JPH04226634A - Nuclear magnetic resonance inspecting device - Google Patents

Abstract

PURPOSE:To improve S/N by executing the sequence for collecting the data on resonance signals successively with each of respective slices, and determining the magnitude of RF signals and the number of repeating times of the sequence for each of the respective slices from the data obtd. there. CONSTITUTION:The sequence of tuning is automatically executed if a tuning program is started after the slices 1 to 3 are set. The slices 1 to 3 are successively selectively excited and the signals therefrom are taken into a host computer. The sensitivity deteriorates gradually in the thickness direction in the sensitivity region of a plane coil 12 and eventually the intensity of the received signals is smaller with the more distant slices. The magnitude of the RF pulses is, thereupon, made larger with the more distant slices. The number of the repeating times of the sequence is set at N1, N2, N3 (N1<N2<N3) with the slices 1 to 3 to uniformize the S/N. Such setting is executed with each slice and thereafter, the sequence for collecting the resonance signals with the set slices 1 to 3 is executed.

Description

[Detailed description of the invention]

0001

[Industrial Field of Application] This invention relates to nuclear magnetic resonance (NMR).
) relates to a nuclear magnetic resonance examination apparatus that performs spectroscopy.

0002

2. Description of the Related Art When spectroscopy is performed using a nuclear magnetic resonance examination apparatus, a plane coil (surface coil) is applied to a subject, and a gradient magnetic field is applied in a direction orthogonal to the plane coil. At the same time, an RF signal of a specific frequency component is supplied to this planar coil to selectively excite a slice at a certain position in a direction perpendicular to the planar coil. When the NMR signal from the slice is received by a planar coil, detected, and Fourier transformed, data regarding the spectrum of the NMR signal can be collected.

In this nuclear magnetic resonance examination apparatus, it is necessary to adjust the size of the RF pulse before the examination, but in the past, the entire subject was excited without applying a gradient magnetic field for slice selection. The size of the RF pulse was determined so that the received signal would be the largest. Then, no matter where the slice is located, an RF pulse of that magnitude is applied.

0004

[Problems to be Solved by the Invention] However, as in the past, the size of the RF pulse is determined so that the received signal is the largest by exciting and receiving the entire volume regardless of the slice position, and the RF If pulses are applied to every slice, spatial non-uniformity in antenna sensitivity results in different signal strengths between slices, causing a problem in that the signal-to-noise ratio differs greatly. In other words, a planar antenna used as a transmitting and receiving antenna, a so-called planar coil (surface coil), has the characteristic that its sensitivity decreases in the direction perpendicular to it. NM
Not only does the R signal itself become smaller, but also the receiving sensitivity is lower, so the S/N ratio of the signal becomes worse than that of slices located nearby.

[0005] In view of the above, an object of the present invention is to provide an improved nuclear magnetic resonance examination apparatus that can obtain data with the same S/N ratio for slices at any position.

[0006]

[Means for Solving the Problems] In order to achieve the above object, in the nuclear magnetic resonance examination apparatus according to the present invention, before starting a resonance signal data acquisition sequence for each slice set in the direction of a gradient magnetic field, A feature is that a resonance signal data collection sequence is sequentially performed for each slice, and the magnitude of the RF signal and the number of repetitions of the sequence are determined for each slice from the data obtained. This makes it possible to determine the magnitude of the RF signal and the number of repetitions of the sequence for each slice from which data is actually obtained, which improves the control characteristics of the magnetic resonance phenomenon, such as obtaining the desired flip angle for any slice. When the signal strength is low or the reception sensitivity is low, the S/N ratio can be increased by increasing the number of sequence repetitions, that is, the number of data additions, and the S/N ratio can be made the same for all slices.

[0007]

DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described in detail below with reference to the drawings. FIG. 1 shows a nuclear magnetic resonance examination apparatus according to an embodiment of the present invention. In this figure, a subject 11 is exposed to a static magnetic field formed by a main magnet 15 and a gradient coil 14 superimposed thereon. It is placed in a gradient magnetic field. The subject 11 has
A planar coil 12, which is a planar antenna for transmitting and receiving an excitation RF signal and receiving an NMR signal, is attached.

The gradient coil 14 is configured to be able to generate a gradient magnetic field whose magnetic field strength is gradient in a direction perpendicular to the planar coil 12. Gradient coil 1
4 is supplied with current from a gradient magnetic field power supply 21 to form a gradient magnetic field. The waveform of the current supplied by the gradient magnetic field power supply 21 is controlled by the gradient magnetic field control device 24 so that the gradient coil 14 forms a gradient magnetic field pulse with a predetermined waveform.

[0009] The planar coil 12 is supplied with RF pulses sent from a high frequency power source 33. This RF pulse is
In the frequency converter 32, R from the synthesizer 34
The RF waveform generator 3 uses the F sine wave signal as a carrier signal.
The sinc waveform from 1 is AM-modulated and amplified by the high-frequency power supply 33.

NMR generated after the object 11 is irradiated with an RF pulse from the planar coil 12 to excite its nuclear spins.
The signal is received by planar coil 12. This received NMR signal is amplified by a preamplifier 35, then detected by a quadrature phase detector 36, and then converted into digital data by an A/D converter 37 and taken into the host computer 41. This quadrature phase detector 36 is a PSD (Phase S
This is a detection circuit based on an active detector method, and uses a circuit that mixes a reference signal sent from the synthesizer 34 and a received signal, and outputs the difference in frequency between the two signals.

Under the control of the host computer 41, the sequence controller 42 provides waveform information and generation timing information of each gradient magnetic field pulse to the gradient magnetic field control device 24.
The F waveform generator 31 is given sinc waveform information and generation timing information of the RF pulse, and the synthesizer 3
4 to control the sampling timing of the A/D converter 37, etc. A console 43 having a display device and an input device such as a keyboard device is connected to the host computer 41 .

[0012] As a pulse sequence for collecting resonance signal data, an ordinary saturation recovery method or the like can be used. In this sequence, as shown in FIG.
By adding
, 3 are sequentially selectively excited and the spins of the relevant portions are tilted by 90° to generate NMR signals from the slices 1, 2, and 3. Data collected from the received NMR signal is taken into the host computer 41. Such a sequence is repeated for each slice 1, 2, and 3, and the data obtained therefrom is added and Fourier transformed to obtain a spectrum of the NMR signal, which is displayed on the display device of the console 43. That will happen.

[0013] Prior to performing such spectroscopy, a tuning sequence is performed. This sequence is similar to the above sequence, and when the tuning program is started after each slice 1, 2, and 3 is set, the tuning sequence is automatically performed at least once for each slice. In this way, slices 1, 2, and 3 are sequentially selectively excited, and signals therefrom are sequentially received and taken into the host computer 41.

The sensitivity region 13 of the planar coil 12 is as shown in FIG. 2, and the sensitivity deteriorates in the depth direction. Therefore, the farther the slice is, the worse the excitation efficiency becomes, making it impossible to tilt the slice 90 degrees, resulting in a lower signal intensity. Furthermore, the farther the slice is, the worse the receiving sensitivity is, so as a result, the farther the slice is, the lower the received signal strength is. Therefore, by processing these data on the host computer 41,
For example, the magnitude of the RF pulse is set to a, b, c (a<b<c) for slices 1, 2, and 3 as shown in FIG. 2, and the farther the slice is, the larger the pulse is. This makes it possible to tilt the slice at any position by 90 degrees. Also, the farther the slice is, the lower the reception sensitivity becomes.
/N ratio becomes bad, so the number of sequence repetitions (number of data additions) is set to N1, N2, N3 (N1<N2<N3) for slices 1, 2, and 3, respectively.
Match the ratio.

[0015] Such settings are made for each slice to complete the tuning process, and thereafter, the resonance signal acquisition sequence for each set slice 1, 2, and 3 is performed according to the settings. Therefore, settings have been made to optimally control the magnetic resonance phenomenon for each slice, and the optimal number of data additions has been set for each slice. As a result, the NMR signal intensity increases for every slice, improving the S/N ratio, and the S/N ratios become uniform between slices.

[0016]

Effects of the Invention As described in the embodiments above, according to the nuclear magnetic resonance examination apparatus of the present invention, despite the spatial non-uniformity of the sensitivity of the planar antenna, the magnetic Since it is possible to optimally control the resonance phenomenon and set the optimal number of data additions, etc., it is possible to collect spectral data with an S/N ratio without variation between slices, and as a result, the S/N ratio is
The N ratio can be improved.

[Brief explanation of the drawing]

FIG. 1 is a block diagram of an embodiment of a nuclear magnetic resonance examination apparatus according to the present invention.

FIG. 2 is an explanatory diagram of the same embodiment.

[Explanation of symbols]

1, 2, 3 Slice

Claims (1)

[Claims] 1. A means for generating a static magnetic field, a means for generating a gradient magnetic field in one direction, a planar antenna disposed substantially perpendicular to the direction of the gradient magnetic field, and an RF signal is applied to the antenna. an excitation means for irradiating and exciting an RF signal to a subject placed in the static magnetic field and the gradient magnetic field; a receiving means for receiving a resonance signal from the subject via the antenna; In addition to controlling the resonance signal data acquisition sequence, which consists of a series of sequences for magnetic field generation, RF signal irradiation, and signal reception, before starting the resonance signal data acquisition sequence for each slice set in the gradient magnetic field direction, A nuclear magnetic resonance examination apparatus characterized by comprising means for performing a tuning resonance signal data collection sequence for each slice and determining the magnitude of the RF signal and the number of repetitions of the sequence.