Mehrdel Baharak, Kratochwil Nicolaus, Seo Youngho, Glodo Jarek, Bhattacharya Pijush, Ariño-Estrada Gerard, Caravaca Javier
Department of Radiology and Biomedical imaging, University of California San Francisco, San Francisco, CA, 94107, USA.
Department of Biomedical Engineering, University of California at Davis, Davis, CA, 95616, USA.
Sci Rep. 2025 May 28;15(1):18731. doi: 10.1038/s41598-025-01396-2.
The Cherenkov emission in inorganic crystal scintillators has been shown to dramatically improve time resolution for time-of-flight positron emission tomography (TOF-PET) for in slow scintillators with a high refractive index such as bismuth germanium oxide (BGO). This is due to the faster nature of the Cherenkov emission (tens of picoseconds) with respect to scintillation (nanosecond). However, the presence of slower scintillation light and the inability of existing detectors to distinguish between Cherenkov and scintillation make it difficult for BGO to achieve a good CTR for all the detected coincidence events. In this paper, we exploit the difference between the Cherenkov and scintillation emission spectra and use dichroic filters to enhance the Cherenkov over scintillation ratio. Dichroic filters transmit or reflect photons based on their wavelength, with a photon attenuation lower than 10%. We investigate several shortpass and longpass dichroic filters in a single-photon configuration with BGO and find the optimal filter that maximizes the Cherenkov over scintillation ratio. We demonstrate that we can enhance the ratio of Cherenkov to scintillation photons by a factor of 2.17 ± 0.38 by employing a shortpass dichroic filter with a cut-off wavelength of 450 nm for BGO, and by a factor of 2.87 ± 0.40 using a longpass dichroic filter with a cut-on wavelength of 550 nm for iodine/beryllium-doped thallium chloride.
无机晶体闪烁体中的切伦科夫发射已被证明能显著提高慢闪烁体（如锗酸铋（BGO），其具有高折射率）的飞行时间正电子发射断层扫描（TOF-PET）的时间分辨率。这是因为切伦科夫发射（几十皮秒）相对于闪烁（纳秒）具有更快的特性。然而，较慢的闪烁光的存在以及现有探测器无法区分切伦科夫光和闪烁光，使得BGO难以对所有检测到的符合事件实现良好的康普顿抑制比（CTR）。在本文中，我们利用切伦科夫发射光谱和闪烁发射光谱之间的差异，并使用二向色滤光片来提高切伦科夫光与闪烁光的比例。二向色滤光片根据光子的波长透射或反射光子，光子衰减低于10%。我们在与BGO的单光子配置中研究了几种短波和长波二向色滤光片，并找到了使切伦科夫光与闪烁光比例最大化的最佳滤光片。我们证明，对于BGO，通过采用截止波长为450 nm的短波二向色滤光片，我们可以将切伦科夫光子与闪烁光子的比例提高2.17±0.38倍；对于碘/铍掺杂的氯化铊，通过使用截止波长为550 nm的长波二向色滤光片，该比例可提高2.87±0.40倍。
