Limits...
Osteoporosis imaging: effects of bone preservation on MDCT-based trabecular bone microstructure parameters and finite element models.

Baum T, Grande Garcia E, Burgkart R, Gordijenko O, Liebl H, Jungmann PM, Gruber M, Zahel T, Rummeny EJ, Waldt S, Bauer JS - BMC Med Imaging (2015)

Bottom Line: Four thoracic vertebrae were harvested from each of three fresh human cadavers (n=12).Multi-detector computed tomography (MDCT) images were obtained at baseline, 3 and 6 month follow-up.In the intervals between MDCT imaging, two vertebrae from each donor were formalin-fixed and frozen, respectively.

View Article: PubMed Central - PubMed

Affiliation: Institut für Radiologie, Klinikum rechts der Isar, Technische Universität München, Ismaninger Str. 22, 81675, München, Germany. thbaum@gmx.de.

ABSTRACT

Background: Osteoporosis is defined as a skeletal disorder characterized by compromised bone strength due to a reduction of bone mass and deterioration of bone microstructure predisposing an individual to an increased risk of fracture. Trabecular bone microstructure analysis and finite element models (FEM) have shown to improve the prediction of bone strength beyond bone mineral density (BMD) measurements. These computational methods have been developed and validated in specimens preserved in formalin solution or by freezing. However, little is known about the effects of preservation on trabecular bone microstructure and FEM. The purpose of this observational study was to investigate the effects of preservation on trabecular bone microstructure and FEM in human vertebrae.

Methods: Four thoracic vertebrae were harvested from each of three fresh human cadavers (n=12). Multi-detector computed tomography (MDCT) images were obtained at baseline, 3 and 6 month follow-up. In the intervals between MDCT imaging, two vertebrae from each donor were formalin-fixed and frozen, respectively. BMD, trabecular bone microstructure parameters (histomorphometry and fractal dimension), and FEM-based apparent compressive modulus (ACM) were determined in the MDCT images and validated by mechanical testing to failure of the vertebrae after 6 months.

Results: Changes of BMD, trabecular bone microstructure parameters, and FEM-based ACM in formalin-fixed and frozen vertebrae over 6 months ranged between 1.0-5.6% and 1.3-6.1%, respectively, and were not statistically significant (p>0.05). BMD, trabecular bone microstructure parameters, and FEM-based ACM as assessed at baseline, 3 and 6 month follow-up correlated significantly with mechanically determined failure load (r=0.89-0.99; p<0.05). The correlation coefficients r were not significantly different for the two preservation methods (p>0.05).

Conclusions: Formalin fixation and freezing up to six months showed no significant effects on trabecular bone microstructure and FEM-based ACM in human vertebrae and may both be used in corresponding in-vitro experiments in the context of osteoporosis.

Show MeSH

Related in: MedlinePlus

MDCT-based FEM of a representative vertebral body. The BMD distribution is color-coded and used for the assignment of the material properties for each element of the FEM
© Copyright Policy - open-access
Related In: Results  -  Collection

License 1 - License 2
getmorefigures.php?uid=PMC4482285&req=5

Fig2: MDCT-based FEM of a representative vertebral body. The BMD distribution is color-coded and used for the assignment of the material properties for each element of the FEM

Mentions: Finite element models (FEM) were computed in the baseline, 3 and 6 month follow-up MDCT images to assess apparent compressive modulus (ACM) of each vertebral body in the superior-inferior direction. Three-dimensional models of the vertebrae were created from the MDCT images by identifying the contour of the vertebrae. The in-plane MDCT resolution was selected as mesh refinement. The uniform hexahedral meshes were generated by using ANSYS Workbench (ANSYS, Canonsburg, PA, USA). The material properties of each element were assigned by using a mapping procedure. Firstly, the elements’ values in [HU] were converted into BMD values ρBMD in [g/cm3 calcium hydroxyapatite] by using the calibration phantom. Secondly, the elements’ information (position and ρBMD) were saved in a text file. Thirdly, a subroutine written in APDL (ANSYS Parametric Design Language) was used to read the text file and assign the material properties to each element (Fig. 2). The equation ρash = 1.22 ρBMD + 0.0526 g/cm3 was used for the conversion of ρBMD into ρash [19, 20]. The isotropic elastic modulus E in [N/mm2] was determined for each element by using the established relationships between E and ρash as reported previously [21–23]: E = 33900ρash2.20; ρash ≤ 0.27, E = 5307ρash + 469; 0.27 < ρash < 0.6, and E = 10200 ρash2.01; ρash ≥ 0.6. Each element was assigned a Poisson’s ratio of ν = 0.3 [23]. Finally, the apparent compressive modulus (ACM) of the FEMs in [N/mm2] was obtained by applying a displacement force on one vertebral endplate and fixing the opposite one.Fig. 2


Osteoporosis imaging: effects of bone preservation on MDCT-based trabecular bone microstructure parameters and finite element models.

Baum T, Grande Garcia E, Burgkart R, Gordijenko O, Liebl H, Jungmann PM, Gruber M, Zahel T, Rummeny EJ, Waldt S, Bauer JS - BMC Med Imaging (2015)

MDCT-based FEM of a representative vertebral body. The BMD distribution is color-coded and used for the assignment of the material properties for each element of the FEM
© Copyright Policy - open-access
Related In: Results  -  Collection

License 1 - License 2
Show All Figures
getmorefigures.php?uid=PMC4482285&req=5

Fig2: MDCT-based FEM of a representative vertebral body. The BMD distribution is color-coded and used for the assignment of the material properties for each element of the FEM
Mentions: Finite element models (FEM) were computed in the baseline, 3 and 6 month follow-up MDCT images to assess apparent compressive modulus (ACM) of each vertebral body in the superior-inferior direction. Three-dimensional models of the vertebrae were created from the MDCT images by identifying the contour of the vertebrae. The in-plane MDCT resolution was selected as mesh refinement. The uniform hexahedral meshes were generated by using ANSYS Workbench (ANSYS, Canonsburg, PA, USA). The material properties of each element were assigned by using a mapping procedure. Firstly, the elements’ values in [HU] were converted into BMD values ρBMD in [g/cm3 calcium hydroxyapatite] by using the calibration phantom. Secondly, the elements’ information (position and ρBMD) were saved in a text file. Thirdly, a subroutine written in APDL (ANSYS Parametric Design Language) was used to read the text file and assign the material properties to each element (Fig. 2). The equation ρash = 1.22 ρBMD + 0.0526 g/cm3 was used for the conversion of ρBMD into ρash [19, 20]. The isotropic elastic modulus E in [N/mm2] was determined for each element by using the established relationships between E and ρash as reported previously [21–23]: E = 33900ρash2.20; ρash ≤ 0.27, E = 5307ρash + 469; 0.27 < ρash < 0.6, and E = 10200 ρash2.01; ρash ≥ 0.6. Each element was assigned a Poisson’s ratio of ν = 0.3 [23]. Finally, the apparent compressive modulus (ACM) of the FEMs in [N/mm2] was obtained by applying a displacement force on one vertebral endplate and fixing the opposite one.Fig. 2

Bottom Line: Four thoracic vertebrae were harvested from each of three fresh human cadavers (n=12).Multi-detector computed tomography (MDCT) images were obtained at baseline, 3 and 6 month follow-up.In the intervals between MDCT imaging, two vertebrae from each donor were formalin-fixed and frozen, respectively.

View Article: PubMed Central - PubMed

Affiliation: Institut für Radiologie, Klinikum rechts der Isar, Technische Universität München, Ismaninger Str. 22, 81675, München, Germany. thbaum@gmx.de.

ABSTRACT

Background: Osteoporosis is defined as a skeletal disorder characterized by compromised bone strength due to a reduction of bone mass and deterioration of bone microstructure predisposing an individual to an increased risk of fracture. Trabecular bone microstructure analysis and finite element models (FEM) have shown to improve the prediction of bone strength beyond bone mineral density (BMD) measurements. These computational methods have been developed and validated in specimens preserved in formalin solution or by freezing. However, little is known about the effects of preservation on trabecular bone microstructure and FEM. The purpose of this observational study was to investigate the effects of preservation on trabecular bone microstructure and FEM in human vertebrae.

Methods: Four thoracic vertebrae were harvested from each of three fresh human cadavers (n=12). Multi-detector computed tomography (MDCT) images were obtained at baseline, 3 and 6 month follow-up. In the intervals between MDCT imaging, two vertebrae from each donor were formalin-fixed and frozen, respectively. BMD, trabecular bone microstructure parameters (histomorphometry and fractal dimension), and FEM-based apparent compressive modulus (ACM) were determined in the MDCT images and validated by mechanical testing to failure of the vertebrae after 6 months.

Results: Changes of BMD, trabecular bone microstructure parameters, and FEM-based ACM in formalin-fixed and frozen vertebrae over 6 months ranged between 1.0-5.6% and 1.3-6.1%, respectively, and were not statistically significant (p>0.05). BMD, trabecular bone microstructure parameters, and FEM-based ACM as assessed at baseline, 3 and 6 month follow-up correlated significantly with mechanically determined failure load (r=0.89-0.99; p<0.05). The correlation coefficients r were not significantly different for the two preservation methods (p>0.05).

Conclusions: Formalin fixation and freezing up to six months showed no significant effects on trabecular bone microstructure and FEM-based ACM in human vertebrae and may both be used in corresponding in-vitro experiments in the context of osteoporosis.

Show MeSH
Related in: MedlinePlus