The resolution limit imposed by radiation damage is quantified in terms of a voxel dose-limited resolution (DLR), applicable to small features within a thick specimen. An analytical formula for this DLR is derived and applied to bright-field mass-thickness contrast from organic (polymer or biological) specimens of thickness between 400 nm and 20 µm. For a permissible dose of 330 MGy (typical of frozen-hydrated tissue), the TEM or STEM image resolution is determined by radiation damage rather than by lens aberrations or beam-broadening effects, which can be restricted by use of a small angle-limiting aperture. DLR is improved by a up to factor of 2 by increasing the primary-electron energy from 300 keV to 3 MeV, or by up to a factor of 3 by heavy-metal staining. For stained samples, a higher electron fluence allows better resolution but the improvement is modest because the voxel DLR is proportional to the 1/4 power of electron dose. The relevance of voxel and columnar DLR is discussed, for both thick and thin samples.

辐射损伤造成的分辨率限制以体素剂量限制分辨率 (DLR) 的形式进行量化，适用于厚样本内的小特征。推导了该 DLR 的分析公式，并将其应用于厚度在 400 nm 至 20 µm 之间的有机（聚合物或生物）样本的明场质量厚度对比。对于 330 MGy 的允许剂量（典型的冷冻水合组织），TEM 或 STEM 图像分辨率由辐射损伤决定，而不是由透镜像差或光束展宽效应决定，后者可以通过使用小角度限制来限制光圈。通过将初级电子能量从 300 keV 增加到 3 MeV，DLR 最多可提高 2 倍，或者通过重金属染色最多可提高 3 倍。对于染色样品，较高的电子注量可提供更好的分辨率，但改进幅度不大，因为体素 DLR 与电子剂量的 1/4 次方成正比。对于厚样品和薄样品，讨论了体素和柱状 DLR 的相关性。