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首页> 外文期刊>Physics in medicine and biology. >Impact of time-of-flight on indirect 3D and direct 4D parametric image reconstruction in the presence of inconsistent dynamic PET data
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Impact of time-of-flight on indirect 3D and direct 4D parametric image reconstruction in the presence of inconsistent dynamic PET data

机译：动态PET数据不一致时飞行时间对间接3D和直接4D参数图像重建的影响

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摘要

Kinetic parameter estimation in dynamic PET suffers from reduced accuracy and precision when parametric maps are estimated using kinetic modelling following image reconstruction of the dynamic data. Direct approaches to parameter estimation attempt to directly estimate the kinetic parameters from the measured dynamic data within a unified framework. Such image reconstruction methods have been shown to generate parametric maps of improved precision and accuracy in dynamic PET. However, due to the interleaving between the tomographic and kinetic modelling steps, any tomographic or kinetic modelling errors in certain regions or frames, tend to spatially or temporally propagate. This results in biased kinetic parameters and thus limits the benefits of such direct methods. Kinetic modelling errors originate from the inability to construct a common single kinetic model for the entire field-of-view, and such errors in erroneously modelled regions could spatially propagate. Adaptive models have been used within 4D image reconstruction to mitigate the problem, though they are complex and difficult to optimize. Tomographic errors in dynamic imaging on the other hand, can originate from involuntary patient motion between dynamic frames, as well as from emission/transmission mismatch. Motion correction schemes can be used, however, if residual errors exist or motion correction is not included in the study protocol, errors in the affected dynamic frames could potentially propagate either temporally, to other frames during the kinetic modelling step or spatially, during the tomographic step. In this work, we demonstrate a new strategy to minimize such error propagation in direct 4D image reconstruction, focusing on the tomographic step rather than the kinetic modelling step, by incorporating time-of-flight (TOF) within a direct 4D reconstruction framework. Using ever improving TOF resolutions (580 ps, 440 ps, 300 ps and 160 ps), we demonstrate that direct 4D TOF image reconstruction can substantially prevent kinetic parameter error propagation either from erroneous kinetic modelling, inter-frame motion or emission/transmission mismatch. Furthermore, we demonstrate the benefits of TOF in parameter estimation when conventional post-reconstruction (3D) methods are used and compare the potential improvements to direct 4D methods. Further improvements could possibly be achieved in the future by combining TOF direct 4D image reconstruction with adaptive kinetic models and interframe motion correction schemes.
机译：当在动态数据的图像重建之后使用动力学建模来估计参数图时，动态PET中的动力学参数估计会降低精度和精度。参数估计的直接方法尝试在统一框架内从测得的动态数据直接估计动力学参数。这种图像重建方法已经显示出可以在动态PET中生成精度和准确性更高的参数图。但是，由于层析成像和动力学建模步骤之间的交错，某些区域或框架中的任何层析成像或动力学建模误差都倾向于在空间或时间上传播。这导致动力学参数有偏差，因此限制了这种直接方法的益处。动力学建模错误源于无法为整个视野构建通用的单一动力学模型，并且在错误建模区域中的此类错误可能会在空间上传播。自适应模型已用于4D图像重建中，以缓解该问题，尽管它们很复杂且难以优化。另一方面，动态成像中的断层扫描错误可能源自动态帧之间患者的非自愿运动，也可能源于发射/传输不匹配。可以使用运动校正方案，但是，如果存在残留错误或研究方案中未包括运动校正，则受影响的动态帧中的错误可能会在动力学建模步骤中在时间上传播到其他帧，或者在断层摄影过程中在空间上传播。步。在这项工作中，我们展示了一种通过将飞行时间（TOF）纳入直接4D重建框架中，从而将直接4D图像重建中的此类误差传播最小化的新策略，重点是层析步骤而不是动力学建模步骤。使用不断提高的TOF分辨率（580 ps，440 ps，300 ps和160 ps），我们证明了直接4D TOF图像重建可以基本上防止由于错误的动力学建模，帧间运动或发射/传输失配而导致的动力学参数误差传播。此外，当使用常规的后重建（3D）方法时，我们证明了TOF在参数估计中的优势，并比较了直接4D方法的潜在改进。通过将TOF直接4D图像重建与自适应动力学模型和帧间运动校正方案相结合，将来可能会实现进一步的改进。

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