15O-water

Oxygen-15 labeled water (15O-water) is a radioactive tracer used in positron emission tomography (PET) imaging to measure and quantify blood flow in various organs, particularly the heart, brain, and tumors. It's considered the gold standard for quantitative myocardial blood flow measurements due to its unique properties. ## Properties and Characteristics 15O-water is a radioactive variation of regular water where the oxygen atom has been replaced by oxygen-15, a positron-emitting isotope with a very short half-life of approximately 2.04 minutes[1][5]. This short half-life allows for multiple scans in rapid sequence with minimal radiation exposure to patients. The key advantages of 15O-water include: - **Free diffusibility**: Unlike other tracers, 15O-water diffuses freely across cell membranes[1] - **100% extraction rate**: This makes it superior to other tracers as no flow-dependent extraction corrections are required[1][5] - **Metabolically inert**: It doesn't undergo metabolic interactions in tissue[1] These properties make 15O-water particularly valuable for quantitative blood flow measurements, especially in myocardial perfusion imaging. ## Production and Administration 15O-water is produced using a cyclotron through the nuclear reaction 15N(p,n)15O[4]. The process involves: 1. Radiation of the 15O target with protons in an N2-15 gas area 2. Transport of the formed O2-15 gas to a module where it's mixed with N2/H2 3. Passing the gas mixture over a palladium pipe at 150°C 4. Collection of the formed 15O-H2O in a physiological salt solution For PET imaging, approximately 370-1850 MBq of 15O-water is administered as an intravenous injection[3][5]. The positron emitted during decay quickly annihilates with an electron, producing two gamma rays of about 511 keV that are detectable by a PET scanner[1]. ## Clinical Applications ### Cardiac Imaging 15O-water PET is considered the non-invasive gold standard for quantitative myocardial blood flow (MBF) studies[1][2]. It can: - Accurately detect hemodynamically significant coronary artery stenosis[2] - Provide prognostic information on mortality and risk of myocardial infarction[2] - Guide management decisions on revascularization[2] Compared to other PET tracers for MBF quantification (82Rb and 13NH3), 15O-water has superior properties due to its complete extraction and free diffusibility[1]. ### Oncology 15O-water PET can be used to measure tumor blood flow (TBF) with good reproducibility[3]. The technique has been extended from its traditional applications in neurology and cardiology to tumors throughout the body. Its short half-life allows multiple replicate studies during the same imaging session, making it a powerful tool for TBF quantification[3]. ### Other Applications 15O-water is also used for imaging blood flow in the greater circulation, including larger vessels, heart, and kidneys[4]. ## Regulatory Status Within the European Union, 15O-water is recognized as a radiopharmaceutical and regulated as a drug. A pharmacopeia monograph exists, allowing hospital facilities to produce and use 15O-water within their national legislation[1]. In the United States, 15O-water is recognized as a radiopharmaceutical and regulated as a drug, but no pharmacopeia monograph currently exists[1]. It is not approved by the US Food and Data Administration (FDA) or the Japanese Ministry of Health, Labour and Welfare for clinical use, limiting its use primarily to research settings[5]. ## Limitations Despite its advantages, 15O-water PET has some limitations: - Requires an on-site cyclotron due to the short half-life of 15O[5] - Less than ideal for visual assessment compared to other tracers[5] - Not widely available for routine clinical use due to regulatory constraints[1][5] Nevertheless, with advances in scanner technology and software, 15O-water PET continues to be a valuable tool for quantitative blood flow measurements in both clinical and research settings.

Other names

oxygen-15 labeled wateroxygen15 labeled wateroxygen 15 labeled water