Automated Prostate Lesion Segmentation in mpMRI Using Multi-Input U-Net and Novel LSTM U-Net with Bi-ConvLSTM
Author Block: S. Fouladi, F. Darvizeh, R. Di Meo, I. Bossi Zanetti, G. Gianini, E. Damiani, A. Maiocchi, D. Fazzini, M. Alì; Milan/IT
Purpose: Prostate cancer (PCa) is the second most commonly diagnosed cancer in men, with an estimated 288,300 new cases and over 34,700 deaths annually in the United States. Early detection and accurate lesion localization are crucial for improving outcomes; however, manual segmentation of multiparametric MRI (mpMRI), including T2-weighted (T2W), diffusion-weighted imaging (DWI), and apparent diffusion coefficient (ADC) sequences, is labor-intensive and prone to interobserver variability. This challenge has motivated the development of automated deep learning solutions.
Methods or Background: We evaluated two datasets: PI-RADS 4–5 (220 training, 33 test) and PI-RADS 3–5 (270 training, 41 test). In the first stage, U-Net, Dense U-Net, and Attention U-Net were trained separately on T2W, DWI, and ADC to benchmark the contribution of each sequence. In the second stage, we implemented a multi-input U-Net with three parallel encoders, each dedicated to one sequence (T2W, DWI, ADC), enabling joint learning while preserving modality-specific features. Finally, building on the strong performance of ADC, we proposed a novel LSTM U-Net with a Bi-ConvLSTM bottleneck to capture temporal dependencies and improve lesion boundary delineation.
Results or Findings: ADC achieved the highest Dice scores (69% for PI-RADS 4–5 and 68% for PI-RADS 3, 4, and 5). The LSTM U-Net on ADC provided competitive accuracy and improved delineation of challenging lesions, highlighting the benefit of temporal modeling.
Conclusion: Segmentation depends on dataset composition and network design. Multi-input sequences improve accuracy, while temporal modeling refines lesion boundaries, supporting AI-assisted prostate cancer diagnosis.
Limitations: The number of images was limited due to the time-consuming process of manual mask creation. Despite this constraint, the results are promising, and performance is expected to further improve with the inclusion of larger datasets.
Funding for this study: Funding The work was partially supported by the MUSA-Multilayered Urban
Sustainability Action project, funded by the European Union-NextGenerationEU,
under the Mission 4 Component 2 Investment Line of the National Recovery and
Resilience Plan (NRRP) Mission 4 Component 2 Investment Line 1.5: Strengthening
of research structures and creation of R&D ”innovation ecosystems”, set up
of ”territorial leaders in R&D” (CUP G43C22001370007, Code ECS00000037);
Program ”piano sostegno alla ricerca” PSR and the PSR-GSA-Linea 6; Project
ReGAInS (code 2023-NAZ-0207/DIP-ECC-DISCO-23), funded by the Italian
University and Research Ministry, within the Excellence Departments program
2023-2027 (law 232/2016).
Has your study been approved by an ethics committee? Yes
Ethics committee - additional information: Approval on September 11, 2024 by CET Lombardia 3 Ethical Committee (Study ID: 5105)