KEYWORDS: Scanners, Data modeling, Education and training, Machine learning, Principal component analysis, Diseases and disorders, Neuroimaging, Data acquisition, Image acquisition, Head
PurposeDistributed learning is widely used to comply with data-sharing regulations and access diverse datasets for training machine learning (ML) models. The traveling model (TM) is a distributed learning approach that sequentially trains with data from one center at a time, which is especially advantageous when dealing with limited local datasets. However, a critical concern emerges when centers utilize different scanners for data acquisition, which could potentially lead models to exploit these differences as shortcuts. Although data harmonization can mitigate this issue, current methods typically rely on large or paired datasets, which can be impractical to obtain in distributed setups.ApproachWe introduced HarmonyTM, a data harmonization method tailored for the TM. HarmonyTM effectively mitigates bias in the model’s feature representation while retaining crucial disease-related information, all without requiring extensive datasets. Specifically, we employed adversarial training to “unlearn” bias from the features used in the model for classifying Parkinson’s disease (PD). We evaluated HarmonyTM using multi-center three-dimensional (3D) neuroimaging datasets from 83 centers using 23 different scanners.ResultsOur results show that HarmonyTM improved PD classification accuracy from 72% to 76% and reduced (unwanted) scanner classification accuracy from 53% to 30% in the TM setup.ConclusionHarmonyTM is a method tailored for harmonizing 3D neuroimaging data within the TM approach, aiming to minimize shortcut learning in distributed setups. This prevents the disease classifier from leveraging scanner-specific details to classify patients with or without PD—a key aspect for deploying ML models for clinical applications.
Parkinson’s disease (PD) is the second most common neurodegenerative disease affecting 2-3% of the population over 65 years of age. Considerable research has investigated the benefit of using neuroimaging to improve PD diagnosis. However, it is challenging for medical experts to manually identify the subtle differences associated with PD in such complex data. It has been shown that machine learning models can achieve human-like accuracies for many computer-aided diagnosis applications. However, model performance usually depends on the amount and diversity of training data available, whereas most Parkinson’s disease classification models were trained on rather small datasets. Training data size and diversity can be increased by curating multi-site datasets. However, this may also increase biological and non-biological variances due to differences in participant cohorts, scanners, and data acquisition protocols. Thus, data harmonization is important to reduce those variances and enable the models to focus primarily on the patterns associated with PD. This work compares intensity harmonization techniques on 1796 MRI scans from twelve studies. Our results show that a histogram matching approach does not improve classification accuracy (78%) compared to the model trained on unharmonized data (baseline). However, it reduces the disparity between sensitivity and specificity from 81% and 73% to 77% and 79%, respectively. Moreover, combining histogram matching and least squares mean tissue intensity harmonization methods outperform the baseline model (accuracy of 74% compared to 67%) for an independent test set. Finally, our analysis considering sex (male, female) and groups (PD, healthy) shows that models trained on harmonized data exhibited reduced performance disparities between groups, which may be interpreted as a form of bias mitigation.
Purpose: Explainability and fairness are two key factors for the effective and ethical clinical implementation of deep learning-based machine learning models in healthcare settings. However, there has been limited work on investigating how unfair performance manifests in explainable artificial intelligence (XAI) methods, and how XAI can be used to investigate potential reasons for unfairness. Thus, the aim of this work was to analyze the effects of previously established sociodemographic-related confounders on classifier performance and explainability methods.Approach: A convolutional neural network (CNN) was trained to predict biological sex from T1-weighted brain MRI datasets of 4547 9- to 10-year-old adolescents from the Adolescent Brain Cognitive Development study. Performance disparities of the trained CNN between White and Black subjects were analyzed and saliency maps were generated for each subgroup at the intersection of sex and race.Results: The classification model demonstrated a significant difference in the percentage of correctly classified White male (90.3 % ± 1.7 % ) and Black male (81.1 % ± 4.5 % ) children. Conversely, slightly higher performance was found for Black female (89.3 % ± 4.8 % ) compared with White female (86.5 % ± 2.0 % ) children. Saliency maps showed subgroup-specific differences, corresponding to brain regions previously associated with pubertal development. In line with this finding, average pubertal development scores of subjects used in this study were significantly different between Black and White females (p < 0.001) and males (p < 0.001).Conclusions: We demonstrate that a CNN with significantly different sex classification performance between Black and White adolescents can identify different important brain regions when comparing subgroup saliency maps. Importance scores vary substantially between subgroups within brain structures associated with pubertal development, a race-associated confounder for predicting sex. We illustrate that unfair models can produce different XAI results between subgroups and that these results may explain potential reasons for biased performance.
Attention deficit/hyperactivity disorder (ADHD) is characterized by symptoms of inattention, hyperactivity, and impulsivity, which affects an estimated 10.2% of children and adolescents in the United States. However, correct diagnosis of the condition can be challenging, with failure rates up to 20%. Machine learning models making use of magnetic resonance imaging (MRI) have the potential to serve as a clinical decision support system to aid in the diagnosis of ADHD in youth to improve diagnostic validity. The purpose of this study was to develop and evaluate an explainable deep learning model for automatic ADHD classification. 254 T1-weighted brain MRI datsets of youth aged 9-11 were obtained from the Adolescent Brain Cognitive Development (ABCD) Study, and the Child Behaviour Checklist DSM-Oriented ADHD Scale was used to partition subjects into ADHD and non-ADHD groups. A fully convolutional neural network (CNN) adapted from a state-of-the-art adult brain age regression model was trained to distinguish between the neurologically normal children and children with ADHD. Saliency voxel attribution maps were generated to identify brain regions relevant for the classification task. The proposed model achieved an accuracy of 71.1%, sensitivity of 68.4%, and specificity of 73.7%. Saliency maps highlighted the orbitofrontal cortex, entorhinal cortex, and amygdala as important regions for the classification, which is consistent with previous literature linking these regions to significant structural differences in youth with ADHD. To the best of our knowledge, this is the first study applying artiicial intelligence explainability methods such as saliency maps to the classification of ADHD using a deep learning model. The proposed deep learning classification model has the potential to aid clinical diagnosis of ADHD while providing interpretable results.
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