Specialised CT scan protocols for 3-D pre-operative planning of total hip replacement.

X-ray computer tomography (CT) provides an accurate source of information in orthopaedics. Many computer aided orthopaedic surgery systems are based on CT images; thus, obtaining high resolution images is important. However, this may result in an excessive radiation dose for the patient. This study is aimed at developing a special CT scanning protocol for the hip region that can be adopted in clinical practise for 3-D pre-operative planning of total hip replacement surgery. Optimisation of CT acquisition parameters is investigated for both axial and spiral CT and the two resulting protocols are compared in terms of effective radiation dose to the patient. Results show that spiral CT with D=3 and P=1.5 in regions with higher morphological and density gradients and D=5 and P=1.5 in regions where the morphology is more regular degrades the image quality slightly but allows acquisition of a higher number of images at comparable costs, increasing the longitudinal resolution of the acquired data set. The effective dose is comparable to that of a standard pelvic CT exam. Adjusting the axial CT scan parameters the effective dose can be reduced, however lowering the accuracy of 3-D bone geometry reconstruction.