Positron autoradiography for intravascular vulnerable plaque imaging

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Purpose: To develop and investigate an intravascular storage phosphor detector for imaging and detection of vulnerable coronary artery plaques. Methods: The concept of the detection of vulnerable plaques (i.e., plaques with inflammation) is based on accumulation of fluorodeoxyglucose (FDG) in inflammation sites. The FDG is labeled with a radioactive isotope 18F (positron source), injected to patient, and accumulated in vulnerable plaques of coronary arteries. The radiation detector is then inserted into coronary artery, records positrons from FDG accumulated in vulnerable plaque, which allows for imaging and detection of the vulnerable plaque. A prototype detector was developed and tested. The detector consisted of a storage phosphor tip, light diffuser, optical fiber, and a thin plastic cover sheet. The detector is flexible, and has 2 mm diameter and 5 cm length. The detector was tested using realistic heart phantom with simulated vulnerable coronary artery plaques. The activities in simulated blood, heart tissue, and vulnerable plaques were matched to those expected in human anatomy. Since the storage phosphor detector is inserted into the coronary artery via x-ray fluoroscopy, the signal gathered from x-rays during the insertion process must be erased. Erasing was performed with a red laser light diffuser inserted into phosphor tip. Results: The coronary artery plaques with 0.54 nCi mm-2 and 1.75 nCi mm-2 activities were reliably imaged with storage phosphor detector. The plaque with 0.18 nCi mm-2 activity was difficult to visualize over the noisy background. Literature reports that human vulnerable plaques are expected to have average area activities of 40 nCi mm-2. Therefore, our detector can image plaques with activities by a factor of 20-70 lower than required. Conclusion: The detector developed under this project can detect vulnerable plaques of human coronary artery. However, the detector is a research prototype and currently is not suitable for in-vivo experiments. More efforts are needed to optimize its design for in-vivo applications.