Vessel distance mapping: A novel methodology for assessing vascular-induced cognitive resilience.

The association between cerebral blood supply and cognition has been widely discussed in the recent literature. One focus of this discussion has been the anatomical variability of the circle of Willis, with morphological differences being present in more than half of the general population. While previous studies have attempted to classify these differences and explore their contribution to hippocampal blood supply and cognition, results have been controversial. To disentangle these previously inconsistent findings, we introduce Vessel Distance Mapping (VDM) as a novel methodology for evaluating blood supply, which allows for obtaining vessel pattern metrics with respect to the surrounding structures, extending the previously established binary classification into a continuous spectrum. To accomplish this, we manually segmented hippocampal vessels obtained from high-resolution 7T time-of-flight MR angiographic imaging in older adults with and without cerebral small vessel disease, generating vessel distance maps by computing the distances of each voxel to its nearest vessel. Greater values of VDM-metrics, which reflected higher vessel distances, were associated with poorer cognitive outcomes in subjects affected by vascular pathology, while this relation was not observed in healthy controls. Therefore, a mixed contribution of vessel pattern and vessel density is proposed to confer cognitive resilience, consistent with previous research findings. In conclusion, VDM provides a novel platform, based on a statistically robust and quantitative method of vascular mapping, for addressing a variety of clinical research questions.

Hippocampal vascularization patterns exert local and distant effects on brain structure but not vascular pathology in old age.

The hippocampus within the medial temporal lobe is highly vulnerable to age-related pathology such as vascular disease. We examined hippocampal vascularization patterns by harnessing the ultra-high resolution of 7 Tesla magnetic resonance angiography. Dual-supply hemispheres with a contribution of the anterior choroidal artery to hippocampal blood supply were distinguished from single-supply ones with a sole dependence on the posterior cerebral artery. A recent study indicated that a dual vascular supply is related to preserved cognition and structural hippocampal integrity in old age and vascular disease. Here, we examined the regional specificity of these structural benefits at the level of medial temporal lobe sub-regions and hemispheres. In a cross-sectional study with an older cohort of 17 patients with cerebral small vessel disease (70.7 ± 9.0 years, 35.5% female) and 27 controls (71.1 ± 8.2 years, 44.4% female), we demonstrate that differences in grey matter volumes related to the hippocampal vascularization pattern were specifically observed in the anterior hippocampus and entorhinal cortex. These regions were especially bigger in dual-supply hemispheres, but also seemed to benefit from a contralateral dual supply. We further show that total grey matter volumes were greater in people with at least one dual-supply hemisphere, indicating that the hippocampal vascularization pattern has more far-reaching structural implications beyond the medial temporal lobe. A mediation analysis identified total grey matter as a mediator of differences in global cognition. However, our analyses on multiple neuroimaging markers for cerebral small vessel disease did not reveal any evidence that an augmented hippocampal vascularization conveys resistance nor resilience against vascular pathology. We propose that an augmented hippocampal vascularization might contribute to maintaining structural integrity in the brain and preserving cognition despite age-related degeneration. As such, the binary hippocampal vascularization pattern could have major implications for brain structure and function in ageing and dementia independent of vascular pathology, while presenting a simple framework with potential applicability to the clinical setting.

Significant dose reduction is feasible in FDG PET/CT protocols without compromising diagnostic quality.

PURPOSE: To reduce the radiation dose to patients by optimizing oncological FDG PET/CT protocols. METHODS: The baseline PET/CT protocol in our institution for oncological PET/CT examinations consisted of the administration of 5.18 MBq/kg of FDG and a CT acquisition with a reference current-time product of 120 mAs. In 2016, FDG activity was reduced to 4.44 and 3.70 MBq/kg and reference CT current-time-product was reduced to 100 and 80 mAs. 322 patients scanned with different protocols were retrospectively evaluated. For each patient, effective dose was calculated. The overall image quality was subjectively rated by the referring physician on a 4-point scale (IQ score: 1 excellent, 2 good, 3 poor but interpretable, 4 poor not interpretable). Image quality was quantitatively evaluated measuring noise in the liver. RESULTS: CT Results: Effective dose was progressively reduced from 9.5 ±â€¯2.8 to 8.0 ±â€¯2.3 and 6.2 ±â€¯1.5 mSv (p < 0.001). A mean dose reduction of 34.9% was achieved. There was a significant degradation of IQ score (p < 0.05) and noise (p < 0.001). Nevertheless, the number of poor quality studies (IQ score >2) did not increase. PET Results: Effective dose was gradually reduced from 6.5 ±â€¯1.4 to 5.7 ±â€¯1.3 and 5.0 ±â€¯1.0 mSv (p < 0.001). Average dose reduction was 23.4%. IQ score (p < 0.05) and noise (p < 0.001) significantly degraded for lower activity protocols. However, all images with reduced activity were scored as interpretable (IQ score ≤ 3). CONCLUSIONS: A significant radiation dose reduction of 28.7% was reached. Despite a slight reduction in image quality, the new regime was successfully implemented with readers reporting unchanged clinical confidence.

Emerging clinical issues and multivariate analyses in PET investigations.

PET using 18F-2-fluoro-2-deoxy-D-glucose (FDG-PET) has been gradually introduced in the diagnostic clinical criteria of the most prevalent neurodegenerative diseases. Moreover, an increasing amount of literature has shown that the information provided by FDG-PET enhances the sensitivity of standard imaging biomarkers in less frequent disorders in which an early differential diagnosis can be of paramount relevance for patient management and outcome. Therefore emerging uses of FDG-PET may be important in prion diseases, autoimmune encephalitis (AE) and amyotrophic lateral sclerosis. Interestingly, FDG-PET findings can also be observed in the early phases of these conditions, even in the presence of normal magnetic resonance imaging scans. Thalamic hypometabolism is a common finding in sporadic Creutzfeldt-Jacob disease and fatal familiar insomnia patients, with further cortical synaptic dysfunction in the former. Limbic and extra-limbic metabolic abnormalities (more often hypermetabolism) can be observed in AE, although specific patterns may be seen within different syndromes associated with antibodies that target neuronal surface or synaptic antigens. FDG-PET shows its usefulness by discriminating patients with amyotrophic lateral sclerosis associated to upper motor neuron onset that evolve to frontotemporal dementia. Besides visual and voxel based image analysis, multivariate analysis as interregional correlation analysis and independent/principal component analysis have been successfully implemented to PET images increasing the accuracy of the discrimination of neurodegenerative diseases. The clinical presentation and current diagnostic criteria of these neurologic disorders as well as the emerging usefulness of FDG-PET in the diagnostic workup are presented and discussed in this review.

Functional neuroimaging studies in asymmetric hearing loss.

This article presents an analysis of the impact of functional neuroimaging studies (positron emission tomography, PET) in asymmetric hearing loss based on the clinical expertise obtained from a group of 21 patients. In these patients, PET studies are performed at rest and after auditory stimulation in order to measure the increase in brain activity in the ipsi- and contralateral cortex, providing supporting evidence to recommend a specific treatment and the side to implant. In conclusion, PET is a useful tool for selected cases in which information on the metabolic status of the auditory pathway can drive the decision regarding the treatment of the most appropriate ear. However, in view of our small sample, further research is needed to confirm our results in this topic.

Hypothalamic hypocretinergic/orexinergic neurons projecting to the oral pontine rapid eye movement sleep inducing site in the cat.

The cat ventral oral pontine reticular nucleus (vRPO) is responsible for the generation and maintenance of rapid eye movement (REM) sleep. Hypothalamic neurons containing the peptide hypocretin-1 (also called orexin-A) which will be herewith defined as orexinergic (Orx) neurons, occupy a pre-eminent place in the integration and stabilization of arousal networks as well as in the physiopathology of narcolepsy/cataplexy. In the previous investigations, low-volume and dose microinjections of hypocretin-1 in cat vRPO produced a specific and significant suppression of REM sleep. The aim of this study is to map the hypothalamic Orx neurons that project to the vRPO and suppress REM sleep generation in the cat. Five adult cats received microinjections of the retrograde tracer cholera toxin (CTb) into the vRPO. Brains were processed employing both CTb staining and antiorexin-A immunocytochemistry techniques. A large number of double-labeled neurons (Orx-CTb) intermingled with the single CTb-positive and single Orx neurons were detected in the ipsilateral lateral, perifornical, dorsal, anterior, perimammillothalamic, and posterior hypothalamic areas but were very scarce in the paraventricular, dorsomedial, ventromedial, and periventricular hypothalamic nuclei. A considerable number of double-labeled neurons were also observed in both the dorsal and the lateral hypothalamic areas in the contralateral hypothalamus. Our results suggest that the widely distributed Orx neuronal hypothalamic groups could physiologically inhibit REM sleep generation in vRPO.