These days, cancer has a harder time hiding out. With modern imaging tools, inquiring researchers can ogle its every move, from a tumors growth to its inner workings to its effects on surrounding tissues.

Imaging, I think, is made for cancer, says Zaver Bhujwalla, director of the In Vivo Cellular Molecular Imaging Center at Johns Hopkins University School of Medicine in Baltimore. You can study so many different aspects of cancer.

For example, scientists can observe metastatic cells changing location in real time or watch for days and weeks as a tumor attracts new vasculature. Utilizing an abundance of tracers and reporter genes, researchers can visualize a cancers biochemistry, including its off-kilter metabolism. They can also monitor where a potential new cancer drug goes and what it does.

With techniques based on radioactivity, light, and sound, an important task for cancer researchers is to make sure we have the correct instrument, says Samuel Achilefu, director of the optical radiology laboratory at Washington University in St. Louis. Lately, one instrument is often not enough, and researchers are combining two or more kinds of images to acquire a picture that includes both anatomical and functional information.

Here, The Scientist takes a look at five imaging options for the cancer researcher, ranging from old standbys to up-and-coming technologies.

REAL-TIME TRACKING OF TUMOR GROWTH: Justin Lathia of the Cleveland Clinic uses intravital microscopy to observe labeled tumor stem cells (green fluorescence) as they induce new vascular growth (yellow fluorescence). The tool allows him to study tissue of a living animal over weeks. Jim Lang

User Justin Lathia, assistant professor of cell biology at the Cleveland Clinic in Ohio

Project In collaboration with Jeremy Rich at the Clinic and Alex Huang at Case Western Reserve University, Lathia studies how cancer stem cells drive tumor growth. Using intravital microscopy to view human brain tumors implanted into mice, the team was able to observe what scientists had previously only inferred: that stem cells indeed build the tumor mass (PLoS ONE, 6:e24807, 2011).

Method The researchers cut a window into the skulls of living mice and mounted a glass coverslip in the opening. They took multiple images of the brain over time, using blood vessels as a guide so they could line up their fluorescence microscope over the same spot for every picture.

Applications Intravital microscopy offers a window into many types of cellular activities, such as different cell populations moving around in a tumor, cancer cells interactions with endothelial tissue, and their migration in and out of the bloodstream, in addition to cell division and growth. Intravital microscopy is best suited for observing a small area.

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Eyes on Cancer