1. A medical imaging system comprising: an X-ray imaging apparatus provided with a Talbot interferometer or a Talbot-Lau interferometer, the X-ray imaging apparatus including: an X-ray source which emits X-rays, an X-ray detector including conversion elements to generate an electrical signal according to the emitted X-rays, and reading the electrical signal generated by the conversion elements, as an image signal, and a subject table to hold a subject for a joint of the subject to be imaged; and an image processor which generates a differential phase image of the subject and optionally generates one of or both of an X-ray absorption image and a small-angle scattering image of the subject on the basis of the image signal of the subject imaged by the X-ray imaging apparatus, wherein the image processor specifies a location of an edge of a bone in the joint on the basis of at least one of the differential phase image, the X-ray absorption image, and the small-angle scattering image; and detects an edge of a cartilage in the joint in the differential phase image on the basis of the specified location of the edge of the bone to quantitatively measure a feature of the cartilage in the joint.