Researchers have developed multiple techniques and procedures to detect cancer cells during the earliest stages of the disease or post-treatment. But one of the major limitations of these technologies is their inability to detect the presence of only a few cancer cells. Now, a research collaboration between the University of Missouri-Columbia and Mexico's Universidad de Guanajuato shows that pulsed photoacoustic techniques, which combine the high optical contrast of optical tomography with the high resolution of ultrasound, can do just that. New developments are necessary, the researchers say, to be able to properly use photoacoustic techniques to recognize different cancer cell types inside the human body or in blood or tissue samples.