Department of Medical Imaging, Toronto General Hospital, Ontario, Canada.
Med Phys. 2010 Aug;37(8):4227-37. doi: 10.1118/1.3447725.
This study aimed to derive a mathematical correction function in order to normalize the CT number measurements for small volume arterial plaque and small vessel mimicking objects, imaged with multidetector CT (MDCT).
A commercially available calcium plaque phantom (QRM GmbH, Moehrendorf, Germany) and a custom built cardiovascular phantom were scanned with 320 and 64 MDCT scanners. The calcium hydroxyapatite plaque phantom contained objects 0.5-5.0 mm in diameter with known CT attenuation nominal values ranging 50-800 HU. The cardiovascular phantom contained vessel mimicking objects 1.0-5.0 mm in diameter with different contrast media. Both phantoms were scanned using clinical protocols for CT angiography and images were reconstructed with different filter kernels. The measured CT number (HU) and diameter of each object were analyzed on three clinical postprocessing workstations. From the resultant data, a mathematical formula was derived based on absorption function exp(--micro.-d) to demonstrate the relation between measured CT numbers and object diameters.
The percentage reduction in measured CT number (HU) for the group of selected filter kernels, apparent during CT angiography, is dependent only on the object size (plaque or vessel diameter). The derived formula of the form 1-c.-exp(-a.-d--b) showed reduction in CT number for objects between 0.5 and 5 mm in diameter, with asymptote reaching background noise for small objects with diameters nearing the CT in-plane resolution (0.35 mm). No reduction was observed for the objects with diameters equal or larger than 5 mm.
A clear mathematical relationship exists between object diameter and reduction in measured CT number in HU. This function is independent of exposure parameters and inherent attenuation properties of the objects studied. Future developments include the incorporation of this mathematical model function into quantification software in order to automatically generate a true assessment of measured CT number (HU) corresponding to plaque physical density rho (g/cm(3)). This is a significant development for the accurate, noninvasive classification of noncalcified arterial plaque.
本研究旨在推导出一个数学校正函数，以对多排 CT（MDCT）成像的小体积动脉斑块和小血管模拟物体的 CT 数测量值进行归一化。
使用商用钙斑块体模（QRM GmbH，Moehrendorf，德国）和定制的心血管体模，对 320 排和 64 排 MDCT 扫描仪进行扫描。钙羟磷灰石斑块体模包含直径为 0.5-5.0mm 的物体，其 CT 衰减标称值范围为 50-800HU。心血管体模包含直径为 1.0-5.0mm 的血管模拟物体，具有不同的对比介质。两个体模均使用 CT 血管造影的临床方案进行扫描，并使用不同的滤波核进行图像重建。在三个临床后处理工作站上分析每个物体的测量 CT 数（HU）和直径。基于吸收函数 exp（--micro.-d），从所得数据中推导出一个数学公式，以证明测量的 CT 数与物体直径之间的关系。
在 CT 血管造影期间，所选滤波核的 CT 数（HU）的测量值降低百分比仅取决于物体的大小（斑块或血管直径）。所推导的公式形式为 1-c.-exp（-a.-d--b），显示直径在 0.5 至 5mm 之间的物体的 CT 数降低，对于直径接近 CT 平面分辨率（0.35mm）的小物体，其渐近线达到背景噪声。对于直径等于或大于 5mm 的物体，没有观察到降低。
物体直径与 HU 中测量的 CT 数降低之间存在明确的数学关系。该函数独立于暴露参数和所研究物体的固有衰减特性。未来的发展包括将此数学模型函数纳入量化软件中，以自动生成与斑块物理密度 rho（g/cm(3)）相对应的测量 CT 数（HU）的真实评估。这是对非钙化动脉斑块进行准确、非侵入性分类的重要进展。
