Background: Musculoskeletal ultrasound (MSUS) is commonly used to detect double contour sign (DCS) to diagnose gout. MSUS is subjective and needs user training and experience for optimal visualisation. Machine learning (ML) models can be used for automatic detection of DCS. We sought to identify the optimal algorithm for detection of DCS on ultrasound images of the fist metatarsophalangeal joint (MTPJ1) using candidate ML algorithms. Methods: MSUS images of MTPJ1 of male patients acquired between January, 2020 and January, 2023 were included in this study. Diagnosis of gout was based on imaging, joint aspiration, serum uric acid level, and clinical evaluation. Images were acquired with a high frequency linear transducer (18 MHz) with a dedicated MSUS machine (Toshiba Xario 200). Patients diagnosed with calcium pyrophosphate crystal disease or gross deformities of MTPJ1 were excluded. Selected images were pre-processed using Keras-OCR. The following candidate ML algorithms were trained: Support Vector machine, tree-based algorithms like Random Forest and Decision Tree and boosting-based algorithms like Gradient Boosting and XGBoost and these were compared with a deep neural network (2D-CNN). Classification outcomes (DCS positive or negative) were compared before and after image augmentation. Classification performance was measured using sensitivity, specificity, and area under the receiver operating curve (AUROC) along with accuracy, precision and F1-score. Results: We used 410 high resolution ultrasound images of MTPJ1 of male patients, 311 patients with gout and positive DCS and 99 patients without gout and no DCS. On average, the final model using XGBoost for detection of DCS showed sensitivity of 94% and specificity of 93.7% and AUROC of 85%. Using XGBoost accuracy and precision were 84.74% and 87% respectively and recall and F1-scores were 94% and 90% respectively. Comparison of different models is given in Table 1. Classification performance improved after augmentation in almost all the models. Conclusions: The classification model based on a boosting based ML model (XGBoost) was trained with a relatively small dataset; however, it showed good accuracy. This proposed system was useful in correct classification of DCS in MSUS images with potential to aid imaging diagnostics of gout in a wider clinical setting.
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