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以学习写作为目的的阅读，最好是已弄懂了专业意义。对于母语不是英语的人，用英语写一本专业书籍并不容易。但是至少可以学习专业内容方面的表述方法，为写专业论文做准备。首先，可以发现，书名、章节标题（title）是短语，一般不含标点符号。其次，可以发现内容一般用第三人称，用一般现在时态，有较多的被动语态和分词短语。这些特点与专业论文摘要和论文的一般惯例是不同的。
下面给出一段专业内容的汉语，请读者按照书籍的写作惯例，翻译成英语。
3.1 CT数与线衰减系数的关系
在图像重组过程中，对一种材料计算的CT数与X射线束的有效能量在同种材料中的线衰减系数 μ 有关，其关系为：
式中 CTN 表示CT数， μ w 是同种有效能量的X射线在水中的线衰减系数。对于现代的精良CT扫描机，常数 K 的值为 1 000，如果将 CTN 表示成豪斯菲尔德单位（HU：Hounsfield Unit），则上式变为：
在HU单位中，空气的CT数为-1 000 HU；水的CT数为 0；致密的骨的CT数为几百个HU；金属，如外科摄，CT数为 1 000 HU以上。在较早的扫描机中， K 常数为另外的值（如早期的EMI扫描机中 K ＝500）。
3.2 用CT数表示物质对X射线的吸收的优点
1.因为CT数表示被测材料和水的衰减系数之比，所以对不同的管压KVP值及X射线束的不同的过滤情况都变化不大。
2.对不同的CT扫描机都基本上是常数。
3.乘以比例因子 1 000，是要将CT数的距离挪大，以免像衰减系数那样堆积在一起。
4. CT数主要反映了物质的体电子密度（电子数/cm 3 ）。CT数与物质的体电子密度有线性关系。
5.对肌肉和软组织CT数主要反映X射线的康普顿散射。
6.骨的CT数主要反映X射线的光电吸收。骨的CT数偏离了与体电子密度（电子数/cm 3 ）的线性关系。
7.对CT数的主要影响是吸收材料的物理性质，主要是材料的物理密度（g/cm 3 ）。对CT数的第二个影响是质量电子密度（电子数/g），因为大多数相互作用都属于康普顿散射，这种相互作用主要与介质的质量电子密度有关而与介质材料的原子序数无关，质量电子密度与物理密度之积叫介质的体电子密度。单位为电子数/cm 3 。CT数与介质体积电子密度的线性关系示于图 4-7。除骨外，所有生物材料都遵从这种线性关系。在骨中，光电吸收的影响变得显著起来，介质的原子序数影响相互作用的几率。因此，骨中CT数偏离图 4-7 中的线性关系百分之几。
附：参考英文翻译
ATTENUATION COEFFICIENTS AND CT NUMBERS
During the image-reconstruction process, the CT number computed for material is related to the linear attenuation coefficient μ of the material for effective energy of the x-ray beam. This relationship is indicated by expression
where μ w is the linear-attenuation coefficient of water at the same effective energy for CT scanners of recent vintage, the constant in this expression has the value 1, 000, and the CT numbers are referred to as Housfield units(HU). The expression for Housfield units is
in Housfield units, air has a value of -1, 000; water has a value of 0; dense bone has a value of some hundreds of Housfield units; and metal, such as that used in surgical clips, may have HU values exceeding 1, 000. In earlier scanners, the constant had other values(for example, in early EMI scanners, the constant had a value of 500).
Because CT numbers are expressed as the ratio of attenuation coefficients between material and water, they do not vary greatly with changes in kVp or filtration of the x-ray beam. Also, they remain relatively constant from one CT scanner to another. The major influences on CT numbers are the physical characteristics of the absorbing materials, primarily the physical(mass)density of the material in units of g/cm 3 . A secondary influence on the values of CT number is the mass electron(electrons per gram)of the medium, since most interactions occur by compton scattering and this mode of interaction varies with the mass electron density but not with the atomic number of the medium. The product of mass electron density(electrons per gram)and the physical density(g/cm 3 )is termed the volume electron density of the medium in units of electrons/cm 3 . The volume electron density usually completely characterizes the CT number of absorbing material. The linear relationship between CT number and volume electron density is shown in Figure 4-7. With the exception of bone, all biological specimens follow this linear relationship almost exactly. In bone, a small but significant fraction of the interactions are photoelectric; and the atomic number of the material influences the likelihood of interaction. Hence, the CT number for bone deviates a few percent from the linear relationship depicted in Figure 4-7.