Isotopes Used in SPECT

Out of the isotopes used in SPECT and for taking planar images (scintigraphy) the Tc-99 isotope of technetium is the most widespread. Generally Tc is produced in so-called technetium generators.
The first 99Mo-99mTc generator was built in 1957. 99Mo can be produced in reactors through neutron activation. 99Mo decays to 99mTc with a half-life of 67 hours. 99mTc is especially suitable for isotope diagnostics as its half-life is 6 hours and its gamma energy is 140 keV. Furthermore, it can easily be bound to several molecules (e.g. phosphonate, tetrafosmin, etc.), thus there is no difficulty in producing a radiopharmaceutical. It is favourable that the activity of the generator can remain high for a relatively long time.

A technetium generator and the decay scheme of Mo-99

 

Other SPECT isotopes:

• Tl-201: myocardial perfusion studies
• In-111: prostate cancer
• Ga-67: infection or lymphoma
• I-123: thyroid
• Xe-133: lung

 
The last two isotopes mentioned are used for planar imaging only. The tendency is to perform as many examinations using technetium as possible.