Kampitak, W. “Real - time Micro - convex probe ultrasound - guided Epidural anesthesia in patients with an abnormal spinal anatomy: Two case reports”. Thai Journal of Anesthesiology, vol. 39, no. 4, June 2016, pp. 313-24, https://he02.tci-thaijo.org/index.php/anesthai/article/view/59449.