In X-ray computed tomography (CT) reducing the number of projections (N_p) acquired for data reconstruction will reduce the measurement acquisition time and, thereby, the cost of the measuring process. However, reducing N_p can also reduce reconstruction quality and the accuracy of dimensional information provided by the CT measurement. This paper assesses changes in dimensional accuracy of X-ray CT data as a function of N_p. The variance of CT dimensional measurements, with respect to reference data obtained from tactile coordinate measurement machines (CMMs), is studied. Two cheese-like hole-cubes made of aluminum material and nylon (a polyamide thermoplastic) are used as measuring workpieces. It is determined that using N_p between 600 and 2000 does not produce major changes in accuracy for size measurements (lengths and diameters), for which absolute deviations between CT and reference data were mainly within the range of 5–10 μm. This range reflects sub-voxel accuracies of CT measurement (the voxel size for CT data reconstruction was 73 μm) when determining component size dimensions. However, for N_p < 600 the accuracy of CT measurements rapidly deteriorates, with deviations that can be much larger than 100 μm. This is worse for measurements of form (flatness and cylindricity). Reducing N_p strongly affects form measurements. To assess form properties of CT reconstructed surfaces, using a large N_p ($\ge$ 2000) is preferable. Although the accuracy of measurements of size also deteriorates with reducing N_p the accuracy loss is less severe, particularly if averaging over several data points. When measuring size, a loss of image quality can be tolerated as a trade-off for time optimization in CT data collection. Assessments of image quality further complement the conclusions presented in this paper.

在X射线计算机断层扫描（CT）中，减少用于数据重建的投影数量（N _p）将减少测量采集时间，从而减少测量过程的成本。但是，减小N _p也会降低重建质量和CT测量提供的尺寸信息的准确性。本文评估了X射线CT数据的尺寸精度随N _p的变化。对于从触觉坐标测量机（CMM）获得的参考数据，研究了CT尺寸测量的方差。将两个由铝材料和尼龙（一种聚酰胺热塑性塑料）制成的类似奶酪的孔立方体用作测量工件。确定使用N _p在600到2000之间不会对尺寸测量（长度和直径）的准确性产生重大变化，因为CT与参考数据之间的绝对偏差主要在5-10μm的范围内。该范围反映了确定组件尺寸时的CT测量的亚体素精度（用于CT数据重建的体素尺寸为73μm）。但是，对于N _p  <600，CT测量的精度会迅速下降，其偏差可能远远大于100μm。这对于形状（平坦度和圆柱度）的测量更差。减小N _p会严重影响形状测量。为了评估CT重建表面的形状特性，请使用较大的N _p（$\ge$2000）为佳。尽管尺寸的测量的准确度也与减少劣化Ñ _p精度损失是较不严重的，特别是如果平均在几个数据点。在测量尺寸时，可以容忍图像质量的损失，作为在CT数据收集中优化时间的折衷方案。图像质量评估进一步补充了本文提出的结论。