Bismuth Organic Liquid Detector with Cherenkov Light and Charge Readout for Positron Emission Tomography

BOLD-PET项目的目标是基于最近使用液体三甲基铋（TMBi）的发展，开发一种快速响应，具有细粒度空间分辨率的高效伽马探测器，用于正电子发射断层扫描（PET）。这种铋质量分数超过80%的液体可以非常有效和准确地探测到来自正电子湮灭的511 keV光子。铋具有最高的核电荷（Z = 83），因此在所有稳定同位素中光电截面最大。在近50%的情况下，511kev的伽马能量通过光电效应转移到该材料中的电子上。由此产生的相对论光电子发出的切伦科夫光和在多次散射相互作用中产生的二次电荷载流子都在液体电离室中被检测到，并辅以光电探测器。基于以往对液体TMBi的研究，我们打算在四个研究伙伴的共同努力下，开发并评估一种同时检测切伦科夫光和电离的新型PET探测器。通过消除相互作用深度效应，同时允许将探测器放置在靠近物体的位置，从而增加探测器的立体角，预计该探测器将具有出色的成像分辨率。TMBi的符合光电效率最高，是LSO/LYSO晶体的两倍。新型探测器应能够通过切伦科夫光检测获得精确的飞行时间信息，以提高重建图像的对比度。为了在这个具有挑战性的项目中取得突破，现有的法国CaLIPSO小组（CEA-IRFU, CNRS-LAL）的专业知识将由高分辨率PET成像和探测器开发（WWU-EIMI小组）以及超纯化以及光和电荷探测器读数（WWU-PHYSICS小组）的专业知识补充。本合作项目的主要目标是开发一种新型的PET成像探测器系统（如人脑PET、小动物PET），投射效率为30%，空间精度为1mm^3，飞行时间分辨率为100 ps （FWHM）。为了实现这些目标，该项目将集中在以下工作领域：(1)TMBi的超纯化和进一步表征TMBi用于伽马辐射探测，(2)电离探测器原型的开发，(3)研究液体TMBi中的切伦科夫光子探测，(4)采用新技术的全PET扫描仪的蒙特卡罗模拟和图像重建，以及(5)评估最终的PET探测演示器，合并电荷和光学读数。

The aim of the BOLD-PET project is to develop a fast-response, high-efficiency gamma detector with fine grained spatial resolution for positron emission tomography (PET) based on recent developments using the liquid TriMethyl Bismuth (TMBi).This liquid with a bismuth mass fraction of more than 80% allows for a very efficient and accurate detection of 511 keV photons originated from positron annihilation. Bismuth has the highest nuclear charge (Z = 83) and thus the largest photoelectric cross section of all stable isotopes. The gamma energy of 511 keV is transferred to electrons in this material in nearly 50 % of the cases through the photoelectric effect. Both the Cherenkov light emitted by the resulting relativistic photo-electron and the secondary charge carriers produced during multiple scattering interactions are detected in a liquid ionisation chamber, supplemented by photodetectors. Based on previous studies of liquid TMBi, we intend to develop and evaluate a novel PET detector with simultaneous detection of Cherenkov light and ionisation in a common effort of four research partners. Excellent imaging resolution is anticipated with the proposed detector by cancelling out Depth Of Interaction effects while allowing for placement of the detector close to the body which is increasing the detector’s solid angle. The TMBi’s coincidence photoelectric efficiency is the highest available, with twice the value of LSO/LYSO crystals. The new detector should be able to use accurate time-of-flight (TOF) information through Cherenkov light detection in order to improve the contrast of the reconstructed image. To achieve a breakthrough in this challenging project, the expertise of the existing French CaLIPSO group (CEA-IRFU, CNRS-LAL) will be supplemented by the expertise on high-resolution PET imaging and detector development (WWU-EIMI group), and ultra-purification as well as light and charge detector readout (WWU-PHYSICS group), both from University of Münster. The main objective of this collaborative project is to develop a novel detector system for PET imaging (e.g. human brain PET, small animal PET) with a projected efficiency of 30%, high spatial precision of 1mm^3, and high time of flight resolution of 100 ps (FWHM). In order to achieve these objectives the project will focus on the following work areas: (1) ultra-purification of TMBi and further characterisation of TMBi for gamma radiation detection, (2) development of an ionisation detector prototype, (3) study of the Cherenkov photon detection in liquid TMBi, (4) Monte Carlo simulation and image reconstruction of a full PET scanner employing the new technology, and (5) evaluation of a final PET detection demonstrator, merging charge and optical readout.