Canonical EEG Microstates Transitions Reflect Switching Among BOLD Resting State Networks and Predict fMRI Signal

Objective. Electroencephalography microstates (EEG-ms), which reflect a large topographical representation of coherent electrophysiological brain activity, are widely adopted to study cognitive processes mechanisms and aberrant alterations in brain disorders. EEG-ms topographies are quasi-stable lasting between 60-120 milliseconds. Some evidence suggests that EEG-ms are the electrophysiological signature of resting-state networks (RSNs). However, the spatial and functional interpretation of EEG-ms and their association with functional MRI (fMRI) remains unclear. Approach. In a large cohort of healthy subjects (n = 52), we conducted several statistical and machine learning approaches analyses on the association among EEG-ms spatio-temporal dynamics and the blood-oxygenation-level dependent (BOLD) simultaneous EEG-fMRI data using statistical and machine learning approaches. Main results. Our results using a generalized linear model unraveled that EEG-ms transitions were largely and negatively associated with blood-oxygenation-level dependent (BOLD) signals in the somatomotor, visual, dorsal attention, and ventral attention fMRI networks with limited association within the default mode network. Additionally, a novel recurrent neural network (RNN) confirmed the association between EEG-ms transitioning and fMRI signal while revealing that EEG-ms dynamics can predict BOLD signals and vice versa. Significance. Results suggest that EEG-ms transitions may represent the deactivation of fMRI RSNs and provide evidence that both modalities can measure common aspects of undergoing brain neuronal activities. Moreover, our results may help to better understand the electrophysiological interpretation of EEG-ms and solve several contradicting findings in the literature.

Noninvasive assessment of kidney dysfunction in children by using blood oxygenation level-dependent MRI and intravoxel incoherent motion diffusion-weighted imaging

Objectives To explore whether multiparametric approach including blood oxygenation level-dependent MRI (BOLD-MRI) and intravoxel incoherent motion diffusion-weighted imaging (IVIM-DWI) can be applied in the assessment of renal function in children with chronic kidney disease (CKD). Materials and methods This prospective study included 74 children (CKD stage 1–3, 51; CKD stage 4–5, 12; healthy volunteers, 11) for renal MRI examinations including coronal T2WI, axial T1WI and T2WI, BOLD-MRI, and DWI sequences. We measured the renal cortex and medulla T2*, ADC, Dt, Dp, and fp values on BOLD and DWI images. Appropriate statistical methods were applied for comparing MRI-derived parameters among the three groups and calculating the correlation coefficients between MRI-derived parameters and clinical data. Receiver operating characteristic (ROC) curves were used to assess the diagnostic performance of MRI-derived parameters. Results There were significant differences in cortex T2*, ADC, Dt, fp and medulla T2*, ADC, Dt among the three groups. Cortex T2*, ADC, Dt, fp and medulla T2*, ADC, Dt had a trend: CKD stage 4–5 < CKD stage 1–3 < healthy volunteers. Cortex and medulla T2*, ADC, Dt were significantly correlated with eGFR, serum creatinine (Scr), cystatin C. In addition, cortex T2* and eGFR showed the highest correlation coefficient (r = 0.824, p < 0.001). Cortex Dt and medulla T2* were optimal parameters for differentiating healthy volunteers and CKD stage 1–3 or CKD stage 4–5 and CKD stage 1–3, respectively. Conclusions BOLD-MRI and IVIM-DWI might be used as a feasible method for noninvasive assessment of renal function in children with CKD.

Existence of Interhemispheric Inhibition between Foot Sections of Human Primary Motor Cortices: Evidence from Negative Blood Oxygenation-Level Dependent Signal

Interhemispheric inhibition (IHI) between the left and right primary motor cortices (M1) plays an important role when people perform an isolated unilateral limb movement. Moreover, negative blood oxygenation-level dependent signal (deactivation) obtained from the M1 ipsilateral to the limb could be a surrogate IHI marker. Studies have reported deactivation in the hand section of the ipsilateral M1 during simple unilateral hand movement. However, deactivation in the foot section during unilateral foot movement has not been reported. Therefore, IHI between the foot sections of the bilateral M1s has been considered very weak or absent. Thirty-seven healthy adults performed active control of the right foot and also passively received vibration to the tendon of the tibialis anterior muscle of the right foot, which activates the foot section of the contralateral M1, with brain activity being examined through functional magnetic resonance imaging. The vibration and active tasks significantly and non-significantly, respectively, deactivated the foot section of the ipsilateral M1, with a corresponding 86% and 60% of the participants showing decreased activity. Thus, there could be IHI between the foot sections of the bilateral M1s. Further, our findings demonstrate between-task differences and similarities in cross-somatotopic deactivation.

PreSurgical and Surgical Planning in Neurosurgical Oncology - A Case-Based Approach to Maximal Safe Surgical Resection in Neurosurgery

Use of functional neuroimaging capabilities such as fMRI, DTI, MRP, MRS, AS-PET-CT, SPECT, and TMS as noninvasive tools to visualize intrinsic brain and spine morphology in relation to function have developed over the past 30 years. Amongst these imaging modalities, functional magnetic resonance imaging (fMRI) is of particular interest since it follows the physiological coupling between neuronal electrical activity and metabolic structural (cellular) activity as it relates to tissue vascularity and perfusion states. This structure–function synesis (from the Greek noun, σύνεσις = being together), leads to three effects that contribute to the fMRI signal: an increase in the blood flow velocity, a change in the mean blood volume, and most importantly, alterations in the blood oxygenation level. The latter effect has lent to the development of blood-oxygenation-level-dependent or BOLD fMRI, which has been used in establishing the topographic relationship between eloquent cortex and neurosurgical planning. As an adjunct to this modality, MRI-based diffusion tensor imaging (DTI) allows further detailed radiographic assessment of fiber tracts in the brain in relationship to the surgical lesion of interest. Herein we review the roles of fMRI and DTI for presurgical mapping to allow for maximal safe resection procedures in neurosurgery with case-based illustrations.

Blood oxygenation level-dependent MRI at 3T for differentiating prostate cancer from benign tissue: a preliminary experience

Objective: Blood oxygenation-level dependent (BOLD) MRI may identify or quantify the regional distribution of hypoxia within a tumor. We aimed to evaluate the feasibility of BOLD MRI at 3 T in differentiating prostate cancer from benign tissue. Methods: A total of 145 patients with biopsy-proven prostate cancer underwent BOLD MRI at 3 T. BOLD MRI was performed using a multiple fast field echo sequence to acquire 12 T2*-weighted images. The R2* value (rate of relaxation, s−1) was measured in the index tumor, and benign peripheral (PZ) and transition zone (TZ), and the results were compared. The variability of R2* measurements was evaluated. Results: Tumor R2* values (25.95 s−1) were significantly different from the benign PZ (27.83 s−1) and benign TZ (21.66 s−1) (p < 0.001). For identifying the tumor, the area under the receiver operating characteristic of R2* was 0.606, with an optimal cut-off value of 22.8 s−1 resulting in 73.8% sensitivity and 52% specificity. In the Bland–Altman test, the mean differences in R2* values were 8.5% for tumors, 13.3% for benign PZ, and 6.8% for benign TZ. No associations between tumor R2* value and Gleason score, age, prostate volume, prostate-specific antigen, or tumor size. Conclusion: BOLD MRI at 3 T appears to be a feasible tool for differentiating between prostate cancer and benign tissue. However, further studies are required for a direct clinical application. Advances in knowledge: The R2* values are significantly different among prostate cancer, benign PZ, and benign TZ.

Evaluation of Renal Oxygenation and Hemodynamics in Patients with Chronic Kidney Disease by Blood Oxygenation Level-dependent Magnetic Resonance Imaging and Intrarenal Doppler Ultrasonography

<b><i>Introduction:</i></b> The basic pathophysiologic derangement of chronic kidney disease (CKD) begins with the loss of nephrons, leading to renal hemodynamic changes, eventually causing a reduced nephron count and renal hypoxia. The purpose of this study was to observe the renal oxygenation and renal hemodynamics of patients with CKD using blood oxygenation level-dependent (BOLD) magnetic resonance imaging (MRI) and intrarenal Doppler ultrasonography (IDU). <b><i>Methods:</i></b> The study enrolled 39 patients with stage 1–4 CKD and 19 healthy volunteers (HVs). Based on their estimated glomerular filtration rate (eGFR), CKD patients were divided into 2 subgroups: a mild renal impairment (MI) group and a moderate to severe renal impairment (MSI) group. We monitored the participants’ mean cortical T2* (COT2*) and mean medullary T2* (MET2*) values on BOLD-MRI, and measured the peak systolic velocities (PSVs), end-diastolic velocities (EDVs), renal resistive index (RI), and kidney length by IDU. We also recorded clinical indicators such as age, sex, body mass index (BMI), 24-h urinary protein (24-h Upr), serum creatinine (sCr), blood urea nitrogen (BUN), and eGFR. BOLD-MRI, IDU measurements, and the clinical indicators were compared in CKD patients and HVs by the analysis of variance and Kruskal-Wallis <i>H</i> test. Spearman’s correlation was used to assess the relationship between data from BOLD-MRI and IDU and clinical indicators. <b><i>Results:</i></b> The COT2* values were significantly higher than the MET2* values in the HV, MI, and MSI groups. COT2*, MET2*, EDV, PSV, and kidney length gradually decreased in the HV, MI, and MSI groups (all <i>p &#x3c;</i> 0.05), whereas RI and 24-h Upr gradually increased (both <i>p</i> &#x3c; 0.05). Spearman correlation analysis showed that COT2* and MET2* were significantly positively correlated with eGFR, PSV, EDV, and kidney length but were significantly negatively correlated with sCr, BUN, and 24-h Upr (all <i>p</i> &#x3c; 0.05). There was no correlation observed between the COT2* and MET2* and the RI and BMI values. <b><i>Conclusions:</i></b> Renal oxygenation and blood flow velocities were found declined as the CKD stage progressed. The BOLD-MRI and IDU techniques may have clinical value by measuring intrarenal oxygenation and renal blood perfusion to judge the severity of renal damage in patients with CKD.

Blood Oxygenation Level-Dependent Response to Multiple Grip Forces in Multiple Sclerosis: Going Beyond the Main Effect of Movement in Brodmann Area 4a and 4p

This study highlights the importance of looking beyond the main effect of movement to study alterations in functional response in the presence of central nervous system pathologies such as multiple sclerosis (MS). Data show that MS selectively affects regional BOLD (blood oxygenation level dependent) responses to variable grip forces (GF). It is known that the anterior and posterior BA 4 areas (BA 4a and BA 4p) are anatomically and functionally distinct. It has also been shown in healthy volunteers that there are linear (first order, typical of BA 4a) and nonlinear (second to fourth order, typical of BA 4p) BOLD responses to different levels of GF applied during a dynamic motor paradigm. After modeling the BOLD response with a polynomial expansion of the applied GFs, the particular case of BA 4a and BA 4p were investigated in healthy volunteers (HV) and MS subjects. The main effect of movement (zeroth order) analysis showed that the BOLD signal is greater in MS compared with healthy volunteers within both BA 4 subregions. At higher order, BOLD-GF responses were similar in BA 4a but showed a marked alteration in BA 4p of MS subjects, with those with greatest disability showing the greatest deviations from the healthy response profile. Therefore, the different behaviors in HV and MS could only be uncovered through a polynomial analysis looking beyond the main effect of movement into the two BA 4 subregions. Future studies will investigate the source of this pathophysiology, combining the present fMRI paradigm with blood perfusion and nonlinear neuronal response analysis.