scholarly journals Feasibility of Functional MRI at Ultralow Magnetic Field via Changes in Cerebral Blood Volume

2018 ◽  
Author(s):  
Kai Buckenmaier ◽  
Anders Pedersen ◽  
Paul SanGiorgio ◽  
Klaus Scheffler ◽  
John Clarke ◽  
...  
Keyword(s):  
Functional Mri ◽  
Blood Volume ◽  
Quantum Interference ◽  
Cerebral Blood Volume ◽  
Human Head ◽  
Lattice Relaxation ◽  
Blood Oxygenation ◽  
Spin Lattice Relaxation ◽  
Cortical Region ◽  
Experimental Conditions

AbstractWe investigate the feasibility of performing functional MRI (fMRI) at ultralow field (ULF) with a Superconducting QUantum Interference Device (SQUID), as used for detecting magnetoencephalography (MEG) signals from the human head. While there is negligible magnetic susceptibility variation to produce blood oxygenation level-dependent (BOLD) contrast at ULF, changes in cerebral blood volume (CBV) may be a sensitive mechanism for fMRI given the five-fold spread in spin-lattice relaxation time (T1) values across the constituents of the human brain. We undertook simulations of functional signal strength for a simplified brain model involving activation of a primary cortical region in a manner consistent with a blocked task experiment. Our simulations involve measured values of T1 at ULF and experimental parameters for the performance of an upgraded ULFMRI scanner. Under ideal experimental conditions we predict a functional signal-to-noise ratio of between 3.1 and 7.1 for an imaging time of 30 minutes, or between 1.5 and 3.5 for a blocked task experiment lasting 7.5 minutes. Our simulations suggest it may be feasible to perform fMRI using a ULFMRI system designed to perform MRI and MEG in situ.

scholarly journals Feasibility of functional MRI at ultralow magnetic field via changes in cerebral blood volume

NeuroImage ◽  
2019 ◽  
Vol 186 ◽  
pp. 185-191 ◽  
Author(s):  
Kai Buckenmaier ◽  
Anders Pedersen ◽  
Paul SanGiorgio ◽  
Klaus Scheffler ◽  
John Clarke ◽  
...  
Keyword(s):  
Magnetic Field ◽  
Functional Mri ◽  
Blood Volume ◽  
Cerebral Blood Volume

Abstract TP20: Prediction of Hemorrhagic Transformation After Endovascular Thrombectomy by Cerebral Blood Volume and Time to Reperfusion

Stroke ◽  
2016 ◽  
Vol 47 (suppl_1) ◽  
Author(s):  
Tomohide Yoshie ◽  
Toshihiro Ueda ◽  
Tatsuro Takada ◽  
Shinji Nogoshi ◽  
Satoshi Takaishi ◽  
...  
Keyword(s):  
Basal Ganglia ◽  
Blood Volume ◽  
Endovascular Therapy ◽  
Cerebral Blood Volume ◽  
Hemorrhagic Transformation ◽  
Cortical Region ◽  
Early Reperfusion ◽  
Endovascular Thrombectomy ◽  
Significant Difference ◽  
Basal Ganglia Hemorrhage

Introduction: Previous studies suggested that low cerebral blood volume (CBV) lesion predicts hemorrhagic transformation after endovascular therapy. Hypothesis: We assessed the hypothesis that delays in time to reperfusion lead to hemorrhagic transformation on T2*-weighted MRI after endovascular therapy in patients with low CBV obtained from pre-treatment CT perfusion (CTP). Methods: We retrospectively analyzed 62 consecutive patients with acute ischemic stroke who were obtained successful reperfusion (TICI 2A-3) by endovascular thrombectomy for internal carotid artery or M1 occlusion. CTP maps were assessed for relative CBV (rCBV) values obtained separately for cortical and basal ganglia regions in the MCA territory. The presence of cortical and basal ganglia hemorrhage (either HI or PH) was assessed on T2*-weighted MRI after endovascular therapy. We analyzed the influence of rCBV in each region, CTP-to-reperfusion time and degree of reperfusion on cortical and basal ganglia hemorrhage. Results: Forty patients developed hemorrhagic transformation. HIs occurred in 16, PH1s in 21, PH2s in 3 and symptomatic hemorrhage in 1 of the patients. rCBV of the cortical region (0.77 versus 0.98, P=0.002) and basal ganglia region (0.64 versus 0.88, P<0.001) were significantly lower in the patients with hemorrhage than in those without. There was no significant difference in CTP-to-reperfusion time between cortical hemorrhage and no cortical hemorrhage groups. However, in the patients with low cortical rCBV (rCBV <0.8) and TICI ≥2b, mean CTP-to-reperfusion time was significantly shorter (70 versus 108 minutes, p=0.021) in the non-cortical hemorrhage group. There was no significant difference in CTP-to-reperfusion time between basal ganglia hemorrhage and non-basal ganglia hemorrhage groups. Conclusions: Early reperfusion decreases risk of cortical hemorrhage in patients with low cortical rCBV. Low rCBV in basal ganglia region is more predictive of basal ganglia hemorrhage than time to reperfusion.

scholarly journals Quantitative Assessment of the Balance between Oxygen Delivery and Consumption in the Rat Brain after Transient Ischemia with T2-BOLD Magnetic Resonance Imaging

2002 ◽  
Vol 22 (3) ◽  
pp. 262-270 ◽  
Author(s):  
Mikko I. Kettunen ◽  
Olli H. J. Gröhn ◽  
M. Johanna Silvennoinen ◽  
Markku Penttonen ◽  
Risto A. Kauppinen
Keyword(s):  
Magnetic Resonance Imaging ◽  
Magnetic Resonance ◽  
Carotid Artery ◽  
Rat Brain ◽  
Blood Volume ◽  
Common Carotid Artery ◽  
Cerebral Blood Volume ◽  
Blood Oxygenation ◽  
Resonance Imaging ◽  
Transient Ischemia

The balance between oxygen consumption and delivery in the rat brain after exposure to transient ischemia was quantitatively studied with single-spin echo T2-BOLD (blood oxygenation level–dependent) magnetic resonance imaging at 4.7 T. The rats were exposed to graded common carotid artery occlusions using a modification of the four-vessel model of Pulsinelli. T2, diffusion, and cerebral blood volume were quantified with magnetic resonance imaging, and CBF was measured with the hydrogen clearance method. A transient common carotid artery occlusion below the CBF value of approximately 20 mL·100 g−1·min−1 was needed to yield a T2 increase of 4.6 ± 1.2 milliseconds (approximately 9% of cerebral T2) and 6.8 ± 1.7 milliseconds (approximately 13% of cerebral T2) after 7 and 15 minutes of ischemia, respectively. Increases in CBF of 103 ± 75% and in cerebral blood volume of 29 ± 20% were detected in the reperfusion phase. These hemodynamic changes alone could account for only approximately one third of the T2 increase in luxury perfusion, suggesting that a substantial increase in blood oxygen saturation (resulting from reduced oxygen extraction by the brain) is needed to explain the magnetic resonance imaging observation.

Different degrees of hydration in water–oil microemulsions by low-resolution 1H magnetic relaxation analysis

1990 ◽  
Vol 68 (9) ◽  
pp. 1041-1048 ◽  
Author(s):  
Donatella Senatra ◽  
Laura Lendinara ◽  
M. Grazia Giri
Keyword(s):  
Magnetic Relaxation ◽  
Free Water ◽  
Water Concentration ◽  
Lattice Relaxation ◽  
Spin Lattice Relaxation ◽  
Exponential Functions ◽  
Scanning Calorimetry ◽  
Experimental Conditions ◽  
Spin Lattice ◽  
Relaxation Curves

The purpose of the research was to establish whether the water configurations, detected by previous differential scanning calorimetry (DSC) analysis, could give rise to different or characteristic nuclear magnetic resonance relaxations. We report the results of a study on water–hexadecane microemulsions at different water contents. The 1H spin–spin and spin–lattice relaxation curves were obtained at 20 MHz and 310 K. The trends of all best-fit relaxation parameters versus water concentration were compared with those obtained for D2O microemulsions with the same experimental conditions and fitting procedures. Two different H2O microemulsion "states" were identified: (i) all the systems without "free water" (defined by DSC as water melting at 273 K) were characterized by 1H spin–spin and spin–lattice relaxation curves well described by two exponential functions and (ii) all the systems with free water were characterized by relaxation curves well described by three exponential functions. The identification of the main phases of the microemulsions interphasal region and continuous medium, besides free water, seems possible on the basis of the 1H magnetic relaxation characteristics.

scholarly journals Modelling the depth-dependent VASO and BOLD responses in human primary visual cortex

2021 ◽  
Author(s):  
Atena Akbari ◽  
Saskia Bollmann ◽  
Tonima Ali ◽  
Markus Barth
Keyword(s):  
Visual Cortex ◽  
Blood Volume ◽  
Primary Visual Cortex ◽  
Cerebral Blood Volume ◽  
Blood Oxygenation ◽  
Physiological Variables ◽  
Oxygenation Level ◽  
Signal Specificity ◽  
Experimental Findings ◽  
Spatial Specificity

Functional magnetic resonance imaging (fMRI) using blood-oxygenation-level-dependent (BOLD) contrast is a common method for studying human brain function non-invasively. Gradient-echo (GRE) BOLD is highly sensitive to the blood oxygenation change in blood vessels; however, the signal specificity can be degraded due to signal leakage from the activated lower layers to the superficial layers in depth-dependent (also called laminar or layer-specific) fMRI. Alternatively, physiological variables such as cerebral blood volume using VAscular-Space-Occupancy (VASO) measurements have shown higher spatial specificity compared to BOLD. To better understand the physiological mechanisms (e.g., blood volume and oxygenation change) and to interpret the measured depth-dependent responses we need models that reflect vascular properties at this scale. For this purpose, we adapted a cortical vascular model previously developed to predict the layer-specific BOLD signal change in human primary visual cortex to also predict layer-specific VASO response. To evaluate the model, we compared the predictions with experimental results of simultaneous VASO and BOLD measurements in a group of healthy participants. Fitting the model to our experimental findings provided an estimate of CBV change in different vascular compartments upon neural activity. We found that stimulus-evoked CBV changes mainly occur in intracortical arteries as well as small arterioles and capillaries and that the contribution from venules is small for a long stimulus (~30 sec). Our results confirm the notion that VASO contrast is less susceptible to large vessel effects compared to BOLD.

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