Department of Medical Physics and Biomedical Engineering, Tehran University of Medical Sciences, Tehran, Iran.
Ann Nucl Med. 2013 Feb;27(2):152-62. doi: 10.1007/s12149-012-0667-3. Epub 2012 Dec 21.
Hybrid PET/MRI presents many advantages in comparison with its counterpart PET/CT in terms of improved soft-tissue contrast, decrease in radiation exposure, and truly simultaneous and multi-parametric imaging capabilities. However, the lack of well-established methodology for MR-based attenuation correction is hampering further development and wider acceptance of this technology. We assess the impact of ignoring bone attenuation and using different tissue classes for generation of the attenuation map on the accuracy of attenuation correction of PET data.
This work was performed using simulation studies based on the XCAT phantom and clinical input data. For the latter, PET and CT images of patients were used as input for the analytic simulation model using realistic activity distributions where CT-based attenuation correction was utilized as reference for comparison. For both phantom and clinical studies, the reference attenuation map was classified into various numbers of tissue classes to produce three (air, soft tissue and lung), four (air, lungs, soft tissue and cortical bones) and five (air, lungs, soft tissue, cortical bones and spongeous bones) class attenuation maps.
The phantom studies demonstrated that ignoring bone increases the relative error by up to 6.8% in the body and up to 31.0% for bony regions. Likewise, the simulated clinical studies showed that the mean relative error reached 15% for lesions located in the body and 30.7% for lesions located in bones, when neglecting bones. These results demonstrate an underestimation of about 30% of tracer uptake when neglecting bone, which in turn imposes substantial loss of quantitative accuracy for PET images produced by hybrid PET/MRI systems.
Considering bones in the attenuation map will considerably improve the accuracy of MR-guided attenuation correction in hybrid PET/MR to enable quantitative PET imaging on hybrid PET/MR technologies.
与 PET/CT 相比，PET/MRI 具有软组织对比度提高、辐射暴露减少以及真正同步和多参数成像能力等诸多优势。然而，由于缺乏成熟的基于磁共振的衰减校正方法，限制了该技术的进一步发展和广泛应用。我们评估了忽略骨衰减和使用不同组织类别生成衰减图对 PET 数据衰减校正准确性的影响。
这项工作是使用基于 XCAT 体模和临床输入数据的模拟研究进行的。对于后者，使用患者的 PET 和 CT 图像作为输入，使用真实的活性分布进行分析模拟模型，其中基于 CT 的衰减校正作为比较的参考。对于体模和临床研究，参考衰减图被分类为不同数量的组织类别，以生成三个（空气、软组织和肺）、四个（空气、肺、软组织和皮质骨）和五个（空气、肺、软组织、皮质骨和海绵骨）类衰减图。
体模研究表明，忽略骨会导致体部的相对误差增加高达 6.8%，骨区的相对误差增加高达 31.0%。同样，模拟的临床研究表明，当忽略骨骼时，位于体部的病变的平均相对误差达到 15%，位于骨骼的病变的平均相对误差达到 30.7%。这些结果表明，忽略骨骼会导致示踪剂摄取的低估约 30%，这反过来又对混合 PET/MRI 系统生成的 PET 图像的定量准确性造成了实质性损失。
在衰减图中考虑骨骼可以显著提高混合 PET/MR 中基于磁共振的衰减校正的准确性，从而实现混合 PET/MR 技术的定量 PET 成像。
