Chemistry Reference
In-Depth Information
5.1.1
Positron Emission Tomography and Single Photon
Emission Computed Tomography
PET and SPECT are part of nuclear imaging techniques. They have
the advantages of high intrinsic sensitivity and unlimited penetration
depth [23]. PET has the additional advantages of being fully
quantitative, providing higher spatial resolution than SPECT [24, 25].
Hundreds of radiotracers based on a wide variety of radionuclides
due to β- or γ-rays have been developed and tested in animal and
clinical studies. Some examples of the radionuclides are summarized
in Table 5.2 [26-28]. The half-lives of these radiotracers are short;
thus they need to be produced on site, which increases the cost
of imaging. For clinical use, these radiotracers are injected into a
patient's bloodstream. The amount of the radiotracers injected is so
small (ng or μg) that the toxicity is usually not a major issue.
In PET, the tracers are incorporated into a biologically
active molecule, such as fluorodeoxyglucose (FDG). The isotope
accumulates in an area of interest in the body, and the radiotracers
decay by positron emission. After some time, the distribution of the
positron-emitting tracer is calculated by tomographic reconstruction
procedures. PET can be used to study neuroreceptors in the brain
and other body tissues. Clinical studies include tumors of the brain,
breast, lung, lower gastrointestinal tract, study of Alzheimer's
disease, Parkinson's disease, epilepsy, and coronary artery disease
affecting heart muscle metabolism [24, 25, 29].
Table 5.2
Examples of radionuclides
Radionuclide
Half-life time
Application
11
C
20.3 min
Used for metabolism studies
13
N
9.9 min
Used as 13NH for hear perfusion study
15
O
123 s
Used for blood flow
18
F
110 min Quantified tumor cell proliferation,
identification of tumor hypoxia
52
Fe
8.2 h
Used for PET bone marrow imaging
64
Cu
12.8 h
Used for cancer and metabolic disorder
99m
Tc
6 h
The most widely used
radiopharmaceutical in nuclear
medicine
122
I
3.76 min Used for blood flow study
131
I
8.1 days Diagnose thyroid disorders, including
cancer
Note:
Adapted from [26-28].
