Neurosurgery notes/Radiology/Nuclear medicine/Single photon emission computed tomography (SPECT)

Single photon emission computed tomography (SPECT)

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Parent item
Nuclear medicine
Sub-item
Technetium-99m

Difference between PET and SPECT

Features
Positron emission tomography (PET)
Single-photon emission computed tomography (SPECT)
Cost
Is very expensive
Is lower cost
Tracer
Uses positron emitting radioisotope (tracer)
• F-18 fluorodeoxyglucose (FDG)
Uses gamma emitting radioisotope (tracer):
• Technetium-99m
• Iodine-123
• Iodine-131
Resolution
Gives better contrast and spatial resolution (cf. SPECT)
Gives poorer contrast and spatial resolution (cf. PET)
Detector
Has a ring of multiple detectors
Usually one large crystal based detector

Mechanism

  • 201T (thalium): potassium analogue
    • Enters cells through Na/K pump → tumour cells have high metabolism → increased thalium absorbed into tumour cell
    • Higher the grade → higher the metabolism → higher the thalium absorbed
  • Tc-99m HMPAO (hexamethylpropyleneamine oxime) labelled WBC
      • A method of measuring regional cerebral blood flow.
      • Use for seizure ictal and interictal SPECT
      • Ligand (traces cerebral perfusion/ binds to a specific brain receptor or transporter/ is taken up by cells) is tagged with a gamma-emitting radionuclide
      • Rotating gamma camera
      • Filtering, back projection, and attenuation correction
      • A three-dimensional image of the distribution of the radionuclide in the brain is obtained
      • Images are assessed visually and semi-quantitative
      notion image

Uses

Initial imaging

  • Assess grade
  • Predict survival category
  • Direct biopsy to areas most active (highest grade)

Treatment response

  • Assess post chemo/radiotherapy
  • Predict survival

Differentiation

  • Radiation necrosis
  • Pseudoprogression
  • Abscess/CNS lymphoma
  • LGG malignant progression
    • Park et al 2012: 201Tl SPECT may play a role in prediction of early tumor progression not only in resected LGAs, but also in biopsy-proven LGAs.

Cisternography

  • Technetium-99m diethylenetriamine pentaacetic acid (Tc-99m DTPA).
  • Tc-99m DTPA is injected intrathecally (into the CSF space) and then imaged using a gamma camera.
  • The distribution of the tracer within the subarachnoid spaces provides information about CSF circulation and any abnormalities.

Indium-111 labelled WBC scan

  • 90% sensitive/ specific
  • Low sensitivity for vertebral osteomyelitis.
  • Imaging the distribution of labelled white blood cells within the body to detect infection or inflammation.
  • Procedure
    • The patient’s blood is withdrawn, and white blood cells are extracted.
    • These white blood cells are then labelled with indium-111 oxine (a radioactive tracer).
    • The labelled white blood cells are injected back into the patient.
    • It is crucial that the patient receives their own white blood cells back, and strict protocols ensure this.
    • The patient is imaged 24 hours later, allowing the white blood cells to migrate to the site of inflammation or infection