翻轉角


翻轉角(flip angle, tip angle)，也可稱作偏折角、傾角，代表了射頻對自旋組成的磁化向量能夠翻轉多少角度；因為是改變進動中之自旋的進動軸，實際上作用等同於章動，故也稱章動角(nutation angle)。


一個射頻脈衝的翻轉角可以透過如下公式計算：



α=γ∫B1(t)dtdisplaystyle alpha =gamma int B_1(t)dtdisplaystyle alpha =gamma int B_1(t)dt。

其中，α代表翻轉角，γ是旋磁比，B1是射頻脈衝波包外形強度；整個式子可以看出此角度是射頻強度對時間的積分，再做一些單位變換。


對一個矩形的脈衝而言，式子相當簡單：



α=γB1Δtdisplaystyle alpha =gamma B_1Delta t,displaystyle alpha =gamma B_1Delta t,。


相關條目


  • 核磁共振

  • 磁振造影




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