scholarly journals Evaluating Network Threshold Selection for Structural and Functional Brain Connectomes

2021 ◽  
Author(s):  
Nicholas Theis ◽  
Jonathan Rubin ◽  
Joshua Cape ◽  
Satish Iyengar ◽  
Raquel E Gur ◽  
...  
Keyword(s):  
Objective Function ◽  
Structural Connectivity ◽  
Real Data ◽  
Accurate Estimate ◽  
Threshold Selection ◽  
Resonance Imaging ◽  
Functional Brain ◽  
Normalized Mutual Information ◽  
Selection For ◽  
Magnetic Resonance Imaging Mri

Structural and functional brain connectomes represent macroscale neurophysical data collected through methods such as magnetic resonance imaging (MRI). Such data may contain noise that contribute to false positive edges, which motivates the use of edge-wise thresholding. Thresholding procedures are useful for reducing network density in graphs to retain only the most informative, non-noisy edges. Nevertheless, limited consensus exists on selecting appropriate threshold levels. We compare existing thresholding methods and introduce a novel thresholding approach in the context of MRI-derived and simulated brain connectomes. Performance is measured using normalized mutual information (NMI), a quantity robust to arbitrary changes in partition labeling, and describes the similarity of community structure between two node-matched networks. We found that the percolation-based threshold and our newly proposed objective function-based threshold exhibited the best performance in terms of NMI. We show an application of these two thresholding methods to real data that showed that both percolation-based and objective function-based thresholding provide statistically similar NMI values between real world FC networks and structural connectivity (SC) counterparts, where shared modular structure is assumed. The two thresholding methods, however, achieve these NMI values at significantly different thresholds (p<0.0001) in both simulated and real networks. Moreover, the threshold obtained from the objective function gives a more accurate estimate of the number of modules present in the network and includes more flexibility in threshold selection, suggesting that this method may represent a useful option for graph thresholding.

scholarly journals Evaluation of AGA and Fukuoka Guidelines for EUS and surgical resection of incidental pancreatic cysts

2017 ◽  
Vol 05 (02) ◽  
pp. E116-E122 ◽  
Author(s):  
Alexander Lee ◽  
Vivek Kadiyala ◽  
Linda Lee
Keyword(s):  
Predictive Value ◽  
International Association ◽  
Pancreatic Cysts ◽  
Lower Sensitivity ◽  
Resonance Imaging ◽  
American Gastroenterological Association ◽  
Risk Patients ◽  
Malignant Lesions ◽  
Selection For ◽  
Magnetic Resonance Imaging Mri

Abstract Objectives Management of asymptomatic pancreatic cysts is challenging. Guidelines by the American Gastroenterological Association (AGA) and International Association of Pancreatology (Fukuoka) seek to identify high-risk patients. We assessed performance of these guidelines in selecting patients for endoscopic ultrasound (EUS) and/or surgery. Methods PART I – We retrospectively studied 143 asymptomatic cysts with magnetic resonance imaging (MRI) followed by EUS. Appropriate selection for EUS was defined as: malignant cytology or surgical pathology, or development of concerning features on MRI as defined by the guidelines. PART II – We retrospectively studied 152 resected cysts to assess the performance of guidelines in selecting cysts for surgery using malignant histology as the outcome. Results PART I – Of 143 EUS, 43 (30.1 %) were male with median age 65.0 years (interquartile range [IQR] 58.0 – 73.0). AGA guideline demonstrated lower sensitivity (17.6 % versus 35.3 %, P = 0.03), higher specificity (94.5 % versus 66.1 %, p < 0.001), and higher accuracy (76.2 % versus 58.7 %, P = 0.002) than Fukuoka. There was no difference in positive predictive value (50.0 % versus 24.5 %, P = 0.15) and negative predictive value (78.6 % versus 76.6 %, p=0.75). PART II – Of 152 resected cysts, 45 (29.8 %) were male with median age 59.0 years (IQR 47.3 – 66.7). There was no difference in performance characteristics of the guidelines in selecting cysts for surgery. AGA and Fukuoka guidelines missed 25.0 % and 18.8 % of malignant cysts, respectively (P = 1.00). Conclusions For referral to EUS, the AGA guideline was highly specific compared to Fukuoka; both suffered from poor sensitivity, although the Fukuoka guideline was relatively more sensitive than AGA. For referral to surgery, both guidelines have modest sensitivity and specificity and miss a similar percentage of malignant lesions.

scholarly journals The role of the pre-commissural fornix in episodic autobiographical memory and simulation

2019 ◽  
Author(s):  
Angharad N. Williams ◽  
Samuel Ridgeway ◽  
Mark Postans ◽  
Kim S. Graham ◽  
Andrew D. Lawrence ◽  
...  
Keyword(s):  
Magnetic Resonance Imaging ◽  
Magnetic Resonance ◽  
Hippocampal Formation ◽  
Structural Connectivity ◽  
Resonance Imaging ◽  
Construction Of Self ◽  
Future Events ◽  
Magnetic Resonance Imaging Mri ◽  
Future Narratives

AbstractNeuropsychological and functional magnetic resonance imaging (MRI) evidence suggests that the ability to vividly remember our personal past, and imagine future scenarios, involves two closely connected regions: the hippocampus and ventromedial prefrontal cortex (vmPFC). Despite evidence of a direct anatomical connection from hippocampus to vmPFC, it is unknown whether hippocampal-vmPFC structural connectivity supports both past and future-oriented episodic thinking. To address this, we applied diffusion-weighted magnetic resonance imaging (dMRI) and a novel deterministic tractography protocol to reconstruct distinct subdivisions of the fornix previously detected in axonal tracer studies, namely pre-commissural (connecting the hippocampus to vmPFC) and post-commissural (linking the hippocampus and medial diencephalon) fornix, in a group of healthy young adult humans who undertook an adapted past-future autobiographical interview. As predicted, we found that inter-individual differences in pre-commissural - but not post-commissural - fornix microstructure (fractional anisotropy) was significantly correlated with the episodic richness of both past and future autobiographical narratives. Notably, these results remained significant when controlling for both non-episodic narrative content and grey matter volumes of the hippocampus and vmPFC. This study provides novel evidence that reconstructing events from one’s personal past, and constructing possible future events, involves a distinct, structurally-instantiated hippocampal-vmPFC pathway.Significance StatementA novel anatomically-guided protocol that allows the pre-commissural and post-commissural fornix fibers to be separately reconstructed in vivo (Christiansen et al., 2016) was applied to reconstruct the pre-commissural subdivision of the white matter fornix tract (anatomically linking the hippocampal formation to the vmPFC) and investigate its contribution to episodic memory and future simulation. We demonstrated that the amount of episodic details contained in past and future narratives, collected via an adapted autobiographical interview, was positively correlated with pre-, but not post-, commissural fornix microstructure. These findings highlight how inter-individual variation in the pre-commissural subdivision of the fornix underpins the construction of self-reflective, contextual events – for both the past and future.

scholarly journals Network alignment and similarity reveal atlas-based topological differences in structural connectomes

2020 ◽  
Author(s):  
Matteo Frigo ◽  
Emilio Cruciani ◽  
David Coudert ◽  
Rachid Deriche ◽  
Emanuele Natale ◽  
...  
Keyword(s):  
Structural Connectivity ◽  
Graph Isomorphism ◽  
Brain Regions ◽  
Jaccard Index ◽  
Brain Atlas ◽  
Resonance Imaging ◽  
Mathematical Properties ◽  
Human Connectome Project ◽  
Magnetic Resonance Imaging Mri ◽  
A New Technique

The interactions between different brain regions can be modeled as a graph, called connectome, whose nodes correspond to parcels from a predefined brain atlas. The edges of the graph encode the strength of the axonal connectivity between regions of the atlas which can be estimated via diffusion Magnetic Resonance Imaging (MRI) tractography. Herein, we aim at providing a novel perspective on the problem of choosing a suitable atlas for structural connectivity studies by assessing how robustly an atlas captures the network topology across different subjects in a homogeneous cohort. We measure this robustness by assessing the alignability of the connectomes, namely the possibility to retrieve graph matchings that provide highly similar graphs. We introduce two novel concepts. First, the graph Jaccard index (GJI), a graph similarity measure based on the well-established Jaccard index between sets; the GJI exhibits natural mathematical properties that are not satisfied by previous approaches. Second, we devise WL-align, a new technique for aligning connectomes obtained by adapting the Weisfeiler-Lehman (WL) graph-isomorphism test. We validated the GJI and WL-align on data from the Human Connectome Project database, inferring a strategy for choosing a suitable parcellation for structural connectivity studies. Code and data are publicly available.

scholarly journals Discordant attributes of structural and functional connectivity in a two-layer multiplex network

2018 ◽  
Author(s):  
Sol Lim ◽  
Filippo Radicchi ◽  
Martijn P van den Heuvel ◽  
Olaf Sporns
Keyword(s):  
Functional Connectivity ◽  
Resting State ◽  
Structural Connectivity ◽  
Brain Regions ◽  
Resting State Networks ◽  
Structural Failure ◽  
Resonance Imaging ◽  
Multiplex Network ◽  
Human Connectome Project ◽  
Magnetic Resonance Imaging Mri

AbstractSeveral studies have suggested that functional connectivity (FC) is constrained by the underlying structural connectivity (SC) and mutually correlated. However, not many studies have focused on differences in the network organization of SC and FC, and on how these differences may inform us about their mutual interaction. To explore this issue, we adopt a multi-layer framework, with SC and FC, constructed using Magnetic Resonance Imaging (MRI) data from the Human Connectome Project, forming a two-layer multiplex network. In particular, we examine whether node strength assortativity within and between the SC and FC layer may confer increased robustness against structural failure. We find that, in general, SC is organized assortatively, indicating brain regions are on average connected to other brain regions with similar node strengths. On the other hand, FC shows disassortative mixing. This discrepancy is apparent also among individual resting-state networks within SC and FC. In addition, these patterns show lateralization, with disassortative mixing within FC subnetworks mainly driven from the left hemisphere. We discuss our findings in the context of robustness to structural failure, and we suggest that discordant and lateralized patterns of associativity in SC and FC may explain laterality of some neurological dysfunctions and recovery.

scholarly journals Brain Structural and Functional Connectivity: A Review of Combined Works of Diffusion Magnetic Resonance Imaging and Electro-Encephalography

2021 ◽  
Vol 15 ◽  
Author(s):  
Parinaz Babaeeghazvini ◽  
Laura M. Rueda-Delgado ◽  
Jolien Gooijers ◽  
Stephan P. Swinnen ◽  
Andreas Daffertshofer
Keyword(s):  
Magnetic Resonance Imaging ◽  
White Matter ◽  
Magnetic Resonance ◽  
Functional Connectivity ◽  
Spectral Power ◽  
Structural Connectivity ◽  
Brain Regions ◽  
Resonance Imaging ◽  
Magnetic Resonance Imaging Mri ◽  
And Diffusion

Implications of structural connections within and between brain regions for their functional counterpart are timely points of discussion. White matter microstructural organization and functional activity can be assessed in unison. At first glance, however, the corresponding findings appear variable, both in the healthy brain and in numerous neuro-pathologies. To identify consistent associations between structural and functional connectivity and possible impacts for the clinic, we reviewed the literature of combined recordings of electro-encephalography (EEG) and diffusion-based magnetic resonance imaging (MRI). It appears that the strength of event-related EEG activity increases with increased integrity of structural connectivity, while latency drops. This agrees with a simple mechanistic perspective: the nature of microstructural white matter influences the transfer of activity. The EEG, however, is often assessed for its spectral content. Spectral power shows associations with structural connectivity that can be negative or positive often dependent on the frequencies under study. Functional connectivity shows even more variations, which are difficult to rank. This might be caused by the diversity of paradigms being investigated, from sleep and resting state to cognitive and motor tasks, from healthy participants to patients. More challenging, though, is the potential dependency of findings on the kind of analysis applied. While this does not diminish the principal capacity of EEG and diffusion-based MRI co-registration, it highlights the urgency to standardize especially EEG analysis.

Top-Ten Tips for Imaging the Brachial Plexus with Ultrasound and MRI

2019 ◽  
Vol 23 (04) ◽  
pp. 405-418 ◽  
Author(s):  
James F. Griffith ◽  
Radhesh Krishna Lalam
Keyword(s):  
Magnetic Resonance Imaging ◽  
Magnetic Resonance ◽  
Brachial Plexus ◽  
Muscle Denervation ◽  
Resonance Imaging ◽  
Neural Injury ◽  
Clinical Indications ◽  
Magnetic Resonance Imaging Mri ◽  
High Level ◽  
Extensive Involvement

AbstractWhen it comes to examining the brachial plexus, ultrasound (US) and magnetic resonance imaging (MRI) are complementary investigations. US is well placed for screening most extraforaminal pathologies, whereas MRI is more sensitive and accurate for specific clinical indications. For example, MRI is probably the preferred technique for assessment of trauma because it enables a thorough evaluation of both the intraspinal and extraspinal elements, although US can depict extraforaminal neural injury with a high level of accuracy. Conversely, US is probably the preferred technique for examination of neurologic amyotrophy because a more extensive involvement beyond the brachial plexus is the norm, although MRI is more sensitive than US for evaluating muscle denervation associated with this entity. With this synergy in mind, this review highlights the tips for examining the brachial plexus with US and MRI.

Use of Magnetic Resonance Imaging (MRI) to Determine the 3D Geometry in the Human Rectum

Endoscopy ◽  
2004 ◽  
Vol 36 (10) ◽  
Author(s):  
BP McMahon ◽  
JB Frøkjær ◽  
A Bergmann ◽  
DH Liao ◽  
E Steffensen ◽  
...  
Keyword(s):  
Magnetic Resonance Imaging ◽  
Magnetic Resonance ◽  
Resonance Imaging ◽  
3D Geometry ◽  
Human Rectum ◽  
Magnetic Resonance Imaging Mri
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