Improved Techniques to Assign Accurate Phase Information Of Respiratory Signals for 4D CT Reconstruction

Abstract

Patient’s respiration can have an effect on movement of tumor range and peripheral organs. Therefore, the respiratory signal was acquired by relation between external markers and movement of patient’s abdomen during radiation therapy in order to minimize the effect of respiration. Based on this technique, many studies of radiation therapy to irradiate at particular part of stable respiratory signals have executed and they have been clinically applied. Nevertheless, the phase-based method is preferred to the amplitude-based method for the ration therapy related to respiration. Because of stabilization of the respiratory signal are limited. In this study, an in-house respiratory signal analysis program was developed for the phase reassignment and the analysis of the irregular respiratory signals. Various irregular respiratory patterns were obtained from clinical experimental volunteers. After then, the in-house program analyzed the factors affecting to phase assignment which is directly related to irradiate sector. The algorithms for separating individual respiratory signals are presented, which made use of baseline signals of input signal to identify the nodes between baseline signals and input signal. This method has advantages that the effect of possible signal drift and noise could be minimized. Therefore, we could achieve irregular peak reduction and noise immunity in phase assignment. Subsequently, accuracy of phase assignment was improved with removal of irregular signals by self-developed algorithm. Furthermore, this program also has a function to detect period and amplitude automatically. This study is considered to be useful for not only image reconstruction and elevation of irradiating accuracy through phase assignment of RPM system but also analysis of respiratory signals. Moreover, this respiratory analysis program can be applied to the 4D CT reconstruction using various respiratory sensors for the reduction of motion artifact.