Millimeter-Wave Imaging for Idiopathic Scoliosis Screening: Diagnostic Accuracy Study

Idiopathic scoliosis is a common 3D spinal deformity with a global prevalence of 2% to 3% in adolescents. Early detection is crucial for timely intervention and preventing curve progression. Although standing full-spine radiography with Cobb angle measurement remains the diagnostic gold standard, its time-consuming nature limits its utility for large-scale screening. Safe, rapid, and noninvasive screening methods are urgently needed to identify high-risk individuals while reserving x-rays for definitive diagnosis.

This study aimed to evaluate the diagnostic accuracy of a custom-developed millimeter-wave imaging system in patients with suspected scoliosis, with radiographic Cobb angle measurement serving as the reference standard, and explore its potential as a first-line screening tool.

This prospective diagnostic accuracy study enrolled consecutive outpatients with suspected scoliosis. All participants underwent rapid millimeter-wave imaging scanning (K_a band, 29-40 GHz with no undressing required) followed by standard standing full-spine radiography. Scoliosis was defined as a Cobb angle of 10° or higher. Millimeter-wave images were evaluated using four morphological indicators: (1) shoulder height asymmetry (≥2 cm), (2) trunk lateral shift (≥2 cm), (3) waistline contour asymmetry (≥5°), and (4) lower-limb height difference (≥1 cm). A multiparameter integration strategy classified screening as positive if more than 2 indicators exceeded threshold values. Cobb angle measurements were performed independently by 2 experienced orthopedic surgeons blinded to millimeter-wave image results and each other's assessments. Diagnostic performance metrics (sensitivity, specificity, positive predictive value, negative predictive value, and overall accuracy) were calculated according to the STARD (Standards for Reporting of Diagnostic Accuracy Studies) guidelines. A multivariate logistic regression model incorporating the 4 morphological parameters was constructed for receiver operating characteristic curve analysis.

Ultimately, 132 participants were included. Radiographic evaluation confirmed 98 (74.2%) cases with scoliosis (Cobb angle≥10°) and 34 (25.8%) negative cases. Millimeter-wave imaging achieved an overall accuracy of 86.4% (114/132; 95% CI 76.5%-94.7%), sensitivity of 85.7% (84/98; 95% CI 75.1%-96.5%), specificity of 88.2% (30/34; 95% CI 70.7%-97.6%), positive predictive value of 95.5%, and negative predictive value of 68.2%. Receiver operating characteristic curve analysis of the multivariate logistic regression model exhibited an area under the curve of 0.862 (95% CI 0.802-0.922), with a sensitivity of 92.9% (91/98) and specificity of 38.2% (13/34). Notably, sensitivity was lower for mild curves (Cobb angle=10°-20°) than for moderate or severe curves (≥20°).

Millimeter-wave imaging represents a feasible, rapid, and non-ionizing radiation screening method for scoliosis with good diagnostic accuracy (accuracy=114/132, 86.4%; sensitivity=84/98, 85.7%; specificity=30/34, 88.2%). Its capability to penetrate clothing and rapid scanning time (approximately 2 seconds) make it suitable for large-scale screening applications. As a first-line screening tool, this method identifies high-risk individuals for targeted referral and definitive radiography. It follows the "as low as reasonably achievable" principle, optimizing scoliosis screening and reducing unnecessary radiation exposure.