  Purpose: To develop a deep learning model that predicts active inflammation
from sacroiliac joint radiographs and to compare the success with radiologists.
Materials and Methods: A total of 1,537 (augmented 1752) grade 0 SIJs of 768
patients were retrospectively analyzed. Gold-standard MRI exams showed active
inflammation in 330 joints according to ASAS criteria. A convolutional neural
network model (JointNET) was developed to detect MRI-based active inflammation
labels solely based on radiographs. Two radiologists blindly evaluated the
radiographs for comparison. Python, PyTorch, and SPSS were used for analyses.
P<0.05 was considered statistically significant. Results: JointNET
differentiated active inflammation from radiographs with a mean AUROC of 89.2
(95% CI:86.8%, 91.7%). The sensitivity was 69.0% (95% CI:65.3%, 72.7%) and
specificity 90.4% (95% CI:87.8 % 92.9%). The mean accuracy was 90.2% (95% CI:
87.6%, 92.8%). The positive predictive value was 74.6% (95% CI: 72.5%, 76.7%)
and negative predictive value was 87.9% (95% CI: 85.4%, 90.5%) when prevalence
was considered 1%. Statistical analyses showed a significant difference between
active inflammation and healthy groups (p<0.05). Radiologists accuracies were
less than 65% to discriminate active inflammation from sacroiliac joint
radiographs. Conclusion: JointNET successfully predicts active inflammation
from sacroiliac joint radiographs, with superior performance to human
observers.
