High-Resolution Radioluminescence Microscopy of ¹⁸F-FDG Uptake by Reconstructing the β-Ionization Track

Abstract

Radioluminescence microscopy is a new method for imaging radionuclide uptake by single live cells with a fluorescence microscope. Here, we report a particle-counting scheme that improves spatial resolution by overcoming the b-range limit. Methods: Short frames (10 ms21 s) were acquired using a high-gain camera coupled to a microscope to capture individual ionization tracks. Optical reconstruction of the b-ionization track (ORBIT) was performed to localize individual b decays, which were aggregated into a composite image. The new approach was evaluated by imaging the uptake of 18 F-FDG in nonconfluent breast cancer cells. Results: After image reconstruction, ORBIT resulted in better definition of individual cells. This effect was particularly noticeable in small clusters (2-4 cells), which occur naturally even for nonconfluent cell cultures. The annihilation and Bremsstrahlung photon background signal was markedly lower. Single-cell measurements of 18 F-FDG uptake that were computed from ORBIT images more closely matched the uptake of the fluorescent glucose analog (Pearson correlation coefficient, 0.54 vs. 0.44, respectively). Conclusion: ORBIT can image the uptake of a radiotracer in living cells with spatial resolution better than the b range. In principle, ORBIT may also allow for greater quantitative accuracy because the decay rate is measured more directly, with no dependency on the b-particle energy.Key Words: radionuclide imaging instrumentation; single-cell analysis; microscopy; autoradiography Nucl Med 2013; 54:1841 54: -1846 54: DOI: 10.2967 Aut oradiography is a well-established method for high-resolution imaging of radionuclide probes in tissues. Film and emulsion methods have the highest spatial resolution but poor sensitivity, dynamic range, and quantitative accuracy and require tedious sample preparation (1,2). Other autoradiography methods (e.g., storage phosphor (3), solid-state detection (4,5), gaseous detectors (6), and thin phosphor (7)) have higher sensitivity and dynamic range but spatial resolution worse than 50 mm. Only a few methods have demonstrated the ability to visualize the uptake of radionuclide probes with single-cell resolution. One of these methods uses a bsensitive avalanche photodiode to measure radionuclide uptake in small groups of cells, cultured in 16 microfluidic chambers (8). An experiment showed that the avalanche photodiode could measure signal from a single cell in the chamber. Another device, the MicroImager, achieved 15-mm spatial resolution for 35 S, which was used to detect in situ hybridization in single neurons (9). A third device, the radioluminescence microscope, was developed to visualize radionuclide uptake in live cells during fluorescence microscopy (10). Radioluminescence microscopy can be used to measure fluorescent and radionuclide signals emanating from a collection of living cells, in a relatively short time. Here we propose a new particlecounting scheme for radioluminescence microscopy with higher spatial resolution and, in principle, quantitative ...

Cherenkov luminescence imaging in transparent media and the imaging of thin or shallow sources

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A Continuously Infused Microfluidic Radioassay System for the Characterization of Cellular Pharmacokinetics

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