Abstract
Images from single-photon emission tomography (SPECT) visualize the distribution of a radiotracer within the human body. On these images, using regions of interest, tracer uptake may, in principle, also be quantified. Absolute quantification is, however, confounded by a variety of factors such as those caused by tissue attenuation, photon scatter or limitations in spatial resolution. Hybrid systems combining SPECT with X-ray computed tomography (CT) provide coregistered image datasets. Based on CT information on tissue attenuation, in particular a correction of the SPECT data for attenuation artefacts can be performed. After cross-calibrating the SPECT camera against a well counter, tissue radioactivity concentration can be measured in absolute units such as in kBq/ml with SPECT in a precision similar to that of positron emission tomography (PET). Possible clinical applications of truly quantitative SPECT are dosimetry of radionuclide therapy, monitoring tumor response to treatment, and the diagnosis of diseases leading to diffuse rather than focal abnormalities of tracer uptake such as three-vessel coronary artery disease (CAD).
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