PET-CT and SPECT-CT
Why in News?
Union Health Minister J.P. Nadda inaugurated PET-CT and SPECT-CT facilities at VMMC & Safdarjung Hospital, New Delhi, under the Department of Nuclear Medicine.
About PET-CT
- Full Form: Positron Emission Tomography–Computed Tomography.
- How it Works: Uses positron-emitting radioisotopes (like Fluorine-18) attached to a tracer (like glucose/FDG). When positrons collide with electrons in the body, they annihilate and release two gamma rays traveling in opposite directions, which are captured by a ring of hundreds of detectors.
- Anatomical Fusion: The functional PET data is perfectly overlaid with a simultaneous CT scan to map the exact location of abnormal cell metabolism.
About SPECT-CT
- Full Form: Single-Photon Emission Computed Tomography–Computed Tomography.
- How it Works: Uses gamma-emitting radioisotopes (like Technetium-99m). The tracer emits a single photon (gamma ray) of radiation, which is picked up by large rectangular detectors that physically rotate around the patient.
- Anatomical Fusion: Combines the single-photon physiological details with a CT scan to clarify and correct for any tissue absorption issues.
PET-CT vs. SPECT-CT
| Feature | PET-CT | SPECT-CT |
| Radiation Type | Emits pairs of gamma rays (from positron annihilation). | Emits a single gamma ray photon. |
| Common Tracer | Fluorine-18 FDG (glucose tracking). | Technetium-99m. |
| Image Resolution | Significantly higher spatial resolution and contrast. | Poorer contrast and lower spatial resolution. |
| Scan Speed | Fast (typically 20 to 45 minutes). | Slower (often taking 1 to 2 hours). |
| Main Clinical Focus | Cancer staging, tumor detection, and microscopic brain lesions. | Bone scans, organ blood flow, and specific cardiac function. |
| Cost & Availability | Highly expensive with short-lived isotopes. | More affordable and widely accessible. |
Key Advantages of Hybrid Scans
- Early Detection: They reveal chemical, functional, and biochemical changes in tissues before an anatomical defect or structural change physically appears on standard X-rays or MRIs.
- Pinpoint Localization: The CT component removes the guesswork by showing exactly where a metabolically active disease or tumour is sitting inside the body.
- Better Biopsy and Surgery Planning: Knowing the exact functional borders of a tumour helps surgeons safely target abnormal tissue without harming healthy surrounding areas.
