CoDG-Net: Structure-Guided Style Diffusion and Collaborative Learning to Mitigate Catastrophic Forgetting in Medical Image Domain Generalization

Yucheng Song; Jincan Wang; Haokang Ding; Zhiqiang Tian; Kangxu Fan; Zhifang Liao

cs.CVOct 4, 2026

CoDG-Net: Structure-Guided Style Diffusion and Collaborative Learning to Mitigate Catastrophic Forgetting in Medical Image Domain Generalization

Authors: Yucheng Song, Jincan Wang, Haokang Ding, Zhiqiang Tian, Kangxu Fan, Zhifang Liao

Organizations: School of Computer Science and Engineering, Central South University, Changsha, China · School of Software Engineering, Xi’an Jiaotong University, Xi’an, Shaanxi, China · College of Computer Science and Artificial Intelligence, Fudan University, Shanghai, China

Abstract

Domain Generalization (DG) for medical image segmentation is both highly challenging and critically important. However, existing medical DG methods largely overlook the issue of Catastrophic Forgetting (CF): \textbf{Models often sacrifice their ability to retain source-domain knowledge while pursuing cross-domain robustness.} This can directly threaten diagnostic safety in already-deployed clinical scenarios. To address this, we investigate data augmentation strategies and catastrophic forgetting for medical image DG segmentation. First, we propose a structure-guided style diffusion augmentation method. Constrained by anatomical structure consistency in the frequency domain, this method performs cross-domain diffusion on the amplitude spectrum, generating samples with more diverse and broader style coverage to better support domain generalization. Then, we design a collaborative learning network with a dual-branch interactive architecture (CoDG-Net), together with a novel learning bias-guided strategy that adaptively regulates knowledge transfer at both the layer level and the task level, thereby effectively mitigating catastrophic forgetting on the source domain. Experiments and ablation studies on single-source and multi-source medical DG benchmark datasets demonstrate that CoDG-Net not only outperforms existing state-of-the-art methods in target-domain segmentation performance, but also achieves a lower forgetting rate on the source-domain data. The code is available at: https://github.com/wangprocess/CoDG-Net.

Figures & tables

Figure 1: Conceptual overview of our research motivation. (a) Original amplitude and phase spectra of fundus images acquired from different devices. (b) Coverage of extended domains after applying traditional data augmentation and diffusion-based generation methods on source domain 1. (c) Comparison of distribution-fitting capability on the source domain.

Figure 2: Overall workflow of the proposed method. First, pseudo-domain style exploration is applied to obtain $D^{P}$ . Second, a diffusion-based style diversification method is used to generate a style-diverse $D^{G}$ . Finally, the generated data are fed into the proposed CoDG-Net for training.

Figure 3: Overall architecture of the proposed CoDG-Net and the bias-guided learning strategies (for clarity, skip connections within each U-Net branch are omitted).

dir_{\text{seg}}\leftarrow\begin{cases}-d\bigl(F_{\text{seg}}^{(t,l)},F_{\text{rec}}^{(t+k,l)}\bigr),&\text{if }Flag_{\text{seg}}\\ \ \ d\bigl(F_{\text{seg}}^{(t,l)},F_{\text{seg}}^{(t+k,l)}\bigr),&\text{else}\end{cases}

Algorithm 2 Task-wise Bias-Guided Strategy.

Method	Source Domain: T2								Source Domain: T1CE
	Dice $\uparrow$				HD $\downarrow$				Dice $\uparrow$				HD $\downarrow$
	Flair	T1	T1CE	Average	Flair	T1	T1CE	Average	Flair	T1	T2	Average	Flair	T1	T2	Average
No Generalization	73.37	5.02	10.69	29.69	11.96	38.65	37.44	29.35	46.64	60.26	15.67	40.85	21.56	18.03	47.76	29.12
Fed-DG Liu et al. (2021)	75.77	5.82	9.51	30.37	14.45	54.03	51.06	39.85	33.03	58.30	4.09	31.72	32.07	22.35	56.08	36.83
SADN Zhou et al. (2022b)	75.87	49.36	38.09	54.44	13.44	20.15	23.56	19.05	47.31	63.64	63.00	57.98	21.03	18.06	17.56	18.88
EGSDG Jiang and Gu (2024)	76.16	62.43	55.87	64.82	13.43	18.84	17.79	16.69	68.49	71.22	73.06	70.92	17.81	12.93	14.74	15.16

Table 1: Comparative results with other related methods on the BraTS dataset (including using T2 as the source domain and using T1CE as the source domain. Red indicates optimal, and underlining indicates suboptimal.)

Method	Target Domain: Domain1				Target Domain: Domain2				Target Domain: Domain3				Target Domain: Domain4
	Disc		Cup		Disc		Cup		Disc		Cup		Disc		Cup
	Dice	ASD	Dice	ASD	Dice	ASD	Dice	ASD	Dice	ASD	Dice	ASD	Dice	ASD	Dice	ASD
No Generalization	82.80	19.03	64.55	26.20	85.99	19.98	76.03	20.31	88.78	16.63	84.14	10.35	85.43	9.93	68.85	25.11
RAM-DSIR Zhou et al. (2022a)	95.75	7.12	85.48	16.05	89.43	13.86	78.82	14.01	94.67	7.11	87.44	9.02	94.10	7.06	85.84	8.29
DCAC Hu et al. (2022)	95.54	6.35	81.43	19.20	87.85	18.28	77.72	17.15	94.28	8.11	86.80	9.14	95.40	5.20	87.68	7.12
DFQ Bi et al. (2024)	96.50	6.01	87.30	15.72	92.52	12.09	81.92	13.05	95.04	7.05	88.95	7.70	94.85	5.84	87.47	6.55

Table 2: Comparison of domain generalization results on Optic Disc/Cup segmentation from fundus images (We follow the practice in domain generalization literature to adopt the leave-one-domain-out strategy. Red indicates optimal, and underlining indicates suboptimal.)

Method	Source Domain: T2		Source Domain: T1CE
Method	Dice $\uparrow$	SFM (Dice) $\downarrow$	Dice $\uparrow$	SFM (Dice) $\downarrow$
No Generalization	84.52	–	78.71	–
Fed-DG	68.68	15.84	59.32	19.39
SADN	73.71	10.81	55.15	23.56
EGSDG	75.93	8.59	63.67	15.04
SLAug	73.53	10.99	60.61	18.1

Table 3: Comparison of source-domain performance and forgetting rate on the BraTS dataset.

Figure 4: Visual comparison of model predictions between the T2 source domain and the T1ce target domain.

Method	SE	SD	DBS	LW	TW	T2(Source)		T2-other(Avg)	T1CE(Source)		T1CE-other(Avg)
Method	SE	SD	DBS	LW	TW	Dice $\uparrow$	SFM $\downarrow$	Dice $\uparrow$	Dice $\uparrow$	SFM $\downarrow$	Dice $\uparrow$
VA1	$\times$	$\times$	$\times$	$\times$	$\times$	84.52	–	29.69	78.71	–	40.85
VA2	$\checkmark$	$\times$	$\times$	$\times$	$\times$	80.56	3.96	51.82	74.98	3.73	44.30
VA3	$\times$	$\checkmark$	$\times$	$\times$	$\times$	83.16	1.36	33.35	76.42	2.29	44.13
VA4	$\checkmark$	$\checkmark$	$\times$	$\times$	$\times$	79.33	5.19	67.59	72.83	5.88	61.71
VA5	$\checkmark$	$\checkmark$	$\checkmark$	$\times$	$\times$	81.09	3.43	52.12	75.25	3.46	56.82

Table 4: Ablation study results on the BraTS dataset.

Figure 5: Activation frequency of collaborative interactions at each intermediate layer in CoDG-Net.

Figure 6: Hyper-parameter sensitivity analysis of the random perturbation probability $\delta$ .

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PhaseAT: Fourier Phase Adversarial Training for Medical Image Domain Generalization

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Division of Computing and Mathematical Sciences Mohamed bin Zayed University of Artificial Intelligence, Abu Dhabi, UAE

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Reliable clinical deployment of deep medical image models is hindered by distribution shifts across scanners, sites, and acquisition protocols. Existing domain generalization (DG) methods often focus on style or intensity diversification, but they can still leave networks dependent on domain-specific texture correlations. Inspired by evidence that Fourier phase encodes semantic structure, we introduce PhaseAT, a phase-aware adversarial training framework for medical DG. PhaseAT forms phase-perturbed training views in the Fourier domain by iteratively updating a bounded phase perturbation while keeping the amplitude spectrum unchanged, thereby stressing spatial organization under matched appearance statistics. Perturbations are applied only to the luminance channel in YCbCr color space to avoid chromatic artifacts. Additionally, a simple phase-saliency mask concentrates updates on the most influential frequencies. The model is trained with a weighted combination of losses on clean and phase-perturbed samples, supporting both single-source and multi-source DG. We validate our method on two challenging medical datasets and demonstrate that PhaseAT achieves over 20% improvement in single-source domain generalization, outperforming several state-of-the-art DG methods. The code implementation is available at: https://github.com/ahmed-sharshar/PhaseAT.

Abstract

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