Among other things, a method comprises imaging a sample displaced between a sensor surface and a surface of a microscopy sample chamber to produce an image of at least a part of the sample. The image is produced using lensless optical microscopy, and the sample contains at least blood from a subject. The method also comprises automatically differentiating cells of different types in the image, generating a count of one or more cell types based on the automatic differentiation, and deriving a radiation dose the subject has absorbed based on the count.