A radiology assembly comprising: • a tube for generating a beam of x-rays that is centered on a main emission direction, • a planar sensor, substantially perpendicular to the main emission direction, that is intended to receive the x-rays, characterized in that it comprises: • a first emitter (15, 16) that is divided into two electromagnetic-field-emitting portions (20, 21; 22, 23), placed so as to emit a first electromagnetic field in a main direction (18, 19) that is substantially perpendicular to the main emission direction, each of the two emitting portions (20, 21; 22, 23) of the divided emitter (15, 16) being positioned on both sides of the beam of x-rays, • a second emitter that is divided into two electromagnetic-field-emitting portions (22, 23), placed so as to emit a second electromagnetic field in a main direction that is substantially perpendicular to the main emission direction and that is secant to the main direction of the first electromagnetic field, each of the two portions (22, 23) of the divided emitter being positioned on both sides of the beam of x-rays, • a so-called planar electromagnetic-field emitter, the so-called planar emitter being a coil composed of windings, the so-called planar emitter being placed so as to emit a third electromagnetic field in a main direction that is substantially parallel to the main emission direction, the windings being passed through by the main emission direction, • electromagnetic-field sensors (29, 30, 31, 32) that are securely fastened to the planar sensor, able to detect the first, second and third electromagnetic field alternatively emitted in their main direction by the first emitter (15, 16), the second emitter (15, 16) and the so-called planar emitter and to generate a first, second, third electrical signal depending on the detected electromagnetic fields, • a means for processing the first, second and third electrical signal, which is intended to determine the relative position of the planar sensor with respect to the generation tube depending on the first, second and third electrical signal. • a tube for generating a beam of x-rays that is centered on a main emission direction, • a planar sensor, substantially perpendicular to the main emission direction, that is intended to receive the x-rays, • a first emitter (15, 16) that is divided into two electromagnetic-field-emitting portions (20, 21; 22, 23), placed so as to emit a first electromagnetic field in a main direction (18, 19) that is substantially perpendicular to the main emission direction, each of the two emitting portions (20, 21; 22, 23) of the divided emitter (15, 16) being positioned on both sides of the beam of x-rays, • a second emitter that is divided into two electromagnetic-field-emitting portions (22, 23), placed so as to emit a second electromagnetic field in a main direction that is substantially perpendicular to the main emission direction and that is secant to the main direction of the first electromagnetic field, each of the two portions (22, 23) of the divided emitter being positioned on both sides of the beam of x-rays, • a so-called planar electromagnetic-field emitter, the so-called planar emitter being a coil composed of windings, the so-called planar emitter being placed so as to emit a third electromagnetic field in a main direction that is substantially parallel to the main emission direction, the windings being passed through by the main emission direction, • electromagnetic-field sensors (29, 30, 31, 32) that are securely fastened to the planar sensor, able to detect the first, second and third electromagnetic field alternatively emitted in their main direction by the first emitter (15, 16), the second emitter (15, 16) and the so-called planar emitter and to generate a first, second, third electrical signal depending on the detected electromagnetic fields, • a means for processing the first, second and third electrical signal, which is intended to determine the relative position of the planar sensor with respect to the generation tube depending on the first, second and third electrical signal.