Info

Sobriety Success

At Home Drug Withdrawal

Get Instant Access

tissue ratio

High

High

Low

Low

Abbreviations:Df*T, dopamine transporter; SERT, serotonin transporter; SPECT, single photon emission computed tomography.

Abbreviations:Df*T, dopamine transporter; SERT, serotonin transporter; SPECT, single photon emission computed tomography.

of cocaine at the ester linkage to provide more in vivo stability of the parent compound. Nonetheless, the kinetic properties of DAT radiotracers are quite different with regard to plasma protein binding, permeability across the blood-brain barrier, binding affinity, selectivity, and elimination. These differences are crucial to the applications of the DAT ligand for imaging (42). For example, although a given DAT tracer may distinguish PD from healthy controls based on the qualitative appearance of striatal uptake, the ability to distinguish the longitudinal changes in severity of PD may be more difficult for tracers with relatively poorer signal-to-noise properties (lower specific to nonspecific brain uptake) (Table 2). The quantitative properties of the radiotracer must be well understood to assess disease progression. Specifically, does the imaging signal provide a measure that is related to Bmax, the density of DAT, and/or the integrity of dopamine neurons? For some tracers, absolute quantitation of the DAT signal may require invasive methods involving full kinetic modeling, whereas other DAT tracers have a pharmacokinetic profile, which simplifies the methods for signal quantification. For example, the unusual binding kinetics of [123I]P-carboxymethoxy-iodophenyl tropane (CIT), with a protracted period of stable specific radiotracer uptake in the brain and extremely slow elimination from the DAT sites in striatum, permit reproducible quantitative determination of DAT density using a simple tissue ratio method (19,43). For DAT tracers with faster washout from specific binding sites, this simple ratio technique overestimates the density of binding sites in healthy striatum relative to PD (44), although these tracers may permit better visual discrimination of the diseased from control cases.

Of the DAT SPECT tracers in development, [123I]|3-CIT, [123I]FP-CIT, [123I]-altropane, and [99mTc]-TRODAT have been the most widely evaluated agents for SPECT imaging (18,20,45) and [18F]-CFT (WIN 35,428) for PET (46,47). None of these tracers is commercially available as yet in North America, although one tropane derivative of cocaine (FP-CIT, DATSCANĀ®) is available as a [123I]-labeled tracer in Europe.

Was this article helpful?

0 0
Drug Free Life

Drug Free Life

How To Beat Drugs And Be On Your Way To Full Recovery. In this book, you will learn all about: Background Info On Drugs, Psychological Treatments Statistics, Rehab, Hypnosis and Much MORE.

Get My Free Ebook


Post a comment