What Is a DAT Scan and How Are the Results Interpreted?

A DaTscan is a brain scan that answers one narrow question: are the nerve endings that use dopamine, the chemical that helps smooth out movement, still there? It is most often ordered when a doctor can’t tell from an exam alone whether a tremor or slowness is Parkinson’s disease or something else.1PubMed Central. Differentiating Parkinson’s Disease from Essential Tremor Using Transcranial Sonography: A Systematic Review and Meta-Analysis The picture is a look at dopamine loss rather than a diagnosis by itself, so the result narrows the possibilities.

What the Scan Actually Shows

The test uses an injected tracer called ioflupane, which latches onto dopamine transporters, proteins found on the tips of dopamine nerve cells.2FDA. DaTscan Highlights of Prescribing Information Because of that, it collects mainly in the striatum, a pair of deep brain structures that coordinate movement, and the area your report will refer to.3FDA. DaTscan Highlights of Prescribing Information The scan was approved in the United States in 2011 to help evaluate adults with suspected parkinsonism.4PubMed. Clinical utility of DaTscanâ„¢ imaging in the evaluation of patients with parkinsonism: a US perspective

In Parkinson’s, dopamine nerve endings die off, so less tracer gathers in the brain’s movement hub. The scan will look abnormal in any disease that destroys these nerve endings, not just Parkinson’s.5American Parkinson Disease Association. What is a DaTscan and should I get one?

That makes it different from an MRI or CT. Those scans show brain structure, and structure usually looks normal in early Parkinson’s. A DaTscan shows chemical function, one specific nerve system at work, which is why a normal MRI and an abnormal DaTscan can exist side by side.

The tracer carries a small amount of radioactive iodine that gives off gamma rays. A special camera rotates slowly around your head and records them, and a computer builds the signals into slices of the brain. The bright areas in the final image are places where more tracer has collected, so healthy transporters show up as glowing shapes.

How Normal and Abnormal Scans Look

On a normal scan, each side of the striatum looks like a bright comma.6PubMed Central. CADA—computer-aided DaTSCAN analysis In Parkinson’s, the loss usually starts at the back part, the putamen, on the side opposite your worse symptoms, then spreads forward to the caudate.7PubMed Central. CADA—computer-aided DaTSCAN analysis The comma shortens into a dot or fades altogether.8PubMed Central. CADA—computer-aided DaTSCAN analysis A report saying “reduced uptake in the posterior putamen” is describing this classic early pattern.

The reader of the images compares the left and right sides, looking for shapes that differ in size or brightness. They check whether the commas are full and rounded or have lost their tails. They also compare the striatum with the surrounding brain, since tracer in the rest of the brain serves as a background reference.

Many reports also give a striatal binding ratio, or SBR, which compares tracer in the striatum with that background.9PubMed Central. Semiquantitative Analysis of Dopamine Transporter Scans in Patients With Parkinson Disease Software may convert this uptake number into a score showing how far you sit from healthy volunteers of a similar age.10PubMed. Different z-score cut-offs for striatal binding ratio (SBR) of DaT SPECT are needed to support the diagnosis of Parkinson’s Disease (PD) and dementia with Lewy bodies (DLB)

Eyes and numbers can disagree, though. Many centers use both together for that reason.11Reports in Medical Imaging. Identification of patterns of abnormalities seen on DaTscan SPECT imaging in patients with non-Parkinson’s movement disorders A “mildly reduced” visual read without abnormal numbers is worth discussing with your neurologist rather than taking as definite.

Symmetric, normal uptake points away from a dopamine-loss disease, while a one-sided reduction matching your worse side fits Parkinson’s, though related conditions can look the same. “Mild” findings are the gray zone where readers disagree most.

What a Normal Result Means

The scan is approved specifically to help separate early Parkinson’s from essential tremor, an inherited shaking that doesn’t destroy dopamine cells.12PubMed Central. Differentiating Parkinson’s Disease from Essential Tremor Using Transcranial Sonography: A Systematic Review and Meta-Analysis It also helps separate Parkinson’s from parkinsonism caused by medications or small strokes.13PubMed Central. Differentiating Parkinson’s Disease from Essential Tremor Using Transcranial Sonography: A Systematic Review and Meta-Analysis So a normal scan in someone with tremor makes essential tremor, or another cause that doesn’t destroy dopamine cells, far more likely.14PubMed Central. Distinguishing essential tremor from Parkinson’s disease: bedside tests and laboratory evaluations

The two tremors can look alike, which is why the scan gets ordered. Essential tremor is usually worse when you hold a cup or write, while Parkinson’s tremor is often strongest at rest, though this is only a rough guide.

After a normal scan, the doctor may stop Parkinson’s medicines that weren’t helping. Essential tremor has its own treatments, such as beta-blockers, and if drug-induced parkinsonism is suspected, a medication review may follow.

A normal scan doesn’t mean nothing is wrong, only that the cause isn’t dopamine loss. Tremor and slowness can also come from medicines, thyroid problems or anxiety, which the scan was never designed to check. If symptoms continue or change, your neurologist may look again at the diagnosis, since a very early scan can occasionally look normal.

What an Abnormal Result Means and What It Can’t Tell You

An abnormal scan means dopamine nerve endings are reduced. That is a finding about brain chemistry, not yet a named disease. The neurologist still has to match an abnormal result to your symptoms and exam. Parkinson’s-like conditions such as progressive supranuclear palsy and multiple system atrophy also damage these nerve endings.15Practical Neurology. Updates in Diagnostic Testing in Parkinson Disease The scan looks abnormal in them too and can’t tell them apart from Parkinson’s.16American Parkinson Disease Association. What is a DaTscan and should I get one? Dementia with Lewy bodies lowers uptake as well, while Alzheimer’s usually doesn’t.17Neurology. DaTscan Findings in Patients with Mild Cognitive Impairment, Alzheimer’s Disease and Dementia with Lewy Bodies (IN3-1.008)

To sort out which disease it is, doctors watch how you respond to levodopa medication. They also look for features typical of atypical forms, such as early falls, eye-movement problems or blood-pressure drops. Time and follow-up visits often clarify the picture, and asking “what else could fit this result?” is a fair question.

The clinical scan shows whether the dopamine system is impaired, not how much, so it isn’t used to follow your disease over time.18American Parkinson Disease Association. What is a DaTscan and should I get one?19American Parkinson Disease Association. What is a DaTscan and should I get one? How you are doing is judged by exam and symptoms instead.

The result does change care. Across studies, the scan changed management in about half of patients and changed the diagnosis in about 3 in 10, often meaning starting, stopping or switching medicines.

How Accurate Is a DaTscan

In people whose parkinsonism was clinically uncertain, the scan correctly identified about 98% with and 98% without dopamine loss.20PubMed Central. The diagnostic accuracy of dopamine transporter SPECT imaging to detect nigrostriatal cell loss in patients with Parkinson’s disease or clinically uncertain parkinsonism: a systematic review In one clinic series, false positives were about 1.4% and false negatives about 4.8%.21Journal of Neurology, Neurosurgery & Psychiatry. PO098 A lesson from the dat scan Still, in one study 5 of 14 essential tremor patients were wrongly read as parkinsonism.22PubMed Central. Distinguishing essential tremor from Parkinson’s disease: bedside tests and laboratory evaluations Reader experience and borderline images matter.

A false positive is a scan that looks abnormal even though the dopamine nerve endings are healthy. A false negative looks normal even though there is dopamine loss. These figures describe how often the test is right overall, not a guarantee for one person.

Several things can throw a result off. Some medicines block the tracer and can make a normal brain look abnormal, while others can raise uptake and hide true loss. Head movement during imaging blurs the picture. A result that clashes with your exam is a good reason to ask about repeating or reviewing it.

Very early disease can also be missed. At the very earliest stage the loss may be small enough to look borderline. If a scan is borderline and symptoms persist, a repeat scan or longer follow-up may be considered.

Medicines to Review Before Your Scan

A drug’s half-life is the time your body takes to clear half of it. Waiting five half-lives usually leaves too little of the drug to block the tracer.23PubMed Central. A systematic review of the potential effects of medications and drugs of abuse on dopamine transporter imaging using [123I]I-FP-CIT SPECT in routine practice Clearance can take longer if other drugs slow it or your body breaks the drug down slowly.24PubMed Central. A systematic review of the potential effects of medications and drugs of abuse on dopamine transporter imaging using [123I]I-FP-CIT SPECT in routine practice Typical waits:

Never stop a prescribed drug without asking the prescriber. Bring a full list of everything you take, including supplements and CBD, and mention recreational drug use honestly, since it affects the result. If you can’t pause a drug, ask whether the scan should be rescheduled.

What Happens on Scan Day

First you take iodine, as a liquid or pill, to stop your thyroid absorbing the tracer.32Davis Phinney Foundation. DaTscan: What It Is, How It Works, and What It Can Tell You Then 30 to 60 minutes later the tracer is injected into an arm vein.33Davis Phinney Foundation. DaTscan: What It Is, How It Works, and What It Can Tell You You wait 3 to 6 hours while it reaches the brain, and may be allowed to leave.34Davis Phinney Foundation. DaTscan: What It Is, How It Works, and What It Can Tell You

For imaging, you lie with your head on a rest, sometimes held by a soft band, while a camera sits close but doesn’t touch you.35St. Luke’s Imaging Services. Nuclear Medicine DaTscan Imaging The imaging takes about 30 to 40 minutes and you must stay very still.36St. Luke’s Imaging Services. Nuclear Medicine DaTscan Imaging The whole visit can last 4 to 8 hours.37American Parkinson Disease Association. What is a DaTscan and should I get one?

Most people feel only a small scratch from the injection, and staff may watch you briefly afterward for any reaction. During the wait you can usually eat, drink and read.

If a tremor makes stillness hard, tell them, because positioning aids help. Afterward, drink fluids and urinate often to clear the tracer.38GE HealthCare. DATSCAN

A nuclear medicine doctor reads the images, and the report goes to your neurologist, who explains it in context. Ask for a copy of the report so you can see the exact wording.

Is a DaTscan Safe

Occasional side effects include headache, nausea, dizziness and dry mouth, usually mild.39Journal of Neurology & Neuromedicine. Neuroradiology and Its Role in Neurodegenerative Diseases Allergic reactions like rash or breathing trouble are rare and appear within minutes.40GE HealthCare. DATSCAN The radiation dose is about 4.35 mSv, roughly a year or so of natural background exposure.41Journal of Neurology & Neuromedicine. Neuroradiology and Its Role in Neurodegenerative Diseases It is a one-time exposure, and the tracer’s radioactivity falls steadily, leaving the body through urine over the following day or so. For most adults, the benefit of an answer about the diagnosis is considered to outweigh this small exposure.

Some people need to take care. People allergic to iodine or the tracer shouldn’t have it.42PubMed Central. DaTscan Ioflupane I 123 Injection Highlights of Prescribing Information Pregnant people should have it only if truly needed.43Journal of Neurology & Neuromedicine. Neuroradiology and Its Role in Neurodegenerative Diseases Breastfeeding must pause because the tracer enters breast milk.44Journal of Neurology & Neuromedicine. Neuroradiology and Its Role in Neurodegenerative Diseases Severe kidney disease can raise exposure and alter images.45Journal of Neurology & Neuromedicine. Neuroradiology and Its Role in Neurodegenerative Diseases

Before booking, tell staff about any iodine or contrast reactions and mention kidney problems or dialysis. If you breastfeed, ask how long to pause and whether to pump beforehand. Ask whether insurance covers the scan, since it is costly.