Fig. 3. The paramedian oblique ultrasound image of the swine lumbar spine. The curved linear ultrasound probe is placed laterally to the spinal process and directed medially to the spinal canal to get the paramedian oblique view. The inclined hyperechoic bony structures are the lamina of each swine spine. There is a narrow acoustic window cephalic to the lamina, including ligament flavum, hypoechoic epidural space, posterior dura, spinal canal, and anterior dura from posterior to anterior. The indwelled epidural catheter is visualized by the ultrasound within the epidural space as a traceable hyperechoic line or spot. L1 = lamina of L1 vertebra; T12 = lamina of T12 vertebra.