Showing posts with label SPECT. Show all posts
Showing posts with label SPECT. Show all posts

Friday, 8 January 2021

Positron Emission Tomography (PET)

Positron Emission Tomography (PET)

Positron Emission Tomography is a functional imaging technique that uses radioactive substances known as radiotracers to visualize and measure changes in metabolic processes, and in other physiological activities including blood flow, regional chemical composition, and absorption. They use different tracers for different imaging, depending on the target process within the body. We inject a radiopharmaceutical—a radioisotope attached to a drug—into the body as a tracer. Gamma cameras emit and detect Gamma rays to form a three-dimensional image, similar to that of an X-ray image. Positron-emission tomography scanners can incorporate a computerized tomography scanner, and we call them positron-emission tomography-computerized tomography scanners. One disadvantage of a positron-emission tomography scanner is its high initial cost and ongoing operating costs.


Positron-emission tomography can give information about:

  1. Metabolic changes
  2. Regional cerebral blood flow
  3. Ligand binding

Clinical Uses 

We can use positron-emission tomography in the assessment of several neurological conditions. It is especially helpful for differentiating dementia of Alzheimer's type from frontotemporal dementias. 

  1. Cerebrovascular disease
  2. Alzheimer’s disease
  3. Epilepsy, prior to neurosurgery
  4. Head injury

Friday, 8 June 2007

Single-photon Emission Tomography SPET

Single-photon Emission Tomography SPET


uses single-photon (gamma-ray) emitting isotopes

given IV or inhaled

the resolution is lower than PET


SPET can give information about:

regional cerebral blood flow

ligand binding

Clinical uses include:

Alzheimer’s disease

When the symptomatology (e.g. hallucinations, epilepsy) occurs when the patient is not near a scanner; we can give a suitable ligand at the material time and the patient scanned afterward


reduced rCBF in frontal regions—‘hypofrontality’

Affective disorders

as that in schizophrenia, with reversal after antidepressant therapy

Alzheimer’s disease

decreased rCBF in posterior parietal and temporal regions

Xenon inhalation

Shows the failure of activation of frontal lobes in schizophrenics performing the Wisconsin Card Sorting Test

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