FastSurferCNN is a per-slice 2D Competitive-Dense-UNet for whole-brain parcellation, the pre-VINN "v1" architecture introduced in Henschel et al. 2020. This ilex bundle ports the FastSurfer release at GitHub commit 070647d (Jun 2022), which is the version DeepPrep pins to. The full triplanar parcellation pipeline combines three independently-trained checkpoints (axial, coronal, sagittal); each sees per-slice 7-thick-slab inputs of shape (7, 256, 256) and predicts per-pixel class logits over a 79-class space (axial / coronal) or 51-class space (sagittal, where left/right hemispheric labels collapse and are recovered downstream). The architecture comprises four CompetitiveEncoderBlocks (the first with an input-variant BN layer), a CompetitiveDenseBlock bottleneck, four CompetitiveDecoderBlocks with skip-connection-Maxout fusion, and a 1x1 classifier Conv2d. The per-block "Maxout" gates take elementwise max of the BN-normalised activation against the previous Maxout output (or the raw input, for the first gate), and the encoder / decoder are coupled via MaxPool / MaxUnpool with stored argmax indices.

Per-slice 2D parcellation along the sagittal plane. 51-class output (left/right hemispheric labels collapse, since a single sagittal slice cannot disambiguate them). The map_prediction_sagittal2full helper in ilex.models.fastsurfer_cnn._preprocessing expands the output to the 79-class space before view aggregation.

Henschel L., Conjeti S., Estrada S., Diers K., Fischl B., Reuter M.

Henschel L., Conjeti S., Estrada S., Diers K., Fischl B., Reuter M. (2020). FastSurfer -- A fast and accurate deep learning based neuroimaging pipeline. NeuroImage 219: 117012. doi:10.1016/j.neuroimage.2020.117012

HF Hub license tag: apache-2.0

Effective terms: Apache-2.0 (Image Analysis Lab, German Center for Neurodegenerative Diseases (DZNE), Bonn) on both the network code and the pretrained weights at commit 070647d. No commercial restrictions; no gating required.

Upstream license reference: https://github.com/Deep-MI/FastSurfer/blob/070647d/LICENSE

Network architecture and training code: copyright (c) Image Analysis Lab, German Center for Neurodegenerative Diseases (DZNE), Bonn, distributed under the Apache-2.0 license at https://github.com/Deep-MI/FastSurfer. Pretrained weights (checkpoints/Axial_Weights_FastSurferCNN, checkpoints/Coronal_Weights_FastSurferCNN, checkpoints/Sagittal_Weights_FastSurferCNN, all under Epoch_30_training_state.pkl) ship from the same Apache-2.0 repository and inherit the same license. The ilex JAX / Equinox port code is separately licensed under Apache-2.0 / GPL-3.0 for the port code itself; the ilex license does not override the upstream Apache-2.0 terms governing the pretrained weights.

Original weights / reference implementation: https://github.com/Deep-MI/FastSurfer/tree/070647d

This artefact was produced by ilex's save/load pipeline. The architecture is implemented in ilex.models.fastsurfer_cnn.FastSurferCNN and the weights have been converted from their upstream format. See the upstream source above for the canonical reference.