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DaTscan (I-123 Ioflupane SPECT)

DaTscan uses I-123 ioflupane (FP-CIT), a cocaine analogue that binds presynaptic dopamine transporters (DAT) on nigrostriatal nerve terminals, to image the integrity of the dopaminergic system. Nigrostriatal degeneration (Parkinson disease and atypical parkinsonian syndromes) reduces striatal DAT binding, whereas essential tremor, drug-induced and psychogenic parkinsonism have normal binding. It therefore differentiates neurodegenerative parkinsonism from conditions with an intact dopaminergic system and supports the diagnosis of dementia with Lewy bodies versus Alzheimer disease.

Indications

  • Differentiation of neurodegenerative parkinsonian syndromes from essential tremor
  • Clarification of drug-induced, vascular or psychogenic parkinsonism (normal scan expected)
  • Support for the diagnosis of dementia with Lewy bodies versus Alzheimer disease
  • Evaluation of a clinically uncertain parkinsonian syndrome to guide management
  • Assessment where the presence of presynaptic dopaminergic deficit will change treatment

Contraindications & Cautions

  • Pregnancy is a relative contraindication; justify and minimise fetal dose
  • Breastfeeding: interrupt and discard milk for ~3-6 days (per label) owing to I-123 and free iodide
  • Known hypersensitivity to ioflupane or to the excipients (contains ethanol)
  • Failure to block the thyroid (potassium iodide or perchlorate) risks free-iodide uptake — mandatory pre-medication
  • Medications that affect DAT binding (e.g. cocaine, amphetamines, some antidepressants and CNS stimulants) may confound results and should be reviewed/withheld

Patient Preparation

  • Block the thyroid with potassium iodide or potassium perchlorate ~1 hour before injection to prevent free-iodide uptake
  • Review and, where safe, withhold drugs that interfere with DAT binding (certain stimulants, cocaine, some SSRIs/SNRIs)
  • Explain the delayed imaging (3-6 hours after injection) and the need to remain still during SPECT
  • Confirm pregnancy/lactation status and arrange milk interruption if breastfeeding
  • Ensure the patient can lie supine with the head immobilised for the acquisition

Technique & Parameters

  • Administer I-123 ioflupane 111-185 MBq intravenously after thyroid blockade
  • Acquire brain SPECT 3-6 hours post-injection with a high-resolution (fan-beam or LEHR) collimator
  • Position with the head immobilised and the smallest possible radius of rotation to maximise resolution
  • Reconstruct with attenuation (and scatter) correction; review transaxial slices parallel to the AC-PC line
  • Perform visual grading and semi-quantitative specific binding ratios (striatum-to-background) where available

Systematic Review

  • Assess overall image quality, symmetry and orientation of the striata
  • Evaluate the shape and intensity of caudate and putaminal uptake on each side
  • Grade the putamen specifically, as it is affected earliest and most severely in Parkinson disease
  • Compare left and right and calculate specific binding ratios against reference data
  • Correlate the pattern with the clinical presentation and note asymmetry corresponding to symptom laterality

Key Findings & Significance

  • Normal scan: symmetric, well-demarcated comma- or crescent-shaped striatal uptake with clear putamen
  • Abnormal (nigrostriatal degeneration): reduced/asymmetric putaminal uptake producing a "period"/"full-stop" or dot appearance, typically worse contralateral to symptoms
  • A normal scan supports essential tremor, drug-induced, vascular or psychogenic parkinsonism
  • Reduced striatal binding supports Parkinson disease and atypical parkinsonism (MSA, PSP, CBD) but does not by itself distinguish among them
  • Abnormal DAT imaging supports dementia with Lewy bodies over Alzheimer disease (which usually has normal binding)

Differential Considerations

  • Abnormal DAT binding: Parkinson disease, multiple system atrophy, progressive supranuclear palsy, corticobasal degeneration, dementia with Lewy bodies
  • Normal DAT binding: essential tremor, drug-induced parkinsonism, vascular parkinsonism, psychogenic parkinsonism, Alzheimer disease
  • Symmetric global reduction: advanced disease or technical/positioning effects
  • False reduction: interfering medications (stimulants, cocaine), poor positioning or attenuation artefact
  • Indeterminate/borderline binding ratios requiring clinical follow-up or repeat imaging

Pearls & Pitfalls

  • DaTscan confirms or excludes a presynaptic dopaminergic deficit but does not distinguish Parkinson disease from atypical parkinsonism
  • The putamen is affected before the caudate and typically asymmetrically, contralateral to the clinically dominant side
  • Always block the thyroid — omission causes free-iodide uptake and image degradation
  • Review the medication list; several drugs alter DAT binding and can cause false-normal or false-reduced studies
  • A normal scan effectively excludes neurodegenerative parkinsonism and reframes the diagnosis toward essential tremor or drug-induced causes

Structured Report

  • State the tracer, activity, thyroid blockade and imaging time
  • Describe striatal shape, symmetry and caudate versus putamen uptake
  • Give the visual grade and semi-quantitative specific binding ratios where used
  • Conclude whether the pattern indicates a presynaptic dopaminergic deficit (abnormal) or is normal
  • Relate the findings to the clinical question and note interfering medications

References

  • Morbelli S, et al. EANM practice guideline/SNMMI procedure standard for dopaminergic imaging in parkinsonian syndromes 1.0. Eur J Nucl Med Mol Imaging 2020
  • Djang DSW, et al. SNM practice guideline for dopamine transporter imaging with I-123 ioflupane SPECT 1.0. J Nucl Med 2012
  • McKeith IG, et al. Diagnosis and management of dementia with Lewy bodies (fourth consensus report). Neurology 2017
  • Booij J, Kemp P. Dopamine transporter imaging with [123I]FP-CIT SPECT. Eur J Nucl Med Mol Imaging

Educational clinical decision support only. Protocols vary by institution and equipment; always confirm with a qualified radiologist and local guidelines before clinical use.