Zhang Tiezhi, Keller Harry, O'Brien Matthew J, Mackie Thomas R, Paliwal Bhudatt
Department of Medical Physics, University of Wisconsin, Madison, Wisconsin 53706, USA.
Med Phys. 2003 Dec;30(12):3165-71. doi: 10.1118/1.1625439.
The signal from a spirometer is directly correlated with respiratory motion and is ideal for target respiratory motion tracking. However, its susceptibility to signal drift deters its application in radiotherapy. In this work, a few approaches are investigated to control spirometer signal drift for a Bernoulli-type spirometer. A method is presented for rapid daily calibration of the spirometer to obtain a flow sensitivity function. Daily calibration assures accurate airflow measurement and also reduces signal drift. Dynamic baseline adjustment further controls the signal drift. The accuracy of these techniques was studied and it was found that the spirometer is able to provide a long-term drift-free breathing signal. The tracking error is comprised of two components: calibration error and stochastic signal baseline variation error. The calibration error is very small (1% of 3 l) and therefore negligible. The stochastic baseline variation error can be as large as 20% of the normal breathing amplitude. In view of these uncertainties, the applications of spirometers in treatment techniques that rely on breathing monitoring are discussed. Spirometer-based monitoring is noted most suitable for deep inspiration breath-hold but less important for free breathing gating techniques.
来自肺活量计的信号与呼吸运动直接相关，是目标呼吸运动跟踪的理想选择。然而，其对信号漂移的敏感性阻碍了它在放射治疗中的应用。在这项工作中，研究了几种方法来控制伯努利型肺活量计的信号漂移。提出了一种对肺活量计进行每日快速校准以获得流量灵敏度函数的方法。每日校准可确保准确的气流测量，还能减少信号漂移。动态基线调整进一步控制信号漂移。研究了这些技术的准确性，发现肺活量计能够提供长期无漂移的呼吸信号。跟踪误差由两个部分组成：校准误差和随机信号基线变化误差。校准误差非常小（3升的1%），因此可以忽略不计。随机基线变化误差可能高达正常呼吸幅度的20%。鉴于这些不确定性，讨论了肺活量计在依赖呼吸监测的治疗技术中的应用。基于肺活量计的监测被认为最适合深吸气屏气，但对自由呼吸门控技术不太重要。
