CN-116491926-B - Infant brain T2 weighted magnetic resonance imaging optimization method

CN116491926BCN 116491926 BCN116491926 BCN 116491926BCN-116491926-B

Abstract

The invention discloses an infant brain T2 weighted magnetic resonance imaging optimization method based on a rapid spin echo sequence. Firstly, collecting T1, T2 and PD of the brain of an infant with the age of 0-24 months for quantitative imaging, obtaining T1, T2 and PD values of white matter and gray matter areas of the infant, and dividing the infant into different month age groups according to the relation characteristic of the white matter T2 value and gray matter T2 value of the infant. Then, based on 3D T2 weighted imaging of the variable flip angle fast spin echo sequence, calculating signal intensities of white matter and gray matter of infants under different refocusing flip angle chains through an extended phase diagram algorithm, and determining the optimal flip angle chain design scheme of each group with white matter/gray matter contrast maximization as a target. The invention fills the blank of infant brain T2 weighted imaging optimization, and establishes the optimal flip angle chain optimization scheme of different month age groups, thereby remarkably improving the infant brain T2 weighted imaging contrast.

Inventors

WU DAN
WU JIANI
ZHANG HONGXI
WANG WENQI

Assignees

浙江大学

Dates

Publication Date: 20260512
Application Date: 20230316

Claims (10)

1. The infant brain T2 weighted magnetic resonance imaging optimization method based on the rapid spin echo sequence is characterized by comprising the following steps of: s1, acquiring longitudinal relaxation time T1, transverse relaxation time T2 and proton density PD quantitative imaging magnetic resonance data of the brains of infants with ages of 0-24 months, and obtaining respective average T1 value, average T2 value and average PD value of white matter and gray matter of each infant brain; S2, dividing the 0-24 month period of the infant into different month groups according to the relative high and low conditions of white matter average T2 value and gray matter average T2 value of the infant brain in each sample, dividing the quantitative imaging magnetic resonance data acquired in S1 according to each month group, and then respectively counting the respective average T1 value, average T2 value and average PD value of the white matter and gray matter of the infant brain in each month group; S3, respectively calculating the signal intensity of the white matter and gray matter of the infant, which is generated by the 3D T2 weighted fast spin echo sequence under each selectable flip angle chain, of each month age group by an extended phase diagram algorithm based on the respective average T1 value, average T2 value and average PD value of the white matter and gray matter of the infant brain of each month age group; S4, converting the signal intensity of white matter and gray matter of the infant brain of each month age group obtained in the S3 under each selectable flip angle chain into the contrast of white matter and gray matter, and respectively selecting the optimal flip angle chain of each month age group from all selectable flip angle chains according to the principle of maximizing the contrast, wherein the optimal flip angle chain is used for carrying out T2 weighted magnetic resonance imaging on the infant brain; the optimal flip angle chain optimization method for each month age group is as follows: S401, for each month age group, respectively calculating the image contrast under each flip angle chain, wherein absolute contrast= |S WM | - |S GM |, relative contrast= (|S WM | - |S GM |)/ (|S WM | + |S GM |),S WM is white matter voxel average signal intensity, and S GM is gray matter voxel average signal intensity; S402, regarding each month age group, taking the improvement of the relative contrast as a main optimization target, taking the improvement of the absolute contrast as a secondary optimization target, taking the specific absorption rate value as a constraint condition, selecting an optimal flip angle chain from all corresponding selectable flip angle chains, and using the optimal flip angle chain as the flip angle chain selected when the infant brain of the month age group carries out T2 weighted magnetic resonance imaging.
2. The method for optimizing infant brain T2-weighted magnetic resonance imaging according to claim 1, wherein the average T1 value, the average T2 value and the average PD value in step S1 are calculated as follows: s101, collecting quantitative imaging magnetic resonance data of T1, T2 and PD of the brains of a plurality of infants with ages of 0-24 months; s102, aiming at the brain quantitative imaging magnetic resonance data of each infant, delineated the interested areas of the gray matter of the cerebral cortex and the white matter under the cerebral cortex; S103, calculating an average T1 value in a white matter region of interest under the cerebral cortex as an infant white matter average T1 value, calculating an average T2 value in the white matter region of interest under the cerebral cortex as an infant white matter average T2 value, calculating an average PD value in the white matter region of interest under the cerebral cortex as an infant white matter average PD value, calculating an average T1 value in a gray matter region of the cerebral cortex as an infant gray matter average T1 value, calculating an average T2 value in a gray matter region of the cerebral cortex as an infant gray matter average T2 value, and calculating an average PD value in the gray matter region of the cerebral cortex as an infant gray matter average PD value based on a region of interest sketched in each infant brain quantitative imaging magnetic resonance data.
3. The method for optimizing infant brain T2 weighted magnetic resonance imaging according to claim 1, wherein the method for grouping the ages of the infants in step S2 comprises the following steps: According to the relation curve of the white matter and gray matter T2 values of infants in different month age groups along with the brain development dynamic change, dividing the infants into three month age groups, wherein the relative high and low conditions of the three groups are respectively as follows: in the first group, the white matter T2 value of the infant in the month age zone is Yu Ying infant's grey matter T2 value; In the second group, the infant brain white matter T2 value in the month age zone is close to the infant brain grey matter T2 value; In the third group, the infant brain white matter T2 value of the month-old period is lower than the infant brain grey matter T2 value.
4. The method of optimizing infant brain T2-weighted magnetic resonance imaging according to claim 3, wherein the three month-old groups are 0-6 months old, 6-12 months old and 12-24 months old, respectively.
5. The method for optimizing infant brain T2-weighted magnetic resonance imaging according to claim 1, wherein the specific implementation step of step S3 is as follows: s301, fixing angle values of alpha max for a flip angle chain comprising four key angles alpha first 、α min 、α cent 、α max , sampling in the respective angle ranges of alpha min and alpha cent , and thus constructing a series of selectable angle combinations, wherein each selectable angle combination corresponds to a set of fixed values of alpha min 、α cent and alpha max , alpha min is necessarily smaller than alpha cent , alpha first is the first angle on the whole flip angle chain, alpha min is the fifth angle on the whole flip angle chain and is also the minimum angle on the flip angle chain, alpha cent is the flip angle corresponding to an echo signal filling the central moment of a K space, and alpha max is the last angle on the flip angle chain; s302, calculating a theoretically achievable static pseudo-steady state signal value by taking alpha min 、α cent and alpha max of each selectable angle combination as a flip angle alpha in a fast spin echo sequence with a constant flip angle The calculation formula is: wherein P (·) is a Legendre polynomial; Then taking alpha min 、α cent 、α max as the static pseudo steady signal value Respectively used as echo signal values S min 、S cent 、S max corresponding to three angles on a static pseudo steady state signal curve, and alpha first corresponding to the current selectable angle combination is obtained based on S min by calculation, wherein the calculation formula is as follows: Then, calculating a static pseudo-steady state signal between S first and S min in a progressive interpolation mode, calculating a static pseudo-steady state signal value between S min and S cent in a progressive interpolation mode, and calculating a static pseudo-steady state signal value between S cent and S max in a linear interpolation mode, so as to obtain a static pseudo-steady state echo signal chain corresponding to the current selectable angle combination; S303, setting T1=0 and T2= infinity under the condition of neglecting the longitudinal recovery and transverse attenuation processes of magnetization vectors for static pseudo-steady state echo signal chains corresponding to each selectable angle combination, and calculating to obtain a turnover angle chain required by the static pseudo-steady state echo signal chain through a reverse algorithm of an extended phase diagram; s304, calculating the average signal intensity S WM of white matter voxels at the moment of filling the K space center point of the 3D T2 weighted fast spin echo sequence by using an extended phase graph algorithm based on the average T1 value, the average T2 value and the average PD value of the white matter of the brain of the infant of the month group according to the echo Time (TE), the flip angle chain length and the echo interval in the preset fast spin echo sequence, and calculating the average signal intensity S GM of gray matter voxels at the moment of filling the K space center point of the 3D T2 weighted fast spin echo sequence by using the extended phase graph algorithm.
6. The method for optimizing infant brain T2-weighted magnetic resonance imaging according to claim 5, wherein the α max is fixed at an angle value between 100-180 degrees.
7. The method of infant brain T2 weighted magnetic resonance imaging optimization according to claim 5, wherein the α max is fixed at 120 degrees.
8. The method for optimizing infant brain T2-weighted magnetic resonance imaging according to claim 7, wherein in S402, when the optimal flip angle chain is selected from all the flip angle chains for each month-old group, the selectable flip angle chains whose specific absorption rate value does not satisfy the first limit range or whose absolute contrast does not satisfy the second limit range are removed first, and then the selectable flip angle chain with the highest relative contrast is selected from the remaining selectable flip angle chains as the optimal flip angle chain for the month-old group.
9. An infant brain T2 weighted magnetic resonance imaging method based on a rapid spin echo sequence is characterized in that an optimal flip angle chain corresponding to a month age group is selected to perform 3D T2 weighted magnetic resonance imaging according to the current month age of a target infant, wherein the optimal flip angle chain when performing 3D T2 weighted magnetic resonance imaging is optimized according to the infant brain T2 weighted magnetic resonance imaging optimization method of any one of claims 1-8, the optimal flip angle chain when performing 3D T2 weighted magnetic resonance imaging is set to 80 degrees, the optimal flip angle chain when performing 3D T2 weighted magnetic resonance imaging is set to 90 degrees, the optimal flip angle chain when performing 3D T2 weighted magnetic resonance imaging is set to 50 degrees, the optimal flip angle chain when performing 3D T2 weighted magnetic resonance imaging is set to 110 degrees, the optimal flip angle chain when performing 3D T2 weighted magnetic resonance imaging is set to 360 degrees, the optimal flip angle chain when performing 3D T2 weighted magnetic resonance imaging is set to be 6 to 120 degrees, the optimal flip angle chain when performing 3D T2 weighted magnetic resonance imaging is set to each of three sets to 120 degrees, and the steady state signals in each set to 120 to equal one of the three sets to 120 degrees according to the three pieces of the steady state signals when the three sets to the steady state signals and each set to the steady state signals A determination is made.
10. The method for T2-weighted magnetic resonance imaging of the infant brain based on the rapid spin echo sequence according to claim 9, wherein the rest parameters in the 3d T2-weighted magnetic resonance imaging are set to be the same in the three month old group, the echo time is set to be 370ms, the flip angle chain length is set to be 180, and the echo interval is set to be 3.7ms.

Description

Infant brain T2 weighted magnetic resonance imaging optimization method Technical Field The application relates to the field of brain magnetic resonance imaging optimization, in particular to infant brain T2 weighted imaging optimization. Background Infant brain magnetic resonance imaging is a safe and versatile method for examining infant brain structures, functions and diseases during early development. However, since the imaging contrast of the brain of the infant is poor, and the image contrast also changes rapidly due to the rapid development of the brain in two years after birth, the gray-white quality of the brain of the infant is difficult to distinguish, and automatic segmentation of the image is difficult to realize. Since premature development of the myelin sheath of white matter (WHITE MATTER, WM) at birth leads to an extended T2 relaxation time, the contrast of white matter to gray matter (GRAY MATTER, GM) in T2-weighted (T2 w) images of neonatal (≤1 month) brains is opposite to that of adult brains. While older infants are similar to adults in contrast, the WM and GM signals behave closely before such reversal occurs, resulting in failure of most segmentation algorithms for a period of time typically between 6-10 months. There are few studies currently optimizing brain T2 weighted imaging for infants from 0 to 24 months of age. Only one study optimizes contrast by adjusting TE and TR, but using this method to improve contrast sacrifices a certain signal-to-noise ratio and greatly prolongs the scan time, reduces the image acquisition efficiency and is therefore not suitable for clinical practice. Therefore, the research is based on a rapid spin echo imaging sequence, and the free flexibility of imaging contrast control by utilizing a variable flip angle chain is utilized, so that a method for calculating a flip angle chain corresponding to a required signal designed under a specific T2 by combining and iterating an expansion phase diagram and a reverse expansion phase diagram is designed, and a design scheme with optimal brain gray-scale contrast under different ages is obtained. The method optimizes the contrast ratio by changing the evolution mode of the signals, can obviously improve the contrast ratio of the infant brain T2 weighted image on the premise of not influencing the signal-to-noise ratio and guaranteeing the acquisition efficiency, and can be applied to clinical magnetic resonance scanning. Disclosure of Invention In order to improve the contrast of the infant brain T2w images in the period of 0-24 months, the invention provides a method for realizing the optimization of infant brain T2w magnetic resonance imaging. The method comprises the steps of firstly, collecting T1, T2 and Proton Density (PD) quantitative imaging of infant brains of 0-24 months, respectively obtaining average T1, T2 and PD values of the infant brains WM and GM, and classifying the infants into different month age groups according to the relation characteristic of the infant brains WM T2 value and GM T2 value. The WM and GM signals under different flip angle chains are then calculated by an extended phase map (EPG) PHASE GRAPH. Subsequently, an optimal flip angle chain optimization scheme for each month-old group is determined. Finally, the optimal flip angle chain optimization scheme is applied to the brain of the target infant to perform 3D T2w magnetic resonance imaging. The invention fills the blank of optimization of weighted imaging of the infant brain T2 in 0-24 months, divides the infant into different month age groups according to the relation characteristic of white matter and gray matter T2 values of the infant brain, and further respectively finds out the optimal flip angle chain optimization schemes of the different month age groups, thereby remarkably improving the weighted imaging contrast of the infant brain T2. The realization of the method is beneficial to the anatomical demarcation of the infant brain and the detection of diseases, and the method is simple and convenient and is convenient to be applied to clinical routine examination. In order to achieve the above purpose, the invention is realized by adopting the following technical scheme: In a first aspect, the invention provides a method for optimizing infant brain T2 weighted magnetic resonance imaging based on a rapid spin echo sequence, comprising the following steps: S1, acquiring longitudinal relaxation time (T1), transverse relaxation time (T2) and Proton Density (PD) quantitative imaging magnetic resonance data of the brains of infants and young children of 0-24 months old, and obtaining respective average T1 value, average T2 value and average PD value of white matter and gray matter of each infant and young infant brain; S2, dividing the 0-24 month period of the infant into different month groups according to the relative high and low conditions of white matter average T2 value and gray matter average T2 value of the infant bra