A physical model mimicking tissue properties, used to test imaging devices under controlled conditions.In physics and medical imaging, a phantom is a specially designed object that mimics the physical properties of human tissue—such as density, absorption, and scattering—under controlled conditions. It serves as a stand-in for a real body part when testing or calibrating imaging devices like X-ray machines, CT scanners, or ultrasound systems. Phantoms allow researchers and engineers to evaluate how well an instrument performs without exposing a living person to radiation or other risks, and they provide a stable, repeatable reference for comparing different devices or techniques.
The use of phantoms dates back to the early 20th century, when physicists and radiologists began using simple water-filled containers or wax blocks to test X-ray equipment. The term 'phantom' was adopted from the idea of a 'ghost' image, as these objects produced images that mimicked real anatomy without being alive.
A phantom is built from materials whose interaction with radiation or sound waves closely matches that of biological tissue. For example, water-based gels or plastics with specific additives can replicate the way X-rays are absorbed by muscle or bone. When an imaging system scans the phantom, the resulting image shows known structures—such as spheres, rods, or gradients—that can be compared against the expected output. Any deviations reveal the system's resolution, contrast, or distortion, allowing precise adjustments.
Phantoms are routinely used in hospitals to calibrate MRI and CT scanners, in research labs to test new imaging algorithms, and in radiation therapy to verify dose delivery before treating patients.
Some phantoms are designed to mimic not just tissue but also its motion, such as a breathing chest phantom used to test imaging of moving organs.
