Transverse interlaminar/interspinous view (TI view). A key view for marking both the midline and each interlaminar/interspinous space. The ligamentum flavum and vertebral bodies were not visible in this view and are usually more hyperechoic in the parasagittal oblique view. Estimated depth can be approximated to transverse process depth when ligamentum flavum or vertebral bodies are not seen on either view. AP, articular process; ESM, erector spinae muscle; ISL, interspinous ligament; ITS, intrathecal space; TVP, transverse process. Informed consent was obtained from the patient for using clinical images.