Effect of SR-microCT radiation on the mechanical integrity of trabecular bone using in situ mechanical testing and digital volume correlation

Abstract

The use of synchrotron radiation micro-computed tomography (SR-microCT) is becoming increasingly popular for studying the relationship between microstructure and bone mechanics subjected to in situ mechanical testing. However, it is well known that the effect of SR X-ray radiation can considerably alter the mechanical properties of bone tissue. Digital volume correlation (DVC) has been extensively used to compute full-field strain distributions in bone specimens subjected to step-wise mechanical loading, but tissue damage from sequential SR-microCT scans has not been previously addressed. Therefore, the aim of this study is to examine the influence of SR irradiation-induced microdamage on the apparent elastic properties of trabecular bone using DVC applied to in situ SR-microCT tomograms obtained with different exposure times. Results showed how DVC was able to identify high local strain levels (> 10,000 µε) corresponding to visible microcracks at high irradiation doses (~ 230 kGy), despite the apparent elastic properties remained unaltered. Microcracks were not detected and bone plasticity was preserved for low irradiation doses (~ 33 kGy), although image quality and consequently, DVC performance were reduced. DVC results suggested some local deterioration of tissue that might have resulted from mechanical strain concentration further enhanced by some level of local irradiation even for low accumulated dose.

Optimization of digital volume correlation computation in SR‐microCT images of trabecular bone and bone‐biomaterial systems

“…), and microcracks appear clearly visible in the tissue after continuous irradiation. Therefore, this study used low exposures times (∼2 min scanning time) and kept the specimens immersed in saline solution during image acquisition, in order to preserve the mechanical integrity of the analysed specimens (Peña‐Fernández et al ., ). These two factors negatively contributed to the quality of the acquired tomograms (Fig.…”

“…The final projection was not used for reconstruction, but was compared to the first image to check for experimental problems including sample deformation and bulk movements (Atwood et al ., ). The exposure time was set to 64 ms per projection, leading to a nominal absorbed radiation dose of 4.7 kGy per scan, therefore minimizing SR irradiation‐induced damage during image acquisition (Peña‐Fernández et al ., ; Fig. ).…”

Applications of X‐ray computed tomography for the evaluation of biomaterial‐mediated bone regeneration in critical‐sized defects

“…Generally, DVC methods can be described in three main steps: (1) generation of volumetric images of samples in both unloaded and loaded conditions; (2) measurement of a discrete displacement field throughout the sample by a correlation procedure between grey‐level intensities of both unloaded and loaded images and (3) calculation of the strain tensor field from the displacement vector field. DVC was firstly applied to XCT images of trabecular bone tissue subjected to uniaxial compression load (Bay, ) and had since been successfully applied to trabecular bone (Gillard et al ., ; Peña Fernández et al ., ; Peña Fernández et al ., ), cortical bone (Christen et al ., ; Peña Fernández et al ., ) and whole bones (Hussein et al ., ; Tozzi et al ., ).…”

“…The attenuation depends not only on the material sample but also on the energy spectrum of the X‐ray source. Because the imaging process is quasi nondestructive, as high levels of exposure to X‐ray radiation are known to induce damage in biological samples (Barth et al ., ; Peña Fernández et al ., ), the internal features of the same sample may be examined multiple times in different conditions. The technical aspects of XCT imaging and analysis have been presented in several chapters and reviews (Hsieh, ; Stock, ; Bouxsein et al ., ; Hampel, ; Hermanek et al ., ).…”

Anisotropic Crack Propagation and Deformation in Dentin Observed by Four-Dimensional X-ray Nano-Computed Tomography

“…Digital volume correlation (DaVis v8.4, LaVision, Germany) was carried out on each of the CT volume image sequences to map the local deformation under the indenter tip. DaVis software is based on a local approach operating on the intensity values (grey-scale) of 3D images, which has been extensively used in hard tissue biomechanics [52,57,58]. Details of the operating principles and algorithm are detailed elsewhere [59].…”