Basic Principles and Techniques

The original work of radionucleotide emission tomography was formed by Kuhl and Edwards in 1963. y This research demonstrated the initial use of radionucleotide tracers to create axial reconstructed images. It became apparent that the relative low resolution of this technique research was a limitation begun to focus on the functional imaging capabilities of this technique. Early work with CT in the early 1970s demonstrated the correlation between focal lesions in the brain and lesions demonstrated by radionucleotide emission tomography. Single photon emission

Figure 23-26 A, Cervical duplex ultrasound showing acoustical shadowing secondary to calcified atherosclerotic placB, C orresponding carotid angiogram confirming stenosis.

Figure 23-27 A, Ultrasound of right internal carotid demonstrating flap consistent with arterial dissectifarrow). B, Diagnostic right internal carotid angiogram confirming arterial dissection.

computed tomography (SPECT) imaging uses radionucleotides that release gamma radiation. Gamma cameras detect the radiation released in 360 degrees and creates multiplanar re-formation of these data. In the early 1980s iodine-based radionucleotides were initially used to determine symmetrical brain function. The uptake and distribution of such radionucleotides within the brain is believed to be proportional to blood flow. y Major breakthroughs occurred in the late 1980s with the introduction of technetium-99m-labeled compounds, the most common of which was hexamethylpropylene amineoxime (HMPAO).

A second major technique that investigates functional and, to a lesser degree, anatomical details within the brain is positron emission tomography (PET). This procedure uses positron-emitting radionucleotides in distinction to SPECT imaging, which uses gamma emitters. Positron-emitting particles decay by releasing two annihilation radiation particles into opposite directions that are at 180 degrees to the other. The data are postprocessed and reformatted into multiple planes. Sokoloff, in 1977, described y C-deoxyglucose. y This was a major advancement in functional imaging of the brain that enabled the measurement of glucose uptake and metabolism. Shortly after, the most commonly used PET agent, y F-deoxyglucose (FDG), was introduced. The development of ligands associated with specific neurochemical receptors or other proteins has broadened the use of PET and SPECT to include a growing number of degenerative or biochemical disorders.

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