Purpose of the study: The objective of this work was to achieve a whole-body 3D study of the bone and joint system in the upright position using the lowest radiation dose possible. Radiation doses can be considerable when acquiring 3D images using computed tomographic millimetric sections which in addition are acquired uniquely in the reclining position and thus limited to a specific region.

Material and methods: Using a gas detector which transforms x-ray protons into electrons (G. Charpak) we constructed a device which enables acquisition of high-quality anteroposterior and lateral whole-body radiographic images with exposure to radiation doses 8 to 10-fold less than classical 2D x-rays. A 3D reconstruction of the entire skeleton was obtained from these two initial images.

Results: The 3D reconstructions were validated and compared with those obtained with computed tomography. The results were concordant and revealed least equivalent to if not better reliability. The advantage was to enable study in the functional upright position an to study weight-bearing joints of the lower-limbs, pelvis, and spine. In addition, radiation exposure for the 3D reconstructions was reduced 800 to 1000 times compared with computed tomography. More than 150 examinations have been performed and validated in patients with diverse pathological conditions as well as in normal control adults and children.

Discussion: There is a very wide potential field of application for this technique in orthopedics, both for 3D analysis of joint deformations and their impact on the whole body, and for therapeutic follow-up, particularly after prosthetic or corrective surgery. For example, the horizontal plane which is very difficult to image and represent mentally for spinal surgery can be clearly planned and controlled. This new imaging technique offers perspectives for intraoperative navigation and for bone mineral density measurements. The double-energy methodology enables short-term evaluation of fracture risk due to osteoporosis of the spine and limbs or pelvis.