Dual Time-Point [18F]Florbetaben PET Delivers Dual Biomarker Information in Mild Cognitive Impairment and Alzheimer’s Disease

Peripapillary Optical Coherence Tomography Angiography in Alzheimer's Disease, Mild Cognitive Impairment, and Normal Cognition

OBJECTIVE

This study aimed to identify peripapillary microvascular changes in Alzheimer's disease (AD) and mild cognitive impairment (MCI).

PATIENTS AND METHODS

In this prospective study, 66 eyes of 36 subjects with AD, 119 eyes of 63 with MCI, and 513 eyes of 265 controls with normal cognition were enrolled. Peripapillary capillary perfusion density (CPD), capillary flux index (CFI), and retinal nerve fiber layer (RNFL) thickness were determined.

RESULTS

Average CPD differed significantly between all three groups (P = 0.001), being significantly greater in AD vs controls (0.446 ± 0.015 vs 0.439 ± 0.017, P = 0.001) and MCI vs controls (0.443 ± 0.020 vs 0.439 ± 0.017, P = 0.007) but not AD vs MCI (P = 0.69). CFI and average RNFL thickness did not significantly differ among groups (all P > 0.05).

CONCLUSION

Peripapillary CPD is increased in eyes with AD or MCI compared to controls despite similar RNFL thickness. [Ophthalmic Surg Lasers Imaging Retina 2024;55:78-84.].

Assessment of perfusion deficit with early phases of [18F]PI-2620 tau-PET versus [18F]flutemetamol-amyloid-PET recordings

PURPOSE

Characteristic features of amyloid-PET (A), tau-PET (T), and FDG-PET (N) can serve for the A/T/N classification of neurodegenerative diseases. Recent studies showed that the early, perfusion-weighted phases of amyloid- or tau-PET recordings serve to detect cerebrometabolic deficits equally to FDG-PET, therefore providing a surrogate of neuronal injury. As such, two channels of diagnostic information can be obtained in the setting of a single PET scan. However, there has hitherto been no comparison of early-phase amyloid- and tau-PET as surrogates for deficits in perfusion/metabolism. Therefore, we undertook to compare [¹⁸F]flutemetamol-amyloid-PET and [¹⁸F]PI-2620 tau-PET as "one-stop shop" dual purpose tracers for the detection of neurodegenerative disease.

METHODS

We obtained early-phase PET recordings with [¹⁸F]PI-2620 (0.5-2.5 min p.i.) and [¹⁸F]flutemetamol (0-10 min p.i.) in 64 patients with suspected neurodegenerative disease. We contrasted global mean normalized images (SUVr) in the patients with a normal cohort of 15 volunteers without evidence of increased pathology to β-amyloid- and tau-PET examinations. Regional group differences of tracer uptake (z-scores) of 246 Brainnetome volumes of interest were calculated for both tracers, and the correlations of the z-scores were evaluated using Pearson's correlation coefficient. Lobar compartments, regions with significant neuronal injury (z-scores <  - 3), and patients with different neurodegenerative disease entities (e.g., Alzheimer's disease or 4R-tauopathies) served for subgroup analysis. Additionally, we used partial regression to correlate regional perfusion alterations with clinical scores in cognition tests.

RESULTS

The z-scores of perfusion-weighted images of both tracers showed high correlations across the brain, especially in the frontal and parietal lobes, which were the brain regions with pronounced perfusion deficit in the patient group (R = 0.83 ± 0.08; range, 0.61-0.95). Z-scores of individual patients correlated well by region (R = 0.57 ± 0.15; range, 0.16-0.90), notably when significant perfusion deficits were present (R = 0.66 ± 0.15; range, 0.28-0.90).

CONCLUSION

The early perfusion phases of [¹⁸F]PI-2620 tau- and [¹⁸F]flutemetamol-amyloid-PET are roughly equivalent indices of perfusion defect indicative of regional and lobar neuronal injury in patients with various neurodegenerative diseases. As such, either tracer may serve for two diagnostic channels by assessment of amyloid/tau status and neuronal activity.

Machine Learning Model to Predict Diagnosis of Mild Cognitive Impairment by Using Radiomic and Amyloid Brain PET

PURPOSE

The study aimed to develop a deep learning model for predicting amnestic mild cognitive impairment (aMCI) diagnosis using radiomic features and amyloid brain PET.

PATIENTS AND METHODS

Subjects (n = 328) from the Alzheimer's Disease Neuroimaging Initiative database and the EudraCT 2015-001184-39 trial (159 males, 169 females), with a mean age of 72 ± 7.4 years, underwent PET/CT with 18 F-florbetaben. The study cohort consisted of normal controls (n = 149) and subjects with aMCI (n = 179). Thirteen gray-level run-length matrix radiomic features and amyloid loads were extracted from 27 cortical brain areas. The least absolute shrinkage and selection operator regression was used to select features with the highest predictive value. A feed-forward neural multilayer network was trained, validated, and tested on 70%, 15%, and 15% of the sample, respectively. Accuracy, precision, F1-score, and area under the curve were used to assess model performance. SUV performance in predicting the diagnosis of aMCI was also assessed and compared with that obtained from the machine learning model.

RESULTS

The machine learning model achieved an area under the receiver operating characteristic curve of 90% (95% confidence interval, 89.4-90.4) on the test set, with 80% and 78% for accuracy and F1-score, respectively. The deep learning model outperformed SUV performance (area under the curve, 71%; 95% confidence interval, 69.7-71.4; 57% accuracy, 48% F1-score).

CONCLUSIONS

Using radiomic and amyloid PET load, the machine learning model identified MCI subjects with 84% specificity at 81% sensitivity. These findings show that a deep learning algorithm based on radiomic data and amyloid load obtained from brain PET images improves the prediction of MCI diagnosis compared with SUV alone.

Future Directions in Molecular Imaging of Neurodegenerative Disorders

The improvement of existing techniques and the development of new molecular imaging methods are an exciting and rapidly developing field in clinical care and research of neurodegenerative disorders. In the clinic, molecular imaging has the potential to improve early and differential diagnosis and to stratify and monitor therapy in these disorders. Meanwhile, in research, these techniques improve our understanding of the underlying pathophysiology and pathobiochemistry of these disorders and allow for drug testing. This article is an overview on our perspective on future developments in neurodegeneration tracers and the associated imaging technologies. For example, we predict that the current portfolio of β-amyloid and tau aggregate tracers will be improved and supplemented by tracers allowing imaging of other protein aggregation pathologies, such as α-synuclein and transactive response DNA binding protein 43 kDa. Future developments will likely also be observed in imaging neurotransmitter systems. This refers to both offering imaging to a broader population in cases involving the dopaminergic, cholinergic, and serotonergic systems and making possible the imaging of systems not yet explored, such as the glutamate and opioid systems. Tracers will be complemented by improved tracers of neuroinflammation and synaptic density. Technologywise, the use of hybrid PET/MRI, dedicated brain PET, and total-body PET scanners, as well as advanced image acquisition and processing protocols, will open doors toward broader and more efficient clinical use and novel research applications. Molecular imaging has the potential of becoming a standard and essential clinical and research tool to diagnose and study neurodegenerative disorders and to guide treatments. On that road, we will need to redefine the role of molecular imaging in relation to that of emerging blood-based biomarkers. Taken together, the unique features of molecular imaging-that is, the potential to provide direct noninvasive information on the presence, extent, localization, and quantity of molecular pathologic processes in the living body-together with the predicted novel tracer and imaging technology developments, provide optimism about a bright future for this approach to improved care and research on neurodegenerative disorders.

[Diagnosing Alzheimer's dementia - a playground for academics or a sensible clinical measure?]

The number of dementia cases continues to increase with Alzheimer's disease as the leading cause. The diagnostic workup of Alzheimer's dementia is complex, and its clinical relevance debatable considering the current lack of disease-modifying treatments. From this perspective, a stepwise diagnostic approach is recommended. Whenever Alzheimer's dementia is suspected, a patient' history a physical and psychiatric examination, neuropsychological tests, routine blood tests and standard cerebral imaging should be conducted. This allows in many cases a diagnosis to be given. In cases remaining unclear, modern biomarker tests are proving increasingly useful. Knowledge of the diagnosis is pivotal for the patients to assess the prognosis, to enable them to make plans for their future and to get access to available treatment. The approval of aducanumab in the USA and other promising monoclonal antibodies currently in phase 3-trials as well as the development of blood biomarkers give us hope for the future.

Paradoxical Cerebral Perfusion in Parkinson's Disease Patients with Orthostatic Hypotension: A Dual-Phase 18F-Florbetaben Positron Emission Tomography Study

BACKGROUND

Orthostatic hypotension (OH) may antedate Parkinson's disease (PD) or be found in early stages of the disease. OH may induce a PD brain to chronic hypotensive insults. 18F-Florbetaben (18F-FBB) tracer has a high first-pass influx rate and can be used with positron emission tomography (PET) as a surrogate marker for early- and late-phase evaluation of cerebral perfusion and cerebral amyloidosis, respectively.

OBJECTIVE

In this study, we evaluated whether 18F-FBB uptake in the early- and late-phases of PD was related to OH. This study manipulated the imaging modality to illustrate the physiology of cerebral flow with OH in PD (PD + OH).

METHODS

A group of 73 early-stage PD patients was evaluated with a head-up tilt-test and 18F-FBB PET imaging. The cognitive status was assessed by a comprehensive battery of neuropsychological tests. PET images were normalized, and both early- and late-phase standardized uptake value ratios (SUVRs) of pre-specified regions were obtained. The associations between regional SUVRs and OH and cognitive status were analyzed.

RESULTS

Twenty (27.4%) participants had OH. Thirteen (17.8%) patients were interpreted as having amyloid pathology based on regional 18F-FBB uptake. Early-phase SUVRs were higher in specific brain regions of PD + OH patients than those without OH. However, late-phase SUVRs did not differ between the groups. The early-phase SUVRs were not influenced by amyloid burden or by interaction between amyloid and orthostatic hypotension. Cognitive functions were not disparate when PD + OH patients were contrasted with non-OH patients in this study.

CONCLUSION

Cerebral blood flow was elevated in patients with early PD + OH. This finding suggests augmented cerebral perfusion in PD + OH might be a compensatory regulation in response to chronic OH.

High Correlation of Static First-Minute-Frame (FMF) PET Imaging after 18F-Labeled Amyloid Tracer Injection with [18F]FDG PET Imaging

Dynamic early-phase PET images acquired with radiotracers binding to fibrillar amyloid-beta (Aβ) have shown to correlate with [18F]fluorodeoxyglucose (FDG) PET images and provide perfusion-like information. Perfusion information of static PET scans acquired during the first minute after radiotracer injection (FMF, first-minute-frame) is compared to [18F]FDG PET images. FMFs of 60 patients acquired with [18F]florbetapir (FBP), [18F]flutemetamol (FMM), and [18F]florbetaben (FBB) are compared to [18F]FDG PET images. Regional standardized uptake value ratios (SUVR) are directly compared and intrapatient Pearson's correlation coefficients are calculated to evaluate the correlation of FMFs to their corresponding [18F]FDG PET images. Additionally, regional interpatient correlations are calculated. The intensity profiles of mean SUVRs among the study cohort (r = 0.98, p < 0.001) and intrapatient analyses show strong correlations between FMFs and [18F]FDG PET images (r = 0.93 ± 0.05). Regional VOI-based analyses also result in high correlation coefficients. The FMF shows similar information to the cerebral metabolic patterns obtained by [18F]FDG PET imaging. Therefore, it could be an alternative to the dynamic imaging of early phase amyloid PET and be used as an additional neurodegeneration biomarker in amyloid PET studies in routine clinical practice while being acquired at the same time as amyloid PET images.

A Systematic Review and Meta-Analysis of Retinal Microvascular Features in Alzheimer's Disease

Objective: The aim of this meta-analysis was to investigate retinal microvascular features in patients with Alzheimer's disease (AD) using optical coherence tomography angiography (OCTA).

Methods: PubMed, Cochrane Library, Embase, and Web of Science databases were systematically searched for published articles comparing retinal microvascular characteristics in subjects with AD and controls. The mean difference (MD) with a 95% confidence interval (CI) was used to assess continuous variables. Review Manager Version (RevMan) 5.30, was employed to analyze the data.

Results: Nine studies were included in the meta-analysis. The analysis revealed that the macular whole enface superficial and deep vessel density (VD) values measured by OCTA were significantly lower in patients with AD than in controls (MD = −1.10, P < 0.0001; MD = −1.61, P = 0.0001, respectively). The value measured by OCTA for parafoveal superficial VD in patients with AD was also remarkably lower than that in the control group (MD = −1.42, P = 0.001), whereas there was no significant difference in the value for parafoveal deep VD (MD = −3.67, P = 0.19), compared to the controls. In addition, the foveal avascular zone (FAZ) was larger in patients with AD than in the control group (MD = 0.08, P = 0.07), although it did not reach statistical significance.

Conclusions: The present meta-analysis indicated that the macular whole enface and parafoveal vessel densities were reduced in patients with AD. Moreover, our pooled data revealed that FAZ is larger in patients with AD. Consequently, OCTA may be utilized as a diagnostic tool to identify and monitor patients with AD.

Association of quality of life with structural, functional and molecular brain imaging in community-dwelling older adults

BACKGROUND

As the population ages, maintaining mental health and well-being of older adults is a public health priority. Beyond objective measures of health, self-perceived quality of life (QoL) is a good indicator of successful aging. In older adults, it has been shown that QoL is related to structural brain changes. However, QoL is a multi-faceted concept and little is known about the specific relationship of each QoL domain to brain structure, nor about the links with other aspects of brain integrity, including white matter microstructure, brain perfusion and amyloid deposition, which are particularly relevant in aging. Therefore, we aimed to better characterize the brain biomarkers associated with each QoL domain using a comprehensive multimodal neuroimaging approach in older adults.

METHODS

One hundred and thirty-five cognitively unimpaired older adults (mean age ± SD: 69.4 ± 3.8 y) underwent structural and diffusion magnetic resonance imaging, together with early and late florbetapir positron emission tomography scans. QoL was assessed using the brief version of the World Health Organization's QoL instrument, which allows measuring four distinct domains of QoL: self-perceived physical health, psychological health, social relationships and environment. Multiple regression analyses were carried out to identify the independent global neuroimaging predictor(s) of each QoL domain, and voxel-wise analyses were then conducted with the significant predictor(s) to highlight the brain regions involved. Age, sex, education and the other QoL domains were entered as covariates in these analyses. Finally, forward stepwise multiple regressions were conducted to determine the specific items of the relevant QoL domain(s) that contributed the most to these brain associations.

RESULTS

Only physical health QoL was associated with global neuroimaging values, specifically gray matter volume and white matter mean kurtosis, with higher physical health QoL being associated with greater brain integrity. These relationships were still significant after correction for objective physical health and physical activity measures. No association was found with global brain perfusion or global amyloid deposition. Voxel-wise analyses revealed that the relationships with physical health QoL concerned the anterior insula and ventrolateral prefrontal cortex, and the corpus callosum, corona radiata, inferior frontal white matter and cingulum. Self-perceived daily living activities and self-perceived pain and discomfort were the items that contributed the most to these associations with gray matter volume and white matter mean kurtosis, respectively.

CONCLUSIONS

Better self-perceived physical health, encompassing daily living activities and pain and discomfort, was the only QoL domain related to brain structural integrity including higher global gray matter volume and global white matter microstructural integrity in cognitively unimpaired older adults. The relationships involved brain structures belonging to the salience network, the pain pathway and the empathy network. While previous studies showed a link between objective measures of physical health, our findings specifically highlight the relevance of monitoring and promoting self-perceived physical health in the older population. Longitudinal studies are needed to assess the direction and causality of the relationships between QoL and brain integrity.

Amyloid-PET and 18F-FDG-PET in the diagnostic investigation of Alzheimer's disease and other dementias

Various biomarkers are available to support the diagnosis of neurodegenerative diseases in clinical and research settings. Among the molecular imaging biomarkers, amyloid-PET, which assesses brain amyloid deposition, and ¹⁸F-fluorodeoxyglucose (¹⁸F-FDG) PET, which assesses glucose metabolism, provide valuable and complementary information. However, uncertainty remains regarding the optimal timepoint, combination, and an order in which these PET biomarkers should be used in diagnostic evaluations because conclusive evidence is missing. Following an expert panel discussion, we reached an agreement on the specific use of the individual biomarkers, based on available evidence and clinical expertise. We propose a diagnostic algorithm with optimal timepoints for these PET biomarkers, also taking into account evidence from other biomarkers, for early and differential diagnosis of neurodegenerative diseases that can lead to dementia. We propose three main diagnostic pathways with distinct biomarker sequences, in which amyloid-PET and ¹⁸F-FDG-PET are placed at different positions in the order of diagnostic evaluations, depending on clinical presentation. We hope that this algorithm can support diagnostic decision making in specialist clinical settings with access to these biomarkers and might stimulate further research towards optimal diagnostic strategies.

PET Parametric Imaging: Past, Present, and Future

Positron emission tomography (PET) is actively used in a diverse range of applications in oncology, cardiology, and neurology. The use of PET in the clinical setting focuses on static (single time frame) imaging at a specific time-point post radiotracer injection and is typically considered as semi-quantitative; e.g. standardized uptake value (SUV) measures. In contrast, dynamic PET imaging requires increased acquisition times but has the advantage that it measures the full spatiotemporal distribution of a radiotracer and, in combination with tracer kinetic modeling, enables the generation of multiparametric images that more directly quantify underlying biological parameters of interest, such as blood flow, glucose metabolism, and receptor binding. Parametric images have the potential for improved detection and for more accurate and earlier therapeutic response assessment. Parametric imaging with dynamic PET has witnessed extensive research in the past four decades. In this paper, we provide an overview of past and present activities and discuss emerging opportunities in the field of parametric imaging for the future.

Positron Emission Tomography (PET) and Neuroimaging in the Personalized Approach to Neurodegenerative Causes of Dementia

Generally, dementia should be considered an acquired syndrome, with multiple possible causes, rather than a specific disease in itself. The leading causes of dementia are neurodegenerative and non-neurodegenerative alterations. Nevertheless, the neurodegenerative group of diseases that lead to cognitive impairment and dementia includes multiple possibilities or mixed pathologies with personalized treatment management for each cause, even if Alzheimer's disease is the most common pathology. Therefore, an accurate differential diagnosis is mandatory in order to select the most appropriate therapy approach. The role of personalized assessment in the treatment of dementia is rapidly growing. Neuroimaging is an essential tool for differential diagnosis of multiple causes of dementia and allows a personalized diagnostic and therapeutic protocol based on risk factors that may improve treatment management, especially in early diagnosis during the prodromal stage. The utility of structural and functional imaging could be increased by standardization of acquisition and analysis methods and by the development of algorithms for automated assessment. The aim of this review is to focus on the most commonly used tracers for differential diagnosis in the dementia field. Particularly, we aim to explore ¹⁸F Fluorodeoxyglucose (FDG) and amyloid positron emission tomography (PET) imaging in Alzheimer's disease and in other neurodegenerative causes of dementia.

Retinal microvascular attenuation in mental cognitive impairment and Alzheimer's disease by optical coherence tomography angiography

PURPOSE

To explore regional variation of the macular microvasculature in patients with mild cognitive impairment (MCI) and Alzheimer's disease (AD), also to detect the association between retinal macular microvascular parameters and the progress of preclinical AD.

METHODS

Prospective study of healthy controls, patients with MCI and patients with AD by using Optical coherence tomography angiography (OCT-A). We quantified foveal avascular zone (FAZ) areas, densities of the superficial retinal capillary plexuses (SRCP) and deep retinal capillary plexuses (DRCP). The SRCP and DRCP were divided into inner (3 mm) and external (6 mm) annular rings, each containing four quadrants (SI, II, TI, NI, SE, IE, TE and NE). The data were analysed statistically by using SPSS 22 software.

RESULTS

Totally, 60 subjects including 21 HC (33 eyes), 21 patients with MCI (32 eyes) and 18 AD patients (28 eyes) were recruited. The microvascular densities of DRCP at all quadrants of the parafovea and perifovea were significantly lower in AD patients compared to HC group (p < 0.05). Compared to the HCs, MCI patients showed significant microvascular loss in most sectors of the parafovea and the SE sector of the DRCP (p < 0.05), but not in the parafovea (p = 0.829) or perifovea (p = 0.824) of the SRCP. No significant difference was found in microvascular density of SRCP among the groups, except at SI between the AD and HC groups (p = 0.048).

CONCLUSION

Our findings demonstrated the macular microvascular attenuation in MCI and AD patients. Both AD and MCI patients showed retinal microvascular density loss, which is more significant in the deep retinal capillary plexuses. Optical coherence tomography angiography (OCT-A) can be used to identify early microvascular abnormalities in AD and MCI. Quantified microvascular density in the DRCP might serve as potential biomarkers of early sign of AD then contribute to forestall the progression of preclinical AD.

Early-phase [18F]PI-2620 tau-PET imaging as a surrogate marker of neuronal injury

Purpose

Second-generation tau radiotracers for use with positron emission tomography (PET) have been developed for visualization of tau deposits in vivo. For several β-amyloid and first-generation tau-PET radiotracers, it has been shown that early-phase images can be used as a surrogate of neuronal injury. Therefore, we investigated the performance of early acquisitions of the novel tau-PET radiotracer [¹⁸F]PI-2620 as a potential substitute for [¹⁸F]fluorodeoxyglucose ([¹⁸F]FDG).

Methods

Twenty-six subjects were referred with suspected tauopathies or overlapping parkinsonian syndromes (Alzheimer’s disease, progressive supranuclear palsy, corticobasal syndrome, multi-system atrophy, Parkinson’s disease, multi-system atrophy, Parkinson's disease, frontotemporal dementia) and received a dynamic [¹⁸F]PI-2620 tau-PET (0–60 min p.i.) and static [¹⁸F]FDG-PET (30–50 min p.i.). Regional standardized uptake value ratios of early-phase images (single frame SUVr) and the blood flow estimate (R₁) of [¹⁸F]PI-2620-PET were correlated with corresponding quantification of [¹⁸F]FDG-PET (global mean/cerebellar normalization). Reduced tracer uptake in cortical target regions was also interpreted visually using 3-dimensional stereotactic surface projections by three more and three less experienced readers. Spearman rank correlation coefficients were calculated between early-phase [¹⁸F]PI-2620 tau-PET and [¹⁸F]FDG-PET images for all cortical regions and frequencies of disagreement between images were compared for both more and less experienced readers.

Results

Highest agreement with [¹⁸F]FDG-PET quantification was reached for [¹⁸F]PI-2620-PET acquisition from 0.5 to 2.5 min p.i. for global mean (lowest R = 0.69) and cerebellar scaling (lowest R = 0.63). Correlation coefficients (summed 0.5–2.5 min SUVr & R₁) displayed strong agreement in all cortical target regions for global mean (R_SUVr 0.76, R_R1 = 0.77) and cerebellar normalization (R_SUVr 0.68, R_R1 = 0.68). Visual interpretation revealed high regional correlations between early-phase tau-PET and [¹⁸F]FDG-PET. There were no relevant differences between more and less experienced readers.

Conclusion

Early-phase imaging of [¹⁸F]PI-2620 can serve as a surrogate biomarker for neuronal injury. Dynamic imaging or a dual time-point protocol for tau-PET imaging could supersede additional [¹⁸F]FDG-PET imaging by indexing both the distribution of tau and the extent of neuronal injury.

Electronic supplementary material

The online version of this article (10.1007/s00259-020-04788-w) contains supplementary material, which is available to authorized users.

Optimized dual-time-window protocols for quantitative [18F]flutemetamol and [18F]florbetaben PET studies

Background

A long dynamic scanning protocol may be required to accurately measure longitudinal changes in amyloid load. However, such a protocol results in a lower patient comfort and scanning efficiency compared to static scans. A compromise can be achieved by implementing dual-time-window protocols. This study aimed to optimize these protocols for quantitative [¹⁸F]flutemetamol and [¹⁸F]florbetaben studies.

Methods

Rate constants for subjects across the Alzheimer’s disease spectrum (i.e., non-displaceable binding potential (BP_ND) in the range 0.02–0.77 and 0.02–1.04 for [¹⁸F]flutemetamol and [¹⁸F]florbetaben, respectively) were established based on clinical [¹⁸F]flutemetamol (N = 6) and [¹⁸F]florbetaben (N = 20) data, and used to simulate tissue time-activity curves (TACs) of 110 min using a reference tissue and plasma input model. Next, noise was added (N = 50) and data points corresponding to different intervals were removed from the TACs, ranging from 0 (i.e., 90–90 = full-kinetic curve) to 80 (i.e., 10–90) minutes, creating a dual-time-window. Resulting TACs were fitted using the simplified reference tissue method (SRTM) to estimate the BP_ND, outliers (≥ 1.5 × BP_ND max) were removed and the bias was assessed using the distribution volume ratio (DVR = BP_ND + 1). To this end, acceptability curves, which display the fraction of data below a certain bias threshold, were generated and the area under those curves were calculated.

Results

[¹⁸F]Flutemetamol and [¹⁸F]florbetaben data demonstrated an increased bias in amyloid estimate for larger intervals and higher noise levels. An acceptable bias (≤ 3.1%) in DVR could be obtained with all except the 10–90 and 20–90-min intervals. Furthermore, a reduced fraction of acceptable data and most outliers were present for these two largest intervals (maximum percentage outliers 48 and 32 for [¹⁸F]flutemetamol and [¹⁸F]florbetaben, respectively).

Conclusions

The length of the interval inversely correlates with the accuracy of the BP_ND estimates. Consequently, a dual-time-window protocol of 0–30 and 90–110 min (=maximum of 60 min interval) allows for accurate estimation of BP_ND values for both tracers.

[¹⁸F]flutemetamol: EudraCT 2007-000784-19, registered 8 February 2007, [¹⁸F]florbetaben: EudraCT 2006-003882-15, registered 2006.

Electronic supplementary material

The online version of this article (10.1186/s13550-019-0499-4) contains supplementary material, which is available to authorized users.