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磁共振原理的临床应用 福建医科大学附属第一医院影像科 方哲明
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？ 从临床应用 名称和用法 ？ 序列 组成 原理 基本原理 实用 看图？
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磁共振图像信息的识别 ------一切来自DICOM
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所有图像上所显示参数来源于 DICOM信息，可以选择性设置
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ET echo train 越多扫描越快 SNR越差 TP target position =层厚+ 层间隙 SL slice FOV field of view 22*22cm P posterior L left Srs:2 SeriesNumber Img:9 Image L window lever W window width
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多回波技术 SE Fast SE Turbo SE GRE 回波链越长，扫描速度越快，信澡比较差
多回波中有效TE时间对应的回波放在K空间的中心 有N个回波数，那扫描时间缩短到约为原来的N分之一
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ET echo train 越多扫描越快 SNR越差 TP target position =层厚+ 层间隙 SL slice FOV field of view 22*22cm P posterier L left Srs:2 SeriesNumber Img:9 Image L window lever W window width
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… 1 层厚 层间距 10-30% 2 3 4
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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
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{ 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
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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
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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
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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
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扫描时间 信噪比 空间分辨率
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FFS？ HFP？ FFP？ Head First Suprine
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采集时间与相位编码数呈正比， ？% ?
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1.5T
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ET echo train HFS Head First Suprine frFSE Fast recovery fast Spin echo
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0.5T
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TI=？
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1.5T 3.0T 不同场强共振频率不同 0.5T
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常见磁共振技术 ------正反相位扫描
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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
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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.
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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
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T1 in phase T1 out phase 3D-vibe T2
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脂肪抑制技术 不同于正反相位的扫描 一个像素范围内有水有脂才低信号 只有两大类压脂原理： 根据脂与水的共振频率差异（FS）
不同于正反相位的扫描 一个像素范围内有水有脂才低信号 只有两大类压脂原理： 根据脂与水的共振频率差异（FS） 脂肪与水的弛豫时间不同（STIR） FS+STIR
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常见磁共振技术 ------弥散加权
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弥散加权技术要点 b值 反映弥散梯度场大小和持续时间 越大区分出弥散差异较小组织的能力越强 但SNR下降
注意DWI上T2穿透效应，ADC参数图可鉴别 颅脑DWI明显高信号的主要是：急性梗死、胆脂瘤和脓肿 体部DWI高信号说明细胞致密：多数恶性肿块、淋巴结转移（脑内髓母细胞瘤DWI也较高）
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？= 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
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T2穿透效应 ADC参数图 DWI 15天 T2 = ADC参数图 DWI 2天 T2 =
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常见磁共振技术 ------血管成像
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血管成像基本原理 MRA ceMRA 血液流动 时间飞跃法 相位对比法 动静脉均可，可反映 血流方向和速度，2D 和3D区别在于3D分辨
率更高且多一维方向性 2D 慢血流 不易饱和 静脉成像 3D 快血流 易饱和 动脉成像 ceMRA 快速扫描+增强 得益于扫描速度的提高， 类似CTA，关键是时相握好； 大部是3D，为更薄层扫描
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3D-TOF 原始图 MIP图 血液流动 3D TOF法
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血液流动 2D TOF法
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ceMRA 快速扫描+增强
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合理解读MRA图 不显影 中断 血液流动 夸大狭窄 快速扫描+增强 注意扫描时相影响 ≠ 血流慢 不要迷恋哥…… 重视MRI中包含的血管信息
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0.5T 1.5T 3.0T MRA质量与场强明显相关 哥只是传说……
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Thank you
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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
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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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