Positron emission tomography (PET) and single-photon emission computed tomography (SPECT) in autism research: literature review

Autism spectrum disorder (ASD) remains a behaviourally defined condition. Its molecular basis is unknown; however, its prevalence has been increasing significantly. There have been several abnormalities in neurotransmitter systems reported in ASD. In our review, we described studies involving positron emission tomography (PET) and single-photon emission computed tomography (SPECT) that can provide useful and corroborative data.We conducted a literature review by comprehensive database searching on EMBASE, Scopus, PubMed, and PsychINFO looking for articles published since January 2009. Thirty-one studies were carefully selected - 22 PET studies and 9 SPECT studies - and reviewed by 2 independent researchers. References of the articles were also cross-checked.Results of the studies, which mainly involve small groups of participants, are frequently inconclusive and often controversial due to the nature of ASD and its wide spectrum. Studies are conducted under different conditions and with poor control for confounding factors which creates difficulties in comparing the data.There is ongoing need to improve methodology of the studies involving molecular imaging in ASD. Lack of consistent findings causes difficulties in evaluation, diagnosis, and treatment of the condition.