Apparatus and methods are described including placing a sample into a sample carrier that comprises a plurality of regions having upper and lower surfaces, having respective heights that are different from each other, and being configured such that cells form a monolayer, the monolayer within respective regions of the sample carrier having respective, different densities from each other, due to the respective regions of the sample carrier having respective heights that are different from each other. Microscopic images are acquired of each of the plurality of regions. Measurements are performed upon cell types that have a relatively high density upon microscopic images of a region of the sample chamber having a relatively low height, and measurements are performed upon cell types that have a relatively low density upon microscopic images of a region of the sample chamber having a relatively great height. Other applications are also described.