核磁共振技术的历史magneticresonanceimagingmri的成像原理.ppt

Magnetic Resonance Imaging T1 and T2 relaxation times of malignant tissuesnormal tissues (exception is melanoma) Ref. 1 Normal tissues Malignant tissues T1 (s) Liver Magnetic Resonance Imaging The spin-echo pulse sequence in MRIA series of 90o 180o RF pulses is given at a repetition time (TR) selected by the operatorThe signal from the tissues is detected at the time of echo (TE), again selected by the operatorTR TE will affect image contrast Ref. 4 Image contrast operator operator (Resonance) Excitation TR =repetition time TE =echo time Repetition and echo time Detection MR Image Magnetic Resonance Imaging Determining image contrast Ref. 7 TR(重複時間):一個脈衝開始到下一個脈衝的時間間隔TR會影響脈衝開始下一個脈衝之間的遲豫的長度 (T1) TE(回音時間):脈衝開始到收集訊號的時間間隔TE會影響RF激發脈衝去除之後的遲豫期間長度 (T2) 以及接受線圈接受到最大的訊號 Saturation recovery TR = time between 90o pulse T1 2T1 3T1 TR Mz 100% M0 63% 50% 90o 90o TR MRI signal Repeat 90opulse TR (time delay between RF pulses) 90opulse (90o – TR – 90o) Ref.1 Magnetic Resonance Imaging Magnetic Resonance Imaging Ref. 1 TE (time delay) 180o pulse Spin echo Repeat Pulse Spin echo pulse sequence(90o – TE – 180o) 90o 180o t t 2TE Inversion recovery Ref. 1 Magnetic Resonance Imaging 蹤向磁化 90o的激化脈衝將脂肪偏離至180o(無訊號) TI TI 180o 180o 180o TR 90o TE FID echo TI (time delay between RF pulses) 180opulse 90o pulse MR signal Repeat after delay equal to several TI (3) 脂肪 (180o – TI – 90o) Magnetic Resonance Imaging T1-weighted oblique sagital MR image of the temporo-mandibular joint open-mouth view The black linear structure (arrow) is the disk located in the normal position superior to the condyle(TR = 500ms, TE = 19ms) Ref. 4 Parameters for MRI (Proton density) (TR) (TE) Ref. 1 Magnetic Resonance Imaging Magnetic Resonance Imaging TR (ms) Repetition time (flip 90o - 90o) TE (ms) Echo time (flip 90o - 180o) Flip Angle of precession (net magnetization) away from Z-axis Ref. 3 當RF脈衝以在處於平衡狀態靜磁場中，磁化向量M完全位於Z軸上 迴旋頻率垂直彈擊靜磁場時，會將磁化向量由Z軸彈開