Maximum entropy reconstruction methods in electron paramagnetic resonance imaging
Maximum entropy reconstruction methods in electron paramagnetic resonance imaging
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DOI：
10.1023/a:1022978322046
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发表时间：
2003-03-01
影响因子：
4.8
通讯作者：
Krishna, MC
中科院分区：
文献类型：
--
作者：
Johnson, CA;McGarry, D;Krishna, MC
电子顺磁共振（EPR）是一种光谱技术，用于检测和表征具有不成对电子（即自由基）的分子。与密切相关的核磁共振（NMR）光谱学不同，EPR作为一种成像方式仍处于发展阶段。尽管许多物理因素阻碍了EPR的发展，但EPR在许多重要的应用领域（包括体内血氧测定）的潜力是相当有希望的。EPR图像通常使用层析成像技术重建，其中最常用的是滤波反向投影（FBP）。应用两种迭代方法对EPR中的最大熵图像进行重建。首先是乘法代数重构技术（MART），这是一种著名的行作用方法。我们提出了第二种方法，称为LSEnt（最小二乘熵），它通过保持与测量值的期望距离来最大化熵并执行正则化。LSEnt在一定程度上是由内点规划的屏障方法驱动的。我们提出的研究中，两个物理幻影的图像，重建使用FBP， MART，和LSEnt，进行比较。与FBP重建的图像相比，使用MART和LSEnt重建的图像具有更小的方差、更好的对比度恢复、主观上更高的分辨率和更少的条纹伪影。这些结果表明，最大熵重建方法（特别是更灵活的LSEnt）可能是克服EPR成像的一些物理挑战的关键。
Electron Paramagnetic Resonance (EPR) is a spectroscopic technique that detects and characterizes molecules with unpaired electrons (i.e., free radicals). Unlike the closely related nuclear magnetic resonance (NMR) spectroscopy, EPR is still under development as an imaging modality. Athough a number of physical factors have hindered its development, EPR's potential is quite promising in a number of important application areas, including in vivo oximetry. EPR images are generally reconstructed using a tomographic imaging technique, of which filtered backprojection (FBP) is the most commonly used. We apply two iterative methods for maximum-entropy image reconstruction in EPR. The first is the multiplicative algebraic reconstruction technique ( MART), a well-known row-action method. We propose a second method, known as LSEnt (least-squares entropy), that maximizes entropy and performs regularization by maintaining a desired distance from the measurements. LSEnt is in part motivated by the barrier method of interior-point programming. We present studies in which images of two physical phantoms, reconstructed using FBP, MART, and LSEnt, are compared. The images reconstructed using MART and LSEnt have lower variance, better contrast recovery, subjectively better resolution, and reduced streaking artifact than those reconstructed using FBP. These results suggest that maximum-entropy reconstruction methods (particularly the more flexible LSEnt) may be critical in overcoming some of the physical challenges of EPR imaging.