Nuclear Medicine is the branch of medicine that uses small amounts of radioactive substances, the radiopharmaceuticals, to obtain functional and anatomical information of the organs and thus diagnose and treat diseases. One of the most important procedures in nuclear medicine is PET or positron emission tomography.
The PET-CT (Positron Emission Tomography – Computed Tomography) is a noninvasive technique that combines two different technologies for imaging diagnosis, PET and CT in a single device. It is a hybrid scanner which provides anatomic and functional information simultaneously.
Positron Emission Tomography detects the metabolic activity of different tissues in the human body. As with other diagnostic techniques in nuclear medicine, PET is based on recognizing and analysing the distribution of a radioisotope administered through intravenous injection in the body.
PET detects metabolic changes caused by minimal alterations in the tissues, using images generated by the decay of radioisotopes. Simultaneously Computed Tomography (CT) provides detailed images of the exact location, size and shape of the diseased tissue.
The combination of data provided by PET (metabolic data) plus CT (anatomical data) gives more information than each one separately.
There are several positron-emitting radioisotopes of medical use. The most frequently used is the Fluorine – 18 attached to a molecule of glucose to obtain the tracer Fluorine-18-deoxy-glucose (18FDG). This marker can identify, locate and quantify the uptake of glucose. A high intake of glucose is characteristic of neoplastic tissues.
The most common diagnostic applications of PET are in oncology. Currently this group represents over 85% of the indications. It is also indicated in the study of neurological disorders, neurodegenerative diseases, epilepsy, feasibility study.
The main general indications of this technique in the field of oncology are:
- Detection of malignant tumors, given the pathophysiological differences in the biological activity between benign and malignant processes.
- Staging and restaging, given the possibility of whole-body studies in a single scan.
- Location of unknown primary tumor.
- Detection of tumor recurrence.
- Differentiation between recurrence and radionecrosis.
- Detection of second primary tumor (especially head and neck cancers).
- Predictability of response to chemotherapy.
- Monitoring of treatment: to early planning of treatment in cases with little or no response.