JPS63214248A - Magnetic resonance imaging apparatus - 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 [Objective of the Invention] (Industrial Application Field) The present invention provides an image of a cross section of a subject by using MR signals induced by the phenomenon of magnetic resonance (hereinafter referred to as MR). Magnetic resonance imaging (hereinafter abbreviated as MRI)
The present invention relates to an apparatus, and more particularly to an improvement in multi-slice imaging using an inversion recovery sequence.

(Prior Art) An inversion recovery sequence will be explained with reference to FIGS. 5 and 6.

FIG. 5 is a timing chart of RF pulse application and echo collection in the inversion recovery sequence, and FIG. 6 is a diagram showing a rotational coordinate system of spins.

In the above sequence, as shown in FIG. 5, first, the magnetization in the thermal equilibrium state is reversed by a 180 degree pulse. That is, when viewed in the spin rotation coordinate system of Fig. 6, Z, which is the direction of the static magnetic field,
“The spin phase aligned in the direction is 18 as shown by A in the figure.
It's flipped 0 degrees.

After this, the spin phase starts to invert in the Z direction according to the longitudinal relaxation time constant T2 as shown by B in the same figure, so after this inversion time (inversion time) TI,
Apply a 90 degree-180 degree pulse as shown in the figure,
The spin is increased by 90° as shown by C in Figure 6 by the degree pulse.
The spins are converged using a 180-degree pulse as shown by the arrow in the same figure, and an echo signal is detected.

After this, after waiting for the magnetization in the cross section to recover, the same sequence is repeated for the same cross section again after a repetition time TR from the first 180 degree pulse, and the longitudinal relaxation time constant T
It is possible to reconstruct an inversion recovery image with a contrast difference based on 2.

Conventionally, multi-slice imaging has also been performed using this inversion recovery sequence.

In multi-slice imaging using the above sequence, the seventh
As shown in the figure, magnetization is selectively reversed using a 180 degree pulse for, for example, three different cross sections during the inversion time TI, and signal observation is also performed by selectively exciting each cross section. ing. After observing the signal, wait for the magnetization of each cross section to recover, and then wait for the repetition time T
After R has passed, a similar sequence is executed for the same three types of cross sections.

(Problems to be Solved by the Invention) In multi-slice imaging using a conventional inversion recovery sequence, the number of multi-slices is regulated by the inversion time TI in order to keep the inversion time TI constant for each section. was. Therefore, the scan time is long (typically TRγ2000m5ec
), there was a drawback that the number of multi-slices was small and limited.

On the other hand, in order to obtain a large number of slices within the inversion time T1, the inter-slice gap must be brought close to zero, but since the above sequence requires an inversion pulse, the slice characteristics are poor and the image quality is degraded due to interference between slices. I couldn't deny it.

SUMMARY OF THE INVENTION Therefore, an object of the present invention is to provide a magnetic resonance imaging apparatus that can eliminate the above-mentioned conventional drawbacks and double the number of slices in multi-slice imaging using an inversion discovery sequence. be.

[Structure of the Invention] (Means for Solving the Problems) The present invention provides magnetization for one or more other slice planes that were not excited during the magnetization recovery period for the previously excited cross section. A magnetic resonance imaging apparatus is configured by providing a control means for controlling the execution of the sequence of inversion, excitation, and signal observation.

(Function) In the present invention, in the latter half of the repetition time TR, magnetization reversal, excitation, and signal observation are performed for other cross sections that were not excited earlier during the magnetization recovery period for the previously excited cross sections. This makes it possible to observe signals on other slice planes using the magnetization recovery period, which was previously unused, and double the number of multi-slices, which was previously limited by the inversion time TI. Can be done.

(Examples) Hereinafter, the present invention will be specifically described with reference to illustrated examples.

FIG. 1 is a pulse sequence diagram for implementing the present invention, and FIG. 2 is a block diagram of the apparatus of this embodiment.

First, the outline of the embodiment apparatus will be explained with reference to FIG.

In the figure, a magnet assembly blade 11 includes a static magnetic field coil 2 that applies a main magnetic field of a constant strength to a subject disposed therein, and a gradient magnetic field that applies x, y, and z gradient magnetic fields to the subject. A coil 3, an excitation coil 4 that applies a high-frequency pulse to excite the spin of an atomic nucleus, and a detection coil 5 that detects a magnetic resonance signal from inside the subject.

The data calculator 11 reconstructs an inversion recovery image based on detected data, and is connected to a display device 12 and a controller 13-6 which is a control means. The controller 13 generates a timing signal for collecting observation data of magnetic resonance signals, and controls the gradient magnetic field coil Bi4 and the gate circuit ]-7, thereby controlling the gradient magnetic fields Gx, GV, a7 and the high frequency pulse RF. control the sequence of occurrence of

The gradient magnetic field control circuit 15 controls the current of the gradient magnetic field coil 3 and applies a gradient magnetic field to the subject.

The static magnetic field control circuit 15 controls the current supplied to the static magnetic field coil 2 and applies a static magnetic field HO to the subject.

The high frequency oscillator 1-6 generates a high frequency whose frequency is controlled by the controller 13. The circuit 17 to game) is
The timing signal from the controller 13 modulates the high frequency signal output from the high frequency oscillator 16 to generate high frequency pulses. The power amplifier 18 amplifies the power of the high frequency pulse output from the gate circuit 17 and supplies it to the excitation coil 4 .

Preamplifier 19 amplifies the magnetic resonance signal from detection coil 5. The phase detection circuit 20 performs phase detection on this amplified magnetic resonance signal. The waveform memory 21 stores a phase-detected waveform signal.

The data processing calculation all controls the operation of the controller 1.3, receives time information from the controller 13, reads out data from the waveform memory 21, and performs signal processing based on the observed magnetic resonance. In addition, the data processing computer 11
Operation instructions for the operator can also be displayed on the display device ]-2.

FIGS. 1 and 3 show operations for performing multi-slice imaging using an inversion recovery sequence in the MHI apparatus configured as described above.

Explain with reference to.

First, the static magnetic field coil 2 is connected to the static magnetic field coil 2 via the static magnetic field control circuit 15.
A uniform static magnetic field HD is applied by passing a current through.

Next, the high frequency oscillator 16. A 180 degree pulse (see FIG. 1), which is an RF pulse obtained through a gate circuit 17 and a power amplifier 18, is divided into several slices, for example, as shown in FIG. The spin of each cross section is reversed by 180 degrees as shown by A in FIG. Note that this magnetization reversal action is performed within the above-mentioned inversion time TI.

Next, after this inversion time of 71 hours has elapsed, as shown in Figure 1, a 90-180 degree spin echo sequence is executed for each cross section (■, ■, ■), and excitation and signal observation for each cross section is performed. conduct.

The sequence up to this point is the same as the conventional one.

The features of this example are the previously excited cross sections (■) and (2).

After observing the signal for ■, while waiting for magnetization recovery for each cross section, the sequence of magnetization reversal, excitation, and signal observation is executed for other cross sections that were not excited first. be.

That is, if the other cross sections are the cross sections ■, ■, and ■ shown in FIG. 3, after observing the signal for the cross section ■ as shown in FIG. Invert, 1
Each is performed by applying an 80 degree pulse. Then, after the inversion time T1 for each cross section of ■, ■, ■ has elapsed, 9
A spin echo sequence of 0 degrees to 1 degrees and 9 degrees to 180 degrees is executed, and excitation and signal observation are performed for each cross section.

In this way, according to the present embodiment, in the second half of the repetition time TR, during the magnetization recovery period for the previously excited cross section, the magnetization is reversed for the other cross sections that were not excited first.
Excitation and signal observation can be performed. Therefore, it is possible to observe signals on other slice planes by using the magnetization recovery period, which has not been used in the past, so it is possible to double the number of multi-slices, which was conventionally limited by the inversion time TI.

Note that the present invention is not limited to the above embodiments, and various modifications can be made within the scope of the gist of the present invention.

For example, in the above embodiment, multi-slices were performed on the cross-sections shown in FIG. A>, as shown in (B), you can perform multi-slices with slice intervals, or as shown in Figure 4 (C), you can specify the next slice plane between the previously excited slice planes. It is also possible to perform multi-slice imaging using the method shown in FIG. It becomes possible.

Effects of the Invention] As described above, according to the present invention, it is possible to provide a magnetic resonance imaging apparatus capable of doubling the number of images that can be multi-slice imaged within the same repetition time as in the prior art.

[Brief explanation of the drawing]

FIG. 1 is a pulse sequence diagram showing an example of implementing the present invention, FIG. 2 is a block diagram of an apparatus according to an embodiment of the present invention, and FIG. 3 is a cross-sectional view of a subject to be subjected to multi-slice imaging. Schematic explanatory diagram shown in Fig. 4 (A), (B), (C)
5 is an explanatory diagram showing the slice plane of multi-slice imaging, FIG. 5 is an explanatory diagram of the inversion recovery sequence, FIG. 6 is a schematic explanatory diagram showing the spin rotation coordinate system, and FIG. 7 is an explanatory diagram of the inversion recovery sequence. FIG. 2 is a sequence diagram illustrating conventional multi-slice imaging using a recovery sequence. 1,300... Control means. Agent Patent Attorney Nori Chika Yudo Norio Ogo

Claims (1)

[Claims] During the inversion time, a 180 degree pulse of magnetization reversal is applied for several slices, and after the inversion time has elapsed, excitation and signal observation are performed for each slice plane using a 90 degree - 180 degree spin echo sequence, and magnetization recovery is performed. By waiting and repeating the above sequence for the same slice plane, in a magnetic resonance imaging apparatus that images an inversion recovery image for a multi-slice plane, during the magnetization recovery period, other magnetization that has not been excited first is detected. A magnetic resonance imaging apparatus characterized in that a control means is provided for executing and controlling the sequence of magnetization reversal, excitation, and signal observation with respect to the above slice plane.