Check Up #11 - Radiology, interventional radiology, and nuclear medicine

Consider CT scans and PET scans. In oncologic radiology, these are two very popular diagnostic tools, meant for imaging the tissues inside the body and detect cancer. 

A CT-scan (CT for computerized tomography) gives detailed, static, images of the body’s internal organs and tissues. This is enough to see a rough image of a tumor, but may not always allow doctors to distinguish the exact frontier between benign and malignant tissues. 

A PET scan (PET for positron emission tomography), on the other hand, entails previously injecting the patient with a small dose of a radioactive tracer substance – in this case, radioactive glucose. Since glucose is more readily absorbed by cancer cells than by healthy cells, the radioactivity accumulates itself inside the tumor cells. This gives much more defined images of where the tumor cells are located, and also to precisely observe, during treatment, whether the tumor is shrinking or not, from one scan to the next – that is, whether the treatment is effective.

Today, CT and PET scans are performed together so as to enable superimposing the PET scan images on the precise anatomy of the patient, supplied by the CT scan. Yet another imaging tool, magnetic resonance imaging (MRI), which involves magnetic fields and not X-rays (so is not radiologic in the strictest sense), can also complement PET imaging.

Radiology is not just observational. It can also be “interventional”, serving to guide surgical interventions without the need for open surgery. Interventional radiology encompasses “minimally invasive procedures that, under the guidance of images obtained through different imaging techniques, enable diagnostic acts, such as guided biopsies, or treatments aimed at the localised destruction of tumours, as well as intra-arterial or intra-tumoural administration of drugs that actively kill cancer cells”, states the Champalimaud Foundation’s website.

As already mentioned, what distinguishes CT scans from PET scans is the introduction, during the latter imaging procedure, of a radioactive substance into the patient’s body. As such, PET scans are a tool of Nuclear Medicine, the specialty of medicine that uses radioactive substances (called radiopharmaceuticals) to diagnosticado and treat disease.

Therapeutical modalities of nuclear medicine use drugs combined with radioactive substances that are going to act on the uptake sites of the drugs. For instance, radioactive iodine, used for the treatment of thyroid cancer, concentrates in the thyroid – because it is basically the only organ in the body that uses iodine –, where radioactivity can then destroy cancer cells. 

Sources

https://www.fchampalimaud.org
https://www.cancerresearchuk.org
https://www.nibib.nih.gov/
https://www.cancer.org/
https://www.cancer.net/
https://www.cancer.gov/

By Ana Gerschenfeld, Health & Science Writer of the Champalimaud Foundation.

Reviewed by: Professor António Parreira, Clinical Director of the Champalimaud Clinical Center.