Department of Medical Physics, Memorial Sloan-Kettering Cancer Center, New York, New York 10021, USA.
Med Phys. 2011 Jan;38(1):531-8. doi: 10.1118/1.3523100.
In this study, the authors validated a novel respiratory tracking device, the multidimensional respiratory tracking (MDRT) system, that was designed to assist in correcting for respiratory motion in PET/CT images. The authors also investigated a novel PET acquisition technique, smart gating (SG), that enables to acquire motion-free PET data prospectively, with minimum user interference and with no additional postprocessing of the PET data.
MDRT uses visual tracking techniques to track simultaneously the two-dimensional (in the vertical plane) motion of multiple fiducial markers using a standard video camera. A threshold window is set at the breathing amplitude of interest using the MDRT GUI. A trigger is generated at a rate of 250 Hz as long as the breathing signal is within the threshold window. The triggers are fed into the PET scanner to initialize one single bin of a gated acquisition every 4 ms. No triggers are delivered as the breathing signal drifts outside the threshold window. Consequently, PET data are acquired only whenever the breathing signal is confined within the amplitude threshold window, thus resulting into a motion-free image set. The accuracy of MDRT in tracking the breathing signal was assessed (1) by comparing the period of an oscillating phantom, as measured by MDRT, to that measured with a photogate timer and (2) by comparing the MDRT output to that of the real-time position management (RPM) in ten patients. The SG PET/CT acquisition was validated in phantoms and in two stereotactic body radiosurgery (SBRS) lung DIBH-PET/CT patients.
MDRT was in agreement with the photogate timer in determining the period of motion to less than 2%. The percent errors between MDRT and RPM in the positions of the peaks and troughs of the ten patients' breathing signals were within 10%. In phantoms, SG technique enables to correct for motion-induced artifacts in the PET images and improve the accuracy of PET quantitation. For the SBRS application, in one patient, the patient's CT lesion was not detected in the corresponding clinical PET images, while it exhibited an SUV of 1.8 in the DIBH image set. In the second patient, DIBH-PET images showed an improved PET-to-CT spatial matching and a 52% increase in the lesion SUV.
MDRT has been shown to be accurate in tracking breathing motion and assisted in implementing a smart-gating PET acquisition technique that allowed to acquire prospectively motion-free PET images.
本研究旨在验证一种新型呼吸追踪设备——多维呼吸追踪（MDRT）系统，该系统旨在帮助校正 PET/CT 图像中的呼吸运动。作者还研究了一种新型的 PET 采集技术——智能门控（SG），该技术可在无运动的情况下前瞻性地采集 PET 数据，用户干预最小，且无需对 PET 数据进行额外的后处理。
MDRT 使用视觉跟踪技术，使用标准摄像机同时跟踪多个基准标记的二维（垂直平面）运动。使用 MDRT GUI 在感兴趣的呼吸幅度上设置一个阈值窗口。只要呼吸信号在阈值窗口内，就以 250 Hz 的速率生成一个触发。触发被馈送到 PET 扫描仪中，以每 4 ms 初始化一个门控采集的单个 bin。当呼吸信号漂移出阈值窗口时，不会发送任何触发。因此，只有当呼吸信号限制在幅度阈值窗口内时，才会采集 PET 数据，从而获得无运动的图像集。通过（1）将 MDRT 测量的振荡体的周期与光电门定时器测量的周期进行比较，以及（2）将 MDRT 输出与十位患者的实时位置管理（RPM）进行比较，评估了 MDRT 跟踪呼吸信号的准确性。在体模和两位立体定向体部放射外科（SBRS）肺部深吸气屏气-PET/CT 患者中验证了 SG PET/CT 采集。
MDRT 与光电门定时器在确定运动周期方面的误差小于 2%。十位患者呼吸信号的波峰和波谷位置，MDRT 和 RPM 之间的百分比误差在 10%以内。在体模中，SG 技术能够校正运动引起的 PET 图像伪影，并提高 PET 定量的准确性。对于 SBRS 应用，在一位患者中，患者的 CT 病变未在相应的临床 PET 图像中检测到，而在深吸气屏气图像集中，其 SUV 值为 1.8。在第二位患者中，深吸气屏气-PET 图像显示出更好的 PET-CT 空间匹配，病变 SUV 值增加了 52%。
MDRT 已被证明在跟踪呼吸运动方面是准确的，并有助于实现智能门控 PET 采集技术，该技术可前瞻性地采集无运动的 PET 图像。
