CN101518445B - Method for separate imaging of water and fat based on inversion recovery technology and system - Google Patents

Abstract

The invention discloses a method for separate imaging of water and fat based on inversion recovery technology, which includes the following steps of: determining a first inversion recovery time when the longitudinal magnetization component of hydrogen atomic nucleus in fat or water is zero; respectively selecting a second inversion recovery time and a third inversion time before and after the first inversion recovery time; during the second and the third inversion recovery time, respectively using a scanning sequence to excite a detected object and obtaining two images simultaneously includinga pure water image and a pure fat image; synthesizing the two obtained images; and when the synthesis removes the pure fat image included in the two images, obtaining a pure water image, when the syn thesis removes the pure water image included in the two images, obtaining a pure fat image. By the use of the invention, the pure water image and the pure fat image can be obtained at one time by using the scanning sequence to excite the detected object and the signal-to-noise ratio of the images is relatively high.

Description

Method for separate imaging of water and fat and system based on inversion recovery technology

Technical field

The present invention relates to mr imaging technique, particularly based on the method for separate imaging of water and fat and the system of inversion recovery (IR, Inversion Recovery) technology.

Background technology

Nuclear magnetic resonance is to utilize the magnetic resonance phenomenon to carry out a kind of technology of imaging.The principle of magnetic resonance phenomenon mainly comprises: the atomic nucleus that comprises the odd number proton, the hydrogen nuclei that extensively exists in the human body for example, its proton has spin motion, just as a small magnet, and the spin axis of these small magnets does not have certain rules, if apply exterior magnetic field, these small magnets will rearrange by the magnetic line of force of exterior magnetic field, be specially at the both direction that is either parallel or anti-parallel to the exterior magnetic field magnetic line of force and arrange, the above-mentioned direction that is parallel to the exterior magnetic field magnetic line of force is called positive longitudinal axis, the above-mentioned direction that is antiparallel to the exterior magnetic field magnetic line of force is called negative longitudinal axis, atomic nucleus only has the longitudinal magnetization component, and this longitudinal magnetization component not only has direction but also have amplitude.Radio frequency (RF, Radio Frequency) pulse excitation with characteristic frequency is in the atomic nucleus in the exterior magnetic field, makes these nuclear spin axiss depart from positive longitudinal axis or negative longitudinal axis, produces resonance, magnetic resonance phenomenon that Here it is.The above-mentioned nuclear spin axis that is excited departs from after positive longitudinal axis or the negative longitudinal axis, and atomic nucleus has had component of transverse magnetisation.

After stopping to launch radio-frequency pulse, the atomic nucleus emission echo-signal that is excited, the energy that absorbs is progressively discharged with form of electromagnetic wave, the state before its phase place and energy level all return to and excite, the echo-signal that atomic nucleus is launched gets final product reconstructed image through further processing such as space encodings.The above-mentioned atomic nucleus recovery process of state before exciting that is excited is called relaxation process, returns to the required time of poised state to be called relaxation time.Relaxation time comprises two kinds of longitudinal relaxation time T1 and spin spinrelaxation T2.

Because hydrogen nuclei and residing minute subenvironment of the hydrogen nuclei in the water in the inside of human body fat are inequality, when using the same radio frequency pulse to excite, their resonant frequency is inequality, and relaxation time is also inequality.According to requirement of actual application, need to obtain respectively pure water image or pure fat image sometimes, at this moment just need make the isolating formation method of water fat.The isolating formation method of water fat that exists comprises following several at present:

The first, the method for selecting based on frequency

In the method for selecting based on frequency, there are some concrete method examples, for example: 1) water exciting method, because the chemical shift that hydrogen nuclei in the water and the hydrogen nuclei in the fat form is about 3.5ppm, utilize this chemical shift can realize using the narrow radio frequency pulse only to excite hydrogen nuclei in the water, rebuild the pure water image.If but the degree of irregularity of the residing exterior magnetic field of human body surpasses 3.5ppm, use this method can't obtain the pure water image, can comprise a part of fatty tissue image in the image, therefore this method is inhomogeneous responsive to external magnetic field, and at low field system (for example 0.35T system), because the frequency shift (FS) very little (being about 50Hz) between water and the fat, the design of narrow radio frequency pulse also has certain difficulty.2) fatty saturation process, similar to above-mentioned water exciting method, in the method, use the hydrogen nuclei in the narrow radio frequency pulse excitation fat, the gradient magnetic that utilization applies makes the hydrogen nuclei magnetic saturation in the fat, uses the conventional sweep sequence to excite subject once more then, because the hydrogen nuclei magnetic saturation in the fat, have only the hydrogen nuclei in the water that imaging is had contribution after this excites, thereby the image that utilizes the echo-signal after exciting to rebuild is the pure water image.The defective of this method is identical with above-mentioned water exciting method, and is promptly inhomogeneous responsive to external magnetic field, and at the system of low magnetic field intensity, the design difficulty of narrow-band impulse is bigger.

The second, Dixon method

The ultimate principle of this method is same phase and two kinds of echo-signals of antiphase of gathering hydrogen nuclei in water and the fat respectively, and the echo-signal of two kinds of outs of phase is taken out fat signal by computing, rebuilds the pure water image, thereby reaches the purpose of fat suppression.The shortcoming of this method is inhomogeneous responsive to external magnetic field, and computational process is comparatively complicated.

In order to obtain isolating pure water and pure fat image simultaneously, a kind of improved 3 Dixon methods are widely used, the principle of this method is to obtain a width of cloth same phase image and two width of cloth antiphase images simultaneously, according to two width of cloth antiphase images, try to achieve the inhomogeneous additive phase that causes of exterior magnetic field, then two width of cloth antiphase images are carried out phase correction, try to achieve the image of water and fat again with the same phase image simultaneously respectively.The deficiency of these 3 Dixon methods is: because the additive phase that two width of cloth antiphase images are tried to achieve can not directly be used for its phase place is corrected, and must twine phase place is counter, yet counter being wrapped on the mathematics of phase place is that a nothing is separated problem, therefore suppose that the inhomogeneous variation spatially of exterior magnetic field is slowly, solution procedure can be quite time-consuming, and similarly computational process is also comparatively complicated.

Three, based on the method for separate imaging of water and fat of IR technology

This technology has different longitudinal relaxation time T1 based on water with fat, has utilized in the fat in the hydrogen nuclei and water the hydrogen nuclei back that is excited different to the time speed that equilibrium state recovers specifically.Use radio-frequency pulse to excite subject, i.e. hydrogen nuclei in simultaneous excitation water and the fat, employed here radio-frequency pulse also is called inversion pulse usually, and it is the equal of that once preparation before formal imaging excites excites.Determine the inversion recovery moment TI of fat, make that the longitudinal magnetization component of hydrogen nuclei in this moment is 0 in the fat, promptly hydrogen nuclei only has component of transverse magnetisation in TI moment fat, again because the longitudinal relaxation time of water and fat is inequality, therefore when the TI time arrives in the water hydrogen nuclei must have the longitudinal magnetization component.Above-mentioned time T I can be determined by following formula: IT=ln2T1 _f, T1 wherein _fThe longitudinal relaxation time of expression fat.

Because using the principle of radio-frequency pulse excimer daughter nucleus is to make atomic nucleus depart from negative longitudinal axis or positive longitudinal axis, and this moment fat in hydrogen nuclei do not deposit the longitudinal magnetization component just, therefore when TI uses the conventional sweep sequence to excite subject constantly, to have only the hydrogen atom in the water to be excited once more, the echo-signal reconstructed image that receives after utilizing this conventional sweep sequence to excite just can obtain the pure water image.Similarly, if obtain the pure fat image, also can profit in a like fashion.

Carry out separate imaging of water and fat though use the IR technology, can not consider the uneven influence of exterior magnetic field, narrow-band impulse difficult design in the time of also the frequency of utilization system of selection can not occurring, but because when obtaining pure water image or pure fat image, the echo-signal of only having used the hydrogen nuclei in the water or in the fat to send makes signal amplitude significantly reduce, again because the randomness that noise occurs, the signal to noise ratio that will make image that significantly reduces of signal amplitude reduces, thereby influences image quality.In addition, want, just obtain the pure water image and the pure fat image also can't be realized by using scanning sequence to excite subject once.

In sum, at present in the method for separate imaging of water and fat that exists, method for separate imaging of water and fat based on the IR technology is the simple method of a kind of computational process, and be subjected to exterior magnetic field Effect on Performance minimum, but the method for separate imaging of water and fat that is based on the IR technology still exist signal noise ratio (snr) of image low, can't excite subject once just to obtain the shortcoming of pure water image and pure fat image by using scanning sequence.

Summary of the invention

In view of this, one object of the present invention is to provide a kind of method for separate imaging of water and fat based on the IR technology, use this method to excite subject once just to obtain pure water image and pure fat image, and the signal to noise ratio of acquisition image is higher by using scanning sequence.

Another object of the present invention is to provide a kind of separate imaging of water and fat system based on the IR technology, use this system to excite subject once just to obtain pure water image and pure fat image by using scanning sequence, and the signal to noise ratio of acquisition image is higher.

Technical scheme of the present invention is achieved in that

A kind of method for separate imaging of water and fat based on inversion recovery technology, with hydrogen nuclei in hydrogen nuclei or the water in the fat of subject be defined as inversion recovery constantly at object, determine that described object longitudinal magnetization component is 0 first inversion recovery moment, key is that this method also comprises:

Described first inversion recovery constantly before and afterwards, select respectively described object longitudinal magnetization component direction is opposite, amplitude is identical second inversion recovery constantly and the 3rd inversion recovery constantly;

In described second inversion recovery moment and the 3rd inversion recovery moment, use scanning sequence to excite subject respectively, obtain two width of cloth images that comprise pure water image and pure fat image simultaneously;

Two width of cloth images that use is obtained synthesize, and obtain a width of cloth pure water image when the pure fat image that comprises in described synthetic elimination two width of cloth images, obtain a width of cloth pure fat image when the pure water image that comprises in described synthetic elimination two width of cloth images.

Preferably, described object is a hydrogen nuclei in the fat; Second inversion recovery moment and the 3rd inversion recovery that the described object longitudinal magnetization of described selection component direction is opposite, amplitude is identical are constantly:

Before the moment, select second inversion recovery moment of hydrogen nuclei in the fat at described first inversion recovery at random;

Described first inversion recovery constantly after, use second inversion recovery moment of selecting, determine the 3rd inversion recovery moment of hydrogen nuclei in the fat, make that the longitudinal magnetization component direction of hydrogen nuclei is opposite in the fat, amplitude is identical in second inversion recovery moment of selecting and definite the 3rd inversion recovery moment.

Preferably, described first inversion recovery is ln2T1 constantly _f, T1 wherein _fLongitudinal relaxation time for hydrogen nuclei in the fat; If second inversion recovery of selecting is TI constantly ₁, the 3rd inversion recovery of determining is TI constantly ₂, adjust surplus and be Δ T and value less than ln2T1 _f

Describedly select at random that second inversion recovery of hydrogen nuclei is constantly in the fat:

TI ₁＝ln2·T1 _f-ΔT；

Second inversion recovery that described use is selected determines that the 3rd inversion recovery of hydrogen nuclei is constantly in the fat constantly:

${\mathrm{TI}}_2=-\ln 2\·{T1}_f\·\ln (1-e^{-{\mathrm{TI}}_1/{T1}_f}).$

Preferably, second inversion recovery that is located at selection constantly and two width of cloth images that obtain constantly of the 3rd inversion recovery of determining be I ₁(x, y) and I ₂(x, y), the pure water image that comprises simultaneously in described two width of cloth images is I _w(x, y), the pure fat image is I _f(x, y); Described two width of cloth images that comprise pure water image and pure fat image simultaneously that obtain are:

$I_1(x,y)=I_w(x,y)\·(1-2e^{-\frac{{\mathrm{TI}}_1}{{T1}_w}})+I_f(x,y)\·(1-2e^{-\frac{{\mathrm{TI}}_1}{{T1}_f}})$

$I_2(x,y)=I_w(x,y)\·(1-2e^{-\frac{{\mathrm{TI}}_2}{{T1}_w}})+I_f(x,y)\·(1-2e^{-\frac{{\mathrm{TI}}_2}{{T1}_f}}).$

Obtaining the width of cloth pure water image during pure fat image that preferably, comprises in described synthetic elimination two width of cloth images is:

$I_w(x,y)=\frac{I_2(x,y)+I_1(x,y)}{2-2e^{-\frac{{\mathrm{TI}}_1}{{T1}_w}}-2e^{-\frac{{\mathrm{TI}}_2}{{T1}_w}}};$

Obtaining the width of cloth pure fat image during pure water image that comprises in described synthetic elimination two width of cloth images is:

$I_f(x,y)=\frac{I_2(x,y)}{1-2{\·e}^{-\frac{{\mathrm{TI}}_2}{{T1}_f}}}-\frac{I_2(x,y)+I_1(x,y)}{2-2e^{-\frac{{\mathrm{TI}}_1}{{T1}_w}}-2e^{-\frac{{\mathrm{TI}}_2}{{T1}_w}}}\·\frac{1-2\·e^{-\frac{{\mathrm{TI}}_2}{{T1}_w}}}{1-2\·e^{-\frac{{\mathrm{TI}}_2}{{T1}_f}}}.$

Preferably, described scanning sequence is a spin-echo sequence, perhaps gradin-echo, perhaps echo wave plane image sequence.

A kind of separate imaging of water and fat system based on inversion recovery technology comprises: excitation module and image-forming module; Key is that this system also comprises determination module;

Described determination module, be used for hydrogen nuclei in the fat hydrogen nuclei of subject or the water be defined as inversion recovery constantly institute at object, determine that described object longitudinal magnetization component is 0 first inversion recovery moment; Described first inversion recovery constantly before and afterwards, select respectively described object longitudinal magnetization component direction is opposite, amplitude is identical second inversion recovery constantly and the 3rd inversion recovery constantly;

Described excitation module is used for using scanning sequence to excite subject respectively in described second inversion recovery moment and the 3rd inversion recovery moment;

Described image-forming module is used for constantly and after the 3rd inversion recovery moment excites subject respectively, obtaining two width of cloth images that comprise pure water image pure fat image simultaneously in described second inversion recovery in described excitation module; Two width of cloth images that use is obtained synthesize, and obtain a width of cloth pure water image when the pure fat image that comprises in described synthetic elimination two width of cloth images, obtain a width of cloth pure fat image when the pure water image that comprises in described synthetic elimination two width of cloth images.

Preferably, described determination module comprises: first determining unit and second determining unit;

Described first determining unit, be used for hydrogen nuclei in the fat hydrogen nuclei of subject or the water be defined as inversion recovery constantly institute at object, determine that described object longitudinal magnetization component is 0 first inversion recovery moment;

Described second determining unit is used at described first inversion recovery selecting second inversion recovery moment of described object at random before the moment; Described first inversion recovery constantly after, use second inversion recovery moment of selecting, determine the 3rd inversion recovery moment of described object, make that the longitudinal magnetization component direction of described object is opposite, amplitude is identical in second inversion recovery moment of selecting and definite the 3rd inversion recovery moment.

As seen, the present invention is based on the method for separate imaging of water and fat and the system of IR technology, select two inversion recoveries constantly at hydrogen nuclei in hydrogen nuclei in the fat or the water, make constantly at these two selected inversion recoveries, the longitudinal magnetization component direction of hydrogen nuclei is opposite in the fat, amplitude is identical, perhaps the longitudinal magnetization component direction of hydrogen nuclei is opposite in the water, amplitude is identical, constantly obtain two width of cloth images that comprise pure water image and pure fat image simultaneously respectively at selected two inversion recoveries, the pure fat pictorial symbol that is comprised in this two width of cloth image is opposite, the pure water pictorial symbol that is perhaps comprised is opposite, therefore uses two width of cloth images that obtain to obtain pure water image and pure fat image by synthesizing.Because two width of cloth images that obtain constantly at selected two inversion recoveries have comprised pure water image and pure fat image simultaneously, promptly considered in the water simultaneously and fat in the echo-signal that sends of hydrogen nuclei, make the signal source of imaging increase, and then the signal amplitude of imaging increases, again owing to consider the randomness that noise occurs, can draw under the situation that signal amplitude increases, can improve the signal to noise ratio of imaging, and can excite subject once by using scanning sequence, re-use this two width of cloth image and just can synthesize pure water image and pure fat image.

Description of drawings

Fig. 1 is the flow chart that the present invention is based on the method for separate imaging of water and fat of IR technology;

Fig. 2 a-Fig. 2 d the present invention is based in the application example of method for separate imaging of water and fat of IR technology the imaging effect sketch map;

Fig. 3 is the separate imaging of water and fat system structure sketch map that the present invention is based on the IR technology.

The specific embodiment

For making objects and advantages of the present invention clearer, the present invention is further detailed explanation below in conjunction with drawings and Examples, and these explanations are nonrestrictive.

At first introduce the method for separate imaging of water and fat based on the IR technology provided by the invention.

Fig. 1 is the flow chart that the present invention is based on the method for separate imaging of water and fat of IR technology, in this flow process, with hydrogen nuclei in hydrogen nuclei or the water in the fat of subject be defined as inversion recovery constantly institute at object, determine that described object longitudinal magnetization component is 0 first inversion recovery moment.This flow process shown in Figure 1 comprises:

Step 101: first inversion recovery constantly before and afterwards, select respectively described object longitudinal magnetization component direction is opposite, amplitude is identical second inversion recovery constantly and the 3rd inversion recovery constantly.

In this step, second inversion recovery moment and the 3rd inversion recovery can make a choice at hydrogen nuclei in hydrogen nuclei in the fat or the water respectively constantly.If constantly at first inversion recovery, the longitudinal magnetization component of hydrogen nuclei is 0 in the fat, then select hydrogen nuclei longitudinal magnetization component direction is opposite in the fat, amplitude is identical second inversion recovery moment and the 3rd inversion recovery moment, and because the relaxation time difference of water and fat, in selected second inversion recovery moment and the 3rd inversion recovery moment, the longitudinal magnetization component of hydrogen nuclei is identical at this moment in the water; If constantly at first inversion recovery, the longitudinal magnetization component of hydrogen nuclei is 0 in the water, then select hydrogen nuclei longitudinal magnetization component in the water be 0 second inversion recovery constantly and the 3rd inversion recovery moment, similarly, because the relaxation time difference of water and fat, in selected second inversion recovery moment and the 3rd inversion recovery moment, the longitudinal magnetization component of hydrogen nuclei is identical at this moment in the fat.

Step 102: in described second inversion recovery moment and the 3rd inversion recovery moment, use scanning sequence to excite subject respectively, obtain two width of cloth images that comprise pure water image and pure fat image simultaneously.

In this step, if in step 101, select be hydrogen nuclei in the fat second inversion recovery constantly and the 3rd inversion recovery moment, then utilize in two width of cloth images that echo-signal obtains, the pure water pictorial symbol that comprises is identical; If in step 101, select the time water in hydrogen nuclei second inversion recovery constantly and the 3rd inversion recovery moment, then utilize in two width of cloth images that echo-signal obtains, the pure fat pictorial symbol that comprises is identical.Therefore constantly at two selected inversion recoveries, to comprise the pure water image considering hydrogen nuclei sends in the water echo-signal and form simultaneously, and consider to be equivalent to the pure fat image of the echo-signal that hydrogen nuclei sends in the fat form in two width of cloth images that obtain by pure water image and pure fat image overlay.

Step 103: use two width of cloth images obtain to synthesize, when described synthetic elimination pure fat image, obtain a width of cloth pure water image, when described synthetic elimination pure water image, obtain a width of cloth pure fat image.

In this step, the second counter-rotating moment and the 3rd counter-rotating with hydrogen nuclei in the fat are example constantly, the longitudinal magnetization component direction of hydrogen nuclei is opposite in the fat, amplitude is identical, and the longitudinal magnetization component direction of hydrogen nuclei is identical in the water, therefore the pure fat pictorial symbol that is comprised in two width of cloth images that obtain is opposite, the pure water pictorial symbol is identical, suppose that the image that second inversion recovery of hydrogen nuclei obtains constantly in the fat is A1, the image that the 3rd inversion recovery of hydrogen nuclei obtains constantly in the fat is A2, can use following principle formula simply to illustrate:

A1=pure water image+pure fat image;

A2=pure water image-pure fat image.

Shown in above-mentioned principle formula, can find the solution this binomial formula.Because therefore the opposite in sign of pure fat image can eliminate the pure fat image with A1 and A2 addition, obtain pure water image=(A1+A2)/2; A1 and A2 subtracted each other to eliminate the pure water image, obtain pure fat image=(A1-A2)/2, if consider pure fat image effect preferably, imaging also can be adopted a kind of preferable mode, the pure water image back substitution that promptly obtains is any one formula wherein, just can obtain pure fat image=(A1-A2)/2.

Second counter-rotating with hydrogen nuclei in the water is that example also can obtain identical synthetic result with the 3rd counter-rotating constantly constantly, but above-mentioned principle formula is just set forth principle based on the simplest situation, during practical application, in two width of cloth images that obtained, based on second inversion recovery moment and the 3rd inversion recovery different choice constantly, the pure water image in this principle formula also may have different coefficients with the pure fat image.

If the second counter-rotating moment and the 3rd counter-rotating with hydrogen nuclei in the water are example constantly, similar with above-mentioned analytical method, the opposite in sign of pure water image in this case just, the symbol of pure fat image is identical, the pure water image that obtains=(A1-A2)/2, and the pure fat image=(A1+A2)/2.

The present invention is based on the method for separate imaging of water and fat of IR technology, select two inversion recoveries constantly at hydrogen nuclei in hydrogen nuclei in the fat or the water, make constantly at these two selected inversion recoveries, the longitudinal magnetization component direction of hydrogen nuclei is opposite in the fat, amplitude is identical, perhaps the longitudinal magnetization component direction of hydrogen nuclei is opposite in the water, amplitude is identical, constantly obtain two width of cloth images that comprise pure water image and pure fat image simultaneously respectively at selected two inversion recoveries, the pure fat pictorial symbol that is comprised in this two width of cloth image is opposite, the pure water pictorial symbol that is perhaps comprised is opposite, therefore uses two width of cloth images that obtain to obtain pure water image and pure fat image by synthesizing.Because two width of cloth images that obtain constantly at selected two inversion recoveries have comprised pure water image and pure fat image simultaneously, promptly considered in the water simultaneously and the echo-signal that hydrogen nuclei sends in the fat, make the signal source of imaging increase, and then the signal amplitude of imaging increases, again owing to consider the randomness that noise occurs, can draw under the situation that signal amplitude increases, can improve the signal to noise ratio of imaging, and can excite subject once by using scanning sequence, re-use this two width of cloth image and just can synthesize pure water image and pure fat image.

Below, introduce the specific embodiment of method provided by the invention, in this specific embodiment, with the longitudinal magnetization component of selecting hydrogen nuclei in the fat is that 0 first inversion recovery is example constantly, this first inversion recovery constantly before and afterwards, second inversion recovery of selecting hydrogen nuclei in the fat respectively is constantly and the 3rd inversion recovery moment.

In the present embodiment, based on the longitudinal magnetization amount of fatty hydrogen nuclei be 0 first inversion recovery constantly, this first inversion recovery constantly before and afterwards, second inversion recovery of selecting hydrogen nuclei in the fat respectively is TI constantly ₁With the 3rd inversion recovery moment TI ₂, the principle of selection can comprise:

1) determine that fatty hydrogen nuclei longitudinal magnetization component in relaxation process is 0 first inversion recovery moment, the method for determining is identical with usual way, this first inversion recovery can be defined as ln2T1 constantly _f, T1 wherein _fLongitudinal relaxation time for hydrogen nuclei in the fat.

2) the 1st) in first inversion recovery determined constantly before and afterwards, select second inversion recovery moment and the 3rd inversion recovery moment among the present invention respectively, the principle of selecting comprises: before first inversion recovery moment, select second inversion recovery TI constantly at random ₁After the moment, use second inversion recovery moment TI that determines at first inversion recovery ₁Determine the 3rd inversion recovery TI constantly ₂, make at TI ₁And TI ₂The longitudinal magnetization component direction of hydrogen nuclei is opposite in the fat constantly, amplitude is identical, and the longitudinal magnetization component direction of hydrogen nuclei is identical in the water.

According to above-mentioned selection principle, second inversion recovery moment TI in the present embodiment ₁With the 3rd inversion recovery moment TI ₂A kind ofly specifically can be expressed from the next for example:

TI ₁＝ln2·T1 _f-ΔT；

${\mathrm{TI}}_2=-\ln 2\·{T1}_f\·\ln (1-e^{-{\mathrm{TI}}_1/{T1}_f}).$

Δ T in the above-mentioned formula is the parameter of optional size, can select less than ln2T1 _fArbitrary value, specifically can select according to practical situations, for example take all factors into consideration after the factors such as imaging time, signal noise ratio (snr) of image and determine.

3) at second inversion recovery moment TI ₁With the 3rd inversion recovery moment TI ₂Use the conventional sweep sequence to excite subject respectively, obtain two width of cloth images through the conventional imaging method, this two width of cloth image all consider simultaneously in the water and fat in the echo-signal that sends of hydrogen nuclei, comprise pure water image and pure fat image, be equivalent to every width of cloth image and all form by pure water image and pure fat image overlay.If use pure water image and above-mentioned two width of cloth images that obtain of pure fat graphical representation, can use following formulate:

$I_1(x,y)=I_w(x,y)\·(1-2e^{-\frac{{\mathrm{TI}}_1}{{T1}_w}})+I_f(x,y)\·(1-2e^{-\frac{{\mathrm{TI}}_1}{{T1}_f}})$

$I_2(x,y)=I_w(x,y)\·(1-2e^{-\frac{{\mathrm{TI}}_2}{{T1}_w}})+I_f(x,y)\·(1-2e^{-\frac{{\mathrm{TI}}_2}{{T1}_f}}).$

Wherein, I ₁(x y) is illustrated in TI ₁First image that the moment obtains, I ₂(x y) is illustrated in TI ₂Second image that the moment obtains, I _w(x, y) expression pure water image, T1 _wThe relaxation time of representing known water, I _f(x, y) expression pure fat image, T1 _fThe relaxation time of representing hydrogen nuclei in the known fat.

By the above-mentioned the 2nd) in formula can know, $I_f(x,y)\·(1-2e^{-\frac{{\mathrm{TI}}_1}{{T1}_f}})=-I_f(x,y)\·(1-2e^{-\frac{{\mathrm{TI}}_2}{{T1}_f}}),$ Bring this relational expression into above-mentioned I ₁(x, y) and I ₂(x can obtain the pure water image I in formula y) _w(x, y) and pure fat image I f (x, formula y) is as follows:

$I_w(x,y)=\frac{I_2(x,y)+I_1(x,y)}{2-2e^{-\frac{{\mathrm{TI}}_1}{{T1}_w}}-2e^{-\frac{{\mathrm{TI}}_2}{{T1}_w}}}$

$I_f(x,y)=\frac{I_2(x,y)}{1-2{\·e}^{-\frac{{\mathrm{TI}}_2}{{T1}_f}}}-\frac{I_2(x,y)+I_1(x,y)}{2-2e^{-\frac{{\mathrm{TI}}_1}{{T1}_w}}-2e^{-\frac{{\mathrm{TI}}_2}{{T1}_w}}}\·\frac{1-2\·e^{-\frac{{\mathrm{TI}}_2}{{T1}_w}}}{1-2\·e^{-\frac{{\mathrm{TI}}_2}{{T1}_f}}}.$

By the above-mentioned the 1st) to the 3rd) in formula describe as can be seen, at second inversion recovery TI constantly ₁With the 3rd inversion recovery moment TI ₂, use the conventional sweep sequence to excite subject respectively, two width of cloth images that process conventional imaging method is comprised pure water image and pure fat image simultaneously use this two width of cloth image just can synthesize pure water image and pure fat image respectively.

Above-mentioned specific embodiment with second inversion recovery of hydrogen nuclei in the fat constantly and the 3rd inversion recovery be example constantly, if be example with hydrogen nuclei in the water, analytical method is still identical, only need are with the T1 in the concrete formula of the foregoing description _fReplace with T1 _w, with I _f(x y) replaces with I _w(x y) gets final product.

Method provided by the invention has obtained following beneficial effect:

1. the acquisition process of pure water image and pure fat image and do not rely on exterior magnetic field, therefore method of the present invention goes for the system of various exterior magnetic field intensity, for example the low field system of 0.35T also can use, simultaneously inhomogeneous also insensitive to external magnetic field.In addition, if adopt adiabatic pulse as inversion pulse, the inventive method is inhomogeneous also insensitive to radio-frequency field.

2. two width of cloth images have constantly been obtained respectively based on second inversion recovery moment and the 3rd inversion recovery, re-use synthetic pure water image of this two width of cloth image and pure fat image, this two width of cloth image all considered in the water simultaneously and fat in the echo-signal of hydrogen nuclei, therefore make the signal source of imaging increase, the signal amplitude of imaging increases, again because the randomness that noise occurs, under the situation that signal amplitude increases, can improve the signal to noise ratio of imaging, thereby improve the quality of image.

3. with respect to existing water fat separation method based on the IR technology, can obtain pure water image and pure fat image simultaneously, though 3 Dixon methods also can obtain pure water image and pure fat image simultaneously in the prior art, but be to use method provided by the invention need not to existing 3 Dixon methods carry out like that such as phase place is instead twined, complicated computational process such as repeated calculation, thereby save time more.

Though 4. in method provided by the invention, need obtain two width of cloth images constantly respectively based on second inversion recovery moment and the 3rd inversion recovery, could use synthetic pure water image of this two width of cloth image and pure fat image then, sweep time is long slightly based on the water fat separation method of IR technology with respect to existing, but be based on above-mentioned the analysis in 2., use method provided by the invention can obtain the better pictures signal to noise ratio, if use existing water fat separation method based on the IR technology, may need to carry out at least twice scanning and obtain at least two width of cloth images, again to the image averaging that obtains to obtain higher signal noise ratio (snr) of image, therefore from this view point, method of the present invention can't expend more sweep time than existing water fat separation method based on the IR technology.

5. second inversion recovery constantly and the 3rd inversion recovery selection mode constantly, can only select hydrogen nuclei longitudinal magnetization component in hydrogen nuclei in the fat or the water in the existing water fat separation method based on the IR end is moment of 0, this mode is more flexible.

Based on the inventive method of above-mentioned introduction, introduce a concrete application example, suppose to comprise in the subject three kinds of materials, be respectively pure water, edible oil (being equivalent to fat) and CuSO from top to bottom ₄Aqueous solution, this three parts material non-overlapping copies.Should be the separation pure water image and the pure fat image that prove that the inventive method can be correct with the purpose of example, the application scenarios setting of the material non-overlapping copies in the subject only is a kind of for example concrete and be not to limit the scope of the invention.In the medical applications of reality, will there be the probability that overlaps each other to a great extent in water in the human body and fatty tissue, but this not image use the inventive method to realize the purpose of separate imaging of water and fat.

Should use in the example, the conventional sweep sequence adopts spin echo (TSE, Turbo Spin Echo) sequence, magnetic resonance imaging system is the low field system of 0.35T, hydrogen nuclei in the corresponding fat, second inversion recovery is selected 60 milliseconds constantly, and the 3rd inversion recovery is selected 160 milliseconds constantly.Fig. 2 a-Fig. 2 d is the imaging effect sketch map that should use in the example, wherein Fig. 2 a and Fig. 2 b show respectively at second inversion recovery constantly and two width of cloth images that obtained of the 3rd inversion recovery moment, and three images from top to bottom are respectively pure water image, pure fat image and the CuSO in the subject ₄The aqueous solution image.Fig. 2 c and Fig. 2 d show two width of cloth images that use second inversion recovery moment and the 3rd inversion recovery to obtain constantly respectively, synthetic pure water image and pure fat image, use method of the present invention as can be seen, can correctly separate pure water image and pure fat image, this separation is different from other materials of water and fat to the relaxation time that exists in the subject (for example should be with the CuSO that is exemplified in the example ₄Aqueous solution) also insensitive.

In the method for the invention, scanning sequence can also adopt gtadient echo (GRE, Gradient Echo) sequence or echo wave plane image (EPI, Echo Planar Image) sequence or the like other conventional sweep sequences.

Secondly, introduce the water fat piece-rate system that the present invention is based on the IR technology.

Fig. 3 is the separate imaging of water and fat system structure sketch map that the present invention is based on the IR technology, and this system comprises: excitation module 31, image-forming module 32 and determination module 33.

Determination module 33, be used for hydrogen nuclei in the fat hydrogen nuclei of subject or the water be defined as inversion recovery constantly institute at object, determine that described object longitudinal magnetization component is 0 first inversion recovery moment; Described first inversion recovery constantly before and afterwards, select respectively described object longitudinal magnetization component direction is opposite, amplitude is identical second inversion recovery constantly and the 3rd inversion recovery constantly.

Excitation module 31 is used for using scanning sequence to excite subject respectively in described second inversion recovery moment and the 3rd inversion recovery moment.

Image-forming module 32 is used for constantly and after the 3rd inversion recovery moment excites subject respectively, obtaining two width of cloth images that comprise pure water image pure fat image simultaneously in described second inversion recovery in excitation module 31; Two width of cloth images that use is obtained synthesize, and obtain a width of cloth pure water image when the pure fat image that comprises in described synthetic elimination two width of cloth images, obtain a width of cloth pure fat image when the pure water image that comprises in described synthetic elimination two width of cloth images.

The present invention is based on the separate imaging of water and fat system of IR technology, select two inversion recoveries constantly by determination module 33 at hydrogen nuclei in hydrogen nuclei in the fat or the water, make constantly at these two selected inversion recoveries, the longitudinal magnetization component direction of hydrogen nuclei is opposite in the fat, amplitude is identical, perhaps the longitudinal magnetization component direction of hydrogen nuclei is opposite in the water, amplitude is identical, and excite subject constantly at selected two inversion recoveries respectively by excitation module 31, obtain two width of cloth images that comprise pure water image and pure fat image simultaneously respectively by image-forming module 32, the pure fat pictorial symbol that is comprised in this two width of cloth image is opposite, the pure water pictorial symbol that is perhaps comprised is opposite, therefore uses synthetic pure water image of two width of cloth images that obtain and pure fat image.Because two width of cloth images that obtain constantly at selected two inversion recoveries have comprised pure water image and pure fat image simultaneously, water signal and fat signal have promptly been considered simultaneously, make the signal source of imaging increase, and then the signal amplitude of imaging increases, again owing to consider the randomness that noise occurs, can draw under the situation that signal amplitude increases, can improve the signal to noise ratio of imaging, and can excite subject once by using scanning sequence, re-use synthetic pure water image of this two width of cloth image and pure fat image, just can realize obtaining pure water image and pure fat image.

Above-mentioned determination module 33 can also comprise: first determining unit 331 and second determining unit 332.

First determining unit 331, be used for hydrogen nuclei in the fat hydrogen nuclei of subject or the water be defined as inversion recovery constantly institute at object, determine that described object longitudinal magnetization component is 0 first inversion recovery moment.

Second determining unit 332 is used at described first inversion recovery selecting second inversion recovery moment of described object at random before the moment; Described first inversion recovery constantly after, use described object second inversion recovery constantly, determine the 3rd inversion recovery moment of described object, make that the longitudinal magnetization component direction of described object is opposite, amplitude is identical in second inversion recovery moment of selecting and definite the 3rd inversion recovery moment.

System provided by the invention is compared with common employed magnetic resonance system, and excitation module 31 can use radio-frequency sending coil to realize, image-forming module 32 can use RF receiving coil and computer generated image unit to realize.This system can carry out work according to method flow provided by the invention, repeats no more here.

In sum, more than be preferred embodiment of the present invention only, be not to be used to limit protection scope of the present invention.Within the spirit and principles in the present invention all, any modification of being done, be equal to replacement, improvement etc., all should be included within protection scope of the present invention.

Claims (8)

1. method for separate imaging of water and fat based on inversion recovery technology, with hydrogen nuclei in hydrogen nuclei or the water in the fat of subject be defined as inversion recovery constantly at object, determine that described object longitudinal magnetization component is 0 first inversion recovery moment, it is characterized in that this method also comprises:

Described first inversion recovery constantly before and afterwards, select respectively described object longitudinal magnetization component direction is opposite, amplitude is identical second inversion recovery constantly and the 3rd inversion recovery constantly;

In described second inversion recovery moment and the 3rd inversion recovery moment, use scanning sequence to excite subject respectively, obtain two width of cloth images that comprise pure water image and pure fat image simultaneously;

Two width of cloth images that use is obtained synthesize, and obtain a width of cloth pure water image when the pure fat image that comprises in described synthetic elimination two width of cloth images, obtain a width of cloth pure fat image when the pure water image that comprises in described synthetic elimination two width of cloth images.

2. the method for claim 1 is characterized in that, before the moment, selects second inversion recovery moment of hydrogen nuclei in the fat at described first inversion recovery at random; Described first inversion recovery constantly after, use second inversion recovery moment of selecting, determine the 3rd inversion recovery moment of hydrogen nuclei in the fat, make that the longitudinal magnetization component direction of hydrogen nuclei is opposite in the fat, amplitude is identical in second inversion recovery moment of selecting and definite the 3rd inversion recovery moment.

3. method as claimed in claim 2 is characterized in that, described first inversion recovery is ln2T1 constantly _f, T1 wherein _fLongitudinal relaxation time for hydrogen nuclei in the fat; If second inversion recovery of selecting is TI constantly ₁, the 3rd inversion recovery of determining is TI constantly ₂, adjust surplus and be Δ T and value less than ln2T1 _f

Describedly select at random that second inversion recovery of hydrogen nuclei is constantly in the fat:

TI ₁＝ln2·T1 _f-ΔT；

Second inversion recovery that described use is selected determines that the 3rd inversion recovery of hydrogen nuclei is constantly in the fat constantly:

${\mathrm{TI}}_2=-{\ln }_2\·{T1}_f\·\ln (1-e^{-{\mathrm{TI}}_1/{T1}_f}).$

4. method as claimed in claim 3 is characterized in that, second inversion recovery that is located at selection is I with two width of cloth images that the 3rd inversion recovery of determining obtains constantly constantly ₁(x, y) and I ₂(x, y), the pure water image that comprises simultaneously in described two width of cloth images is I _w(x, y), the pure fat image is I _f(x, y); Described two width of cloth images that comprise pure water image and pure fat image simultaneously that obtain are:

$I_1(x,y)=I_w(x,y)\·(1-{2e}^{-\frac{{\mathrm{TI}}_1}{{T1}_w}})+I_f(x,y)\·(1-{2e}^{-\frac{{\mathrm{TI}}_1}{{T1}_f}})$

$I_2(x,y)=I_w(x,y)\·(1-{2e}^{-\frac{{\mathrm{TI}}_2}{{T1}_w}})+I_f(x,y)\·(1-{2e}^{-\frac{{\mathrm{TI}}_2}{{T1}_f}})$

Wherein, T1 _wThe relaxation time of representing known water.

5. method as claimed in claim 4 is characterized in that, obtains the width of cloth pure water image during pure fat image that comprises in described synthetic elimination two width of cloth images to be:

$I_w(x,y)=\frac{I_2(x,y)+I_1(x,y)}{2-2e^{-\frac{{\mathrm{TI}}_1}{{T1}_w}}-2e^{-\frac{{\mathrm{TI}}_2}{{T1}_w}}};$

Obtaining the width of cloth pure fat image during pure water image that comprises in described synthetic elimination two width of cloth images is:

$I_f(x,y)=\frac{I_2(x,y)}{1-2\·e^{-\frac{{\mathrm{TI}}_2}{{T1}_f}}}-\frac{I_2(x,y)+I_1(x,y)}{2-2e^{-\frac{{\mathrm{TI}}_1}{{T1}_w}}-2e^{-\frac{{\mathrm{TI}}_2}{{T1}_w}}}\·\frac{1-2\·e^{-\frac{{\mathrm{TI}}_2}{{T1}_w}}}{1-2\·e^{-\frac{T{I}_2}{{T1}_f}}}.$

6. as any described method of claim 1 to 5, it is characterized in that described scanning sequence is a spin-echo sequence, perhaps gradin-echo, perhaps echo wave plane image sequence.

7. the separate imaging of water and fat system based on inversion recovery technology comprises: excitation module and image-forming module; It is characterized in that this system also comprises determination module;

Described determination module, be used for hydrogen nuclei in the fat hydrogen nuclei of subject or the water be defined as inversion recovery constantly institute at object, determine that described object longitudinal magnetization component is 0 first inversion recovery moment; Described first inversion recovery constantly before and afterwards, select respectively described object longitudinal magnetization component direction is opposite, amplitude is identical second inversion recovery constantly and the 3rd inversion recovery constantly;

Described excitation module is used for using scanning sequence to excite subject respectively in described second inversion recovery moment and the 3rd inversion recovery moment;

Described image-forming module is used for constantly and after the 3rd inversion recovery moment excites subject respectively, obtaining two width of cloth images that comprise pure water image pure fat image simultaneously in described second inversion recovery in described excitation module; Two width of cloth images that use is obtained synthesize, and obtain a width of cloth pure water image when the pure fat image that comprises in described synthetic elimination two width of cloth images, obtain a width of cloth pure fat image when the pure water image that comprises in described synthetic elimination two width of cloth images.

8. system as claimed in claim 7 is characterized in that, described determination module comprises: first determining unit and second determining unit;

Described first determining unit, be used for hydrogen nuclei in the fat hydrogen nuclei of subject or the water be defined as inversion recovery constantly institute at object, determine that described object longitudinal magnetization component is 0 first inversion recovery moment;

Described second determining unit is used at described first inversion recovery selecting second inversion recovery moment of described object at random before the moment; Described first inversion recovery constantly after, use second inversion recovery moment of selecting, determine the 3rd inversion recovery moment of described object, make that the longitudinal magnetization component direction of described object is opposite, amplitude is identical in second inversion recovery moment of selecting and definite the 3rd inversion recovery moment.

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