The Dopamine Transporter Scan (DaTscan) is a specialized neuroimaging procedure that assists physicians in diagnosing neurological conditions. It uses Single-Photon Emission Computed Tomography (SPECT) to visualize the density of dopamine transporters (DATs) in the brain. The scan provides objective evidence of dopamine deficiency, a common feature in several movement and cognitive disorders. By mapping the concentration of these transporters, the DAT scan helps distinguish disorders that affect the brain’s dopaminergic system from those that do not, such as certain forms of tremor or dementia.
How the DAT Scan Works
The DAT scan uses a radioactive tracer, Ioflupane I 123, which binds specifically to dopamine transporters in the brain’s striatum. The striatum, composed of the caudate nucleus and the putamen, is rich in dopaminergic nerve terminals that regulate movement and reward. The tracer mimics dopamine’s natural binding, adhering to the DAT proteins located on the surface of presynaptic neurons.
Following an intravenous injection, the Ioflupane I 123 travels through the bloodstream and crosses the blood-brain barrier to reach the target area. The amount of radiation emitted by the tracer that accumulates in the striatum is directly proportional to the number of functional dopamine transporters present. A specialized camera, the SPECT scanner, then detects the gamma radiation emitted by the Iodine-123 isotope in the tracer.
The imaging process typically begins a few hours after the injection, allowing the tracer to fully distribute and background radiation to clear. The SPECT camera rotates around the patient’s head, capturing cross-sectional images of the brain. These images are reconstructed by a computer to create a three-dimensional map, revealing the density and location of the dopamine transporters within the striatum. The non-invasive procedure generally takes between 30 and 45 minutes to complete, providing a functional assessment of the nigrostriatal pathway.
Confirming Lewy Body Dementia
The DAT scan is a significant diagnostic aid in the clinical evaluation of Dementia with Lewy Bodies (DLB) because the condition is characterized by a profound loss of dopamine-producing neurons. These neurons originate in the substantia nigra and project to the striatum, where they communicate through dopamine and utilize DATs for neurotransmitter recycling. In DLB, the progressive degeneration of this nigrostriatal pathway causes a substantial reduction in the number of dopamine transporters available for the tracer to bind to.
This objective evidence of dopamine transporter loss is a supportive biomarker for a DLB diagnosis, which can often be difficult to distinguish clinically from Alzheimer’s Disease (AD) in its early stages. Unlike DLB, AD primarily affects memory-related cortical structures and typically preserves the integrity of the dopamine transporter system. Consequently, a patient with AD is expected to have a normal DAT scan, demonstrating a clear distinction from the reduced uptake seen in DLB.
Accurate differentiation is important because DLB patients can have severe adverse reactions to certain medications, such as typical antipsychotics, which are sometimes mistakenly prescribed. The presence of a highly abnormal DAT scan provides strong supporting evidence for DLB, guiding clinicians toward appropriate treatment strategies and management of motor and cognitive symptoms.
The scan results are integrated with the patient’s clinical presentation to meet the established diagnostic criteria for probable DLB. These clinical features include fluctuating cognition, recurrent visual hallucinations, and parkinsonian motor features. While the scan confirms a presynaptic dopaminergic deficit consistent with a synucleinopathy, it cannot distinguish DLB from Parkinson’s Disease (PD) or Parkinson’s Disease Dementia (PDD) without additional clinical context.
Understanding the Scan Images
Neurologists interpret the DAT scan images primarily through visual assessment of the tracer’s uptake pattern in the striatum. In a healthy brain, the striatum displays a characteristic, symmetrical pattern of tracer accumulation that resembles two commas or crescent shapes in the transverse view. This “comma” shape is formed by the dense concentration of dopamine transporters in the caudate nucleus (the head) and the putamen (the tail).
In a patient with a disorder like Lewy Body Dementia, the visual pattern is distinctly abnormal due to the loss of dopamine neurons, which affects the putamen earlier and more severely than the caudate nucleus. The image progresses from the normal “comma” shape to a pattern that often resembles a “period” or an “oval,” where the tracer uptake is significantly diminished in the putamen but relatively preserved in the caudate. This visual change, indicative of reduced binding, provides a clear sign of presynaptic dopaminergic degeneration.
The degree of abnormality is quantified through semi-quantitative analysis, which measures the ratio of tracer uptake in the striatum compared to a reference region, such as the occipital cortex. A significantly reduced uptake ratio supports a diagnosis of a synucleinopathy, such as DLB or PD. Conversely, a scan showing the symmetrical, comma-shaped pattern confirms a normal density of dopamine transporters, effectively ruling out DLB or PD.