磁共振原理的临床应用

？ 从临床应用 名称和用法 ？ 序列 组成 原理 基本原理 实用

Chemical shift of the second kind In-Phase " in phase" "out of phase" Out-of Phase *Note*- GE & SPGR sequences have no refocusing pulses 34

Chemical shift of the second kind TE (.5 T) 0 msec 7 msec 14 msec 21 msec TE (1.0 T) 0 msec 4.4 msec 9.2 msec 14 msec TE (1.5 T) 0 msec 2.2 msec 4.4 msec 6.6 msec " in phase" " out of phase" 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.

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 水 脂

？= DWI高信号 =？ T2穿透效应 T2加权 ADC值 质子加权 因此ADC参数图更为可靠

2D 按顺序 按顺序采集一幅图像意为当一层所有的激发脉冲全部结束后再进行下一层扫描。 按顺序采集= 无交叉伪影 1 按顺序采集= 无交叉伪影 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. 完成一层扫描后再进行下一层扫描 5

{ 3D 采集 3D容积块 在 3D容积采集时 ,发射宽的脉冲激发整个扫描容积块。空间编码必须加在相位，频率和层面三个轴上。 3D 容积 层面编码 { 3D容积块 相位编码 3D uses a wide RF transmit bandwidth which is needed to cover a large anatomical area. 频率编码 6

空间分辨率 两个物体能被分辨时之间的最小距离。 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. 11

空间分辨率 三个参数影响分辨率: FOV 矩阵 层厚 小 FOV、大矩阵、薄层为高分辨率。 列 行 体素 The three scan parameters that affect spatial resolution for all MR image acquisition modes are FOV, matrix, and slice thickness. Changing any of the three affects the voxel volume. Changing either FOV or matrix affects the in plane resolution. Changing the slice thickness affects the depth resolution. What affect do you think changing the voxel volume will have on the SNR? Answer: it will increase or decrease the SNR as the voxel shape changes. 12

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。 16 cm FOV Think of the pixel as representing a chunk of anatomy and all the protons within that chunk will have their signals averaged together and assigned to a cell on the matrix. If the chunk gets bigger, each cell on the matrix is representing more and more protons so the resolution goes down. If the chunk gets smaller, each cell on the matrix is representing fewer protons so the resolution goes up. This slide illustrates that the 16 cm FOV produces pixels that are smaller in comparison with the 24 cm FOV. Since the pixels are smaller, the anatomy within each cell of the matrix, is smaller and the resolution is greater in comparison with the 24 cm FOV. What are some clinical areas (anatomical) where high spatial resolution is a necessity? Answer: TMJ, orbits, joints, pituitary... What are some clinical area (anatomically) where high spatial resolution isn’t as critical? Answer: Abdominal imaging 16 cm FOV 24 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

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