Abstract
Purpose: A new imaging modality Cherenkov-excited luminescence scanned imaging (CELSI) is demonstrated illustrating that LINAC beams induce Cherenkov emission within tissue, and that in-turn can excite luminescence of optical probes. This is achieved in a highly spatially confined fashion thereby allowing scanned imaging of distributions of luminescent sources. Methods: A 5 mm thick line-excitation megavoltage X-ray beam (6 MV) was collimated and moved by the multi-leaf collimator (MLC) of a linear accelerator (LINAC), to scan in 3 orthogonal directions. The scan in this demonstration was through a rat abdomen for lymph node imaging. The node was injected with oxygen-sensitive phosphor (Oxyphor PtG4), having strong luminescence lifetime, which is sensitive to the local oxygen concentration. During the scanning, Cherenkov-excited luminescence was continuously integrated by an intensified charge-coupled device (ICCD) synchronized to radiation pulses, and the position of the total signal was back-projected to the position of the scanning beam. Results: The lymph node was accurately located in the axillary region by CELSI imaging. Through lifetime measurement of the luminescence signal from within the lymph node, the pO2 was found to be reporting the true oxygenation level. Phantom studies validated that an inclusion with size below 1 mm could be reconstructed through a layer of 20 mm thick tissue equivalent phantom material. Concentrations of PtG4 down to 100 nM were detectable and capillary tubes containing the probe with diameters down to 200 µm could be resolved by CELSI, at 5 mm depth in tissue equivalent phantoms. Conclusion: CELSI is reported here for the first time, as an innovative optical molecular imaging technique by utilizing the LINAC as an optical scanning and excitation device. Potential applications of CELSI include reconstructions of interested optical probes and recoveries of local physiological information with relatively high spatial resolution.
Published Version
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