Limitations of using micro-computed tomography to predict bone-implant contact and mechanical fixation

Fixation of metallic implants to bone through osseointegration is important in orthopaedics and dentistry. Model systems for studying this phenomenon would benefit from a non-destructive imaging modality so that mechanical and morphological endpoints can more readily be examined in the same specimens. The purpose of this study was to assess the utility of an automated microcomputed tomography (μCT) program for predicting bone-implant contact (BIC) and mechanical fixation strength in a rat model. Femurs in which 1.5-mm-diameter titanium implants had been in place for 4 weeks were either embedded in polymethylmethacrylate (PMMA) for preparation of 1-mm-thick cross-sectional slabs (16 femurs: 32 slabs) or were used for mechanical implant pull-out testing (n= 18 femurs). All samples were scanned by μCT at 70 kVp with 16 μm voxels and assessed by the manufacturer's software for assessing 'osseointegration volume per total volume' (OV/TV). OV/TV measures bone volume per total volume (BV/TV) in a 3-voxel-thick ring that by default excludes the 3 voxels immediately adjacent to the implant to avoid metal-induced artefacts. The plastic-embedded samples were also analysed by backscatter scanning electron microscopy (bSEM) to provide a direct comparison of OV/TV with a well-accepted technique for BIC. In μCT images in which the implant was directly embedded within PMMA, there was a zone of elevated attenuation (>50% of the attenuation value used to segment bone from marrow) which extended 48 μm away from the implant surface. Comparison of the bSEM and μCT images showed high correlations for BV/TV measurements in areas not affected by metal-induced artefacts. In addition for bSEM images, we found that there were high correlations between peri-implant BV/TV within 12 μm of the implant surface and BIC (correlation coefficients ≥0.8, p < 0.05). OV/TV as measured on μCT images was not significantly correlated with BIC as measured on the corresponding bSEM images. However, OV/TV was significantly, but weakly, correlated with implant pull-out strength (r= 0.401, p= 0.049) and energy to failure (r= 0.435, p= 0.035). Thus, the need for the 48-μm-thick exclusion zone in the OV/TV program to avoid metal-induced artefacts with the scanner used in this study means that it is not possible to make bone measurements sufficiently close to the implant surface to obtain an accurate assessment of BIC. Current generation laboratory-based μCT scanners typically have voxel sizes of 6-8 μm or larger which will still not overcome this limitation. Thus, peri-implant bone measurements at these resolutions should only be used as a guide to predict implant fixation and should not be over-interpreted as a measurement of BIC. Newer generation laboratory-based μCT scanners have several improvements including better spatial resolution and X-ray sources and appear to have less severe metal-induced artefacts, but will need appropriate validation as they become available to researchers. Regardless of the μCT scanner being used, we recommend that detailed validation studies be performed for any study using metal implants because variation in the composition and geometry of the particular implants used may lead to different artefact patterns.     

Winning the Battles, Losing the War? Rethinking Methodology for Forensic Computing Research

In the last 10 years, Forensic computing (FC) has emerged in response to the challenges of illegal, criminal and other inappropriate on-line behaviours. As awareness of the need for the accurate and legally admissible collection, collation, analysis and presentation of digital data has grown, so has recognition of the challenges this requirement poses for technical, legal and organisational responses to these on-line behaviours. Despite recognition of the multi-dimensional nature of these behaviours and the challenges faced, agreement on coherent frameworks for understanding and responding to these issues, their impacts and their interrelationships appears to remain a long way off. As a consequence, while significant advances have been made within technical, organisational and legal ‘solution centred paradigms’, the net result appears to be a case of ‘winning the battles but losing the war’ on computer misuse and e-crime. This paper examines this situation and reflects on its implications for academic researchers’ methodological approach to understanding and responding to these challenges. This paper suggests the need to reconceptualise the term ‘solution’ and advocates an additional methodological step, (that it is anticipated will generate data) for the development of a framework to map the value propositions of, and interrelationships between the individual sets of responses within the dynamically evolving FC landscape. By exposing issues, responses and underlying assumptions it is anticipated that this will improve the possibility of calibrated responses that more effectively and coherently balance the interests for security, privacy and legal admissibility.     

Changes in oxytocin and cortisol levels in primiparous cows after changing from 21 days of suckling calves to machine milking

Four first-calvers of the Black-Pied breed with calves sucking their milk until day 21 of lactation were included in a trial. One suckler cow had four calves. The trial took place within five days which included days 20 and 21 in the first-calvers, that means the last two days with sucking calves (designated as day 1 and day 2 of trial-first and second calf sucking) and days 22 and 24, that means the first and third day after the cows were moved to a cowshed (designated as the third and fifth day of trial-first and third evening machine milking). The first-calvers were separated from the calves and moved to a cowshed at 8 o'clock a.m. on day 3 of trial (Tab. I). The responses to calf sucking were investigated after four-hour prevention of calves to approach the cows (12.00-16.00 p.m.). Blood was sampled with a catheter which was introduced into the vena jugularis a day before the trial outset. Blood samples for cortisol determination were taken in two-hour intervals (when the cows were moved to the cowshed twice in half-an-hour interval and once in an hour interval). Blood samplings were effectuated by day, before, during and after milking, or sucking. Machine milking was finished within 7 to 8 minutes. Two to four calves were intensively sucking a cow within the first 15 minutes, then sucking was irregular. Plasma samples were deep-frozen and stored at -20 degrees C until determinations were performed. Oxytocin and cortisol in the blood plasma were determined by radioassays. In the first evening machine milking (day 3) the second cow yielded 8.23 kg milk while on day 5 in the third milking it was 7.98 kg. The other first-calvers gave by 30-45% less milk on day 3 in comparison with evening milking on day 5 (Tab. II). A trend of the higher average values of oxytocin was observed in machine milking on day 5 of trial if compared with the values recorded during calf sucking, or the first milking (day 3), Fig. 1a, Tab. III. The mean oxytocin concentration during 7-minute milking (12.39 +/- 5.81 pg/ml) was significantly lower in the first-calvers on day 3 in comparison with the mean values recorded on day 5 (28.01 +/- 18.56 pg/ml; P < 0.001), or during sucking (18.32 +/- 7.15 pg/ml; P < 0.01).(ABSTRACT TRUNCATED AT 400 WORDS)