POSITRON EMISSION TOMOGRAPHY(PET Scan)

POSITRON EMISSION TOMOGRAPHY

 

• PET allows the visualisation of the metabolic activity of disease.
• Helps in diagnosis of malignant tumours and their recurrence.
• Also helps in the staging of tumours and the monitoring of their response to therapy, and in the diagnosis of osteomyelitis.
• The positron-emitting tracers may be used to define:
  1. Amino-acid uptake (11C-methionine; 11 C-tyrosine),
  2. Bone turnover (18F-fluoride).
  3. DNA turnover (18F-fluoro methyl thymidine (FLT)),
  4. Glucose metabolism (18F-fluorodeoxyglucose (FDG)),
  5. Tissue hypoxia (18F-fluoromisonidazole)
• Tumours and infection show increased uptake of FDG

 

PET and Tumours

• FDG imaging of soft-tissue sarcomas can distinguish high-grade from low grade tumours and benign lesion

• The separation of low-grade from benign lesions is not possible.
• Metabolic imaging with FDG combined with MRI may be useful in directing the surgeon to the most malignant area within a large heterogeneous mass and helps in biopsy
• FDG PET is useful in the localisation of distant and multisystem disease in patients with soft-tissue sarcomas or sarcomas of bone.
• The localisation of metastases from soft tissue sarcoma to the lung, however, is not as sensitive as that with CT, although metastases from osteosarcoma are easily visualised.
• Definition of the primary tumour with glucose metabolism, amino-acid uptake, DNA turnover, tissue hypoxia may have a predictive value equal to or higher than histological techniques
• These tracers will also provide information to direct and monitor the response to neoadjuvant therapy

• PET has been shown to be cost-effective in the management of lung cancer by reducing morbidity from unnecessary operative intervention and allowing better selection of patients for definitive surgery.

Infection

• FDG PET also helps in the diagnosis of infection
• FDG has accuracy for diagnosing infection in the peripheral skeleton of 96% and in the central skeleton of approximately 96%.
• FDG has the potential advantage of a single-step procedure with imaging one hour after the injection, rapid loss of radioactivity from the patient and a radiation dose comparable to the leucocyte imaging techniques