JNM: Optical imaging technique sheds light on medical isotopes
An optical imaging technique, Cerenkov luminescence imaging (CLI), shows excellent promise as a potential new method for rapid, high-throughput screening of radiopharmaceuticals, said a study published in the July issue of the Journal of Nuclear Medicine.

Noting that the combination of nuclear tomography with optical techniques has yet to be established, the use of the inherent optical emissions from the decay of radiopharmaceuticals for CLI of tumors in vivo was reported by Alessandro Ruggiero, MD, of the nuclear medicine service at the department of radiology at Memorial Sloan-Kettering Cancer Center in New York City, and colleagues, who correlated these results with those obtained from supportive immuno-PET studies.

The researchers evaluated visible light emission observed from several radionuclides, including the positron emitters 18F, 64Cu, 89Zr and 124I; b-emitter 131I; and a-particle emitter 225Ac for potential use in CLI. CLI was used with PET imaging to visualize immune-deficient, tumor-bearing mice.

The combination of optical imaging with nuclear medicine may offer a new path for imaging medical isotopes, the authors noted, and may provide optical imaging with “an array of approved nuclear tracers already in clinical use today, which can be used immediately, as opposed to fluorescent dyes."

The researchers found that Cerenkov radiation can be observed from a range of positron-b- and a-emitting radionuclides using standard optical imaging devices. The change in light emission intensity vs. time was determined to correlate with radionuclide decay and was also found to correlate linearly with the activity concentration and the measured PET signal in vivo.

In the mice, tumor-specific radiotracer uptake could be visualized by both immuno-PET and CLI. “Optical and immuno-PET signal intensities were found to increase over time from 24 to 96 hours, and biodistribution studies were found to correlate well with both imaging modalities,” wrote the authors.

CLI’s ability to image radionuclides that do not emit either positrons or gamma rays is valuable, noted Ruggiero, as this is a current limitation for nuclear imaging modalities. “These results pave the way for further use and development of CLI as a novel optical imaging modality for the rapid, cost effective, high-throughput screening of radiopharmaceuticals,” he said.
In addition, the authors noted that this optical imaging technique may be beneficial for endoscopy and surgical procedures because of the ability to visualize tumor lesions, which could provide real-time information and guide surgeons.

Studies involving the utilization of Cerenkov radiation emitted by various radionuclides are currently underway at the cancer center.