Projection Effect Errors in Biomaterials and Bone Research

Micoradiography and backscattered electron (BSE) imaging are techniques used to investigate the morphologic, histometric, and mineral content changes at the bone/biomaterials interface. Investigators have shown that the superimposition of multiple tissue layers can cause errors with both the morphologic observations and the histometric measurements of bone. The objective of this study was to document errors in the bone mineral content measurements associated with overlapping tissues. Using a digital image analysis system, microradiographic and BSE images from canine cortical and cancellous bone were captured and analyzed. The results of this study showed that microradiography had more projection effect errors associated with the morphology and histometry. The BSE technique provided substantially better resolution of the bone morphology and showed significantly more (p$0.05) bone surface perimeter than the microradiographic technique. Contrary to the literature, the BSE images did not show less bone area than the microradiographic images of the identical regions. This discrepancy was explained by projection effect errors and over penetration artifacts of the X-ray beam. Unique to this study was the documentation that microradiography has inherent projection effect errors associated with mineral content measurements. The SSE images had significantly more (p$0.05) graylevels present than the microradiographic images. Due to the limited tissue overlap, the BSE images provide excellent morphologic resolution, accurate bone histometry and the ability to accurately measure the mineral content of cortical and cancellous bone at a microscopic level

Stereoscopic Analysis of Trabecular Bone Orientation in Proximal Human Tibias

The three-dimensional orientation of trabeculae is a key factor in determining the load carrying capabilities of cancellous bone. Previous biomechanical studies have shown that proximal tibias resected parallel to the articulating surface are stronger and stiffer than the contralateral tibias resected perpendicular to the long axis of the bone. However, morphologic evidence was not provided to help explain the mechanical differences. To determine the orientation of the trabeculae in the medial condyle for both parallel cut and perpendicular cut specimens, a scanning electron microscope and stereoscopic techniques were used. Data showed that tibias cut parallel to the articular surface had trabeculae oriented nearly vertical with a mean angle of 4.5° ± 14.7° (range, 0° to 56.3°). The contralateral tibias cut perpendicular to the long axis of the tibia had trabeculae oriented at a mean angle of 36.0° ± 12.2° (range, 16.1° to 67.4 °) from vertical. The differences between the two resection techniques were shown to be significant (p s. 0.01) using an Analysis of Variance. This study provided morphologic evidence to explain why previous specimens cut parallel to the articular surface had stronger and stiffer cancellous bone than the contralateral specimens cut perpendicular to the long axis of the tibia. This information is important in understanding the load carrying capabilities of cancellous bone and how it may be applied to improving the clinical results of primary total knee arthroplasty

Validation of Energy Dispersive X-Ray Spectrometry as a Method to Standardize Backscattered Electron Images of Bone

The use of backscattered electron (BSE) imaging as a tool for the qualitative measurement of mineral content in bone has been well documented. The challenge still remains to develop BSE imaging as a tool for quantitative mineral content analysis in bone. The limiting factor has been the ability to standardize the BSE signal within and between laboratories. Energy dispersive x-ray spectrometry (EDX) has been proposed as a method to standardize the BSE operating environment. The goal of this study is to investigate the relationship between EDX-determined wt.% Ca measurements and BSE graylevels. A comparison with traditional ash content measurements will indicate the validity of the procedure. A comparative study was performed on a series of bones representing a broad range of mineralization. Results confirmed a high correlation between BSE graylevels and wt.% Ca measured with EDX. However, the BSE method consistently underestimated the mineral content of bone determined by traditional ash measurements. The results suggest that quantitative BSE imaging can be standardized by EDX measurements, but an empirically determined correction may be necessary if comparisons with known and accepted mineral content measurement techniques are to be performed. Further investigation into the nature of this empirical correction is warranted before the procedure can be universally applied to bone mineral content analysis

Consistency in Calibrated Backscattered Electron Images of Calcified Tissues and Minerals Analyzed in Multiple Imaging Sessions

Pure metal standards have been used to calibrate the operating environment in quantitative backscattered electron (BSE) imaging of mineralized tissue, allowing comparisons to be made between various mineralization states of bone at the microscopic level. It has not previously been documented that calibration procedures produce consistent, reliable results over multiple imaging sessions. In this study, BSE images were obtained from bones, pure metals, and a naturally occurring mineral in multiple imaging sessions over a six day period. The graylevel histogram profile (GHP) from each specimen was analyzed for changes in the shape and relative placement on the graylevel spectrum. Computer controlled calibration and a retrospective calibration method using pure aluminum and pure magnesium-aluminum-zinc demonstrated consistency between imaging sessions. Calibrated weighted mean gray levels (WMGLs) for biological materials had an average standard deviation of 5.9 graylevels (2.4% variation) during the course of the study. WMGLs for inorganic materials had an average standard deviation of 0.9 graylevels (0.4% variation). A trend towards increased image brightness, due to specimen and/or embedding media degradation, was observed in the biological tissues. No increase in brightness was observed for the inorganic specimens. Kurtosis and skewness tests revealed a slight deviation from normality in all specimens, which remained consistent between multiple imaging sessions. These results demonstrate that BSE image analysis of bones and mineral can be calibrated with negligible precision error allowing comparisons between data within and between multiple imaging sessions

Reproducible Method for Calibrating the Backscattered Electron Signal for Quantitative Assessment of Mineral Content in Bone

Backscattered electron (BSE) imaging shows promise for orthopaedic and bone research. BSE images of bone may be captured on-line directly from the scanning electron microscope (SEM), and then analyzed to produce a backscattered electron profile (BSEP), a modified image graylevel histogram which is representative of the mineral content in bone. The goals of this work were 1) develop a reproducible graylevel calibration technique for bone specimens, and 2) determine a conservative time interval during which SEM operating conditions would remain stable. Calibration standards containing pure aluminum and pure magnesium wires were placed in the SEM with human cancellous bone. Baseline imaging conditions were first established by adjusting the SEM until the bone image displayed good resolution and graylevel separation between regions of different mineral content. Microscope brightness and contrast controls were randomly changed to initiate the new operating conditions of another imaging session, and graylevel values from the calibration metals were used to readjust the microscope back to baseline operating conditions. Weighted mean graylevel values of the BSEPs from calibration trials were compared to those of the baseline. Data showed that bone images could be reproduced within 1.2 percent. It was also concluded that our equipment required calibration checks at 20 minute intervals

Optimal Flying Wings: A Numerical Optimization Study

Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/97067/1/AIAA2012-1758.pd

The beneficial effect of hydroxyapatite lasts: A randomized radiostereometric trial comparing hydroxyapatite-coated, uncoated, and cemented tibial components for up to 16 years

Analysis and Stochastic