Is SAM 2 Better than SAM in Medical Image Segmentation?

TL;DR

This study compares SAM and SAM 2 in zero-shot medical image segmentation across various modalities, finding that SAM 2 does not consistently outperform SAM and struggles with low contrast images.

Contribution

The paper provides a comprehensive evaluation of SAM 2's performance in medical segmentation, highlighting its limitations and comparative performance with SAM across multiple datasets.

Findings

SAM 2 does not generally outperform SAM in medical segmentation.

SAM 2 performs worse in low contrast modalities like CT and ultrasound.

Both models suffer from over-segmentation on fuzzy boundaries.

Abstract

The Segment Anything Model (SAM) has demonstrated impressive performance in zero-shot promptable segmentation on natural images. The recently released Segment Anything Model 2 (SAM 2) claims to outperform SAM on images and extends the model's capabilities to video segmentation. Evaluating the performance of this new model in medical image segmentation, specifically in a zero-shot promptable manner, is crucial. In this work, we conducted extensive studies using multiple datasets from various imaging modalities to compare the performance of SAM and SAM 2. We employed two point-prompt strategies: (i) multiple positive prompts where one prompt is placed near the centroid of the target structure, while the remaining prompts are randomly placed within the structure, and (ii) combined positive and negative prompts where one positive prompt is placed near the centroid of the target structure, and two negative prompts are positioned outside the structure, maximizing the distance from the positive prompt and from each other. The evaluation encompassed 24 unique organ-modality combinations, including abdominal structures, cardiac structures, fetal head images, skin lesions and polyp images across 11 publicly available MRI, CT, ultrasound, dermoscopy, and endoscopy datasets. Preliminary results based on 2D images indicate that while SAM 2 may perform slightly better in a few cases, it does not generally surpass SAM for medical image segmentation. Notably, SAM 2 performs worse than SAM in lower contrast imaging modalities, such as CT and ultrasound. However, for MRI images, SAM 2 performs on par with or better than SAM. Like SAM, SAM 2 also suffers from over-segmentation issues, particularly when the boundaries of the target organ are fuzzy.