27 research outputs found
Deepbet: Fast brain extraction of T1-weighted MRI using Convolutional Neural Networks
Brain extraction in magnetic resonance imaging (MRI) data is an important
segmentation step in many neuroimaging preprocessing pipelines. Image
segmentation is one of the research fields in which deep learning had the
biggest impact in recent years enabling high precision segmentation with
minimal compute. Consequently, traditional brain extraction methods are now
being replaced by deep learning-based methods. Here, we used a unique dataset
comprising 568 T1-weighted (T1w) MR images from 191 different studies in
combination with cutting edge deep learning methods to build a fast,
high-precision brain extraction tool called deepbet. deepbet uses LinkNet, a
modern UNet architecture, in a two stage prediction process. This increases its
segmentation performance, setting a novel state-of-the-art performance during
cross-validation with a median Dice score (DSC) of 99.0% on unseen datasets,
outperforming current state of the art models (DSC = 97.8% and DSC = 97.9%).
While current methods are more sensitive to outliers, resulting in Dice scores
as low as 76.5%, deepbet manages to achieve a Dice score of > 96.9% for all
samples. Finally, our model accelerates brain extraction by a factor of ~10
compared to current methods, enabling the processing of one image in ~2 seconds
on low level hardware
Systematic Overestimation of Machine Learning Performance in Neuroimaging Studies of Depression
We currently observe a disconcerting phenomenon in machine learning studies
in psychiatry: While we would expect larger samples to yield better results due
to the availability of more data, larger machine learning studies consistently
show much weaker performance than the numerous small-scale studies. Here, we
systematically investigated this effect focusing on one of the most heavily
studied questions in the field, namely the classification of patients suffering
from Major Depressive Disorder (MDD) and healthy controls. Drawing upon a
balanced sample of MDD patients and healthy controls from our
recent international Predictive Analytics Competition (PAC), we first trained
and tested a classification model on the full dataset which yielded an accuracy
of 61%. Next, we mimicked the process by which researchers would draw samples
of various sizes ( to ) from the population and showed a strong
risk of overestimation. Specifically, for small sample sizes (), we
observe accuracies of up to 95%. For medium sample sizes () accuracies
up to 75% were found. Importantly, further investigation showed that
sufficiently large test sets effectively protect against performance
overestimation whereas larger datasets per se do not. While these results
question the validity of a substantial part of the current literature, we
outline the relatively low-cost remedy of larger test sets
DenseNet and Support Vector Machine classifications of major depressive disorder using vertex-wise cortical features
Major depressive disorder (MDD) is a complex psychiatric disorder that
affects the lives of hundreds of millions of individuals around the globe. Even
today, researchers debate if morphological alterations in the brain are linked
to MDD, likely due to the heterogeneity of this disorder. The application of
deep learning tools to neuroimaging data, capable of capturing complex
non-linear patterns, has the potential to provide diagnostic and predictive
biomarkers for MDD. However, previous attempts to demarcate MDD patients and
healthy controls (HC) based on segmented cortical features via linear machine
learning approaches have reported low accuracies. In this study, we used
globally representative data from the ENIGMA-MDD working group containing an
extensive sample of people with MDD (N=2,772) and HC (N=4,240), which allows a
comprehensive analysis with generalizable results. Based on the hypothesis that
integration of vertex-wise cortical features can improve classification
performance, we evaluated the classification of a DenseNet and a Support Vector
Machine (SVM), with the expectation that the former would outperform the
latter. As we analyzed a multi-site sample, we additionally applied the ComBat
harmonization tool to remove potential nuisance effects of site. We found that
both classifiers exhibited close to chance performance (balanced accuracy
DenseNet: 51%; SVM: 53%), when estimated on unseen sites. Slightly higher
classification performance (balanced accuracy DenseNet: 58%; SVM: 55%) was
found when the cross-validation folds contained subjects from all sites,
indicating site effect. In conclusion, the integration of vertex-wise
morphometric features and the use of the non-linear classifier did not lead to
the differentiability between MDD and HC. Our results support the notion that
MDD classification on this combination of features and classifiers is
unfeasible
Predicting intelligence from brain gray matter volume
A positive association between brain size and intelligence is firmly established, but whether region-specific anatomical differences contribute to general intelligence remains an open question. Results from voxel-based morphometry (VBM) - one of the most widely used morphometric methods - have remained inconclusive so far. Here, we applied cross-validated machine learning-based predictive modeling to test whether out-of-sample prediction of individual intelligence scores is possible on the basis of voxel-wise gray matter volume. Features were derived from structural magnetic resonance imaging data (N = 308) using (a) a purely data-driven method (principal component analysis) and (b) a domain knowledge-based approach (atlas parcellation). When using relative gray matter (corrected for total brain size), only the atlas-based approach provided significant prediction, while absolute gray matter (uncorrected) allowed for above-chance prediction with both approaches. Importantly, in all significant predictions, the absolute error was relatively high, i.e., greater than ten IQ points, and in the atlas-based models, the predicted IQ scores varied closely around the sample mean. This renders the practical value even of statistically significant prediction results questionable. Analyses based on the gray matter of functional brain networks yielded significant predictions for the fronto-parietal network and the cerebellum. However, the mean absolute errors were not reduced in contrast to the global models, suggesting that general intelligence may be related more to global than region-specific differences in gray matter volume. More generally, our study highlights the importance of predictive statistical analysis approaches for clarifying the neurobiological bases of intelligence and provides important suggestions for future research using predictive modeling
From multivariate methods to an AI ecosystem
Depression constitutes a leading cause of disability worldwide. Despite extensive research on its interaction with psychobiological factors, associated pathways are far from being elucidated. Metabolomics, assessing the final products of complex biochemical reactions, has emerged as a valuable tool for exploring molecular pathways. We conducted a metabolome-wide association analysis to investigate the link between the serum metabolome and depressed mood (DM) in 1411 participants of the KORA (Cooperative Health Research in the Augsburg Region) F4 study (discovery cohort). Serum metabolomics data comprised 353 unique metabolites measured by Metabolon. We identified 72 (5.1%) KORA participants with DM. Linear regression tests were conducted modeling each metabolite value by DM status, adjusted for age, sex, body-mass index, antihypertensive, cardiovascular, antidiabetic, and thyroid gland hormone drugs, corticoids and antidepressants. Sensitivity analyses were performed in subcohorts stratified for sex, suicidal ideation, and use of antidepressants. We replicated our results in an independent sample of 968 participants of the SHIP-Trend (Study of Health in Pomerania) study including 52 (5.4%) individuals with DM (replication cohort). We found significantly lower laurylcarnitine levels in KORA F4 participants with DM after multiple testing correction according to Benjamini/Hochberg. This finding was replicated in the independent SHIP-Trend study. Laurylcarnitine remained significantly associated (p value < 0.05) with depression in samples stratified for sex, suicidal ideation, and antidepressant medication. Decreased blood laurylcarnitine levels in depressed individuals may point to impaired fatty acid oxidation and/or mitochondrial function in depressive disorders, possibly representing a novel therapeutic target