ABSTRACT
SPECT has long been considered less accurate than PET as far as quantification is concerned. The main reason is that unlike PET, SPECT has been plagued by the lack of practical attenuation correction for a long time, while attenuation is responsible for the largest bias in quantification when not compensated for. The advent of SPECT-computed tomography (CT) scanners brought a real breakthrough toward accurate SPECT quantification by making attenuation correction both practical and reliable. Many reports now demonstrate that SPECT can accurately estimate tracer uptake, providing that appropriate reconstruction and correction procedures are used. This opens new perspectives regarding the use of SPECT images in applications for which accurate quantification is required. An important example is the use of quantitative SPECT images as an input for dosimetric calculations in radioimmunotherapy protocols, so that the dose-effect relationship can be investigated. Many other clinical investigations could also benefit from reliable quantification in SPECT, including differential diagnosis of neurodegenerative disease, or therapy monitoring in patients with neurodegenerative or cardiovascular diseases.
