Medical applications

Radioisotopes and radiopharmaceuticals

The applications of nuclear science are widespread in medicine, especially as methods of diagnosis and treatment. Numerous techniques of nuclear medicine are based on substances that contain radioisotopes, currently called radiopharmaceutical substances.

Radiopharmaceuticals act mainly as tracers. A wide range of specific components of human body may be highlighted and traced through radiopharmaceutical substances. A radiopharmaceutical substance is, basically, a common chemical compound, which was “labelled” radioactive and its route can thus be traced with radiation measuring devices.

Radioisotopes can also be used to assess the cell membrane permeability, to determine the activity of certain organs etc. Once inside the body, the distribution of radiolabelled compounds is monitored through a network of gamma detectors placed around the patient. The computer processes the collected data, and the doctors analyse the outcome: the high concentrations of radiolabelled compounds within or around an organ indicate hyperactivity, and the low concentrations can indicate a hypo activity of the respective organ.

The magnetic resonance imaging is based on the vibrations generated by nuclei when they are bombarded with radio waves in a magnetic field (Nuclear Magnetic Resonance-NMR).

The magnetic resonance imaging is used as an analytical instrument in scanning different parts of the body, especially in brain scan.

Advanced resolution images of different tissues from the human body, more accurate than through computerized tomography (CAT) or through ecography (based on ultrasounds) can also be obtained. The resolution of magnetic resonance images is one of the most advanced, of the order 0,5 to 1 mm.

An NMR imaging device consists of an empty cylinder where the patient is placed. A high reactance coil crosses cylinder walls. When the coil is supplied with electricity, a strong magnetic field concentrated in the cylinder’s centre ensures the nuclei resonance in the investigated areas of the body. The incoming signals are converted to images by the computer, and specialists analyse the final images.

Tracers

Radioisotopes emit radiation that can be detected and measured, by using specific detectors (Geiger, with scintillation etc.). The detection of the emitted radiation allows the precise location of the radioisotopes and the route crossed by these.

The technique is called tracing and the radioisotopes thus used are called tracers.
This technique can be used to determine the movement of a compound in the plants’ or animals’ body. This is achieved by radioisotope administration (in food or by injection), followed by monitoring its route within the plant or organism.

Therapy through irradiation

Cancer cells with high multiplying rate are also sensitive to radiation. Rigorous determined irradiation regimes (very narrow beam, focused on the affected areas) might destroy cancer cells, with manageable side effects at the level of the entire body.

Radiation can also be used to sterilize the reusable surgical instruments in hospitals, by the irradiation of bacteria and viruses, especially in the case of materials sensitive to heat and steam, and also to sterilize the blood for transfusions.

Emission Tomography

SPET

Single Photon Emission Tomography (SPET) technique supposes the administration of a radiopharmaceutical substance in the patient’s body, followed by the rotation of a radiation detector around the patient, in order to detect the emitted radiation from different angles of the body. These data acquired at different angles are processed by the computer, and thus result the images that are analysed by the specialist.

CAT

Computer Aided Tomography (CAT) uses the general concept of data acquisition and processing by rotating a detector around a patient, to detect the radiation emitted at different angles. In this respect, SPET may be considered a CAT version.

PET

A new highly effective method of medical diagnosis is Positron Tomography (Positron Emission Tomography – PET), that allows obtaining of high resolution morpho-functional images, based on capturing a radiotracer according to the metabolism of various organs and structures.

The method consists in labelling some biological substances (for ex. glucose, aminoacids, ligand-receptors, etc.), with isotopes emitting positrons (11C, 18F, 13N, 15O), after that the labelled material is introduced into the patient’s body, following the establishment of its distribution image.

A positron emitted by isotopes’ beta decay collides with an electron in the tissue, two gamma rays being given off.

PET-CT fusion imaging (Positron Emission Tomography) / CT (Computerized Tomograph) can locate the disease exactly and can precisely identify the pathology. In the case of cancer, the cancer cells start from the level of a gene that changes its behaviour, and determines an anarchic cell increase. Cancer cells need a more energetic support than a normal cell, provided by glucose.

Using PET-CT the glucose labelled by an isotope is introduced in the body, it spreads throughout the body, and the lesion appears as a hot white spot. Till now, the patients were examined by CT or RMN; using the contrast substance yields in a hot spot on an organ, but this exam didn’t tell the whether the respective cell was cancerous or not. PET/CT can detect cancer before it reaches the tissues level, i.e. four to six years before manifesting, the cancer cell can thus be identified and killed. Only pathological cells are destroyed, that’s why the technique was called “targeted radiotherapy”.

The main PET-CT applications of imaging method are:

• The detection in early stage of the primitive and metastatic cancers;
• The diagnosis of malignant tumors;
• Estimation the chemotherapy/radiotherapy effectiveness in oncology, by assessing the metabolism of the remaining tissues;
• Noninvasive applications in the diagnosis of cardiovascular diseases, with superior results to coronarography;
• Psychiatric and neurological diseases (Alzheimer, senile dementia etc.);
• Septic determinations, undetected through other methods.