Molecular neuroimaging using single-photon emission computed tomography (SPECT) has allowed for direct visualization of functional systems in the living human brain. DaTSCAN is a radiopharmaceutical approved 2 years ago by the FDA with indications for “striatal dopamine transporter visualization using SPECT brain imaging to assist in the evaluation of adult patients with suspected Parkinsonian syndromes.” In these patients, DaTSCAN may be used to help differentiate essential tremor from tremor resulting from one of the parkinsonian syndromes (IDP, MSA, PSP). DaTSCAN is an adjunct to other diagnostic evaluations.
Dopamine Transporter (DAT) Imaging
DAT imaging offers certain advantages. First, DAT is largely limited to presynaptic membranes which, in the striatum, are predominantly the axonal terminals of substantia nigra neurons. Therefore, DAT allows direct visualization of the integrity of the neurons that appear most vulnerable to degeneration in IPD. Second, a minimum of metabolic processing, and therefore shorter incubation time during imaging, is possible.
Two derivatives are approved in Europe: I 123 beta CIT, marketed as Dopascan, and I123 Ioflupane, marketed as DaTSCAN. The DaTSCAN has been in use in Europe for 12 years, giving our European colleagues extensive experience with making full use of this marker.
The Value of Quantitative Analysis
One observation, based on the extensive experience in Europe, has been the value of quantitative or semiquantitative analysis. Visual interpretation of the DaTSCAN does not make full use of its capabilities. For example, when specific binding ratios relative to the occipital cortex are quantified (such as provided with the Hermes BRASS system), a Z-score derived from a normal database can be calculated. This has utility in differentiating accurately between Parkinson disease, which typically has an asymmetric dopaminergic denervation in the putamen and caudate, and non-parkinsonian causes of tremor, which show nonsignificant Z-scores. Such causes of tremor include medications and essential tremor.
Quantitative DaTSCAN analysis also is critical in the case of the positive DaTSCAN to assist in differentiation of IPD and other parkinsonian syndromes (MSA, DLB, PSP) that tend to have a symmetrical denervation. However, DaTSCAN cannot reliably distinguish these parkinsonian syndromes alone.
As published in Neurology Times