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Published June 7, 2013 | Accepted Version
Journal Article Open

Betabox: a beta particle imaging system based on a position sensitive avalanche photodiode


A beta camera has been developed that allows planar imaging of the spatial and temporal distribution of beta particles using a 14 × 14 mm^2 position sensitive avalanche photodiode (PSAPD). This camera system, which we call Betabox, can be directly coupled to microfluidic chips designed for cell incubation or other biological applications. Betabox allows for imaging the cellular uptake of molecular imaging probes labeled with charged particle emitters such as ^(18)F inside these chips. In this work, we investigate the quantitative imaging capabilities of Betabox for ^(18)F beta particles, in terms of background rate, efficiency, spatial resolution, and count rate. Measurements of background and spatial resolution are considered both at room temperature (21 °C ± 1 °C) and at an elevated operating temperature (37 °C ± 1 °C), as is often required for biological assays. The background rate measured with a 4 keV energy cutoff is below 2 cph mm^(−2) at both 21 and 37 °C. The absolute efficiency of Betabox for the detection of ^(18)F positron sources in contact with a PSAPD with the surface passivated from ambient light and damage is 46% ± 1%. The lower detection limit is estimated using the Rose Criterion to be 0.2 cps mm^(−2) for 1 min acquisitions and a 62 × 62 µm^2 pixel size. The upper detection limit is approximately 21 000 cps. The spatial resolution at both 21 and 37 °C ranges from 0.4 mm FWHM at the center of the field of view (FOV), and degrades to 1 mm at a distance of 5 mm away from center yielding a useful FOV of approximately 10 × 10 mm^2. We also investigate the effects on spatial resolution and sensitivity that result from the use of a polymer based microfluidic chip. For these studies we place varying layers of low-density polyethylene (LDPE) between the detector and the source and find that the spatial resolution degrades by ~180 µm for every 100 µm of LDPE film. Sensitivity is reduced by half with the inclusion of ~200 µm of additional LDPE film. Lastly, we demonstrate the practical utilization of Betabox, with an imaging test of its linearity, when coupled to a polydimethylsiloxane microfluidic chip designed for cell based assays.

Additional Information

© 2013 Institute of Physics and Engineering in Medicine. Received 17 December 2012, in final form 6 April 2013. Published 8 May 2013. The authors would like to thank the staff of the Crump Imaging facility at UCLA including Waldemar Ladno, Darin Williams, and Jeff Collins for their assistance with obtaining ^(18)F solution for this study. The authors would also like to thank Hongkai Wang for valuable discussions on image distortion correction and David Prout for assistance on signal processing. Arion Chatziioannou and Nam Vu are coauthors of a patent owned by the University of California that includes the technology described in this work. This work was supported in part by the National Institutes of Health (R25CA098010 and U54CA119347), the Department of Energy (DE-SC0001249) and the UCLA Foundation from a donation made by Ralph and Marjorie Crump for the UCLA Crump Institute for Molecular Imaging.

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Accepted Version - nihms478901.pdf


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