Positronium (Ps), a hydrogen-like atom consisting of a positron and an electron, is efficiently formed in the human body during positron emission tomography (PET) examination, and its decay rate into gamma-ray photons is significantly influenced by the chemical environment, especially the dissolved oxygen concentration (pO₂) due to the unpaired electrons. However, the functionality of PET has been underestimated by neglecting the specific information provided by Ps. By comparing the decay rates in O₂-, N₂-, and air-saturated waters, here we show that Ps probes the absolute value of pO₂ with a good linearity and a resolution better than 10 mmHg. This is a sufficient sensitivity for discriminating a hypoxic region in a tumor at approximately 6 mmHg from healthy tissues at approximately 40 mmHg. This method depends only on the fundamental properties of Ps and is independent of specific radiopharmaceuticals. The applications of Ps spin states and reactions will greatly enhance PET functionalities in the next decade.

正电子（Ps）是由正电子和电子组成的类氢原子，在正电子发射断层扫描（PET）检查过程中会在人体中有效形成，其对伽马射线光子的衰减速率受化学环境的影响很大，特别是由于未成对电子而产生的溶解氧浓度（pO ₂）。但是，由于忽略了Ps提供的特定信息，因此低估了PET的功能。通过比较O _2-，N _2-和空气饱和水的衰减速率，我们在这里表明Ps探测pO ₂的绝对值具有良好的线性度和优于10 mmHg的分辨率。这对于区分大约6 mmHg的肿瘤中的低氧区域与大约40 mmHg的健康组织具有足够的敏感性。该方法仅取决于Ps的基本特性，并且与特定的放射性药物无关。在未来十年中，Ps自旋态和反应的应用将大大增强PET的功能性。