Animal imaging emerges onto the research agenda

Data collected by the European Association of Radiology in 2005 revealed that more than 60 centers in Europe have facilities for animal imaging research. Of these, 12 are in Germany, 10 in France, six in the U.K., and five each in the Netherlands and Belgium.

It is interesting to see that all of these facilities are organized around MR imaging. Several use MRI alone, while many others use MRI in association with optical imaging techniques. Some facilities work with PET and MRI, either with or without optical imaging. What we might call the "optimal imaging platform" of MRI, optical imaging, PET, and microCT is seldom in place.

Animal imaging has become synonymous with molecular imaging. Small animal imaging was already being practiced when institutions started setting up dedicated molecular imaging programs, but when somebody today speaks of animal imaging laboratories, we implicitly refer to molecular imaging. If you take a look at the centers for in vivo cellular and molecular imaging funded by the U.S. National Institutes of Health and National Cancer Institute, for example, all operate in association with animal imaging facilities.

Some well-established U.S. centers with molecular imaging programs illustrate how animal imaging facilities are organized. There is generally a multidisciplinary faculty, reflecting an emphasis on basic science rather than radiology. The Stanford Center for Innovation in In-Vivo Imaging is headed up by a scientist and staffed by 13 Ph.D. researchers and three radiologists. Staff members have expertise in a wide range of disciplines, including chemistry, bioengineering, computer science, and molecular biology.

Such centers generally run large-scale programs with the overall aim of developing in vivo molecular imaging for diagnosis and treatment. This requires the creation of new probes and, in parallel, the development of new modalities. The former requires skills in chemistry and molecular biology, while the latter depends on physics and bioengineering knowledge. Data processing and computer science are essential to both strands.

Some of these centers also run a small-scale clinical research program focused on articulating in vivo animal imaging results into applications in humans. This helps with the rapid translation of novel imaging agents and techniques from the bench to the bedside. The laboratories generally have a large selection of instrumentation. Equipment for small animal imaging is fairly compact. You don't need that much space to install a microPET scanner or optical imaging device. Many of these instruments will simply sit on a table. Finding sufficient space for computing is more critical, given the growing importance of data processing and virtual image reconstruction.

Each modality has its own advantages and disadvantages for small animal imaging. MRI and PET are the most expensive, while ultrasound and optical imaging systems are the least costly. MicroCT scanners occupy the middle ground. Nuclear medicine techniques remain the most sensitive, followed by MRI and then CT.

But sensitivity is not the end of the story. Nuclear medicine could potentially be used for imaging the nucleus, cytoplasm, cell membrane, and organs, while also providing functional information. Optical techniques meet all these requirements with the exception of functional imaging. CT is perhaps most limited, offering only organ imaging and functional data, but it remains invaluable for the evaluation of morphology.

Looking at the limitations and advantages of the different techniques, it is interesting to consider how different modalities can be used in combination. The fate of cells implanted in vivo could be monitored by microPET, bioluminescence, or MRI. Nuclear medicine and optical imaging could both help target areas of angiogenesis. But CT, MRI, ultrasound, and nuclear medicine could all provide information on angiogenic flow, permeability, and distribution.

For instance, researchers from the University of Paris V are using a variety of animal imaging techniques to develop specific quantitative methods for early evaluation and new anticancer therapies such as antiangiogenic drugs.

The first step in setting up a small animal imaging facility is to develop a research program. Second, you must recruit a multidisciplinary faculty and adopt a multimodality imaging approach. Then, manage the program in terms of its individual strengths, weaknesses, and opportunities.

PROF. FRIJA is secretary-general of the French Society of Radiology (SFR), secretary-general of the European Society of Radiology, and head of the radiology department at European Hospital Georges Pompidou in Paris. This column is based on his presentation at ECR 2006.