Expert Highlights Clinical Significance of Molecular Imaging

Neurodegeneration, coronary artery disease, and cancer are key areas in which molecular imaging could have a significant clinical impact, a keynote speaker said during an address at World Molecular Imaging Congress in September.

Molecular imaging research is benefiting enormously from the energy of a relatively young, enthusiastic workforce, according to Dr. Markus Schwaiger, director of the nuclear medicine department at the Technical University of Munich in Germany.

The clinical community should be aware of the scale of research activity, said Schwaiger, who presented the inaugural lecture at WMIC 2008, held in Nice, France. His message to scientists was to concentrate on agents that relate to actual disease processes.

“It is important to develop new imaging probes that have a specific biological meaning, but in the end, they have to be representative of the disease process to be clinically useful,” he said. “What we need is for imaging sciences to lead to optimal imaging services.”

Schwaiger highlighted three areas in which molecular imaging could make a real clinical impact: neurodegeneration, coronary artery disease, and cancer. Imaging could, for example, make it easier to differentiate Alzheimer’s disease from other forms of dementia. PET (Positron Emission Tomography) probes that home in on amyloid plaques in the brain are being investigated for this purpose.

Identification of patients at risk of heart attack is another area where novel imaging probes could be of value. Schwaiger showed an example of a fluorine-18-labeled myocardial perfusion tracer and the results of myocardial viability PET imaging with nitrogen-13 ammonia and F-18 FDG.

One key area for cancer management is metabolic imaging. FDG-PET is widely used for this application already. An analysis of almost 23,000 studies from over 1170 centers has revealed that this strategy allowed biopsies to be avoided in 70% of cases.

“With the advent of targeted therapy, there is also a great need to have imaging techniques that allow you to visualize the target,” he said. “For example, if you have a drug designed to target HER2 receptors on cancer cells, then you would like to see if the patient is expressing this protein.”

The bench to bedside journey for an imaging probe typically takes eight to 10 years and costs between $100 million and $200 million. Schwaiger listed more than 20 agents that are partway through this process and undergoing preclinical or clinical trials. These included indium-111-labeled Herceptin, F-18 fluorothymidine (FLT), and technetium-99m EC20 (FolateScan).

The sheer cost of the transition process makes it impossible to investigate all promising imaging probes at the same time. The imaging community should work closely with researchers to set priorities and help find funding for the approvals process, Schwaiger said.

“It is good to have many probes under development, but in the end you have to be selective,” he said. “There are large regulatory hurdles that need to be addressed before these agents can get into the clinical arena.”

Schwaiger also discussed the growing importance of a multimodality approach in molecular imaging. The first PET/MR (Positron Emission/Magnetic Resonance) system for brain imaging is currently being tested on patients at the University of Tübingen in Germany. Emerging optical techniques that have greater imaging depth are being considered as candidates for hybrid imaging systems as well. Combinations under investigation include optical/ultrasound and optical/CT (Computed Tomography — CAT Scan).

“This is a clear message that came out of the Nice meeting,” he said. “All people involved in method development are trying to combine the strengths of the various modalities in multimodality instrumentation.”

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