What does magnetic vibration t 1 t2 mean?

The length of magnetic * * * vibration t 1 and t2 has the following meanings:

1, T 1 weighted imaging (T 1WI) means to highlight the longitudinal relaxation difference of tissues. The shorter t 1, the stronger the finger signal, and the longer t 1, the weaker the finger signal. T 1 is generally used to observe anatomy.

2.T2 weighted imaging (T2WI) refers to the T2 lateral relaxation difference of prominent tissues. The shorter t2, the weaker the signal, and the longer t2, the stronger the signal. Generally, t2 is helpful for observing pathological changes and sensitive to bleeding.

discrepancy

In any image sequence, the larger the transverse magnetization vector during signal acquisition, the stronger the MR signal.

T 1 weighted image is short TR, short TE-T 1 weighted image, T 1 image characteristics: the shorter the tissue T 1, the faster the recovery and the stronger the signal; The longer the tissue T 1, the slower the recovery and the weaker the signal.

T2-weighted image length TR, long TE-T2-weighted image, T2-weighted image characteristics: the longer the tissue T2, the slower the recovery and the stronger the signal; The shorter T2, the faster recovery and the weaker signal.

Proton density weighted image length TR and short TE- proton density weighted image, image characteristics: the greater the rH of the tissue, the stronger the signal; The smaller the relative humidity, the weaker the signal.

T 1 weighted, TIWI T2 weighted, T2WI and PdWI proton density weighted imaging.

Extended data

MRI is multi-parameter imaging. In order to analyze images conveniently, it is hoped that the gray level of MRI images is mainly determined by specific imaging parameters, which is called weighted imaging (WI). For example, when the gray level of an image is mainly determined by T 1, it is a T 1 weighted image; when it is mainly determined by T2, it is a T2-weighted image; when it is mainly determined by proton density, it is a proton density-weighted image.

When the static magnetic field is uniform, the decay rate of the free induction decay signal (FID) reflects the time constant T2 of the spin-spin interaction of the sample. In the case of static magnetic field inhomogeneity, the attenuation of FID signal will also be affected by magnetic field inhomogeneity, so the attenuation is faster, which is described by time constant T2'.

If the FID signal is collected immediately after the 90 pulse, the initial amplitude of the FID signal is proportional to M0, and the latter is proportional to the number of protons in the unit volume, so the initial amplitude of the FID signal reflects the average density of protons in the sample, and the obtained MRI image is the proton density image.

If the FID signal is not collected immediately after the 90 pulse, but waiting for a period of time, the amplitude of the FID signal collected is not only related to the proton density, but also affected by T2 ′ (when the static magnetic field is uneven), so the obtained MRI image has a certain degree of T2 weighting.

Baidu Encyclopedia: Weighted Pictures