Single-photon emission computed tomography
Single photon emission computed tomography ( SPECT short of English Single Photon Emission Computed Tomography ) is a diagnostic procedure for the preparation of sectional images of living organisms, and thus a variation of the emission computed tomography. SPECT images show the distribution of a radiopharmaceutical in the body. They are suitable, depending on the nature of the radiopharmaceutical, to assess the function of various organs.
Principle and implementation
Based on the principle of scintigraphy, the patient is to begin studying a radiopharmaceutical ( radionuclide or labeled with a radionuclide substance) administered, usually given as an injection into an arm vein. The radionuclides used emit gamma radiation that is detected by gamma camera. One or more such cameras rotate around the body and detecting the emitted radiation from different directions in space. For these planar images (called projections) can be by means of inverse Radon transform back close and this is then represented as a slice images through the body, for example the distribution of the radiopharmaceutical within the body. In contrast to "static" SPECT studies in which only the distribution of the radiopharmaceutical is determined at a time, there are also so-called "dynamic" tests, whereby by repeated measurements at intervals of minutes, hours or days an assessment temporal change of the distribution of radioactivity reached (for example with 133Xe ). Frequent application will SPECT within cardiology, which ( measured by an additional ECG, for example ) in relation with the heartbeat of the measured decays registered. The latter method is called gated SPECT, because the data are sorted into different gates or bins.
Other areas of application
- Myocardial SPECT to study the vitality of the heart muscle ( myocardial scintigraphy ). The radiopharmaceutical used is usually the technetium isotope 99mTc ( isonitrile methoxyisobutyl ) in MIBI.
- Bone SPECT for localization of regions with altered bone metabolism in skeletal scintigraphy.
- Brain and Cerebral SPECT: FP - CIT (abbr. for 123I -N- ω - 2β - carbomethoxy - fluoropropyl - 3β -(4- iodophenyl ) nortropane ) and IBZM - ( Short for 123I - Jodbenzamid ) SPECT in the diagnosis and differentiation of Parkinson syndromes and compared with other degenerative brain diseases
- Epilepsy SPECT, see Hirnperfusionsszintigrafie
- Octreotide SPECT in the somatostatin receptor scintigraphy in neuroendocrine tumors
- 123I - Metaiodobenzylguanidin ( MIBG scintigraphy ) in adrenergic tumors such as the adrenal medulla, called pheochromocytoma
Comparison and combination with other methods
The SPECT heard such as positron emission tomography (PET ) to the functional imaging techniques: the images produced mainly give information on metabolic processes in the body being examined. The morphology of the body can, however, only roughly assess because it is not or only partially included in the mapped metabolic information and in addition, the resolution is inferior to other methods. X-ray computed tomography ( CT) is more suitable for the representation of the morphology.
Newer devices systems such as SPECT / CT allows combining the advantages of the morphological and functional imaging on a camera and data analysis on the same computer system. The resulting so-called fusion images allow the accurate mapping of functional abnormalities of the anatomical structures. This process is of particular importance in the assessment of various cancers and their follow-up examinations.
Compared to PET SPECT is less expensive and cheaper, since on the one hand no short-lived radionuclides are used, which have to be produced in close proximity to the scanner, and the scanner on the other hand are much more cost effective (less electronics). Today, the applications of the two methods, however, go seamlessly into each other. Also in SPECT come now those usually used for PET rapidly disintegrating radionuclides used. The main disadvantages are the lower compared to the PET spatial resolution and lower sensitivity of the cameras. The reason is the camera principle, in which the direction information of the radiation is obtained by means of collimators, which act effectively as filters and virtually all radiation from the camera away except that which comes from a well-defined direction. This reduces the imaging efficiency significantly related to the necessary use of the radionuclide in comparison to PET.
In diagnostic nuclear medicine with SPECT alone is resorted to γ - emitters (usually 99mTc), since other types of radiation ( α - and β - radiation) in the tissue have a very short range to be measured outside the body can. These types of radiation found in nuclear medical therapy use. β - emitters are used in the PET, there, however, the photon emission ( γ - radiation), as a secondary ( from primary or positron β particles triggered ) effect ( annihilation radiation ) is used.