Jackson James, Pan Tinsu, Tonkopi Elena, Swanston Nancy, Macapinlac Homer A, Rohren Eric M
Department of Nuclear Medicine, University of Texas M.D. Anderson Cancer Center, Houston, Texas 77030, USA.
J Nucl Med Technol. 2011 Jun;39(2):83-90. doi: 10.2967/jnmt.110.075283. Epub 2011 May 12.
Automated tube current modulation (ATCM) has been shown to be a useful tool for reducing CT dose. However, its implementation can be complicated, because the correlation between noise index (NI) settings and noise production can change as parameters are manipulated. The goal was to create a methodology to prospectively select ATCM parameters and retrospectively ensure consistent image quality.
An anthropomorphic phantom was scanned at various NIs to determine a baseline NI versus image noise. The noise was measured in SDs of the CT number reported in Hounsfield units. A physician then reviewed 45 studies performed with the same fixed-tube-current protocol to obtain a preferred noise level. The noise level was compared with our phantom baseline scans to find a suitable NI value. This value was implemented in clinical operation. Then, the next 50 patient examinations were retrospectively reviewed to ensure that image quality was maintained to our physician's cutoff noise levels. Radiation dose reductions through tube current reduction were measured for all CT slices of each patient study.
In the phantom study, tube current modulation was observed at an NI of 15. The preferred noise level established in the physician's review correlated with an NI of 20. In our postimplementation analysis, we found that our noise level was 10.75 SDs in Hounsfield units. CT dose reductions of up to 52% were seen.
We were able to prospectively select an NI for ATCM CT by correlating phantom scans to a physician's preferred noise level while maintaining consistent image quality.
自动管电流调制（ATCM）已被证明是一种降低CT剂量的有用工具。然而，其实施可能会很复杂，因为随着参数的调整，噪声指数（NI）设置与噪声产生之间的相关性可能会发生变化。目标是创建一种方法，用于前瞻性地选择ATCM参数，并回顾性地确保图像质量的一致性。
使用不同的NI对一个仿真人体模型进行扫描，以确定基线NI与图像噪声之间的关系。噪声以亨氏单位报告的CT值的标准差来测量。然后，一位医生回顾了45项使用相同固定管电流协议进行的研究，以获得一个偏好的噪声水平。将该噪声水平与我们的模型基线扫描结果进行比较，以找到合适的NI值。该值应用于临床操作中。然后，回顾性地检查接下来的50例患者检查，以确保图像质量保持在我们医生设定的截止噪声水平。测量了每个患者研究的所有CT切片通过降低管电流所实现的辐射剂量减少情况。
在模型研究中，观察到在NI为15时出现管电流调制。医生回顾中确定的偏好噪声水平与NI为20时相关。在我们的实施后分析中，我们发现我们的噪声水平在亨氏单位中为10.75个标准差。CT剂量减少高达52%。
我们能够通过将模型扫描与医生偏好的噪声水平相关联，同时保持一致的图像质量，前瞻性地为ATCM CT选择一个NI。
