PET imaging isn't the only alternative for pre-clinical tests. Biophotonic imaging is similar to PET scanning in its ability to streamline animal testing. Instead of tiny radioactively tagged drugs, though, it uses a charge coupled device camera (CCD) to track agents that have been tagged with a bioluminescent protein from, for instance, a firefly that emits light, according to Pam Contag, president and co-CEO of imaging company Xenogen.

"We believe that animal [studies] at the molecular level will yield more predictive data about the drugs that [companies] are considering putting into the market," says Contag.

Pharmaceutical companies can use imaging to more quickly identify drugs that would fail in clinical evaluations, Contag says, which can save millions of research dollars. "Fail fast and fail early," Contag says, adding that companies may test up to 100 variations of a drug before coming out with a product.

Despite the potential advantages of imaging technology, though, Contag says pharmaceutical companies continue to use conventional animal-testing processes, because to move a new drug through the approval process, they must provide data to the Food and Drug Administration (FDA) that is based upon more than one testing and measurement method.

And the drug companies believe that if they rapidly adopt imaging methodologies, they will be required by regulatory agencies such as the FDA to perform new imaging experiments in addition to the current animal tests, according to Jarrod Bailey, a project development coordinator at the University of Newcastle and a member of the Physicians Committee for Responsible Medicine.

While that challenge -- searching for more cost-effective and ethical testing methods while also satisfying the FDA -- has proven to be a difficult one for pharmaceutical companies, they are experimenting with imaging processes.

Hong Zhang, a research scientist at Vertex Pharmaceuticals, says conducting experiments with Xenogen's imaging technology can reduce the number of animals used by 75 percent and yield more accurate results about whether a particular drug is reaching its intended target. Zhang says that imaging "allows us to dynamically follow an animal and study the progression of a disease from 24 to 48 to 72 hours."

However, Vertex continues to use invasive surgical procedures that require destroying animal subjects in order to conduct traditional experiments, particularly those that measure one point in time, as opposed to experiments that track drug tests over an extended period.

"The sensitivity [of measuring through imaging] is limited compared to traditional techniques," Zhang says.

In the near future, though, Bailey, along with many other researchers, believes that imaging technologies will become a more effective --and humane -- tool for early-stage drug trials.

"PET scanning is exactly what the doctor ordered," says Bailey.