A DaTscan is a specialized nuclear medicine imaging test used to visualize the density and distribution of dopamine transporters (DaT) in the brain. It uses a radioactive tracer that binds to these transporters, proteins found on dopamine-releasing neurons. This imaging technique provides functional information about the dopaminergic system, helping medical professionals differentiate essential tremor from movement disorders like Parkinsonian syndromes. The test serves as an adjunct to a comprehensive clinical evaluation when the diagnosis is uncertain.
Pre-Scan Preparation
Preparation begins with a review of the patient’s current medications. Specific medications must be temporarily stopped because certain drugs can interfere with the tracer’s binding to dopamine transporters. These interfering agents often include some antidepressants, attention deficit disorder treatments, and certain over-the-counter decongestants. Discontinuation can range from a few days to a couple of weeks, depending on the drug’s half-life.
On the day of the scan, a thyroid-blocking agent is administered to prevent the thyroid gland from taking up radioactive iodine. This agent, typically a solution like Lugol’s or a tablet containing potassium iodide or perchlorate, is taken orally at least one hour before the radiotracer injection. The purpose of this pre-treatment is to saturate the thyroid with non-radioactive iodine, minimizing the gland’s exposure to the small amount of free radioactive iodine present in the tracer solution.
Administration of the Radiotracer
The procedure begins with the injection of the radiotracer, Ioflupane I-123. A technician secures an intravenous (IV) line, usually in the arm, for administration. The radiotracer is a pharmaceutical dose of iodine-123 labeled molecules designed to seek out and attach to the dopamine transporters in the brain.
The Ioflupane I-123 is administered slowly into the vein, typically over 15 to 30 seconds, to minimize discomfort at the injection site. The amount of radioactivity injected generally falls between 111 and 185 MBq (3 to 5 mCi). This step starts the clock for the tracer to circulate and concentrate in the brain’s target areas.
The Waiting and Imaging Process
After the injection, a waiting period is required for the tracer to distribute and bind effectively within the brain. This uptake period usually lasts between three and six hours, giving the Ioflupane I-123 sufficient time to cross the blood-brain barrier and attach to the dopamine transporters in the striatum. Patients are generally permitted to leave the facility during this interval, but they must return on time for the subsequent imaging session.
Once the waiting period is complete, the patient returns for the Single-Photon Emission Computed Tomography (SPECT) scan. The patient is asked to lie still on a narrow table, and their head is carefully positioned within a specialized headrest. Flexible restraints, such as a strip of tape across the forehead, may be used to minimize head movement during image acquisition.
The SPECT camera, a large device containing detector heads, slowly rotates around the patient’s head, capturing the gamma rays emitted by the concentrated Ioflupane I-123 tracer. Remaining completely motionless is necessary during this phase to ensure image clarity and accuracy. The scanning portion typically takes 30 to 45 minutes.
Post-Scan Care and Image Interpretation
Following the scan, patients are instructed to increase their fluid intake and to void frequently for up to 48 hours. This simple measure helps the body flush out any remaining unbound radiotracer, which minimizes the patient’s overall radiation exposure. The images are then processed and sent to a nuclear medicine physician or radiologist for detailed analysis and interpretation.
The interpretation focuses on the visual pattern of the tracer uptake within the striatum, which is composed of the caudate nucleus and the putamen. A normal DaTscan will show two symmetrical, distinct areas of activity that resemble a pair of commas or crescents. This pattern reflects a healthy density of dopamine transporters in both sides of the brain.
In contrast, an abnormal scan demonstrates reduced or asymmetrical uptake, often appearing as a dot or oval on one or both sides. This diminished signal indicates a loss of dopamine transporters, which is consistent with the degeneration of dopamine-producing neurons found in Parkinsonian syndromes. The final report summarizes these visual findings, supporting the referring physician’s diagnostic process.