Limitations of clinical CT in assessing cortical thickness and density

• Published in: Physics in medicine & biology Vol. 43; no. 3; pp. 619 - 626
• Main Authors: Newman, D L, Dougherty, G, Obaid, A Al, Hajrasy, H Al
• Format: Journal Article
• Language: English
• Published: Bristol IOP Publishing 01.03.1998; Institute of Physics
• Subjects: Algorithms; Aluminum; Biological and medical sciences; Biophysical Phenomena; Biophysics; Bone and Bones - diagnostic imaging; Bone Density; Humans; Image Processing, Computer-Assisted; Investigative techniques, diagnostic techniques (general aspects); Medical sciences; Osteoarticular system. Muscles; Osteoporosis - diagnostic imaging; Radiodiagnosis. Nmr imagery. Nmr spectrometry; Tomography, X-Ray Computed - methods; Tomography, X-Ray Computed - statistics & numerical data; Thickness; Osteoarticular system; Density measurement; Radiodiagnosis; Limitation; Medical imagery; Computerized axial tomography; Cortical bone; Image reconstruction; Thickness measurement; Test object
• ISSN: 0031-9155; 1361-6560
• DOI: 10.1088/0031-9155/43/3/013

The peak CT number (CT) and full width at half maximum (FWHM) were obtained from the image profiles of aluminium of thickness ranging from 0.1-9.5 mm. The scans were performed at different fields of view (FOVs) and with different reconstruction algorithms ('bone' and 'standard'). Above 3 mm, CT and FWHM provide measures of the density and thickness which are largely independent of FOV (i.e. pixel size) and algorithm. Below 3 mm, CT falls progressively whilst FWHM remains relatively constant. At these small thicknesses the effect of FOV on CT is more pronounced when the bone algorithm is used, whilst FWHM remains relatively constant and independent of both FOV and algorithm. The results are discussed in terms of thickness relative to pixel size and spatial resolution as characterized by the point spread function. A linear relationship was found between the product CT x FWHM and thickness that is independent of both FOV and algorithm. This product may be useful in studies of cortical bone and changes due to osteoporosis.