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Water-18O for PET

Water-18O for PET


Introduction to PET and Cyclotron

Positron Emission Tomography (PET) is a nuclear medicine medical imaging technique where radioactive 'tracer' isotopes, which emit a positron, are injected into a living subject (usually blood circuit). After traveling less than one millimeter the positron annihilates with an electron, producing a pair of gamma ray photons in opposite directions. The technique depends on simultaneous or "coincidental" detection of this pair of photons. Photons which do not come in pairs (within a few nanoseconds) are ignored. By measuring where the gamma rays end up, their origin in the body can be plotted, allowing the chemical uptake or activity of certain part of the body to be determined. It is used heavily in clinical oncology (medical imaging of tumors and search for metastases) and in human brain and heart research.

PET scanning is invasive, in that radioactive material is injected into the subject/patient. However, the total dose of radiation is small, usually around 7 mSv. This can be compared to 2.2 mSv average annual background radiation in the UK, 0.02 mSv for a chest X-Ray, up to 8 mSv for a CT scan of the chest, 2-6 mSv per annum for aircrew, and 7.8 mSv per annum background exposure in Cornwall (Data from UK National Radiation Protection Board).

Alternative methods of scanning are single photon emission computerized tomography (SPECT), computed tomography (CT), magnetic resonance imaging (MRI) and functional magnetic resonance imaging (fMRI). The spatial and temporal resolution of images developed using PET may not be as good as with some of the other techniques.

However, while other imaging scans such as CT and MRI, isolate organic anatomical changes in the body, PET scanners are capable of detecting areas of molecular biology detail (even prior to anatomical change) via the use of radioisotopes that have different rates of uptake depending on the type of tissue involved. The changing of regional blood flow in various anatomical structures (as a measure of the injected positron emitter) can be visualized and relatively quantified with a PET scan.

Radionuclides used in PET scanning are typically isotopes with short half lives such as Carbon-11, Nitrogen-13, Oxygen-15, and Fluorine-18 (half-lives of 20 min, 10 min, 2 min, and 110 min resp.). Due to their short half-lives, the isotopes must be produced in a cyclotron at or near the site of the PET scanner. These isotopes are incorporated into compounds normally used by the body, such as glucose, water or ammonia, and then injected into the body to trace where they become distributed.

PET as a technique for scientific investigation is limited by the need for clearance by ethics committees to inject radioactive material into subjects, and also by the fact that it is not advisable to subject any one subject to too many scans. Furthermore, due to the high costs of cyclotrons needed to produce the short-lived radioisotopes for PET scanning, few hospitals and universities are capable of performing PET scans.

Applications of PET scanning

PET is a valuable technique for some diseases and disorders, because it is possible to target the radio-chemicals used for particular bodily functions.

  • Oncology
    PET scanning with the tracer (18F) fluorodeoxyglucose (FDG, FDG-PET) is widely used in clinical oncology. This tracer mimics glucose and is avidly taken up and retained by most tumors.
    As a result FDG-PET can be used for diagnosis, staging, and monitoring treatment of cancers.

     
  • Neurology
    PET scanning of the brain is based on an assumption that areas of high radioactivity are associated with brain activity. What is actually measured indirectly is the flow of blood to different parts of the brain, which is generally believed to be correlated, and usually measured using the tracer (15O) oxygen.

     
  • Cardiology
    In clinical cardiology FDG-PET can identify so-called "hibernating myocardium", but its cost-effectiveness in this role versus SPECT is unclear.

     
  • Psychology
    To measure neurological activity in amnesiac patients.

 

A cyclotron is a machine to accelerate beams of charged particles by using a high frequency alternating voltage across a magnetic field to spiral the beam out and eventually deflect it once the beam's radius equals its container's. At this point the particles' speed is generally very high, approaching the speed of light. The cyclotron was invented by Ernest Lawrence in 1929, who used it in experiments which required particles of speeds of up to 1 MeV. Cyclotrons are used today in the treatment of cancer, as the particles produced ionize tumors and help to stop or slow cancerous growth.

  • Deuterium Oxide
  • Deuterium Oxide-18O
  • Water-17O
  • Water-18O (download Water-18O form)

 

DLW - 10% - Energy Expenditure Studies

The study of organismal energy expenditure by using 18O and deuterium to measure carbon dioxide production of free-living animals and humans. Total energy expenditure is calculated from carbon dioxide production using the standard equations of indirect calorimetry (TEE). The measurement of total energy expenditure by Water-18O, 10% and doubly labeled water (DLW, 10% D,10% 18O) has become an important tool for the study of energy metabolism, especially with regard to the study of human obesity.

Doubly Labeled Water Technique

A form of indirect calorimetry based on the elimination of deuterium and oxygen (18) from urine, the doubly labeled water technique measures the turnover of hydrogen and oxygen into water and carbon dioxide; energy expenditure is calculated from the difference. This method of determining energy expenditure is useful because it enables researchers to measure total carbon dioxide production over a long period of time--from five to 20 days--and yet only requires periodic sampling of urine. People being tested can continue their normal routines because the method does not require special arrangements or devices.

The prevalence of obesity has increased considerably in our society over the last decade. The affluence of food (increased energy intake) and the low physical activity level (decreased energy expenditure) challenges the energy balance. Therefore methods to assess general underlying physiological mechanisms such as energy metabolism and substrate oxidation are indispensable.
The amount of energy necessary for normal functioning in rest (resting metabolic rate), the increase in energy expenditure after food consumption (diet induced thermogenesis) and the amount of energy expended on physical activity collectively constitute daily energy expenditure. Measurement of these aspects of energy metabolism enable evaluation and assessment of the effect of lifestyle interventions and food products.

95+ % for FDG, Fluor-18 Products / PET

Sterility & Pyrogenicity testing

We can test products for sterility and pyrogenicity. Testing is done in bulk form, before subdivision packaging. This bulk test does not guarantee that the subdivision or repackaged product is sterile and pyrogen free when it is received or used by the customer. It does not imply suitability for any particular purpose. If the product must be sterile and pyrogen free for the intended application, we recommend that the product is tested prior to actual use. Upon request we will ultrafilter products that are to be tested for sterility and pyrogenicity for an additional fee.