Research of flying focal spot of the CT tube based on dynamic magnetic focusing
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摘要: 作为CT设备的核心器件，CT球管采用动态磁聚焦技术以利于大电流输出时小焦点的实现。飞焦点技术可以多角度记录每次扫描的每个投影，提高采样率，从而大幅改善图像清晰度，提高成像质量。当CT球管为1 A大电流输出时，采用CST软件对双磁四极透镜关键参数进行模拟仿真及优化，满足焦点目标尺寸为0.2 mm×0.6 mm的同时具备飞焦点功能。Abstract: CT tube is the core component of CT equipment. CT tube adopts dynamic magnetic focusing technology to facilitate the realization of small focus when there is large current output. Flying focal spot technology can record each projection of each scan from multiple angles, improve the sampling rate, and greatly improve the image definition and quality. CST software is used to simulate the CT tube based on dynamic magnetic focusing. When the CT tube outputs high current of 1 A, the key parameters of the dual magnetic quadrupole lens are optimized to get the target size of focus of 0.2 mm×0.6 mm and the function of flying focus.
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Key words:
- core component /
- CT tube /
- dynamic magnetic focusing /
- dual magnetic quadrupole lens /
- flying focal spot
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图 2 CT球管双磁四极透镜动态磁聚焦飞焦点扫描结构
Figure 2. Dynamic magnetic focusing flying focus scanning structure of double magnetic quadrupole lens CT tube
图 4 双磁四极透镜系统CST仿真结构
Figure 4. CST simulation structure of dual magnetic quadrupole lens system
1—focusing electrode; 2—cathode; 3—anode head; 4—first stage quadrupole lens core; 5—first stage quadrupole lens coil; 6—second stage quadrupole lens core; 7—second stage quadrupole lens coil; 8—deflection coil; 9—enclosure; 10—anode target.
图 5 最大磁场变化与x，y轴方向焦斑尺寸大小关系图
Figure 5. Maximum magnetic field vs focal spot size in x and y axes
图 6 四极透镜磁场沿x-y轴方向的分布
Figure 6. Distribution of the magnetic field of quadrupole lens along the x-y axis
图 9 焦斑x，y轴向偏移量随x，y轴向偏转电流关系
Figure 9. Relationship between x, y-axis of fset of focal spot and x, y-axis deflection current
表 1 国外部分机构在动态磁聚焦飞焦点技术的应用
Table 1. Application of foreign institutions in dynamic magnetic focusing flying focus technology
number institution CT tube flying focal spot technology image resolution improvement 1 Siemens[7] Straton z-Sharp technology（z-axis double sampling） each probe unit yields two alternately overlapping X-line projections without a dose increase, substantially improving the spatial resolution and imaging quality 2 Philips iMRC precise flying focal spot (SFS，the x-axial and z-axial flying focal spot technology) double sampling rate is obtained in plane and longitudinal direction, which is equivalent to 4 times of detector, and high spatial resolution is obtained in axial position and spiral scanning 3 Dunlee CT5000 xDFS(the x-axial flying focal spot),zDFS(the z-axial flying focal spot) improve imaging quality, provide sharp and clear images, zDFS double the number of slices, and there is no need for detectors with higher spatial resolution 
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