Figure 5
From: Optically Guided Epidural Needle Placement Using 405-nm Wavelength for Accurate Puncture

Signal change while the needle tip is entering epidural space from ligamentum flavum. (A) Reflected light intensities when needle tip penetrates the ligamentum flavum and enters the epidural space. (B) Decrease of reflection light intensities at different vertebrae while needle enters epidural space from ligamentum flavum.