In vivo assessment of trabecular bone structure using fractal analysis of distal radius radiographs.

~Received 24 January 2000; accepted for publication 29 August 2000!Our purpose in this study was ~i! to measure trabecular bone structure using fractal analysis of distalradius radiographs in subjects with and without osteoporotic hip fractures, and ~ii! to compare thesemeasures with bone mineral density ~BMD! as well as with measures of trabecular bone structurederived from high resolution magnetic resonance ~MR! images. Distal radius radiographs wereobtained using semi-industrial films~55 kVp, 400 mAs! in 30 postmenopausal patients, who hadsuffered osteoporotic hip fractures ~74.81/28.2 years! in the last 24 months and 27 postmeno-pausal age-matched~74.61/26.6 yr! normal volunteers. Radiographs were digitized at 50 mm. AFourier power spectrum-based fractal dimension ~FD! characterizing the trabecular pattern wasmeasured in a region of interest proximal to the joint line. The fractal dimension was calculatedover two spatial frequency ~f! ranges: FD1 was calculated over 0.5,log(f),1.0, FD2 over thehigher range 1.0,log(f),1.5. Trabecular BMD in the radius was obtained using peripheral quan-titative computed tomography ~pQCT!~Stratec GmbH, Germany!. In addition BMD of the proxi-mal femur was determined using dual x-ray absorptiometry~DXA!~QDR 2000, Hologic, MA!.Ina subset of patients ~16 controls and 18 with hip fractures!, high resolution MR imaging of the distalradius ~spatial resolution of 15631563500 mm! was used to obtain measures analogous to bonehistomorphometry. There were significant differences (p,0.05) between the fracture and nonfrac-ture groups in the total femur BMD ~13%!, trabecular BMD in the distal radius ~4%!, and the fractaldimension in the radiographs ~FD2!~3%!. The correlations between FD2 and the total femur BMDas well as trabecular bone BMD in the distal radius were 20.48 (p,0.006) and 20.22 (p,0.33); respectively; FD1 increased with BMD and showed lower correlations. FD2 showed goodcorrelations with App. Tb.N ~20.71! and App. Tb.Sp ~0.69! (p,0.01), moderate correlation withApp BV/TV ~20.53! (p,0.05), and no significant correlation with App. Tb.Th. The correlationsbetween structural measures and FD1 showed the inverse trend and were typically lower. The oddsratios for a hip fracture were 2.44 for total femur BMD, 1.5 for trabecular BMD ~radius!, and 1.5for FD2, respectively. In summary, the fractal measures derived from radiographs of the radiusshow differences between subjects with and without hip fractures, the predictive power of measuresin the distal radius are comparable to radial trabecular BMD but lower than that of total hip BMD.© 2000 American Association of Physicists in Medicine. @S0094-2405~00!01311-0#Key words: structure analysis, trabecular bone, fractal dimension, osteoporosis, distal radiusI. INTRODUCTIONTrabecular architecture has been shown to be an importantfactor in assessing bone strength.