A Dual-Decomposition Spinal X-Ray Image Synthesizer Based on Three-Dimensional Spinal Ultrasonic Data for Radiation-Free Follow-Up of Scoliosis

Spinal X-ray effectively visualizes the overall spinal situation and vertebral details. However, X-ray is unsuitable for long-term follow-up or frequent monitoring due to its radiation hazard. Motivated by this, we propose a model named dual-decomposition radiograph synthesizer (DDRS) to predict the X-ray image of the present moment, given the previous X-ray image and a pair of three-dimensional spinal ultrasound data, for a practical and radiation-free evaluation of spinal deformity in follow-up or monitoring. The DDRS used a novel dual-decomposition strategy to ensure the quality of synthesized images. First, the DDRS innovatively converted the X-ray image synthesis into a fusion between the spinal pose and anatomical information. A parallel architecture was used to extract and aggregate the two information from ultrasound and X-ray images. Second, an intermodality calibration module and a global-local cooperated feature extractor are further introduced to implement our synthesis strategy effectively. The intermodality calibration module provides an accurate spinal pose description by correcting a potential pose difference during two image acquisition times. The global-local cooperated feature extractor contributes to preserving spinal anatomical information in the previous X-ray image by exploring global dependencies and highlighting local details. Extensive experiments were conducted on a real clinical dataset. Results show that a mean structural similarity (SSIM) of 0.89 was obtained between synthesized X-ray images provided by the DDRS and real ones, and further comparisons with existing outstanding image synthesizers also display a 17.1% improvement in mean SSIM, illustrating the potential of our synthesizer in a radiation-free follow-up of scoliosis.