Pauline Bléry, Yves Amouriq, Jeanpierre Guédon, Paul Pilet, Nicolas Normand, Nicolas Durand, Florent Espitalier, Aurore Arlicot, Olivier Malard, Pierre Weiss
The squamous cell carcinomas of the upper aero-digestive tract represent about ten percent of cancers. External
radiation therapy leads to esthetic and functional consequences, and to a decrease of the bone mechanical
abilities. For these patients, the oral prosthetic rehabilitation, including possibilities of dental implant placement,
is difficult. The effects of radiotherapy on bone microarchitecture parameters are not well known. Thus, the
purpose of this study is to assess the effects of external radiation on bone micro architecture in an experimental
model of 25 rats using micro CT. 15 rats were irradiated on the hind limbs by a single dose of 20 Grays, and 10
rats were non irradiated. Images of irradiated and healthy bone were compared. Bone microarchitecture
parameters (including trabecular thickness, trabecular number, trabecular separation, connectivity density and
tissue and bone volume) between irradiated and non-irradiated bones were calculated and compared using a
Mann and Whitney test. After 7 and 12 weeks, images of irradiated and healthy bone are different. Differences on
the irradiated and the healthy bone populations exhibit a statistical significance. Trabecular number, connectivity
density and closed porosity are less important on irradiated bone. Trabecular thickness and separation increase
for irradiated bone. These parameters indicate a decrease of irradiated bone properties. Finally, the external
irradiation induces changes on the bone micro architecture. This knowledge is of prime importance for better oral
prosthetic rehabilitation, including implant placement.
Bone microarchitecture is the predictor of bone quality or bone disease. It can only be measured on a bone biopsy,
which is invasive and not available for all clinical situations. Texture analysis on radiographs is a common way to
investigate bone microarchitecture. But relationship between three-dimension histomorphometric parameters and two-dimension
texture parameters is not always well known, with poor results. The aim of this study is to performed
angulated radiographs of the same region of interest and see if a better relationship between texture analysis on several
radiographs and histomorphometric parameters can be developed. Computed radiography images of dog (Beagle)
mandible section in molar regions were compared with high-resolution micro-CT (Computed-Tomograph) volumes.
Four radiographs with 27° angle (up, down, left, right, using Rinn ring and customized arm positioning system) were
performed from initial radiograph position. Bone texture parameters were calculated on all images. Texture parameters
were also computed from new images obtained by difference between angulated images. Results of fractal values in
different trabecular areas give some caracterisation of bone microarchitecture.
Shape description is an important step in image analysis. The skeleton is used as a simple, compact representation of a
shape. A skeleton represents the line centered in the shape and must be homotopic and one point wide. Current skeletonization
algorithms compute the skeleton over several image scans, using either thinning algorithms or distance transforms.
The principle of thinning is to delete points as one goes along, preserving the topology of the shape. On the other hand,
the maxima of the local distance transform identifies the skeleton and is an equivalent way to calculate the medial axis.
However, with this method, the skeleton obtained is disconnected so it is required to connect all the points of the medial
axis to produce the skeleton. In this study we introduce a translated distance transform and adapt an existing distance driven
homotopic algorithm to perform skeletonization with a single scan and thus allow the processing of unbounded images.
This method is applied, in our study, on micro scanner images of trabecular bones. We wish to characterize the bone micro
architecture in order to quantify bone integrity.
For some authors trabecular bone is highly visible in intraoral radiographs. For other authors, the observed intrabony
trabecular pattern is a representation of only the endosteal surface of cortical bone, not of intermedullary striae. The
purpose of this preliminary study was to investigate the true anatomical structures that are visible in routine dental
radiographs and classically denoted trabecular bone. This is a major point for bone texture analysis on radiographs.
Computed radiography (CR) images of dog mandible section in molar region were compared with simulations calculated
from high-resolution micro-CT volumes. Calculated simulations were obtained using the Mojette Transform. By
digitally editing the CT volume, the simulations were separated into trabecular and cortical components into a region of
interest. Different images were compared and correlated, some bone micro-architecture parameters calculated. A high
correlation was found between computed radiographs and calculated simulations from micro-CT. The Mojette transform
was successful to obtain high quality images. Cortical bone did not contribute to change in a major way simulated
images. These first results imply that intrabony trabecular pattern observed on radiographs can not only be a
representation of the cortical bone endosteal surface and that trabecular bone is highly visible in intraoral radiographs.
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