Identifying final pathology of FNA-indeterminant nodules before surgical resection could decrease the number of unnecessary surgeries and total cost to patients. This project explores how radiomics (RM) and deep learning (DTLM) models may be combined to improve the potential for clinical interpretability of machine learning models in the task of classifying indeterminant thyroid nodules on ultrasound. Two radiomic and deep learning combination models were created: a simple classifier combination model (SCM) and an interpretability-driven combination model (ICM). SCM provided a nodule malignancy score. ICM merged radiomic and deep learning features through correlation and provided echogenicity-related, composition-related, and shape/margin-related malignancy scores which were averaged to yield an overall nodule malignancy score. Models were trained and tested on a de-identified dataset of 476 grayscale ultrasound images collected under IRB approval containing 222 images from 69 indeterminant nodules with a final pathology of malignant and 254 images from 82 indeterminant nodules with a final pathology of benign. Models were tested using 5- fold cross-validation by nodule over 100 iterations. Receiver-operating characteristic (ROC) analysis was conducted with area under the ROC curve (AUC) serving as the statistic of merit for model performance. Models yielded mean AUC [95%CI] of 0.75 [.67,.83], 0.70 [.62,.78], 0.77 [0.70,0.84], 0.76 [.69,.84] for RM, DTLM, SCM, and ICM respectively. This work failed to demonstrate a statistically significant difference in model performances. However, the ICM presents a novel method for combining radiomics and deep learning features focused on improving interpretability for clinical implementation in the task of indeterminant thyroid nodule classification.
Background: Ultrasound (US)-guided fine needle aspiration (FNA) cytology is the gold standard for the evaluation of thyroid nodules. However, up to 30% of FNA results are indeterminate, requiring further testing. In this study, we present a machine-learning analysis of indeterminate thyroid nodules on ultrasound with the aim to improve cancer diagnosis.
Methods: Ultrasound images were collected from two institutions and labeled according to their FNA (F) and surgical pathology (S) diagnoses [malignant (M), benign (B), and indeterminate (I)]. Subgroup breakdown (FS) included: 90 BB, 83 IB, 70 MM, and 59 IM thyroid nodules. Margins of thyroid nodules were manually annotated, and computerized radiomic texture analysis was conducted within tumor contours. Initial investigation was conducted using five-fold cross-validation paradigm with a two-class Bayesian artificial neural networks classifier, including stepwise feature selection. Testing was conducted on an independent set and compared with a commercial molecular testing platform. Performance was evaluated using receiver operating characteristic analysis in the task of distinguishing between malignant and benign nodules.
Results: About 1052 ultrasound images from 302 thyroid nodules were used for radiomic feature extraction and analysis. On the training/validation set comprising 263 nodules, five-fold cross-validation yielded area under curves (AUCs) of 0.75 [Standard Error (SE) = 0.04; P < 0.001] and 0.67 (SE = 0.05; P = 0.0012) for the classification tasks of MM versus BB, and IM versus IB, respectively. On an independent test set of 19 IM/IB cases, the algorithm for distinguishing indeterminate nodules yielded an AUC value of 0.88 (SE = 0.09; P < 0.001), which was higher than the AUC of a commercially available molecular testing platform (AUC = 0.81, SE = 0.11; P < 0.005).
Conclusion: Machine learning of computer-extracted texture features on gray-scale ultrasound images showed promising results classifying indeterminate thyroid nodules according to their surgical pathology.
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