Update on stereology for light microscopy.

The quantitative investigation of images taken from light microscopy observation is one of the pillars of biological and biomedical investigation. The main objective is the count of objects, usually cells. In addition, the measurement of several morphological parameters, such as the diameter of cells, the length of vessels, etc., can also be important for the quantitative assessment of the features of a tissue. Whereas counting and measuring histological elements may appear easy, especially today with the availability of dedicated software, in fact it is not, since what we can count and measure on light microscopy images are not the true histological elements but actually profiles of them. Obviously, the number and size of profiles of an object do not correspond to the object number and size and thus significant mistakes can be made in the interpretation of the quantitative data obtained from profiles. To cope with this problem, over the last decades, a number of design-based stereological tools have been developed in order to obtain unbiased and reliable quantitative estimates of cell and tissue elements that originate from light microscopy images. This paper reviews the basic principles of the stereological tools from the first disector applications through some of the most recently devised methods.