Bruyant Philippe P, Gennert Michael A, Speckert Glen C, Beach Richard D, Morgenstern Joel D, Kumar Neeru, Nadella Suman, King Michael A
PP Bruyant, RD Beach and MA King are with the University of Massachusetts, Worcester, MA. MA Gennert, N. Kumar and S. Nadella are with the Worcester Polytechnic Institute, Worcester, MA. Joel D. Morgenstern is with Video Internet & Imaging Inc., Uxbridge MA. Glen C. Speckert is with SpeckTech Inc. Melrose MA, USA.
IEEE Trans Nucl Sci. 2005 Oct;52(5 I):1288-1294. doi: 10.1109/TNS.2005.858208.
Our overall research goal is to devise a robust method of tracking and compensating patient motion by combining an emission data based approach with a visual tracking system (VTS) that provides an independent estimate of motion. Herein, we present the latest hardware configuration of the VTS, a test of the accuracy of motion tracking by it, and our solution for synchronization between the SPECT and the optical acquisitions. The current version of the VTS includes stereo imaging with sets of optical network cameras with attached light sources, a SPECT/VTS calibration phantom, a black stretchable garment with reflective spheres to track chest motion, and a computer to control the cameras. The computer also stores the JPEG files generated by the optical cameras with synchronization to the list-mode acquisition of events on our SPECT system. Five Axis PTZ 2130 network cameras (Axis Communications AB, Lund, Sweden) were used to track motion of spheres with a highly retro-reflective coating using stereo methods. The calibration phantom is comprised of seven reflective spheres designed such that radioactivity can be added to the tip of the mounts holding the spheres. This phantom is used to determine the transformation to be applied to convert the motion detected by the VTS into the SPECT coordinates system. The ability of the VTS to track motion was assessed by comparing its results to those of the Polaris infra-red tracking system (Northern Digital Inc. Waterloo, ON, Canada). The difference in the motions assessed by the two systems was generally less than 1mm. Synchronization was assessed in two ways. First, optical cameras were aimed at a digital clock and the elapsed time estimated by the cameras was compared to the actual time shown by the clock in the images. Second, synchronization was also assessed by moving a radioactive and reflective sphere three times during concurrent VTS and SPECT acquisitions and comparing the time at which motion occurred in the optical and SPECT images. The results show that optical and SPECT images stay synchronized within a 150 ms range. The 100Mbit network load is less than 10%, and the computer's CPU load is between 15 and 25%; thus, the VTS can be improved by adding more cameras or by increasing the image size and/or resolution while keeping an acquisition rate of 30 images per second per camera.
我们的总体研究目标是通过将基于发射数据的方法与提供独立运动估计的视觉跟踪系统（VTS）相结合，设计出一种强大的跟踪和补偿患者运动的方法。在此，我们展示了VTS的最新硬件配置、对其运动跟踪准确性的测试，以及我们针对单光子发射计算机断层扫描（SPECT）与光学采集之间同步的解决方案。VTS的当前版本包括带有附加光源的光学网络摄像机组的立体成像、一个SPECT/VTS校准体模、一件带有反光球以跟踪胸部运动的黑色可拉伸衣物，以及一台控制摄像机的计算机。该计算机还存储由光学摄像机生成的JPEG文件，并与我们SPECT系统上事件的列表模式采集进行同步。使用五轴云台2130网络摄像机（瑞典隆德的Axis Communications AB公司）通过立体方法跟踪具有高反光涂层的球体的运动。校准体模由七个反光球组成，其设计使得放射性物质可以添加到固定球体的支架尖端。这个体模用于确定要应用的变换，以便将VTS检测到的运动转换到SPECT坐标系中。通过将VTS的结果与北极星红外跟踪系统（加拿大安大略省滑铁卢的北方数字公司）的结果进行比较，评估了VTS跟踪运动的能力。两个系统评估的运动差异通常小于1毫米。通过两种方式评估同步。首先，将光学摄像机对准一个数字时钟，并将摄像机估计的经过时间与图像中时钟显示的实际时间进行比较。其次，还通过在同时进行VTS和SPECT采集期间三次移动一个放射性和反光球体，并比较光学图像和SPECT图像中运动发生的时间来评估同步。结果表明，光学图像和SPECT图像在150毫秒范围内保持同步。100兆位网络负载小于10%，计算机的中央处理器（CPU）负载在15%到25%之间；因此，在保持每台摄像机每秒30帧图像采集速率的同时，通过添加更多摄像机或增加图像大小和/或分辨率，可以改进VTS。
