Blood Oxygenation Level-dependent fMRI Research Articles

Development of computational models for microtesla-level magnetic brain scanning: a novel avenue for device development

BackgroundDetection of locally increased blood concentration and perfusion is critical for assessment of functional cortical activity as well as diagnosis of conditions such as intracerebral hemorrhage (ICH). Current paradigms for assessment of regional blood concentration in the brain rely on computed tomography (CT), magnetic resonance imaging (MRI), and perfusion blood oxygen level dependent functional magnetic resonance imaging (BOLD-fMRI).ResultsIn this study, we developed computational models to test the feasibility of novel magnetic sensors capable of detecting hemodynamic changes within the brain on a microtesla-level. We show that low-field magnetic sensors can accurately detect changes in magnetic flux density and eddy current damping signals resulting from increases in local blood concentration. These models predicted that blood volume changes as small as 1.26 mL may be resolved by the sensors, implying potential use for diagnosis of ICH and assessment of regional blood flow as a proxy for cerebral metabolism and neuronal activity. We then translated findings from our computational model to demonstrate feasibility of accurate detection of modeled ICH in a simulated human cadaver setting.ConclusionsOverall, microtesla-level magnetic scanning is feasible, safe, and has distinct advantages compared to current standards of care. Computational modeling may facilitate rapid prototype development and testing of novel medical devices with minimal risk to human participants prior to device construction and clinical trials.

Hemodynamic and metabolic correspondence of resting-state voxel-based physiological metrics in healthy adults

Voxel-based physiological (VBP) variables derived from blood oxygen level dependent (BOLD) fMRI time-course variations include: amplitude of low frequency fluctuations (ALFF), fractional amplitude of low frequency fluctuations (fALFF) and regional homogeneity (ReHo). Although these BOLD-derived variables can detect between-group (e.g. disease vs control) spatial pattern differences, physiological interpretations are not well established. The primary objective of this study was to quantify spatial correspondences between BOLD VBP variables and PET measurements of cerebral metabolic rate and hemodynamics, being well-validated physiological standards. To this end, quantitative, whole-brain PET images of metabolic rate of glucose (MRGlu; 18FDG) and oxygen (MRO2; 15OO), blood flow (BF; H215O) and blood volume (BV; C15O) were obtained in 16 healthy controls. In the same subjects, BOLD time-courses were obtained for computation of ALFF, fALFF and ReHo images. PET variables were compared pair-wise with BOLD variables. In group-averaged, across-region analyses, ALFF corresponded significantly only with BV (R = 0.64; p < 0.0001). fALFF corresponded most strongly with MRGlu (R = 0.79; p < 0.0001), but also significantly (p < 0.0001) with MRO2 (R = 0.68), BF (R = 0.68) and BV (R=0.68). ReHo performed similarly to fALFF, with significant strong correspondence (p < 0.0001) with MRGlu (R = 0.78), MRO2 (R = 0.54), and, but less strongly with BF (R = 0.50) and BV (R=0.50). Mutual information analyses further clarified these physiological interpretations. When conditioned by BV, ALFF retained no significant MRGlu, MRO2 or BF information. When conditioned by MRGlu, fALFF and ReHo retained no significant MRO2, BF or BV information. Of concern, however, the strength of PET-BOLD correspondences varied markedly by brain region, which calls for future investigation on physiological interpretations at a regional and per-subject basis.

Study of Brain Structure and Function in Chronic Mountain Sickness Based on fMRI.

Objective: Headache and memory impairment are the primary clinical symptoms of chronic mountain sickness (CMS). In this study, we used voxel-based morphometry (VBM) and the amplitude of the low-frequency fluctuation method (ALFF) based on blood oxygen level-dependent functional magnetic resonance imaging (BOLD-fMRI) to identify changes in the brain structure and function caused by CMS.Materials and Methods: T1W anatomical images and a resting-state functional MRI (fMRI) of the whole brain were performed in 24 patients diagnosed with CMS and 25 normal controls matched for age, sex, years of education, and living altitude. MRI images were acquired, followed by VBM and ALFF data analyses.Results: Compared with the control group, the CMS group had increased gray matter volume in the left cerebellum crus II area, left inferior temporal gyrus, right middle temporal gyrus, right insula, right caudate nucleus, and bilateral lentiform nucleus along with decreased gray matter volume in the left middle occipital gyrus and left middle temporal gyrus. White matter was decreased in the bilateral middle temporal gyrus and increased in the right Heschl's gyrus. Resting-state fMRI in patients with CMS showed increased spontaneous brain activity in the left supramarginal gyrus, left parahippocampal gyrus, and left middle temporal gyrus along with decreased spontaneous brain activity in the right cerebellum crus I area and right supplementary motor area.Conclusion: Patients with CMS had differences in gray and white matter volume and abnormal spontaneous brain activity in multiple brain regions compared to the controls. This suggests that long-term chronic hypoxia may induce changes in brain structure and function, resulting in CMS.

Tonic, Burst, and Burst-Cycle Spinal Cord Stimulation Lead to Differential Brain Activation Patterns as Detected by Functional Magnetic Resonance Imaging

ObjectiveThe objective of this preclinical study was to examine the responses of the brain to noxious stimulation in the presence and absence of different modes of spinal cord stimulation (SCS) using blood-oxygen-level-dependent functional magnetic resonance imaging (BOLD-fMRI). Materials and MethodsSprague-Dawley rats were randomized to groups based on the mode of SCS delivered which included tonic stimulation (n = 27), burst stimulation (n = 30), and burst-cycle stimulation (n = 29). The control (sham) group (n = 28) received no SCS. The SCS electrode was inserted between T10 and T12 spinal levels prior to fMRI session. The experimental protocol for fMRI acquisition consisted of an initial noxious stimulation phase, a treatment phase wherein the SCS was turned on concurrently with noxious stimulation, and a residual effect phase wherein the noxious stimulation alone was turned on. The responses were statistically analyzed through paired t-test and the results were presented as z-scores for the quantitative analysis of the fMRI data. ResultsThe treatment with different SCS modes attenuated the BOLD brain responses to noxious hindlimb stimulation. The tonic, burst, and burst-cycle SCS treatment attenuated BOLD responses in the caudate putamen (CPu), insula (In), and secondary somatosensory cortex (S2). There was little to no corresponding change in sham control in these three regions. The burst and burst-cycle SCS demonstrated greater attenuation of BOLD signals in CPu, In, and S2 compared to tonic stimulation. ConclusionThe high-resolution fMRI study using a rat model demonstrated the potential of different SCS modes to act on several pain-matrix-related regions of the brain in response to noxious stimulation. The burst and burst-cycle SCS exhibited greater brain activity reduction in response to noxious hindlimb stimulation in the caudate putamen, insula, and secondary somatosensory cortex compared to tonic stimulation.

Mapping grip-force related brain activity after a fatiguing motor task in multiple sclerosis

BackgroundMotor fatigue is common in multiple sclerosis (MS), but its pathophysiology is still poorly understood. Here we used functional magnetic resonance imaging (fMRI) to delineate how the acute induction of motor fatigue alters functional activity of the motor system and how these activity changes are related to motor fatigue. MethodForty-four right-handed mildly disabled patients with relapsing-remitting MS and 25 healthy controls performed a maximal tonic precision grip with their right hand until they developed motor fatigue. Before and after the fatiguing task, participants performed a non-fatiguing tonic grip force task, producing 15–20% of their maximum grip force based on visual feedback. Task related brain activity was mapped with blood-oxygen level dependent fMRI at 3 T. Statistical parametric mapping was used to identify relative changes in task-related activation from the pre-fatigue to the recovery MRI session. ResultsFollowing fatigue induction, task performance was perturbed in both groups, and task-related activation increased in the right (ipsilateral) primary motor hand area. In patients with MS, task-related activity increased bilaterally during the recovery phase in the ventrolateral portion of the middle putamen and lateral prefrontal cortex relative to controls. The more patients increased task-related activity in left dorsal premotor cortex after the fatiguing task, the less they experienced motor fatigue during daily life. ConclusionPatients with MS show enhanced functional engagement of the associative cortico-basal ganglia loop following acute induction of motor fatigue in the contralateral hand. This may reflect increased mental effort to generate movements in the recovery phase after fatigue induction. The ability to recruit the contralateral dorsal premotor cortex after fatigue induction may constitute a protective mechanism against experiencing motor fatigue in everyday life.

Comparing BOLD and VASO-CBV population receptive field estimates in human visual cortex

Vascular Space Occupancy (VASO) is an alternative fMRI approach based on changes in Cerebral Blood Volume (CBV). VASO-CBV fMRI can provide higher spatial specificity than the blood oxygenation level-dependent (BOLD) method because the CBV response is thought to be limited to smaller vessels. To investigate how this technique compares to BOLD fMRI for cognitive neuroscience applications, we compared population receptive field (pRF) mapping estimates between BOLD and VASO-CBV. We hypothesized that VASO-CBV would elicit distinct pRF properties compared to BOLD. Specifically, since pRF size estimates also depend on vascular sources, we hypothesized that reduced vascular blurring might yield narrower pRFs for VASO-CBV measurements. We used a VASO sequence with a double readout 3D EPI sequence at 7T to simultaneously measure VASO-CBV and BOLD responses in the visual cortex while participants viewed conventional pRF mapping stimuli. Both VASO-CBV and BOLD images show similar eccentricity and polar angle maps across all participants. Compared to BOLD-based measurements, VASO-CBV yielded lower tSNR and variance explained. The pRF size changed with eccentricity similarly for VASO-CBV and BOLD, and the pRF size estimates were similar for VASO-CBV and BOLD, even when we equate variance explained between VASO-CBV and BOLD. This result suggests that the vascular component of the pRF size is not dominating in either VASO-CBV or BOLD.

Prior Methamphetamine Use Disorder History Does Not Impair Interoceptive Processing of Soft Touch in HIV Infection.

Introduction: Interoception, defined as the sense of the internal state of one’s body, helps motivate goal-directed behavior. Prior work has shown that methamphetamine (METH) use disorder is associated with altered interoception, and that this may contribute to risky behavior. As people with HIV (PWH) may also experience disrupted bodily sensations (e.g., neuropathy), an important question is whether PWH with a history of METH use disorder might exhibit greater impairment of interoceptive processing. Methods: Eighty-three participants stratified by HIV infection and a past history of methamphetamine use disorder experienced a soft touch paradigm that included slow brush strokes on the left forearm and palm during blood-oxygen level-dependent functional MRI acquisition. To assess differences in interoception and reward, voxelwise analyses were constrained to the insula, a hub for the evaluation of interoceptive cues, and the striatum, which is engaged in reward processing. Results: Overall, individuals with a history of METH use disorder had an attenuated neural response to pleasant touch in both the insula and striatum. Longer abstinence was associated with greater neural response to touch in the insula, suggesting some improvement in responsivity. However, only PWH with no METH use disorder history had lower brain activation in the insula relative to non-using seronegative controls. Conclusions: Our findings suggest that while METH use disorder history and HIV infection independently disrupt the neural processes associated with interoception, PWH with METH use disorder histories do not show significant differences relative to non-using seronegative controls. These findings suggest that the effects of HIV infection and past methamphetamine use might not be additive with respect to interoceptive processing impairment.

Point-spread function of the BOLD response across columns and cortical depth in human extra-striate cortex.

Columns and layers are fundamental organizational units of the brain. Well known examples of cortical columns are the ocular dominance columns (ODCs) in primary visual cortex and the column-like stripe-based arrangement in the second visual area V2. The spatial scale of columns and layers is beyond the reach of conventional neuroimaging, but the advent of high field magnetic resonance imaging (MRI) scanners (UHF, 7 Tesla and above) has opened the possibility to acquire data at this spatial scale, in-vivo and non-invasively in humans. The most prominent non-invasive technique to measure brain function is blood oxygen level dependent (BOLD) fMRI, measuring brain activity indirectly, via changes in hemodynamics. A key determinant of the ability of high-resolution BOLD fMRI to accurately resolve columns and layers is the point-spread function (PSF) of the BOLD response in relation to the spatial extent of neuronal activity. In this study we take advantage of the stripe-based arrangement present in visual area V2, coupled with sub-millimetre anatomical and gradient-echo BOLD (GE BOLD) acquisition at 7 T to obtain PSF estimates and along cortical depth in human participants. Results show that the BOLD PSF is maximal in the superficial part of the cortex (1.78 mm), and it decreases with increasing cortical depth (0.83 mm close to white matter).

Hemodynamic and metabolic changes during hypercapnia with normoxia and hyperoxia using pCASL and TRUST MRI in healthy adults

Blood oxygenation level-dependent (BOLD) or arterial spin labeling (ASL) MRI with hypercapnic stimuli allow for measuring cerebrovascular reactivity (CVR). Hypercapnic stimuli are also employed in calibrated BOLD functional MRI for quantifying neuronally-evoked changes in cerebral oxygen metabolism (CMRO2). It is often assumed that hypercapnic stimuli (with or without hyperoxia) are iso-metabolic; increasing arterial CO2 or O2 does not affect CMRO2. We evaluated the null hypothesis that two common hypercapnic stimuli, ‘CO2 in air’ and carbogen, are iso-metabolic. TRUST and ASL MRI were used to measure the cerebral venous oxygenation and cerebral blood flow (CBF), from which the oxygen extraction fraction (OEF) and CMRO2 were calculated for room-air, ‘CO2 in air’ and carbogen. As expected, CBF significantly increased (9.9% ± 9.3% and 12.1% ± 8.8% for ‘CO2 in air’ and carbogen, respectively). CMRO2 decreased for ‘CO2 in air’ (−13.4% ± 13.0%, p < 0.01) compared to room-air, while the CMRO2 during carbogen did not significantly change. Our findings indicate that ‘CO2 in air’ is not iso-metabolic, while carbogen appears to elicit a mixed effect; the CMRO2 reduction during hypercapnia is mitigated when including hyperoxia. These findings can be important for interpreting measurements using hypercapnic or hypercapnic-hyperoxic (carbogen) stimuli.

Mapping cortico-subcortical sensitivity to 4 Hz amplitude modulation depth in human auditory system with functional MRI

Temporal modulations in the envelope of acoustic waveforms at rates around 4 Hz constitute a strong acoustic cue in speech and other natural sounds. It is often assumed that the ascending auditory pathway is increasingly sensitive to slow amplitude modulation (AM), but sensitivity to AM is typically considered separately for individual stages of the auditory system. Here, we used blood oxygen level dependent (BOLD) fMRI in twenty human subjects (10 male) to measure sensitivity of regional neural activity in the auditory system to 4 Hz temporal modulations. Participants were exposed to AM noise stimuli varying parametrically in modulation depth to characterize modulation-depth effects on BOLD responses. A Bayesian hierarchical modeling approach was used to model potentially nonlinear relations between AM depth and group-level BOLD responses in auditory regions of interest (ROIs). Sound stimulation activated the auditory brainstem and cortex structures in single subjects. BOLD responses to noise exposure in core and belt auditory cortices scaled positively with modulation depth. This finding was corroborated by whole-brain cluster-level inference. Sensitivity to AM depth variations was particularly pronounced in the Heschl's gyrus but also found in higher-order auditory cortical regions. None of the sound-responsive subcortical auditory structures showed a BOLD response profile that reflected the parametric variation in AM depth. The results are compatible with the notion that early auditory cortical regions play a key role in processing low-rate modulation content of sounds in the human auditory system.

An ICA Investigation into the Effect of Physiological Noise Correction on Dimensionality and Spatial Maps of Intrinsic Connectivity Networks.

Physiological processes such as cardiac pulsations and respiration can induce signal modulations in functional magnetic resonance imaging (fMRI) time series, and confound inferences made about neural processing from analyses of the blood oxygenation level-dependent (BOLD) signals. Retrospective image space correction of physiological noise (RETROICOR) is a widely used approach to reduce physiological signals in data. Independent component analysis (ICA) is a valuable blind source separation method for analyzing brain networks, referred to as intrinsic connectivity networks (ICNs). Previously, we showed that temporal properties of the ICA-derived networks such as spectral power and functional network connectivity could be impacted by RETROICOR corrections. The goal of this study is to investigate the effect of retrospective correction of physiological artifacts on the ICA dimensionality (model order) and intensities of ICN spatial maps. To this aim, brain BOLD fMRI, heartbeat, and respiration were measured in 22 healthy subjects during resting state. ICA dimensionality was estimated using minimum description length (MDL) based on i.i.d. data samples and smoothness FWHM kernel, and entropy-rate based order selection by finite memory length model (ER-FM) and autoregressive model (ER-AR). Differences in spatial maps between the raw and denoised data were compared using the paired t-test and false discovery rate (FDR) thresholding was used to correct for multiple comparisons. Results showed that ICA dimensionality was greater in the raw data compared to the denoised data. Significant differences were found in the intensities of spatial maps for three ICNs: basal ganglia, precuneus, and frontal network. These preliminary results indicate that the retrospective physiological noise correction can induce change in the resting state spatial map intensity related to the within-network connectivity. More research is needed to understand this effect.

Glioma Radiation Therapy on a High Field 1.5 MR-Linac: Workflow and Initial Experience

The development of high-field strength MR-guided radiotherapy systems enables daily MR imaging, the opportunity for adaptive radiotherapy, and functional imaging acquisition. This study reports the workflow implementation, treatment times, and initial experience of glioma radiotherapy on the 1.5T MR-Linac (MRL).Selected glioma patients treated with concurrent chemoradiation (chemoRT) between October 2019 and August 2020 were identified from a prospective database. All patients were treated on the MRL with backup plans on conventional Linac if the MRL was unavailable. Workflow timings were recorded and online adaptive plans were generated using the Adapt-To-Position (ATP) workflow derived from a pre-beam T1-weighted MRI. Temporal variation within the FLAIR hyperintense region (FHR) was assessed by the Dice similarity coefficient (DSC) and relative FHR volumes, compared to the initial FLAIR contour at the first MRL fraction. Multi-parametric images were acquired on the MR-Linac during radiation treatment, including diffusion-weighted imaging (DWI), chemical exchange saturation transfer (CEST), magnetization transfer (MT), and blood oxygenation level dependent (BOLD) resting-state fMRI. The behavior of selected functional parameter values was investigated within the FHR at the imaged fractions.Ten high grade glioma patients completed chemoRT to a median dose of 60 Gy (range, 54-60 Gy) in 30 fractions (range, 30-33), receiving a total of 287 fractions on the MRL. The mean in-room time per fraction was 37.3 minutes (range, 24-51 minutes), and 42.9 minutes if including post-beam research imaging. Three patients (30%) required re-planning between fractions 15 to 19 due to progression of tumor and/or edema identified on daily MRL imaging. At the 10, 20, and 30 day post-first fraction time points, 3, 3, and 4 patients had a FLAIR volume that changed by at least 20% relative to the first MRL fraction, respectively. Multi-parametric images including DWI, CEST, MT, and BOLD resting-state fMRI were successfully acquired on the MR-Linac. The median apparent diffusion coefficients (ADC) within the FHR and volumes of FLAIR were significantly correlated when the data from all patients and time points were pooled (r = 0.68, P < 10-3).We report the first clinical series of glioma patients treated with chemoRT on the MRL. The workflow and treatment times were clinically acceptable, and daily online MRL imaging triggered adaptive re-planning for selected patients. Acquisition of multi-parametric imaging sequences was feasible on the MRL during routine treatment workflow. ADC parameter changes could be reliably tracked during chemoRT, and mature clinical outcomes data is anticipated to define the role of functional imaging in adaptive radiotherapy.C. Tseng: Advisory Board; Sanofi. H. Chen: Employee; North York General Hospital. J. Stewart: None. A. Lau: None. R. Chan: None. L.S. Lawrence: Student affiliated with University of Toronto; Sunnybrook Research Institute. M. Campbell: None. S.D. Myrehaug: Advisory Board; Novartis AG.H. Soliman: None. Z.A. Husain: Independent Contractor; RadOncQuestions LLC. Research Grant; Merck. Travel Expenses; Elekta; NIH Head and neck PULA task force. J. Detsky: None. P. Maralani: None. B.M. Keller: None. M.E. Ruschin: Patent/License Fees/Copyright; Elekta AB.A. Sahgal: Research Grant; Elekta.

Identification of Negative BOLD Responses in Epilepsy Using Windkessel Models.

Alongside positive blood oxygenation level–dependent (BOLD) responses associated with interictal epileptic discharges, a variety of negative BOLD responses (NBRs) are typically found in epileptic patients. Previous studies suggest that, in general, up to four mechanisms might underlie the genesis of NBRs in the brain: (i) neuronal disruption of network activity, (ii) altered balance of neurometabolic/vascular couplings, (iii) arterial blood stealing, and (iv) enhanced cortical inhibition. Detecting and classifying these mechanisms from BOLD signals are pivotal for the improvement of the specificity of the electroencephalography–functional magnetic resonance imaging (EEG-fMRI) image modality to identify the seizure-onset zones in refractory local epilepsy. This requires models with physiological interpretation that furnish the understanding of how these mechanisms are fingerprinted by their BOLD responses. Here, we used a Windkessel model with viscoelastic compliance/inductance in combination with dynamic models of both neuronal population activity and tissue/blood O2 to classify the hemodynamic response functions (HRFs) linked to the above mechanisms in the irritative zones of epileptic patients. First, we evaluated the most relevant imprints on the BOLD response caused by variations of key model parameters. Second, we demonstrated that a general linear model is enough to accurately represent the four different types of NBRs. Third, we tested the ability of a machine learning classifier, built from a simulated ensemble of HRFs, to predict the mechanism underlying the BOLD signal from irritative zones. Cross-validation indicates that these four mechanisms can be classified from realistic fMRI BOLD signals. To demonstrate proof of concept, we applied our methodology to EEG-fMRI data from five epileptic patients undergoing neurosurgery, suggesting the presence of some of these mechanisms. We concluded that a proper identification and interpretation of NBR mechanisms in epilepsy can be performed by combining general linear models and biophysically inspired models.

Analysis of Mental State of Patients after Drug Addiction and Withdrawal Guided by PETCT Image Based on Optimized Image Fusion Algorithm

Blood oxygen level-dependent functional magnetic resonance imaging (BOLD-fMRI) studies have shown that drug-dependent patients are activated in different addictive brain areas under the stimulation of relevant environmental cues, which in turn leads to craving and relapse. This study uses magnetic resonance spectroscopy to measure brain temperature to explore the brain temperature changes in different addictive brain regions of heroin and methamphetamine addicts in a short-term withdrawal state and to explore whether the quantitative index of brain temperature change can be used as a diagnostic drug Methods. The subjects were scanned by resting-state MRI spectroscopy first and then subjected to MRI spectroscopy scanning under visual stimulation. The subjects were required to watch the heroin/meth-related clue pictures carefully during visual stimulation. The measured chemical shift value of N-acetyl-aspartic acid (NAA) is substituted into the brain temperature calculation formula T = 37 + 100 to obtain the brain temperature before and after visual stimulation. In addition, the anxiety and depression states of heroin and methamphetamine-dependent patients were evaluated. Results. There was no statistically significant change in the brain temperature of the prefrontal cortex before and after visual stimulation in heroin and methamphetamine-dependent subjects; compared with the normal group, there was no change in prefrontal cortex brain temperature before and after visual stimulation in heroin and methamphetamine-dependent subjects. Statistical Significance. The changes of hippocampal temperature before and after visual stimulation in methamphetamine-dependent patients were not statistically significant; compared with the normal group, there was no statistically significant difference in the changes of hippocampal temperature before and after visual stimulation in methamphetamine-dependent patients. Conclusion. This study initially found that the visual cues related to heroin and methamphetamine were not enough to cause significant changes in the brain temperature of the prefrontal cortex.

Multilevel Clustering-Evolutionary Random Support Vector Machine Cluster Algorithm-Based Blood Oxygenation Level-Dependent Functional Magnetic Resonance Imaging Images in Analysis of Therapeutic Effects on Cerebral Ischemic Stroke

The study aimed to explore the relationship between cerebral ischemic stroke (CIS) and the patient’s limb movement through the blood oxygenation level-dependent functional magnetic resonance imaging (BOLD-fMRI) based on multilevel clustering-evolutionary random support vector machine cluster (MCRSVMC). Specifically, 20 CIS patients were defined as the experimental group; another 20 healthy volunteers were defined as the control group. All subjects performed finger movement and verb association task. The performance of support vector machine (SVM) and MCRSVMC algorithm was compared and applied to functional magnetic resonance imaging (fMRI) of blood oxygen level in all subjects. The results showed that the average accuracy of MCRSVMC algorithm was significantly higher than that of support vector machine (86.75%, 65.84%; P &lt; 0.05 ). The sensitivity of MCRSVMC algorithm was significantly higher than that of support vector machine (92.52%, 75.41%; P &lt; 0.05 ). In addition, the specificity of MCRSVMC algorithm was significantly higher than that of support vector machine (86.39%, 68.24%; P &lt; 0.05 ). When CIS patients performed finger exercise, the sensory motor areas on both sides were significantly activated, and the activated sensory motor areas on both sides were significantly bigger than the ipsilateral area. The activation rate of the left-sensory motor area (L-SM1) was 87.5%, the activation rate of the right-sensory motor area (R-SM1) was 25%, the activation rate of the left-side auxiliary motor area (L-SMA) was 62.5%, and the activation rate of the right-side auxiliary motor area (R-SMA) was 37.5%. In conclusion, the MCRSVMC algorithm proposed in this study is highly efficient and stable. BOLD-fMRI diagnosis of motor function in CIS patients is mainly related to compensation around the lesion, which occurs on the healthy side after recovery.

Multilevel Clustering-Evolutionary Random Support Vector Machine Cluster Algorithm-Based Functional Magnetic Resonance Imaging in Diagnosing Cerebral Ischemic Stroke

This study was to explore the value of the blood oxygenation level dependent-functional magnetic resonance imaging (BOLD-fMRI) image classification based on the multilevel clustering-evolutionary random support vector machine cluster (MCRSVMC) algorithm in the diagnosis and treatment of patients with cognitive impairment after cerebral ischemic stroke (CIS). The MCRSVMC algorithm was optimized using a clustering algorithm, and it was compared with other algorithms in terms of accuracy (ACC), sensitivity (SEN), and specificity (SPE) of classifying the brain area images. 36 patients with cognitive impairment after CIS and nondementia patients were divided into a control group (drug treatment) and an intervention group (drug + acupuncture) according to different treatment methods, with 18 cases in each group. The changes in regional homogeneity (ReHo) of BOLD-fMRI images and the differences in scores of the Montreal Cognitive Assessment Scale (MoCA), scores of Loewenstein Occupational Therapy Cognitive Assessment (LOTCA), and scores of Functional Independence Measure (FIM) between the two groups of patients were compared before and after treatment. The results revealed that the average classification ACC, SEN, and SPE of the MCRSVMC algorithm were 84.25 ± 4.13%, 91.07 ± 3.51%, and 89 ± 3.96%, respectively, which were all obviously better than those of other algorithms ( P &lt; 0.01 ). When the number of support vector machine (SVM) classifiers and the number of important features were 410 and 260, respectively, the classification ACC of MCRSVMC algorithm was 0.9429 and 0.9092, respectively. After treatment, the MoCA score, LOTCA score, and FIM score of the patients in the intervention group were higher than those of the control group ( P &lt; 0.05 ). The ReHo values of the right inferior temporal gyrus and right inferior frontal gyrus of patients in the intervention group were much higher than those of the control group ( P &lt; 0.05 ). It indicated that the classification ACC, SEN, and SPE of the magnetic resonance imaging (MRI) based on the MCRSVMC algorithm in this study were greatly improved, and the acupuncture method was more effective in the treatment of patients with cognitive dysfunction after CIS.

Functional Activities Detected in the Olfactory Bulb and Associated Olfactory Regions in the Human Brain Using T2-Prepared BOLD Functional MRI at 7T.

Olfaction is a fundamental sense that plays a vital role in daily life in humans, and can be altered in neuropsychiatric and neurodegenerative diseases. Blood oxygenation level-dependent (BOLD) functional magnetic resonance imaging (fMRI) using conventional echo-planar-imaging (EPI) based sequences can be challenging in brain regions important for olfactory processing, such as the olfactory bulb (OB) and orbitofrontal cortex, mainly due to the signal dropout and distortion artifacts caused by large susceptibility effects from the sinonasal cavity and temporal bone. To date, few studies have demonstrated successful fMRI in the OB in humans. T2-prepared (T2prep) BOLD fMRI is an alternative approach developed especially for performing fMRI in regions affected by large susceptibility artifacts. The purpose of this technical study is to evaluate T2prep BOLD fMRI for olfactory functional experiments in humans. Olfactory fMRI scans were performed on 7T in 14 healthy participants. T2prep BOLD showed greater sensitivity than GRE EPI BOLD in the OB, orbitofrontal cortex and the temporal pole. Functional activation was detected using T2prep BOLD in the OB and associated olfactory regions. Habituation effects and a bi-phasic pattern of fMRI signal changes during olfactory stimulation were observed in all regions. Both positively and negatively activated regions were observed during olfactory stimulation. These signal characteristics are generally consistent with literature and showed a good intra-subject reproducibility comparable to previous human BOLD fMRI studies. In conclusion, the methodology demonstrated in this study holds promise for future olfactory fMRI studies in the OB and other brain regions that suffer from large susceptibility artifacts.

Assessment of single-vessel cerebral blood velocity by phase contrast fMRI.

Current approaches to high-field functional MRI (fMRI) provide 2 means to map hemodynamics at the level of single vessels in the brain. One is through changes in deoxyhemoglobin in venules, i.e., blood oxygenation level-dependent (BOLD) fMRI, while the second is through changes in arteriole diameter, i.e., cerebral blood volume (CBV) fMRI. Here, we introduce cerebral blood flow-related velocity-based fMRI, denoted CBFv-fMRI, which uses high-resolution phase contrast (PC) MRI to form velocity measurements of flow. We use CBFv-fMRI in measure changes in blood velocity in single penetrating microvessels across rat parietal cortex. In contrast to the venule-dominated BOLD and arteriole-dominated CBV fMRI signals, CBFv-fMRI is comparable from both arterioles and venules. A single fMRI platform is used to map changes in blood pO2 (BOLD), volume (CBV), and velocity (CBFv). This combined high-resolution single-vessel fMRI mapping scheme enables vessel-specific hemodynamic mapping in animal models of normal and diseased states and further has translational potential to map vascular dementia in diseased or injured human brains with ultra-high-field fMRI.

Sensory Recruitment Revisited: Ipsilateral V1 Involved in Visual Working Memory.

The "sensory recruitment hypothesis" posits an essential role of sensory cortices in working memory, beyond the well-accepted frontoparietal areas. Yet, this hypothesis has recently been challenged. In the present study, participants performed a delayed orientation recall task while high-spatial-resolution 3T functional magnetic resonance imaging (fMRI) signals were measured in posterior cortices. A multivariate inverted encoding model approach was used to decode remembered orientations based on blood oxygen level-dependent fMRI signals from visual cortices during the delay period. We found that not only did activity in the contralateral primary visual cortex (V1) retain high-fidelity representations of the visual stimuli, but activity in the ipsilateral V1 also contained such orientation tuning. Moreover, although the encoded tuning was faded in the contralateral V1 during the late delay period, tuning information in the ipsilateral V1 remained sustained. Furthermore, the ipsilateral representation was presented in secondary visual cortex (V2) as well, but not in other higher-level visual areas. These results thus supported the sensory recruitment hypothesis and extended it to the ipsilateral sensory areas, which indicated the distributed involvement of visual areas in visual working memory.

A line through the brain: implementation of human line-scanning at 7T for ultra-high spatiotemporal resolution fMRI

Functional magnetic resonance imaging (fMRI) is a widely used tool in neuroscience to detect neurally evoked responses, e.g. the blood oxygenation level-dependent (BOLD) signal. Typically, BOLD fMRI has millimeter spatial resolution and temporal resolution of one to few seconds. To study the sub-millimeter structures and activity of the cortical gray matter, the field needs an fMRI method with high spatial and temporal resolution. Line-scanning fMRI achieves very high spatial resolution and high sampling rate, at the cost of a sacrifice in volume coverage. Here, we present a human line-scanning implementation on a 7T MRI system. First, we investigate the quality of the saturation pulses that suppress MR signal outside the line. Second, we established the best coil combination for reconstruction. Finally, we applied the line-scanning method in the occipital lobe during a visual stimulation task, showing BOLD responses along cortical depth, every 250 µm with a 200 ms repetition time (TR). We found a good correspondence of t-statistics values with 2D gradient-echo echo planar imaging (GE-EPI) BOLD fMRI data with the same temporal resolution and voxel volume (R = 0.6 ± 0.2). In summary, we demonstrate the feasibility of line-scanning in humans and this opens line-scanning fMRI for applications in cognitive and clinical neuroscience.