# Adaptive Bandelet Transform and Transfer Learning for Geometry-Aware Thyroid Cancer Ultrasound Classification

## TL;DR

This paper introduces a new method for thyroid cancer classification in ultrasound images by combining a geometry-adaptive Bandelet Transform with transfer learning, achieving high accuracy with limited data.

## Contribution

The novel integration of geometry-adaptive Bandelet Transform with transfer learning improves data-efficient classification of thyroid nodules in ultrasound.

## Key findings

- The proposed BT+TL (VGG19) model achieves 98.91% accuracy on the DDTI dataset.
- BT-based preprocessing outperforms classical wavelet representations across multiple thresholds.
- The model shows high sensitivity (98.11%) and specificity (97.31%) for thyroid nodule classification.

## Abstract

Background and Objectives: Classification of thyroid nodules (TN) in ultrasound remains challenging due to limited labelled data and the limited capacity of conventional feature representations to capture complex, multi-directional textures. This work aims to improve data-efficient TN classification by integrating a geometry-adaptive Bandelet Transform (BT) with transfer learning (TL) to enhance feature representation and generalisation. Methods: The proposed pipeline first applies BT to strengthen directional and structural encoding in ultrasound images via quadtree-driven geometric adaptation. It then mitigates class imbalance using SMOTE and increases data diversity through targeted data augmentation. The resulting representations are classified using multiple ImageNet-pretrained architectures, where VGG19 yields the most consistent performance. Results: Experiments on the publicly available DDTI dataset show that BT-based preprocessing consistently improves performance over classical wavelet representations across multiple quadtree thresholds, with the best results obtained at T=30. Under this setting, the proposed BT+TL (VGG19) model achieves 98.91% accuracy, 98.11% sensitivity, 97.31% specificity, and a 98.89% F1-score, outperforming comparable approaches reported in the literature. Conclusions: Coupling geometry-adaptive transforms with modern TL backbones provides a robust and data-efficient strategy for ultrasound TN classification, particularly under limited annotation and challenging texture variability. The complete project is publicly available.