SPECT in ParkinsonismDr Gulab Soni
SPECT-Principle• Image and quantify a physiological function or molecular target of
interest (e.g., blood flow, metabolism, receptor binding) in vivo by noninvasively assessing the spatial and temporal distribution of the radiation emitted by an intravenously injected target-specific probe (radiotracer)• Molecular imaging techniques
Single-Photon Emission Computed Tomography(SPECT)• SPECT employs gamma-emitting radionuclides that decay by emitting
a single gamma ray• Spatial resolution of modern SPECT is only about 7 to 10 mm• Single SPECT acquisition usually takes 20 to 30 minutes• Radionuclides for SPECT-1) Technetium-99m (99mTc; half-life = 6.02 hours) 2) Iodine-123 (123I; half-life = 13.2 hours)
Clinical application of SPECT• Diagnostic utility• Prognostic utility-disease progression
SPECT in Parkinsonism Imaging of the dopaminergic system Perfusion imaging
Imaging of the dopaminergic system 1) Dopamine synthesis2) Dopamine storage in synaptic vesicles3) Dopamine transporters4) Dopamine receptors
Radiotracer used for SPECT in ParkinsonismTargeting Tracer
Dopamine reuptake(dopamine transport)
123I-β-CIT,123I-FP-β-CIT,123I-IPT,123I-Altropane,123I-β-PE2I99Tcm-TRODAT-1
D2 dopamine receptor 123I-Iodospiperone,123I-Iodobenzamide (123I-IBZM),123I-Iodolisuride, 123I-IBF
Dopamine transporters• Dopamine transporters (DAT) are located in the presynaptic
dopaminergic nerve terminal. • Dopamine reuptake through the DAT is the primary mechanism of
dopamine removal from the region of the synaptic cleft • DAT-specific tracers used for SPECT imaging are cocaine analogue and
ability to assess decreased DAT density, which may precede clinical symptoms in PD
Dopamine transporters• The reduction is typically more severe in the striatum contralateral to
the earliest and most affected body side • Striatal DAT levels, particularly in the putamen, correlate with disease
severity and decrease with PD progression
Dopamine receptors• SPECT studies with [123I]IBJM showed that striatal dopamine D2
binding to the postsynaptic dopaminergic receptors was either normal or increased in PD patients• This increase has been interpreted as a compensatory reaction to the
reduction of striatal dopaminergic terminals • D2 receptor upregulation is most evident at early stages and
contralateral to the clinically most affected side and is usually the site of onset in PD.
Dopamine receptors• D2 receptor imaging is widely used for the differential diagnosis of
parkinsonism, since uptake is typically normal or increased in patients with PD, whereas patients with other forms of parkinsonism, such as multiple system atrophy and progressive supranuclear palsy show reduced tracer uptake• Chronic pharmacologic treatment may reduce D2 receptor availability,
probably due to downregulation• Shows 59 to 80% sensitivity and 46 to 50% specificity in differentiating
PD from other atypical PD
Clinical indications for DaT-SPECT imaging Indications1) Only 1 of 3 cardinal clinical signs with or without asymmetry2) Poor response to L-dopa3) Lack of disease progression(Cardinal signs are resting tremor, rigidity, and bradykinesia and postural instability)
DAT-SPECTDifferentiating between Parkinson’s Essential tremorDystonic tremorDrug-induced parkinsonismPsychogenic parkinsonismVascular parkinsonism
DAT-SPECT • Specificity-100% • Sensitivity : 38% to 100%• 15% of patients diagnosed as having PD had normal DaT-SPECT study
findings classified as “scans without evidence of dopaminergic deficit” (SWEDD)
DAT-SPECT• Because most dopaminergic
transmission occurs in the striatum, this area will show the maximum uptake of DaT radiotracers, with minimal background activity in the remainder of the brain.• In scans with normal findings, the
striata appear as symmetric “comma” shapes• Any asymmetry or distortion of this
shape, in the absence of patient motion, implies an abnormal scan finding.
Brain perfusion imaging
Perfusion-SPECT
Brain perfusion SPECT• Used for measuring regional cerebral blood flow (rCBF) are lipophilic
agents which are transported from the vascular compartment to the normal brain tissue compartment by diffusion and are distributed proportionally to regional tissue blood flow• Tc-99m hexamethyl-propylene amine oxime (Tc-99m HMPAO) • Tc-99m ethyl cysteinate dimer (Tc-99m ECD)
Brain perfusion SPECT• Approximately 10% of Parkinson’s disease patients develop dementia,
with parietal, temporal, and occipital lobe hypoperfusion seen on brain SPECT studies. • Demented Parkinson’s disease patients and AD patients share a
common pattern of marked posterior hypoperfusion. However, the defects are more prominent and extensive in AD
Spampinato U, Habert MO, Mas JL, et al. (99mTc)-HM-PAO SPECT and cognitive impairment in Parkinson’s disease: a comparison with dementia of the Alzheimer type. J Neurol Neurosurg Psychiatry. 1991;54:787–792
Summary of nuclear imaging in
Parkinsonism
PET vs SPECT
Positron emission tomography (PET)• Very expensive• Uses positron emitting
radioisotope (tracer)a) 18F• Better contrast and spatial
resolution• Short half life of tracer
Single-photon emission computed tomography (SPECT)• Lower cost• Uses gamma emitting
radioisotope (tracer)a) Technetium-99mb) Iodine-123• Less contrast and spatial
resolution • Long half life of tracer
PET & SPECT in Parkinsonism
DAT-SPECT
FDG-PET
THANK-U
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