Med-ReLU: A Parameter-Free Hybrid Activation Function for Deep Artificial Neural Network Used in Medical Image Segmentation

Deep learning (DL), derived from the domain of Artificial Neural Networks (ANN), forms one of the most essential components of modern deep learning algorithms. DL segmentation models rely on layer-by-layer convolution-based feature representation, guided by forward and backward propagation. A critical aspect of this process is the selection of an appropriate activation function (AF) to ensure robust model learning. However, existing activation functions often fail to effectively address the vanishing gradient problem or are complicated by the need for manual parameter tuning. Most current research on activation function design focuses on classification tasks using natural image datasets such as MNIST, CIFAR-10, and CIFAR-100. To address this gap, this study proposes Med-ReLU, a novel activation function specifically designed for medical image segmentation. Med-ReLU prevents deep learning models from suffering dead neurons or vanishing gradient issues. It is a hybrid activation function that combines the properties of ReLU and Softsign. For positive inputs, Med-ReLU adopts the linear behavior of ReLU to avoid vanishing gradients, while for negative inputs, it exhibits the Softsign’s polynomial convergence, ensuring robust training and avoiding inactive neurons across the training set. The training performance and segmentation accuracy of Med-ReLU have been thoroughly evaluated, demonstrating stable learning behavior and resistance to overfitting. It consistently outperforms state-of-the-art activation functions in medical image segmentation tasks. Designed as a parameter-free function, Med-ReLU is simple to implement in complex deep learning architectures, and its effectiveness spans various neural network models and anomaly detection scenarios.