The technique defined as single-photon emission computed tomography, otherwise known as a SPECT scan, is a method of obtaining an image of organs, and above all, an assessment of their functions, with the use of small doses of radioactive isotopes (radiomarkers). Isotopes are usually administered directly into the veins, but may be administered orally in exceptional cases. These are special monograms and patterns, on the basis of which the isotope dose is calculated depending on body weight and surface. The most frequently used radioisotope is technet-99m, but iod-131, tal-201 and gal-67 are also used, albeit less frequently. These isotopes are usually related to properly selected chemical reactions causing them to collect in a particular organ. Thus, sulphur colloid is taken up by Kupffer cells in the liver; albumin balls are held in the capillaries of the lungs; technet combined with phosphates gathers in bones.
Radioisotopes used in scintigraphy emit gamma radiation which is relatively harmless for the organism. Beta radiation, which can cause damage to cells, is used in radioisotope therapy. The absorbed dose fluctuates from 0.1 to 1Gy. The distribution of isotopes and the direction of flow, secretion and excretion, are imaged on the computer monitor by means of devices called gamma cameras, in which the detector moves over the examined organ. Gamma cameras are a new generation of nuclear medicine equipment. The large head of this machine covers the entire examined organ (liver, heart, brain, kidneys) with its field of vision, and the examination lasts much shorter than a traditional scintigraphy. The results of the examination can be stored in the memory of the computer, on which it is possible to change the colour scales, filter or smooth the image, and above all examine the functionality of the organs. Mobile gamma cameras (rotating) enable the obtainment of slice images (tomographic), similarly to computed tomography. These images are obtained by rotating the head of the scanner around the patient’s body.
The basic benefit of isotope methods is an examination of the functions of the organs: blood flow, filtration of the primary urine, bile flow in hepatic ducts etc. Thus, unless the X-ray techniques better render the structure of the organ, it is difficult to find a better diagnostic technique than isotope methods in terms of the examination of the function of internal organs. Moreover, in many cases, the isotope examinations make it possible to avoid radiological examinations burdened with the risk of complications – combined with the catheterization of vessels or administration of iodine-based contrast media (arteriography, cholangiography, coronarography, urography).
Especially useful isotope scans are:
- Perfusion and ventilation scintigraphy of the lungs in the assessment of pulmonary circulation disorders, including pulmonary embolisms
- Perfusion scintigraphy of the myocardium, as a selective examination and preceding coronarography (angiography of coronary vessels)
- Static scintigraphy of the liver in the diagnosis and control of chronic hepatitis
- Isotope examinations of the kidneys in the diagnosis of renal causes of hypertension