SPECT - Tomoscintigraphy (assessment exams)

Content

Introduction

Tomoscintigraphy (SPECT, from the English Single Photon Emission Computed Tomography also called SPET) is a nuclear medicine exam based on the administration of a radiopharmaceutical (chemical substances that have the property of interacting specifically with the biological system but which, once injected in vivo, can also be followed from the outside) and on the subsequent detection of gamma photons emitted by the radioactive substance which is part of the radiopharmaceutical.

Gamma radiation, like visible light, but much more energetic, is detected by a kind of camera, commonly called gamma camera, which revolves around the person undergoing the exam.

By suitably processing the electrical signals coming from the gamma camera tomographic images are obtained, or “photographs” of the distribution of the radiopharmaceutical on virtual “slices” (layers) of the person's body. The layered images can be combined to obtain a "three-dimensional image of the distribution of the radiopharmaceutical.

The principle of operation is not very different from that of a CT scan (or CT in English): the main difference is that while in the CT the source of the radiation is external to the person, in the SPECT the source of the radiation (the radiopharmaceutical) is internal to the person. person and the images are linked not so much to the shape of the organs and tissues, as in the CT scan, but above all to the way in which the organism transforms the radiopharmaceutical. SPECT therefore provides important details on the functioning of the tissues / organs under examination.

The two diagnostic techniques, CT and SPECT, are in many respects complementary and are often used simultaneously, to obtain the maximum possible information.

Radiopharmaceuticals used for a SPECT examination contain radionuclides that emit gamma photons of well-defined energy.

The main areas of application of this technique for images they are cardiology, neurology and oncology. For example, tomoscintigraphy of the heart allows to study its blood flow and vital capacity.

The examination is generally performed both at rest and during exercise. Often, even on two different days. By comparing the two different images obtained, the nuclear doctor will be able to distinguish, for example, a zone of ischemia from one of a heart attack.

SPECT also allows to study brain diseases and, in particular, cerebrovascular diseases, epilepsies, neurodegenerative diseases and brain tumors. In this case, the radiopharmaceutical is distributed in the central nervous system in proportion to the blood flow of the affected area and the tomographic images represent the regional circulation.

The test

The tomoscintigraphic examination involves the administration, generally intravenously, of a specific radiopharmaceutical based on the analysis to be performed.For some tests such as, for example, brain tomoscintigraphy, radiopharmaceuticals can be administered by mouth (orally), intravenously, intraperitoneally or locally.

Between the administration of the radiopharmaceutical and the acquisition of the scintigraphic images there is a waiting time (approximately 1 hour) to allow the radiopharmaceutical to distribute itself in the areas to be investigated. Generally, you are asked to drink water to hydrate yourself well both in the waiting phase and after the examination to favor the elimination of that part of the radiopharmaceutical which is not absorbed by the organism.

The modest amount of radioactivity assumed by the person during the examination (and the short decay times of the radioactive substance) does not create particular inconvenience to the personal and family members; at the end of the examination, normal activities can be resumed, generally following in the 24 hours later, some simple precautionary rules, provided by the staff.

In the case of presumed or confirmed pregnancy, the woman is required to inform the nuclear doctor of her condition. The doctor will evaluate whether, for clinical reasons, it is necessary to proceed with the examination. If the woman is breastfeeding, a temporary suspension of breastfeeding may be necessary. The withdrawal period depends on the type of radiopharmaceutical used.

The tomoscintigraphic examination can be performed at the same time as a therapeutic treatment with a radiopharmaceutical (metabolic radiotherapy). In this case, after the administration of the radiopharmaceutical, in a quantity greater than that foreseen for the ascertainment of diseases (diagnostic examination), must be hospitalized in special radio-protected rooms for a period ranging from 2 to 5 days. During this period the radiopharmaceutical carries out its therapeutic function, is gradually disposed of by the organism and / or the corresponding radiosotope decays naturally (it loses its characteristic radioactivity).Upon reaching levels of radioactivity considered acceptable according to current regulations, and such as not to create problems for family members, people can be discharged and return home.

Bibliography

Italian Association of Nuclear Medicine and Molecular Imaging (AIMN)

World Health Organization (WHO). Nuclear medicine (NM) exams in children (English)

In-depth link

International Atomic Energy Agency (IAEA). Radiation protection in nuclear medicine (English)

Italian Association of Medical and Health Physics (AIFM). Nuclear Medicine and the Medical Physicist

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