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Radiolabeled PET

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Radiolabeled PET

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Radiolabeled PET

  1. 1. Radiolabeled PET imaging tracers for in vivo detection of pre-symptomatic Alzheimer’s disease [EXCERPT] Copyright © by Lorena Tonarelli, M.Sc. 2014 Alzheimer’s disease (AD) is a progressive neurodegenerative disorder characterized by the formation, in the brain, of extracellu- lar β-amyloid deposits and intraneuronal τ- protein tangles, which correlate to cogni- tive decline. [1,2] Currently, the diagnosis of AD is based on clinical criteria. However, these have low sensitivity and specificity, and only allow making a diagnosis of probable or possible Alzheimer’s disease. Conventional mag- netic resonance (MR) and computed tomo- graphy (CT) imaging also have low sensitiv- ity and specificity. They are primarily used as adjuncts to clinical diagnosis to help ex- clude other types of dementia, and to as- sess the degree of brain atrophy. Conse- quently, a definite diagnosis of AD can be achieved only at autopsy. [3] Non-invasive radio-labeled positron emis- sion tomography (PET) imaging tracers have been developed in the past 20 years, which can detect, in vivo, β-amyloid and τ- protein deposits, well before AD symp- toms become apparent. The most widely studied of these tracers are the 11C- Pittsburgh Compound B (11C-PIB) and 18F-(2-(1-{6-[(2-[18F]fluoroethyl)(methyl)a mino]-2-naphthyl}ethylidene)malononitrile)( 18F-FDDNP). [4,5,6] Another 18F-labeled PET β-amyloid tracer under study is 18F- AV-45 (florbetapir F18). [7] Patients undergo PET imaging after receiv- ing an intravenous injection of the selected biomarker. This travels to the brain, where it binds uniquely to β-amyloid (11C-PIB and florbetapir F18) or to β-amyloid and τ (18F-FDDNP). [4,5,6,7] Amyloid aggre- gates become apparent in the scans within as little as 30 minutes. [8] Both qualitative and quantitive β-amyloid pathology data obtained with radio-labeled PET imaging correlate well with visual ob- servations at autopsy. [9] To date, no ad- verse events have been reported, in stud- ies, following the use of radiolabeled PET tracers. [8] Clinically relevant advantages An advantage of 18F-labeled PET amyloid- β imaging tracers over conventional diag- nostic methods is the possibility of reach- ing a diagnosis in vivo. Other benefits in- clude: 2

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