Image reconstruction and image quality evaluation for a 64-slice CT scanner with z-flying focal spot
Image reconstruction and image quality evaluation for a 64-slice CT scanner with z-flying focal spot
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DOI：
10.1118/1.1949787
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发表时间：
2005-08-01
期刊：
影响因子：
3.8
通讯作者：
McCollough, CH
中科院分区：
文献类型：
--
作者：
Flohr, TG;Stierstorfer, K;McCollough, CH
我们提出了一种新的多排CT（MDCT）的z采样技术的理论概述和性能评价，依赖于在纵向（z飞行焦点）的焦点的周期性运动，同时采集切片的数量增加一倍。在最近推出的MDCT扫描仪中已经实现了z飞行焦斑技术。使用32 X 0.6 mm准直，该扫描仪在其螺旋（螺旋）操作模式下每次旋转采集64个重叠的0.6 mm切片，目的是提高纵向分辨率并减少螺旋伪影。等中心点处的纵向采样距离为0.3mm。z飞行焦斑技术对图像重建的影响。我们目前的测量螺旋切片灵敏度曲线（SSP）和纵向分辨率，无论是在等中心和偏离中心。我们评估的间距依赖的图像噪声测量中心20厘米的水幻影。为了研究螺旋图像的质量，我们提出了一个拟人化的胸部幻影和病人扫描图像。螺旋SSP的半峰全宽（FWHM）仅显示出作为节距的函数的微小变化，测量值相差小于0。标称值0.6、0.75、1、1.5和2 mm之间的差值为15 mm。最小切片的实测FWHM在等中心点处的范围为0.66和0.68 mm之间，间距0.55（0.72 mm）除外。在居中的z分辨率体模中，可以独立于间距（对应于0.33 mm纵向分辨率）可视化高达15 1 p/cm的条形图案。偏离中心100 mm，可以看到高达14 1 p/cm的条形图案，对应于可以在z方向上分辨的0.36 mm的物体尺寸。恒定有效mAs的图像噪声几乎与间距无关。测量值示出了作为间距的函数的小于7%的变化，这证明了在任何间距处所施加的辐射剂量的正确利用。除0.6 mm外，所有切片的图像噪声和切片宽度（相应SSP的FWHM）的平方根的乘积均为常数。对于最薄切片，相对图像噪声增加了17%。螺旋风车型伪影可通过z-飞行焦斑技术有效抑制，该技术有可能保持低伪影水平，最高间距为1.5，以这种方式增加了临床上可使用的最大体积覆盖速度。(c)2005年美国医学物理学家协会。
We present a theoretical overview and a performance evaluation of a novel z-sampling technique for multidetector row CT (MDCT), relying on a periodic motion of the focal spot in the longitudinal direction (z-flying focal spot) to double the number of simultaneously acquired slices. The z-flying focal spot technique has been implemented in a recently introduced MDCT scanner. Using 32 X 0.6 mm collimation, this scanner acquires 64 overlapping 0.6 mm slices per rotation in its spiral (helical) mode of operation, with the goal of improved longitudinal resolution and reduction of spiral artifacts. The longitudinal sampling distance at isocenter is 0.3 mm. We discuss in detail the. impact of the z-flying focal spot technique on image reconstruction. We present measurements of spiral slice sensitivity profiles (SSPs) and of longitudinal resolution, both in the isocenter and off-center. We evaluate the pitch dependence of the image noise measured in a centered 20 cm water phantom. To investigate spiral image quality we present images of an anthropomorphic thorax phantom and patient scans. The full width at half maximum (FWHM) of the spiral SSPs shows only minor variations as a function of the pitch, measured values differ by less than 0. 15 mm from the nominal values 0.6, 0.75, 1, 1.5, and 2 mm. The measured FWHM of the smallest slice ranges between 0.66 and 0.68 mm at isocenter, except for pitch 0.55 (0.72 mm). In a centered z-resolution phantom, bar patterns up to 15 1p/cm can be visualized independent of the pitch, corresponding to 0.33 mm longitudinal resolution. 100 mm off-center, bar patterns up to 14 1p/cm are visible, corresponding to an object size of 0.36 mm that can be resolved in the z direction. Image noise for constant effective mAs is almost independent of the pitch. Measured values show a variation of less than 7% as a function of the pitch, which demonstrates correct utilization of the applied radiation dose at any pitch. The product of image noise and square root of,the slice width (FWHM of the respective SSP) is the same constant for all slices except 0.6 mm. For the thinnest slice, relative image noise is increased by 17%. Spiral windmill-type artifacts are effectively suppressed with the z-flying focal spot technique, which has the potential to maintain a low artifact level up to pitch 1.5, in this way increasing the maximum volume coverage speed that can be clinically used. (c) 2005 American Association of Physicists in Medicine.