Institute of Medical Physics, Erlangen, Germany.
Med Phys. 2009 Dec;36(12):5683-94. doi: 10.1118/1.3259734.
Cardiac CT achieves its high temporal resolution by lowering the scan range from 2pi to pi plus fan angle (partial scan). This, however, introduces CT-value variations, depending on the angular position of the pi range. These partial scan artifacts are of the order of a few HU and prevent the quantitative evaluation of perfusion measurements. The authors present the new algorithm partial scan artifact reduction (PSAR) that corrects a dynamic phase-correlated scan without a priori information.
In general, a full scan does not suffer from partial scan artifacts since all projections in [0, 2pi] contribute to the data. To maintain the optimum temporal resolution and the phase correlation, PSAR creates an artificial full scan pn(AF) by projectionwise averaging a set of neighboring partial scans pn(P) from the same perfusion examination (typically N approximately 30 phase-correlated partial scans distributed over 20 s and n = 1, ..., N). Corresponding to the angular range of each partial scan, the authors extract virtual partial scans pn(V) from the artificial full scan pn(AF). A standard reconstruction yields the corresponding images fn(P), fn(AF), and fn(V). Subtracting the virtual partial scan image fn(V) from the artificial full scan image fn(AF) yields an artifact image that can be used to correct the original partial scan image: fn(C) = fn(P) - fn(V) + fn(AF), where fn(C) is the corrected image.
The authors evaluated the effects of scattered radiation on the partial scan artifacts using simulated and measured water phantoms and found a strong correlation. The PSAR algorithm has been validated with a simulated semianthropomorphic heart phantom and with measurements of a dynamic biological perfusion phantom. For the stationary phantoms, real full scans have been performed to provide theoretical reference values. The improvement in the root mean square errors between the full and the partial scans with respect to the errors between the full and the corrected scans is up to 54% for the simulations and 90% for the measurements.
The phase-correlated data now appear accurate enough for a quantitative analysis of cardiac perfusion.
心脏 CT 通过将扫描范围从 2π降低到 π加扇形角（部分扫描）来实现其高时间分辨率。然而，这会导致 CT 值变化，具体取决于 π 范围的角度位置。这些部分扫描伪影的数量级为几个 HU，会妨碍灌注测量的定量评估。作者提出了一种新的算法，即部分扫描伪影减少（PSAR），该算法可在没有先验信息的情况下对动态相位相关扫描进行校正。
一般来说，完整扫描不会受到部分扫描伪影的影响，因为 [0, 2π] 中的所有投影都有助于数据。为了保持最佳的时间分辨率和相位相关性，PSAR 通过在相同的灌注检查中对一组相邻的部分扫描 pn(P)进行投影平均来创建人工全扫描 pn(AF)（通常 N 大约为 30 个分布在 20 s 内的与相位相关的部分扫描，n = 1，...，N）。与每个部分扫描的角度范围相对应，作者从人工全扫描 pn(AF)中提取虚拟部分扫描 pn(V)。标准重建生成相应的图像 fn(P)、fn(AF)和 fn(V)。从人工全扫描图像 fn(AF)中减去虚拟部分扫描图像 fn(V)可得到一个伪影图像，该图像可用于校正原始部分扫描图像：fn(C) = fn(P) - fn(V) + fn(AF)，其中 fn(C)是校正后的图像。
作者使用模拟和测量的水体模评估了散射辐射对部分扫描伪影的影响，发现两者之间存在很强的相关性。PSAR 算法已通过模拟半拟人心脏体模和动态生物灌注体模的测量得到验证。对于静止体模，已进行了真实的全扫描，以提供理论参考值。与全扫描和校正扫描之间的误差相比，模拟和测量中全扫描和部分扫描之间的均方根误差的改善高达 54%和 90%。
现在，相位相关数据足以进行心脏灌注的定量分析。
