A medical imaging system comprising: an X-ray Talbot imaging apparatus comprising: an X-ray source adapted to emit X-rays, an X-ray detector including conversion elements to generate an electrical signal according to the emitted X-rays, and adapted to read the electrical signal generated by the conversion elements, as an image signal, a subject table to hold a subject for a joint of the subject to be imaged, and a controller adapted to generate a reconstructed image from the image signal of the imaged subject, the reconstructed image including at least a differential phase image; and an image processing apparatus adapted to measures a thickness of cartilage in the joint in the differential phase image or an image generated from the differential phase image, by reference to at least one of i) an edge of a bone in the joint identified in the reconstructed image or an image generated from the reconstructed image, and ii) an edge of the cartilage identified in the differential phase image or the image generated from the differential phase image, characterised in that the image processing apparatus is adapted to fit the identified edge (A,B) of the cartilage or bone to a curved line based on a plurality of points (p1, p2, p3) determined on the edge (A,B) of the cartilage or bone, and adapted to measure the thickness of the cartilage on a normal line to the curved line at a position (P,p) specified on the edge (A,B) of the cartilage or bone, and wherein the image processing apparatus is adapted to fit the edge (A,B) of the cartilage or bone to an arc based on at least three points (p1, p2, p3) determined on the edge (A,B) of the cartilage or bone, adapted to determine a center of the arc, and adapted to measure the thickness of the cartilage on a straight line passing through the specified position (P,p) on the edge (A,B) of the cartilage or bone and the center of the arc, and wherein the image processing apparatus adapted to fit the edge of the bone to the arc based on the at least three points (p1, p2, p3) determined on the edge of the bone adapted to generate another arc obtained by enlarging a radius of the arc to which the edge of the bone is fitted, and adapted to estimate the another arc to be a shape (A*) of the cartilage before deformation due to abrasion or defect. an X-ray Talbot imaging apparatus comprising: an X-ray source adapted to emit X-rays, an X-ray detector including conversion elements to generate an electrical signal according to the emitted X-rays, and adapted to read the electrical signal generated by the conversion elements, as an image signal, a subject table to hold a subject for a joint of the subject to be imaged, and a controller adapted to generate a reconstructed image from the image signal of the imaged subject, the reconstructed image including at least a differential phase image; and an X-ray source adapted to emit X-rays, an X-ray detector including conversion elements to generate an electrical signal according to the emitted X-rays, and adapted to read the electrical signal generated by the conversion elements, as an image signal, a subject table to hold a subject for a joint of the subject to be imaged, and a controller adapted to generate a reconstructed image from the image signal of the imaged subject, the reconstructed image including at least a differential phase image; and an image processing apparatus adapted to measures a thickness of cartilage in the joint in the differential phase image or an image generated from the differential phase image, by reference to at least one of i) an edge of a bone in the joint identified in the reconstructed image or an image generated from the reconstructed image, and ii) an edge of the cartilage identified in the differential phase image or the image generated from the differential phase image, characterised in that the image processing apparatus is adapted to fit the identified edge (A,B) of the cartilage or bone to a curved line based on a plurality of points (p1, p2, p3) determined on the edge (A,B) of the cartilage or bone, and adapted to measure the thickness of the cartilage on a normal line to the curved line at a position (P,p) specified on the edge (A,B) of the cartilage or bone, and i) an edge of a bone in the joint identified in the reconstructed image or an image generated from the reconstructed image, and ii) an edge of the cartilage identified in the differential phase image or the image generated from the differential phase image, characterised in that the image processing apparatus is adapted to fit the identified edge (A,B) of the cartilage or bone to a curved line based on a plurality of points (p1, p2, p3) determined on the edge (A,B) of the cartilage or bone, and adapted to measure the thickness of the cartilage on a normal line to the curved line at a position (P,p) specified on the edge (A,B) of the cartilage or bone, and