Method for measuring the gradient field of a nuclear magnetic resonance (NMR) system based on the diffusion effect

A method for measuring a gradient field of a nuclear magnetic resonance (NMR) system based on a diffusion effect comprising the following steps:

• S100:
• acquiring M sets of echo signals in a non-uniform field NMR system, wherein the echo signal is a four-dimensional array S(m, n, a, p);
• wherein a first dimension denotes an echo spacing vector τ with a length of M;
• a second dimension denotes an echo train length N;
• a third dimension denotes an averaging number A;
• and
• a fourth dimension denotes a number of sampling points of a single readout data, wherein the number is P;
• S200:
• data preprocessing:
• converting the echo signal S(m, n, a, p) into a one-dimensional or two-dimensional array S′:
• S210:
• performing Fourier transform on the fourth dimension of the echo signal S to acquire frequency domain data and reserving a low-frequency part;
• S220:
• averaging data;
• S230:
• taking logarithm of all data;
• and
• S240:
• calculating a time series t(m);
• S300:
• calculating an equivalent coefficient a by a fitting function:
• S′=ƒ(α,T2,t(m))
• wherein T2 is a known time constant for decay of transverse magnetization after radio frequency (RF)-pulse on a standard quantitative phantom;
• and
• S400:
• calculating a gradient field by a calculation function:
• G
• =
• c
• *
• a
• γ
• 2
• ⁢
• D
• wherein γ denotes the gyromagnetic ratio, D denotes a known apparent diffusion coefficient (ADC) of the standard quantitative phantom, c denotes a constant coefficient, and G denotes the gradient field.