CN110742589A - Novel fat reference magnetic resonance temperature imaging method - Google Patents
Novel fat reference magnetic resonance temperature imaging method Download PDFInfo
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- CN110742589A CN110742589A CN201911068120.4A CN201911068120A CN110742589A CN 110742589 A CN110742589 A CN 110742589A CN 201911068120 A CN201911068120 A CN 201911068120A CN 110742589 A CN110742589 A CN 110742589A
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- A—HUMAN NECESSITIES
- A61—MEDICAL OR VETERINARY SCIENCE; HYGIENE
- A61B—DIAGNOSIS; SURGERY; IDENTIFICATION
- A61B5/00—Measuring for diagnostic purposes; Identification of persons
- A61B5/01—Measuring temperature of body parts ; Diagnostic temperature sensing, e.g. for malignant or inflamed tissue
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- A—HUMAN NECESSITIES
- A61—MEDICAL OR VETERINARY SCIENCE; HYGIENE
- A61B—DIAGNOSIS; SURGERY; IDENTIFICATION
- A61B5/00—Measuring for diagnostic purposes; Identification of persons
- A61B5/0033—Features or image-related aspects of imaging apparatus classified in A61B5/00, e.g. for MRI, optical tomography or impedance tomography apparatus; arrangements of imaging apparatus in a room
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- A—HUMAN NECESSITIES
- A61—MEDICAL OR VETERINARY SCIENCE; HYGIENE
- A61B—DIAGNOSIS; SURGERY; IDENTIFICATION
- A61B5/00—Measuring for diagnostic purposes; Identification of persons
- A61B5/05—Detecting, measuring or recording for diagnosis by means of electric currents or magnetic fields; Measuring using microwaves or radio waves
- A61B5/055—Detecting, measuring or recording for diagnosis by means of electric currents or magnetic fields; Measuring using microwaves or radio waves involving electronic [EMR] or nuclear [NMR] magnetic resonance, e.g. magnetic resonance imaging
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- A—HUMAN NECESSITIES
- A61—MEDICAL OR VETERINARY SCIENCE; HYGIENE
- A61B—DIAGNOSIS; SURGERY; IDENTIFICATION
- A61B5/00—Measuring for diagnostic purposes; Identification of persons
- A61B5/72—Signal processing specially adapted for physiological signals or for diagnostic purposes
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- G—PHYSICS
- G06—COMPUTING; CALCULATING OR COUNTING
- G06T—IMAGE DATA PROCESSING OR GENERATION, IN GENERAL
- G06T11/00—2D [Two Dimensional] image generation
Abstract
A new fat reference magnetic resonance temperature imaging method relates to the field of magnetic resonance imaging, and comprises the following steps: firstly, determining a temperature distribution interval according to the physical characteristics of fat-containing tissues; determining the range of water-fat chemical shift difference according to the relationship between the water-fat component chemical shift difference and the temperature; step three, determining the interval of the echo time for enabling the water-fat chemical shift difference to reach the water-fat antiphase according to the distribution of the water-fat chemical shift difference in the step two; discretizing the echo time of the interval in the third step, and respectively scanning and imaging according to the discretized echo time; the method for obtaining the tissue temperature by comparing the signal amplitude values corresponding to the discrete echo time is simple and easy to implement, does not need complex post-processing, corrects the influence of T2 by using a mature chemical shift coding imaging method, and ensures the accuracy of temperature estimation.
Description
Technical Field
The invention relates to magnetic resonance imaging, in particular to a novel fat reference magnetic resonance temperature imaging method.
Background
The magnetic resonance temperature imaging can monitor the internal temperature distribution and change of the tested object in a non-invasive and real-time manner in vivo. Magnetic resonance can monitor temperature based on various temperature sensitive parameters, commonly used being proton concentration (PD), relaxation time (relaxation time), diffusion coefficient and Proton Resonance Frequency Shift (PRFS). Because the proton resonance frequency in water is linear with temperature, and the linear relationship is tissue independent, PRFS-based magnetic resonance temperature imaging techniques are most widely used. However, this technique cannot be used with fat-containing tissues, and therefore the hydrogen protons in the fat are not sensitive to temperature, which makes the fat-containing tissue appear non-linear with temperature changes, and this non-linear relationship is related to the ratio of water to fat in the tissue. In order to achieve temperature imaging of adipose tissue, the effects of fat are eliminated or corrected.
Proton resonance frequency drift magnetic resonance temperature imaging utilizes the linear relation of the resonance frequency of hydrogen protons in water and temperature to carry out temperature imaging, and generally, the temperature sensitivity coefficient of the proton resonance frequency drift magnetic resonance temperature imaging is-0.01 ppm/DEG C and is not related to tissues. In the practical application process, a gradient echo sequence is acquired, the same imaging parameters are utilized to acquire images at different time points, and the difference of proton resonance frequency caused by temperature is converted into the difference of phase images; and (3) subtracting the phase images acquired at different time points before and after the temperature change image, and dividing the difference by the corresponding coefficient and the echo time to obtain the temperature change image. However, the hydrogen protons in fat are not sensitive to temperature, and this technique cannot be directly applied to temperature imaging of adipose tissue, and to overcome this drawback, different techniques have been proposed by different groups.
Commonly used techniques include fat suppression and fat referencing. Wherein the fat inhibition is to adopt a fat pre-saturation or water excitation sequence to inhibit signals of hydrogen protons in fat, so that the acquired image only contains the signals of the hydrogen protons in water. This technique is extremely sensitive to main magnetic field inhomogeneities and it also increases the noise of the temperature image. The fat reference technology utilizes gradient multi-echo imaging to simultaneously acquire hydrogen proton signals in water and fat, and the hydrogen proton signals are obtained by directly or indirectly fitting the temperature through a signal model.
The foregoing prior algorithm has the disadvantage that fat in the signal model adopts a unimodal model, which has a plurality of fat peaks in the actual fat hydrogen proton magnetic resonance spectrum, because the result obtained by the method is biased. The signal model is simplified, and some parameters are assumed to be invariant with temperature, but in actual data acquisition, the parameters also vary with acquisition times and temperature, so that the temperature image obtained by the method is also inaccurate.
Disclosure of Invention
The invention aims to provide a novel fat reference magnetic resonance temperature imaging method to solve the problems of result deviation and inaccurate temperature image in the background technology.
In order to achieve the purpose, the invention provides the following technical scheme: a new fat reference magnetic resonance temperature imaging method is characterized in that: the method comprises the following steps:
firstly, determining a temperature distribution interval according to the physical characteristics of fat-containing tissues;
determining the range of water-fat chemical shift difference according to the relationship between the water-fat component chemical shift difference and the temperature;
step three, determining the interval of the echo time for enabling the water-fat chemical shift difference to reach the water-fat antiphase according to the distribution of the water-fat chemical shift difference in the step two;
discretizing the echo time of the interval in the third step, and respectively scanning and imaging according to the discretized echo time;
and fifthly, determining the current temperature of the fat-containing tissue by the chemical shift difference corresponding to the echo time when the image signal reaches the minimum value.
As a preferred embodiment of the present invention, the magnetic resonance signal model in which the temperature distribution region contains two components, namely water and fat, is:
where Sn is the signal strength at echo time TEn; w and F are the intensity values of water and fat, complex; gamma is the gyromagnetic ratio, B0Is the main magnetic field strength, α is the hydrogen proton temperature coefficient in water, the unit is ppm/deg.C, generally thought to be α -0.01 ppm/deg.C, the chemical shift of water is set to 0, fat has P fat peaks, and the corresponding relative amplitude and chemical shift are βpAnd fF,pAnd is and
is the transverse relaxation time of the tissue; f. ofBIs field drift due to non-uniformity of the main magnetic field; n is the total number of collected echoes; Δ T is the temperature difference from the baseline temperature;
as a preferred technical solution of the present invention, the amplitude signal is:
the signal model, signal value | snI and temperature Δ T, TEnIn connection with, selecting a suitable echo time TEnThe signal value can be minimized, and the main components of water and fat are in opposite phase at the moment, so that the temperature value can be obtained by reverse estimation.
Compared with the prior art, the invention has the beneficial effects that: the method for obtaining the tissue temperature by comparing the signal amplitude values corresponding to the discrete echo time is simple and easy to implement, does not need complex post-processing, corrects the influence of T2 by using a mature chemical shift coding imaging method, and ensures the accuracy of temperature estimation.
Drawings
FIG. 1 is a diagram illustrating the relationship between echo time and signal value according to the present invention;
Detailed Description
The technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the drawings in the embodiments of the present invention, and it is obvious that the described embodiments are only a part of the embodiments of the present invention, and not all of the embodiments. All other embodiments, which can be derived by a person skilled in the art from the embodiments given herein without making any creative effort, shall fall within the protection scope of the present invention.
Referring to fig. 1, a new fat reference magnetic resonance temperature imaging method is characterized in that: the method comprises the following steps:
firstly, determining a temperature distribution interval according to the physical characteristics of fat-containing tissues;
determining the range of water-fat chemical shift difference according to the relationship between the water-fat component chemical shift difference and the temperature;
step three, determining the interval of the echo time for enabling the water-fat chemical shift difference to reach the water-fat antiphase according to the distribution of the water-fat chemical shift difference in the step two;
discretizing the echo time of the interval in the third step, and respectively scanning and imaging according to the discretized echo time;
and fifthly, determining the current temperature of the fat-containing tissue by the chemical shift difference corresponding to the echo time when the image signal reaches the minimum value.
According to the formula
Assuming a reasonable initial temperature Δ T0Performing water-fat separation by using a mature magnetic resonance chemical shift coding imaging technology to obtain transverse relaxation time T2;
according to the formula
Remove the effect of T2 on the signal values:
comparing different TEsnSignal value of | s'nThe minimum signal value corresponds to the water and fat main components and presents an opposite phase, and because the only temperature value corresponds to the opposite phase within a reasonable temperature range, the current temperature value of the tissue can be determined
As a preferred embodiment of the present invention, the magnetic resonance signal model in which the temperature distribution region contains two components, namely water and fat, is:
where Sn is the signal strength at echo time TEn; w and F are the intensity values of water and fat, complex; gamma is the gyromagnetic ratio, B0Is the main magnetic field strength, α is the hydrogen proton temperature coefficient in water, the unit is ppm/deg.C, generally thought to be α -0.01 ppm/deg.C, the chemical shift of water is set to 0, fat has P fat peaks, and the corresponding relative amplitude and chemical shift are βpAnd fF,pAnd is and
is the transverse relaxation time of the tissue; f. ofBIs field drift due to non-uniformity of the main magnetic field; n is the total number of collected echoes; Δ T is the temperature difference from the baseline temperature;
as a preferred technical solution of the present invention, the amplitude signal is:
the signal model, signal value | snI and temperature Δ T, TEnIn connection with, selecting a suitable echo time TEnThe signal value can be minimized, and the main components of water and fat are in opposite phase at the moment, so that the temperature value can be obtained by reverse estimation.
To verify the bookThe feasibility of the invention utilizes numerical simulation to verify the relationship between echo time and signal value: according to the formula
Setting the signals of the water and fat components to be 50, and setting T2 to be 0; signal to noise ratio of 100, chemical shift of water set to 0, fat with 6 fat peaks, corresponding relative amplitude and chemical shift of [ 0.0870.6940.1280.0040.0390.048 ]]And [ -3.80-3.40-2.60-1.94-0.390.60]ppm; the range of the echo time TE is set to be 3-5 ms, and the step length is 0.02 ms. As a result, as shown in the first figure, at TE 3.44ms, the signal takes a minimum value that is temperature dependent, and there is a unique relationship between the echo time and temperature.
In the description of the present invention, it is to be understood that the indicated orientations or positional relationships are based on the orientations or positional relationships shown in the drawings and are only for convenience in describing the present invention and simplifying the description, but are not intended to indicate or imply that the indicated devices or elements must have a particular orientation, be constructed and operated in a particular orientation, and are not to be construed as limiting the present invention.
Although embodiments of the present invention have been shown and described, it will be appreciated by those skilled in the art that changes, modifications, substitutions and alterations can be made in these embodiments without departing from the principles and spirit of the invention, the scope of which is defined in the appended claims and their equivalents.
Claims (3)
1. A new fat reference magnetic resonance temperature imaging method is characterized in that: the method comprises the following steps:
firstly, determining a temperature distribution interval according to the physical characteristics of fat-containing tissues;
determining the range of water-fat chemical shift difference according to the relationship between the water-fat component chemical shift difference and the temperature;
step three, determining the interval of the echo time for enabling the water-fat chemical shift difference to reach the water-fat antiphase according to the distribution of the water-fat chemical shift difference in the step two;
discretizing the echo time of the interval in the third step, and respectively scanning and imaging according to the discretized echo time;
and fifthly, determining the current temperature of the fat-containing tissue by the chemical shift difference corresponding to the echo time when the image signal reaches the minimum value.
2. The new fat reference magnetic resonance temperature imaging method according to claim 1, characterized in that: the magnetic resonance signal model of the temperature distribution interval containing the water and fat components is as follows:
where Sn is the signal strength at echo time TEn; w and F are the intensity values of water and fat, complex; gamma is the gyromagnetic ratio, B0Is the main magnetic field strength, α is the hydrogen proton temperature coefficient in water, the unit is ppm/deg.C, generally thought to be α -0.01 ppm/deg.C, the chemical shift of water is set to 0, fat has P fat peaks, and the corresponding relative amplitude and chemical shift are βpAnd fF,pAnd is and
is the transverse relaxation time of the tissue; f. ofBIs field drift due to non-uniformity of the main magnetic field; n is the total number of collected echoes; Δ T is the temperature difference from the baseline temperature.
3. The new fat reference magnetic resonance temperature imaging method according to claim 2, characterized in that:
the amplitude signal is:
the signal model, signal value | snI and the temperature Delta T,TEnIn connection with, selecting a suitable echo time TEnThe signal value can be minimized, and the main components of water and fat are in opposite phase at the moment, so that the temperature value can be obtained by reverse estimation.
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