Table 1

Eight predefined anatomical areas of interest

Area of interest	Definition
TAP	The fascial plane between the transversus abdominis and internal oblique muscles
Posterior QL	The fascial plane between the posterior aspect of the QL muscle and the middle layer of the thoracolumbar fascia
Anterior QL	The fascial plane between the anterior aspect of the QL and psoas muscle
Intercostal plane	The fascial plane along the inferior border of the ribs
Lumbar paravertebral space	Presence of injectate between the transverse processes and the psoas muscle in the proximity of the lumbar intervertebral foramen
Lumbar nerve roots	Presence of injectate in contact with the nerve roots or within the psoas compartment
Sympathetic chain	Presence of injectate on the lateral side of a vertebral body
Thoracic paravertebral space	Presence of injectate at or cranial to T12 in the thoracic paravertebral space