Quantum dots have been used in a wide variety of biomedical applications. A key advantage of these particles is that
their optical properties depend predictably on size, which enables tuning of the emission wavelength. Recently, it was
found that CdSe/ZnS quantum dots lose their ability to photoluminescence after exposure to gamma radiation (J. Phys.
Chem. C., 113: 2580-2585 (2009). A method for readout of the loss of quantum dot photoluminescence during exposure
to radiation could enable a multitude of real-time dosimetry applications. Here, we report on a method to image
photoluminescence from quantum dots from a distance and under ambient lighting conditions. The approach was to
construct and test a time-gated imaging system that incorporated pulsed illumination. The system was constructed from a
pulsed green laser (Nd:YAG, 20 pulses/s, 5 ns pulse duration, ~5 mJ/pulse), a time-gated camera (LaVision Picostar, 2
ns gate width), and optical components to enable coaxial illumination and imaging. Using the system to image samples
of equivalent concentration to the previous end-point work, quantum dot photoluminescence was measureable under
ambient room lighting at a distance of 25 cm from the sample with a signal to background of 7.5:1. Continuous exposure
of samples to pulsed laser produced no measureable loss of photoluminescence over a time period of one hour. With
improvements to the light collection optics the range of the system is expected to increase to several metres, which will
enable imaging of samples during exposure to a gamma radiation source.
Photoacoustic imaging is a hybrid imaging modality capable of producing contrast similar to optical
imaging techniques but with increased penetration depth and resolution in turbid media by encoding the information
as acoustic waves. In general, it is important to characterize system performance by parameters such as sensitivity,
resolution, and contrast. However, system characterization can extend beyond these metrics by implementing
advanced analysis via singular value decomposition. A method was developed to experimentally measure a matrix
that represented the imaging operator for the system. Analysis of the imaging operator was done via singular value
decomposition so that the capability of the system to reconstruct objects and the inherent system sensitivity to those
objects could be understood. The results provided by singular value decomposition were compared to simulations
performed on an ideal system with matching transducer arrangement and defined object space.
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