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Evaluating Perceptual Metrics for Medical Image Translation Tasks: Limitations and Insights

Core Concepts
Perceptual metrics commonly used in general image translation, such as FID, do not reliably correlate with segmentation-based metrics for evaluating medical image translation tasks. The suitability of these metrics is limited due to the anatomical constraints and requirements of medical image translation.
The paper investigates the use of perceptual metrics, such as FID, KID, and SWD, for evaluating medical image translation tasks, and compares them to segmentation-based metrics. The authors evaluate two medical image translation tasks: (1) subtle intra-modality breast MRI translation and (2) more drastic inter-modality translation of lumbar spine MRI to CT. The results show that perceptual metrics do not consistently align with common segmentation metrics for medical image translation. No single perceptual metric reliably correlates with segmentation metrics for both tasks, and the commonly used FID is especially inconsistent. The authors advise caution in using FID for evaluating medical image translation. The pixel-level SWD metric shows better correlation than the learned feature metrics (FID, KID, IS) for the subtle intra-modality breast MRI translation, but fails for the more complex inter-modality MRI-to-CT translation. This suggests that perceptual metrics designed for assessing image realism may not be fully suitable for medical image translation, which requires preserving anatomical and semantic content. The authors conclude that a broader evaluation approach and research into more universally applicable metrics are needed in the field of medical image translation.
Breast MRI Siemens→GE Translation: Dice score for breast segmentation: 0.927 - 0.950 Dice score for fibroglandular tissue (FGT) segmentation: 0.277 - 0.707 FID*: 107 - 156 KID: 0.049 - 0.089 SWD: 500 - 1037 IS: 2.46 - 3.00 Lumbar Spine MRI→CT Translation: Dice score for bone segmentation: 0.007 - 0.942 FID*: 208 - 323 KID: 0.161 - 0.300 SWD: 932 - 1553 IS: 2.14 - 2.93

Key Insights Distilled From

by Nicholas Kon... at 04-12-2024
Rethinking Perceptual Metrics for Medical Image Translation

Deeper Inquiries

How can perceptual metrics be adapted or extended to better capture the anatomical and semantic constraints of medical image translation tasks?

Perceptual metrics can be enhanced to better align with the anatomical and semantic constraints of medical image translation tasks by incorporating domain-specific knowledge and features. One approach could involve developing hybrid metrics that combine traditional perceptual metrics with anatomical consistency measures. For instance, integrating anatomical segmentation information into the evaluation process could provide a more comprehensive assessment of how well the translated images preserve the underlying anatomical structures. Additionally, training perceptual models on medical image datasets specifically curated for the task at hand could improve their ability to capture the nuances of medical imaging, such as organ shapes and tissue textures.

What alternative evaluation approaches or novel metrics could be developed to more comprehensively assess the performance of medical image translation models?

To more comprehensively evaluate the performance of medical image translation models, novel metrics that focus on anatomical fidelity, semantic consistency, and clinical relevance could be developed. One potential approach is to design metrics that measure the similarity of key anatomical landmarks or structures between the original and translated images. This could involve leveraging domain-specific knowledge from radiologists or medical experts to define critical regions for evaluation. Furthermore, introducing metrics that assess the clinical utility of the translated images, such as their impact on downstream tasks like diagnosis or treatment planning, could provide a more holistic evaluation of model performance.

What are the potential implications of the limitations of perceptual metrics on the development and deployment of medical image translation technologies in real-world clinical applications?

The limitations of perceptual metrics in capturing the anatomical and semantic constraints of medical image translation tasks could have significant implications for the development and deployment of these technologies in real-world clinical settings. Relying solely on perceptual metrics for model evaluation may lead to inaccuracies in assessing the clinical relevance and utility of the translated images. This could result in the deployment of models that perform well on perceptual metrics but fail to preserve critical anatomical details necessary for accurate medical interpretation. To address these limitations, further research and development of evaluation metrics tailored to medical imaging are essential. Without more robust evaluation approaches, there is a risk of deploying translation models that do not meet the stringent requirements of clinical applications, potentially compromising patient care and diagnostic accuracy. Therefore, it is crucial to invest in the refinement of evaluation methodologies to ensure the safe and effective integration of medical image translation technologies into clinical practice.