Gill Farrar

18F-flutemetamol amyloid imaging in Alzheimer disease and mild cognitive impairment: a phase 2 trial.

The most widely studied positron emission tomography ligand for in vivo β‐amyloid imaging is 11C‐Pittsburgh compound B (11C‐PIB). Its availability, however, is limited by the need for an on‐site cyclotron. Validation of the 18F‐labeled PIB derivative 18F‐flutemetamol could significantly enhance access to this novel technology.

Positron emission tomography with [18F]flutemetamol and [11C]PiB for in vivo detection of cerebral cortical amyloid in normal pressure hydrocephalus patients

This study determined the correlation between uptake of the amyloid positron emission tomography (PET) imaging agent [18F]flutemetamol and amyloid‐β measured by immunohistochemical and histochemical staining in a frontal cortical biopsy.

Fibrillar and Oligomeric β‐Amyloid as Distinct Local Biomarkers for Alzheimer's Disease

Abstract:  β‐amyloid is a key component of Alzheimers disease (AD) pathology. Researchers in both academic and industry are actively pursuing the development of imaging tracers and techniques to noninvasively measure local levels of β‐amyloid in the Alzheimers brain. This presentation summarizes recent data and discusses the opportunities and challenges of imaging plaques containing fibrillar β‐amyloid for the early diagnosis and therapeutic monitoring of amyloid targeted therapies. Further, the value and feasibility of measuring the recently described soluble oligomeric form of β‐amyloid as an alternative noninvasive biomarker is also discussed.

Prospective Flutemetamol Positron Emission Tomography and Histopathology in Normal Pressure Hydrocephalus

Backgound/Objective: To determine the level of association between uptake of the amyloid positron emission tomography (PET) imaging agent [18F]flutemetamol and the level of amyloid-ß measured by immunohistochemical and histochemical staining in a frontal cortical region biopsy site. Methods: Seventeen patients with probable normal pressure hydrocephalus (NPH) underwent prospective [18F]flutemetamol PET and subsequent frontal cortical brain biopsy during ventriculoperitoneal shunting. Tissue amyloid-ß was evaluated using the monoclonal antibody 4G8, thioflavin S and Bielschowsky silver stain. Results: Four of the 17 patients (23.5%) had amyloid-ß pathology based on the overall pathology read and also showed increased [18F]flutemetamol uptake. [18F]Flutemetamol standardized uptake values from the biopsy site were significantly associated with biopsy specimen amyloid-ß levels (Pearsons r = 0.67; p = 0.006). There was also good correlation between the biopsy specimen amyloid-ß level and uptake of [18F]flutemetamol in the region contralateral to the biopsy site (r = 0.67; p = 0.006), as well as with composite cortical [18F]flutemetamol uptake (r = 0.65; p = 0.008). The blinded visual read showed a high level of agreement between all readers (κ = 0.88). Two of 3 readers were in full agreement on all images; 1 reader disagreed on 1 of the 17 NPH cases. Blinded visual assessments of PET images by 1 reader were associated with 100% sensitivity to the overall pathology read, and assessments by the 2 others were associated with 75% sensitivity (overall sensitivity by majority read was 75%); specificity of all readers was 100%. Conclusions: [18F]Flutemetamol detects brain amyloid-ß in vivo and shows promise as a valuable tool to study and possibly facilitate diagnosis of Alzheimers disease both in patients with suspected NPH and among the wider population.

No Association of Lower Hippocampal Volume With Alzheimer’s Disease Pathology in Late-Life Depression

OBJECTIVE Hippocampal volume is commonly decreased in late-life depression. According to the depression-as-late-life-neuropsychiatric-disorder model, lower hippocampal volume in late-life depression is associated with neurodegenerative changes. The purpose of this prospective study was to examine whether lower hippocampal volume in late-life depression is associated with Alzheimers disease pathology. METHOD Of 108 subjects who participated, complete, good-quality data sets were available for 100: 48 currently depressed older adults and 52 age- and gender-matched healthy comparison subjects who underwent structural MRI, [18F]flutemetamol amyloid positron emission tomography imaging, apolipoprotein E genotyping, and neuropsychological assessment. Hippocampal volumes were defined manually and normalized for total intracranial volume. Amyloid binding was quantified using the standardized uptake value ratio in one cortical composite volume of interest. The authors investigated group differences in hippocampal volume (both including and excluding amyloid-positive participants), group differences in amyloid uptake and in the proportion of positive amyloid scans, and the association between hippocampal volume and cortical amyloid uptake. RESULTS A significant difference was observed in mean normalized total hippocampal volume between patients and comparison subjects, but there were no group differences in cortical amyloid uptake or proportion of amyloid-positive subjects. The difference in hippocampal volume remained significant after the amyloid-positive subjects were excluded. There was no association between hippocampal volume and amyloid uptake in either patients or comparison subjects. CONCLUSIONS Lower hippocampal volume was not related to amyloid pathology in this sample of patients with late-life depression. These data counter the common belief that changes in hippocampal volume in late-life depression are due to prodromal Alzheimers disease.

Post-mortem histopathology underlying β-amyloid PET imaging following flutemetamol F 18 injection

In vivo imaging of fibrillar β-amyloid deposits may assist clinical diagnosis of Alzheimer’s disease (AD), aid treatment selection for patients, assist clinical trials of therapeutic drugs through subject selection, and be used as an outcome measure. A recent phase III trial of [18F]flutemetamol positron emission tomography (PET) imaging in 106 end-of-life subjects demonstrated the ability to identify fibrillar β-amyloid by comparing in vivo PET to post-mortem histopathology. Post-mortem analyses demonstrated a broad and continuous spectrum of β-amyloid pathology in AD and other dementing and non-dementing disease groups. The GE067-026 trial demonstrated 91% sensitivity and 90% specificity of [18F]flutemetamol PET by majority read for the presence of moderate or frequent plaques. The probability of an abnormal [18F]flutemetamol scan increased with neocortical plaque density and AD diagnosis. All dementia cases with non-AD neurodegenerative diseases and those without histopathological features of β-amyloid deposits were [18F]flutemetamol negative. Majority PET assessments accurately reflected the amyloid plaque burden in 90% of cases. However, ten cases demonstrated a mismatch between PET image interpretations and post-mortem findings. Although tracer retention was best associated with amyloid in neuritic plaques, amyloid in diffuse plaques and cerebral amyloid angiopathy best explain three [18F]flutemetamol positive cases with mismatched (sparse) neuritic plaque burden. Advanced cortical atrophy was associated with the seven false negative [18F]flutemetamol images. The interpretation of images from pathologically equivocal cases was associated with low reader confidence and inter-reader agreement. Our results support that amyloid in neuritic plaque burden is the primary form of β-amyloid pathology detectable with [18F]flutemetamol PET imaging. ClinicalTrials.gov NCT01165554. Registered June 21, 2010; NCT02090855. Registered March 11, 2014.

Performance of [18F]flutemetamol amyloid imaging against the neuritic plaque component of CERAD and the current (2012) NIA-AA recommendations for the neuropathologic diagnosis of Alzheimer's disease

Performance of the amyloid tracer [18F]flutemetamol was evaluated against three pathology standard of truth (SoT) measures including neuritic plaques (CERAD “original” and “modified” and the amyloid component of the 2012 NIA‐AA guidelines).

The in vivo and in vitro metabolic profile of 99mTc-NC100668, a new tracer for imaging venous thromboembolism: Identification and biodistribution of the principal radiolabeled metabolite

99mTc-NC100668 [Acetyl-Asn-Gln-Glu-Gln-Val-Ser-Pro-Tyr(3-iodo)-Thr-Leu-Leu-Lys-Gly-NC100194] is a radiopharmaceutical imaging agent being developed to aid the diagnosis of thromboembolism. The stability profile of 99mTc-NC100668 was investigated by high-performance liquid chromatography (HPLC) after in vitro exposure to blood and plasma obtained from rat and human, as well as to urine and bile obtained from rat. The metabolic profile of 99mTc-NC100668 exposed to human and rat hepatic S9 (a liver homogenate-rich cytochrome P450) was also studied. The profile of 99mTc-labeled species in plasma, urine, and bile was investigated following i.v. administration of 99mTc-NC100668 to rat. The major species observed in vitro and in vivo consisted of the 99mTc-chelator (NC100194) [N,N-Bis(N-(1,1-dimethyl-2-(hydroxylimino-)propyl)aminoethyl)aminoethylamine] attached to the C-terminal amino acid residue and referred to as 99mTc-complex of Gly-NC100194. The identity of the major metabolite was confirmed by cochromatography with an authentic standard and the genuine metabolite using a second HPLC method. The minor metabolites were sodium pertechnetate (99mTc) and 99mTc-NC100194. In addition, a small number of other species were transiently observed in vitro; they were not investigated further. The biodistribution of the major metabolite was studied in male Wistar rats. The affinity of the major metabolite toward plasma clot was established using a plasma clot-forming assay. A minor uptake of 99mTc-complex of Gly-NC100194 in the plasma clot and a rapid removal from the body were noted. In conclusion, the metabolites of 99mTc-NC100668 are not anticipated to have a negative impact on the ability of the test substance to image blood clots.

MEASUREMENT OF PATHOLOGICAL AMYLOID IN ROUTINE CLINICAL ASSESSMENT: THE CLINICAL IMPACT OF VISUAL [ 18 F]FLUTEMETAMOL PET AND CSF ANALYSIS

Some sulcal regions show expansion with tight high convexity and others contraction. Data from regions with AUROCS in excess of 0.7 were used to build an LDA model with an AUROC of 0.94 (Figure 3). Conclusions:An entirely automated method can be used to predict classification of tight high convexity. By combining both contracted and expanded CSF spaces, the LDA classifier captures many of the patients with DESH, an important radiological feature of iNPH, and is consistent with the hypothesis that tight high convexity is neither atrophy nor inflammation but a shifting of tissue.

A Systematic Review and Aggregated Analysis on the Impact of Amyloid PET Brain Imaging on the Diagnosis, Diagnostic Confidence, and Management of Patients being Evaluated for Alzheimer's Disease

Background: Amyloid PET (aPET) imaging could improve patient outcomes in clinical practice, but the extent of impact needs quantification. Objective: To provide an aggregated quantitative analysis of the value added by aPET in cognitively impaired subjects. Methods: Systematic literature searches were performed in Embase and Medline until January 2017. 1,531 cases over 12 studies were included (1,142 cases over seven studies in the primary analysis where aPET was the key biomarker; the remaining cases included as defined groups in the secondary analysis). Data was abstracted by consensus among two observers and assessed for bias. Clinical utility was measured by diagnostic change, diagnostic confidence, and patient management before and after aPET. Three groups were further analyzed: control patients for whom feedback of aPET scan results was delayed; aPET Appropriate Use Criteria (AUC+) cases; and patients undergoing additional FDG/CSF testing. Results: For 1,142 cases with only aPET, 31.3% of diagnoses were revised, whereas 3.2% of diagnoses changed in the delayed aPET control group (p < 0.0001). Increased diagnostic confidence following aPET was found for 62.1% of 870 patients. Management changes with aPET were found in 72.2% of 740 cases and in 55.5% of 299 cases in the control group (p < 0.0001). The diagnostic value of aPET in AUC+ patients or when FDG/CSF were additionally available did not substantially differ from the value of aPET alone in the wider population. Conclusions: Amyloid PET contributed to diagnostic revision in almost a third of cases and demonstrated value in increasing diagnostic confidence and refining management plans.