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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.

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Representative MDCT image of a vertebra: a circular region of interest (white) was placed in the ventral half of the vertebral body in the 15 most central slices equidistant to its endplates. The calibration phantom was positioned below the plastic box containing the vertebrae
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Fig1: Representative MDCT image of a vertebra: a circular region of interest (white) was placed in the ventral half of the vertebral body in the 15 most central slices equidistant to its endplates. The calibration phantom was positioned below the plastic box containing the vertebrae

Mentions: MDCT images obtained at baseline, 3 and 6 month follow-up were transferred to a remote LINUX workstation and loaded into an in-house developed program based on IDL (Interactive Data Language, Research Systems, Bolder, CO, USA). Firstly, the 15 most central slices displaying the vertebra equidistant to its endplates were identified. Then, 15 circular regions of interest (ROIs) were manually placed in the ventral half of the vertebral body in the selected slices of the MDCT images similar to QCT-based BMD measurements [5]. The circular ROIs had a diameter of 10 mm (Fig. 1). ROIs’ pixel attenuations in [HU; Hounsfield Units] were converted into BMD values in [mg/cm3 calcium hydroxyapatite] by using the calibration phantom. Afterwards, MDCT images were binarized to calculate trabecular bone microstructure parameters. An optimized global threshold was applied to all MDCT images. Similar to previous studies, 200 mg/cm3 calcium hydroxyapatite was identified as optimized global threshold [16, 17]. Four morphometric parameters were calculated in the ROIs in analogy to standard histomorphometry using the mean intercept length method [18]: bone volume divided by total volume (BV/TV), trabecular number (TbN; [mm−1]), trabecular separation (TbSp; [mm]), and trabecular thickness (TbTh; [mm]). Parameters were labeled as apparent (app.) values, since given the limited spatial resolution they cannot depict the true trabecular microstructure. Furthermore, fractal dimension (FD) as texture measurement of the trabecular bone microstructure was determined in the MDCT images using a box counting algorithm as previously described [16]. The reproducibility error expressed as the root mean square error coefficient of variation amounted to 1.2 % for BMD and ranged between 0.5 % and 2.0 % as outlined in a previous study [16].Fig. 1


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)

Representative MDCT image of a vertebra: a circular region of interest (white) was placed in the ventral half of the vertebral body in the 15 most central slices equidistant to its endplates. The calibration phantom was positioned below the plastic box containing the vertebrae
© Copyright Policy - open-access
Related In: Results  -  Collection

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

Fig1: Representative MDCT image of a vertebra: a circular region of interest (white) was placed in the ventral half of the vertebral body in the 15 most central slices equidistant to its endplates. The calibration phantom was positioned below the plastic box containing the vertebrae
Mentions: MDCT images obtained at baseline, 3 and 6 month follow-up were transferred to a remote LINUX workstation and loaded into an in-house developed program based on IDL (Interactive Data Language, Research Systems, Bolder, CO, USA). Firstly, the 15 most central slices displaying the vertebra equidistant to its endplates were identified. Then, 15 circular regions of interest (ROIs) were manually placed in the ventral half of the vertebral body in the selected slices of the MDCT images similar to QCT-based BMD measurements [5]. The circular ROIs had a diameter of 10 mm (Fig. 1). ROIs’ pixel attenuations in [HU; Hounsfield Units] were converted into BMD values in [mg/cm3 calcium hydroxyapatite] by using the calibration phantom. Afterwards, MDCT images were binarized to calculate trabecular bone microstructure parameters. An optimized global threshold was applied to all MDCT images. Similar to previous studies, 200 mg/cm3 calcium hydroxyapatite was identified as optimized global threshold [16, 17]. Four morphometric parameters were calculated in the ROIs in analogy to standard histomorphometry using the mean intercept length method [18]: bone volume divided by total volume (BV/TV), trabecular number (TbN; [mm−1]), trabecular separation (TbSp; [mm]), and trabecular thickness (TbTh; [mm]). Parameters were labeled as apparent (app.) values, since given the limited spatial resolution they cannot depict the true trabecular microstructure. Furthermore, fractal dimension (FD) as texture measurement of the trabecular bone microstructure was determined in the MDCT images using a box counting algorithm as previously described [16]. The reproducibility error expressed as the root mean square error coefficient of variation amounted to 1.2 % for BMD and ranged between 0.5 % and 2.0 % as outlined in a previous study [16].Fig. 1

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