Rollano-Hijarrubia Empar, Stokking R, van der Meer Frits, Niessen Wiro J
Departments of Radiology and Medical Informatics, Erasmus MC-University Medical Center Rotterdam, Dr Molewaterplein 50, Rotterdam, Zuid-Holland 3015 GE, The Netherlands.
Acad Radiol. 2006 Jul;13(7):893-908. doi: 10.1016/j.acra.2006.03.009.
The aim of this work is to study how the limited spatial resolution of a computed tomographic (CT) system affects the imaging of small high-density structures. This knowledge is relevant not only to understand and interpret clinical data, but also to apply and develop quantification methods for calcifications and stented vessels.
A dedicated phantom containing small differently sized aluminum cylinders was imaged on a 64-slice multidetector row CT (MDCT) while varying acquisition and reconstruction parameters from a high-resolution protocol. In addition, a bead phantom was imaged to estimate the point spread function (PSF) for the different parameter settings. The accuracy in determining object density and size was established for various imaging protocols and compared with simulations based on the estimated PSF.
Attenuation values and size measurements were accurate for objects larger than two times the size of the system PSF at the full-width-at-half-maximum. For smaller objects, attenuation values were increasingly underestimated and size was increasingly overestimated. The convolution kernel had the most influence on object signal and size. Use of edge-enhancing kernels yielded more accurate size measurements and higher signal for small objects. However, their application was constrained by noise amplification and edge-ringing artifacts, which led to lower signal-to-noise ratio, degrading the visualization of low densities and small high-density objects.
Results presented in this report provide insight into limitations in the quantification of small high-density structures and their effect on the visualization of surrounding tissues with recently developed MDCT systems.
本研究旨在探讨计算机断层扫描（CT）系统有限的空间分辨率如何影响小高密度结构的成像。这些知识不仅有助于理解和解读临床数据，还能应用于钙化和支架血管的量化方法开发。
使用一个包含不同尺寸小铝质圆柱体的专用体模，在64层多排探测器CT（MDCT）上成像，同时改变高分辨率协议中的采集和重建参数。此外，对一个珠子体模进行成像，以估计不同参数设置下的点扩散函数（PSF）。确定了各种成像协议下物体密度和大小测量的准确性，并与基于估计PSF的模拟结果进行比较。
对于尺寸大于系统半高宽处PSF两倍的物体，衰减值和大小测量准确。对于较小的物体，衰减值越来越被低估，大小越来越被高估。卷积核对物体信号和大小影响最大。使用边缘增强核可获得更准确的大小测量结果，并且小物体的信号更高。然而，其应用受到噪声放大和边缘振铃伪影的限制，这导致信噪比降低，降低了低密度和小高密度物体的可视化效果。
本报告中的结果揭示了小高密度结构量化的局限性及其对使用最新开发的MDCT系统观察周围组织的影响。
