电影式电子射野影像装置（cine EPID）图像采集帧率对无标记软组织跟踪的影响。

The impact of cine EPID image acquisition frame rate on markerless soft-tissue tracking.

作者信息

Yip Stephen, Rottmann Joerg, Berbeco Ross

机构信息

Department of Radiation Oncology, Brigham and Women's Hospital, Dana-Farber Cancer Institute and Harvard Medical School, Boston, Massachusetts 02115.

出版信息

Med Phys. 2014 Jun;41(6):061702. doi: 10.1118/1.4873322.

DOI:10.1118/1.4873322

PMID:24877797

原文链接:https://pmc.ncbi.nlm.nih.gov/articles/PMC4032434/

Abstract

PURPOSE

Although reduction of the cine electronic portal imaging device (EPID) acquisition frame rate through multiple frame averaging may reduce hardware memory burden and decrease image noise, it can hinder the continuity of soft-tissue motion leading to poor autotracking results. The impact of motion blurring and image noise on the tracking performance was investigated.

METHODS

Phantom and patient images were acquired at a frame rate of 12.87 Hz with an amorphous silicon portal imager (AS1000, Varian Medical Systems, Palo Alto, CA). The maximum frame rate of 12.87 Hz is imposed by the EPID. Low frame rate images were obtained by continuous frame averaging. A previously validated tracking algorithm was employed for autotracking. The difference between the programmed and autotracked positions of a Las Vegas phantom moving in the superior-inferior direction defined the tracking error (δ). Motion blurring was assessed by measuring the area change of the circle with the greatest depth. Additionally, lung tumors on 1747 frames acquired at 11 field angles from four radiotherapy patients are manually and automatically tracked with varying frame averaging. δ was defined by the position difference of the two tracking methods. Image noise was defined as the standard deviation of the background intensity. Motion blurring and image noise are correlated with δ using Pearson correlation coefficient (R).

RESULTS

For both phantom and patient studies, the autotracking errors increased at frame rates lower than 4.29 Hz. Above 4.29 Hz, changes in errors were negligible withδ < 1.60 mm. Motion blurring and image noise were observed to increase and decrease with frame averaging, respectively. Motion blurring and tracking errors were significantly correlated for the phantom (R = 0.94) and patient studies (R = 0.72). Moderate to poor correlation was found between image noise and tracking error with R -0.58 and -0.19 for both studies, respectively.

CONCLUSIONS

Cine EPID image acquisition at the frame rate of at least 4.29 Hz is recommended. Motion blurring in the images with frame rates below 4.29 Hz can significantly reduce the accuracy of autotracking.

摘要

目的

虽然通过多帧平均降低电影电子射野影像装置（EPID）的采集帧率可减轻硬件内存负担并减少图像噪声，但这可能会妨碍软组织运动的连续性，导致自动跟踪效果不佳。本研究调查了运动模糊和图像噪声对跟踪性能的影响。

方法

使用非晶硅射野成像仪（AS1000，瓦里安医疗系统公司，加利福尼亚州帕洛阿尔托）以12.87 Hz的帧率采集体模和患者图像。EPID规定的最大帧率为12.87 Hz。通过连续帧平均获得低帧率图像。采用一种先前经验证的跟踪算法进行自动跟踪。在上下方向移动的拉斯维加斯体模的编程位置与自动跟踪位置之间的差异定义为跟踪误差（δ）。通过测量深度最大的圆的面积变化来评估运动模糊。此外，从4名放射治疗患者的11个射野角度采集的1747帧图像上的肺部肿瘤，采用不同的帧平均进行手动和自动跟踪。δ由两种跟踪方法的位置差异定义。图像噪声定义为背景强度的标准差。使用Pearson相关系数（R）将运动模糊和图像噪声与δ进行相关性分析。

结果

对于体模和患者研究，当帧率低于4.29 Hz时，自动跟踪误差均增加。在4.29 Hz以上，误差变化可忽略不计，δ < 1.60 mm。观察到运动模糊随帧平均增加，而图像噪声随帧平均减少。在体模研究（R = 0.94）和患者研究（R = 0.72）中，运动模糊与跟踪误差显著相关。两项研究中，图像噪声与跟踪误差之间的相关性均为中等至较差，R分别为 -0.58和 -0.19。