Toward ideal imaging equipment

At Stony Brook University, State University of New York, assistant professor Emilia Entcheva and one of her graduate students, Harold Bien, regularly perform fluorescence imaging to monitor dynamic events in cell cultures; they have reviewed state-of-the-art imaging equipment and offer suggestions for its improvement.

Simultaneously imaging multiple cells requires a large working distance, but because most currently available objectives that offer a large working distance have a low numerical aperture, they do not gather light well and have a lower spatial resolution. Large-diameter lenses, a tandem-lens assembly and contact fluorescence imaging can compensate for the lack of adequate objectives, but none of these are perfect solutions.

The reviewers said that the detector is the most important part of the optical setup. For cell culture imaging, photodiode array detectors are most widely used because they offer good temporal resolution and a good signal-to-noise ratio. However, they have a low spatial resolution. CCDs tend to provide high spatial or high temporal resolution, but not both. Although CMOS detectors offer rapid detection but lower resolution, they are becoming popular and are rapidly developing. Therefore, their resolution could improve. The authors were most excited by electron-multiplying CCDs because they offer fast imaging at low light levels.

Imaging results in large amounts of computer information that is difficult to process in real time. This problem can be partially solved with additional memory, a bus with a high data transfer rate, protocols that enable rapid writing to the hard drive and a frame grabber. However, the authors note that the ability of peripherals to process data may be the greatest limiting factor for real-time data recording, and they call for improvements such as better signal processing algorithms and greater memory. (Progress in Biophysics and Molecular Biology, October 2006, pp. 232-257.)