Magnetic resonance cest imaging sequence and device based on frequency stabilization module

A magnetic resonance CEST imaging device based on a frequency stabilization module, comprising a frequency stabilization module and a CEST imaging module;

• wherein the frequency stabilization module is configured to perform Step 1 through Step 5,
• Step 1:
• in the frequency stabilization module, exciting a target slice with a radio frequency pulse having a flip angle smaller than 90°, and collecting three lines of non-phase-encoded k-space data at three different moments t1, t2, and t3, respectively, where t2−t1<t3−t2<2(t2−t1);
• Step 2:
• obtaining a fine estimated value of a main magnetic field frequency drift by calculating a phase difference between a first line of non-phase-encoded k-space data and a second line of non-phase encoded k-space data;
• Step 3:
• obtaining a coarse estimated value of the main magnetic field frequency drift by calculating a difference between a phase difference between the second line of non-phase encoded k-space data and a third line of non-phase encoded k-space data and the phase difference between the first line of non-phase-encoded k-space data and the second line of non-phase encoded k-space data;
• Step 4:
• comparing a difference between the coarse estimated value and the fine estimated value with a threshold, and if the difference between the coarse estimated value and the fine estimated value is smaller than the threshold, then selecting the fine estimated value as a value of the main magnetic field frequency drift;
• otherwise, selecting the coarse estimated value as the value of the main magnetic field frequency drift;
• and
• Step 5:
• adjusting a center frequency of the radio frequency pulse based on the value of the main magnetic field frequency drift, and then performing magnetic resonance CEST imaging based on the adjusted center frequency of the radio frequency pulse;
• wherein in the frequency stabilization module, the fine estimated value in the Step 2 is calculated by:
• first, averaging phase differences between individual data sampling points in the first line of non-phase-encoded k-space data and individual data sampling points in the second line of non-phase-encoded k-space data to obtain the phase difference between the first line of non-phase-encoded k-space data and the second line of non-phase-encoded k-space data, and then calculating the fine estimated value Δffine of the main magnetic field frequency drift based on a relationship between a phase and a frequency, and a calculation process is based on:
• Δ
• ⁢
• ⁢
• f
• fine
• =
• φ
• _
• 2
• -
• 1
• 2
• ⁢
• π
• ·
• Δ
• ⁢
• ⁢
• TE
• 2
• -
• 1
• ,
• where ΔTE2-1 is an interval between the moments t1 and t2, and φ2-1 is the phase difference between the first line of non-phase encoded k-space data and the second line of the non-phase encoded k-space data and is calculated based on:
• φ
• _
• 2
• -
• 1
• =
• ∑
• i
• =
• 1
• n
• ⁢
• φ
• i
• 2
• -
• 1
• n
• ,
• where φi2-1 is a phase difference between an ith data sampling point in the first line of non-phase encoded k-space data and an ith data sampling point in the second line of the non-phase encoded k-space data, and n is a number of sampling points in each line of non-phase encoded space data;
• wherein in the frequency stabilization module, the coarse estimated value in the Step 3 is calculated by:
• calculating the difference between the phase difference between the second line of non-phase-encoded k-space data and the third line of non-phase encoded space data and the phase difference between the first line of non-phase-encoded k-space data and the second line of non-phase encoded space data, to obtain the coarse estimated value Δfcoarse of the main magnetic field frequency drift, and a calculation process is based on:
• Δ
• ⁢
• ⁢
• f
• coarse
• =
• φ
• _
• 3
• -
• 2
• -
• φ
• _
• 2
• -
• 1
• 2
• ⁢
• π
• ·
• τ
• ,
• where τ is a blank interval between the moments t2 and t3, τ=(t3−t2)−(t2−t1), and φ3-2 is the phase difference between the second line of non-phase encoded k-space data and the third line of non-phase encoded k-space data and is calculated based on:
• φ
• _
• 3
• -
• 2
• =
• ∑
• i
• =
• 1
• n
• ⁢
• φ
• i
• 3
• -
• 2
• n
• ,
• where φi3-2 is a phase difference between the ith data sampling point in the second line of non-phase encoded k-space data and an ith data sampling point in the third line of non-phase encoded k-space data;
• wherein in the frequency stabilization module, the value of the main magnetic field frequency drift in the Step 4 is determined by:
• if (Δfcoarse−Δffine)<fthreshold, then selecting the fine estimated value as the value of the main magnetic field frequency drift;
• otherwise, selecting the coarse estimated value as the value of the main magnetic field frequency drift;
• wherein the threshold is
• f
• threshold
• =
• 1
• τ
• .