CN110514742A - 基于仿体和频域cbe的聚焦式超声波消融的温度成像方法 - Google Patents
基于仿体和频域cbe的聚焦式超声波消融的温度成像方法 Download PDFInfo
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Abstract
本发明涉及一种基于仿体和频域CBE的聚焦式超声波消融的温度成像方法,包括下列步骤:制作仿体;对仿体进行HIFU灼烧实验;超声影像系统置于仿体上方以获取超声逆散射信号,即RF data;通过滑动窗,将影像切割为数个小窗;利用傅里叶变换将窗内的空间域信号转换至频率域;截取用于CBE成像频率范围即3±0.75MHz内的信号,并找出范围内的最大振幅;将最大振幅取平方,则获得频域范围内最大逆散射能量;根据各个窗的最大逆散射能量的变化值,得到频域CBE值,进行成像。
Description
技术领域
本发明属于医学图像研究领域,涉及一种高能聚焦式超声波热疗过程中的超声温度成像方法。
背景技术
近些年来,癌症愈演愈烈,成为夺走人类生命健康的一大杀手。根据美国癌症协会(American Cancer Society,ACS)的纪录,现今癌症治疗的主要方式分别为:手术切除、化学治疗、放射治疗、标靶治疗、免疫治疗。除上述五种治疗方法外,肿瘤热治疗在近二十年也逐渐受到医学界的注目。
高强度聚焦超声(HIFU)是一种广泛使用的无创热疗工具。为控制HIFU的治疗质量,需要对组织中的灼烧点进行定位[1-2]。超声成像能够监测加热区域;特别地,逆散射能量变化(CBE)参数成像可以使组织中的热信息可视化。逆散射能量变化法为近代测量温度影像的主流,具有图像处理快速、可直接转换能量信号等优势。
华盛顿大学Arthur学者提出超声波逆散射能量变化温度影像主要和逆散射子特性有关[3],而在后续研究中发现,组织内散射子的CBE值与温度变化几乎呈线性关系[4]。因此,可通过取得不同温度下CBE值以得出组织温度,并可进一步转换为温度影像。相较于其他超声波影像成像方式,CBE演算法于37℃到50℃之间几乎呈单调函数的关系[5]。推算出单一散射子背向散射能量变化与温度变化关系的归一化模型,如(1-1)式:
其中,α(T)为衰减系数,η(T)为背向散射系数。若散射子的尺寸小于超声波波长,则模型可简化为式(1-2)
CBE=η(T)/η(37) (1-2)
CBE影像是在像素点到像素点的基础上进行的成像,对散斑运动和超声背散射信号特征的变化是敏感的。集成逆散射能量变化(ICBE)影像算法[6]在传统CBE算法的基础上运用滑窗技术,这种窗口到窗口的方法可以实现温度分布的可视化,且无需执行额外的运动补偿或相位校正处理。
然而,在HIFU热点定位过程中,温度上升较小,导致热点处的CBE值较小。因此,在空间域中构建的常规CBE成像虽可以呈现HIFU热区,但容易受到噪声的影响。在这种情况下,空间域CBE图像亮暗区对比度较低,导致HIFU加热点可视化成程度低,严重影响到CBE影像对HIFU灼烧点的术中监控。
参考文献:
[1]Wu F,Wang Z B,Chen W Z,et al.Extracorporeal high intensity focusedultrasound ablation in the treatment of patients with large hepatocellularcarcinoma[J].Annals of surgical oncology,2004,11(12):1061.
[2]Illing R O,Kennedy J E,Wu F,et al.The safety and feasibility ofextracorporeal high-intensity focused ultrasound(HIFU)for the treatment ofliver and kidney tumours in a Western population[J].British journal ofcancer,2005,93(8):890.
[3]Arthur R M,Broadstone S R.Imaging via inversion of ellipsoidalprojections of solutions to the linear acoustic wave equation(medicalultrasound)[J].IEEE transactions on medical imaging,1989,8(1):89-95.
[4]Arthur R M,Straube W L,Trobaugh J W,et al.Non-invasive estimationof hyperthermia temperatures with ultrasound[J].International journal ofhyperthermia,2005,21(6):589-600.
[5]W L S.Theoretical estimation of the temperature dependence ofbackscattered ultrasonic power for noninvasive thermometry.Ultrasound inmedicine&biology1994;9.
[6]An approach for the visualization of temperature distribution intissues according to changes in ultrasonic backscattered energy
发明内容
本发明的目的是提供一种基于HIFU灼烧仿体模拟实验的超声波温度成像方法,为克服空间域CBE影像算法在HIFU监控过程中热区可视化水平低的问题提供仿真基础,技术方案如下:
一种基于仿体和频域CBE的聚焦式超声波消融的温度成像方法,包括下列步骤:
1)制作仿体;
2)对仿体进行HIFU灼烧实验;
3)超声影像系统置于仿体上方以获取超声逆散射信号,即RF data;
4)通过滑动窗,将影像切割为数个小窗。
5)利用傅里叶变换将窗内的空间域信号转换至频率域;
6)截取用于CBE成像频率范围即3±0.75MHz内的信号,并找出范围内的最大振幅;
7)将最大振幅取平方,则获得频域范围内最大逆散射能量;
8)根据各个窗的最大逆散射能量的变化值,得到频域CBE值,进行成像。
实验成果表明,与空间域CBE成像相比,频域CBE成像将影像亮暗区对比度由8.3提升至12.06,可以提高HIFU热区的可视化水平。为进一步实现HIFU灼烧热点的监控奠定了基础。
附图说明
附图1为本发明实验使用的石墨仿体图。
附图2为本发明使用的实验装置图。
附图3为本发明的算法流程图。
附图4为空间域及频域超声背散射能量变化影像对比度的比较图。
具体实施方法
本发明基于空间域集成背散射能量变化方法发明而来,利用频域信号进行CBE成像,有效的抑制了CBE影像背景处的噪声,提升了亮暗区的对比度,改善了热区的可视化程度。
在进行频域CBE测算过程中,将背散射信号经过傅里叶变换转换至频率域,通过截取特定频域范围内的信号可有效的消除噪声的影响。且计算出的频域CBE值也与温度变化值有较高的相关性。
具体步骤如下:
1)利用Terason3000超声影像系统获取超声逆散射信号,即RF data。
2)通过滑动窗,将影像切割为数个小窗。
3)利用傅里叶变换将窗内的空间域信号转换至频率域。
4)截取用于CBE成像频率范围内的信号,并找出该范围内的最大振幅。
5)将最大振幅取平方,则可获得频域范围内最大逆散射能量。
6)将各个窗的最大逆散射能量使用常规逆散射能量变化的计算方式,可以得到频域CBE值进行成像。
实施例如下:
本发明通过HIFU灼烧体外仿体实验进行验证。仿体实体图如图1所示。将2g琼脂粉溶解在200ml水中而制备成琼脂液,再将10g平均直径小于20μm的石墨粉加入到琼脂液中。煮沸冷却后制成散射子浓度为128scatterers/mm3的仿体,大小约为5×6×7cm3。
高能聚焦式超声波灼烧仿体的实验装置如图2所示,此装置由三个系统组成:HIFU系统,超声波监测系统和温度系统。在HIFU系统中,连续波首先由信号发生器产生,然后由功率放大器放大。最后,将放大的信号发送到HIFU探头。HIFU探头的频率为2.12MHz,焦距为5.5厘米。放大的信号也将被发送到功率计,以监控HIFU的输出功率。超声波监测系统是超声波扫描仪,使用弧形探头进行扫描。探头的中心频率为3MHz,脉冲长度为0.7mm。若要使用平面波复合成像则需更换相应的成像系统。在温度系统中,将热电偶温度计插入仿体中以收取温度数据。为了保证每次实验的起始温度相同,恒温器须将水箱温度控制在33℃。
HIFU分别以5W,10W,15W的功率对仿体进行灼烧。因为需要比较超声图像和模拟温度之间的关系,所以需要获得超声信号和温度信息。超声信息通过Terason3000系统获取,温度信息有热电偶温度计插入仿体获取。然而,当热电偶刺入仿体时,由于热电偶由金属制成,因此超声灰度图像上将出现阴影伪影。当RF数据用于计算时,所获得的图像和信号强度可能具有偏差。为了解决不能同时获得温度信息和射频信号的问题,本实验将进行两次,分别获得超声信号和温度信息。
在第一次实验中,在没有热电偶的情况下获得超声RF数据。第二次插入热电偶。为避免伪温升的发生,热电偶应略微偏移3mm,以便可以离开HIFU的聚焦区域,然后记录仿体的温度变化。在每次实验之前,将仿体冷却至33℃的背景温度。
对获取的超声数据信息进行频域CBE的测算,并计算影像热区与背景区的对比度。之后需将超声信息与温度信息进行相关性的测算,以确保所提出的频域CBE算法对温度监测的准确性。将取得的结果与空间域CBE影像进行比较,验证频域CBE提升HIFU灼烧区可视化水平的潜力。
Claims (1)
1.一种基于仿体和频域CBE的聚焦式超声波消融的温度成像方法,包括下列步骤:
1)制作仿体;
2)对仿体进行HIFU灼烧实验;
3)超声影像系统置于仿体上方以获取超声逆散射信号,即RF data;
4)通过滑动窗,将影像切割为数个小窗。
5)利用傅里叶变换将窗内的空间域信号转换至频率域;
6)截取用于CBE成像频率范围即3±0.75MHz内的信号,并找出范围内的最大振幅;
7)将最大振幅取平方,则获得频域范围内最大逆散射能量;
8)根据各个窗的最大逆散射能量的变化值,得到频域CBE值,进行成像。
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XIA JINGJING等: "An Approach for the Visualization of Temperature Distribution in Tissues According to Changes in Ultrasonic Backscattered Energy", 《COMPUTATIONAL AND MATHEMATICAL METHODS IN MEDICINE》 * |
黄振维: "超音波热影像及声学干扰特征用于海扶刀热点定位:可行性研究", 《台湾博硕士论文知识加值系统》 * |
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