Batchelar Deidre L, Cunningham Ian A
Imaging Research Laboratories, The John P. Robarts Research Institute, London, Ontario, Canada.
Med Phys. 2002 Aug;29(8):1651-60. doi: 10.1118/1.1493216.
Coherent-scatter computed tomography (CSCT) is a novel imaging method we are developing to produce cross-sectional images based on the low-angle (<10 degrees) scatter properties of tissue. At diagnostic energies, this scatter is primarily coherent with properties dependent upon the molecular structure of the scatterer. This facilitates the production of material-specific maps of each component in a conglomerate. Our particular goal is to obtain quantitative maps of bone-mineral content. A diagnostic x-ray source and image intensifier are used to acquire scatter patterns under first-generation CT geometry. An accurate measurement of the scatter patterns is necessary to correctly identify and quantify tissue composition. This requires corrections for exposure fluctuations, temporal lag in the intensifier, and self-attenuation within the specimen. The effect of lag is corrected using an approximate convolution method. Self-attenuation causes a cupping artifact in the CSCT images and is corrected using measurements of the transmitted primary beam. An accurate correction is required for reliable density measurements from material-specific images. The correction is shown to introduce negligible noise to the images and a theoretical expression for CSCT image SNR is confirmed by experiment. With these corrections, the scatter intensity is proportional to the number of scattering centers interrogated and quantitative measurements of each material (in g/cm3) are obtained. Results are demonstrated using both a series of poly(methyl methacrylate) (PMMA) sheets of increasing thickness (2-12 mm) and a series of 5 acrylic rods containing varying amounts of hydroxyapatite (0-0.400 g/cm3), simulating the physiological range of bone-mineral density (BMD) found in trabecular bone. The excellent agreement between known and measured BMD demonstrates the viability of CSCT as a tool for densitometry.
相干散射计算机断层扫描（CSCT）是我们正在开发的一种新型成像方法，用于基于组织的低角度（<10度）散射特性生成横截面图像。在诊断能量下，这种散射主要是相干的，其特性取决于散射体的分子结构。这有助于生成聚集体中各组分的物质特异性图谱。我们的特定目标是获得骨矿物质含量的定量图谱。使用诊断X射线源和图像增强器在第一代CT几何结构下获取散射图案。准确测量散射图案对于正确识别和量化组织成分是必要的。这需要对曝光波动、图像增强器中的时间延迟以及样本内的自衰减进行校正。使用近似卷积方法校正延迟效应。自衰减会在CSCT图像中导致杯状伪影，并使用透射主光束的测量值进行校正。为了从物质特异性图像进行可靠的密度测量，需要进行精确校正。结果表明该校正对图像引入的噪声可忽略不计，并且通过实验证实了CSCT图像信噪比的理论表达式。通过这些校正，散射强度与被询问散射中心的数量成正比，并获得了每种物质（以g/cm³为单位）的定量测量值。使用一系列厚度不断增加（2 - 12毫米）的聚甲基丙烯酸甲酯（PMMA）片材以及一系列含有不同量羟基磷灰石（0 - 0.400 g/cm³）的5根丙烯酸棒来展示结果，模拟小梁骨中发现的骨矿物质密度（BMD）的生理范围。已知BMD与测量BMD之间极好的一致性证明了CSCT作为一种骨密度测量工具的可行性。
