Real-time transverse process detection in ultrasound

PURPOSE: Ultrasound offers a safe radiation-free approach to visualize the spine and measure or assess scoliosis. However, ultrasound assessment also poses major challenges. We propose a real-time algorithm and software implementation to automatically delineate the posterior surface patches of transverse processes in tracked ultrasound; a necessary step toward the ultimate goal of spinal curvature measurement. METHODS: Following a pre-filtering of each captured ultrasound image, the shadows cast by each transverse process bone is examined and contours which are likely posterior bone surface are kept. From these contours, a three-dimensional volume of the bone surfaces is created in real-time as the operator acquires the images. The processing algorithm was implemented on the PLUS and 3D Slicer open-source software platforms. RESULTS: The algorithm was tested with images captured using the SonixTouch ultrasound scanner, Ultrasonix C5-2 curvilinear transducer and NDI trakSTAR electromagnetic tracker. Ultrasound data was collected from patients presenting with idiopathic adolescent scoliosis. The system was able to produce posterior surface patches of the transverse process in real-time, as the images were acquired by a non-expert sonographer. The resulting transverse process surface patches were compared with manual segmentation by an expert. The average Hausdorff distance was 3.0 mm when compared to the expert segmentation. CONCLUSION: The resulting surface patches are expected to be sufficiently accurate for driving a deformable registration between the ultrasound space and a generic spine model, to allow for three-dimensional visualization of the spine and measuring its curvature.