Perfusion scintigraphy of the brain (synonym: perfusion scintigraphy of the brain) is used in nuclear medicine diagnostics as a dynamic scintigraphy procedure. The general principle of scintigraphic examinations is based on the fact that the patient is administered a radioactive substance (radionuclides, also called “tracers”), which, depending on its chemical structure, is deposited in different target organs/tissues and can then be registered externally by a scintillation detector or gamma camera. Since many pathological (diseased) processes such as inflammations or tumors have an altered metabolism and are thus inclined to store the radionuclides in increased or decreased amounts, they can be localized in scintigraphy. Dynamic scintigraphy is an extension of static scintigraphy and provides additional information about different phases of activity in the examined area. In the brain, the registration of perfusion (blood flow) has a special significance. The perfusion-dependent distribution of the radionuclide and thus an increase or decrease in blood flow can be recorded. If, for example, a reduced inflow of radioactive activity is detectable compared to the other half of the brain, a one-sided perfusion disturbance (stenosis or occlusion of a cerebral artery) can be assumed. Hypervascularized (vessel-rich) tumors such as angiomas, on the other hand, become conspicuous because of their strong perfusion and accumulation of the radionuclide.
Indications (areas of application)
Perfusion scintigraphy allows accurate assessment of regional brain perfusion. Inferior perfusion is detectable earlier than in computed tomography (CT) or magnetic resonance imaging (MRI). Nevertheless, it should be noted that nowadays sonography of the carotids (neck vessels; carotid artery), MR angiography or DSA (digital subtraction angiography) are usually preferred to perfusion scintigraphy for the clarification of cerebral perfusion disorders. Perfusion scintigraphy may be indicated for the following questions:
- Suspected impaired cerebral perfusion reserve (blood flow reserve of the brain): reversible perfusion defects or the early phase of ischemic apoplexy (stroke; reduced blood flow to certain parts of the brain due to vascular constriction/occlusion) can be diagnosed early with scintigraphy.
- Localization of epileptic foci: Between seizures, the seizure focus usually shows decreased perfusion.
- Differential diagnosis and early detection of degenerative diseases (diseases associated with neuronal death, e.g., dementias): Reduced blood flow in certain basal ganglia parts are characteristic of various forms of dementia, for example.
- Suspected brain involvement in collagenoses (group of connective tissue diseases caused by autoimmune processes): systemic lupus erythematosus (SLE), polymyositis (PM) or dermatomyositis (DM), Sjögren’s syndrome (Sj), scleroderma (SSc) and Sharp syndrome (“mixed connective tissue disease”, MCTD).
- HIV encephalopathy (HIVE) (infection of the central nervous system with HIV): if MRI is unremarkable, perfusion scintigraphy can also be performed.
- In addition, perfusion scintigraphy can be used to diagnose brain death.
Contraindications
Relative contraindications
- Lactation phase (breastfeeding phase) – breastfeeding must be interrupted for 48 hours to prevent risk to the child.
- Repeat examination – no repeat scintigraphy should be performed within three months due to radiation exposure.
Absolute contraindications
- Gravidity (pregnancy)
Before the examination
- The patient must rest for 15-20 min in a darkened room to turn off the activity of certain brain areas (vision, speech, etc.) to ensure uniform brain perfusion.
- If necessary, the examination can be repeated with vasodilator (vasodilating) drugs to determine the maximum possible reserves: For this purpose, the patient receives acetazolamide (Diamox), which serves to dilate the cerebral vessels, before the second examination. Comparing the stress examination (with Diamox) with the baseline examination, one can determine the perfusion reserve by subtraction.
- The patient should take care not to consume any vasodilative (vasodilating) or vasoconstrictive (vasoconstricting) substances on the day of the examination. A few hours before the examination you should therefore refrain from: Smoking, black tea or coffee.
The procedure
- The radiopharmaceutical is applied intravenously to the supine patient. As in the preparatory phase, rest must be maintained during this procedure. The room is usually darkened, and the examination procedure should have been clarified beforehand, so that no more talking is done with the patient.
- The radionuclide used is [99mTc]technetium. In order for the 99mTc-labeled radiopharmaceutical to pass the blood-brain barrier, lipophilic (fat-soluble) structures must be chemically added. Two substances are commercially available: 99mTc-labeled hexamethylpropyleneamine oxine (99mTc- HMPAO) and 99mTc-labeled ethylcysteinate dimer (99mTc-ECD).
- After lipophilic substances are well absorbed intracerebrally (into brain tissue), they are converted intracellularly (within cells) into a hydrophilic (water-soluble) form so that they cannot leave the cell and accumulate (accumulate).
- Radionuclide activity is measured after 60 min of quiescence using a gamma camera. The simplest way of registration of activity distribution is planar scintigraphy, which allows images in several planes, but with superpositions. Nowadays, high-resolution multi-head SPECT (single photon emission computed tomography) systems are used, which rotate around the patient during the examination and ensure an image of the brain tissue without superimposition due to the cross-sectional principle.
Possible complications
- Intravenous application of radiopharmaceutical may result in local vascular and nerve lesions (injuries).
- Radiation exposure from the radionuclide used is rather low. Nevertheless, the theoretical risk of radiation-induced late malignancy (leukemia or carcinoma) is increased, so that a risk-benefit assessment should be performed.
