MR和CT原理1.ppt

磁共振原理的临床应用 从临床应用 原理 序列 基本原理 名称和用法 组成 ？ ？ 实用 34 in phase out of phase Chemical shift of the second kind In-Phase Out-of Phase *Note*- GE SPGR sequences have no refocusing pulses TE (1.5 T) 0 msec 2.2 msec 4.4 msec 6.6 msec in phase out of phase in phase out of phase TE (.5 T) 0 msec 7 msec 14 msec 21 msec Chemical shift of the second kind TE (1.0 T) 0 msec 4.4 msec 9.2 msec 14 msec 水 脂 纯水、纯脂信号都不低； 反相位上信号越低不等于脂质越多 一个像素单位 质子加权 T2加权 ADC值 ？= DWI高信号 =？ 因此ADC参数图更为可靠 T2穿透效应 空间分辨率 两个物体能被分辨时之间的最小距离。 11 空间分辨率 三个参数影响分辨率: FOV 矩阵 层厚 列 行 体素 12 小 FOV、大矩阵、薄层为高分辨率。 FOV FOV 是指图像上显示的解剖部位大小。FOV越大，象素越大，分辨率越低。FOV的变化以厘米为单位。 24 cm FOV 16 cm FOV 13 正反相位 T2穿透效应 血流高信号？低信号？ 血肿信号变化？ 造影剂原理 空间分辨率？FOV？SNR?三者关系 快速采集技术 磁共振有哪些加权成像？ 压脂技术有哪几种？与正反相位扫描区别在哪？ 磁共振血管成像的方法有哪些？ 血流是高信号？低信号？ 水成像的方法有哪些？ 造影剂的原理？MTC fMRI DTI MRS 采集技术 Thank you TE is the scan timing parameter than controls when we listen to the echo and therefore the effects we’ll see from chemical shift of the second kind. What happens if the number of slices programmed doesn’t fit within the TR? Answer: it has no affect since the system only collects one slice at a time. What happens if the slices are spaced too close together? Answer: no cross-talk since, again, only one slice is excited at a time and therefore any protons excited outside the slice borders do not experience another excitation pulse. 3D uses a wide RF transmit bandwidth which is needed to cover a large anatomical area. If these two objects produce signals that are going to be assigned to the same pixel on an image matrix, would we be able to tell them apart? Answer: no, there signals would be averages and a single intensity would be assigned to the pixel on the matrix. What would we do to see these two objects as separate and distinct from one another? Answer: we would have to change the size of the pixel. * * TE is the scan timing parameter than controls when we listen to the echo and therefore the effects we’ll see from c