Radiopharmaceuticals for single-photon emission computed tomography brain imaging1

In the past 10 years, significant progress on the development of new brain-imaging agents for single-photon emission computed tomography has been made. Most of the new radiopharmaceuticals are designed to bind specific neurotransmitter receptor or transporter sites in the central nervous system. Most of the site-specific brain radiopharmaceuticals are labeled with ¹²³I. Results from imaging of benzodiazepine (γ-aminobutyric acid) receptors by ¹²³Iiomazenil are useful in identifying epileptic seizure foci and changes of this receptor in psychiatric disorders. Imaging of dopamine D2/D3 receptors ([¹²³I]iodobenzamide and [¹²³I]epidepride) and transporters [¹²³I]CIT (2-beta-carboxymethoxy-3-beta(4-iodophenyl)tropane) and [¹²³I]FP-β-CIT (N-propyl-2-beta-carboxymethoxy-3-beta(4-iodophenyl)-nortropane has proven to be a simple but powerful tool for differential diagnosis of Parkinson's and other neurodegenerative diseases. A ^99mTc-labeled agent, [^99mTc]TRODAT (technetium, 2-[[2-[[[3-(4-chlorophenyl)-8-methyl-8-azabicyclo [3, 2, 1]oct-2-yl]methyl](2-mercaptoethyl)amino]ethyl]amino] ethanethiolato(3-)]oxo-[1R-(exo-exo)]-), for imaging dopamine transporters in the brain has been successfully applied in the diagnosis of Parkinson's disease. Despite the fact that ¹²³I radiopharmaceuticals have been widely used in Japan and in Europe, clinical application of ¹²³I-labeled brain radiopharmaceuticals in the United States is limited because of the difficulties in supplying such agents. Development of ^99mTc agents will likely extend the application of site-specific brain radiopharmaceuticals for routine applications in aiding the diagnosis and monitoring treatments of various neurologic and psychiatric disorders.

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