<P> One of the disadvantages of PET scanners is their operating cost . </P> <P> PET is both a medical and research tool . It is used heavily in clinical oncology (medical imaging of tumours and the search for metastases), and for clinical diagnosis of certain diffuse brain diseases such as those causing various types of dementias . PET is also an important research tool to map normal human brain and heart function, and support drug development . </P> <P> PET is also used in pre-clinical studies using animals, where it allows repeated investigations into the same subjects . This is particularly valuable in cancer research, as it results in an increase in the statistical quality of the data (subjects can act as their own control) and substantially reduces the numbers of animals required for a given study . </P> <P> Alternative methods of scanning include x-ray computed tomography (CT), magnetic resonance imaging (MRI) and functional magnetic resonance imaging (fMRI), ultrasound and single - photon emission computed tomography (SPECT). </P>

What is the main advantage of carbon-11 compared to fluorine-18 for pet imaging studies