Citation: Freitas, N.; Silva, D.; Mavioso, C.; Cardoso, M.J.; Cardoso, J.S. Deep Edge Detection Methods for the Automatic Calculation of the Breast Contour. Bioengineering 2023, 10, 401. https://doi.org/10.3390/ bioengineering10040401 Academic Editor: Luca Mesin Received: 6 February 2023 Revised: 21 March 2023 Accepted: 23 March 2023 Published: 24 March 2023 Copyright: © 2023 by the authors. Licensee MDPI, Basel, Switzerland. This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY) license (https:// creativecommons.org/licenses/by/ 4.0/). bioengineering Article Deep Edge Detection Methods for the Automatic Calculation of the Breast Contour Nuno Freitas 1,2, * ,† , Daniel Silva 1,2, * ,† , Carlos Mavioso 3 , Maria J. Cardoso 2,3,4 and Jaime S. Cardoso 1,2, * 1 Faculdade de Engenharia, Universidade do Porto, 4099-002 Porto, Portugal 2 INESC TEC, 4200-465 Porto, Portugal 3 Breast Unit, Champalimaud Foundation, 1400-038 Lisbon, Portugal 4 Faculty of Medicine, University of Lisbon, 1649-004 Lisbon, Portugal * Correspondence: nuno.p.silva@inesctec.pt (N.F.); daniel.j.barros@inesctec.pt (D.S.); jaime.cardoso@inesctec.pt (J.S.C.) † These authors contributed equally to this work. Abstract: Breast cancer conservative treatment (BCCT) is a form of treatment commonly used for patients with early breast cancer. This procedure consists of removing the cancer and a small margin of surrounding tissue, while leaving the healthy tissue intact. In recent years, this procedure has become increasingly common due to identical survival rates and better cosmetic outcomes than other alternatives. Although significant research has been conducted on BCCT, there is no gold-standard for evaluating the aesthetic results of the treatment. Recent works have proposed the automatic classification of cosmetic results based on breast features extracted from digital photographs. The computation of most of these features requires the representation of the breast contour, which becomes key to the aesthetic evaluation of BCCT. State-of-the-art methods use conventional image processing tools that automatically detect breast contours based on the shortest path applied to the Sobel filter result in a 2D digital photograph of the patient. However, because the Sobel filter is a general edge detector, it treats edges indistinguishably, i.e., it detects too many edges that are not relevant to breast contour detection and too few weak breast contours. In this paper, we propose an improvement to this method that replaces the Sobel filter with a novel neural network solution to improve breast contour detection based on the shortest path. The proposed solution learns effective representations for the edges between the breasts and the torso wall. We obtain state of the art results on a dataset that was used for developing previous models. Furthermore, we tested these models on a new dataset that contains more variable photographs and show that this new approach shows better generalization capabilities as the previously developed deep models do not perform so well when faced with a different dataset for testing. The main contribution of this paper is to further improve the capabilities of models that perform the objective classification of BCCT aesthetic results automatically by improving upon the current standard technique for detecting breast contours in digital photographs. To that end, the models introduced are simple to train and test on new datasets which makes this approach easily reproducible. Keywords: breast cancer; aesthetic assessment of breast cancer surgery outcomes; artificial intelli- gence; breast cancer conservative treatment; edge detection; computer vision 1. Introduction Breast cancer is the most frequently diagnosed form of cancer in women worldwide. According to recent data [1], the incidence of this type of cancer has been rising. Despite that, the mortality rate has been steadily decreasing in the past years, leading to an increased interest in the patient’s Quality of Life (QoL) after treatment [2]. Breast cancer conservative treatment (BCCT) has become a frequent alternative to mastectomy as it achieves similar survival rates while improving the cosmetic outcome. Bioengineering 2023, 10, 401. https://doi.org/10.3390/bioengineering10040401 https://www.mdpi.com/journal/bioengineering