X线CT成像质量评估中的调制传递函数的测试与分析

目的 通过测量CT系统调制传递函数客观有效地反映CT系统空间分辨能力。方法 扫描CT测试体模中点源模块，获得系统的点扩散函数和线扩散函数，对其进行傅立叶变换并对计算结果进行校正。结果 利用自行开发的处理程序绘出CT系统的调制传递函数（MTF）曲线并给出50％，10％，2％MTF值。结论 通过计算CT系统的MTF可以全面而客观地反映系统对于细节的识别能力。     

基于环形阵列的乳腺超声检测仿真及成像方法研究

目的 ：研究一种适用于环形阵列的乳腺超声仿真和成像方法，实现对数值体模超声扫查过程的三维快速仿真，并重建得到对应的声速分布图。方法：先使用k-Wave对环形阵列及乳腺体模进行三维仿真并获得超声反射波和透射波的波形数据。再采用改进的小波赤池信息量准则（wavelet Akaike information criterion,wavelet-AIC）法提取声波第一到达时间，采用最短路径法得到正向模型，采用将L2型正则化作为惩罚项的混合版本的最小平方QR分解（least squares QR-factorization,LSQR）法求解反问题，采用迭代更新初始声速分布的方法实现对体模的声速分布成像。结果：优化后的三维仿真方法相比优化前仿真时间缩短了约33%，空间占用减少了约98%；改进后的成像方法计算得到的声速分布图更加清晰且与实际声速分布情况更为接近，其与体模声速分布图之间的均方根误差、相关系数和结构相似性分别为10.90 m/s、0.856、0.836。结论：该方法提高了环形阵列超声成像三维仿真速度，且得到的声速分布图可以正确显示体模的结构和声速差异，为下一步采用实际获取信号进行成像奠定...     

多排螺旋CT自适应统计迭代重建算法的客观评价

目的：对GE公司最新研发的自适应统计迭代重建算法（ASIR）进行物理测试和体模验证。方法：采用国际通用CT成像测试体模扫描图像,测量不同算法重建图像的图像噪声、低对比分辨力（CNR）和系统调制传递函数（MTF）。结果：采用ASIR重建算法可以明显降低图像噪声,提高CNR而MTF保持不变（t=-1．706,P〉0．05）。结论：ASIR算法可以在显著降低图像噪声的同时保证图像空间分辨力不变,在提高CT图像质量和降低辐射剂量方面具有较高的临床应用价值。     

基于CORDIC算法的血管内超声成像系统数字坐标转换的FPGA实现

为了方便医生利用血管内超声成像系统更好地获取心血管图像,做出更加精准的诊断,该研究提出了一种基于CORDIC算法的血管内超声成像系统的数字坐标转换方法,通过角度旋转和定向计算将极坐标转换为直角坐标。利用FPGA在血管内超声成像系统平台上进行实验仿真测试,实验仿真表明,CORDIC算法能有效地输出正余弦值,与传统的查找表方法相比,速度更快,实时性更强,消耗硬件资源少,更适用于血管内超声成像系统。     

超声弹性成像监测冷冻手术的仿真实验研究

从生物组织冻结前后其弹性模量会发生显著改变的角度出发,在提出了低温外科手术中监测冰球形成与消融过程的超声弹性成像方法的研究基础上,设计了3类概念性超声弹性监测试验：含玻璃体模、常温组织体模及冻结组织体模仿真试验,首次从实验上证实了超声弹性成像方法在低温外科手术中对冰球实施高对比度成像的可行性。文章分析了该方法在应用中的一些测量误差,指出了进一步改进的方向。冰球这种与水呈高弹性对比度的临床监测对象,可望成为超声弹性成像医学应用中的一个重要主题。     

冠状动脉CTA成像中高对比剂增强效果对狭窄成像准确度影响的量化评价研究

本文应用搏动心脏体模模拟左心室和不同内径、不同程度狭窄的冠状动脉,使用LightSpeed容积CT作为扫描设备,针对动态心脏体模,应用图像处理技术研究并实现对冠状动脉狭窄率进行准确稳定的客观评价方法。应用两组不同的对比剂增强效果参数对具有两种不同管径和三种不同狭窄程度的体模进行心脏成像,使用客观评价方法计算冠状动脉狭窄率并分析两种增强效果对冠状动脉成像准确度的影响,进行成像质量优化研究。     

CT系统目测分辨率与系统调制传递函数相关性分析

目的对CT系统MTF（调制传递函数）和目测分辨率之间的关系进行研究。方法扫描CT测试体模中分辨率测试模块,获得系统MTF和目测空间分辨率。结果当MTF为10%时所对应的空间频率与清晰分辨的线对卡分辨率一致,当MTF为2%-5%时对应的空间频率与目测极限分辨率接近。结论通过CT系统MTF和目测分辨率相关关系研究,可以客观反映系统对细节识别能力与人眼识别能力之间的对应关系,从而提高CT质量控制水平。     

X射线计算机断层摄影成像物理指标检测与评价的研究

本文就北京市的CT机成像物理性能检测工作，对检测设备、检测方法、检测结果评价分析进行了研究，经过大量实测研究取得了一些可行性结论，例如：MTF＝10％时的空间分辨力与视觉模块图像分辨力相当，实测对比度与视觉可分辨孔径乘积评价扫描系统的密度分辨力是科学的可行的；CT值均匀度对模体尺寸的依赖性是用于婴幼儿扫描CT机的重要指标；50mGy剂量限值是检测评价密度分辨力的基本条件，研究结果用于北京市CT机成像物理性能检测评价，取得了满意的物理成像性质质控效果。作者还对今后的检测评价提出了新建议。     

计算机辅助多角度穿刺系统的研究

目的：建立应用于介入性超声的计算机辅助多角度穿刺系统。方法：设计计算机辅助多角度穿刺系统．利用高精度磁定位器实时跟踪超声探头和穿刺针，进行三维超声图像重建，穿刺中实时显示超声图像平面、穿刺针与三维超声的空间位置关系．在计算机辅助下，通过一个5自由度的被动机器人引导装置辅助穿刺。使用系统分别对固定于水槽中和标准声学体模中的直径为10mm的球形穿刺目标进行穿刺操作．评估系统的穿刺准确度。结果：建立的系统可以完成超声引导的多角度穿刺操作．所有实验均命中穿刺目标．误差在5mm以内。结论：超声引导多角度穿刺系统可以摆脱穿刺引导架的角度限制．实现介入操作中灵活准确的穿刺。     

扇形扫描三维超声成像系统体积测量

设计制作了两种用于三维超声系统体积测定的水中体模和Agar体模。实验结果表明,随着扫描深度的增大,在水中的体积测量误差从4%到7%逐渐增大;在Agar中的体积测量误差从6%到10%逐渐增大。所设计制作的体模与该体积参数的测定方法为建立三维超声诊断仪检测标准以及三维超声系统的临床应用作了初步探索。     

Simulation of the modulation transfer function dependent on the partial Fourier fraction in dynamic contrast enhancement magnetic resonance imaging

The image characteristics in dynamic contrast-enhanced magnetic resonance imaging (DCE-MRI) depend on the partial Fourier fraction and contrast medium concentration. These characteristics were assessed and the modulation transfer function (MTF) was calculated by computer simulation. A digital phantom was created from signal intensity data acquired at different contrast medium concentrations on a breast model. The frequency images [created by fast Fourier transform (FFT)] were divided into 512 parts and rearranged to form a new image. The inverse FFT of this image yielded the MTF. From the reference data, three linear models (low, medium, and high) and three exponential models (slow, medium, and rapid) of the signal intensity were created. Smaller partial Fourier fractions, and higher gradients in the linear models, corresponded to faster MTF decline. The MTF more gradually decreased in the exponential models than in the linear models. The MTF, which reflects the image characteristics in DCE-MRI, was more degraded as the partial Fourier fraction decreased.     

An automated microemboli detection and classification system using backscatter RF signals and differential evolution

Embolic phenomena, whether air or particulate emboli, can induce immediate damages like heart attack or ischemic stroke. Embolus composition (gaseous or particulate matter) is vital in predicting clinically significant complications. Embolus detection using Doppler methods have shown their limits to differentiate solid and gaseous embolus. Radio-frequency (RF) ultrasound signals backscattered by the emboli contain additional information on the embolus in comparison to the traditionally used Doppler signals. Gaseous bubbles show a nonlinear behavior under specific conditions of the ultrasound excitation wave, this nonlinear behavior is exploited to differentiate solid from gaseous microemboli. In order to verify the usefulness of RF ultrasound signal processing in the detection and classification of microemboli, an in vitro set-up is developed. Sonovue micro bubbles are exploited to mimic the acoustic behavior of gaseous emboli. They are injected at two different concentrations (0.025 and 0.05 µl/ml) in a nonrecirculating flow phantom containing a tube of 0.8 mm in diameter. The tissue mimicking material surrounding the tube is chosen to imitate the acoustic behavior of solid emboli. Both gaseous and solid emboli are imaged using an Anthares ultrasound scanner with a probe emitting at a transmit frequency of 1.82 MHz and at two mechanical indices (MI) 0.2 and 0.6. We propose in this experimental study to exploit discrete wavelet transform and a dimensionality reduction algorithm based on differential evolution technique in the analysis and the characterization of the backscattered RF ultrasound signals from the emboli. Several features are evaluated from the detail coefficients. It should be noted that the features used in this study are the same used in the paper by Aydin et al. These all features are used as inputs to the classification models without using feature selection method. Then we perform feature selection using differential evolution algorithm with support vector machines classifier. The experimental results show clearly that our proposed method achieves better average classification rates compared to the results obtained in a previous study using also the same backscatter RF signals.     

超声引导下微波消融治疗机器人系统的初步研究

目的:研究应用于超声引导下微波消融治疗的机器人系统。方法:设计超声引导微波消融治疗机器人系统,主要由三维超声导航、穿刺机器人和空间定位装置组成。利用磁定位器实时跟踪超声探头和穿刺针,构建三维超声,穿刺操作中实时显示二维超声图像平面在三维超声中的位置及与穿刺针的空间位置关系,利用一个五自由度的被动机械人引导装置辅助穿刺。建立水槽实验模型,利用该模型进行初步实验。结果:所有实验均命中穿刺目标,误差在0.5cm以内。结论:利用超声引导微波消融治疗机器人系统可以实现三维空间的准确定位,并摆脱穿刺引导架的角度限制,实现灵活准确的穿刺操作。     

平行板电离室两种校准方法研究

目的 研究用γ光子线束(⁶⁰Co模体法)和高能电子线束(电子束法)校准平行板电离室吸收剂量因子方法。方法 电子束法:0.65cc指形电离室放在水中有效点深度2.88 cm (考虑电离室半径),平行板电离室(NACP02)放在水中有效点深度2.70 cm,都距监督指形电离室3 cm处,电子线束能量18 MeV,照射野15 cm×15 cm,SSD=100 cm,照射:300MU,测量;不加监督电离室,并按上述条件照射并测量;根据国际原子能机构(IAEA)381号报告,分别计算平行板电离室空气吸收剂量校准因子。⁶⁰Co模体法:水模体30 cm×30 cm×30 cm,0.65cc指形电离室放在水中深度5cm,照射野10 cm×10 cm,SSD=80 cm,照射时间60s;水模体25 cm×25 cm×25 cm,平行板电离室放在水中有效点深度5cm,其他条件相同,计算平行板电离室空气吸收剂量校准因子。最后将两种方法校准结果进行比较。结果 电子束方法校准平行板电离室结果为52.30 Gy/C·kg ^-1(不加监督电离室的值为52.27Gy/C·kg ^-1)。⁶⁰Co模体法校准平行板电离室结果为52.33 Gy/C·kg ^-1。结论 电子束法与⁶⁰Co模体法校准平行板电离室空气吸收剂量因子偏差仅为0.05%。因此,测量电子线束输出剂量,对平行板电离室的校准既可选择高能电子线束也可选择⁶⁰ Co光子γ线束。     

实时三平面超声成像对正常人群左心房功能的评价

目的：探讨实时三平面超声成像（RTTU）对测量正常人群左心房功能的可行性和临床应用价值。方法：使用实时三平面超声技术，评价32例健康体检的成年人左心房功能（包括左心房存贮容积、管道容积及主动射血分数），同时用二维超声心动图检测上述参数，比较两种方法的相关性和一致性。结果：两种超声检查方法在左心房存贮容积（LARV）、左心房管道容积（LACV）及左心房射血分数（LVEF）等指标方面相比，无差异；LARV、LACV及LAEF在三平面图像和二维超声图像显示具有较好的相关性，差异有统计学意义（r^LARV=0.82，r^LACA=0.85,r^LARV=0.88,P〈0．05）。结论：实时三平面超声成像与二维超声心动图在评价正常人左心房功能时有良好的相关烂。     

Three-dimensional radiochromic film dosimetry for volumetric modulated arc therapy using a spiral water phantom

We validated 3D radiochromic film dosimetry for volumetric modulated arc therapy (VMAT) using a newly developed spiral water phantom. The phantom consists of a main body and an insert box, each of which has an acrylic wall thickness of 3 mm and is filled with water. The insert box includes a spiral film box used for dose-distribution measurement, and a film holder for positioning a radiochromic film. The film holder has two parallel walls whose facing inner surfaces are equipped with spiral grooves in a mirrored configuration. The film is inserted into the spiral grooves by its side edges and runs along them to be positioned on a spiral plane. Dose calculation was performed by applying clinical VMAT plans to the spiral water phantom using a commercial Monte Carlo-based treatment-planning system, Monaco, whereas dose was measured by delivering the VMAT beams to the phantom. The calculated dose distributions were resampled on the spiral plane, and the dose distributions recorded on the film were scanned. Comparisons between the calculated and measured dose distributions yielded an average gamma-index pass rate of 87.0% (range, 91.2–84.6%) in nine prostate VMAT plans under 3 mm/3% criteria with a dose-calculation grid size of 2 mm. The pass rates were increased beyond 90% (average, 91.1%; range, 90.1–92.0%) when the dose-calculation grid size was decreased to 1 mm. We have confirmed that 3D radiochromic film dosimetry using the spiral water phantom is a simple and cost-effective approach to VMAT dose verification.