Methods and systems for image-based guidance in deep-brain stimulation. An endoscope system includes a waveguide tube, a right-angle prism, a light source, and a photoacoustic transducer. Light from the light source propagates along the length of the waveguide tube via internal reflection within the wall. The right-angle prism is positioned to redirect light emitted at a distal end of the waveguide tube in a direction perpendicular to the length of the waveguide tube. Light emitted in the perpendicular direction causes soundwaves to be generated by the surrounding tissue via photoacoustic effect. Those soundwaves are then conducted through the interior channel of the waveguide tube from the distal end of the waveguide tube to a proximal end of the waveguide tube where the soundwaves are detected by the photoacoustic transducer, which is acoustically coupled to the interior channel of the waveguide tube at the proximal end of the waveguide tube.
