Mr. Prerak Mody Profile

Prerak Mody

at Leiden Univ Medical Ctr

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Publications (2)

Proceedings Article | 3 April 2023 Presentation + Paper

Analyzing components of a transformer under different dataset scales in 3D prostate CT segmentation

Yicong Tan, Prerak Mody, Viktor van der Valk, Marius Staring, Jan van Gemert

Proceedings Volume 12464, 1246408 (2023) https://doi.org/10.1117/12.2651572

KEYWORDS: Transformers, Convolution, Data modeling, Image segmentation, Medical imaging, Education and training, Computed tomography, Prostate, 3D modeling, Surgery

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Literature on medical imaging segmentation claims that hybrid UNet models containing both Transformer and convolutional blocks perform better than purely convolutional UNet models. This recently touted success of hybrid Transformers warrants an investigation into which of its components contribute to its performance. Also, previous work has a limitation of analysis only at fixed dataset scales as well as unfair comparisons with other models where parameter counts are not equivalent. Here, we investigate the performance of a hybrid Transformer network i.e. the nnFormer for organ segmentation in prostate CT scans. We do this in context of replacing its various components and by constructing learning curves by plotting model performance at different dataset scales. To compare with literature, the first experiment replaces all the shifted-window(swin) Transformer blocks of the nnFormer with convolutions. Results show that the convolution prevails as the data scale increases. In the second experiment, to reduce complexity, the self-attention mechanism within the swin-Transformer block is replaced with an similar albeit simpler spatial mixing operation i.e. max-pooling. We observe improved performance for max-pooling in smaller dataset scales, indicating that the window-based Transformer may not be the best choice in both small and larger dataset scales. Finally, since convolution has an inherent local inductive bias of positional information, we conduct a third experiment to imbibe such a property to the Transformer by exploring two kinds of positional encodings. The results show that there are insignificant improvements after adding positional encoding, indicating the hybrid swin-Transformers deficiency in capturing positional information given our dataset at its various scales. Through this work, we hope to motivate the community to use learning curves under fair experimental settings to evaluate the efficacy of newer architectures like Transformers for their medical imaging tasks. Code is available on https://github.com/prerakmody/ window-transformer-prostate-segmentation.

Proceedings Article | 4 April 2022 Presentation + Paper

Comparing Bayesian models for organ contouring in head and neck radiotherapy

Prerak Mody, Nicolas Chaves-de-Plaza, Klaus Hildebrandt, René van Egmond, Huib de Ridder, Marius Staring

Proceedings Volume 12032, 120320F (2022) https://doi.org/10.1117/12.2611083

KEYWORDS: Radiotherapy, Machine learning, Bayesian inference, Quality testing methods, Image segmentation, Volume segmentation

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