University of Cambridge Department of Engineering, Trumpington Street, Cambridge CB2 1PZ, UK.
Med Image Anal. 2010 Jun;14(3):276-90. doi: 10.1016/j.media.2010.01.003. Epub 2010 Jan 25.
The distribution of cortical bone in the proximal femur is believed to be a critical component in determining fracture resistance. Current CT technology is limited in its ability to measure cortical thickness, especially in the sub-millimetre range which lies within the point spread function of today's clinical scanners. In this paper, we present a novel technique that is capable of producing unbiased thickness estimates down to 0.3mm. The technique relies on a mathematical model of the anatomy and the imaging system, which is fitted to the data at a large number of sites around the proximal femur, producing around 17,000 independent thickness estimates per specimen. In a series of experiments on 16 cadaveric femurs, estimation errors were measured as -0.01+/-0.58mm (mean+/-1std.dev.) for cortical thicknesses in the range 0.3-4mm. This compares with 0.25+/-0.69mm for simple thresholding and 0.90+/-0.92mm for a variant of the 50% relative threshold method. In the clinically relevant sub-millimetre range, thresholding increasingly fails to detect the cortex at all, whereas the new technique continues to perform well. The many cortical thickness estimates can be displayed as a colour map painted onto the femoral surface. Computation of the surfaces and colour maps is largely automatic, requiring around 15min on a modest laptop computer.
股骨近端皮质骨的分布被认为是决定骨折抵抗力的关键因素。目前的 CT 技术在测量皮质厚度方面能力有限，特别是在亚毫米范围内，这处于当今临床扫描仪的点扩散函数范围内。在本文中，我们提出了一种新的技术，能够产生无偏的厚度估计值，低至 0.3mm。该技术依赖于解剖结构和成像系统的数学模型，该模型适用于股骨近端的大量位置的数据，为每个标本产生约 17000 个独立的厚度估计值。在对 16 具尸体股骨的一系列实验中，对于 0.3-4mm 范围内的皮质厚度，测量到的估计误差为-0.01+/-0.58mm（平均值+/-1std.dev.）。与简单的阈值法相比，这一误差为 0.25+/-0.69mm，与 50%相对阈值方法的变体相比，误差为 0.90+/-0.92mm。在临床相关的亚毫米范围内，阈值法越来越无法检测到皮质，而新技术仍能很好地执行。许多皮质厚度估计值可以显示为绘制在股骨表面的彩色地图。表面和彩色地图的计算主要是自动的，在一台普通的笔记本电脑上大约需要 15 分钟。
