A DaTscan is a specialized imaging test that provides a detailed look at the brain’s dopamine system. It uses a small quantity of a radioactive tracer and a specialized camera to visualize the density of dopamine transporters, which are proteins responsible for moving dopamine back into nerve cells. The resulting images help doctors assess the health of this particular system within the brain.
Purpose of a DaTscan
The primary role of a DaTscan is to assist neurologists in differentiating between conditions with similar symptoms, such as tremors. It helps distinguish essential tremor from a group of conditions known as Parkinsonian syndromes. These syndromes, including Parkinson’s disease, multiple system atrophy (MSA), and progressive supranuclear palsy (PSP), are characterized by a loss of nerve cells that produce dopamine. Essential tremor, while causing shaking, is not associated with this type of nerve cell loss.
A DaTscan does not diagnose a specific disease on its own. Instead, it detects the presence or absence of a reduction in dopamine transporters in a brain region called the striatum. This information serves as a biological marker for the health of the dopaminergic system. This objective data can increase a doctor’s confidence in a diagnosis when symptoms are unclear, helping to guide treatment decisions.
The DaTscan Procedure
The DaTscan process occurs over several hours, beginning with preparatory steps. About an hour before the scan, you will receive a medication like potassium iodide to protect your thyroid gland from the radioactive tracer. Your doctor will review your current medications, as some may need to be temporarily stopped. Staying well-hydrated is also encouraged to help your body eliminate the tracer after the test.
Next, you will receive a slow intravenous (IV) injection of the imaging agent, Ioflupane I-123. After the injection, there is a waiting period of three to four hours. This delay allows the tracer to travel through the bloodstream and accumulate in the striatum, the brain’s target area for the scan.
For the final part, you will lie on a table with your head in a holder. A large SPECT camera will be placed close to your head without touching you. You must remain as still as possible for 30 to 45 minutes while the camera rotates around your head to capture images. The process is painless, though staying still can be challenging for some.
Understanding DaTscan Results
Interpreting DaTscan images involves a visual assessment of the striatum, which is composed of the caudate nucleus and the putamen. Radiologists often use a simple analogy to describe the findings. A normal scan, indicating a healthy population of dopamine transporters, shows two bright, comma-shaped regions of tracer activity on each side of the brain. These “commas” appear symmetrical and distinct from the surrounding brain tissue.
An abnormal scan result is characterized by a different shape and intensity. When there is a loss of dopamine transporters, the tracer uptake is less intense, and the shape appears more rounded, often described as a “period” instead of a comma. This change is frequently more pronounced in the putamen and can be asymmetrical, with one side of the brain showing more loss. This finding indicates a deficiency in the dopamine system.
The scan’s results are not a standalone diagnosis. A neurologist interprets the images within the full clinical context of your symptoms, medical history, and physical examination. While an abnormal scan can confirm a Parkinsonian syndrome, it cannot distinguish between specific types like Parkinson’s disease, MSA, or PSP, as all show a similar pattern of dopamine transporter loss.
Safety and Comparison to Other Scans
The radiation dose from a DaTscan is low, approximately 3.94 to 4.6 millisieverts (mSv). This amount is comparable to the natural background radiation a person is exposed to in the U.S. over about a year. Side effects are rare, with headache being the most common, affecting about 1% of patients. The risk of a significant allergic reaction to the tracer is also very low.
A DaTscan provides different information than MRI or CT scans. MRIs and CTs are structural scans that show the brain’s physical anatomy, such as its size, shape, or the presence of tumors. In contrast, a DaTscan is a functional scan that reveals how the dopamine system is working by visualizing dopamine transporter density. This is why a person can have a normal brain MRI but an abnormal DaTscan, as dopamine function loss occurs at a cellular level before causing visible structural changes.