Optical Luminescence Imaging Could Lead to More Cost-Effective Radiotracers

Dr. Grimm explained that his group's work, along with current work from groups at the University of California Davis (USA; Simon Cherry, Ph.D.) and Stanford University (Stanford, CA, USA; Sanjiv Sam Gambhir, M.D., Ph.D.), may open a new avenue for optical imaging to move into the clinic.

When light travels through water, its speed decreases. A particle that moves faster than light produces a shock wave (much like the sonic boom that broke the sound barrier), which emits a visible blue light known as Cherenkov radiation. The researchers reported that their study is among the first to investigate Cherenkov radiation's applications for medical imaging using optical imaging techniques.

Optical imaging is a molecular imaging procedure in which light-producing molecules designed to attach to specific cells or molecules are injected into the bloodstream and then detected by an optical imaging device. It typically requires either excitation by an external light source or by a biologic process. Cherenkov imaging produces the light from the radioactivity, so no external illumination is needed. Combining optical imaging with nuclear medicine presents a new path for imaging medical isotopes, according to Dr. Grimm said. "It provides optical imaging with an array of approved nuclear tracers already in clinical use today, which can be used immediately, as opposed to fluorescent dyes," he added.

For the study, researchers evaluated several radionuclides for potential use with CLI. Researchers used CLI and positron emission tomography (PET) imaging to visualize tumor-bearing mice. The results show that CLI visualizes radiotracer uptake in vivo. The resulting decrease of light over time correlates with the radioactive decay of the injected tracer.

An added benefit of this technique is its ability to image radionuclides that do not emit either positrons or gamma rays--a current limitation for nuclear imaging modalities. CLI brings to light isotopes that could not be visualized previously. Moreover, optical imaging techniques show potential for endoscopy and surgery applications because of the ability to visualize tumor lesions, which could provide real-time data to surgeons and help guide procedures.

"The benefits of optical imaging are numerous, and we're on a path to realizing them," concluded Dr. Grimm. "We are optimistic that these new techniques will one day be available to physicians as another tool for the diagnosis and treatment of disease.

The study was published in the July 2010 issue of the Journal of Nuclear Medicine (JNM).

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