CN1462607A

CN1462607A - Fast rotatory spin echo imaging method of magnetic resonance for medical treatment diagnosis

Info

Publication number: CN1462607A
Application number: CN03111595A
Authority: CN
Inventors: 秦松茂; 施金泉
Original assignee: SHENYANG DONGRUAN DIGITAL MEDICAL SYSTEM CO Ltd
Current assignee: Philips and Neusoft Medical Systems Co Ltd
Priority date: 2003-04-30
Filing date: 2003-04-30
Publication date: 2003-12-24

Abstract

A high-speed spin echo imaging method for the magnetic resonance used for medical diagnosis includes testing system states including uniform state, eddy state, echo signals, and excited echo, optimizing the K space encoding, choosing effective better echo, and phase compensating and correcting. Its advantages are high effect to eliminate false image from scanned MRI image, and high quality and stability of image.

Description

A kind of medical diagnosis quick spin echo imaging method of magnetic resonance

Affiliated technical field

The invention belongs to medical diagnosis and use the mr techniques field, particularly a kind of medical diagnosis magnetic resonance quick spin echo imaging method.

Background technology

Medical magnetic resonance imaging (MRI) technology is the novel video diagnostic technology that recent two decades grows up.The characteristics of MRI scanogram are good contrast, and the resolution height has the feature that dissect to show, lesion tissue shows responsive, but and any direction cut a layer imaging.The MRI system has been widely used in medicine clinical research and diagnosis extremely at present.But the magnetic resonance imaging imaging time is generally longer, and particularly in low field intensity MRI system, the single pass time can reach a few minutes usually, and conventional T2 can be for 8 minutes as scanning.In order to add fast scan speed, present MRI system adopts a kind of fast spin echo method (FSE) mostly, and this method can shorten sweep time at double.But this fast scanning method is had relatively high expectations to the uniformity in magnetic field in the system, eddy current state, RF waveform etc.And in common low permanent-magnet type system, therefore always in various degree the existence of these undesirable elements directly have influence on the quality of image.

Summary of the invention

At the not high problem of existing medical magnetic resonance quick spin echo imaging method image quality, the invention provides a kind of code optimization and phase compensation method of quick-speed spin echo pulse sequence, to guarantee the high-quality fast scan imaging of MRI system.

The undesirable element that low field permanent-magnet type magnetic resonance system influences picture quality mainly contains: the eddy current effect that gradient pulse causes on magnet; The magnetic field heterogeneity of magnet imaging space; The stimulated echo of non-expectation or non-benign; Some error in the control of spectrometer pulse train.

At the harmful effect that above factor is brought, the inventive method has following steps: at first system mode is carried out test analysis, content comprises:

1, uniform state test.Uniform state is tested the multimetering that distributes in the available spheroid, and main indexes has the shimming range size, the uniformity, DISTRIBUTION OF MAGNETIC FIELD form etc.

2, figure (2) is seen in eddy current state verification (eddy axis).The eddy current state is tested with a dedicated sequences.Main test applies the eddy current magnetism that causes after the gradient to the influence degree of signal and the time length of eddy current magnetism.Can realize by the state of cancelling measuring-signal in the different time after the gradient.Signal is that the signal condition that different time measures shows among the figure (2).

3, the test of echo-signal.See figure (3).Amplitude, real part, the imaginary part of each echo-signal on the echo train of FSE are shown, just can analyze the state of echo-signal.

According to the system mode of testing above, adopt following measure then:

1) the K space encoding is optimized.K(S ₁、S ₂……S ₁)I≤L。Wherein L is the total step number of phase code, and I is the actual scanning step number, is non-omnidistance scanning when L＜N.The K space is the original coding space of MRI system scan, and dissimilar codings can produce different effects.If the non-ideal factor of system (as mentioned above) exists, the different arrangement of isocoding also can be brought difference.So with regard to certain system, coding has its specificity, the coding that designs for certain particular system just may be the forced coding of this system.

2) preferred good effectively echo.E(e ₁、e ₂……e _n)n≤N。Wherein N is the echo sum, and n is effective number of echoes.In the echo train of FSE (figure (3)), each echo-signal is all writing down specific phase information, and also may carry bad composition in these signals.For example, phase difference of bringing of the improper magnetic field that causes of the not stimulated echo of coordination phase, or eddy current or the like.So can be by the analytical test of system being found out good effectively echo, and abandon some unfavorable echoes.

3) compensation of the initiative of the echo position phase on different time, the spatial domain and correction.Echo-signal itself in the echo train of FSE is comprising the transverse relaxation decay, and the decay that bad magnetic field causes etc. are so also can do suitable restorative correction to signal.Equally, because the influence in bad magnetic field on the room and time, even selected echo still has the improper difference that some is gone up mutually, so also be necessary the position of different echoes is carried out corresponding compensation and correction mutually.

φe _n(α)→φe _n(α+Δα _n)

Wherein: φ is the phase angle, and e is an echo, φ e _nIt is the phase angle of n echo

The inventive method can make the pseudo-shadow of image be eliminated, and picture quality is improved significantly, in aspect stable image quality such as thin slice scan, oblique layer scannings.

Description of drawings

Fig. 1 is a fast spin echo scanning impulse sequence chart in the inventive method,

Fig. 2 is the eddy axis figure of eddy current state verification in the inventive method,

Fig. 3 is the echo-signal state diagram of echo-signal test in the inventive method,

The image that obtains after the echo-signal of Fig. 4 for normal collection in the inventive method,

Fig. 5 masks the image of gathering after first echo-signal that obtains in the inventive method,

Fig. 6 is the image that obtains before the inventive method meta compensates mutually and proofreaies and correct,

Fig. 7 is the image that obtains after the inventive method meta compensates mutually and proofreaies and correct.

Among the figure: HZ hertz, echol echo, FID free damping signal

The RF radio-frequency pulse, the GS slice selective gradient, GR reads gradient

GP position phase gradient

The specific embodiment

By step of the present invention, at first system mode is carried out test analysis.Comprise: uniform state test, eddy current state verification and echo-signal test, test result as shown in the figure.

Its FSE scanning impulse sequence such as Fig. 1;

Its eddy current state verification gained eddy axis such as Fig. 2;

The amplitude of its echo-signal test gained echo-signal and mutually situation such as Fig. 3;

According to the situation of test, take following measure:

Optimize the K space encoding;

Preferred good effectively echo, Fig. 4 are the image that obtains after the normal echo-signal of gathering; Fig. 5 masks the image that collects after first echo-signal; Following phase compensation and correction (unit is for spending) are set as figure (3) in amplitude by the test echo-signal and position situation mutually:

Position phase correction value delta α=-6.3 of the 1st echo

Position phase correction value delta α=3.2 of the 2nd echo

Position phase correction value delta α=-17.5 of the 3rd echo

Position phase correction value delta α=0 of the 4th echo

Position phase correction value delta α=0 of the 5th echo

Figure (6) is for phase compensation with the image that obtains before proofreading and correct in this example, and figure (7) is for phase compensation with the image that obtains after proofreading and correct.

Claims

1, a kind of medical diagnosis is characterized in that at first system mode being tested with the quick spin echo imaging method of magnetic resonance, comprising: uniform state test, eddy current state verification, echo-signal test, take following measure according to the test macro state:

(1) optimize the K space encoding,

(2) preferred good effectively echo,

(3) compensation of the initiative of the echo position phase on different time, the spatial domain and correction.

2, medical diagnosis according to claim 1 is characterized in that with the quick spin echo imaging method of magnetic resonance described shimming state verification is the multimetering that distributes with in the spheroid, mainly surveys size, the uniformity and the DISTRIBUTION OF MAGNETIC FIELD form of shimming scope.

3, the medical diagnosis according to claim 1 quick spin echo imaging method of magnetic resonance, it is characterized in that described eddy current state verification, be to test with a dedicated sequences, test applies the eddy current magnetism that causes after the gradient to the influence degree of signal and the time of eddy current magnetism influence.

4, the medical diagnosis according to claim 1 quick spin echo imaging method of magnetic resonance, the test that it is characterized in that described echo-signal is that amplitude, real part, the imaginary part with each echo-signal on the echo train of fast spin echo shows, and analyzes the state of echo-signal.

5, medical diagnosis according to claim 1 is with the quick spin echo imaging method of magnetic resonance, it is characterized in that described preferred good effectively echo is meant to find out effective echo, abandons bad echo.