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INTRODUCTION: Cerebral small vessel disease (SVD) and amyloid beta (Aβ) pathology frequently co‐exist. The impact of concurrent pathology on the pattern of hippocampal atrophy, a key substrate of memory impacted early and extensively in dementia, remains poorly understood. METHODS: In a unique cohort of mixed Alzheimer's disease and moderate–severe SVD, we examined whether total and regional neuroimaging measures of SVD, white matter hyperintensities (WMH), and Aβ, as assessed by 18F‐AV45 positron emission tomography, exert additive or synergistic effects on hippocampal volume and shape. RESULTS: Frontal WMH, occipital WMH, and Aβ were independently associated with smaller hippocampal volume. Frontal WMH had a spatially distinct impact on hippocampal shape relative to Aβ. In contrast, hippocampal shape alterations associated with occipital WMH spatially overlapped with Aβ‐vulnerable subregions. DISCUSSION: Hippocampal degeneration is differentially sensitive to SVD and Aβ pathology. The pattern of hippocampal atrophy could serve as a disease‐specific biomarker, and thus guide clinical diagnosis and individualized treatment strategies for mixed dementia. [ABSTRACT FROM AUTHOR]

Rationale and Objectives: 129Xe MRI has been developed to noninvasively visualize and quantify the functional consequence of airway obstruction in asthma. Its widespread application requires evidence of intersite reproducibility and agreement. Our objective was to evaluate reproducibility and agreement of 129Xe ventilation MRI measurements in severe asthmatics at two sites.Materials and Methods: In seven adults with severe asthma, 129Xe ventilation MRI was acquired pre- and post-bronchodilator at two geographic sites within 24-hours. 129Xe MRI signal-to-noise ratio (SNR) was calculated and ventilation abnormalities were quantified as the whole-lung and slice-by-slice ventilation defect percent (VDP). Intraclass correlation coefficients (ICC) and Bland-Altman analysis were used to determine intersite 129Xe VDP reproducibility and agreement.Results: Whole-lung and slice-by-slice 129Xe VDP measured at both sites were correlated and reproducible (pre-bronchodilator: whole-lung ICC = 0.90, p = 0.005, slice-by-slice ICC = 0.78, p < 0.0001; post-bronchodilator: whole-lung ICC = 0.94, p < 0.0001, slice-by-slice ICC = 0.83, p < 0.0001) notwithstanding intersite differences in the 129Xe-dose-equivalent-volume (101 ± 15 mL site 1, 49 ± 6 mL site 2, p < 0.0001), gas-mixture (129Xe/4He site 1; 129Xe/N2 site 2) and SNR (40 ± 19 site 1, 23 ± 5 site 2, p = 0.02). Qualitative 129Xe gas distribution differences were observed between sites and slice-by-slice 129Xe VDP, but not whole-lung 129Xe VDP, was significantly lower at site 1 (pre-bronchodilator VDP: whole-lung bias = -3%, p > 0.99, slice-by-slice bias = -3%, p = 0.0001; post-bronchodilator VDP: whole-lung bias = -2%, p = 0.59, slice-by-slice-bias = -2%, p = 0.0003).Conclusion: 129Xe MRI VDP at two different sites measured within 24-hours in the same severe asthmatics were correlated. Qualitative and quantitative intersite differences in 129Xe regional gas distribution and VDP point to site-specific variability that may be due to differences in gas-mixture composition or SNR. [ABSTRACT FROM AUTHOR]

Objectives: To assess the effect of ankle, knee, and hip kinematics on patellofemoral and tibiofemoral joint reaction forces (JRF) during bicycling. Secondarily, to assess if sex, horizontal saddle position, or crank arm length were related to JRFs, after accounting for kinematics.Design: Experimental cross-sectional study.Methods: Forty healthy adults (mean (SD); 28.6 (7.2) years, 24.2 (2.6)kg/m2, 17 women) bicycled under 18 bicycling positions. One position used commercial guidelines and 17 randomly deviated from commercial. Resultant patellofemoral as well as compressive and shear tibiofemoral JRFs were calculated. Linear mixed-effects models with a random intercept of leg-nested-in-participant were used.Results: Patellofemoral resultant forces were most sensitive to all joint kinematics (i.e., sensitivity was defined as the slope of single predictor models); all JRFs were least sensitive to minimum knee flexion. Tibiofemoral compression was predicted by minimum hip flexion and maximum ankle dorsiflexion (R2=0.90). Tibiofemoral shear (R2=0.86) and the resultant patellofemoral JRF (R2=0.90) were predicted by minimum hip flexion, maximum ankle dorsiflexion, minimum knee flexion, and the interaction between minimum hip flexion and minimum knee flexion. Adding sex as a factor improved fit of all models. This sex-effect was driven by differences in cycling intensity, reflected by the tangential crank arm force. Horizontal saddle position and crank arm length were not related to JRFs.Conclusions: Optimizing joint kinematics should be the primary goal of bicycle-fit. JRFs were least sensitive to the current gold standard for assessing bicycle-fit, minimum knee flexion. Bicycle-fit is of particular importance for those working at high intensities. [ABSTRACT FROM AUTHOR]

Copyright of Journal of Ultrasound is the property of Springer Nature and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Copyright of Journal of Medical Imaging & Radiation Sciences is the property of Elsevier B.V. and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Background: Small vessel disease (SVD) often co‐exists with Alzheimer's disease (AD) pathology (up to 60%) and may facilitate AD progression. However, SVD is currently not integrated as a pathological factor within the ATN research criteria. Up to now, the majority of studies that investigated effects of SVD on brain atrophy and cognition were limited to either AD cohorts with low SVD burden (e.g., ADNI) or cognitively normal elderly with high SVD burden. Thus, there is a need to investigate the effects of SVD in a cohort spanning low to severe SVD and amyloid‐beta pathology. Method: Our study included 118 subjects in total. Fifty‐nine subjects were recruited in a multi‐site study (MITNEC) from dementia and SVD‐stroke clinics (64% amyloid‐beta+) who had severe SVD burden as quantified by white matter hyperintensity volumes [WMH; median(IQR): 30.2(22.2)cm3] and Fazekas score 2.5‐3. In addition, we included 59 cognitively normal/early‐MCI subjects from ADNI (44% amyloid‐beta+) with low‐to‐moderate WMH [median(IQR): 5.8(9.1)cm3]. We performed vertex‐wise regressions, investigating associations of cortical thickness with amyloid‐beta (18F‐florbetapir‐SUVRpons) or vascular burden (WMH), corrected for WMH or amyloid‐beta, respectively, and age, sex, education. Further, mediation analyses investigated whether the effects of amyloid‐beta or vascular burden on cognition (MMSE, MoCA, Trails‐B, semantic fluency, ANART, and Boston‐naming) were mediated by cortical thickness. Result: We observed a significant effect of vascular burden on cortical thickness independent of amyloid‐beta. This effect was stronger than the vascular‐independent effect of amyloid‐beta on thickness (Fig. 1). Furthermore, we observed additive effects of vascular burden and amyloid‐beta on cognition (semantic fluency: ß=‐0.29 [p=0.002] and ß=‐0.27 [p=0.001], respectively; Trails‐B: ß=+0.18 [p=0.03] and ß=+0.22 [p=0.02], respectively). Here, the effects on semantic fluency were significantly mediated by cortical thickness (vascular→thickness→semantic: 35% mediation, 95%CI[‐0.19,‐0.02]; amyloid‐beta→thickness→semantic: 19% mediation, 95%CI[‐0.11,‐0.003]) (Fig. 1). Conclusion: In our study of mixed AD/SVD and control subjects, the effect of SVD burden (WMH) exceeded the effect of amyloid‐beta on neurodegeneration alone. Furthermore, vascular burden contributed to semantic loss both directly and through its impact on neurodegeneration. As such, the presence of cerebrovascular comorbidities supports the idea of combinational therapeutic approaches where SVD factors may be targeted alongside amyloid‐beta to halt neurodegeneration and cognitive decline. [ABSTRACT FROM AUTHOR]

Abstract: Objective: The objective of the study was to investigate the cerebrovascular hemodynamic response of cervical spine positions including rotation and cervical spine manipulation in vivo using magnetic resonance imaging technology on the vertebral artery (VA). Methods: This pilot study was conducted as a blinded examiner cohort with 4 randomized clinical tasks. Ten healthy male participants aged 24 to 30 years (mean, 26.8 years) volunteered to participate in the study. None of the participants had a history of disabling neck, arm, or headache pain within the last 6 months. They did not have any current or history of neurologic symptoms. In a neutral head position, physiologic measures of VA blood flow and velocity at the C1-2 spinal level were obtained using phase-contrast magnetic resonance imaging after 3 different head positions and a chiropractic upper cervical spinal manipulation. A total of 30 flow-encoded phase-contrast images were collected over the cardiac cycle, in each of the 4 conditions, and were used to provide a blood flow profile for one complete cardiac cycle. Differences between flow (in milliliters per second) and velocity (in centimeters per second) variables were evaluated using repeated-measures analysis of variance. Results: The side-to-side difference between ipsilateral and contralateral VA velocities was not significant for either velocities (P = .14) or flows (P = .19) throughout the conditions. There were no other interactions or trends toward a difference for any of the other blood flow or velocity variables. Conclusions: There were no significant changes in blood flow or velocity in the vertebral arteries of healthy young male adults after various head positions and cervical spine manipulations. [Copyright &y& Elsevier]

Abstract: Typical clinical evaluation of the tumour microvascular environment is performed by dynamic contrast enhanced MRI (dceMRI). However, this approach has been defined by numerous mathematical models each with their own physiologic assumptions which often leads to inconclusive results in the assessment of microstructure. Alternatively, Blood Oxygen Level Dependent (BOLD) Magnetic Resonance Imaging (MRI) is already known to be sensitive to the microvascular environment through fluctuation in the oxyhemoglobin to deoxyhemoglobin ratio. Consequently, quantification of the BOLD signal''s temporal complexity using a fractal dimension index allows maps to be generated that are physiologically distinctive in nature and allow potential insight into tumour microvasculature with no a priori assumptions as in dceMRI. Here, using rectal carcinoma as an example, we present this novel approach to tumour microvascular evaluation using fractal dimension parametric mapping. [Copyright &y& Elsevier]

Phosphorus magnetic resonance spectroscopy and spectroscopic imaging (31P-MRS/MRSI) non-invasively provide very important information regarding energy metabolism as they can detect high-energy metabolites and membrane phospholipids in vivo. They have repeatedly proven their utility in the study of healthy and disease conditions in skeletal muscle and brain tissue, as many disorders are related to imbalances in bioenergetics processes. However, they are not often used in a clinic setting, as there are technical challenges imposed by the low sensitivity and low concentration of metabolites leading to low signal to noise ratio (SNR), coarse spatial resolution and very long acquisition times. This paper presents an overview of the main techniques used for the acquisition, data reconstruction and processing of 31P-MRS/MRSI experiments with emphasis in methodological aspects, as well as some of their main applications in the study of skeletal muscle and brain tissue. Also, recent advances in the development of accelerated methods for acquisition of 31P-MR data are discussed. [ABSTRACT FROM AUTHOR]