Department of Radiology, University of Washington Medical Center, 4000 15th Avenue NE, Box 357987, Seattle, Washington 98195-7987, USA.
Med Phys. 2010 Mar;37(3):1191-200. doi: 10.1118/1.3315368.
In cardiac PET and PET/CT imaging, misaligned transmission and emission images are a common problem due to respiratory and cardiac motion. This misalignment leads to erroneous attenuation correction and can cause errors in perfusion mapping and quantification. This study develops and tests a method for automated alignment of attenuation and emission data.
The CT-based attenuation map is iteratively transformed until the attenuation corrected emission data minimize an objective function based on the Radon consistency conditions. The alignment process is derived from previous work by Welch et al. ["Attenuation correction in PET using consistency information," IEEE Trans. Nucl. Sci. 45, 3134-3141 (1998)] for stand-alone PET imaging. The process was evaluated with the simulated data and measured patient data from multiple cardiac ammonia PET/CT exams. The alignment procedure was applied to simulations of five different noise levels with three different initial attenuation maps. For the measured patient data, the alignment procedure was applied to eight attenuation-emission combinations with initially acceptable alignment and eight combinations with unacceptable alignment. The initially acceptable alignment studies were forced out of alignment a known amount and quantitatively evaluated for alignment and perfusion accuracy. The initially unacceptable studies were compared to the proposed aligned images in a blinded side-by-side review.
The proposed automatic alignment procedure reduced errors in the simulated data and iteratively approaches global minimum solutions with the patient data. In simulations, the alignment procedure reduced the root mean square error to less than 5 mm and reduces the axial translation error to less than 1 mm. In patient studies, the procedure reduced the translation error by > 50% and resolved perfusion artifacts after a known misalignment for the eight initially acceptable patient combinations. The side-by-side review of the proposed aligned attenuation-emission maps and initially misaligned attenuation-emission maps revealed that reviewers preferred the proposed aligned maps in all cases, except one inconclusive case.
The proposed alignment procedure offers an automatic method to reduce attenuation correction artifacts in cardiac PET/CT and provides a viable supplement to subjective manual realignment tools.
在心脏 PET 和 PET/CT 成像中，由于呼吸和心脏运动，传输和发射图像的配准问题是一个常见问题。这种配准错误会导致衰减校正错误，并可能导致灌注图和量化错误。本研究开发并测试了一种自动对准衰减和发射数据的方法。
基于 CT 的衰减图被迭代地转换，直到基于 Radon 一致性条件的衰减校正发射数据最小化目标函数。该对齐过程源自 Welch 等人的先前工作["使用一致性信息进行 PET 中的衰减校正"，IEEE Trans. Nucl. Sci. 45, 3134-3141（1998）]，用于独立的 PET 成像。该过程使用来自多个心脏氨 PET/CT 检查的模拟数据和测量的患者数据进行了评估。对齐过程应用于五种不同噪声水平和三种不同初始衰减图的模拟。对于测量的患者数据，将对齐过程应用于初始对齐可接受的 8 个衰减-发射组合和初始对齐不可接受的 8 个组合。对最初可接受的对齐研究进行了已知程度的强制失准，并对其对齐和灌注精度进行了定量评估。将最初不可接受的研究与提出的对齐图像进行了盲法并排比较。
所提出的自动对齐程序减少了模拟数据中的误差，并通过患者数据迭代地接近全局最小解。在模拟中，对齐程序将均方根误差降低到 5 毫米以下，并将轴向平移误差降低到 1 毫米以下。在患者研究中，该程序将平移误差降低了>50%，并在 8 个初始可接受的患者组合中已知失准后解决了灌注伪影。提出的对齐衰减-发射图和初始失准衰减-发射图的并排比较表明，除了一个不确定的病例外，所有情况下，审阅者都更喜欢提出的对齐图。
所提出的对齐程序为减少心脏 PET/CT 中的衰减校正伪影提供了一种自动方法，并为主观手动重新对准工具提供了一种可行的补充。
