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随着PET/CT显像技术在临床中的迅速开展,PET/磁共振(magnetic resonance,MR)也应运而生,其分为一体机和分体机,所谓一体机就是将PET探测器和MR线圈有机地结合在一起,并能同步进行扫描,在具有完整的MR功能的同时还能够完成PET的所有成像模式[1]。一体机PET/MR在发展的过程中克服了许多困难,比如在探测器电子学与强磁场、强梯度场和射频场的兼容上、PET数据的衰减校正上等,由于物体对γ射线的衰减严重影响PET的定量精度和图像质量,因此衰减校正必不可少。笔者对PRT/MR衰减校正的4种方法进行了综述。
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地图集法、组织分割法、发射数据重建法和透射扫描法都有各自的优势和不足(表 1)。目前临床上PET/MR多使用组织分割和地图集法进行衰减校正。但我们相信直接通过发射数据计算出衰减图像的方法将有不可替代的优势和发展前景。
方法 优点 缺点 地图集法 可获得一个连续的衰减系数的图像 个体间的解剖学差异影响衰减校正的结果 组织分割法 不同的组织分别赋予对应的衰减系数 需要开发不同的序列来分割组织 发射数据重建法 直接利用PET发射数据中的衰减信息进行衰减校正,受解剖结构差异的影响小 技术难度大,算法复杂 投射扫描法 同时获得发射图像和透射图像 外置放射源,空间限制多 表 1 PET/MR的4种衰减校正方法的优缺点
Table 1. The advantages and disadvantages of four attenuation correction methods for PET/MR
PET/MR的衰减校正技术
Overview of PET/MR attenuation correction
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摘要: PET/MR是目前最先进的分子影像设备,PET图像需要通过衰减校正来得到真实的放射性药物活度分布并对其进行量化。笔者主要对PET/MR的衰减校正原理和衰减校正的方法进行综述,重点介绍地图集法、组织分割法和具有发展前景的发射数据重建法。Abstract: PET/MR is the most advanced molecular imaging device nowadays. The PET image needs to be quantified by attenuation correction(AC) to obtain the real activity distribution of radioactive drugs. The principle of AC of PET/MR and four methods of AC are briefly described in this paper.This paper mainly introduces the tissue segmentation and atlas method. A more promising launch data reconstruction method is also introduced in this paper.
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表 1 PET/MR的4种衰减校正方法的优缺点
Table 1. The advantages and disadvantages of four attenuation correction methods for PET/MR
方法 优点 缺点 地图集法 可获得一个连续的衰减系数的图像 个体间的解剖学差异影响衰减校正的结果 组织分割法 不同的组织分别赋予对应的衰减系数 需要开发不同的序列来分割组织 发射数据重建法 直接利用PET发射数据中的衰减信息进行衰减校正,受解剖结构差异的影响小 技术难度大,算法复杂 投射扫描法 同时获得发射图像和透射图像 外置放射源,空间限制多 -
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