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A new anisotropy index on trabecular bone radiographic images using the fast Fourier transform.

Brunet-Imbault B, Lemineur G, Chappard C, Harba R, Benhamou CL - BMC Med Imaging (2005)

Bottom Line: The analysis of the FFT spectra was performed by two observers, the Coefficients of Variation were 1.5% and 3.1 % for intra-and inter-observer reproducibility, respectively.From the ROC analysis, the Area Under Curve (AUC) were respectively 0.65, 0.62, 0.64, 0.77 for lumbar spine, femoral neck, total femoral BMD and DA.The highest DA values in fracture cases suggest that the structure is more anisotropic in osteoporosis due to preferential deletion of trabeculae in some directions.

View Article: PubMed Central - HTML - PubMed

Affiliation: Equipe Inserm 658, Hôpital Porte Madeleine, BP 2439, 45032 Orléans Cedex 1, France. brunet-imbault@libertysurf.fr

ABSTRACT

Background: The degree of anisotropy (DA) on radiographs is related to bone structure, we present a new index to assess DA.

Methods: In a region of interest from calcaneus radiographs, we applied a Fast Fourier Transform (FFT). All the FFT spectra involve the horizontal and vertical components corresponding respectively to longitudinal and transversal trabeculae. By visual inspection, we measured the spreading angles: Dispersion Longitudinal Index (DLI) and Dispersion Transverse Index (DTI) and calculated DA = 180/(DLI+DTI). To test the reliability of DA assessment, we synthesized images simulating radiological projections of periodic structures with elements more or less disoriented.

Results: Firstly, we tested synthetic images which comprised a large variety of structures from highly anisotropic structure to the almost isotropic, DA was ranging from 1.3 to 3.8 respectively. The analysis of the FFT spectra was performed by two observers, the Coefficients of Variation were 1.5% and 3.1 % for intra-and inter-observer reproducibility, respectively. In 22 post-menopausal women with osteoporotic fracture cases and 44 age-matched controls, DA values were respectively 1.87 +/- 0.15 versus 1.72 +/- 0.18 (p = 0.001). From the ROC analysis, the Area Under Curve (AUC) were respectively 0.65, 0.62, 0.64, 0.77 for lumbar spine, femoral neck, total femoral BMD and DA.

Conclusion: The highest DA values in fracture cases suggest that the structure is more anisotropic in osteoporosis due to preferential deletion of trabeculae in some directions.

No MeSH data available.


Related in: MedlinePlus

Vertebral fracture case a Region of Interest (ROI) of the digitized radiographic image of calcaneus trabecular bone. b FFT spectrum DLI : Dispersion Longitudinal Index, spreading angle of the longitudinal trabeculae DTI : Dispersion Transverse Index, spreading angle of the transverse trabeculae
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Figure 3: Vertebral fracture case a Region of Interest (ROI) of the digitized radiographic image of calcaneus trabecular bone. b FFT spectrum DLI : Dispersion Longitudinal Index, spreading angle of the longitudinal trabeculae DTI : Dispersion Transverse Index, spreading angle of the transverse trabeculae

Mentions: Trabecular bone was assimilated to an oriented structure with two main directions, the ROI including longitudinal and transversal trabeculae (Figure 1). All the FFT spectra of the calcaneus radiographs involved horizontal and vertical conponents (Figures 2 and 3). The horizontal components were indicative of the longitudinal trabeculae fabric and the vertical components were indicative of the transverse trabeculae fabric. We have to notice that the so-called horizontal and vertebral trabeculae were so described on the ROI, which was slightly rotated by comparison to the original image. The limit between high energy area representing trabeculae and low energy area corresponding to the noise on the FFT spectrum were visually determined by the operator. We measured the spreading angles of the longitudinal and the transversal trabeculae named respectively the Dispersion Longitudinal Index (DLI) and the Dispersion Transverse Index (DTI). In order to obtain an average value, the DTI and DLI parameters were measured in the two symmetrical parts of the FFT spectrum conponents (Figures 2b and 3b).


A new anisotropy index on trabecular bone radiographic images using the fast Fourier transform.

Brunet-Imbault B, Lemineur G, Chappard C, Harba R, Benhamou CL - BMC Med Imaging (2005)

Vertebral fracture case a Region of Interest (ROI) of the digitized radiographic image of calcaneus trabecular bone. b FFT spectrum DLI : Dispersion Longitudinal Index, spreading angle of the longitudinal trabeculae DTI : Dispersion Transverse Index, spreading angle of the transverse trabeculae
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Related In: Results  -  Collection

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Figure 3: Vertebral fracture case a Region of Interest (ROI) of the digitized radiographic image of calcaneus trabecular bone. b FFT spectrum DLI : Dispersion Longitudinal Index, spreading angle of the longitudinal trabeculae DTI : Dispersion Transverse Index, spreading angle of the transverse trabeculae
Mentions: Trabecular bone was assimilated to an oriented structure with two main directions, the ROI including longitudinal and transversal trabeculae (Figure 1). All the FFT spectra of the calcaneus radiographs involved horizontal and vertical conponents (Figures 2 and 3). The horizontal components were indicative of the longitudinal trabeculae fabric and the vertical components were indicative of the transverse trabeculae fabric. We have to notice that the so-called horizontal and vertebral trabeculae were so described on the ROI, which was slightly rotated by comparison to the original image. The limit between high energy area representing trabeculae and low energy area corresponding to the noise on the FFT spectrum were visually determined by the operator. We measured the spreading angles of the longitudinal and the transversal trabeculae named respectively the Dispersion Longitudinal Index (DLI) and the Dispersion Transverse Index (DTI). In order to obtain an average value, the DTI and DLI parameters were measured in the two symmetrical parts of the FFT spectrum conponents (Figures 2b and 3b).

Bottom Line: The analysis of the FFT spectra was performed by two observers, the Coefficients of Variation were 1.5% and 3.1 % for intra-and inter-observer reproducibility, respectively.From the ROC analysis, the Area Under Curve (AUC) were respectively 0.65, 0.62, 0.64, 0.77 for lumbar spine, femoral neck, total femoral BMD and DA.The highest DA values in fracture cases suggest that the structure is more anisotropic in osteoporosis due to preferential deletion of trabeculae in some directions.

View Article: PubMed Central - HTML - PubMed

Affiliation: Equipe Inserm 658, Hôpital Porte Madeleine, BP 2439, 45032 Orléans Cedex 1, France. brunet-imbault@libertysurf.fr

ABSTRACT

Background: The degree of anisotropy (DA) on radiographs is related to bone structure, we present a new index to assess DA.

Methods: In a region of interest from calcaneus radiographs, we applied a Fast Fourier Transform (FFT). All the FFT spectra involve the horizontal and vertical components corresponding respectively to longitudinal and transversal trabeculae. By visual inspection, we measured the spreading angles: Dispersion Longitudinal Index (DLI) and Dispersion Transverse Index (DTI) and calculated DA = 180/(DLI+DTI). To test the reliability of DA assessment, we synthesized images simulating radiological projections of periodic structures with elements more or less disoriented.

Results: Firstly, we tested synthetic images which comprised a large variety of structures from highly anisotropic structure to the almost isotropic, DA was ranging from 1.3 to 3.8 respectively. The analysis of the FFT spectra was performed by two observers, the Coefficients of Variation were 1.5% and 3.1 % for intra-and inter-observer reproducibility, respectively. In 22 post-menopausal women with osteoporotic fracture cases and 44 age-matched controls, DA values were respectively 1.87 +/- 0.15 versus 1.72 +/- 0.18 (p = 0.001). From the ROC analysis, the Area Under Curve (AUC) were respectively 0.65, 0.62, 0.64, 0.77 for lumbar spine, femoral neck, total femoral BMD and DA.

Conclusion: The highest DA values in fracture cases suggest that the structure is more anisotropic in osteoporosis due to preferential deletion of trabeculae in some directions.

No MeSH data available.


Related in: MedlinePlus