[临床医学]磁共振成像原理简化版1.ppt

总论内容概要 磁共振的历史 磁共振成像成像的原理与设备 磁共振成像的检查技术 磁共振成像的图像特点 磁共振成像的优越性、局限性 磁共振成像的临床应用 进动 Precession 质子的自旋轴围绕磁力线作快速锥形的旋转运动，叫做进动 （ Precession ）       To show it differnetly: here is the moment taht the protons are flipped over 90 degrees and relaxate back into the Z-direction.... ... ... ... ... ... ... ... ... ... ... ... ... ... ... ... ... ... ... ... ... ... ...and now you see that there is no magnatisation left in the Z-direction. The magnetisation is now completely in the X-Y-plane. 与 that is what we call 激励. (Show this again, because many things happen at the same 时间).(与 it took Harry a 长 时间 to make these slides). Once the protons are tilted over 90 degrees, we can switch of the transmitter... and now we need a receive coil and a receiver, because... While the protons realign into the direction of the main magnetic field, they transmit a signal. At the same frequency as we have put into them. ... ... ... ... ... ... ... ... ... ... ... As you might have seen, the signal gets weaker while the protons turn more towards the direction of the main magnetic field. 时间 90 o 磁化强度 难于被测量! 可以通过感应信号间接测量 信号的产生 T1 对比 100 0 信号的产生 不同加权图像的获得 90 o 重复 时间 TR 90 o 信号的产生 纵向弛豫与横向弛豫的关系 0 时间 100 0 时间 100 90 o 90 o 回波 时间 TE 信号的产生 纵向弛豫与横向弛豫的关系 180o ...and it rotates around it‘s own axis.electric charge and rotation generate magnetism. Compare with electromotor（发动机）. Electricity and magnets generate rotation! In the body there are many protons. When we put those protons in a magnetic field.... ...they will orient themselves into the direction of this magnetic field. When we look at the coordinate system(座标系) to the right, we can say that the summed magnetization is building up in the Z-direction. ... ... The core of an atom is called the nucleus. The nucleus exists of neutrons and protons. neutrons do not have an electrical charge, but protons do. Around this nucleus electrons are spinning. Electrons posses a negative electrical charge. In MRI we use the water atom as the sou