3 SPECT and SPECT/CT in Neuroscience

10.1055/b-0038-149735

3 SPECT and SPECT/CT in Neuroscience

Tarun Singhal and Chun K. Kim

3.1 Radiopharmaceuticals for Brain SPECT Imaging

Brain perfusion agents: for example, technetium-99 m (^99mTc)-ethyl cysteinate dimer (ECD) and ^99mTc-hexamethylpropyleneamine oxime (HMPAO).
Neurotransmitter agents: for example, iodine-123 (¹²³I)-ioflupane.
Brain tumor agents: for example, thallium-201 (²⁰¹Tl)-chloride.

3.2 Perfusion SPECT Imaging in Dementia

Dementia is a chronic, progressive neurodegenerative condition that affects multiple higher cognitive functional domains. There are several subtypes of dementia based on underlying pathology. Single-photon emission computed tomography (SPECT) demonstrates hypoperfusion patterns that differ among various dementia subtypes. These patterns are often analogous to patterns of hypometabolism seen on fluorodeoxyglucose positron emission tomography (FDG-PET).

3.2.1 Alzheimer’s Disease

Posterior temporal and inferior parietal hypoperfusion generally precedes the onset of clinical symptoms (► Fig. 3.1 a). Precuneus hypoperfusion may be seen in some cases. A review of sagittal images is often helpful in diagnosis (► Fig. 3.1 b). Frontal hypoperfusion may be seen in advanced stages. There is usual sparing of the sensorimotor cortex and occipital lobes. Hypoperfusion may be asymmetric in the early stages and may extend to involve both hemispheres. ¹

**Fig. 3.1** Alzheimer’s disease. (a) Three selected axial SPECT images show bilateral temporoparietal hypoperfusion with relative sparing of basal ganglia, frontal lobes, and occipital lobes. (b) A sagittal SPECT image shows precuneus hypoperfusion. Precuneus hypoperfusion (*arrow*) is an early sign of Alzheimer’s disease.

3.2.2 Frontotemporal Dementia

Bilateral frontal and anterior temporal hypoperfusion is seen in patients with predominantly behavioral variant frontotemporal dementia (► Fig. 3.2). Frontal hypoperfusion may also be seen in depression and schizophrenia, and clinical correlation is necessary to interpret SPECT findings.

**Fig. 3.2** Frontotemporal dementia. (a) Sagittal and (b) axial SPECT images show bilateral anterior temporal and frontal hypoperfusion with sparing of the posterior temporal, parietal, and occipital cortices.

3.2.3 Vascular Dementia

Patchy areas of hypoperfusion involving the cortical hemispheres or subcortical structures may be seen in patients with vascular dementia (► Fig. 3.3).

**Fig. 3.3** Vascular dementia. (a) Axial SPECT images show heterogeneous radiotracer activity in the cerebral cortex with decreased activity in the right caudate (*arrow*) reflecting subcortical involvement. (b) Axial T2-weighted fluid attenuation inversion recovery MR image of the brain showing microangiopathic changes (periventricular hyperintensities).

3.2.4 Primary Progressive Aphasia

Left temporal hypoperfusion (particularly in right-handed individuals) is seen in the semantic dementia variant of primary progressive aphasia (► Fig. 3.4). Semantic dementia is clinically characterized by a fluent aphasia and is associated with frontotemporal dementia-type pathology. However, patients with a logopenic variant of primary progressive aphasia (clinically characterized by slow speech, word retrieval difficulty, and speech paucity and dysfluency) may show an asymmetric Alzheimer’sdisease pattern, often affecting the language-dominant left hemisphere (► Fig. 3.5).

**Fig. 3.4** Primary progressive aphasia (semantic dementia). An axial SPECT image shows asymmetric left temporal hypoperfusion.

**Fig. 3.5** Logopenic variant of primary progressive aphasia. (a) Coronal and (b) axial SPECT images show asymmetric left temporal and parietal hypoperfusion.

3.2.5 Corticobasal Degeneration and Progressive Supranuclear Palsy

In addition to cerebral cortex involvement, these syndromes may present with hypoperfusion in the basal ganglia involving the caudate and putamen.

3.2.6 Diffuse Lewy Body Disease

The hypoperfusion pattern in Lewy body dementia is similar to that seen in Alzheimer’s disease, except that there is prominent involvement of the occipital lobes.

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