SPECT成像的多路平行束准直器研究

发布时间：2018-06-05 21:15

本文选题：多通道平行孔准直器 + SPECT　；参考：《南京大学》2013年博士论文

【摘要】：SPECT是一种常用的核医学成像技术。通过对患者体内的放射性核素进行成像可以显示体内的生理活动。为了提高准直器的灵敏度,减少测量时间,同时保持平行束准直器大视野的优点,本文提出了将多路技术引入平行束准直器,构成多通道平行束准直器。多通道平行束准直器通过在原来平行束准直器的断层内屏蔽体上增开一组伽马射线通道来达到在平行束准直器中构建多路技术的目的。为了了解多通道平行束准直器的性能,文中首先从准直器的几何条件出发,利用等效孔长的表达形式,给出了引入多通道系统后带来的斜平行孔的点源扩展函数。从而进一步推导出多通道平行束准直器轴向和横向的点源扩展函数函数。然后从多通道平行孔准直器点源扩展函数出发推导出多通道平行束准直器的灵敏度和传统的半高宽形式的空间分辨率,由于引入了多路技术,除了半高宽分辨率外,为了完整评价多通道的影响还给出了均方根分辨率的表达形式。为了验证数学推导的正确性,本文利用MCNP程序进行蒙特卡洛模拟,提出了粒子轨迹分析的算法,用于对模拟结果中的粒子轨迹进行记录和分析,并且比较了模拟数据计算结果与理论预测。通过这种算法可以区分入射探测器粒子中的散射粒子和透射粒子,并且分析了散射和透射对点源扩展函数、灵敏度以及分辨率的影响。在确定了准直器性能之后,我们对准直器建立了二维的数学模型,并且给出了系统矩阵的张角修正计算方法。为了评价准直器本身性质,在图像重建过程中本文首先使用无噪音的模拟数据进行图像重建,利用均匀圆柱模体观察重建过程中的伪影情况,利用Jaszczak模体观察成像过程中的分辨率变化情况。然后使用含有泊松分布噪音的模拟数据研究准直器系统的噪声性质,利用均匀圆柱模体观察图像收敛和噪声放大情况,利用多热区模体观察多通道平行束准直器对不同深度图像的重建效果。本文利用蒙特卡罗方法模拟实际情况进行图像重建,用MLEM迭代算法在不同的准直器材料条件下验证了透射修正算法,最后进行了OSEM迭代算法图像重建的初步研究。多通道平行束准直器在研究过程中表现出很多优良特性。通过多通道技术的应用准直器获得了更高的灵敏度。由于光子可以通过伽马射线通道到达探测器表面,这使得系统的灵敏度最多可增加近一倍。其次与其他增加灵敏度的方法相比,多通道平行束准直器保持了较高的空间分辨率。从理论推导、蒙特卡罗模拟和图像重建的结果可以看出：当伽马射线通道较小时,多通道平行束准直器对空间分辨率的影响很小,甚至在伽马射线通道较大时,其依旧具有好于同等灵敏度的平行孔准直器的空间分辨率。多通道平行束准直器具有较高透射和较小的散射。从蒙特卡罗的结果可知,多通道平行束准直器透射虽然比平行束准直器高,但文章中同时给出了在系统矩阵计算过程当中通过采用等效屏蔽体孔长的算法,在图像重建过程中对透射进行修正的方法。同时蒙特卡罗模拟表明散射在探测数据中所占比例很小(约1%)。在从重建后的图像中可以看出,多通道平行束准直器无额外伪影产生。并且通过分析不同深度热区图像可知,其分辨率的变化比平行束准直器小。同时,与平行束准直器相比,多通道平行束准直器有较低的噪音放大速度和迭代收敛速度,以及在噪声条件下更好的成像效果。从对蒙特卡罗数据的模拟中可以看出较高的子集数和噪音水平情况下,可以得到较好的图像重建效果。
[Abstract]:SPECT is a commonly used nuclear medical imaging technology. By imaging the radionuclides in the patient's body, the physiological activity in the body can be displayed. In order to improve the sensitivity of the collimator, reduce the measurement time, and maintain the advantages of the parallel beam collimator, this paper introduces a multi-channel technique into a parallel beam collimator to form a multipass system. A parallel beam collimator. A multichannel collimator is used to create a multi-channel technique in a parallel beam collimator by adding a group of gamma ray channels on the shield of the original parallel beam collimator.
In order to understand the performance of multichannel parallel beam collimator, starting from the geometric condition of collimator and using the expression of the equivalent hole length, the point source extension function of the oblique parallel hole is given after the introduction of the multi-channel system, and the extended function function of the axial and transverse point source of the multichannel parallel beam collimator is further derived. Then the sensitivity of multichannel parallel beam collimator and the traditional half width and wide spatial resolution are derived from the point source extension function of the multichannel parallel hole collimator. In addition to the half width and width resolution, the expression of the root mean square resolution is also given in order to evaluate the influence of the multichannel. The correctness of the mathematical deduction is verified. In this paper, the Monte Carlo simulation is used in the MCNP program. The algorithm of particle trajectory analysis is proposed to record and analyze the particle trajectories in the simulation results, and the results of the simulated data and the theoretical prediction are compared. By this method, the scattering particles in the incident detector particles can be distinguished from the scattering particles. The effect of scattering and transmission on the point source expansion function, sensitivity and resolution is analyzed. After determining the collimator performance, we establish a two-dimensional mathematical model for collimator, and give the calculation method of the angle correction of the system matrix, which is to evaluate the property of the collimator itself and the process of image reconstruction. In this paper, we first use the non noise simulation data to reconstruct the image, and observe the artifacts in the reconstruction process by using the uniform cylindrical mold body, and use the Jaszczak model body to observe the change of the resolution in the imaging process. Then use the simulated data containing the noise of Poisson distribution to study the noise properties of the quasi straight system and use the uniform cylinder. The image convergence and noise amplification are observed by the model body, and the multi channel parallel beam collimator is used to observe the reconstruction effect of different depth images. In this paper, the Monte Carlo method is used to simulate the actual situation to reconstruct the image. The transmission correction algorithm is verified with the MLEM iterative algorithm under the different collimator material conditions. Finally, the transmission correction algorithm is verified. A preliminary study of the image reconstruction of the OSEM iterative algorithm.
The multichannel collimator shows a lot of excellent characteristics in the study process. The collimator obtains higher sensitivity through the application of multichannel technology. As the photon can reach the detector surface through the gamma ray channel, this makes the sensitivity of the system almost doubled. From the theoretical deduction, the results of Monte Carlo simulation and image reconstruction show that when the gamma ray channel is smaller, the multi channel parallel beam collimator has little influence on the spatial resolution, even when the gamma ray channel is larger, it is still better than the same spirit. The multi-channel parallel beam collimator has higher transmission and smaller scattering. From the results of Monte Carlo, the transmission of multi channel collimator is higher than that of parallel beam collimator, but the equivalent shielding body length is also used in the system matrix calculation. The Monte Carlo simulation shows that the proportion of scattering in the detection data is very small (about 1%). It can be seen from the reconstructed image that there is no additional artifact in the multi channel collimator. And the resolution is known by analyzing the images of different depth heat regions. The change is smaller than the parallel beam collimator. At the same time, compared with the parallel beam collimator, the multichannel parallel beam collimator has a lower noise amplification rate and iterative convergence rate, and a better imaging effect under the noise condition. A higher number of subsets and noise levels can be seen from the simulation of the Monte Carlo data. Good image reconstruction effect.
【学位授予单位】：南京大学
【学位级别】：博士
【学位授予年份】：2013
【分类号】：R310

【共引文献】