PET and the multitracer concept in the study of neurodegenerative diseases

Brain SPECT as a Biomarker of Neurodegeneration in Dementia in the Era of Molecular Imaging: Still a Valid Option?

Biomarkers are playing a progressively leading role in both clinical practice and scientific research in dementia. Although amyloid and tau biomarkers have gained ground in the clinical community in recent years, neurodegeneration biomarkers continue to play a key role due to their ability to identify different patterns of brain involvement that sign the transition between asymptomatic and symptomatic stages of the disease with high sensitivity and specificity. Both ¹⁸F-FDG positron emission tomography (PET) and perfusion single photon emission computed tomography (SPECT) have proved useful to reveal the functional alterations underlying various neurodegenerative diseases. Although the focus of nuclear neuroimaging has shifted to PET, the lower cost and wider availability of SPECT make it a still valid alternative for the study of patients with dementia. This review discusses the principles of both techniques, compares their diagnostic performance for the diagnosis of neurodegenerative diseases and highlights the role of SPECT to characterize patients from low- and middle-income countries, where special care of additional costs is particularly needed to meet the new recommendations for the diagnosis and characterization of patients with dementia.

Clinical Impact of PET With 18F-FDG and 11C-PIB in Patients With Dementia in a Developing Country

Introduction: The objective of this study was to evaluate the clinical impact PET with ¹⁸F-FDG and ¹¹C-PIB in patients with dementia in a developing country.

Methodology: Retrospective study of the patients referred for the evaluation of dementia to the only PET center in Uruguay. A total of 248 patients were identified, from which 70 patients were included based on the availability of medical history and clinical follow-up. Main outcomes included change in diagnosis, diagnostic dilemma and AD treatment. We evaluated the association of clinical outcomes with PET concordance with baseline diagnosis, diagnostic dilemma, level of education, AD pathology/Non-AD pathology (AD/Non-AD), baseline diagnosis and ¹¹C-PIB PET result.

Results: Baseline clinical diagnosis was concordant with ¹⁸F-FDG and ¹¹C-PIB PET results in 64.7 and 77.1% of the patients, respectively. Change in diagnosis after PET was identified in 30.0% of the patients and was associated with discordant ¹⁸F-FDG (p = 0.002) and ¹¹C-PIB (p < 0.001) PET results, previous diagnostic dilemma (p = 0.005), low education (p = 0.027), Non-AD baseline diagnosis (p = 0.027), and negative ¹¹C-PIB PET result (p < 0.001). Only the last variable remained significant in the multivariate analysis (adjusted p = 0.038). Diagnostic dilemma decreased after PET from 15.7 to 7.1% (p = 0.11) and was associated with Non-AD diagnosis (p = 0.002) and negative ¹¹C-PIB PET result (p = 0.003). Change in AD treatment after PET occurred in 45.7% of the patients.

Conclusion:¹⁸F-FDG and ¹¹C-PIB PET had a significant clinical impact in terms of change in diagnosis and treatment in patients with dementia in a developing country, similar to that reported in high-income countries.

[PET imaging for better understanding of normal and pathological neurotransmission]

Positron emission tomography imaging is still an expanding field of preclinical and clinical investigations exploring the brain and its normal and pathological functions. In addition to technological improvements in PET scanners, the availability of suitable radiotracers for unexplored pharmacological targets is a key factor in this expansion. Many radiotracers (or radiopharmaceuticals, when administered to humans) have been developed by multidisciplinary teams to visualize and quantify a growing numbers of brain receptors, transporters, enzymes and other targets. The development of new PET radiotracers still represents an exciting challenge, given the large number of neurochemical functions that remain to be explored. In this article, we review the development context of the first preclinical radiotracers and their passage to humans. The main current contributions of PET radiotracers are described in terms of imaging neuronal metabolism, quantification of receptors and transporters, neurodegenerative and neuroinflammatory imaging. The different approaches to functional imaging of neurotransmission are also discussed. Finally, the contributions of PET imaging to the research and development of new brain drugs are described.