呼吸运动对4D锥形束CT图像质量影响分析

目的 研究四维锥形束CT (4D-CBCT)的成像质量与呼吸运动特征参数间的关系。 方法 将Catphan500图像质量检测模体通过固定装置固定在Mapcheck XY运动平台之上,通过控制平台模拟静止以及19种呼吸运动状态,在各种运动状态下使用Synergy加速器对图像质量检测模块进行4D-CBCT扫描。通过分析重建图像的10个分时相下图像的几何精确性、空间分辨率、低对比可识别度、CT值均匀性以及运动位置准确性等指标,得到4D-CBCT的图像质量和运动方向、幅度和周期3个特征参数的关系。 结果 当静止或只有左右方向时,重建图像不正常,图像质量显著差于有头脚方向运动的情况。对比度噪声比随运动周期增加而降低,当周期从2 s增加为6 s时,对比度噪声比从3.33降低到1.72(P<0.01),几何精确度、空间分辨率和矢状位受呼吸运动影响不显著。 结论 4D-CBCT图像质量中对比度噪声比、水平和垂直方向的几何精确性以及运动位置精确性受呼吸运动影响显著,图像空间分辨率和矢状位几何精确性受呼吸运动影响不显著,4D-CBCT需要周期性的SI方向的运动介入,过于平缓或者无周期性规律的运动会影响图像质量甚至导致图像不能正确重建。4D-CBCT图像重建需要SI方向的周期性运动介入,图像质量同时受呼吸运动振幅和周期的影响,4D-CBCT扫描推荐患者呼吸周期<6 s,振幅>0.75 cm。     

用数字模体模拟利用4DCT计算累积剂量偏差

目的 用计算机仿真模拟评估由于患者呼吸不均匀导致的用4DCT图像与用扫描4DCT时的实时呼吸图像计算的累积剂量之间的差异。 方法 用某个患者的4DCT图像生成数字模体,通过计算机模拟各种形式的不均匀呼吸曲线形成4DCT图像及扫描4DCT时的实时呼吸图像。在参考图像上制作一个6个野均分的IMRT计划,用4DCT和扫描4DCT时的实时呼吸图像分别计算累积剂量且记为D^4D和D^all,并计算二者之间的差异,评价呼吸运动模式变化对该差异的影响。结果两种累积剂量之间的差异依赖于平均运动幅度和幅度标准差的变化。当平均运动幅度从5 mm增加到15 mm时,靶区ΔD_min(ΔD₉₉)从2.39%(2.04%)增加到11.91%(5.24%),而当幅度的标准差从平均幅度的15%增加到平均幅度的45%时,靶区ΔD_min(ΔD₉₉)从5.93%(2.15%)增加到14.65%(5.01%);当平均周期从3 s增加到5 s或者周期标准差从平均周期的10%增加到40%时,靶区ΔD_min(ΔD₉₉)均>6.0%(2.0%)而<9.0%(3.0%);当肿瘤直径为2 cm、3 cm以及4 cm时,靶区ΔD_min(ΔD₉₉)分别为11.88%(5.50%)、6.91%(2.42%)以及7.53%(3.62%)。 结论 当呼吸运动不均匀时,用4DCT计算的累积剂量和用扫描4DCT时的实时呼吸图像计算的累积剂量之间存在较大差异,且该差异依赖于呼吸运动的平均幅度和幅度的标准差,而平均周期及周期标准差的变化对其影响不大,该差异随肿瘤体积变化的趋势不明显。     

肺癌精准放射治疗中呼吸运动解决方案

随着图像引导放疗技术的不断发展，摆位误差对肺癌三维适形调强放疗的影响明显减小，然而，影响肺癌精准放疗剂量提升的另一重要因素——呼吸运动，仍然困扰着肿瘤放疗工作者。目前，解决呼吸运动对肺癌放疗影响的方法大致包括个体化内靶体积（internal target volume，ITV）勾画、呼吸控制技术、呼吸门控放疗以及实时跟踪放疗等技术。     

CT辅助逆向工程技术在畸齿矫正中的应用研究

如何快速、高精度获取齿形CAD模型是目前畸齿矫正行业中的技术难题。介绍了一种基于3D-CT的牙颌数字模型快速获取方法。利用3D-CT扫描获得牙齿石膏阳模精细的三维灰度图像;对三维CT图像进行相应的图像、图形处理,获取实物内外表面点云数据;并将其输入CAD设计平台,逆求出实物原型的CAD模型。与传统逆求方法相比,该方法具有扫描速度快、点云数据各向等分辨率和逆求精度高的优点。     

动态X射线图像中消融导管尖端自动跟踪方法

射频导管消融手术已经开始成为一种常见的针对心律失常手术的治疗方案。从动态X线图像中自动跟踪导管尖端可以为计算机辅助诊断和导管三维姿态重构提供基础。本研究的目标是发展一种稳健的能够自动识别和跟踪消融大头电极导管的方法。为此,本文提出了一种结合阈值法和形态学运算识别消融大头电极导管尖端,然后利用光流法对动态X射线图像中消融大头电极导管尖端进行自动跟踪的方法。利用临床上34个动态X射线图像序列验证该算法,跟踪结果的平均误差为1.126 mm±0.748 mm,跟踪每帧图像耗时大约7 ms,因此该方法能比较精确地实时跟踪消融大头电极导管尖端在动态X射线图像中的运动。     

基于三维投影的视频序列静态全景合成算法

视频序列静态全景合成技术是视频图像分析的关键技术。本文提出了一种基于三维投影的视频序列静态全景合成算法,该算法通过引入三维投影原理,将视频序列中各帧图像依次投影到全景图像平面,推导出在同一三维坐标下各帧图像与全景图像之间的变换关系,并采用各帧图像间的运动参数联合生成全景图像。实验结果表明,该方法能够生成较高质量的全景图。     

间歇式屏气CBCT图像采集优选模式研究

目的 旨在建立一种实用型间歇式屏气CBCT图像采集优选模式。方法 利用自制呼吸运动模型模拟肿瘤患者膈肌附近肿块在屏气和自由呼吸状态下的运动情况并行CBCT扫描。扫描模式有常规屏气CBCT扫描(主要分为屏气间隙暂停扫描、进行自由呼吸、自由呼吸不计入扫描过程)及间歇式屏气CBCT扫描Ⅰ型和Ⅱ型(主要分为若干个屏气和自由呼吸时段,以近3∶1比例作间歇式调配并一次完成扫描),将常规屏气CBCT扫描作为标准技术,与2种间歇式屏气CBCT扫描就图像质量及使用该图像实现三维配准的精度进行量化比较分析。间歇式屏气CBCT图像质量参数与常规屏气CBCT图像行配对t检验。结果 2种间歇式屏气CBCT图像均产生运动伪影,其重建像素值与常规扫描相比较为一致(P>0.05),均匀性无明显改变(P=0.02、0.53),但图像信噪比分别减少30%和60%(P<0.05)。图像配准误差除上下方向最大为0.4 cm以外,其余均在0.1 cm以内。结论 在体模研究阶段,间歇式屏气CBCT扫描图像采集模式并未明显降低图像质量和配准精度,其实际临床的可行性还需在大量患者身上进一步得到验证。     

模拟呼吸运动对肿瘤三维技术放疗的剂量分布影响

目的 通过模拟呼吸运动研究呼吸运动对三维技术放疗剂量分布的影响。方法 对11例肺癌患者进行三维技术放疗计划设计,将二维半导体阵列Mapcheck放在呼吸模拟运动平板3 cm等效水模上,使用近似呼吸运动周期为3.5 s,运动幅度分别为±3、±5、±10、±15 mm,比较运动和静止状态下Mapcheck实测的剂量分布和治疗计划系统输出的相应平面剂量分布。两组数据行配对t检验。结果 呼吸运动均能降低靶区剂量分布的适形度,剂量分布产生模糊效应;11例患者呼吸运动状态下,3DCRT-QA的γ通过率平均值(3%/3 mm)均大于动态IMRT-QA的,且相互比较的P均<0.05;通过Mapcheck系统分析出呼吸运动对3DCRT剂量分布的影响主要集中在靶区周边,可对动态IMRT的影响分布于整个靶区。结论 对呼吸运动幅度较大的肿瘤建议采用3DCRT技术,更能确保运动的肿瘤得到预期较准确的剂量分布,若采用IMRT技术应根据情况对运动肿瘤进行呼吸运动补偿等方法以确保肿瘤相对静止。     

KVX线锥形束CT呼吸运动目标成像的体模研究

目的:研究呼吸运动对安装于Varian23EX加速器的KV X线锥形束CT(cone beamCT,CBCT)成像结果的影响.方法:利用自行研制的运动体模系统,模体直径分别为1、2和3 cm,设定横轴方向运动幅度分别为0.5、1.0和1.5 cm,纵轴方向分别为0.5、10.和2.0 cm,体模往返运动频率分别为12、20和25次/min,模拟呼吸运动并行CBCT扫描.结果:1)实际直径分别为10、20和30 mm的静止体模CBCT图像清晰,无变形,测量的直径分别为9.8±0.66[95% CI(9.1～10.5)mm]、19.9±0.75C95%CI(19.1～20.7)mm]和(29.7±0.69)mm [95%CI(29.0～30.4)mm],横轴方向和纵轴方向的大小与体模实际大小相符合,误差均<1 mm.2)横轴和纵轴方向的呼吸运动对体模CBCT成像都有明显的影响.与静止体模CBCT图像相比,横轴和纵轴方向的体模运动都使CBCT图像清晰度下降、变形以及体积增大.在设定的运动幅度和运动频率范围内,3种大小的运动体模CBCT图像在横轴方向和纵轴方向的大小都与设定的体模实际运动范围(模体直径加运动幅度)相符合.差值均<3 mm.结论:呼吸运动对CBCT成像影响明显,成像结果反应规律性呼吸运动物体的实际运动范围.     

满三维图像重建的卷积反投影算法

本文用构造δ序列的方法,给出了一种n维Radon变换反演的卷积反投影算法,证明了该算法在图像的连续点收敛于原图像,当n=2时,就是广泛用于图像重建的卷积反投影算法,由此也给出了卷积反投影方法收敛性的另一种推导。当n=3时,是新的满三维重建的卷积反投影算法,由于三维反演公式具有局部性,该算法对研究三维局部重建有启示。并基于三维情形,利用模拟数据进行了数值仿真,说明该算法是一种有效的三维图像重建算法。     

Nonrigid registration method to assess reproducibility of breath-holding with ABC in lung cancer

PURPOSE: To study the interfraction reproducibility of breath-holding using active breath control (ABC), and to develop computerized tools to evaluate three-dimensional (3D) intrathoracic motion in each patient. METHODS AND MATERIALS: Since June 2002, 11 patients with non-small-cell lung cancer enrolled in a Phase II trial have undergone four CT scans: one during free-breathing (reference) and three using ABC. Patients left the room between breath-hold scans. The patient's breath was held at the same predefined phase of the breathing cycle (about 70% of the vital capacity) using the ABC device, then patients received 3D-conformal radiotherapy. Automated computerized tools for breath-hold CT scans were developed to analyze lung and tumor interfraction residual motions with 3D nonrigid registration. RESULTS: All patients but one were safely treated with ABC for 7 weeks. For 6 patients, the lung volume differences were <5%. The mean 3D displacement inside the lungs was between 2.3 mm (SD 1.4) and 4 mm (SD 3.3), and the gross tumor volume residual motion was 0.9 mm (SD 0.4) to 5.9 mm (SD 0.7). The residual motion was slightly greater in the inferior part of the lung than the superior. For 2 patients, we detected volume changes >300 cm(3) and displacements >10 mm, probably owing to atelectasia and emphysema. One patient was excluded, and two others had incomplete data sets. CONCLUSION: Breath-holding with ABC was effective in 6 patients, and discrepancies were clinically accountable in 2. The proposed 3D nonrigid registration method allows for personalized evaluation of breath-holding reproducibility with ABC. It will be used to adapt the patient-specific internal margins.     

基于四维CT的平静呼吸状态下肾脏各方向运动幅度及影响因素分析

目的:探索平静呼吸状态下正常肾脏在三维方向的运动幅度及其相关的影响因素。方法:收集2018—2019年间行四维CT且能够平静呼吸的28例患者数据,肿瘤类别包括肝肿瘤、胰腺肿瘤或肺肿瘤。腹窗条件下逐层、逐呼吸时相勾画肾脏外轮廓并找到几何中心及三维方向坐标数值;计算左、右肾各个方向及三维方向位移。记录周围脏器体积及患者年龄...     

Respiratory gated radiotherapy: the 4D radiotherapy

Respiration-gated radiotherapy offers a significant potential for improvement in the irradiation of tumor sites affected by respiratory motion such as lung, breast and liver tumors. An increased conformality of irradiation fields leading to decreased complications rates of organs at risk (lung, heart...) is expected. Respiratory gating is in line with the need for improved precision required by radiotherapy techniques such as 3D conformal radiotherapy or intensity modulated radiotherapy. Reduction of respiratory motion can be achieved by using either breath hold techniques or respiration synchronized gating techniques. Breath hold techniques can be achieved with active, in which airflow of the patient is temporarily blocked by a valve, or passive techniques, in which the patient voluntarily breath-hold. Synchronized gating techniques use external devices (CCD camera for the GEMS/Varian system tested at Curie Institute) to predict the phase of the respiration cycle while the patient breaths freely. A new strategy is currently developed: the 4D Respiration correlated CT. It consists of retrospectively reconstruct CT slices at different phases of the breathing cycle allowing to measure residual movements and to choose the optimal patient's breathing phase where tumor movements are lower. These techniques presently investigated in several medical centers worldwide. The first results are very promising.     

Practical recommendations for breathing-adapted radiotherapy]

Respiration-gated radiotherapy offers a significant potential for improvement in the irradiation of tumor sites affected by respiratory motion such as lung, breast and liver tumors. An increased conformality of irradiation fields leading to decreased complications rates of organs at risk (lung, heart...) is expected. Respiratory gating is in line with the need for improved precision required by radiotherapy techniques such as 3D conformal radiotherapy or intensity modulated radiotherapy. Reduction of respiratory motion can be achieved by using either breath-hold techniques or respiration synchronized gating techniques. Breath-hold techniques can be achieved with active techniques, in which airflow of the patient is temporarily blocked by a valve, or passive techniques, in which the patient voluntarily holds his/her breath. Synchronized gating techniques use external devices to predict the phase of the respiration cycle while the patient breaths freely. This work summarizes the different experiences of the centers of the STIC 2003 project. It describes the different techniques, gives an overview of the literature and proposes a practice based on our experience.     

基于视觉运动捕获数据的三维模型驱动方法

基于视觉运动捕获数据的三维模型驱动涉及到将三维位置数据转化为模型运动数据,和三维模型的动作驱动。视觉运动捕获的三维运动数据,由于缺乏骨架各关节点间的旋转信息,不能直接用于三维模型的驱动。本文提出了依据各关节点的相关性,求解骨架关节点的旋转信息,并计算出各关节点的欧拉角,将原始据转换为模型运动数据。然后,将转换后的运动数据应用于三维模型,通过改进后的线性混合皮肤变形算法（LBS）,实现了基于三维运动参数的三维模型驱动。文中实验结果验证了算法的有效性。     

Deep inspiration breath hold level variability and deformation in locoregional breast irradiation

Purpose

The purpose of this study was to evaluate the dosimetric effect of breath hold level variability and deformation on breast, chest wall, internal mammary chain (IMC) nodes, and heart.

基于CT图像重建腰椎活动节段三维有限元模型及其应用

腰椎节段三维有限元模型既要求在视觉上与实际相似 ,又要求易于网格划分和数学求解。本文基于中国人体腰椎L4 - 5活动节段的系列二维截面CT图像 ,采用轮廓线的描述方式提取平面数据 ,通过将平面数据坐标进行三维化处理 ,获得腰椎节段的三维体数据 ,最后直接利用ANSYS有限元分析软件 ,采用自底向上的建模方式重建腰椎节段的三维有限元模型 ,并利用该模型研究了L4 - 5腰椎间盘的生物力学行为。结果表明 ,该模型具有很好的视觉效果和数学求解能力。     

The reproducibility of organ position using active breathing control (ABC) during liver radiotherapy

Purpose: To evaluate the intrafraction and interfraction reproducibility of liver immobilization using active breathing control (ABC).

Methods and Materials: Patients with unresectable intrahepatic tumors who could comfortably hold their breath for at least 20 s were treated with focal liver radiation using ABC for liver immobilization. Fluoroscopy was used to measure any potential motion during ABC breath holds. Preceding each radiotherapy fraction, with the patient setup in the nominal treatment position using ABC, orthogonal radiographs were taken using room-mounted diagnostic X-ray tubes and a digital imager. The radiographs were compared to reference images using a 2D alignment tool. The treatment table was moved to produce acceptable setup, and repeat orthogonal verification images were obtained. The positions of the diaphragm and the liver (assessed by localization of implanted radiopaque intra-arterial microcoils) relative to the skeleton were subsequently analyzed. The intrafraction reproducibility (from repeat radiographs obtained within the time period of one fraction before treatment) and interfraction reproducibility (from comparisons of the first radiograph for each treatment with a reference radiograph) of the diaphragm and the hepatic microcoil positions relative to the skeleton with repeat breath holds using ABC were then measured. Caudal-cranial (CC), anterior-posterior (AP), and medial-lateral (ML) reproducibility of the hepatic microcoils relative to the skeleton were also determined from three-dimensional alignment of repeat CT scans obtained in the treatment position.

Results: A total of 262 fractions of radiation were delivered using ABC breath holds in 8 patients. No motion of the diaphragm or hepatic microcoils was observed on fluoroscopy during ABC breath holds. From analyses of 158 sets of positioning radiographs, the average intrafraction CC reproducibility (σ) of the diaphragm and hepatic microcoil position relative to the skeleton using ABC repeat breath holds was 2.5 mm (range 1.8–3.7 mm) and 2.3 mm (range 1.2–3.7 mm) respectively. However, based on 262 sets of positioning radiographs, the average interfraction CC reproducibility (σ) of the diaphragm and hepatic microcoils was 4.4 mm (range 3.0–6.1 mm) and 4.3 mm (range 3.1–5.7 mm), indicating a change of diaphragm and microcoil position relative to the skeleton over the course of treatment with repeat breath holds at the same phase of the respiratory cycle. The average population absolute intrafraction CC offset in diaphragm and microcoil position relative to skeleton was 2.4 mm and 2.1 mm respectively; the average absolute interfraction CC offset was 5.2 mm. Analyses of repeat CT scans demonstrated that the average intrafraction excursion of the hepatic microcoils relative to the skeleton in the CC, AP, and ML directions was 1.9 mm, 0.6 mm, and 0.6 mm respectively and the average interfraction CC, AP, and ML excursion of the hepatic microcoils was 6.6 mm, 3.2 mm, and 3.3 mm respectively.

Conclusion: Radiotherapy using ABC for patients with intrahepatic cancer is feasible, with good intrafraction reproducibility of liver position using ABC. However, the interfraction reproducibility of organ position with ABC suggests the need for daily on-line imaging and repositioning if treatment margins smaller than those required for free breathing are a goal.     

Respiratory motion of the heart and positional reproducibility under active breathing control

PURPOSE: To reduce cardiotoxicity from breast radiotherapy (RT), innovative techniques are under investigation. Information about cardiac motion with respiration and positional reproducibility under active breathing control (ABC) is necessary to evaluate these techniques. METHODS AND MATERIALS: Patients requiring loco-regional RT for breast cancer were scanned by computed tomography using an ABC device at various breath-hold states, before and during treatment. Ten patients were studied. For each patient, 12 datasets were analyzed. Mutual information-based regional rigid alignment was used to determine the magnitude and reproducibility of cardiac motion as a function of breathing state. For each scan session, motion was quantified by evaluating the displacement of a point along the left anterior descending artery (LAD) with respect to its position at end expiration. Long-term positional reproducibility was also assessed. RESULTS: Displacement of the LAD was greatest in the inferior direction, moderate in the anterior direction, and lowest in the left-right direction. At shallow breathing states, the average displacement of LAD position was up to 6 mm in the inferior direction. The maximum displacement in any patient was 2.8 cm in the inferior direction, between expiration and deep-inspiration breath hold. At end expiration, the long-term reproducibility (SD) of the LAD position was 3 mm in the A-P, 6 mm in the S-I, and 4 mm in the L-R directions. At deep-inspiration breath hold, long-term reproducibility was 3 mm in the A-P, 7 mm in the S-I, and 3 mm in the L-R directions. CONCLUSIONS: These data demonstrate the extent of LAD displacement that occurs with shallow breathing and with deep-inspiration breath hold. This information may guide optimization studies considering the effects of respiratory motion and reproducibility of cardiac position on cardiac dose, both with and without ABC.     

基于遗传算法的三维表面距离测量方法

三维信息处理中,距离是重要的特征信息之一。本文提出了一种基于遗传算法的三维表面距离测量方法 ,根据特定条件在模型表面上逼近两点间最近距离。首先给出和模型相交的平面束数学描述;其次选择特定平面作为种子,以三维表面距离构建适应度函数,利用遗传算法在平面束中找出最优平面;最后结合局部性原理,降低算法复杂度。通过实际三维模型的实验,取得了99.71%的正确率,验证了方法的有效性。