Single-cell radioluminescence microscopy with two-fold higher sensitivity using dual scintillator configuration

Abstract

11Radioluminescence microscopy (RLM) is an imaging technique that allows quantitative analysis 12 of clinical radiolabeled drugs and probes in single cells. However, the modality suffers from slow 13 data acquisition (10 -15 minutes), thus critically affecting experiments with short-lived 14 radioactive drugs. To overcome this issue, we suggest an approach that significantly accelerates 15 data collection. Instead of using a single scintillator to image the decay of radioactive molecules, 16 we sandwiched the radiolabeled cells between two scintillators. As proof of concept, we imaged 17 cells labeled with [ 18 F]FDG, a radioactive glucose popularly used in oncology to image tumors. 18Results show that the double scintillator configuration increases the microscope sensitivity by two-19 fold, thus reducing the image acquisition time by half to achieve the same result as the single 20 scintillator approach. The experimental results were also compared with Geant4 Monte Carlo 21 simulation to confirm the two-fold increase in sensitivity with only minor degradation in spatial 2 22 resolution. Overall, these findings suggest that the double scintillator configuration can be used to 23 perform time-sensitive studies such as cell pharmacokinetics or cell uptake of short-lived 24 radiotracers. 25 26 157 Cell ROI are shown in Fig 3b for single and double scintillator configurations. As expected, 158 [ 18 F]FDG uptake demonstrated a heterogeneous behavior, with some cells taking up the radiotracer 159 3 -4 times more than other cells. Furthermore, the measured average cell uptake was increased by 160 two-fold when the second scintillator was added. The average uptake values were 407 ± 156 161 counts/cell for the double scintillator configuration and 200 ± 90 counts/cell for the single 162 scintillator case. Linear regression (dotted red line) of the two datasets found a linear relationship 163 between the two datasets, y = 1.59 x + 87.86 (r 2 > 0.83). 9 164 165 Fig 3. Graphs representing single vs. double scintillator results. Scatter plot of decay counts 166 detected in 90 μm ROI (N = 66) for (a) background devoid of cells and (b) areas containing single 167 cells. The solid blue line and dotted red lines represent the linear regression fit. 168 169 Spatial Resolution 170The spatial resolution of the single and dual scintillator cases was quantitatively assessed by 171 drawing a line profile across two radioactive cells (Fig 4a). The profile was normalized according 172 to the maximum count values for both configurations (Fig 4b). Results clearly show two peaks 173 separated by a valley, which correspond to two cells with [ 18 F]FDG uptake along the line profile. 174Furthermore, no qualitative discrepancies in peak, valley, and background values can be observed 175 between the two configurations. This simple comparison suggests that the sensitivity of RLM can 176 be increased without significant degradation in spatial resolution. 177 178 Fig 4. Radioactive decay profile of two closely positioned cells. (a) A profile is ...