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1.
medRxiv ; 2024 Jul 12.
Article in English | MEDLINE | ID: mdl-39040201

ABSTRACT

A major challenge for human neuroimaging using functional MRI is the differentiation of neuronal excitation and inhibition which may induce positive and negative BOLD responses. Here we present an innovative multi-contrast laminar functional MRI technique that offers comprehensive and quantitative imaging of neurovascular (CBF, CBV, BOLD) and metabolic (CMRO2) responses across cortical layers at 7 Tesla. This technique was first validated through a finger-tapping experiment, revealing 'double-peak' laminar activation patterns within the primary motor cortex. By employing a ring-shaped visual stimulus that elicited positive and negative BOLD responses, we further observed distinct neurovascular and metabolic responses across cortical layers and eccentricities in the primary visual cortex. This suggests potential feedback inhibition of neuronal activities in both superficial and deep cortical layers underlying the negative BOLD signals in the fovea, and also illustrates the neuronal activities in visual areas adjacent to the activated eccentricities.

2.
Chronic Stress (Thousand Oaks) ; 7: 24705470231203655, 2023.
Article in English | MEDLINE | ID: mdl-37780807

ABSTRACT

Background: Posttraumatic stress disorder (PTSD) is a significant burden among combat Veterans returning from the wars in Iraq and Afghanistan. While empirically supported treatments have demonstrated reductions in PTSD symptomatology, there remains a need to improve treatment effectiveness. Functional magnetic resonance imaging (fMRI) neurofeedback has emerged as a possible treatment to ameliorate PTSD symptom severity. Virtual reality (VR) approaches have also shown promise in increasing treatment compliance and outcomes. To facilitate fMRI neurofeedback-associated therapies, it would be advantageous to accurately classify internal brain stress levels while Veterans are exposed to trauma-associated VR imagery. Methods: Across 2 sessions, we used fMRI to collect neural responses to trauma-associated VR-like stimuli among male combat Veterans with PTSD symptoms (N = 8). Veterans reported their self-perceived stress level on a scale from 1 to 8 every 15 s throughout the fMRI sessions. In our proposed framework, we precisely sample the fMRI data on cortical gray matter, blurring the data along the gray-matter manifold to reduce noise and dimensionality while preserving maximum neural information. Then, we independently applied 3 machine learning (ML) algorithms to this fMRI data collected across 2 sessions, separately for each Veteran, to build individualized ML models that predicted their internal brain states (self-reported stress responses). Results: We accurately classified the 8-class self-reported stress responses with a mean (± standard error) root mean square error of 0.6 (± 0.1) across all Veterans using the best ML approach. Conclusions: The findings demonstrate the predictive ability of ML algorithms applied to whole-brain cortical fMRI data collected during individual Veteran sessions. The framework we have developed to preprocess whole-brain cortical fMRI data and train ML models across sessions would provide a valuable tool to enable individualized real-time fMRI neurofeedback during VR-like exposure therapy for PTSD.

3.
Res Sq ; 2023 Sep 05.
Article in English | MEDLINE | ID: mdl-37720046

ABSTRACT

In functional magnetic resonance imaging, the hemodynamic response function (HRF) is a transient, stereotypical response to local changes in cerebral hemodynamics and oxygen metabolism due to briefly (< 4 s) evoked neural activity. Accordingly, the HRF is often used as an impulse response with the assumption of linearity in data analysis. In cognitive aging studies, it has been very common to interpret differences in brain activation as age-related changes in neural activity. Contrary to this assumption, however, evidence has accrued that normal aging may also significantly affect the vasculature, thereby affecting cerebral hemodynamics and metabolism, confounding interpretation of fMRI aging studies. In this study, use was made of a multisensory stimulus to evoke the HRF in ~ 87% of cerebral cortex in cognitively intact adults with ages ranging from 22-75 years. The stimulus evokes both positive and negative HRFs, which were characterized using model-free parameters in native-space coordinates. Results showed significant age trends in HRF parameter distributions in terms of both amplitudes (e.g., peak amplitude and CNR) and temporal dynamics (e.g., full-width-at-half-maximum). This work sets the stage for using HRF methods as a biomarker for age-related pathology.

4.
Front Neurosci ; 16: 1009295, 2022.
Article in English | MEDLINE | ID: mdl-36303946

ABSTRACT

Subcortical brain regions are absolutely essential for normal human function. These phylogenetically early brain regions play critical roles in human behaviors such as the orientation of attention, arousal, and the modulation of sensory signals to cerebral cortex. Despite the critical health importance of subcortical brain regions, there has been a dearth of research on their neurovascular responses. Blood oxygen level dependent (BOLD) functional MRI (fMRI) experiments can help fill this gap in our understanding. The BOLD hemodynamic response function (HRF) evoked by brief (<4 s) neural activation is crucial for the interpretation of fMRI results because linear analysis between neural activity and the BOLD response relies on the HRF. Moreover, the HRF is a consequence of underlying local blood flow and oxygen metabolism, so characterization of the HRF enables understanding of neurovascular and neurometabolic coupling. We measured the subcortical HRF at 9.4T and 3T with high spatiotemporal resolution using protocols that enabled reliable delineation of HRFs in individual subjects. These results were compared with the HRF in visual cortex. The HRF was faster in subcortical regions than cortical regions at both field strengths. There was no significant undershoot in subcortical areas while there was a significant post-stimulus undershoot that was tightly coupled with its peak amplitude in cortex. The different BOLD temporal dynamics indicate different vascular dynamics and neurometabolic responses between cortex and subcortical nuclei.

5.
Hum Brain Mapp ; 43(16): 4924-4942, 2022 11.
Article in English | MEDLINE | ID: mdl-35965416

ABSTRACT

The hemodynamic response function (HRF) measured with functional magnetic resonance imaging is generated by vascular and metabolic responses evoked by brief (<4 s) stimuli. It is known that the human HRF varies across cortex, between subjects, with stimulus paradigms, and even between different measurements in the same cortical location. However, our results demonstrate that strong HRFs are remarkably repeatable across sessions separated by time intervals up to 3 months. In this study, a multisensory stimulus was used to activate and measure the HRF across the majority of cortex (>70%, with lesser reliability observed in some areas of prefrontal cortex). HRFs were measured with high spatial resolution (2-mm voxels) in central gray matter to minimize variations caused by partial-volume effects. HRF amplitudes and temporal dynamics were highly repeatable across four sessions in 20 subjects. Positive and negative HRFs were consistently observed across sessions and subjects. Negative HRFs were generally weaker and, thus, more variable than positive HRFs. Statistical measurements showed that across-session variability is highly correlated to the variability across events within a session; these measurements also indicated a normal distribution of variability across cortex. The overall repeatability of the HRFs over long time scales generally supports the long-term use of event-related functional magnetic resonance imaging protocols.


Subject(s)
Brain Mapping , Oxygen , Humans , Brain Mapping/methods , Reproducibility of Results , Hemodynamics/physiology , Cerebral Cortex/diagnostic imaging , Cerebral Cortex/physiology , Magnetic Resonance Imaging/methods
6.
Sci Rep ; 11(1): 12544, 2021 06 15.
Article in English | MEDLINE | ID: mdl-34131162

ABSTRACT

Knowledge on the organization of motor function in the reticulospinal tract (RST) is limited by the lack of methods for measuring RST function in humans. Behavioral studies suggest the involvement of the RST in long latency responses (LLRs). LLRs, elicited by precisely controlled perturbations, can therefore act as a viable paradigm to measure motor-related RST activity using functional Magnetic Resonance Imaging (fMRI). Here we present StretchfMRI, a novel technique developed to study RST function associated with LLRs. StretchfMRI combines robotic perturbations with electromyography and fMRI to simultaneously quantify muscular and neural activity during stretch-evoked LLRs without loss of reliability. Using StretchfMRI, we established the muscle-specific organization of LLR activity in the brainstem. The observed organization is partially consistent with animal models, with activity primarily in the ipsilateral medulla for flexors and in the contralateral pons for extensors, but also includes other areas, such as the midbrain and bilateral pontomedullary contributions.


Subject(s)
Brain Stem/physiology , Cerebellum/physiology , Medulla Oblongata/physiology , Motor Cortex/physiology , Adult , Animals , Brain Stem/diagnostic imaging , Cerebellum/diagnostic imaging , Electromyography , Female , Humans , Magnetic Resonance Imaging , Male , Medulla Oblongata/diagnostic imaging , Motor Cortex/diagnostic imaging , Muscle, Skeletal/diagnostic imaging , Muscle, Skeletal/physiology , Neurons/physiology , Reaction Time/physiology , Spinal Cord/diagnostic imaging , Spinal Cord/physiology , Young Adult
7.
J Neurophysiol ; 125(4): 1045-1057, 2021 04 01.
Article in English | MEDLINE | ID: mdl-33625949

ABSTRACT

Functional magnetic resonance imaging (fMRI) measures blood-oxygen-level-dependent (BOLD) contrast that is generally assumed to be linearly related to excitatory neural activity. The positive hemodynamic response function (pHRF) is the positive BOLD response (PBR) evoked by a brief neural stimulation; the pHRF is often used as the impulse response for linear analysis of neural excitation. Many fMRI studies have observed a negative BOLD response (NBR) that is often associated with neural suppression. However, the temporal dynamics of the NBR evoked by a brief stimulus, the negative HRF (nHRF), remains unclear. Here, a unilateral visual stimulus was presented in a slow event-related design to elicit both pHRFs in the stimulus representation (SR), and nHRFs elsewhere. The observed nHRFs were not inverted versions of the pHRF previously reported. They were characterized by a stronger initial negative response followed by a significantly later positive peak. In contralateral primary visual cortex (V1), these differences varied with eccentricity from the SR. Similar nHRFs were observed in ipsilateral V1 with less eccentricity variation. Experiments with the blocked version of the same stimulus confirmed that brain regions presenting the unexpected nHRF dynamics correspond to those presenting a strong NBR. These data demonstrated that shift-invariant temporal linearity did not hold for the NBR while confirming that the PBR maintained rough linearity. Modeling indicated that the observed nHRFs can be created by suppression of both blood flow and oxygen metabolism. Critically, the nHRF can be misinterpreted as a pHRF due to their similarity, which could confound linear analysis for event-related fMRI experiments.NEW & NOTEWORTHY We investigate dynamics of the negative hemodynamic response function (nHRF), the negative blood-oxygen-level-dependent (BOLD) response (NBR) evoked by a brief stimulus, in human early visual cortex. Here, we show that the nHRFs are not inverted versions of the corresponding pHRFs. The nHRF has complex dynamics that varied significantly with eccentricity. The results also show shift-invariant temporal linearity does not hold for the NBR.


Subject(s)
Brain Mapping , Neurovascular Coupling/physiology , Retina/physiology , Visual Cortex/physiology , Visual Perception/physiology , Adult , Female , Humans , Image Processing, Computer-Assisted , Magnetic Resonance Imaging , Male , Middle Aged , Young Adult
8.
Annu Int Conf IEEE Eng Med Biol Soc ; 2020: 2889-2892, 2020 07.
Article in English | MEDLINE | ID: mdl-33018610

ABSTRACT

Understanding the fundamental roles of brainstem function resulting in proper motor control is critical to motor-rehabilitation after brain injuries. In particular, vestibular and reticular formation nuclei are thought to be associated with spasticity in chronic stroke patients. We used two kinds of stimuli in 10 healthy subjects to activate these nuclei while collecting high-resolution (1.5-mm) fMRI across the majority of brainstem. Optokinetic stimuli evoked illusory self-motion to activate the vestibular nuclei. Acoustic-startle stimuli were sets of loud tones designed to activate of the reticular formation. We summarized the response represented in a form of activation volume, mean percent signal change, and the phase delay (time lag) following the stimulus. We observed patterns of significant activations in the brainstem but did not find significant differences between the stimulus. We conclude that more sensitive measurement techniques are needed to reliably detect vestibular and reticular formation nuclei responses.


Subject(s)
Reticular Formation , Vestibular Nuclei , Acoustic Stimulation , Acoustics , Humans , Magnetic Resonance Imaging
9.
Hum Brain Mapp ; 41(18): 5083-5096, 2020 12 15.
Article in English | MEDLINE | ID: mdl-32870572

ABSTRACT

Dorsal human midbrain contains two nuclei with clear laminar organization, the superior and inferior colliculi. These nuclei extend in depth between the superficial dorsal surface of midbrain and a deep midbrain nucleus, the periaqueductal gray matter (PAG). The PAG, in turn, surrounds the cerebral aqueduct (CA). This study examined the use of two depth metrics to characterize depth and thickness relationships within dorsal midbrain using the superficial surface of midbrain and CA as references. The first utilized nearest-neighbor Euclidean distance from one reference surface, while the second used a level-set approach that combines signed distances from both reference surfaces. Both depth methods provided similar functional depth profiles generated by saccadic eye movements in a functional MRI task, confirming their efficacy for delineating depth for superficial functional activity. Next, the boundaries of the PAG were estimated using Euclidean distance together with elliptical fitting, indicating that the PAG can be readily characterized by a smooth surface surrounding PAG. Finally, we used the level-set approach to measure tissue depth between the superficial surface and the PAG, thus characterizing the variable thickness of the colliculi. Overall, this study demonstrates depth-mapping schemes for human midbrain that enables accurate segmentation of the PAG and consistent depth and thickness estimates of the superior and inferior colliculi.


Subject(s)
Cerebral Aqueduct/anatomy & histology , Inferior Colliculi/anatomy & histology , Magnetic Resonance Imaging/methods , Neuroimaging/methods , Periaqueductal Gray/anatomy & histology , Superior Colliculi/anatomy & histology , Adult , Cerebral Aqueduct/diagnostic imaging , Cerebral Aqueduct/physiology , Functional Neuroimaging , Humans , Inferior Colliculi/diagnostic imaging , Inferior Colliculi/physiology , Periaqueductal Gray/diagnostic imaging , Periaqueductal Gray/physiology , Saccades/physiology , Superior Colliculi/diagnostic imaging , Superior Colliculi/physiology
10.
Article in English | MEDLINE | ID: mdl-32084508

ABSTRACT

Previous magnetic resonance imaging studies of post-traumatic stress disorder (PTSD) have reported cortical volume alterations in the parahippocampal, anterior cingulate cortex, and temporal pole. It is unclear, however, if these cortical regions are specifically associated with PTSD or associated with common comorbidities. Here, we present the result of cortical volume differences between PTSD and healthy and psychiatric controls. In this study, healthy controls (n = 67) were matched for demographic characteristics (age, sex, race) and psychiatric controls (n = 67) were matched for demographic characteristics plus all other psychiatric diagnoses (past and current) to a group of PTSD patients (N = 67). We assessed group differences of 34 bilateral cortical structure volumes using statistically defined brain regions-of-interest from FreeSurfer between PTSD patients and healthy controls. We found 10 regions to be significantly different between PTSD and healthy controls and analyzed the group differences between PTSD and psychiatric controls within these regions. The right temporal pole volume in PTSD was found to be significantly smaller than both healthy and psychiatry controls. Our finding suggests only right temporal pole volume reduction is specifically associated with PTSD, and also highlights the need for using appropriate controls in psychiatry research.


Subject(s)
Magnetic Resonance Imaging/trends , Stress Disorders, Post-Traumatic/diagnostic imaging , Stress Disorders, Post-Traumatic/psychology , Temporal Lobe/diagnostic imaging , Adult , Female , Humans , Male , Mental Disorders/diagnostic imaging , Mental Disorders/epidemiology , Mental Disorders/psychology , Stress Disorders, Post-Traumatic/epidemiology , Young Adult
11.
J Cereb Blood Flow Metab ; 40(9): 1823-1837, 2020 09.
Article in English | MEDLINE | ID: mdl-31429358

ABSTRACT

The blood oxygen-level dependent (BOLD) functional magnetic resonance imaging (fMRI) signal depends on an interplay of cerebral blood flow (CBF), oxygen metabolism, and cerebral blood volume. Despite wide usage of BOLD fMRI, it is not clear how these physiological components create the BOLD signal. Here, baseline CBF and its dynamics evoked by a brief stimulus (2 s) in human visual cortex were measured at 3T. We found a stereotypical CBF response: immediate increase, rising to a peak a few second after the stimulus, followed by a significant undershoot. The BOLD hemodynamic response function (HRF) was also measured in the same session. Strong correlations between HRF and CBF peak responses indicate that the flow responses evoked by neural activation in nearby gray matter drive the early HRF. Remarkably, peak CBF and HRF were also strongly modulated by baseline perfusion. The CBF undershoot was reliable and significantly correlated with the HRF undershoot. However, late-time dynamics of the HRF and CBF suggest that oxygen metabolism can also contribute to the HRF undershoot. Combined measurement of the CBF and HRF for brief neural activation is a useful tool to understand the temporal dynamics of neurovascular and neurometabolic coupling.


Subject(s)
Cerebrovascular Circulation/physiology , Visual Cortex/physiology , Adult , Brain Mapping , Cerebral Blood Volume , Female , Gray Matter/blood supply , Gray Matter/physiology , Hemodynamics/physiology , Humans , Magnetic Resonance Imaging , Male , Middle Aged , Neurovascular Coupling/physiology , Oxygen/blood , Oxygen Consumption/physiology , Photic Stimulation , Young Adult
12.
Magn Reson Med ; 83(2): 681-694, 2020 02.
Article in English | MEDLINE | ID: mdl-31423634

ABSTRACT

PURPOSE: Functional MRI contrast has generally been associated with changes in transverse relaxivity caused by blood oxygen concentration, the so-called blood oxygen level dependent contrast. However, this interpretation of fMRI contrast has been called into question by several recent experiments at high spatial resolution. Experiments were conducted to examine contrast dependencies that cannot be explained only by differences in relaxivity in a single-spin population. METHODS: Measurements of functional signal and contrast were obtained in human early visual cortex during a high-contrast visual stimulation over a large range of TEs and for several flip angles. Small voxels (1.5 mm) were used to restrict the measurements to cortical gray matter in early visual areas identified using retinotopic mapping procedures. RESULTS: Measurements were consistent with models that include 2 spin populations. The dominant population has a relatively short transverse lifetime that is strongly modulated by activation. However, functional contrast is also affected by volume changes between this short-lived population and the longer-lived population. CONCLUSION: Some of the previously observed "nonclassical" behaviors of functional contrast can be explained by these interacting dual-spin populations.


Subject(s)
Brain Mapping , Image Processing, Computer-Assisted/methods , Magnetic Resonance Imaging , Oxygen/blood , Retina/pathology , Visual Cortex/diagnostic imaging , Adult , Algorithms , Blood/metabolism , Cerebral Cortex/physiology , Cerebrovascular Circulation , Contrast Media , Female , Humans , Male , Middle Aged , Models, Statistical , Photic Stimulation , Signal-To-Noise Ratio , Young Adult
13.
IEEE Int Conf Rehabil Robot ; 2019: 1247-1253, 2019 06.
Article in English | MEDLINE | ID: mdl-31374800

ABSTRACT

Increased reticulospinal (RS) function has been observed to cause both positive and negative outcomes in the recovery of motor function after corticospinal lesions such as stroke. Current knowledge of RS function is limited by the lack of accurate, noninvasive methods for measuring RS function. Recent studies suggest that the RS tract may be involved in processing and generating Long Latency Responses (LLRs). As such, LLRs, elicited by applying precisely controlled perturbations, can thus act as a reliable stimulus to measure brainstem function using fMRI with high signal-to-noise ratio.In this paper, we present StretchfMRI, a novel technique that enables simultaneous recording of neural and muscular activity during motor responses conditioned by robotic perturbations, which allows direct investigation of the neural correlates of LLRs.Via preliminary validation experiments, we demonstrate that our technique can reliably elicit and identify LLRs in two wrist muscles-Flexor Carpi Radialis and Extensor Carpi Ulnaris. Moreover, via a single-subject pilot experiment, we show that the occurrence of an LLR in a flexor and extensor muscles modulates neural activity in distinct regions of the brainstem. The observed somatotopic organization is in agreement with the double reciprocal model of RS function observed in animal models, in which the right medullary and left pontine reticular formation are responsible for control of the motor activity in flexors and extensors, respectively.


Subject(s)
Magnetic Resonance Imaging/methods , Muscle, Skeletal/physiology , Electromyography , Forearm/physiology , Humans , Reticular Formation/physiology , Wrist Joint/physiology
14.
Neuroimage ; 173: 322-331, 2018 06.
Article in English | MEDLINE | ID: mdl-29501554

ABSTRACT

A brief (<4 s) period of neural activation evokes a stereotypical sequence of vascular and metabolic events to create the hemodynamic response function (HRF) measured using functional magnetic resonance imaging (fMRI). Linear analysis of fMRI data requires that the HRF be treated as an impulse response, so the character and temporal stability of the HRF are critical issues. Here, a simple audiovisual stimulus combined with a fast-paced task was used to evoke a strong HRF across a majority, ∼77%, of cortex during a single scanning session. High spatiotemporal resolution (2-mm voxels, 1.25-s acquisition time) was used to focus HRF measurements specifically on the gray matter for whole brain. The majority of activated cortex responds with positive HRFs, while ∼27% responds with negative (inverted) HRFs. Spatial patterns of the HRF response amplitudes were found to be similar across subjects. Timing of the initial positive lobe of the HRF was relatively stable across the cortical surface with a mean of 6.1 ±â€¯0.6 s across subjects, yet small but significant timing variations were also evident in specific regions of cortex. The results provide guidance for linear analysis of fMRI data. More importantly, this method provides a means to quantify neurovascular function across most of the brain, with potential clinical utility for the diagnosis of brain pathologies such as traumatic brain injury.


Subject(s)
Cerebral Cortex/diagnostic imaging , Hemodynamics/physiology , Neurovascular Coupling/physiology , Adult , Brain Mapping/methods , Cerebral Cortex/physiology , Female , Humans , Image Processing, Computer-Assisted , Magnetic Resonance Imaging/methods , Male , Middle Aged , Young Adult
15.
Neuroimage ; 171: 199-208, 2018 05 01.
Article in English | MEDLINE | ID: mdl-29292132

ABSTRACT

The superior colliculus (SC) is a layered midbrain structure involved in directing both head and eye movements and coordinating visual attention. Although a retinotopic organization for the mediation of saccadic eye-movements has been shown in monkey SC, in human SC the topography of saccades has not been confirmed. Here, a novel experimental paradigm was performed by five participants (one female) while high-resolution (1.2-mm) functional magnetic resonance imaging was used to measure activity evoked by saccadic eye movements within human SC. Results provide three critical observations about the topography of the SC: (1) saccades along the superior-inferior visual axis are mapped across the medial-lateral anatomy of the SC; (2) the saccadic eye-movement representation is in register with the retinotopic organization of visual stimulation; and (3) activity evoked by saccades occurs deeper within SC than that evoked by visual stimulation. These approaches lay the foundation for studying the organization of human subcortical - and enhanced cortical mapping - of eye-movement mechanisms.


Subject(s)
Attention/physiology , Brain Mapping/methods , Saccades/physiology , Superior Colliculi/physiology , Female , Humans , Magnetic Resonance Imaging , Male , Photic Stimulation , Visual Perception/physiology
16.
IEEE Trans Biomed Eng ; 65(7): 1595-1606, 2018 07.
Article in English | MEDLINE | ID: mdl-28829302

ABSTRACT

OBJECTIVE: To develop a quantitative set of methods for testing the functional magnetic resonance imaging (fMRI) compatibility of an electrically-active mechatronic device developed to support sensorimotor protocols during fMRI. METHODS: The set of methods includes phantom and in vivo experiments to measure the effect of a progressively broader set of noise sources potentially introduced by the device. Phantom experiments measure the radio-frequency (RF) noise and temporal noise-to-signal ratio (tNSR) introduced by the device. The in vivo experiment assesses the effect of the device on measured brain activation for a human subject performing a representative sensorimotor task. The proposed protocol was validated via experiments using a 3T MRI scanner operated under nominal conditions and with the inclusion of an electrically-active mechatronic device - the MR-SoftWrist - as the equipment under test (EUT). RESULTS: Quantitative analysis of RF noise data allows detection of active RF noise sources both in controlled RF noise conditions, and in conditions resembling improper filtering of the EUT's electrical signals. In conditions where no RF noise was detectable, the presence and operation of the EUT did not introduce any significant increase in tNSR. A quantitative analysis conducted on in vivo measurements of the number of active voxels in visual and motor areas further showed no significant difference between EUT and baseline conditions. CONCLUSION AND SIGNIFICANCE: The proposed set of quantitative methods supports the development and troubleshooting of electrically-active mechatronic devices for use in sensorimotor protocols with fMRI, and may be used for future testing of such devices.


Subject(s)
Magnetic Resonance Imaging/methods , Motor Skills/physiology , Robotics/methods , Brain/diagnostic imaging , Brain/physiology , Humans , Phantoms, Imaging , Signal-To-Noise Ratio , Task Performance and Analysis
17.
Magn Reson Med ; 79(4): 1931-1940, 2018 04.
Article in English | MEDLINE | ID: mdl-28736924

ABSTRACT

PURPOSE: High-resolution functional magnetic resonance imaging of human subcortical brain structures is challenging because of their deep location in the cranium, and their comparatively weak blood oxygen level dependent responses to strong stimuli. Magnetic resonance imaging data for subcortical brain regions exhibit both low signal-to-noise ratio and low functional contrast-to-noise ratio. To overcome these challenges, this work evaluates the use of dual-echo spiral variants that combine outward and inward trajectories. Specifically, in-in, in-out, and out-out combinations are evaluated. For completeness, single-echo spiral-in and parallel-receive-accelerated echo-planar-imaging sequences are also evaluated. METHODS: Sequence evaluation was based on comparison of functional contrast-to-noise ratio within retinotopically predefined regions of interest. Superior colliculus was chosen as sample subcortical brain region because it exhibits a strong visual response. All sequences were compared relative to a single-echo spiral-out trajectory to establish a within-session reference. RESULTS: In superior colliculus, the dual-echo out-out outperformed the reference trajectory by 55% in contrast-to-noise ratio, while all other trajectories had performance similar to the reference. The sequences were also compared in early visual cortex. Here, both dual-echo spiral out-out and in-out outperformed the reference by ∼25%. CONCLUSION: Dual-echo spiral variants offer improved contrast-to-noise ratio performance for high-resolution imaging for both superior colliculus and cortex. Magn Reson Med 79:1931-1940, 2018. © 2017 International Society for Magnetic Resonance in Medicine.


Subject(s)
Carcinoma/diagnostic imaging , Echo-Planar Imaging , Head and Neck Neoplasms/diagnostic imaging , Macrophages/pathology , Superior Colliculi/diagnostic imaging , Adult , Algorithms , Brain/diagnostic imaging , Brain Mapping , Female , Fluorine , Humans , Image Interpretation, Computer-Assisted , Image Processing, Computer-Assisted , Male , Middle Aged , Oxygen/blood , Signal-To-Noise Ratio
18.
Magn Reson Imaging ; 39: 53-63, 2017 06.
Article in English | MEDLINE | ID: mdl-28137626

ABSTRACT

Functional magnetic resonance imaging (fMRI) often relies on a hemodynamic response function (HRF), the stereotypical blood oxygen level dependent (BOLD) response elicited by a brief (<4s) stimulus. Early measurements of the HRF used coarse spatial resolutions (≥3mm voxels) that would generally include contributions from white matter, gray matter, and the extra-pial compartment (the space between the pial surface and skull including pial blood vessels) within each voxel. To resolve these contributions, high-resolution fMRI (0.9-mm voxels) was performed at 3T in early visual cortex and its apposed white-matter and extra-pial compartments. The results characterized the depth dependence of the HRF and its reliability during nine fMRI sessions. Significant HRFs were observed in white-matter and extra-pial compartments as well as in gray matter. White-matter HRFs were faster and weaker than in the gray matter, while extra-pial HRFs were comparatively slower and stronger. Depth trends of the HRF peak amplitude were stable throughout a broad depth range that included all three compartments for each session. Across sessions, however, the depth trend of HRF peak amplitudes was stable only in the white matter and deep-intermediate gray matter, while there were strong session-to-session variations in the superficial gray matter and the extra-pial compartment. Thus, high-resolution fMRI can resolve significant and dynamically distinct HRFs in gray matter, white matter, and extra-pial compartments.


Subject(s)
Brain Mapping/methods , Hemodynamics/physiology , Magnetic Resonance Imaging/methods , Visual Cortex/diagnostic imaging , Visual Cortex/physiology , Adult , Female , Humans , Male , Middle Aged , Oxygen/blood , Reproducibility of Results , Young Adult
19.
IEEE Trans Neural Syst Rehabil Eng ; 25(9): 1489-1499, 2017 09.
Article in English | MEDLINE | ID: mdl-28114022

ABSTRACT

We demonstrate the interaction control capabilities of the MR-SoftWrist, a novel MR-compatible robot capable of applying accurate kinesthetic feedback to wrist pointing movements executed during fMRI. The MR-SoftWrist, based on a novel design that combines parallel piezoelectric actuation with compliant force feedback, is capable of delivering 1.5 N [Formula: see text] of torque to the wrist of an interacting subject about the flexion/extension and radial/ulnar deviation axes. The robot workspace, defined by admissible wrist rotation angles, fully includes a circle with a 20 deg radius. Via dynamic characterization, we demonstrate capability for transparent operation with low (10% of maximum torque output) backdrivability torques at nominal speeds. Moreover, we demonstrate a 5.5 Hz stiffness control bandwidth for a 14 dB range of virtual stiffness values, corresponding to 25%-125% of the device's physical reflected stiffness in the nominal configuration. We finally validate the possibility of operation during fMRI via a case study involving one healthy subject. Our validation experiment demonstrates the capability of the device to apply kinesthetic feedback to elicit distinguishable kinetic and neural responses without significant degradation of image quality or task-induced head movements. With this study, we demonstrate the feasibility of MR-compatible devices like the MR-SoftWrist to be used in support of motor control experiments investigating wrist pointing under robot-applied force fields. Such future studies may elucidate fundamental neural mechanisms enabling robot-assisted motor skill learning, which is crucial for robot-aided neurorehabilitation.


Subject(s)
Feedback, Sensory/physiology , Magnetic Resonance Imaging/instrumentation , Movement/physiology , Range of Motion, Articular/physiology , Robotics/instrumentation , Wrist Joint/physiology , Adult , Equipment Design , Equipment Failure Analysis , Humans , Kinesthesis/physiology , Male , Man-Machine Systems , Reproducibility of Results , Sensitivity and Specificity
20.
Bull Menninger Clin ; 80(4): 348-356, 2016.
Article in English | MEDLINE | ID: mdl-27936900

ABSTRACT

Functional magnetic resonance imaging (fMRI) is widely used to study brain circuitry in healthy controls and in psychiatry. A major problem of fMRI studies is motion, which affects the quality of images, is a major source of noise, and can confound data if, for example, the experimental groups move differently. Despite continual reminders to experimental subjects about keeping still, however, movement in the scanner remains a problem. The authors hypothesized that showing head movement during a scanning session may help subjects learn how to keep their head still. The authors scanned subjects and displayed in real time a plot of head movement that had three regions. The authors found, in a limited sample, that the improvements were marginal and inconsistent. Thus, they concluded that this strategy, even if likely to work for some people, is probably not sufficiently successful to be implemented at this time.


Subject(s)
Feedback, Psychological , Head Movements , Magnetic Resonance Imaging/standards , Adult , Female , Humans , Magnetic Resonance Imaging/methods , Male
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