PET studies for research purposes, especially pharmacokinetic and receptor kinetic investigations, are very important. Several hundreds of different mole­cules labeled with positron emitters have been administered to animals and humans. The greatest advantage of PET is that any organic molecule can be labeled with positron emitters (see Table 12.6). It is possible to obtain images of such a small number of molecules in a living organism (e. g., bound to recep­tors) that otherwise can only be detected in sections (by autoradiography) or in vitro.

12.6.2 Imaging Myocardial Metabolism

If a myocardial perfusion SPECT study performed after infarction (as described in Section 12.5.3) shows perfusion defects in both stress and rest images, the study of glucose metabolism is the best known method of distinguishing between two states: long-term diminished blood supply may have resulted in dead (unviable) myocar­dium, or the cells may still be viable but hibernated, meaning that although they do not presently contract because of the long-lasting oxygen deficiency, the pump function of the heart may improve after restoring the blood supply. Unfortunately, the glucose molecule cannot be labeled with gamma emitter radionuclides since the molecule is too small and its atoms do not have gamma-emitting radioisotopes. However, FDG (mentioned in Section 12.6.2) allows the imaging of glucose metab­olism. While a healthy myocardium gets energy from burning glucose after eating and from fatty acids in fasting state, a hibernated myocardium can consume only glucose, and a scar does not utilize significant amounts of either glucose or fatty acids. So, for instance, in fasting state, only a hibernated myocardium accumulates FDG. A hibernated myocardium can be revived by angioplasty or coronary artery bypass graft surgery, while scars cannot be improved by either therapeutic approach.

Further Reading

Nobelprize. org. (2012). George de Hevesy — Biography. Retrieved March 23, 2012, from http://www. nobelprize. org/nobel_prizes/chemistry/laureates/1943/hevesy-bio. html [Online].

Nobelprize. org. (2012). Rosalyn Yalow — Autobiography. Retrieved March 23, 2012, from http://www. nobelprize. org/nobel_prizes/medicine/laureates/1977/yalow. html [Online].

Wagner, Henry N. (2003). Hal Anger: Nuclear Medicine’s Quiet Genius. J Nucl Med, 44, 26N, 28N, 34N.

NuclearPathways Project. (2011). Ernest O. Lawrence. Retrieved March 23, 2012, from http://www. atomicarchive. com/Bios/Lawrence. shtml [Online].

European Association of Nuclear Medicine (2010). Status of Nuclear Medicine in Europe — 2009. EANM, Vienna.

World Health Organisation. (2004). The top 10 causes of death. Retrieved March 23, 2012, from http://www. who. int/mediacentre/factsheets/fs310/en/index. html [Online].

Magill, J. and Galy, J. (2005). Radioactivity Radionuclides Radiation. Springer, Berlin.

Powsner, R. A. and Powsner, E. R. (2006). Essential Nuclear Medicine Physics. 2nd ed. Blackwell, Malden.