A new method for the detection of ionizing radiation with the potential to improve the coincidence time resolution in positron emission tomography (PET) was investigated. This method is based on Pockels effect (i.e., linear electro-optic modulation effect) and pump-probe measurement with cadmium telluride (CdTe) and lithium niobate (LiNbO3). In this work, the performance of the two detector materials were compared experimentally. CdTe detector material demonstrated a repeatable change in modulation signal level after laser diode illumination, while LiNbO3 crystal gave no response to laser diode as the radiation source, suggesting the shorter carrier lifetime and lower carrier mobility found of LiNbO3 material. The modulation signal induced by 511 KeV photons in LiNbO3 and CdTe both can be detected through the new method. We found that the CdTe crystal could provide a higher sensitivity to 511 KeV photons than the LiNbO3 crystal under the same bias voltage. In addition, the amplitude of modulation signal increased linearly with the bias voltage before saturation. The modulation signal strength in LiNbO3 crystal was continued to increase after 2200 V due to its high resistivity which could reduce the dark current in detector and thus reduce the noise level during experiment, while the modulation signal of CdTe with low resistivity tended to be saturated at the bias voltage of higher than 1400 V. Therefore, further increasing the bias voltage for both detector crystals may hypothetically enhance the modulation strength and detection sensitivity of PET.
Yuli Wang, Zehao Li, and Jianfeng Xu, "Investigation of Pockels effect in optical property modulation-based radiation detection method for positron emission tomography," Proc. SPIE 10953, Medical Imaging 2019: Biomedical Applications in Molecular, Structural, and Functional Imaging, 1095306 (Presented at SPIE Medical Imaging: February 19, 2019; Published: 19 March 2019); https://doi.org/10.1117/12.2512015.
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