Multi T1-weighted contrast MRI with fluid and white matter suppression at 1.5 T

INTRODUCTION

The fluid and white matter suppression sequence (FLAWS) provides two T1-weighted co-registered datasets: a white matter (WM) suppressed contrast (FLAWS1) and a cerebrospinal fluid (CSF) suppressed contrast (FLAWS2). FLAWS has the potential to improve the contrast of the subcortical brain regions that are important for Deep Brain Stimulation surgery planning. However, to date FLAWS has not been optimized for 1.5 T. In this study, the FLAWS sequence was optimized for use at 1.5 T. In addition, the contrast-enhancement properties of FLAWS image combinations were investigated using two voxel-wise FLAWS combined images: the division (FLAWS-div) and the high contrast (FLAWS-hc) image.

METHODS

FLAWS sequence parameters were optimized for 1.5 T imaging using an approach based on the use of a profit function under constraints for brain tissue signal and contrast maximization. MR experiments were performed on eleven healthy volunteers (age 18-30). Contrast (CN) and contrast to noise ratio (CNR) between brain tissues were measured in each volunteer. Furthermore, a qualitative assessment was performed to ensure that the separation between the internal globus pallidus (GPi) and the external globus pallidus (GPe) is identifiable in FLAWS1.

RESULTS

The optimized set of sequence parameters for FLAWS at 1.5 T provided contrasts similar to those obtained in a previous study at 3 T. The separation between the GPi and the GPe was clearly identified in FLAWS1. The CN of FLAWS-hc was higher than that of FLAWS1 and FLAWS2, but was not different from the CN of FLAWS-div. The CNR of FLAWS-hc was higher than that of FLAWS-div.

CONCLUSION

Both qualitative and quantitative assessments validated the optimization of the FLAWS sequence at 1.5 T. Quantitative assessments also showed that FLAWS-hc provides an enhanced contrast compared to FLAWS1 and FLAWS2, with a higher CNR than FLAWS-div.

Rates of age- and amyloid β-associated cortical atrophy in older adults with superior memory performance

Introduction

Superior cognitive performance in older adults may reflect underlying resistance to age-associated neurodegeneration. While elevated amyloid β (Aβ) deposition (Aβ+) has been associated with increased cortical atrophy, it remains unknown whether “SuperAgers” may be protected from Aβ-associated neurodegeneration.

Methods

Neuropsychologically defined SuperAgers (n = 172) and cognitively normal for age (n = 172) older adults from the Australian Imaging, Biomarkers and Lifestyle study were case matched. Rates of cortical atrophy over 8 years were examined by SuperAger classification and Aβ status.

Results

Of the case-matched SuperAgers and cognitively normal for age older adults, 40.7% and 40.1%, respectively, were Aβ+. Rates of age- and Aβ-associated atrophy did not differ between the groups on any measure. Aβ− individuals displayed the slowest rates of atrophy.

Discussion

Maintenance of superior memory in late life does not reflect resistance to age- or Aβ-associated atrophy. However, those individuals who reached old age without cognitive impairment nor elevated Aβ deposition (i.e. Aβ−) displayed reduced rates of cortical atrophy.

Increased cerebral blood flow with increased amyloid burden in the preclinical phase of alzheimer's disease

BACKGROUND

Arterial spin labeling (ASL) is an emerging MRI technique for noninvasive measurement of cerebral blood flow (CBF) that has been used to show hemodynamic changes in the brains of people with Alzheimer's disease (AD). CBF changes have been measured using positron emission tomography (PET) across the AD spectrum, but ASL showed limited success in measuring CBF variations in the preclinical phase of AD, where amyloid β (Aβ) plaques accumulate in the decades prior to symptom onset.

PURPOSE

To investigate the relationship between CBF measured by multiphase-pseudocontinuous-ASL (MP-PCASL) and Aβ burden as measured by ¹¹ C-PiB PET imaging in a study of cognitively normal (CN) subjects age over 65.

STUDY TYPE

Cross-sectional.

POPULATION

Forty-six CN subjects including 33 with low levels of Aβ burden and 13 with high levels of Aβ.

FIELD STRENGTH/SEQUENCE

3T/3D MP-PCASL.

ASSESSMENT

The MP-PCASL method was chosen because it has a high signal-to-noise ratio. Furthermore, the data were analyzed using an efficient processing pipeline consisting of motion correction, ASL motion correction imprecision removal, temporal and spatial filtering, and partial volume effect correction.

STATISTICAL TESTS

General Linear Model.

RESULTS

In CN subjects positive for Aβ burden (n = 13), we observed a positive correlation between CBF and Aβ burden in the hippocampus, amygdala, caudate (P < 0.01), frontal, temporal, and insula (P < 0.05).

DATA CONCLUSION

To the best of our knowledge, this is the first study using MP-PCASL in the study of AD, and the results suggest a potential compensatory hemodynamic mechanism that protects against pathology in the early stages of AD.

LEVEL OF EVIDENCE

1 Technical Efficacy: Stage 3 J. Magn. Reson. Imaging 2020;51:505-513.

Comparison of 18F-florbetaben quantification results using the standard Centiloid, MR-based, and MR-less CapAIBL® approaches: Validation against histopathology

INTRODUCTION

¹⁸F-florbetaben is currently approved for the visual rule out of β-amyloid (Aβ) pathology. It is also used for recruitment and as an outcome measure in therapeutic trials, requiring accurate and reproducible quantification of Aβ burden in the brain.

METHODS

Data from eighty-eight subjects (52 male subjects, aged 79.8 ± 10.6 years) who underwent antemortem ¹⁸F-florbetaben positron emission tomography scan and magnetic resonance imaging less than a year before neuropathological assessment at autopsy were evaluated. Image analysis was performed using the standard Centiloid (CL) statistical parametric mapping approach and CapAIBL^®. Imaging results were compared against autopsy data.

RESULTS

Against combined Bielschowsky silver staining and immunohistochemistry histopathological scores, statistical parametric mapping had 96% sensitivity, 96% specificity, and 95% accuracy, whereas magnetic resonance-less CapAIBL standardized uptake value ratio_{Whole Cerebellum} had 94% sensitivity, 96% specificity, and 95% accuracy. Based on the combined histopathological scores, a CL threshold band of 19 ± 7 CL was determined.

DISCUSSION

Quantification of ¹⁸F-florbetaben positron emission tomography scans using magnetic resonance-based and magnetic resonance-less CapAIBL^® approaches showed high agreement, establishing a pathology-based threshold in CL.

COMT val158met is not associated with Aβ-amyloid and APOE ε4 related cognitive decline in cognitively normal older adults

The non-synonymous single nucleotide polymorphism (SNP), Val158Met within the Catechol-O-methyltransferase (COMT) gene has been associated with altered levels of cognition and memory performance in cognitively normal adults. This study aimed to investigate the independent and interactional effects of COMT Val158Met on cognitive performance. In particular, it was hypothesised that COMT Val158Met would modify the effect of neocortical Aβ-amyloid (Aβ) accumulation and carriage of the apolipoprotein E (APOE) ε4 allele on cognition in preclinical Alzheimer's disease (AD). In 598 cognitively normal older adults with known neocortical Aβ levels, linear mixed modelling revealed no significant independent or interactional associations between COMT Val158Met and cognitive decline. These findings do not support previous associations between COMT Val158Met and cognitive performance and suggest this variant does not influence Aβ-amyloid or APOE ε4 driven cognitive decline in a well characterised cohort of cognitively normal older adults.

Sensitivity of a Preclinical Alzheimer's Cognitive Composite (PACC) to amyloid β load in preclinical Alzheimer's disease

Introduction: Preclinical Alzheimer's disease (AD) is characterized by amyloid-related cognitive decline. Reduction in this decline is used to determine the efficacy of drug therapies designed to forestall the disease in preclinical AD clinical trials, measured by a Preclinical Alzheimer's Cognitive Composite (PACC). Most studies estimate rates of cognitive change by comparing cognitively normal (CN) older adults with abnormally high beta-amyloid (Aβ+) to those with low levels (Aβ-). However, participants of preclinical AD clinical trials must be Aβ+ for entry. Therefore, we estimated the effect of very high amyloid (Aβ++) and Aβ+ on cognitive change over three years measured by different versions of the PACC in individuals with preclinical AD. Method: CN older adults underwent Aβ neuroimaging and neuropsychological assessments over three years as part of the Australian Imaging, Biomarkers and Lifestyle (AIBL) study. Three cognitive composite scores were computed: the Alzheimer's Disease Cooperative Study (ADCS)-PACC, the ADCS-PACC with no Mini-Mental State Examination (MMSE), and the z-scores of Attention, Verbal Fluency and Episodic Memory for Nondemented Older Adults (ZAVEN) composite. Results: Compared to the Aβ++ group, the Aβ+ group showed a slower rate of cognitive decline with the largest magnitude of difference reflected by the ADCS-PACC (d = 0.85). The ADCS-PACC excluding the MMSE and the ZAVEN also reflected a moderate to large magnitude of difference between groups (d = 0.62, d = 0.72, respectively). Conclusions: When all individuals have abnormal Aβ, the level of Aβ at baseline is associated with the rate of subsequent decline. The ADCS-PACC was the most sensitive composite score in showing that lower Aβ is associated with a slower rate of cognitive decline; however, there are limitations to the use of the MMSE. These results provide a benchmark of comparison for preclinical AD clinical trials aiming to slow cognitive deterioration.

Klotho allele status is not associated with Aβ and APOE ε4-related cognitive decline in preclinical Alzheimer's disease

The longevity gene Klotho (KL), specifically the functional KL-VS variant, has previously been associated with cognition and rates of cognitive decline. This study aimed to determine whether KL-VS associations with cognition were observable in preclinical Alzheimer's disease (AD). The study also aimed to determine whether there was a combined influence of KL-VS, neocortical amyloid-β (Aβ) burden, and carriage of the apolipoprotein E (APOE) ε4 allele on cognitive decline. This study involved 581 Aβ-imaged, cognitively normal older adults, enrolled in the Australian Imaging, Biomarkers and Lifestyle Study of Aging. Linear mixed effects models revealed no significant associations between KL-VS and cognitive decline independently or in combination with Aβ burden and APOE ε4 genotype. Overall, previous associations reported between KL-VS and cognitive decline are not observed at the preclinical stages of AD. Furthermore, the results do not support the hypothesis that KL-VS has a modifying effect on Aβ burden and APOE ε4-driven cognitive decline in preclinical AD.

A Polygenic Risk Score Derived From Episodic Memory Weighted Genetic Variants Is Associated With Cognitive Decline in Preclinical Alzheimer's Disease

Studies of Alzheimer’s disease risk-weighted polygenic risk scores (PRSs) for cognitive performance have reported inconsistent associations. This inconsistency is particularly evident when PRSs are assessed independent of APOE genotype. As such, the development and assessment of phenotype-specific weightings to derive PRSs for cognitive decline in preclinical AD is warranted. To this end a episodic memory-weighted PRS (emPRS) was derived and assessed against decline in cognitive performance in 226 healthy cognitively normal older adults with high brain Aβ-amyloid burden participants from the Australian Imaging, Biomarkers and Lifestyle (AIBL) study. The effect size for decline in a verbal episodic memory was determined individually for 27 genetic variants in a reference sample (n = 151). These were then summed to generate a emPRS either including APOE (emPRS^c¯APOE) or excluding APOE (emPRS^s¯APOE). Resultant emPRS were then evaluated, in a test sample (n = 75), against decline in global cognition, verbal episodic memory and a pre-Alzheimer’s cognitive composite (AIBL-PACC) over 7.5 years. The mean (SD) age of the 226 participants was 72.2 (6.6) years and 116 (51.3%) were female. Reference and test samples did not differ significantly demographically. Whilst no association of emPRSs were observed with baseline cognition, the emPRS^c¯APOE was associated with longitudinal global cognition (-0.237, P = 0.0002), verbal episodic memory (-0.259, P = 0.00003) and the AIBL-PACC (-0.381, P = 0.02). The emPRS^s¯APOE was also associated with global cognition (-0.169, P = 0.021) and verbal episodic memory (-0.208, P = 0.004). Stratification by APOE ε4 revealed that the association between the emPRS and verbal episodic memory was limited to carriage of no ε4 or one ε4 allele. This was also observed for global cognition. The emPRS and rates of decline in AIBL-PACC were associated in those carrying one ε4 allele. Overall, the described novel emPRS has utility for the prediction of decline in cognition in preclinical AD. This study provides evidence to support the further use and evaluation of phenotype weightings in PRS development.

A lightweight rapid application development framework for biomedical image analysis

Biomedical imaging analysis typically comprises a variety of complex tasks requiring sophisticated algorithms and visualising high dimensional data. The successful integration and deployment of the enabling software to clinical (research) partners, for rigorous evaluation and testing, is a crucial step to facilitate adoption of research innovations within medical settings. In this paper, we introduce the Simple Medical Imaging Library Interface (SMILI), an object oriented open-source framework with a compact suite of objects geared for rapid biomedical imaging (cross-platform) application development and deployment. SMILI supports the development of both command-line (shell and Python scripting) and graphical applications utilising the same set of processing algorithms. It provides a substantial subset of features when compared to more complex packages, yet it is small enough to ship with clinical applications with limited overhead and has a license suitable for commercial use. After describing where SMILI fits within the existing biomedical imaging software ecosystem, by comparing it to other state-of-the-art offerings, we demonstrate its capabilities in creating a clinical application for manual measurement of cam-type lesions of the femoral head-neck region for the investigation of femoro-acetabular impingement (FAI) from three dimensional (3D) magnetic resonance (MR) images of the hip. This application for the investigation of FAI proved to be convenient for radiological analyses and resulted in high intra (ICC=0.97) and inter-observer (ICC=0.95) reliabilities for measurement of α-angles of the femoral head-neck region. We believe that SMILI is particularly well suited for prototyping biomedical imaging applications requiring user interaction and/or visualisation of 3D mesh, scalar, vector or tensor data.