Automated quantification of 18F-flutemetamol PET activity for categorizing scans as negative or positive for brain amyloid: concordance with visual image reads

Clinical trials of the PET amyloid imaging agent (18)F-flutemetamol have used visual assessment to classify PET scans as negative or positive for brain amyloid. However, quantification provides additional information about regional and global tracer uptake and may have utility for image assessment over time and across different centers. Using postmortem brain neuritic plaque density data as a truth standard to derive a standardized uptake value ratio (SUVR) threshold, we assessed a fully automated quantification method comparing visual and quantitative scan categorizations. We also compared the histopathology-derived SUVR threshold with one derived from healthy controls.

METHODS

Data from 345 consenting subjects enrolled in 8 prior clinical trials of (18)F-flutemetamol injection were used. We grouped subjects into 3 cohorts: an autopsy cohort (n = 68) comprising terminally ill patients with postmortem confirmation of brain amyloid status; a test cohort (n = 172) comprising 33 patients with clinically probable Alzheimer disease, 80 patients with mild cognitive impairment, and 59 healthy volunteers; and a healthy cohort of 105 volunteers, used to define a reference range for SUVR. Visual image categorizations for comparison were from a previous study. A fully automated PET-only quantification method was used to compute regional neocortical SUVRs that were combined into a single composite SUVR. An SUVR threshold for classifying scans as positive or negative was derived by ranking the PET scans from the autopsy cohort based on their composite SUVR and comparing data with the standard of truth based on postmortem brain amyloid status for subjects in the autopsy cohort. The derived threshold was used to categorize the 172 scans in the test cohort as negative or positive, and results were compared with categorization using visual assessment. Different reference and composite region definitions were assessed. Threshold levels were also compared with corresponding thresholds derived from the healthy group.

RESULTS

Automated quantification (using pons as the reference region) demonstrated 91% sensitivity and 88% specificity and gave 3 false-positive and 4 false-negative scans. All 3 false-positive cases were either borderline-normal by standard of truth or had moderate to heavy cortical diffuse plaque burden. In the test cohort, the concordance between quantitative and visual read categorization ranged from 97.1% to 99.4% depending on the selection of reference and composite regions. The threshold derived from the healthy group was close to the histopathology-derived threshold.

CONCLUSION

Categorization of (18)F-flutemetamol amyloid imaging data using an automated PET-only quantification method showed good agreement with histopathologic classification of neuritic plaque density and a strong concordance with visual read results.

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 [(18)F]flutemetamol and the level of amyloid-β measured by immunohistochemical and histochemical staining in a frontal cortical region biopsy site.

METHODS

Seventeen patients with probable normal pressure hydrocephalus (NPH) underwent prospective [(18)F]flutemetamol PET and subsequent frontal cortical brain biopsy during ventriculoperitoneal shunting. Tissue amyloid-β was evaluated using the monoclonal antibody 4G8, thioflavin S and Bielschowsky silver stain.

RESULTS

Four of the 17 patients (23.5%) had amyloid-β pathology based on the overall pathology read and also showed increased [(18)F]flutemetamol uptake. [(18)F]Flutemetamol standardized uptake values from the biopsy site were significantly associated with biopsy specimen amyloid-β levels (Pearson's r = 0.67; p = 0.006). There was also good correlation between the biopsy specimen amyloid-β level and uptake of [(18)F]flutemetamol in the region contralateral to the biopsy site (r = 0.67; p = 0.006), as well as with composite cortical [(18)F]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

[(18)F]Flutemetamol detects brain amyloid-β in vivo and shows promise as a valuable tool to study and possibly facilitate diagnosis of Alzheimer's disease both in patients with suspected NPH and among the wider population.

An in vivo evaluation of cerebral cortical amyloid with [18F]flutemetamol using positron emission tomography compared with parietal biopsy samples in living normal pressure hydrocephalus patients

PURPOSE

The primary objectives of this study were to assess the safety of [(18)F]flutemetamol injection and determine the level of association between the quantitative estimates of brain uptake of [(18)F]flutemetamol and the quantitative immunohistochemical (IHC) estimates of amyloid levels in cerebral cortex biopsies obtained during shunt placement in patients with normal pressure hydrocephalus (NPH).

PROCEDURES

Parietal lobe biopsies were obtained from 12 subjects (mean (SD), 71 (8.1) years), during shunt placement for NPH. Shunt procedures and biopsies were performed within 8 weeks after the positron emission tomography (PET) imaging, and followed by a computed tomography scan. The quantitative estimates of the brain uptake of [(18)F]flutemetamol (standard uptake value ratios (SUVRs)) from the biopsy site, contralateral to the biopsy site, and composite were made from the analysis of PET images. The quantitative IHC levels of amyloid load were estimated using a monoclonal antiamyloid β antibody, 4 G8 (in percent area), as the standard of truth (N = 8, of which 5 had full histopathology staining). The primary analysis determined the level of association between the SUVR (with cerebellum as the reference region) from the biopsy site, and the level of amyloid was determined from IHC estimates of amyloid in the biopsy sample.

RESULTS

[(18)F]Flutemetamol injection was found to be well tolerated. The biopsied area well represented the amyloid deposition throughout the cortex in this small sample. The biopsy site SUVR was significantly correlated with the biopsy specimen amyloid β level (expressed as percent of biopsy specimen area staining with 4 G8). The full model was significant (p = 0.0174). In the secondary efficacy analyses, contralateral (to biopsy site) and composite SUVR values correlated significantly with the percent of biopsy specimen staining for amyloid β based on 4 G8. Blinded visual [(18)F]flutemetamol image interpretations showed a sensitivity of 100 % and a specificity of 100 % with pathology reads staining for amyloid plaque with Bielschowsky and thioflavin S and overall pathology read. The results of the blinded reader agreement for [(18)F]flutemetamol PET showed full agreement among three readers.

CONCLUSIONS

PET imaging of NPH patients following the administration of [(18)F]flutemetamol injection was highly correlated with the presence of fibrillar amyloid β in subsequent cortical biopsy samples in this small sample. Administration of [(18)F]flutemetamol injection was well tolerated.

Using the Receptivity model to uncover 'urine blindness': perceptions on the re-use of urine

Population growth, climatic changes and over-exploitation of natural resources are at the basis of the world's food crisis, which counts almost one million people without sufficient food sustenance. These changes require novel environmental practices which are based on nutrient recovery and management in agriculture. This contribution analyses and discusses users' perceptions on re-use of urine as fertilizer through the lenses of the Receptivity model. A search was performed on Scopus (as well as other web search engines) using the keywords: urine, nutrient recovery and sanitation. Results shows how questions related to awareness, association, acquisition and application of the environmental change can represent hurdles to novel models of nutrient recovery and the use of urine in agriculture. Examples of hurdles identified from the literature relate to poor understanding of potential for urine reuse, social stigma attached to using dry sanitation and applying urine in agriculture and poor operational knowledge of application of urine in agriculture. Conclusion relates to the illustration of implications of such challenges on the design of environmental interventions.

Micro-endoscope for in vivo widefield high spatial resolution fluorescent imaging

In this paper we report the design, testing and use of a scannerless probe specifically for minimally invasive imaging of deep tissue in vivo with an epi-fluorescence modality. The probe images a 500 μm diameter field of view through a 710 μm outer diameter probe with a maximum tissue penetration depth of 15 mm specifically configured for eGFP imaging. Example results are given from imaging the pituitary gland of rats and zebrafish hearts with lateral resolution of 2.5 μm.

Myasthenia gravis and neuromyelitis optica spectrum disorder: a multicenter study of 16 patients

OBJECTIVE

To describe 16 patients with a coincidence of 2 rare diseases: aquaporin-4 antibody (AQP4-Ab)-mediated neuromyelitis optica spectrum disorder (AQP4-NMOSD) and acetylcholine receptor antibody (AChR-Ab)-mediated myasthenia gravis (AChR-MG).

METHODS

The clinical details and antibody results of 16 patients with AChR-MG and AQP4-NMOSD were analyzed retrospectively.

RESULTS

All had early-onset AChR-MG, the majority with mild generalized disease, and a high proportion achieved remission. Fifteen were female; 11 were Caucasian. In 14/16, the MG preceded NMOSD (median interval: 16 years) and 11 of these had had a thymectomy although 1 only after NMOSD onset. In 4/5 patients tested, AQP4-Abs were detectable between 4 and 16 years prior to disease onset, including 2 patients with detectable AQP4-Abs prior to thymectomy. AChR-Abs decreased and the AQP4-Ab levels increased over time in concordance with the relevant disease. AChR-Abs were detectable at NMOSD onset in the one sample available from 1 of the 2 patients with NMOSD before MG.

CONCLUSIONS

Although both conditions are rare, the association of MG and NMOSD occurs much more frequently than by chance and the MG appears to follow a benign course. AChR-Abs or AQP4-Abs may be present years before onset of the relevant disease and the antibody titers against AQP4 and AChR tend to change in opposite directions. Although most cases had MG prior to NMOSD onset, and had undergone thymectomy, NMOSD can occur first and in patients who have not had their thymus removed.

Management of suspected viral encephalitis in adults--Association of British Neurologists and British Infection Association National Guidelines

In the 1980s the outcome of patients with herpes simplex encephalitis was shown to be dramatically improved with aciclovir treatment. Delays in starting treatment, particularly beyond 48 h after hospital admission, are associated with a worse prognosis. Several comprehensive reviews of the investigation and management of encephalitis have been published. However, their impact on day-to day clinical practice appears to be limited. The emergency management of meningitis in children and adults was revolutionised by the introduction of a simple algorithm as part of management guidelines. In February 2008 a group of clinicians met in Liverpool to begin the development process for clinical care guidelines based around a similar simple algorithm, supported by an evidence base, whose implementation is hoped would improve the management of patients with suspected encephalitis.