CN101744616B - Transmitting frequency calibration method for chemical saturation in MRI and MRI system - Google Patents
Transmitting frequency calibration method for chemical saturation in MRI and MRI system Download PDFInfo
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Abstract
The invention relates to a transmitting frequency calibration method for chemical saturation in MRI and a MRI system. The invention provides a transmitting frequency calibration method for chemical saturation, which relates to the chemical saturation imaging technology of magnetic resonance imaging (MRI) technology. The method of the invention adopts the decrease of water signal amplitude as standard to judge that the fat is fully saturated, therefore obtaining the transmitting frequency of fat saturation. And in addition, the invention also can confirm the best saturation transmitting frequency through combining with other prescan method. With the method of the invention, the fat-suppression effect is stable than before, and the method is less rely on the experience of the operator, and the image quality of chemical saturation (particularly the image quality of chemical saturation in low field MRI) is improved.
Description
Technical field
The present invention relates to nuclear magnetic resonance (MRI) technology, relate in particular to chemical saturated imaging technique.
Background technology
The MRI system is to obtain the image of human body according to nuclear magnetic resonance principle work.Tissue is by the similar molecular composition that contains water and the fat of hydrogen atom.The atomic nucleus of hydrogen atom has the magnetic moment that is associated, and this magnetic moment is the module of the clean magnetic attribute of hydrogen nuclei.When tissue is in magnetic field B
0Lower time of effect, magnetic field B
0With the magnetic momente interaction of hydrogen nuclei and make the nuclear arrangement of sub-fraction and magnetic field B
0In the same way.Magnetic field B
0Also make nuclear in the same way magnetic moment with frequency (ω) (being called precession frequency, frequency of precession) around magnetic field B
0The direction precession.Precession frequency depends on magnetic field B
0Intensity and nuclear gyromagnetic ratio (γ), gyromagnetic ratio is nuclear particular attribute.On mathematics, B
0, ω and γ have following relation:
ω=γ * B
0Equation (1)
Above-mentioned nuclear precession frequency is called Larmor (larmor) frequency.The radio-frequency pulse that applies the Larmor frequency with hydrogen nuclei to hydrogen nuclei when the MRI system is when (frequency of the radio-frequency pulse that applies is called tranmitting frequency), if hydrogen nuclei during also with this Larmor frequency precession, nuclear magnetic resonance, NMR will occur.When nuclear magnetic resonance, NMR occured, the hydrogen nuclei of precession was with the form emitted energy of specific radiofrequency signal.The MRI system produces radiofrequency signal to generate the MRI image by processing by the resonance hydrogen nuclei in the hydrone (being present in the scanning position).In many application, the radiofrequency signal that is produced by the resonance hydrogen nuclei in the non-hydrone is undesired, because they can reduce the quality of MRI image.
Usually, all contain a large amount of fat in each position of human body, this is so that often produce motion artifacts, the pseudo-shadow of chemical shift or other related artifacts on MRI, thereby so that not only anatomical structure show fuzzylyyer, and limited the demonstration of pathological changes and some sign.Therefore, chemistry saturated fat inhibition technology becomes very important technology in the MRI inspection, it is used for eliminating the impact of motion artifacts, the pseudo-shadow of chemical shift etc., profile and the edge of anatomical structure and pathological changes can more clearly be shown, the more important thing is to show the unenhanced pathological changes that can not show and some characteristic signs.
It is varied that MRI chemistry saturated fat suppresses technology, but generally speaking mainly based on two kinds of mechanism: the chemical shift of (1) fat and water; (2) the longitudinal relaxation difference of fat and its hetero-organization.
(1) chemical shift phenomenon
Same magnetic atom nuclear is in the same magnetic field environment, if not disturbed by other factors, its precession frequency should be identical.But we know that general material normally exists with molecular forms, and other atomic nucleus in the molecule or electronics will exert an influence to a certain magnetic atom nuclear.If so same magnetic atom nuclear is in different molecular, even if be in the same uniform main field, difference will appear in its precession frequency.In magnetic resonance, we call the chemical shift phenomenon to this phenomenon.The degree of chemical shift is directly proportional with the intensity of main field, and field intensity is higher, and chemical shift is more obvious.
During routine MRI, imaging to as if proton, the precession frequency that is in the proton in the different molecular also difference will occur, also namely have chemical shift.In tissue, most typical chemical shift of proton phenomenon is present between hydrone and the fat.The about 3.5PPM of proton precession frequency phase-difference in these two kinds of molecules differs about 220HZ under the field intensity of 1.5T, be about 150HZ under the 1.0T field intensity, is about 75HZ under the 0.5T field intensity.The precession frequency difference of proton provides a point of penetration for the fat suppression technology in fat and the water.
(2) the longitudinal relaxation difference of fat and its hetero-organization
In human normal tissue, the longitudinal relaxation of fat is fastest, and the T1 value is the shortest.Under the different field intensity, the T1 value of tissue also will change, and under the field intensity of 1.5T, the T1 value of fatty tissue is about 250ms, is significantly shorter than its hetero-organization.The T1 value difference of fatty tissue and its hetero-organization is not a point of penetration of fat suppression technology yet.
In the fat suppression technology that MRI commonly uses, it is one of the most frequently used fat suppression technology that frequency is selected saturation, and what this technology was utilized is exactly the chemical shift effect of fat and water.Because chemical shift, will there be difference in the precession frequency of proton in Fat and moisture.If before the excitation pulse of imaging sequence applies, apply continuously first several prepulsings, the frequency of these prepulsings is consistent with proton precession frequency in the fat, like this fatty tissue will saturated phenomenon be occured by continuous agitation, and the proton in the hydrone since the precession frequency difference be not excited.At this moment apply the real radio-frequency pulse that excites, fatty tissue be because saturatedly can not accept energy again again, thereby do not produce signal, and the generation signal that can be excited of the proton in the hydrone, thereby reaches the purpose of fat suppression.
But there is following shortcoming in the method: (1) field intensity dependency is larger.Because the degree of chemical shift phenomenon is directly proportional with main field strength.Under high field intensity, the proton precession frequency difference in fat and the water is larger, so the selectivity prepulsing that applies certain frequency carries out the fat suppression ratio and is easier to.But under low field intensity, the proton precession frequency difference in fat and the water is very little, carries out frequency and selects relatively difficulty of fat suppression.Therefore the method effect on the middle high field intensity scanner unit more than the 1.0T is better, but on the low field intensity scanner unit below the 0.5T poor effect, thereby should not adopt.(2) require very high to the uniformity in magnetic field.Because this technology utilization is the minute differences of the precession frequency of proton in the precession frequency of proton in the fat and the hydrone, if Magnetic field inhomogeneity, then will directly affect the precession frequency of proton, the frequency of prepulsing will be inconsistent with the precession frequency of proton in the fat, thereby have a strong impact on fat suppression effect.Therefore before this technology of use is carried out fat suppression, need to carry out the automatic or manual shimming to main field, should remove in the patient body simultaneously or body surface might affect any article of uniformity of magnetic field.When (3) carrying out large FOV scanning, neighboring area, visual field fat suppression effect is relatively poor, and this is also relevant with the uniformity and the gradient linearity in magnetic field.
Put it briefly, in practice, the reason that affects fat suppression effect has following several basically: for example:
1) poor field uniformity;
2) be not easy to obtain correct mid frequency;
3) error of mid frequency; This is the frequency error that is brought by system itself.
4) central frequency deviation.This is owing to material self character (for example temperature) causes.These reasons all may cause the radio frequency saturation pulse can not accurately act on the proton of fat (or water), mid frequency mistake or coarse may cause inferior or wrong chemical saturated image, especially in the low field intensity MRI of for example 0.35T system, thereby so that present frequency selects saturation to be difficult to reach good effect.
For the listed above the 4th) plant unfavorable factor, existing prior art is by following the tracks of central frequency deviation and it being compensated to reduce its impact.But to the negative consequence that first three kind factor produces, present prescan method obtains inaccurate tranmitting frequency sometimes, thereby causes saturation effect bad.
Frequency selects the prescan method of saturation mainly to comprise following process:
-in manual prescan, obtain fat signal and water signal;
-apply chemical saturated radio frequency, make fat signal saturated;
-adjust chemical saturated radio frequency until fatty by fully saturated.
The shortcoming that this method exists is: on the one hand, depend on to a great extent operator's experience; On the other hand, in some cases, be difficult to judge that whether fat is by finely saturated, because fat signal and water signal may mix.
Summary of the invention
The purpose of this invention is to provide a kind of for the saturated tranmitting frequency calibration steps of chemistry, its less experience that depends on the operator, thus make the result more sane.
According to an aspect of the present invention, a kind of chemical saturated tranmitting frequency calibration steps for MRI is provided, it begins to be judged fat by saturated fine by saturated with the water signal, to begin tranmitting frequency when the saturated chemical saturation emission frequency after as calibration corresponding to the water signal.Determine in the time of wherein can beginning to descend with the water signal amplitude that the water signal begins by saturated; Alternatively, record the water signal amplitude by basic prescan method, and with it as reference water signal amplitude; Adjust the saturated tranmitting frequency of chemistry and also measure corresponding water signal amplitude, when measured water signal amplitude drops to preset range with reference to the water signal amplitude, in the time of for example in 70% to 90% the scope, determine that the water signal begins by saturated.
Particularly, the tranmitting frequency calibration steps that above-mentioned chemistry according to the present invention is saturated suppresses fat signal with inversion pulse fat suppression method, to determine the frequency location of water signal peak and fat signal peak value; By adjusting the saturated tranmitting frequency of chemistry, frequency of utilization selects saturation to suppress fat signal, measures simultaneously the amplitude of water signal peak; Judge according to the variation of water signal amplitude whether the water signal begins by saturated; Set the water signal and begin chemical saturation emission frequency when the saturated chemical saturation emission frequency after for calibration.
The saturated tranmitting frequency calibration steps of above-mentioned chemistry according to the present invention can carry out respectively the saturated tranmitting frequency calibration of chemistry to each of a plurality of scan slices of being scanned object; Also can select to be scanned a scan slice in a plurality of scan slices of object as datum layer, this datum layer is carried out the saturated tranmitting frequency calibration of chemistry; Record the tranmitting frequency of other scan slice that is scanned object and calculate them with respect to the difference on the frequency of datum layer; Determine the chemical saturation emission frequency of other scan slice according to the chemical saturation emission frequency of measured difference on the frequency and the calibrated datum layer that obtains.Alternatively, the difference on the frequency that wherein calculates between other scan slice and the described datum layer also can be by obtaining the B that describes each scan slice
0The B of the distribution in magnetic field
0Field pattern obtains.
According to a further aspect in the invention, provide a kind of MRI system, it comprises: the main field magnet unit for generation of high-intensity magnetic field, is called B
0Magnetic field; Gradient coil unit is for generation of being superimposed upon B
0Gradient magnetic on the magnetic field; The RF coil unit is used for the transmitting RF pulse; Gradient drive is connected in gradient coil unit, is used to gradient coil unit to provide and drives signal to produce gradient magnetic; The RF driver is connected in the RF coil unit, is used to the RF coil unit to provide and drives signal with the transmitting RF pulse; Data acquisition unit is connected in the RF coil unit, is used for by sampling to receive or catch the signal that is received by the RF coil unit, and collects or gather same signal as numerical data; Controller is connected with gradient drive, RF driver, data acquisition unit, is used for these parts are controlled to carry out shooting or imaging.Wherein said controller comprises processing unit, this processing unit comprises: chemical saturation emission frequency calibration module, be used for beginning to be judged that by saturated the fat of one scan section is by finely saturated with the water signal, the tranmitting frequency of this moment is set as for the tranmitting frequency after the calibration of this scan slice, launches this tranmitting frequency by RF driver drives RF coil unit this scan slice is scanned.
Above-mentioned according to MRI of the present invention system in, described chemical saturation emission frequency calibration module begins to descend with the water signal amplitude and is defined as the water signal and begins by saturated.Particularly, described chemical saturation emission frequency calibration module comprises: determine the frequency location module, it suppresses the fat signal that one scan is cut into slices with inversion pulse fat suppression method, with the water signal peak of definite this scan slice and the frequency location of fat signal peak value; Measure the module of water signal amplitude, adjust the saturated tranmitting frequency of chemistry, frequency of utilization selects saturation to suppress the fat signal of this scan slice, measures the water signal amplitude; Judge whether the water signal begins by saturated module, variation according to the water signal amplitude of measuring judges whether the water signal begins by saturated, set chemical saturation emission frequency module, the water signal is begun when saturated corresponding tranmitting frequency be set as chemical saturation emission frequency for this scan slice.
In above-mentioned MRI according to the present invention system, described chemical saturation emission frequency calibration module also comprises: with reference to water signal amplitude determination module, its frequency location based on measured water signal peak, the basic prescan method of use, measure the water signal amplitude of this scan slice, and with the water signal amplitude that the records reference water signal amplitude as this scan slice; Judge whether the water signal begins by saturated module, with measured water signal amplitude with compare with reference to the water signal amplitude, when its preset range in reference water signal amplitude, in the time of for example in 70% to 90% the scope, judge that this moment, the water signal began by saturated.
In above-mentioned MRI according to the present invention system, described chemical saturation emission frequency calibration module is carried out respectively chemical saturation emission frequency calibration to each scan slice in a plurality of scan slices.Alternatively, this chemistry saturation emission frequency calibration module also comprises the difference on the frequency computing module, and this module is by measuring the frequency of each scan slice, and selecting one of them scan slice is datum layer, calculates other scan slice with respect to the difference on the frequency of datum layer; Described chemical saturation emission frequency calibration module is carried out the saturated tranmitting frequency calibration of chemistry to datum layer, then the chemical saturation emission frequency of acquisition after for the calibration of this datum layer determine the chemical saturation emission frequency of other scan slice according to the chemical saturation emission frequency of resulting difference on the frequency and the calibrated datum layer that obtains; Alternatively, described other scan slice can be by describing the B of each scan slice with respect to the difference on the frequency of datum layer
0The B of the distribution in magnetic field
0Field pattern obtains.
The present invention utilizes the water signal to begin by saturated as judging that fat by abundant saturated standard, sets fatty saturation emission frequency with this, thereby makes the calibration of chemical saturation emission frequency less depend on operator's experience.Further, the present invention adopts a series of prescan methods in order to determine best saturation emission frequency, and this makes fat suppression effect than more sane in the past.
In addition, the MRI system utilizes the present invention can realize automatically searching for the saturated best tranmitting frequency of chemistry, the interference that this not needing can realize the operator reaches the purpose of improving the saturated picture quality of chemistry, the chemical saturated picture quality when especially improving low field MRI.
Description of drawings
Fig. 1 shows according to existing criterion and judges to have preferably fatty saturated curve chart;
Fig. 2 shows according to new standard of the present invention and judges to have preferably fatty saturated curve chart;
The MRI that uses the criterion of prior art when Fig. 3 shows 0.35T and obtain;
The MRI that uses criterion of the present invention when Fig. 4 shows 0.35T and obtain;
Fig. 5 shows the flow chart that obtains the tranmitting frequency of a scan slice with method of the present invention;
Fig. 6 shows the block diagram according to MRI of the present invention system;
Fig. 7 shows the block diagram according to chemical saturation emission frequency calibration module of the present invention.
The specific embodiment
Below by specific embodiment the present invention is described in further detail, but the present invention is not restricted to this.
Prior art judges that whether fat is by saturated that good standard is: if the peak value of fat is minimum, judge that then fat reaches capacity.As shown in Figure 1, it shows according to existing criterion judges to have preferably fatty saturated curve chart, and wherein abscissa represents tranmitting frequency, the amplitude of vertical coordinate representation signal intensity.In Fig. 1, the curve with lower peak value represents fat, and it is suppressed to minimum, and the curve with higher peak value represents water.
And method of the present invention adopts and a kind ofly new judges that fat is whether by saturated good standard: if water begins by saturated, judge that then fat is by finely saturated.As shown in Figure 2, it shows according to new standard of the present invention judges to have preferably fatty saturated curve chart, and wherein abscissa represents tranmitting frequency, the amplitude of vertical coordinate representation signal intensity.In Fig. 2, the curve with lower peak value represents water, and the curve with higher peak value represents fat, and at this moment the peak value of water signal begins to reduce, and thinks that fat is by saturated.Although the peak value of the peakedness ratio water signal of fat signal shown in the figure is high, this moment fat be this shows by fully saturated, and the curve chart that uses new criterion of the present invention to draw is different from the curve chart that the standard of using prior art draws.
The experiment proved that new criterion of the present invention is better than the criterion of prior art.As shown in Figure 3 and Figure 4, use the criterion of prior art when Fig. 3 shows 0.35T and the MRI that obtains, use criterion of the present invention when Fig. 4 shows 0.35T and the MRI that obtains.Contrast as can be known from Fig. 3 and Fig. 4, Fig. 4 demonstrates the fat that has suppressed preferably skeleton and periphery from anatomy, Fig. 3 then demonstrates part fat from anatomy not to be suppressed fully, therefore, utilize new criterion of the present invention can distinguish more accurately fat and water than the criterion of prior art.
The method of using new criterion according to the present invention to carry out chemical saturation frequency calibration is described below by the specific embodiment.
The method according to this invention will be considered following factor usually when carrying out chemical saturation frequency calibration:
1) position of fat signal peak value in frequency domain
2) position of water signal peak in frequency domain
3) amplitude of fat signal peak value
4) amplitude of water signal peak
Usually, because B
0Uniformity is very poor in some cases in the field, this so that water and fat on frequency, might not naturally separate, especially the frequency gap of water and fat is very little in the time of low, so basic prescan method usually can not be distinguished fat signal peak value and water signal peak well.Therefore, the present invention at first uses inversion pulse to suppress fatty method fat signal is suppressed, and determines thus the frequency location of water signal and fat signal, but at this moment chemical saturated not necessarily fine.Afterwards, use basic prescan method, record the amplitude of water signal and fat signal, the water signal that obtains although it is so has any to mix, sometimes the water signal peak almost disappears, but can determine according to the frequency location of determined water signal before the amplitude of water signal, and with the amplitude of the water signal that obtains as reference water signal amplitude.Next, frequency of utilization selects saturation to suppress fat signal, and the water signal peak can clearly be seen.Then, adjust frequency and select the tranmitting frequency of chemical saturation pulse and monitor the water signal amplitude to change, when finding that the water signal amplitude begins to reduce, illustrate that the water signal has just begun by saturated, determine at this moment fat by fully saturated, the fatty saturation emission frequency that at this moment tranmitting frequency is defined as optimizing.Replacedly, to change along with the variation of fatty saturation emission frequency owing to the water signal amplitude and with reference to the ratio between the water signal amplitude, so set the scope of this ratio to determine that water has just begun by saturated, for example, can set the water signal amplitude and with reference to the ratio between the water signal amplitude in 70% to 90% scope, when monitoring the water signal amplitude in described preset range the time, determine the fatty saturation emission frequency of tranmitting frequency for optimizing of this moment.
From above as can be known, the present invention combines more existing prescan methods and new criterion of the present invention, can determine more exactly fatty saturation emission frequency, thereby make fat suppression effect than more sane in the past, can access good chemical saturated image.
In the practice, one of method that MRI system on human body region carries out scanning imagery is that the human body that will be scanned into picture is divided into a plurality of sections (being called scan slice), then to the one by one imaging of each scan slice.The image that makes up subsequently these scan slices forms the image of the human body that is scanned into picture.Can determine chemical saturation emission frequency with method above-mentioned respectively to every layer, but this can need the long prescan time.In order to reduce the prescan time, following two kinds of methods are arranged:
1) measures the tranmitting frequency of each scan slice, select one of them scan slice as datum layer, calculate other scan slice with respect to the difference on the frequency between the datum layer.Based on foregoing according to the chemical saturation emission frequency of determining this datum layer for chemical saturation emission transmitting frequency calibration method of the present invention.Then calibrate the chemical saturation emission frequency of described other scan slice by the difference on the frequency between other scan slice and this datum layer;
2) obtain to pass the B that is scanned into as each scan slice at position
0The distribution in magnetic field namely obtains B
0Field pattern selects one of them scan slice as datum layer, uses B
0Field pattern obtains other scan slice with respect to the difference on the frequency between the datum layer.Based on foregoing according to the fatty saturation emission frequency of determining this datum layer for chemical saturation emission transmitting frequency calibration method of the present invention; The chemical saturation emission frequency of the optimization that obtains other each scan slice with respect to the difference on the frequency between the datum layer according to chemical saturation emission frequency and other scan slice of determined datum layer.
According to front equation (1) as can be known, tranmitting frequency and magnetic field B
0Proportional, therefore obtain expression B
0The B of Distribution of Magnetic Field
0Behind the field pattern, just can obtain the difference on the frequency of each scan slice.Usually, B
0Distribution of Magnetic Field can obtain by two gtadient echo methods (dual gradient echo method), dual rotary echo method (dual spin echo method) and double echo helical scanning (dual echo spiralscan).
Describe a concrete embodiment of the present invention in detail below by flow chart.
Fig. 5 shows the flow chart that obtains the tranmitting frequency of a scan slice for the chemical saturated tranmitting frequency calibration steps of MRI with of the present invention.Different scan slices, tranmitting frequency can be different, but all can obtain with method shown in Figure 5.As shown in Figure 5,
At step S501, begin method of the present invention;
At step S502, suppress fat signal with inversion pulse fat suppression method, to determine the frequency location of water signal peak and fat signal peak value, shown in the right part of flg of arrow indication among Fig. 5, determined that the left side peak value is the water signal peak, the right side peak value is the fat signal peak value;
At step S503, measure the amplitude of water signal peak with basic prescan method based on the frequency location of the water signal peak that obtains, with it as reference water signal amplitude;
At step S504, frequency of utilization selects chemical saturation process to suppress fat signal, measures simultaneously the water signal amplitude;
At step S505, judge whether the water signal has just begun by saturated, for example, the water signal amplitude has just begun to descend; Perhaps the water signal amplitude drops in 70% to 90% the scope with reference to the water signal amplitude.When the water signal not when saturated, new tranmitting frequency then is set, re-start step S504, S505; When the water signal has just begun then to continue the following step when saturated;
At step S506, the tranmitting frequency that the water signal has just been begun when saturated is set as fatty saturation emission frequency;
At step S507, utilize the fatty saturation emission frequency that sets to scan.
Want to be noted that above-mentioned steps of the present invention is not limited to described order, those skilled in the art can carry out suitable adjustment to it as required.
In addition, according to the present invention, aforesaid operations may be programmed in the MRI system.When user selection fat was saturated, the MRI system can automatically perform aforesaid operations, and obtains good fatty saturated image.Utilize this method, system can automatically search for the saturated best tranmitting frequency of chemistry and not need operator's interference, and this can improve the saturated picture quality of chemistry, especially can improve the chemical saturated picture quality when low field MRI.
Fig. 6 shows the system according to MRI of the present invention.As shown in Figure 6, MRI of the present invention system comprises main field magnet unit 102, gradient coil unit 106, RF (radio frequency) coil unit 108, platform driver 120, gradient drive 130, RF driver 140, data acquisition unit 150, controller 160, data processor 170, display unit 180, and operating unit 190.
Main field magnet unit 102 is called B for generation of high-intensity magnetic field
0Magnetic field.
Gradient coil unit 106 is for generation of being superimposed upon B
0Gradient magnetic on the magnetic field, it produces a gradient magnetic at least, preferably, produces three gradient magnetics.
RF coil unit 108 is used for the transmitting RF pulse, exciting the spin that is scanned the hydrogen nuclei in the object, and receives the magnetic resonance signal that the spin that excites produces.Described RF coil unit 108 can be carried out by same coil or discrete coil and transmit and receive.
Gradient drive 130 is connected in gradient coil unit 106, is used to gradient coil unit 106 to provide and drives signal to produce gradient magnetic.
RF driver 140 is connected in RF coil unit 108, is used to RF coil unit 108 to provide and drives signal with the transmitting RF pulse.
Data acquisition unit 150 is connected in RF coil unit 108, is used for by sampling to receive or catch the signal that is received by RF coil unit 108, and collects or gather same signal as numerical data.
Controller 160 is connected with platform driver 120, gradient drive 130, RF driver 140, data acquisition unit 150, is used for respectively these parts being controlled to carry out shooting or imaging.
Data processor 170 is connected in the outlet side of data acquisition unit 150, and the data that storage and deal with data collecting unit 150 gather generate the reconstructed image of sweep object etc.
Display unit 180 is connected to data processor 170 with operating unit 190.Display unit 180 shows from reconstructed image and the various information of data processor 170 outputs.Operating unit 190 is by operator operation, and input various command and information are waited until data processor 170.The operator can control this device on interactively basis by display unit 180 and operating unit 190.
In above-mentioned MRI of the present invention system, described controller 160 comprises processing unit, and this processing unit comprises chemical saturation emission frequency calibration module.This chemistry saturation emission frequency calibration module is used for beginning to be judged that by saturated the fat of a scan slice that is scanned object is by finely saturated with the water signal, the tranmitting frequency of this moment is set as for the chemical saturation emission frequency after the calibration of this scan slice, and the tranmitting frequency after 108 these calibrations of emission of RF driver 140 driving RF coil units is to scan this scan slice.
Wherein said chemical saturation emission frequency calibration module can judge as follows that the water signal has just begun by saturated:
Begin to descend with the water signal amplitude and be judged to be the water signal and just begun by saturated.
Alternatively, record the water signal amplitude of this scan slice by basic prescan method and with it as reference water signal amplitude; Adjust the tranmitting frequency of chemical saturation pulse, frequency of utilization selects saturation to suppress the fat signal of this scan slice, measures the water signal amplitude; When the water signal amplitude is in the preset range of reference water signal amplitude, judge that the water signal has just begun by saturated.Wherein said preset range with reference to the water signal amplitude can according to circumstances have different limited ranges, for example can be 70% to 90% scope of reference water signal amplitude.
Below in conjunction with accompanying drawing 7 chemical saturation emission frequency calibration module of the present invention is described.
As shown in Figure 7, it has provided the preferred embodiment a kind of of chemical saturation emission frequency calibration module 700, and it comprises:
Determine frequency location module 710, it suppresses the fat signal that one scan is cut into slices with inversion pulse fat suppression method, with the water signal peak of definite this scan slice and the frequency location of fat signal peak value;
Determine the module 720 with reference to the water signal amplitude, it uses basic prescan method, measure the water signal peak of this scan slice based on the frequency location of determining frequency location module 710 determined water signal peaks, and with the amplitude of the water signal peak that the obtains reference water signal amplitude as this scan slice;
Measure the module 730 of water signal amplitude, it adjusts the tranmitting frequency of chemical saturation pulse, and frequency of utilization selects saturation to suppress the fat signal of this scan slice, measures the water signal amplitude;
Judge whether the water signal begins by saturated module 740, with measured water signal amplitude with compare with reference to the water signal amplitude, judge that when measured water signal amplitude begins to descend this moment, the water signal just began by saturated; Alternatively, when measured water signal amplitude drops in the preset range (for example 70% to 90% scope) with reference to the water signal amplitude, judge that this moment, the water signal just began by saturated;
Set chemical saturation pulse tranmitting frequency module 750, the water signal is begun when saturated corresponding tranmitting frequency be set as chemical saturation emission frequency for this scan slice.
Utilize chemical saturation emission frequency calibration module 700 shown in Figure 7 to calibrate one by one the tranmitting frequency of each scan slice of being scanned object.But, in order to reduce the prescan time, can measure in advance the difference on the frequency of each scan slice.For this reason, described chemical saturation emission frequency calibration module 700 can also comprise a difference on the frequency computing module, it measures the frequency of each scan slice, selects one of them scan slice as datum layer, and calculates other scan slice with respect to the difference on the frequency between the datum layer.700 pairs of these datum layers of described chemical saturation emission frequency calibration module carry out the saturated tranmitting frequency calibration of chemistry, obtain for the chemical saturation emission frequency after the calibration of this datum layer; Then determine the chemical saturation emission frequency of other scan slice according to the chemical saturation emission frequency of other measured scan slice and the difference on the frequency between the datum layer and the calibrated datum layer that obtains.
Alternatively, described difference on the frequency computing module can also be by obtaining the B that describes each scan slice
0The B of Distribution of Magnetic Field
0Field pattern is measured the frequency of each scan slice, then selects one of them scan slice as datum layer, calculates other scan slice with respect to the difference on the frequency between the datum layer
Want to be noted that, the embodiment of chemical saturation emission frequency calibration module 700 Just One Of Those Things kind comparative optimizations shown in Figure 7, the module that has wherein might not be necessary, for example, when beginning descend to judge fat signal with the water signal amplitude by saturated when fine, definite module with reference to the water signal amplitude wherein can be optional.In addition, the division of above-mentioned module is a kind of embodiment, be not to be limited to this, alternatively, above-mentioned module can further be segmented or several module can make up a module, for example above-mentioned definite module 720 with reference to the water signal amplitude can be attached to judge whether the water signal begins by in the saturated module 740.
In addition, said units of the present invention or module can be realized by software or hardware or software and hardware combining.
It should be noted that, although the above shows, has described the present invention in the mode of embodiment, but should be understood that, in the situation that does not break away from spirit of the present invention, those skilled in the art can to the form of described unit or module and details, with and operation carry out various omissions and replacement and change.For example apparently, finish the identical function of essence in the identical mode of essence and belong to scope of the present invention with those unit of acquisition identical result and/or all combinations of method step.
Claims (18)
1. chemical saturated tranmitting frequency calibration steps that is used for MRI comprises:
Suppress fat signal with inversion pulse fat suppression method, to determine the frequency location of water signal peak and fat signal peak value;
By adjusting the saturated tranmitting frequency of chemistry, frequency of utilization selects saturation to suppress fat signal, measures simultaneously the amplitude of water signal peak;
Judge according to the variation of water signal peak amplitude whether the water signal begins by saturated;
Set the water signal and begin tranmitting frequency when the saturated chemical saturation emission frequency after for calibration.
2. the tranmitting frequency calibration steps that chemistry according to claim 1 is saturated when the water signal amplitude begins to descend, determines that the water signal has just begun by saturated.
3. the tranmitting frequency calibration steps that chemistry according to claim 2 is saturated, by basic prescan method record the water signal amplitude and with it as reference water signal amplitude; Adjust the saturated tranmitting frequency of chemistry and measure corresponding water signal amplitude, in the time of in measured water signal amplitude drops to reference to the preset range of water signal amplitude, be defined as the water signal and begin by saturated.
4. the tranmitting frequency calibration steps that chemistry according to claim 1 is saturated, described variation according to water signal peak amplitude judges whether the water signal begins to be determined that by saturated step the water signal has just begun by saturated when the water signal amplitude begins to descend.
5. the tranmitting frequency calibration steps that chemistry according to claim 4 is saturated, describedly when beginning to descend, the water signal amplitude determines that the water signal has just begun to be comprised by saturated:
By basic prescan method record the water signal amplitude and with it as reference water signal amplitude;
Adjust the saturated tranmitting frequency of chemistry and measure corresponding water signal amplitude, in the time of in measured water signal amplitude drops to reference to the preset range of water signal amplitude, be defined as the water signal and begin by saturated.
6. the tranmitting frequency calibration steps that chemistry according to claim 5 is saturated, described preset range with reference to the water signal amplitude are the 70-90% with reference to the water signal amplitude.
7. the tranmitting frequency calibration steps that any one described chemistry is saturated according to claim 1-6 carries out respectively the saturated tranmitting frequency calibration of chemistry to each scan slices of a plurality of scan slices of being scanned object.
8. the tranmitting frequency calibration steps that any one described chemistry is saturated according to claim 1-6,
Selection is scanned a scan slice in a plurality of scan slices of object as datum layer, and this datum layer is carried out the saturated tranmitting frequency calibration of chemistry;
Record the tranmitting frequency of other scan slice that is scanned object and calculate them with respect to the difference on the frequency of datum layer;
Determine the chemical saturation emission frequency of other scan slice according to the chemical saturation emission frequency of measured difference on the frequency and the calibrated datum layer that obtains.
9. the tranmitting frequency calibration steps that any one described chemistry is saturated according to claim 1-6,
Selection is scanned a scan slice in a plurality of scan slices of object as datum layer, and this datum layer is carried out the saturated tranmitting frequency calibration of chemistry;
Obtain the B that describes each scan slice
0The B of Distribution of Magnetic Field
0Field pattern is based on B
0Field pattern obtains the difference on the frequency between other scan slice and the described datum layer;
Determine the chemical saturation emission frequency of other scan slice according to the chemical saturation emission frequency of measured difference on the frequency and the calibrated datum layer that obtains.
10. chemical saturated tranmitting frequency calibrating installation that is used for MRI comprises:
Determine the frequency location module, it suppresses the fat signal that one scan is cut into slices with inversion pulse fat suppression method, with the water signal peak of definite this scan slice and the frequency location of fat signal peak value;
Measure the module of water signal amplitude, adjust the saturated tranmitting frequency of chemistry, frequency of utilization selects saturation to suppress the fat signal of this scan slice, measures the water signal amplitude;
Judge whether the water signal begins by saturated module, judges according to the variation of the water signal amplitude of measuring whether the water signal begins by saturated,
Set chemical saturation emission frequency module, the water signal is begun when saturated corresponding tranmitting frequency be set as chemical saturation emission frequency for this scan slice.
11. the chemical saturated tranmitting frequency calibrating installation that is used for MRI according to claim 10, described chemical saturation emission frequency calibration module begin decline with the water signal amplitude and are defined as the water signal and begin by saturated.
12. the chemical saturated tranmitting frequency calibrating installation that is used for MRI according to claim 11, the basic prescan method of described chemical saturation emission frequency calibration module use record the water signal amplitude and with it as reference water signal amplitude; Adjust the saturated tranmitting frequency of chemistry and measure corresponding water signal amplitude, in the time of in measured water signal amplitude drops to reference to the preset range of water signal amplitude, be defined as the water signal and begin by saturated.
13. whether the chemical saturated tranmitting frequency calibrating installation that is used for MRI according to claim 10, described judgement water signal begin to be begun decline by saturated module with the water signal amplitude be defined as the water signal and begin by saturated.
14. the chemical saturated tranmitting frequency calibrating installation that is used for MRI according to claim 13, described chemical saturation emission frequency calibration module also comprises:
With reference to water signal amplitude determination module, it uses basic prescan method, measures the water signal amplitude of this scan slice, and with the water signal amplitude that the records reference water signal amplitude as this scan slice;
Describedly judge whether the water signal begins by saturated module, with measured water signal amplitude with compare with reference to the water signal amplitude, in the time of in it drops to reference to the preset range of water signal amplitude, judge that the water signal begins by saturated.
15. the chemical saturated tranmitting frequency calibrating installation that is used for MRI according to claim 14, described preset range with reference to the water signal amplitude is the 70-90% with reference to the water signal amplitude.
16. each described chemical saturated tranmitting frequency calibrating installation for MRI according to claim 10-15, described chemical saturation emission frequency calibration module is carried out respectively chemical saturation emission frequency calibration to each scan slice in a plurality of scan slices.
17. each described chemical saturated tranmitting frequency calibrating installation for MRI according to claim 10-15, this chemistry saturation emission frequency calibration module also comprises:
The difference on the frequency computing module is measured the frequency of each scan slice, gets one of them scan slice as datum layer, calculates other scan slice with respect to the difference on the frequency of this datum layer;
Described chemical saturation emission frequency calibration module is carried out the saturated tranmitting frequency calibration of chemistry to this datum layer, then the chemical saturation emission frequency of acquisition after for the calibration of this datum layer determine the chemical saturation emission frequency of other scan slice with respect to the calibrated chemical saturation emission frequency of the difference on the frequency of datum layer and the datum layer that obtains based on resulting other scan slice.
18. each described chemical saturated tranmitting frequency calibrating installation for MRI according to claim 10-15, this chemistry saturation emission frequency calibration module also comprises:
The difference on the frequency computing module obtains the B that describes each scan slice
0The B of Distribution of Magnetic Field
0Field pattern is got one of them scan slice as datum layer, based on B
0Field pattern obtains other scan slice with respect to the difference on the frequency of this datum layer;
Described chemical saturation emission frequency calibration module is carried out the saturated tranmitting frequency calibration of chemistry to this datum layer, then the chemical saturation emission frequency of acquisition after for the calibration of this datum layer determine the chemical saturation emission frequency of other scan slice with respect to the calibrated chemical saturation emission frequency of the difference on the frequency of datum layer and the datum layer that obtains based on resulting other scan slice.
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| CN106466182B (en) * | 2015-08-18 | 2020-03-31 | 上海联影医疗科技有限公司 | Magnetic resonance imaging method and system |
| CN106952261B (en) * | 2017-04-06 | 2019-11-22 | 深圳安科高技术股份有限公司 | A kind of image processing method and device inhibiting fat signal |
| CN107121653A (en) * | 2017-05-12 | 2017-09-01 | 杭州全景医学影像诊断有限公司 | The method that fat presses down water process magnetic resonance spectrum imaging data is pressed down based on frequency domain |
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| CN109330594B (en) * | 2018-08-24 | 2022-05-27 | 上海联影医疗科技股份有限公司 | Method for obtaining parameters of saturation band, spectral imaging method, system and medium |
| CN109738841B (en) * | 2019-02-21 | 2021-05-28 | 奥泰医疗系统有限责任公司 | Optimization method for selecting flip angle of saturated pressure fat pulse by chemical shift |
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