Question: Which are the biotracers used for detection of Alzheimer's disease using PET?

Context:
(18)F-flutemetamol PET and structural MRI provided additive information in the diagnostic classification of aMCI subjects, suggesting an amyloid-independent neurodegenerative component among aMCI subjects in this sample.
This pooled analysis of four studies determined the level of association between uptake of the fibrillar amyloid β positron emission tomography (PET) imaging agent [(18)F]flutemetamol (Pittsburgh Compound B analog with a 5.5 times longer half-life to enable it to be used in the clinical setting) 
is implicated in the development of late-onset Alzheimer's disease (AD). We sought to determine the associations between beta amyloid (Aβ) plaque deposition in vivo using Pittsburgh compound B (PiB) and several indices of cholesterol homeostasis (i.e., total cholesterol, high-density lipoprotein cholesterol, low-density lipoprotein cholesterol, triglycerides, apolipoprotein E (ApoE), clusterin, oxysterol metabolites of cholesterol, and previously reported genes associated with late-onset AD) in 175 nondemented elderly subjects. High Aβ dep
g biomarkers of Alzheimer's disease include amyloid deposition [imaged with [(11)C]Pittsburgh compound B (PiB) PET], altered glucose metabolism (imaged with [(18)F]fluro-deoxyglucose PET), and structural atrophy (imaged by MRI). Recently we published the initial subset of imaging findings for specific regions in a cohort of individuals with autosomal dominant Alzheimer's disease. We now exte
Criteria for preclinical Alzheimer disease (AD) propose β-amyloid (Aβ) plaques to initiate neurodegeneration within AD-affected regions. However, some cognitively normal older individuals harbor neural injury similar to patients with AD, without concurrent Aβ burden. Such findings challenge the proposed sequence and suggest that Aβ-independent precursors underlie AD-typical neurodegenerative patterns. OBJECTIVE T
ol is a positron emission tomography (PET) tracer for in vivo amyloid imaging. The ability to classify amyloid scans in a binary manner as 'normal' versus 'Alzheimer-like', is of high clinical relevance. We evaluated whether a supervised machine learning technique, support vector machines (SVM), can replicate the assignments made by visual readers blind to the clinical diagnosis, which image components have highest diagnostic value according to SVM and how (18)F-flutemetamol-based classification using SVM relates to structural MRI-based classification using SVM within the same subjects. By means of SVM with a linear kernel, we analyzed (18)F-flutemetamol scans and volumetric MRI scans from 72 cases from the (18)F-flutemetamol phase 2 study (27 clinically probable Alzheimer's disease (AD), 20 amnestic mild cognitive impairment (MCI), 25 controls). In a leave-one-out approach, we trained the (18)F-flutemetamol based classifier by means of the visual reads and tested whether the classifier was able to reproduce the assignment based on visual reads and which voxels had the highest feature weights. The (18)F-flutemetamol based classifier was able to replicate the assignments obtained by visual reads with 100% accuracy. The voxels with highest feature weights were in the striatum, precuneus, cingulate and middle frontal gyrus. Second, to determine concordance between the gray matter volume- and the (18)F-flutemetamol-based classification, we trained the classifier with the clinical diagnosis as gold standard. Overall sensitivity of the (18)F-flutemetamol- and the gray matter volume-based classifiers were identical (85.2%), albeit with discordant classification in three cases. Specificity of the (18)F-flutemetamol based classifier was 92% compared to 68% for MRI. In the MCI 
disease (AD) is defined histologically by the presence of extracellular β-amyloid (Aβ) plaques and intraneuronal neurofibrillary tangles in the cerebral cortex. The diagnosis of dementia, along with the prediction of who will develop dementia, has been assisted by magnetic resonance imaging and positron emission tomography (PET) by using [(18)F]fluorodeoxyglucose (FDG). These techniques, however, are not specific for AD. Based on the chemistry of histologic staining dyes, several Aβ-specific positron-emitting radiotracers have been developed to image neuropathology of AD. Among these, [(11)C]PiB is the most studied Aβ-binding PET radiopharmaceutical in the world. The histologic and biochemical specificity of PiB binding across different regions of the AD brain was demonstrated by showing a direct correlation between Aβ-containing amyloid plaques and in vivo [(11)C]PiB retention measured by PET imaging. Because (11)C is not ideal for commercialization, several (18)F-labeled tracers have been developed. At this time, [(18)F]3'-F-PiB (Flutemetamol), (18)F-AV-45 (Florbetapir), and (18)F-AV-1 (Florbetaben) are undergoing extensive phase II and III clinical trials. This article provides a brief review of the amyloid biology and chemistry of Aβ-specific (11)C and (18)F-PET radiopharmaceuticals. Clinical trials have clearly documented that PET radiopharmaceuticals capable of assessing Aβ content in vivo in the brains of AD subjects and subjects with mild cognitive impairment will be important as diagnostic agents to detect in vivo amyloid brain pathology. In addition,
is well known that many clinical and genetic factors have been associated with beta-amyloid deposition, few studies have examined the interactions of such factors across different stages of Alzheimer's pathogenesis. METHODS: We used 18F-florbetapir F18 PET imaging to quantify neuritic beta-amyloid plaque density across four cortical regions in 602 elderly (55-94 years) subjects from the national ADNI biomarker study. The group comprised of 194 normal elderly, 212 early mild cognitive impairment [EMCI], 132 late mild cognitive impairment [LMCI], and 64 mild Alzheimer's (AD). FINDINGS: In a model incorporating multiple predictive factors, the effect of apolipoprotein E ε4 and diagnosis was significant on all four cortical regions. The highest signals were seen in cingulate followed by frontal and parietal with lowest signals in temporal lobe (p<0.0001). The effect of apolipoprotein E ε4 (Cohen's D 0.96) on beta-amyloid plaque density was approximately twice as large as the effect of a diagnosis of AD (Cohen's D 0.51) and thrice as large as the effect of a diagnosis of LMCI (Cohen's D 0.34) (p<0.0001). Surprisingly, ApoE ε4+ normal controls had greater mean plaque density across all cortical regions than ε4- EMCI and ε4- LMCI (p<0.0001, p=0.0009) and showed higher, though non-significant, mean value than ε4- AD patients (p<0.27). ApoE ε4+ EMCI and LMCI subjects had significantly greater mean plaque density across all cortical regions than ε4- AD patients (p<0.027, p<0.0001). INTERPRETATION: Neuritic amyloid plaque load across progressive clinical stages of AD varies strongly by ApoE4 genotype. These findings support the need for better pathology-based and supported diagnosis in routine practice. Our data als
sitron emission tomography (PET) radiotracers, fluorodeoxyglucose F 18 ((18)F-FDG) is the compound most widely used in the diagnosis of neurodegenerative dementias. However, this compound shows a level of specificity and sensitivity for early Alzheimer's disease detection that is lower than that provided by high-affinity ligands for β-amyloid (Aβ). Among the new widely available fluorine 18 ((18)F)-labeled Aβ ligands, florbetapir F 18 ((18))F-AV-45; Amyvid™) showed clear qualitative and quantitative correlations between in vivo PET imaging and postmortem histopathologic analysis of Aβ. Florbetapir F 18 stands out for its high Aβ affinity and its pharmacokinetic properties that allow 10-minute PET scan imaging within 90 minutes after administration (dose = 370 MBq). Importantly, no safety concerns for florbetapir F 18 were found in preclinical studies. In 2012, the U.S. Food and Drug Administration (FDA) approved Amyvid as a radiotracer helpful for excluding the presence of Aβ in the brain. It was the
 (Abeta) plaque formation is a hallmark of Alzheimer's disease (AD) and precedes the onset of dementia. Abeta imaging should allow earlier diagnosis, but clinical application is hindered by the short decay half-life of current Abeta-specific ligands. (18)F-BAY94-9172 is an Abeta ligand that, due to the half-life of (18)F, is suitable for clinical use. We thus studied the effectiveness of this ligand in identifying patients with AD. METHODS: 15 

Answer: Pittsburgh compound B (PIB) was the first radiotracer capable of highlighting deposits of beta-amyloid—one pathological hallmark of Alzheimer's disease—in living individuals during a PET scan. The Alzheimer's Association helped fund early PIB development. The Association in 2006 also awarded a $2.1 million grant to the Alzheimer's Disease Neuroimaging Initiative (ADNI) to expand this long-term, nationwide study to include PIB-PET imaging.

18F flutemetamol (flute), another radiotracer that highlights beta-amyloid in a PET scan, is structurally identical to PIB except for one fluorine atom in place of a carbon atom. That small chemical change enables flutemetamol to remain stable significantly longer than does PIB, potentially increasing its usefulness outside research settings. In phase II study results reported in the Annals of Neurology, flutemetamol performed similarly to PIB. Additional testing is under way.

Florbetapir F 18 (18F-AV-45) is also a radiotracer that highlights brain beta-amyloid during a PET scan. At the 2010 Alzheimer's Association International Conference on Alzheimer's Disease (AAICAD), florbetapir's developer first reported data, later published in the JAMA, showing nearly perfect correlation between brain amyloid levels detected by florbetapir PET scans in study volunteers and levels found in autopsies of the same individuals a few months later. The developer has sought Food and Drug Administration (FDA) approval to market florbetapir under the brand name Amyvid. The FDA has said it will withhold approval until the developer establishes a professional training program to ensure accuracy and consistency in reading and interpreting Amyvid scans.

Florbetaben (BAY 94-9172) is another radiotracer designed to detect beta-amyloid during a PET scan. Phase II study results and other florbetaben data were reported at the 2010 Alzheimer's Association International Conference on Alzheimer's Disease (AAICAD). Phase II data were also later published in Lancet Neurology. Further studies are now under way.
Exact answer: Pittsburgh compound B
Florbetaben (BAY 94-9172)
Florbetapir F 18 (18F-AV-45)
18F flutemetamol (flute)