We thank Dr. Weed and colleagues for their recent article on ultrasound imaging of the posterior longitudinal ligament and vertebral bodies [1]. They reported an association between the lack of ability to identify an acoustic window between adjacent laminae of the lumbar spine and subsequent difficulty with injections for spinal anesthesia. However, the interaction of ultrasound waves with bone is complex and involves reflection, absorption and scattering that can result in reverberation artifacts [2]. While deeper structures can be obscured, the characteristic nature of the shadowing depends on the surface properties of the bone.
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