Study of material properties important for an optical property modulation-based radiation detection method for positron emission tomography

Recent work shows that Pockels effect and optics pump-probe measurement could be utilized as a novel method for 511 keV ionizing radiation photon detection for positron emission tomography (PET) which could potentially overcome the inherent physical limitation for coincidence time resolution of around 100 ps (Tao et al 2016 Phys. Med. Biol. 61 7600-22). In this paper, we embrace this observation and introduce a two-crossed-polarizers based setup to achieve similar detection concept, which is a simpler and more compact setup with comparable ionizing radiation detection capability as the setup used in the previously proposed work. We evaluated the performance of our experimental setup with Lithium Niobate (LiNbO 3 ) and Cadmium Telluride (CdTe) detector crystals, and the desired properties of an ideal detector crystal were discussed. The modulation signal induced by 511 keV photons in both LiNbO 3 and CdTe can be detected with repeatable signal amplitude using two-crossed-polarizers based method, while CdTe could provide eight times higher detection sensitivity to 511 keV photons than LiNbO 3 under the same bias voltage, suggesting high effective Z number and high density properties of CdTe, as well as a shorter carrier lifetime and lower carrier mobility of LiNbO 3 . In addition, the strength of modulation signal increased linearly with bias voltage before saturation. The modulation signal strength in LiNbO 3 continued to increase after 2000 V due to its high resistivity which could reduce the dark current in the detector, while the modulation signal of CdTe with low resistivity tended to be saturated at a bias voltage higher than 1200 V. Therefore, further increasing the bias voltage for detector crystals (especially for LiNbO 3 ) may enhance the modulation strength and improve the detection sensitivity for annihilation photons.

Section: Results With Radionuclide Source As Ionizing Radiationsupporting

confidence: 73%

Two-crossed-polarizers based optical property modulation method for ionizing radiation detection for positron emission tomography

Wang¹,

Li²,

Yi³

et al. 2019

“…Recently, researchers have also been investigating the potential for improving CTR by exploiting prompt emissions such as hot intra-band luminescence, Cherenkov yield from the primary photoelectron, or other methods that exploit sub-ps optical phenomena [Lecoq et al 2014, Gundacker et al 2016b, Dolenec 2013, Kwon et al 2016, Brunner et al 2017, Tao et al 2016, Tao et al 2017]. The ultimate goal of efforts to develop TOF-PET detectors with the ability to localize 511 keV photon interactions along LORs with an accuracy that approaches the spatial resolution limits dictated by positron range, 511 keV photon accolinearity, and detector element width [Levin et al 1999].…”

Section: Materials and Experimental Methodsmentioning

confidence: 99%

Evaluation of a clinical TOF-PET detector design that achieves ⩽100 ps coincidence time resolution

Cates

Levin

2018

Commercially available clinical positron emission tomography (PET) detectors employ scintillation crystals that are long (≥20 mm length) and narrow (4–5 mm width) optically coupled on their narrow end to a photosensor. The aspect ratio of this traditional crystal rod configuration and 511 keV photon attenuation properties yield significant variances in scintillation light collection efficiency and transit time to the photodetector, due to variations in the 511 keV photon interaction depth in the crystal. These variances contribute significant to coincidence time resolution degradation. If instead, crystals are coupled to a photosensor on their long side, near-complete light collection efficiency can be achieved, and scintillation photon transit time jitter is reduced. In this work, we compare the achievable coincidence time resolution (CTR) of LGSO:Ce(0.025 mol%) crystals 3–20 mm in length when optically coupled to silicon photomultipliers (SiPMs) on either their short end or long side face. In this “side readout” configuration, a CTR of 102±2 ps FWHM was measured with 2.9×.2.9×20 mm3 crystals coupled to rows of 3×3 mm2 SensL-J SiPMs using leading edge time pickoff and a single timing channel. This is in contrast to a CTR of 137±3 ps FWHM when the same crystals were coupled to single 3×3 mm2 SiPMs on their narrow ends. We further study the statistical limit on CTR using side readout via the Cramér-Rao lower bound (CRLB), with consideration given to ongoing work to further improve photosensor technologies and exploit fast phenomena to ultimately achieve 10 ps FWHM CTR. Potential design aspects of scalable front-end signal processing readout electronics using this side readout configuration are discussed. Altogether, we demonstrate that the side readout configuration offers an immediate solution for 100 ps CTR clinical PET detectors and mitigates factors prohibiting future efforts to achieve 10 ps FWHM CTR.

“…To achieve sub-10 ps time resolution, efforts have been made in using scintillator crystals as detector materials (Cates and Levin 2016. As another way to achieve ionization radiation detection that shows promise to significantly improve the CTR, a new detection method was proposed that utilizes optical property modulation (Tao et al 2016(Tao et al , 2017(Tao et al , 2020. Previously, an optical pump-probe concept was used to implement a setup with two crossed polarizers for the detection of ionizing radiation (Wang et al 2019a).…”

Section: Introductionmentioning

confidence: 99%

Further investigations of a radiation detector based on ionization-induced modulation of optical polarization

Wang¹,

Tao²,

Abbaszadeh³

et al. 2021

Self Cite

Optical property modulation induced by ionizing radiation is a promising approach for ultra-fast, lower time jitter detection of photon arrival time. If successful, this method can be utilized in time-of-flight positron emission tomography to achieve a coincidence time resolution approaching 10 ps. In this work, the optical property modulation based method is further developed with focus on a detection setup based on two crossed polarizers. Previous work demonstrated that such an optical setup could be utilized in radiation detection, though its detection sensitivity needed improvement. This work investigates the angle between polarizers and electric field distribution within the detection crystal to understand and improve the detection sensitivity of an optical polarization modulation based method. For this work, cadmium telluride (CdTe) was studied as the detector crystal . The ‘magic’ angle (i.e. optimal working angle) of the two crossed polarizers based optical setup with CdTe were explored theoretically and experimentally. The experimental results show that the detection sensitivity could be improved by around 10% by determining the appropriate ‘magic’ angle. We then studied the dependence of detection sensitivity on electric field distribution as well as on the bias voltage across the detector crystal using CdTe crystals. The experimental results show that a smaller electrode on the detector crystal, or a more concentrated electric field distribution could improve detection sensitivity. For CdTe, a detector crystal sample with 2.5 mm × 2.5 mm square electrode has twice the detection sensitivity of a detector crystal with 5 mm × 5 mm square electrode. Increasing the bias voltage before saturation for CdTe could further enhance the modulation strength and thus, the sensitivity. Our investigations demonstrated that by determining the proper working angle of polarizers and bias electrical distribution to the detector, we could improve the sensitivity of the proposed optical setup.