Final answer:
The breathing technique is the device that enhances visualization of the spinous processes during a lateral thoracic spine radiographic projection, as it adjusts lung contrast.
Step-by-step explanation:
The device that will improve visualization of the spinous processes on the lateral projection of the thoracic spine is the c. breathing technique. This is because optimal visualization of the thoracic spine in lateral radiographs can often be enhanced with proper breathing techniques like sustaining full inspiration or expiration. This practice increases or decreases the amount of air in the lungs, which alters the contrast of the spine against the surrounding lung tissue. Other choices, such as a lead apron or a gonad shield, are designed to protect patients from unnecessary radiation exposure rather than to improve the visualization of specific anatomical structures during imaging. A plumb line is not typically used in radiographic imaging to enhance the visibility of anatomical structures.