has confirmed that the same results can be obtained for other tissues as well.

Next, as a method to suppress artifacts based on CSF flow, body movement, etc., we use the gradient moment nulling method.
ng method) will be explained as an example. What is the gradient moment nulling method?CB-FAST
In this case, the phase shift based on CSF flow, body movement, etc. is made zero by deforming the gradient waveform before or after echo signal observation, or before and after echo signal observation. CE-FA
In the S'r pulse sequence, the gradient waveform may be modified in the dotted line portion of FIG. 5 so as to satisfy the following equation.

......■ ......■ ......■ Here, Gift) and Xi(t) are the gradient magnetic field and position in the i direction at a certain time t, respectively. (However, i-x
, y, z) Also, C is a constant that does not depend on velocity, acceleration, etc.

Now, assuming that the position x (t) of the material at a certain time t based on the flow of CSF, body movement, etc. is approximated by the following equation, and when changing the gradient waveform only in the latter half, as shown in Figure 6. become.

xft) =Co +vt −−−−−−■Here C
0: initial position, V: speed Note that the present invention is not limited to the above embodiments, and various modifications can be made within the scope of the claims. For example, although the gradient waveform was transformed into a half-wave sine shape, any waveform may be used as long as it satisfies equations (2) to (2).

(Effects of the Invention) As explained above, according to the present invention, when imaging CSF using the CE-FAST pulse sequence, C
The pulse repetition time TR of the E-FAST pulse sequence satisfies T2)4<TR<T2CSF, and
CE before or after detecting the NMR signal, or before and after detecting the NMR signal.
- Modify the gradient waveform of the FAST pulse sequence to
Since the configuration is such that the phase shift based on SF flow, body movement, etc. is reduced to zero, artifacts caused by CSF flow, body movement, etc. can be suppressed, and CSF angiography images can be captured in a short time. It becomes possible.

[Brief explanation of the drawing]

FIG. 1 is a block diagram of a nuclear magnetic resonance imaging diagnostic apparatus implementing the present invention, and FIG. 2 is a diagram showing a known CE-FAST pulse sequence. FIG. 3, FIG. 4, and FIG. 5 are diagrams for explaining the operation of an embodiment of the present invention. FIG. 6 is a diagram of one embodiment of the present invention. FIG. 7 is a diagram showing a basic type of a known SE method pulse sequence. 1... Magnet assembly, 2... Static magnetic field power supply,
3... Gradient magnetic field drive circuit, 4... RF power amplifier,
5... Preamplifier, 6... Sequence storage circuit, 7... Computer, 8... Gate modulation circuit, 9...
RF oscillation circuit, 10...phase detector, 11...AD
Converter, 12... operation console, 13... display device,

Claims (1)

[Claims] (1) In a method of collecting NMR signals based on nuclear magnetic resonance phenomena using a CE-FAST pulse sequence and photographing a target tissue, the pulse repetition time TR of the CE-FAST pulse sequence is T2M<TR<T2CSF. In addition to satisfying
C before or after detecting the NMR signal, or before and after detecting the NMR signal.
A CSF imaging method characterized in that the gradient waveform of the E-FAST pulse sequence is modified so that a phase shift based on CSF flow, body movement, etc. is reduced to zero. However, in the formula, T2M is the transverse relaxation time T of tissues other than CSF.
2. T2CSF is the transverse relaxation time T2 of CSF.