Functional magnetic resonance imaging.

A Double Dissociation of Ventromedial Prefrontal Cortical Responses to Sad and Happy Stimuli in Depressed and Healthy Individuals

Differential time courses and specificity of amygdala activity in posttraumatic stress disorder subjects and normal control subjects

Although blood oxygenation level dependent (BOLD) functional magnetic resonance imaging (fMRI) experiments of brain activity generally rely on the magnitude of the signal, they also provide frequency information that can be derived from the phase of the signal. However, because of confounding effects of instrumental and physiological origin, BOLD related frequency information is difficult to extract and therefore rarely used. Here, we explored the use of high field (7 T) and dedicated signal processing methods to extract frequency information and use it to quantify and interpret blood oxygenation and blood volume changes. We found that optimized preprocessing improves detection of task-evoked and spontaneous changes in phase signals and resonance frequency shifts over large areas of the cortex with sensitivity comparable to that of magnitude signals. Moreover, our results suggest the feasibility of mapping BOLD quantitative susceptibility changes in at least part of the activated area and its largest draining veins. Comparison with magnitude data suggests that the observed susceptibility changes originate from neuronal activity through induced blood volume and oxygenation changes in pial and intracortical veins. Further, from frequency shifts and susceptibility values, we estimated that, relative to baseline, the fractional oxygen saturation in large vessels increased by 0.02–0.05 during stimulation, which is consistent to previously published estimates. Together, these findings demonstrate that valuable information can be derived from fMRI imaging of BOLD frequency shifts and quantitative susceptibility changes.

Objective To investigate the significance of blood oxygenation level dependent functional magnetic resonance imaging (BOLD-fMRI) and ambulatory urodynamics monitoring (AUM) to find the cause of primary monosymptomatic nocturnal enuresis (PMNE) in children. Methods Thirty-seven children with PMNE (20 males and 17 females) were selected, with a mean age of (11.3±4.1) years old.A clinical management tool, 3-day urination record, daytime BOLD-fMRI scan, conventional urodynamics (CUD) and AUM were performed respectively.Thirty-seven gender-age matched children(19 males, 18 females) who would receive surgery treatment because of upper urinary tract disease and were confirmed to have no lower urinary tract dysfunction by CUD were enrolled as controls, with a mean age of (11.1±2.9) years old, and 13 cases underwent BOLD-fMRI scanning. Results It was found that the ALFF value of the left middle frontal gyrus of PMNE was decreased and the ReHo value of the left superior occipital gyrus was increased compared with the control group by the resting BOLD-fMRI.The maximum voiding volume of PNME children was (303.11±87.48) mL, the total urine volume at night was (568.65±208.48) mL, and the nighttime bladder volume was (217.43±81.53) mL.The incidence of maximum voiding volume reduction, nocturnal polyuria and decreased nocturnal bladder volume were 24.32% and 56.76%, and 64.86%, respectively.However, AUM results showed that maximum detrusor pressure in the PMNE group was (39.22±7.78) cmH2O(1 cmH2O=0.098 kPa), which was statistically significantly higher than that in CUD (32.22±9.00) cmH2O, and the difference was statistically significant (P 0.05). Conclusions The abnormal functions of the left middle frontal gyrus and left superior occipital gyrus, nighttime DO and the decrease of bladder capacity at night are considered to be key causes of enuresis in children with PMNE.AUM and resting state BOLD-fMRI evaluations are helpful in differentiating the pathogenesis of PMNE. Key words: Enuresis; Ambulatory urodynamics monitoring; Functional magnetic resonance imaging; Resting state

Concurrent fNIRS and fMRI processing allows independent visualization of the propagation of pressure waves and bulk blood flow in the cerebral vasculature

BackgroundHeme arginate can induce heme oxygenase-1 to protect tissue against ischemia-reperfusion injury. Blood oxygen level dependent (BOLD) functional magnetic resonance imaging measures changes in tissue oxygenation with a high spatial and temporal resolution. BOLD imaging was applied to test the effect of heme arginate on experimental ischemia reperfusion injury in the calf muscles.MethodsA two period, controlled, observer blinded, crossover trial was performed in 12 healthy male subjects. Heme arginate (1 mg/kg body weight) or placebo were infused 24 h prior to a 20 min leg ischemia induced by a thigh cuff. 3 Tesla BOLD-imaging of the calf was performed and signal time courses from soleus, gastrocnemius and tibialis anterior muscle were available from 11 participants for technical reasons.ResultsPeak reactive hyperemia signal of the musculature was significantly increased and occurred earlier after heme arginate compared to placebo (106.2±0.6% at 175±16s vs. 104.5±0.6% at 221±19s; p = 0.025 for peak reperfusion and p = 0.012 for time to peak).ConclusionsA single high dose of heme arginate improves reperfusion patterns during ischemia reperfusion injury in humans. BOLD sensitive, functional MRI is applicable for the assessment of experimental ischemia reperfusion injury in skeletal muscle.Trial registrationClinicalTrials: NCT01461512EudraCT: 2008-006967-35

Objective To evaluate the rehabilitating effect of hyperbaric oxygen on visual pathway lesions with blood oxygen level dependent functional magnetic resonance imaging (BOLD-fMRI) and diffusion tensor imaging (DTI). Methods Sixteen patients with visual pathway lesions (the study group) and twelve healthy volunteers (the control group) were assessed using BOLD-fMRI and DTI. After hyperbaric oxygen therapy, the patients in the study group were again assessed using BOLD-fMRI and DTI. The activated regions of the BOLD-fMRI scan and the fractional anisotropy (FA) value determined from the DTI were calculated. Results Before hyperbaric oxygen treatment, there were significant differences between control and study groups in their BOLD-fMRI activated regions and the FA values of their radiation optics (P≤0.01). After hyperbaric oxygen treatment, there were no significant differences. Conclusion Combining BOLD-fMRI with DT1 could be used to evaluate the rehabilitation effect of hy-perbaric oxygen treatment in patients with visual pathway lesions. Key words: Visual rehabilitation ; Functional magnetic resonance imaging ; Diffusion tensor imaging ; Hyperbaric oxygen therapy ;

The adaptation of neuronal responses to stimulation, in which a peak transient response is followed by a sustained plateau, has been well-studied. The blood oxygenation level dependent (BOLD) functional magnetic resonance imaging (fMRI) signal has also been shown to exhibit adaptation on a longer time scale. However, some regions such as the visual and auditory cortices exhibit significant BOLD adaptation, whereas other such as the whisker barrel cortex may not adapt. In the sensory cortex a combination of thalamic inputs and intracortical activity drives hemodynamic changes, although the relative contributions of these components are not entirely understood. The aim of this study is to assess the role of thalamic inputs vs. intracortical processing in shaping BOLD adaptation during stimulation in the somatosensory cortex. Using simultaneous fMRI and electrophysiology in awake rabbits, we measured BOLD, local field potentials (LFPs), single- and multi-unit activity in the cortex during whisker and optogenetic stimulation. This design allowed us to compare BOLD and haemodynamic responses during activation of the normal thalamocortical sensory pathway (i.e., both inputs and intracortical activity) vs. the direct optical activation of intracortical circuitry alone. Our findings show that whereas LFP and multi-unit (MUA) responses adapted, neither optogenetic nor sensory stimulation produced significant BOLD adaptation. We observed for both paradigms a variety of excitatory and inhibitory single unit responses. We conclude that sensory feed-forward thalamic inputs are not primarily responsible for shaping BOLD adaptation to stimuli; but the single-unit results point to a role in this behaviour for specific excitatory and inhibitory neuronal sub-populations, which may not correlate with aggregate neuronal activity.

By combining flow-dephased and flow-rephased diffusion weighting with blood oxygenation level dependent functional magnetic resonance imaging, it is possible to study flow dynamics in the venous network of the human brain. Thereby, ballistic flow, which conserves direction and velocity during echo time, is separated from diffusive flow with many changes in direction and velocity. By using this technique with very low diffusion/flow weighting, the mean velocity of ballistic flow was quantified in this study. The result of 10.9+/-3.2 cm/s strongly indicates that large venous vessels are the source of ballistic flow.

Blood oxygen level dependent (BOLD) functional magnetic resonance imaging (fMRI) is the most widely used method for mapping neural activity in the brain. The interpretation of altered BOLD signals is problematic when cerebral blood flow (CBF) or cerebral blood volume change because of aging and/or neurodegenerative diseases. In this study, a recently developed quantitative arterial spin labeling (ASL) approach, bolus-tracking ASL (btASL), was applied to an fMRI experiment in the rat brain. The mean transit time (MTT), capillary transit time (CTT), relative cerebral blood volume of labeled water (rCBV(lw)), relative cerebral blood flow (rCBF), and perfusion coefficient in the forelimb region of the somatosensory cortex were quantified during neuronal activation and in the resting state. The average MTT and CTT were 1.939+/-0.175 and 1.606+/-0.106 secs, respectively, in the resting state. Both times decreased significantly to 1.616+/-0.207 and 1.305+/-0.201 secs, respectively, during activation. The rCBV(lw), rCBF, and perfusion coefficient increased on average by a factor of 1.123+/-0.006, 1.353+/-0.078, and 1.479+/-0.148, respectively, during activation. In contrast to BOLD techniques, btASL yields physiologically relevant indices of the functional hyperemia that accompanies neuronal activation.

MRI offers techniques for non-invasively measuring a range of aspects of brain tissue function. Blood oxygenation level dependent (BOLD) functional magnetic resonance imaging (fMRI) is widely used to assess neural activity, based on the brain's haemodynamic response, while arterial spin labelling (ASL) MRI is a non-invasive method of quantitatively mapping cerebral perfusion. Both techniques can be applied to measure cerebrovascular reactivity (CVR), an important marker of the health of the cerebrovascular system. BOLD, ASL and CVR have been applied to study a variety of disease processes and are already used in certain clinical circumstances. The brainstem is a critical component of the central nervous system and is implicated in a variety of disease processes. However, its function is difficult to study using MRI because of its small size and susceptibility to physiological noise. In this article, we review the physical and biological underpinnings of BOLD and ASL and their application to measure CVR, discuss the challenges associated with applying them to the brainstem and the opportunities for brainstem MRI in the research and clinical settings. With further optimisation, functional MRI techniques could feasibly be used to assess brainstem haemodynamics and neural activity in the clinical setting.

Simultaneous task-based BOLD-fMRI and [18-F] FDG functional PET for measurement of neuronal metabolism in the human visual cortex

Although functional lateralization in the human brain has been studied intensively, there remains significant controversy over the brain mechanisms that instantiate it. The main objective of the present study is to characterize the regions associated with the generation of different movements by the fingers of both hands by right- and left-handed people. Thirteen right- and left-handers were studied using blood oxygen level dependent (BOLD) functional magnetic resonance imaging (fMRI) during performance of single and sequential finger movement tasks. We used single-shot whole-brain spiral fMRI to map the functional components of the motor system during these tasks. Regions of interest included the primary motor and sensory cortices, the pre-motor cortices and the cerebellum. Sequential movements were associated with intense brain activation in several bilateral regions, whereas single movements were associated with less activation in fewer regions, but with greater laterality. Right- and left-handers differed in their pattern of activation, sharing a pattern of activation on simple movements but responding differently to sequential movements. On simple movements, the brain activation patterns of left- and right-handers were similar in volume, number of areas and laterality. By contrast, on sequential movement, left-handers activated larger volumes and a larger number of brain areas than right-handers, and showed significantly less brain lateralization. These results highlight differences in the functional organization of motor areas in right- and left-handed people. The discrepancies that might reflect differences in the network features of motor systems in these two groups, could also determine differences in motor activity that occur during recovery from injury (e.g. after stroke).

The peripartum period begins during late pregnancy and extends across parturition into early lactation. During this period, the maternal brain undergoes changes resulting from central and peripheral alterations in hormone and neurotransmitter levels. These changes manifest behaviorally, anatomically, and physiologically, and lead to development of maternal behaviors. In order to address how these changes affect maternal brain response to survival-pertinent exogenous stimuli, three studies were conducted. The studies used blood oxygen level dependent (BOLD) functional magnetic resonance imaging (fMRI) in awake rats to evaluate differences between maternal and non-maternal brain responses to predatory fear, pain, and reward, while also addressing the modulatory influence of offspring presence on maternal brain responsiveness. In order to understand these patterns of response, a Maternal Motivation-Decision Model is proposed, which is a derivation of Fields' Motivation-Decision Model of pain and reward processing. The Maternal Motivation-Decision Model predicts that, due to endocrine-induced alterations in the maternal brain, maternal focus shifts away from self-preservation and onto offspring care and survival. Therefore, any exogenous stimulus will be relatively devalued for the dam compared to offspring care, and as a result, maternal processing of environmental stimuli will be altered to accommodate for maximal offspring survival.

Alterations in regional homogeneity of resting-state brain activity in autism spectrum disorders