The accuracy of three-dimensional model generation. What makes it accurate to be used for surgical planning?

Computerized treatment planning is routinely used in cranio-maxillofacial applications. For these therapeutic applications, it is of critical importance to have a precise model of the structures in question. Improved imaging techniques and advances in software engineering have moved three-dimensional (3D) computer models from the research and development area into routine clinical application. The importance of high-resolution source imaging is well understood by surgeons. The influence of image processing is poorly understood in the surgical community and we hypothesize that this may be a source of significant error. We evaluated the workflow for creating a virtual model using computed tomography data, and the impact that image processing decisions have on final virtual model accuracy. We chose to create a model of the dental surface since it is one of the most complex structures in the area. Individual image processing steps are explained and the magnitudes of their influence on model quality are demonstrated and compared. This study demonstrates that inappropriate image processing can introduce errors of similar magnitude as the use of inadequate source data. Finally, the study shows that errors caused by inappropriate image processing amplify the inaccuracies of low-resolution source imagery and eliminate the benefits of high-resolution source imaging.

Orbital form analysis: problems with design and positioning of precontoured orbital implants: a serial study using post-processed clinical CT data in unaffected orbits

Inter-individual size and shape (form) variation for the orbital floor and medial wall was assessed and compared with its posterior partition. Reconstruction of the posterior partition is known to be a surgical challenge in complex orbital defect repair when using standard manual implant contouring and positioning techniques. The size variation of both regions was assessed, alone and combined, in statistical form analysis using three-dimensional computer models of left and mirrored right orbits, obtained from 70 clinical computed tomography (CT) scans of adult European Caucasians with unaffected orbits. Major shape and size variability for both regions was observed, but to a larger extent for the entire orbital floor and medial wall, with males having significantly larger regions but with no differing shape patterns. Statistical modeling was used to identify characteristic shape patterns in given orbits. The size, shape and positioning of precontoured implants are decisive criteria for the adequate repair of complex orbital defects. The results indicate that optimal form conditions for prefabricated implants exist in a restricted area corresponding to the transition of the posterior orbital floor and medial wall.

Diabetes as a risk factor for herpes zoster infection: results of a population-based study in Israel

BACKGROUND

Studies showed that diabetes mellitus (DM) is often accompanied by impaired cell-mediated immunity, which potentially may increase the risk for infectious diseases, including herpes zoster (HZ). However, data on the relation between DM and HZ are scarce. This case-control study explored the association between DM and HZ.

PATIENTS AND METHODS

This study was nested within a cohort of all members of a large health maintenance organization (HMO) in Israel. Cases totaled 22,294 members who were diagnosed with HZ between 2002 and 2006. Controls (n=88,895) were randomly selected from the remaining HMO population using frequency-matched age, sex, and duration of follow-up. Personal data on history of DM, lymphoma, leukemia, or AIDS, were obtained from computerized medical records.

RESULTS

Adjusted analyses showed that the risk of HZ was associated with history of leukemia, lymphoma, use of steroids or antineoplastic medications, and AIDS, particularly among patients below 45 years of age. In a multivariate analysis, DM was associated with an increased risk of HZ (OR=1.53; 95% CI: 1.44-1.62).

CONCLUSIONS

The data suggest that individuals with DM are at increased risk of HZ. Well-designed cohort studies may help to clarify the nature of this association.