Automatic, three-segment, MR-based attenuation correction for whole-body PET/MR data
Automatic, three-segment, MR-based attenuation correction for whole-body PET/MR data
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DOI：
10.1007/s00259-010-1603-1
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发表时间：
2011-01-01
影响因子：
9.1
通讯作者：
Krombach, G. A.
中科院分区：
文献类型：
--
作者：
Schulz, V.;Torres-Espallardo, I.;Krombach, G. A.
正电子发射断层扫描（PET）和磁共振（MR）断层扫描在单一设备中的结合，预计将是继PET/CT之后未来分子成像应用的下一步。与CT相比，MR的主要优势在于其多样的软组织对比度以及在无电离辐射的情况下获取功能信息的能力。然而，MR无法测量一个能直接推导出高能光子衰减值的物理量。为克服这一问题，我们提出一种全自动方法，该方法使用专用的T1加权MR序列并结合定制的图像处理技术来推导全身PET的衰减图。该算法利用区域生长技术并结合强度分析进行自动阈值估计，自动识别身体外轮廓和肺部。生成衰减图无需用户干预。
在一项临床研究中，使用同一患者（n = 15）的全身PET/CT和MR图像对所提出的基于MR的衰减校正（AC）方法的准确性进行了评估。通过与原始MR图像比较，采用四点量表对身体和肺轮廓（左右方向）的分割进行评估（平均值>3.8）。使用弹性配准的基于MR和基于CT（分割的和未分割的）的衰减图重建PET图像。基于MR的AC表现出与基于CT的AC相似的行为，以及与基于分割CT的AC所提供的相似的准确性。使用预定义衰减系数与基于CT的AC进行标准化摄取值（SUV）比较，结果显示骨病变的差异最大（SUVmax的平均值±标准偏差：MR为 -3.0%±3.9%；分割CT为 -6.5%±4.1%）。对用基于分割MR、基于CT和基于分割CT的AC校正的PET图像进行盲法比较，结果显示病变可检测性相同，但发现图像质量略有差异。
我们基于MR的衰减校正方法提供了与分割CT相似的校正准确性。根据参与盲法研究的专家的意见，这些差异不影响PET图像的诊断价值。
The combination of positron emission tomography (PET) and magnetic resonance (MR) tomography in a single device is anticipated to be the next step following PET/CT for future molecular imaging application. Compared to CT, the main advantages of MR are versatile soft tissue contrast and its capability to acquire functional information without ionizing radiation. However, MR is not capable of measuring a physical quantity that would allow a direct derivation of the attenuation values for high-energy photons.To overcome this problem, we propose a fully automated approach that uses a dedicated T1-weighted MR sequence in combination with a customized image processing technique to derive attenuation maps for whole-body PET. The algorithm automatically identifies the outer contour of the body and the lungs using region-growing techniques in combination with an intensity analysis for automatic threshold estimation. No user interaction is required to generate the attenuation map.The accuracy of the proposed MR-based attenuation correction (AC) approach was evaluated in a clinical study using whole-body PET/CT and MR images of the same patients (n = 15). The segmentation of the body and lung contour (L-R directions) was evaluated via a four-point scale in comparison to the original MR image (mean values > 3.8). PET images were reconstructed using elastically registered MR-based and CT-based (segmented and non-segmented) attenuation maps. The MR-based AC showed similar behaviour as CT-based AC and similar accuracy as offered by segmented CT-based AC. Standardized uptake value (SUV) comparisons with reference to CT-based AC using predefined attenuation coefficients showed the largest difference for bone lesions (mean value +/- standard variation of SUVmax: -3.0% +/- 3.9% for MR; -6.5% +/- 4.1% for segmented CT). A blind comparison of PET images corrected with segmented MR-based, CT-based and segmented CT-based AC afforded identical lesion detectability, but slight differences in image quality were found.Our MRaEurobased attenuation correction method offers similar correction accuracy as offered by segmented CT. According to the specialists involved in the blind study, these differences do not affect the diagnostic value of the PET images.