CN102759723B - Method for generating magnetic resonance T2* image - Google Patents

Abstract

The invention discloses a method for generating a magnetic resonance T2* image. The method comprises the following steps: collecting by a multi-gradient echo sequence so as to obtain a magnetic resonance image; counting background image noise of a tested body so as to obtain a noise intensity level; carrying out numerical integration on time of magnetic resonance signals of different echo times, which correspond to pixels of the images of the tested body in the magnetic resonance image so as to obtain a fixed integral value; subtracting a time integral of the noise intensity level of the magnetic resonance image from the fixed integral value so as to obtain a signal integral value of the pixels of the images in the tested body, and dividing a magnetic resonance signal difference between a first echo and the last echo so as to obtain a T2* value; and figuring up a T2* value of all pixels in the tested body in the magnetic resonance image so as to obtain the T2* magnetic resonance image. The method for generating the T2* magnetic resonance image, provided by the invention, has the advantages of fastness and precision.

Description

A kind of magnetic resonance T2* image generating method

Technical field

The invention belongs to the technical field of nuclear magnetic resonance, be specifically related to a kind of magnetic resonance T ₂ ^*the generation method of image.

Background technology

Nuclear magnetic resonance has the features such as not damaged, soft tissue contrast are high, any direction tomography, has been widely used at present medical clinic applications.Horizontal weighting relaxation time T ₂ ^*to weigh under the effect that has comprised Magnetic field inhomogeneity factor, the physical quantity of the relaxation process speed of magnetic resonance signal.The size of its value is subject to the joint effect of bio-tissue inner and outer magnetic field inhomogeneities.Ferromagnetic material in bio-tissue can have a significant impact surrounding magnetic field inhomogeneities, accelerates the relaxation of magnetic resonance signal, T ₂ ^*therefore value also obviously declines.On clinical medicine, T ₂ ^*become one of current standard of weighing iron-holder in biological tissue, T ₂ ^*image is widely used in clinically including with tissue disease research and the diagnosis that ferrum amount is relevant, the cardiac muscle causing as Cerebral Hemorrhage Disease, Parkinson disease, Alzheimer disease, iron excess and hepatic disease etc.

Traditional calculating T ₂ ^*the method of image is first with many gradin-echos, to collect magnetic resonance image (MRI), then extracts the signal that in image, each pixel collects at different echo time TE, then according to the T of magnetic resonance signal ₂ ^*decay formula, utilizes the iteration minimization algorithm of Levenberg-Marquardt (being listed as civilian Burger-Ma Kuaertefa) to do nonlinear fitting to signal value, thereby calculates T ₂ ^*value.All pixels are carried out to the Fitting Calculation, finally obtain T2* image.

Above-mentioned many gtadient echos magnetic resonance image (MRI) signal is done to Levenberg-Marquardt nonlinear fitting calculate T ₂ ^*, there is oversize shortcoming computation time in the method for image.For a 3 d image data, owing to wanting individual element to calculate T ₂ ^*value, need to do even ten million Levenberg-Marquardt nonlinear fitting conventionally millions of times, and required time is very long.The method also cannot be eliminated effect of noise in magnetic resonance signal, has reduced calculating T ₂ ^*the accuracy of value.In addition, the method needs initial value to estimate before numerical fitting, and initial estimate accuracy tends to affect the convergence of fitting result, has further limited the accuracy of the method.

Summary of the invention

The present invention is directed to above-mentioned prior art and obtain magnetic resonance T ₂ ^*the weak points such as in the method for image, the existing time is long, accuracy is limited, propose a kind of magnetic resonance T ₂ ^*image generating method, can accurately generate fast and obtain magnetic resonance T ₂ ^*image.For realizing above object, the present invention proposes following technical scheme:

The present invention proposes a kind of quick accurate Calculation of numerical integration of utilizing and obtains magnetic resonance T ₂ ^*the method of image.First the method adds up tested external background noise in the magnetic resonance image (MRI) of many gradin-echos, thereby obtains the noise intensity level of magnetic resonance image (MRI).Then to pixel in tested body, the picture signal under corresponding all different echo times is done numerical integration and is calculated, and deduct background noise level intensity level that statistics obtains with echo time integration, thereby eliminate the impact of noise on result of calculation.Then, the magnetic resonance signal integrated value calculating, divided by the magnetic resonance signal difference between first echo and last echo, is accurately obtained to T fast ₂ ^*value.All pixels in tested body are calculated to T according to said method ₂ ^*value, finally obtains T ₂ ^*image.

Comprising the following steps of the inventive method:

A) with many echo gradient echo sequence, collect several different echo time magnetic resonance image (MRI);

B) tested external background image noise in described magnetic resonance image (MRI) is added up, obtained the average noise strength of described magnetic resonance image (MRI);

C) magnetic resonance signal of corresponding different echo times of the pixel of tested in-vivo image in described magnetic resonance image (MRI) is done to numerical integration to the time and calculate, obtain constant volume score value;

D) described constant volume score value is deducted described magnetic resonance image (MRI) noise intensity level with echo time integration, obtain the signal integration value of the pixel of tested in-vivo image in described magnetic resonance image (MRI), divided by the magnetic resonance signal difference between first echo and last echo, obtain T again ₂ ^*value;

E) all pixels in tested body in described magnetic resonance image (MRI) are calculated to T ₂ ^*value, obtains described magnetic resonance T ₂ ^*image.

Wherein, described step B) in, the noise mean intensity of magnetic resonance image (MRI) is the meansigma methods of all pixel signal intensities in background image, is expressed as formula [1]

$\stackrel{\‾}{\mathrm{\δ}}=\left({\mathrm{\Σ}}_{i=1}^N{S}_i\right)/N---\left[1\right]$

Wherein, S _ifor the pixel signal intensities in background image, N is the number of pixels of background image.

Wherein, described step C) with following formula [2], carry out numerical integration calculating.

$I={\mathrm{\Σ}}_{i=1}^N\left\{\right[S\left({\mathrm{TE}}_i\right)+S\left({\mathrm{TE}}_{i+1}\right)]\×({\mathrm{TE}}_{i+1}-{\mathrm{TE}}_i)/2\}---\left[2\right]$

Wherein, described step D), according to following formula [3], calculate T2* value.

${T_2}^{*}=[I-\stackrel{\‾}{\mathrm{\δ}}({\mathrm{TE}}_N-{\mathrm{TE}}_1)]/[S\left({\mathrm{TE}}_1\right)-S\left({\mathrm{TE}}_N\right)]---\left[3\right]$

In the present invention, " many echo gradient echo sequence " is the conventional sequence in nuclear magnetic resonance, its feature is after a radio-frequency drive, to adopt the mode that adds gradient magnetic repeatedly to return poly-collection to magnetic resonance signal, and a plurality of echo-signals that collect are T with echo time TE ₂ ^*decay.

In the present invention, " numerical integration " means the computerese of the value of a certain definite integral being done to numerical computations.

The inventive method is with traditional calculating T ₂ ^*method is compared, and does not need to do iterative computation, and the present invention generates magnetic resonance image (MRI) T ₂ ^*the speed of method can improve more than hundreds of times.Meanwhile, this method adds up owing to the definite integral of the magnetic resonance signal of pixel in tested body being deducted in computational process the background noise level integration obtaining, and has reduced the impact of background noise; In addition, utilize this method to calculate T ₂ ^*do not need T ₂ ^*carry out initial estimate.Therefore, the inventive method can significantly improve T ₂ ^*value is calculated and gained magnetic resonance T ₂ ^*the accuracy of image.The inventive method is applicable to radiology department's research to the quantitative various relevant diseases of iron in human clinically.

Accompanying drawing explanation

Fig. 1 is the data legend that in the inventive method, many echo gradient of magnetic resonance echo acquirement obtains.

Fig. 2 is a certain pixel magnetic resonance of the present invention T ₂ ^*the numerical integration of deamplification is expressed figure.

Fig. 3 is the brain magnetic resonance T that utilizes the inventive method to obtain ₂ ^*image.

The specific embodiment

In conjunction with following specific embodiments and the drawings, the present invention is described in further detail.Implement process of the present invention, condition, experimental technique etc., except the content of mentioning specially below, be universal knowledege and the common practise of this area, the present invention is not particularly limited content.

T of the present invention ₂ ^*magnetic resonance image (MRI) generation method, carries out numerical integration calculating pixel T to collect the magnetic resonance signal of all pixels in tested body in magnetic resonance image (MRI) with many echo gradient echo sequence ₂ ^*value, and utilize the background noise levels level of magnetic resonance image (MRI) to T ₂ ^*value is revised, thereby reduces background noise to T ₂ ^*the impact of value result of calculation.The method can obtain T quickly and accurately ₂ ^*magnetic resonance image (MRI).Wherein, the background noise levels level of magnetic resonance image (MRI) obtains by tested external background image noise in magnetic resonance image (MRI) being done to statistics.

Following step-by-step instructions the inventive method is being carried out T to collecting magnetic resonance image (MRI) with many gradin-echos ₂ ^*value is calculated, and generates and obtains T ₂ ^*the specific implementation process of magnetic resonance image (MRI).Wherein, the magnetic resonance image data of collection is many echo gradient of human brain echo sequence, and data from Siemens 3.0T magnetic resonance imaging system, the echo number adopting in the present embodiment is 8.

A) utilize many echo gradient echo sequence of magnetic resonance imaging system to gather the magnetic resonance image data of tested human brain, obtain the magnetic resonance image (MRI) of different echo times.

Wherein, the magnetic resonance image data that utilizes many gradin-echos to gather tested human brain is embodied as the general process of magnetic resonance imaging, a plurality of 3-D views that the magnetic resonance image (MRI) obtaining is collected by different echo time TE.The echo number adopting in the present embodiment is 8, therefore obtains 8 3-D views, and the signal of these 8 3-D views is T along with the increase of echo time TE ₂ ^*decay, as shown in Figure 1.

The signal intensity of single pixel can be expressed as formula [4] with the variation of TE time:

$S\left(t\right)=S_0\exp (-t/{T_2}^{*})+\mathrm{\δ}\left(t\right)---\left[4\right]$

Wherein, S ₀, S (t) time of being respectively is 0 and magnetic resonance signal during t, δ (t) is signal noise, for being greater than 0 random quantity.

B) tested external background image noise in above-mentioned magnetic resonance image (MRI) is added up, obtained the average noise strength of magnetic resonance image (MRI).In the present embodiment, for obtaining the noise mean intensity of magnetic resonance image (MRI), extraction step A) magnetic resonance signal of tested external background area in the magnetic resonance image (MRI) that obtains, the meansigma methods of the magnetic resonance signal of statistics background image, obtain noise mean intensity, specifically can be expressed as formula [1].Wherein, S _ibe the pixel signal intensities in background image, N is the number of pixels of background image.

$\stackrel{\‾}{\mathrm{\δ}}=\left({\mathrm{\Σ}}_{i=1}^N{S}_i\right)/N---\left[1\right]$

C) magnetic resonance signal under the corresponding different echo time TE of interior each pixel of tested brain in extraction of magnetic resonance image, with first echo time TE ₁for lower limit of integral, last echo time TE _nfor upper limit of integral, the magnetic resonance signal of this pixel is done to numerical integration and calculate, formula [4] is carried out to numerical integration and calculate formula [5], obtain the constant volume score value I of the magnetic resonance signal of this pixel.

$\begin{array}{c}I={\∫}_{{\mathrm{TE}}_2}^{{\mathrm{TE}}_N}S\left(t\right)\mathrm{dt}=-{T_2}^{*}[S_0\exp (-\frac{{\mathrm{TE}}_N}{{T_2}^{*}})-S_0\exp (-\frac{{\mathrm{TE}}_1}{{T_2}^{*}})]+\stackrel{\‾}{\mathrm{\δ}}({\mathrm{TE}}_N-{\mathrm{TE}}_1)\\ =-{T_2}^{*}[S\left({\mathrm{TE}}_N\right)-S\left({\mathrm{TE}}_1\right)]+\stackrel{\‾}{\mathrm{\δ}}({\mathrm{TE}}_N-{\mathrm{TE}}_1)\end{array}---\left[5\right]$

Above formula [5] adopts trapezoidal area integration method to calculate, and specifically for solution procedure, formula [2] is expressed as follows:

$I={\mathrm{\Σ}}_{i=1}^N\left\{\right[S\left({\mathrm{TE}}_i\right)+S\left({\mathrm{TE}}_{i+1}\right)]\×({\mathrm{TE}}_{i+1}-{\mathrm{TE}}_i)/2\}---\left[2\right]$

In above-mentioned formula, I represents the constant volume score value of magnetic resonance signal.

Shown in Fig. 2, be certain pixel magnetic resonance T in the interior prefrontal lobe white matter of tested brain region in the present embodiment ₂ ^*the constant volume score value of deamplification is expressed figure.

For example, in the present embodiment, 8 echo time TE values are respectively 4.3,9.1,13.9,18.7,23.5,28.3,33.1 and 37.9 (units: ms).In corresponding tested brain, the signal value of prefrontal lobe white matter region above-mentioned certain pixel is wherein 4369,4092,3834,3382,3277,2640,2501 and 2428.Substitution formula [2] evaluation integration obtains 110997.6.

D) according to formula [4], to calculate the integration that constant volume score value deducts the meansigma methods of the magnetic resonance signal of adding up the background image obtaining according to formula [2], divided by the magnetic resonance signal difference between first echo and last echo, obtain the T of this pixel in tested brain again ₂ ^*value.

${T_2}^{*}=[I-\stackrel{\‾}{\mathrm{\δ}}({\mathrm{TE}}_N-{\mathrm{TE}}_1)]/[S\left({\mathrm{TE}}_1\right)-S\left({\mathrm{TE}}_N\right)]---\left[3\right]$

In the present embodiment, statistics obtains background area pixels meansigma methods be 66.9, so the time integral of noise intensity level is 66.9 * (37.9-4.3)=2247.8

By result substitution formula [3], calculate T ₂ ^*=(110997.6-2247.8)/(4369-2428)=56.0ms.

E) to all pixel pointwise repeating step C in tested body in magnetic resonance image (MRI)) and D) calculate the T of all pixels in body ₂ ^*value, thus magnetic resonance T obtained ₂ ^*image.Magnetic resonance T ₂ ^*image can save as binary data format, also can require (as dicom, niffty, bmp etc.) to be write as image file according to certain picture format.

Be illustrated in figure 3 the T that the present embodiment utilizes the brain that the inventive method obtains ₂ ^*magnetic resonance image (MRI).

Protection content of the present invention is not limited to above embodiment.Do not deviating under the spirit and scope of inventive concept, variation and advantage that those skilled in the art can expect are all included in the present invention, and take appending claims as protection domain.

Claims (4)

1. a T ₂ ^*magnetic resonance image (MRI) generation method, is characterized in that, said method comprising the steps of:

A) with many echo gradient echo sequence, collect magnetic resonance image (MRI);

B) tested external background image noise in described magnetic resonance image (MRI) is added up, calculated the meansigma methods of all pixel signal intensities in the background image of described magnetic resonance image (MRI), obtain the noise intensity level of described magnetic resonance image (MRI);

C) magnetic resonance signal of corresponding different echo times of the pixel of tested in-vivo image in described magnetic resonance image (MRI) is done to numerical integration to the time and calculate, obtain constant volume score value;

D) described constant volume score value is deducted described magnetic resonance image (MRI) noise intensity level with echo time integration, obtain the signal integration value of the pixel of tested in-vivo image in described magnetic resonance image (MRI), divided by the magnetic resonance signal difference between first echo and last echo, obtain T again ₂ ^*value;

E) all pixels in tested body in described magnetic resonance image (MRI) are calculated to T ₂ ^*value, obtains described T ₂ ^*magnetic resonance image (MRI).

2. T as claimed in claim 1 ₂ ^*magnetic resonance image (MRI) generation method, is characterized in that, described step B) in the noise intensity level of magnetic resonance image (MRI) be the meansigma methods of all pixel signal intensities in background image, be expressed as formula [1]

$\stackrel{\‾}{\mathrm{\δ}}=\left({\mathrm{\Σ}}_{i=1}^N{S}_i\right)/N---\left[1\right]$

Wherein, S _ifor the pixel signal intensities in background image, N is the number of pixels of background image.

3. T as claimed in claim 1 ₂ ^*magnetic resonance image (MRI) generation method, is characterized in that, described step C) with following formula [2], carry out numerical integration calculating

$I={\mathrm{\Σ}}_{i=1}^N\left\{\right[S\left({\mathrm{TE}}_i\right)+S\left({\mathrm{TE}}_{i+1}\right)]\×({\mathrm{TE}}_{i+1}-{\mathrm{TE}}_i)/2\}---\left[2\right]$

Wherein, TE _ibe the echo time of i gtadient echo, TE _i+1it is the echo time of i+1 gtadient echo; S (TE _i) be the magnetic resonance image (MRI) signal magnitude of i gtadient echo, S (TE _i+1) be the magnetic resonance image (MRI) signal magnitude of i+1 gtadient echo.

4. T as claimed in claim 1 ₂ ^*magnetic resonance image (MRI) generation method, is characterized in that, described step D) middle according to following formula [3] calculating T2* value

${T_2}^{*}=[I-\stackrel{\‾}{\mathrm{\δ}}({\mathrm{TE}}_N-{\mathrm{TE}}_1)]/[S\left({\mathrm{TE}}_1\right)-S\left({\mathrm{TE}}_N\right)]---\left[3\right]$

Wherein, TE ₁be the echo time of the 1st gtadient echo, TE _nit is the echo time of N gtadient echo; S (TE ₁) be the magnetic resonance image (MRI) signal magnitude of the 1st gtadient echo, S (TE _n) be the magnetic resonance image (MRI) signal magnitude of N gtadient echo.