The decision to undertake a long-term imaging project is not trivial. Experts suggest questions that researchers should ask themselves before starting out.

How frequently do you need to take an image?

Tracking individual cells often requires taking an image every few minutes. The more dense and mobile the cells are, the less time can elapse between images. For example, Michel Cayouette at the Clinical Research Institute of Montréal, Canada, takes images of retinal progenitor cells every seven minutes until they develop into neurons, at which stage he slows the rate of image acquisition to roughly once an hour.

Can your cells survive the experiment?

Repeated imaging can harm cells, especially when the imaging requires high-energy light. But the tolerance of different cells for fluorescence varies widely. Blood-forming stem cells are generally more robust than neural stem cells, for example, and thus can be imaged more frequently without affecting cell behaviour, notes Tannishtha Reya, a stem-cell biologist at Duke University in Durham, North Carolina.

Can you keep calm?

Inexperienced researchers sometimes set up their long-term microscope systems in the middle of a heavily trafficked work station or worse, under ventilation systems. Such disturbances can easily overwhelm a system's ability to maintain stable conditions and can cause obfuscating artefacts, cautions Cayouette.

Can you follow your cells?

Following cells in culture gets complicated once cells start crawling under and over each other. To track individual cells at low densities, labelling nuclei with Hoeschst often works well, says Thorsten Schlaeger at the Children's Hospital Boston in Massachusetts, although he cautions that some cells stain poorly, and non-toxic genetic labels can work better. If cells must be grown at high density, consider mixing in a few labelled cells and tracking just these.

Are you computationally prepared?

Crunching through large data sets can easily go beyond the capacity of standard lab computers, and a single experiment can completely fill a computer's hard drive. Researchers need appropriate servers and back-up systems. A dedicated informatics set-up and the help of a programmer are “highly desirable”, says Schlaeger.

M.B.