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• Transverse relaxation When there is a B1, µlean to it, but B1 disappear, this tendency disappear too. The component of µin XY plate are dispersed in different directions.
吸收RF能量达到不稳定状态的过程.
饱和现象
• 低能态核吸收射频电磁波的辐射能跃迁 到高能级，如高能态核无法返回到低能 态，那末随着跃迁的不断进行，处于低 能态的1H核数目与处于高能态1H核数目 相等。上述这种现象称为饱和。
相干饱和与非相干饱和
Classical DescriBaidu Nhomakorabeation 激励过程经典解释
90ºPulse and 180ºPulse
• If the rf pulse make macro magnetic moment deflect 90º, we call this rf pulse 90ºpulse.
• If the rf pulse make macro magnetic moment deflect 180º, we call this rf pulse 180ºpulse.
• The frequency of rf pulse must equate to the frequency of procession of nuclei.
Resonance Absorption/激励
The electric magnetic wave will induces the nuclear magnetic moment from their lower energy to their higher energy state when get energy from outside in form of radio frequency. This process is called resonance absorption.
(医学影像物理学)14磁化强度矢 量
磁化强度矢量
• 单位体积内的磁矩矢量之和
M0 : Number of parallel nuclei >Number of antiparallel nuclei
M0 i
M0, Macro magnetic moment µ, nuclear magnetic moment
So we can regard M will rotate around B0 and B1 . This kind of Rotation is
called nutation(章动).
围绕旋转磁场旋进造成的能量变化,由M偏转的角度体现.
偏转角/翻转角
影响偏转角度的因素:
• RF脉冲功率的大小 • RF脉冲的作用时间.
• 射频脉冲与旋转磁场/施加方向 • 在静止磁场与旋转磁场共同作用下的
章动 • 围绕旋转磁场旋进造成的能量变化
射频脉冲与旋转磁场
• 射频脉冲与旋转磁场的等效 • 旋转坐标系与其中的B1场
在静止磁场与旋转磁场共同作用 下的章动
Rf pulse bring a revolving magnetic field B1, M will rotate following B1 also.
Transverse relaxation
• Longitudinal relaxation The nuclei in parallel state become more and more with the release of energy. So in this direction the macro magnetic momentum recover gradually.
• Macro magnetic moment M0 can be divided into vertical component and horizontal component, in these two direction, they are independent process.
Longitudinal relaxation and
• 关于翻转角的说明
resonance emission
When resonance absorption is ceased, Nuclear magnetic moments will come to their lower energy state from their higher energy. The energy gotten from outside will be released and returned to outside in form of electric –magnetic wave. This process is called resonance emission.
Mz M0
Mxy 0
Radio Frequency Pulse
• Rf pulse is generated by an current pulse in the coil near the sample.
• The function of rf pulse correspond to the periodic force
Relaxation Process
• After excitation by the rf pulse, the process that NMR recover to thermal equilibrium is called relaxation.
• Relaxation process is characterized by two time constants designated T1 and T2.
Condition of rf pulse
EgNB0
Ehv
vE/h gNB 0/h 2gN/h
2 πv2 πgNB 0/h B
• The energy absorption of nuclei is in form of quantum, just like photo-electron effect.
