Han Silu, Liang Xiao, Li Tian, Yin Fang-Fang, Cai Jing
Medical Physics Graduate Program, Duke University Medical Center, Durham, NNC, USA.
Department of Biomedical Engineering, The University of Arizona, Tucson, AZ, USA.
Quant Imaging Med Surg. 2021 Jan;11(1):32-42. doi: 10.21037/qims-20-41.
To investigate the feasibility of generating maximum intensity projection (MIP) images to determine internal target volume (ITV) using slice-stacking MRI (SS-MRI) technique.
Slice-stacking is a technique which applies a multi-slice MRI acquisition to generate a 3D MIP for ITV contouring, without reconstructing 4D-MRI. 4D digital extended cardiac-torso (XCAT) phantom was used to generate MIP images with sequential 2D HASTE sequence, with different tumor diameters (10, 30 and 50 mm) and with simulated regular and irregular (patient) breathing motions. A reference MIP was generated using all acquisition images. Consecutive repetitions were then used to generate MIP to analyze the relationship between Dice's similarity coefficient (DSC) and the number of repetitions, and the relationship between the relative ITV volume difference and the number of repetitions. Images from XCAT phantom and from three hepatic carcinoma patients were collected in this study to demonstrate the feasibility of this technique.
For both regular and irregular breathing motion, the average DSC of ITV is >0.94 and the average relative ITV volume difference is <10% (approximately 0.15 cm) when using 5 repeated scanning images to reconstruct MIP for tumor diameter of 10 mm. As tumor diameter increases, the DSC of ITV is >0.97 and the relative ITV volume difference is <5% for regular breathing motion, and the DSC of ITV is >0.97 and the relative ITV volume difference is <5.5% for irregular breathing motion when using 5 repeated scanning images to reconstruct MIP. In patient image study, the mean relative ITV volume difference is <3% and the mean DSC is 0.99 when using 5 repeated scanning images to reconstruct MIP.
The number of scans required to generate tumor ITV for slice-stacking method (5-7 repetition) is 3-4 times less than that of 4D-MRI (15-20 repetitions). It is feasible to generate a fast clinically acceptable ITV using slice-stacking method with sequential 2D MR images.
探讨使用多层叠加磁共振成像（SS-MRI）技术生成最大密度投影（MIP）图像以确定内部靶区（ITV）的可行性。
多层叠加是一种应用多层磁共振成像采集来生成用于ITV轮廓勾画的三维MIP的技术，无需重建四维磁共振成像。使用四维数字扩展心脏-躯干（XCAT）体模，通过连续二维快速自旋回波（HASTE）序列生成MIP图像，设置不同的肿瘤直径（10、30和50毫米）以及模拟的规则和不规则（患者）呼吸运动。使用所有采集图像生成参考MIP。然后通过连续重复来生成MIP，以分析戴斯相似系数（DSC）与重复次数之间的关系，以及相对ITV体积差异与重复次数之间的关系。本研究收集了来自XCAT体模和三名肝癌患者的图像，以证明该技术的可行性。
对于规则和不规则呼吸运动，当使用5次重复扫描图像重建10毫米肿瘤直径的MIP时，ITV的平均DSC>0.94，平均相对ITV体积差异<10%（约0.15厘米）。随着肿瘤直径增加，当使用5次重复扫描图像重建MIP时，对于规则呼吸运动，ITV的DSC>0.97，相对ITV体积差异<5%；对于不规则呼吸运动，ITV的DSC>0.97，相对ITV体积差异<5.5%。在患者图像研究中，当使用5次重复扫描图像重建MIP时，平均相对ITV体积差异<3%，平均DSC为0.99。
多层叠加法生成肿瘤ITV所需的扫描次数（5 - 7次重复）比四维磁共振成像（15 - 20次重复）少3 - 4倍。使用连续二维磁共振图像的多层叠加法快速生成临床可接受的ITV是可行的。
