title: High resolution cortical bone thickness measurement from clinical CT data.
abstract: The distribution of cortical bone in the proximal femur is believed to be a critical component in determining fracture resistance. Current CT technology is limited in its ability to measure cortical thickness, especially in the sub-millimetre range which lies within the point spread function of today's clinical scanners. In this paper, we present a novel technique that is capable of producing unbiased thickness estimates down to 0.3mm. The technique relies on a mathematical model of the anatomy and the imaging system, which is fitted to the data at a large number of sites around the proximal femur, producing around 17,000 independent thickness estimates per specimen. In a series of experiments on 16 cadaveric femurs, estimation errors were measured as -0.01+/-0.58mm (mean+/-1std.dev.) for cortical thicknesses in the range 0.3-4mm. This compares with 0.25+/-0.69mm for simple thresholding and 0.90+/-0.92mm for a variant of the 50% relative threshold method. In the clinically relevant sub-millimetre range, thresholding increasingly fails to detect the cortex at all, whereas the new technique continues to perform well. The many cortical thickness estimates can be displayed as a colour map painted onto the femoral surface. Computation of the surfaces and colour maps is largely automatic, requiring around 15min on a modest laptop computer.
authors.affiliation: University of Cambridge Department of Engineering, Trumpington Street, Cambridge CB2 1PZ, UK. gmt11@cam.ac.uk
authors.forename: G M
authors.initials: GM
authors.lastname: Treece
authors.forename: A H
authors.initials: AH
authors.lastname: Gee
authors.forename: P M
authors.initials: PM
authors.lastname: Mayhew
authors.forename: K E S
authors.initials: KE
authors.lastname: Poole
mesh_terms: D000328:Adult; D000369:Aged, 80 and over; D000465:Algorithms; D015519:Bone Density; D003198:Computer Simulation; D005260:Female; D005264:Femoral Fractures / Q000000981:diagnostic imaging*; D005269:Femur / Q000000981:diagnostic imaging* / Q000293:injuries*; D006801:Humans; D021621:Imaging, Three-Dimensional / Q000379:methods*; D008297:Male; D008954:Models, Biological; D010363:Pattern Recognition, Automated / Q000379:methods; D011856:Radiographic Image Enhancement / Q000379:methods; D011857:Radiographic Image Interpretation, Computer-Assisted / Q000379:methods*; D015203:Reproducibility of Results; D012680:Sensitivity and Specificity; D014057:Tomography, X-Ray Computed / Q000379:methods*