A study of volumetric visualization and quantitative evaluation of bone trabeculae in helical CT

Computed tomography color mapping for evaluation of bone ongrowth on the surface of a titanium-coated polyetheretherketone cage in vivo: A pilot study

Bone ongrowth on the surfaces of titanium (Ti)-coated polyetheretherketone (PEEK) materials has been demonstrated in animal models; however, whether this occurs on the surfaces of Ti-coated PEEK cages in lumbar interbody fusion has not been demonstrated clinically in vivo. This prospective observational study was aimed to develop and validate a computed tomography (CT) color mapping based on Hounsfield unit (HU) values for evaluation of bone ongrowth on the surfaces of the Ti-coated PEEK cage after posterior lumbar interbody fusion (PLIF).Twenty-four consecutive patients (11 men and 13 women; mean age, 67.0 years; range, 20-82 years) who underwent single- or 2-level PLIF since March 2015 were included. Two Ti-coated PEEK cages were inserted in all PLIF segments. From reconstructed sagittal planes from postoperative CT scans (within 1 week and 6 months postoperatively), bone ongrowth on the surfaces of cage frames was evaluated by CT color mapping. Inter- and intraobserver reliability of the assessment of bone ongrowth by CT color mapping was evaluated by Cohen's kappa coefficient. The relation between CT color mapping and HU values on the surfaces of cage frames was also analyzed.A total of 248 surfaces of cage frames were evaluated. Bone ongrowth was observed in 134 of 248 surfaces (54.0%) by CT color mapping. Intraobserver reliability for the evaluation of bone ongrowth was kappa = 0.831, and interobserver reliability was kappa = 0.713. The HU values in the local regions of interest (ROIs) on the surfaces of cage frames where the postoperative bone ongrowth existed on CT color mapping increased significantly postoperatively (P < .001), and the median postoperative change rate of the HU values in the local ROIs was 22.4%.The assessment of bone ongrowth on the surfaces of Ti-coated PEEK cages by CT color mapping had adequate inter- and intraobserver reliability, which was useful especially in detecting local increase in HU values on the surfaces of the cages. This method is an easy and visually comprehensible method for the assessment of bone ongrowth in the bone-implant interface.

Augmented mandibular bone structurally adapts to functional loading

Long-term changes in trabecular bone structure during the 10 years following onlay grafting with simultaneous mandibular implant placement were studied. Extraoral radiographs of both mandibular sides in eight patients were taken regularly. Bone structure was analysed using a custom-written image analysis program. Parameters studied were trabecular area and perimeter and marrow cavity area and perimeter. After skeletonisation of the trabecular network, the number of end points and branching points, skeleton length, and branch angle were determined. The observed structural changes agree with the development of a more complex and more delicate or fine osseous structure. The bone shows more trabecular branching. All changes are most pronounced in the graft spongiosa, but are also found in the graft cortex and in the original mandible. The mean trabecular branch angle becomes more horizontal. The applied technique can be used to analyse long-term changes in the architecture of bone grafts. Changes found in the graft architecture correspond to changes expected after functional adaptation to loading.

Evaluation of early tissue reactions after lumbar intertransverse process fusion using CT in a rabbit

OBJECTIVE

The objective of the study was to evaluate tissue reactions such as bone genesis, cartilage genesis and graft materials in the early phase of lumbar intertransverse process fusion in a rabbit model using computed tomography (CT) imaging with CT intensity (Hounsfield units) measurement, and to compare these data with histological results.

MATERIALS AND METHODS

Lumbar intertransverse process fusion was performed on 18 rabbits. Four graft materials were used: autograft bone (n = 3); collagen membrane soaked with recombinant human bone morphogenetic protein-2 (rhBMP-2) (n = 5); granular calcium phosphate (n = 5); and granular calcium phosphate coated with rhBMP-2 (n = 5). All rabbits were euthanized 3 weeks post-operatively and lumbar spines were removed for CT imaging and histological examination.

RESULTS

Computed tomography imaging demonstrated that each fusion mass component had the appropriate CT intensity range. CT also showed the different distributions and intensities of bone genesis in the fusion masses between the groups. Each component of tissue reactions was identified successfully on CT images using the CT intensity difference. Using CT color mapping, these observations could be easily visualized, and the results correlated well with histological findings.

CONCLUSIONS

The use of CT intensity is an effective approach for observing and comparing early tissue reactions such as newly synthesized bone, newly synthesized cartilage, and graft materials after lumbar intertransverse process fusion in a rabbit model.

Cone beam computed tomography 3D reconstruction of the mandibular condyle

OBJECTIVE

To determine the ideal window level and width needed for cone beam computed three-dimensional (3D) reconstruction of the condyle.

MATERIALS AND METHODS

Linear dimensions were measured with a digital caliper to assess the anatomic truth for 50 dry human mandibular condyles. Condyles were scanned with the i-CAT cone beam computed tomography (CBCT) and 3D-models were reconstructed. Three linear three-dimensional measurements were made on each of the 50 condyles at 8 different Hounsfield unit (HU) windows. These measurements were compared with the anatomic truth. Volumetric measurements were also completed on all 50 condyles, at 23 different window levels, to define the volumetric distribution of bone mineral density (BMD) within the condyle.

RESULTS

Significant differences were found in two of the three linear measurement groups at and below the recommended viewing window for osseous structures. The most accurate measurements were made within the soft tissue range for HU window levels. Volumetric distribution measurements revealed that the condyles were mostly comprised of low-density bone, and that condyles exhibiting significant changes in linear measurements were shown to have higher percentages of low-density bone than those condyles with little change from the anatomic truth.

CONCLUSIONS

CBCT assessment of the mandibular condyle, using the 3D reconstruction, is most accurate when accomplished at density levels below that recommended for osseous examination. However, utilizing lower window levels which extend into the soft tissue range, may compromise one's capacity to view the bony topography.

Time-lapse observation of rat periodontal ligament during function and tooth movement, using microcomputed tomography

The aim of this study was to observe the time-lapse changes in the rat periodontal ligament (PDL) during function and tooth movement. Under Nembutal anaesthesia, time-lapse changes in the thickness of the PDL of the first molars were investigated in five 12-week-old adolescent rats with microcomputed tomography. Three-dimensional (3D) images were reconstructed from the data. Histological observation was also performed, using undecalcified frozen sections of the maxillary first molar area. The PDL appeared as a radiolucent furrow on the 3D images. A slight change in the thickness of the PDL was observed 1 hour after initiation of orthodontic force loading, which became significant after 6 hours, with the appearance of pressure-tension zones during the tooth movement. These changes were more significant 3 days after orthodontic loading. Histological observation of the lingual cervical PDL (pressure zone) in nine 12- to 13-week-old rats demonstrated that the periodontal space had become narrow and the cellular elements appeared to be densely packed in the narrowed PDL 6 hours after orthodontic loading. Degeneration of tissues appeared 3 days after loading. Observation of the buccal cervical PDL (tension zone) demonstrated that the PDL was extended 6 hours after orthodontic force loading, and the extension continued for up to 3 days. Alkaline phosphatase activity was distributed in the PDL, except for the degenerating tissues in the pressure zone 3 days after loading. The results suggest that the periodontal reaction was initiated within 6 hours after orthodontic force loading, which was related to the structural changes of the PDL. The changes probably induced an early response in individual cells of the PDL.