Dual-wavelength hybrid optoacoustic-ultrasound biomicroscopy for functional imaging of large-scale cerebral vascular networks

A critical link exists between pathological changes of cerebral vasculature and diseases affecting brain function. Microscopic techniques have played an indispensable role in the study of neurovascular anatomy and functions. Yet, investigations are often hindered by suboptimal trade-offs between the spatiotemporal resolution, field-of-view (FOV) and type of contrast offered by the existing optical microscopy techniques. We present a hybrid dual-wavelength optoacoustic (OA) biomicroscope capable of rapid transcranial visualization of large-scale cerebral vascular networks. The system offers 3-dimensional views of the morphology and oxygenation status of the cerebral vasculature with single capillary resolution and a FOV exceeding 6 × 8 mm² , thus covering the entire cortical vasculature in mice. The large-scale OA imaging capacity is complemented by simultaneously acquired pulse-echo ultrasound (US) biomicroscopy scans of the mouse skull. The new approach holds great potential to provide better insights into cerebrovascular function and facilitate efficient studies into neurological and vascular abnormalities of the brain.

Functional optoacoustic neuro-tomography of calcium fluxes in adult zebrafish brain in vivo

Genetically-encoded calcium indicators (GECIs) have revolutionized neuroimaging by enabling mapping of the activity of entire neuronal populations in vivo. Visualization of these powerful activity sensors has to date been limited to depth-restricted microscopic studies due to intense light scattering in the brain. We demonstrate, for the first time, in vivo real-time volumetric optoacoustic monitoring of calcium transients in adult transgenic zebrafish expressing the GCaMP5G calcium indicator. Fast changes in optoacoustic traces associated with GCaMP5G activity were detectable in the presence of other strongly absorbing endogenous chromophores, such as hemoglobin. The new functional optoacoustic neuroimaging method can visualize neural activity at penetration depths and spatio-temporal resolution scales not covered with the existing neuroimaging techniques.

Functional optoacoustic neuro-tomography for scalable whole-brain monitoring of calcium indicators

Non-invasive observation of spatiotemporal activity of large neural populations distributed over entire brains is a longstanding goal of neuroscience. We developed a volumetric multispectral optoacoustic tomography platform for imaging neural activation deep in scattering brains. It can record 100 volumetric frames per second across scalable fields of view ranging between 50 and 1000 mm³ with respective spatial resolution of 35-200 μm. Experiments performed in immobilized and freely swimming larvae and in adult zebrafish brains expressing the genetically encoded calcium indicator GCaMP5G demonstrate, for the first time, the fundamental ability to directly track neural dynamics using optoacoustics while overcoming the longstanding penetration barrier of optical imaging in scattering brains. The newly developed platform thus offers unprecedented capabilities for functional whole-brain observations of fast calcium dynamics; in combination with optoacoustics' well-established capacity for resolving vascular hemodynamics, it could open new vistas in the study of neural activity and neurovascular coupling in health and disease.

Adaptive control of cardiac contraction to changes in loading: from theory of sarcomere dynamics to whole-heart function

The heart accommodates to rapid changes in demands. This review elucidates the adaptive control of cardiac function by loading conditions, and integrates the sarcomeric control of contraction (SCC) with isolated trabeculae and in vivo whole-heart studies. The SCC includes two feedback mechanisms: (1) cooperativity that regulates cross-bridge (XB) recruitment and the force-length relationship, and (2) mechanical feedback, whereby the filament-sliding velocity determines the XB-weakening rate and the force-velocity relationship. An isolated rat trabeculae study tested the suggested mechanisms during sarcomeric lengthening. The observations indicate that lengthening decreases the XB-weakening rate in a velocity-dependent manner, congruent with the suggested hypothesis and in contrast to alternative theories. A whole-heart level study in sheep reveals the existence of a preload-independent linear relationship between the external work (EW) and pressure-time integral during transient vena cava occlusions, for any given afterload, and not just at isovolumic contractions. The slope of this relationship decreases as the afterload increases. These findings highlight the mechanisms underlying the pressure (Frank's phenomenon) and EW (Starling's phenomenon) generation and the roles that the preload and afterload play. The theoretical, isolated fibers and whole-heart studies provide complementary information that strengthens our understanding of cardiac function from the top-down and bottom-up.

Theory of cardiac sarcomere contraction and the adaptive control of cardiac function to changes in demands

This chapter explores the adaptive control of cardiac function by the loading conditions and relates the observed phenomena to our theory of the sarcomeric control of contraction. Our theory includes two feedback mechanisms: cooperativity-regulated cross-bridge recruitment and energy consumption, and mechanical feedback that determines the interplay between the external work and the force-time integral. The latter also suggests that cardiac efficiency is load independent. This paper explores the regulation of cardiac function by loading conditions, and the role of afterload in adult sheep in situ (n=8). Different afterloads were imposed by partial aortic occlusions. Transient inferior vena cava occlusions (IVCOs) were pre-formed at each steady afterload. A novel, highly linear relationship was found between the external work and pressure-time integral during each transient IVCO at constant afterload. Of interest, the slope of this relationship was afterload-dependent also during fast transient changes in the afterload. These observations are congruent with the suggested adaptive sarcomeric control of contraction, and may provide a powerful tool for quantifying cardiac function.

The external work-pressure time integral relationships and the afterload dependence of Frank-Starling mechanism

The mechanisms underlying the Frank-Starling Law of the heart are elusive and the prevalent notion suggests that it is afterload independent. However, isolated fiber studies reveal that the afterload determines cardiac function through cross-bridge dependent mechanisms. The study explores the roles of the afterload, in situ. The LV was exposed by left-thoracotomy in adult sheep (72.6+/-8.2 kg, n=8). Pressure transducers were inserted into the LV and aorta, a flowmeter was placed around the aortic root, and the LV volume was assessed by sonocrystals. Occluders around the aorta and the inferior vena cava enabled control of the afterload and preload. Different afterloads were imposed by partial aortic occlusions. Transient inferior vena cava occlusions (IVCOs) were preformed whenever the afterload was steady. A highly linear relationship was found between the external work (EW) and pressure time integral (PTI) (R(2)=0.98+/-0.01) during each transient IVCO (n=48). The slope of the EW-PTI relationship (WPTiR) was preload independent since, for any given afterload, the EW and PTI lay on a straight line. Interestingly, the slope of the WPTiR was afterload dependant: The slope was 33.3+/-4.1 mJ/mmHg.s at baselines and decreased by 1.0+/-0.50 mJ/mmHg.s with every 1 mmHg.min/L increase in the peripheral resistance. A unique WPTiR was obtained during both the occlusion and release phases of each IVCO, while two distinct EW-preload or PTI-preload relationships were observed. The novel WPTiR ties the Frank (pressure development) and Starling (EW production) phenomena together. The dependence of the WPTiR on the afterload highlights the adaptive control of the Frank-Starling mechanisms to changes in the afterload.

["Flare-up" during endodontic treatment--etiology and management]

"Flare-ups" during or following endodontic treatment are not uncommon. A "Flare-up" refers to post-operative pain and/or swelling resulting from bacterial, mechanical or chemical irritation. Prompt diagnosis and treatment are essential for reducing patients' pain and discomfort. Prevention of bacterial, chemical or mechanical invasion to the periapical tissues is the best approach. Other treatment modalities which reduce the probability of periradicular tissue irritation should also be adopted. Etiology, prevention, diagnosis and treatment options of "flare-up" cases are discussed as well as indications for analgesics, in accordance with the severity of the pain.

[Fixation of injured tooth]

In cases of an avulsed or luxated tooth, splinting of the injured tooth is recommended. Splint is defined as a fixation of the injured tooth to adjacent teeth in the dental arch. The preferred splint type is semi-rigid, which should be placed for 10 to 14 days and enable proper oral hygiene and will not cause any kind of impingement to the gingiva. It is effective in reducing the replacement resorption process, which affects the periodontal tissue surrounding roots exposed to dental trauma.

Cognitive impairment in dementia: correlations with atrophy and cerebrovascular disease quantified by magnetic resonance imaging

This project assessed the contributions of atrophy and cerebrovascular disease (CVD) to cognitive impairment in dementia. Ten individuals with clinically diagnosed pure VaD were age-, sex-, and education-matched to individuals with AD. All participants underwent neuropsychological testing and MRI which were processed to generate quantitative indices of atrophy and CVD. A linear regression, including thalamic lesion and vCSF volumes, predicted cognitive status (R2 = .74; p < .0005). Three VaD subgroups were identified: thalamic lesion (n = 4), hippocampal infarcts (n = 3), and other (n = 3). In participants without thalamic lesion, vCSF predicted general cognition (R2 = .48), hippocampal atrophy predicted memory impairment (R2 = .33), and white matter lesions predicted executive dysfunction (R2 = .48). Both atrophy and CVD burden correlated highly with cognitive impairment and should be simultaneously assessed in studies of brain-behaviour relations in dementia.

Quantifying head motion associated with motor tasks used in fMRI

In functional magnetic resonance imaging (fMRI) studies, long experiment times and small intensity changes associated with brain activation frequently lead to image artifacts due to head motion. Methods to minimize and correct for head motion by restraint, fast imaging, and retrospective image registration are typically combined but do not completely solve the problem, particularly for specific patient populations. As an initial step toward optimizing future designs of head restraints and improving motion correction techniques, the head motion characteristics of groups of stroke subjects, age-matched controls, and young adults were investigated with the aid of an MR simulator and a highly accurate position tracking system. Position measurements were recorded during motor tasks involving either the hand or the foot. Head motion was strongly dependent on the subject group and less upon the task conditions based on ANOVA calculations (P < 0.05). The stroke subjects exhibited approximately twice the head motion compared to that of age-matched controls, and the latter's head motion was about twice that of young adults. Moreover, the range of head motion in stroke subjects over all tasks was approximately 2 +/- 1 mm, with the motion occurring predominantly as translation in the superior-inferior direction and pitch rotation (nodding). These results lead to several recommendations on the design of fMRI motor experiments and suggest that improved motion correction strategies are required to examine such patient populations comprehensively.