Hippocampal subfield imaging and fractional anisotropy show parallel changes in Alzheimer's disease tau progression using simultaneous tau-PET/MRI at 3T

INTRODUCTION

Alzheimer's disease (AD) is the most common form of dementia, characterized primarily by abnormal aggregation of two proteins, tau and amyloid beta. We assessed tau pathology and white matter connectivity changes in subfields of the hippocampus simultaneously in vivo in AD.

METHODS

Twenty-four subjects were scanned using simultaneous time-of-flight 18F-PI-2620 tau positron emission tomography/3-Tesla magnetic resonance imaging and automated segmentation.

RESULTS

We observed extensive tau elevation in the entorhinal/perirhinal regions, intermediate tau elevation in cornu ammonis 1/subiculum, and an absence of tau elevation in the dentate gyrus, relative to controls. Diffusion tensor imaging showed parahippocampal gyral fractional anisotropy was lower in AD and mild cognitive impairment compared to controls and strongly correlated with early tau accumulation in the entorhinal and perirhinal cortices.

DISCUSSION

This study demonstrates the potential for quantifiable patterns of 18F-PI2620 binding in hippocampus subfields, accompanied by diffusion and volume metrics, to be valuable markers of AD.

A Locally Adaptive Phase Aberration Correction (LAPAC) Method for Synthetic Aperture Sequences

Phase aberration is a phenomenon caused by heterogeneity of the speed of sound in tissue, in which the actual speed of sound of the tissue is different than the assumed speed of sound used for beamforming. It reduces the quality and resolution of ultrasonic images and impairs clinical diagnostic capabilities. Although phase aberration correction (PAC) methods can reduce these detrimental effects, most practical implementations of PAC methods are based on the near field phase screen model, which have limited ability to represent the true aberration induced by inhomogeneous tissue. Accordingly, we propose a locally adaptive phase aberration correction (LAPAC) method that is applied through the use of synthetic aperture. The method is tested using full-wave simulations of models of human abdominal wall, experiments with tissue aberrators, and in vivo carotid images. LAPAC is compared with conventional phase aberration correction (cPAC) where aberration profiles are computed at a preselected depth and applied to the beamformer's time delays. For all experiments, LAPAC shows an average of 1 to 2 dB higher contrast than cPAC, and enhancements of 3 to 7 dB with respect to the uncorrected cases. We conclude that LAPAC may be a viable option to enhance ultrasound image quality images even in the presence of clinically relevant aberrating conditions.

Effects of Phase Aberration and Phase Aberration Correction on the Minimum Variance Beamformer

The minimum variance (MV) beamformer has the potential to enhance the resolution and contrast of ultrasound images but is sensitive to steering vector errors. Robust MV beamformers have been proposed but mainly evaluated in the presence of gross sound speed mismatches, and the impact of phase aberration correction (PAC) methods in mitigating the effects of phase aberration in MV beamformed images has not been explored. In this study, an analysis of the effects of aberration on conventional MV and eigenspace MV (ESMV) beamformers is carried out. In addition, the impact of three PAC algorithms on the performance of MV beamforming is analyzed. The different beamformers were tested on simulated data and on experimental data corrupted with electronic and tissue-based aberration. It is shown that all gains in performance of the MV beamformer with respect to delay-and-sum (DAS) are lost at high aberration strengths. For instance, with an electronic aberration of 60 ns, the lateral resolution of DAS degrades by 17% while MV degrades by 73% with respect to the images with no aberration. Moreover, although ESMV shows robustness at low aberration levels, its degradation at higher aberrations is approximately the same as that of regular MV. It is also shown that basic PAC methods improve the aberrated MV beamformer. For example, in the case of electronic aberration, multi-lag reduces degradation in lateral resolution from 73% to 28% and contrast loss from 85% to 25%. These enhancements allow the combination of MV and PAC to outperform DAS and PAC and ESMV in moderate and strong aberrations. We conclude that the effect of aberration on the MV beamformer is stronger than previously reported in the literature and that PAC is needed to improve its clinical potential.

Unsuspected bronchospasm in association with topical timolol--a common problem in elderly people: can we easily identify those affected and do cardioselective agents lead to improvement?

The extent of impairment of respiratory function in a group of 52 elderly, glaucomatous patients receiving topical timolol therapy was investigated. To predict those patients who were likely to benefit from changing therapy, symptoms were elicited by direct questioning, and lung spirometry was measured before and after inhalation of salbutamol. Changing from timolol to either pilocarpine or the cardioselective betaxolol produced improvement in lung function tests. Mean peak flow increased from 278 l/min to 328 l/min (p < 0.001), forced expiratory volume in 1s (FEV1) from 1.66 l to 1.85 l (p < 0.001) and forced vital capacity (FVC) from 2.41 to 2.64 l (p < 0.001). Spirometry in a control group of 20 subjects was unchanged. Nineteen of 47 patients demonstrated a clinically significant (defined as 15% or more) increase in all values of lung function tests. Change to pilocarpine or betaxolol was equally effective in producing improvement but betaxolol had fewer side-effects. The presence of exertional dyspnoea, cough with sputum, raised dyspnoea score and improved lung function tests after salbutamol identified those patients experiencing clinically significant bronchospasm with an 89% specificity and 74% sensitivity.

Improved lung function tests on changing from topical timolol: non-selective beta-blockade impairs lung function tests in elderly patients

Fifty-two elderly glaucomatous patients, without a history of asthma or obstructive airways disease, who were using topical timolol for control of intraocular pressure were recruited. Their topical therapy was changed to either betaxolol or pilocarpine. The change was associated with improvement in mean peak flow from 278 l/min to 328 l/min (t = 5.73, p < 0.001), mean FEV1 from 1.66 l to 1.85 l (t = 7.09, p < 0.001) and mean FVC from 2.40 l to 2.64 l (t = 5.07, p < 0.001). Change to either betaxolol or pilocarpine was associated with improved lung function tests. Lung function tests in a control group of 20 showed no significant changes. Both drugs maintained control of intraocular pressure but betaxolol had fewer ocular side effects.

The role of human salivary acidic proline-rich proteins in the formation of acquired dental pellicle in vivo and their fate after adsorption to the human enamel surface

The pellicles formed on fragments of human dental enamel worn on a palatal appliance for 1 min to 24 h were removed by acid extraction and the total amounts of protein and of acidic proline-rich proteins were determined. The percentage of total extracted protein constituted by the proline-rich proteins increased during the first hour of formation to about 37 per cent. Little difference was seen in total proline-rich protein between pellicles formed in a 1 and a 24-h period, but there was a gradual degradation of the proteins. There was no preferential retention of the N- or C-terminal parts of the proteins. Extracts of old acquired dental pellicle contained less than 0.1 per cent proline-rich proteins and pellicles more than 24 h old showed degradation of the adsorbed proline-rich proteins; there is no indication that the N-terminal part which contains the known biological activities was retained to a greater extent than the C-terminal part.