In Section II, relaxation processes and relaxation time in resonance were introduced. The contrast of proton density is one of the techniques to characterize different tissues.

• 第二章介绍了弛豫过程和弛豫时间。不同的氢核密度具有不同的弛豫过程和弛豫时间的,在实际应用中可以区分不同物质的种类。