Martine Wevers

MRI and x-ray CT study of spatial distribution of core breakdown in 'Conference' pears.

Two non-destructive tomographic techniques, X-ray CT imaging and magnetic resonance imaging (MRI), were applied to study the development of core breakdown disorder in Conference pears (Pyrus communis cv. Conference). This disorder, which is characterized by brown discoloration of the tissue and development of cavities, is induced by elevated CO(2) and decreased O(2) levels during controlled atmosphere storage. Tomographic images of pears stored for 10 months under disorder inducing conditions, were acquired with both techniques and compared to the actual slices. Both X-ray and MRI were able to differentiate between unaffected tissue, brown tissue and cavities. A simple image-processing program, based on threshold values, was developed to determine the area percentage of affected and unaffected tissue as well as the cavity and core area per slice. For all three imaging techniques the area percentage brown tissue per slice increased with the diameter of the pear, but was systematically underestimated by 12% and 6% for, respectively, X-ray and MRI, compared to the actual slices. The area percentage cavity corresponded very well for all techniques. It was also found that the contours of the brown tissue were parallel to the fruit boundaries, suggesting a relation between the disorder symptoms and gas diffusion properties of the fruit. It was concluded that MRI is the most appropriate technique to study the development of core breakdown disorder during postharvest storage in future experiments.

Use of microfocus computerized tomography as a new technique for characterizing bone tissue around oral implants.

Qualitative and quantitative analysis of peri-implant tissues around retrieved oral implants is typically done by means of light microscopy on thin histological sections containing the metal surface and the undecalcified bone. It remains, however, a labor-intensive and thus time-consuming job. Moreover, it is a destructive technique that allows tissue quantification in only a limited number of two-dimensional sections. As an alternative, we evaluated the bone structure around screw-shaped titanium implants by means of microfocus computerized tomography (micro-CT) because it presents a number of advantages compared to conventional sectioning techniques: micro-CT is nondestructive, fast, and allows a fully three-dimensional characterization of the bone structure around the implant. Images can be reconstructed in an arbitrary plane, and three-dimensional reconstructions are also possible. Because of its high resolution, individual trabeculae can be visualized. The accuracy of micro-CT was qualitatively evaluated by comparing histological sections with the corresponding CT slices for the same specimen. The overall trabecular structure is very similar according to both techniques. Even very close to the interface, the titanium implant does not seem to produce significant artifacts. Furthermore, because the complete digital data on the trabecular bone structure around the implant is available, it is possible to create finite-element models of the bone-implant system that model the trabeculae in detail so that mechanical stress transfer at the interface can be studied at the level of individual trabeculae. Therefore, micro-CT seems to be very promising for the in vitro assessment of the three-dimensional bone structure around oral implants. Further research will be needed to evaluate its accuracy in a more quantitative way.

Analysis of the time course of core breakdown in 'Conference' pears by means of MRI and X-ray CT

Abstract Core breakdown in ‘Conference’ pears is a storage disorder, which is characterised by brown discolouration of the tissue and development of cavities. At the moment of purchase the consumer cannot detect these symptoms from the outside. In this paper magnetic resonance imaging (MRI) and X-ray computer tomography (X-ray CT) were applied to study non-destructively the time course of the disorder symptoms. Pears stored under disorder-inducing conditions were followed with both tomographic techniques during 6 months of controlled atmosphere storage. After 2 months, incipient browning could be detected with both techniques. However, the contrast between affected and unaffected tissue was higher on the MR images than on the X-ray CT scans. Two patterns of browning, radial and local, were observed. In the former, the contours of the brown tissue were concentric. Both patterns did not evolve or grow spatially over time, but only increased in their contrast to healthy tissue during storage. This result suggests a relation between the disorder and gas exchange properties of the fruit with the environment. It was also observed that the cavities grow at the expense of the brown tissue. To quantify the browning rate a contrast value was defined based on the ratio of pixel intensities of affected and unaffected tissue. The average browning rate did not differ substantially between the different pears and was equal to 0.0065±0.0005 days −1 .

X-ray CT and Magnetic Resonance Imaging to Study the Development of Core Breakdown in ‘Conference’ Pears

Two non-destructive tomographic techniques, X-ray CT imaging and magnetic resonance nimaging (MRI), were applied to study the development of core breakdown disorder in nConference pears (Pyrus communis cv.). This disorder, which is characterized by brown ndiscoloration of the tissue and development of cavities, is induced by elevated carbon dioxide nand decreased oxygen levels during controlled atmosphere storage. Tomographic images of npears stored for 10 months under disorder inducing conditions, were acquired with both ntechniques. The pears were cut into slices afterwards for comparison purposes. Both X-ray and nMRI were able to differentiate between unaffected tissue, brown tissue and cavities. A semi-automatic nimage processing program, based on threshold values, was developed to determine the narea percentage of affected (brown) and unaffected tissue as well as the cavity and core area per nslice. For all three imaging techniques the area percentage brown tissue per slice increased with nthe diameter of the pear, but was systematically underestimated by 12% and 6% for, nrespectively, X-ray and MRI, compared to the actual slices. The area percentage cavity ncorresponded very well for all techniques. It was also found that the contours of the brown tissue nwere parallel to the fruit boundaries, indicating that the disorder is gas diffusion related. It was nconcluded that MRI is the most appropriate technique to study the development of core nbreakdown disorder during postharvest storage in future experiments. However, from modeling nperspective, X-ray scans are more suited for validation purposes of respiration-diffusion models nof intact pears.

The effect of strain rate amplitude on peri-implant bone (re)modelling: A guinea pig experimental study

†Department of Prosthetic Dentistry, BIOMAT Research Group, Catholic University, Leuven, Belgium ‡Division of Biomechanics and Engineering Design, Department of Mechanical Engineering, Catholic University, Leuven, Belgium {Department of Biomaterials / Dentistry, University Medical Center, University of Nijmegen, Nijmegen, The Netherlands §Department of Metallurgy and Materials Engineering, Catholic University, Leuven, Belgium