Spiral computed tomography based maxillary sinus imaging in relation to tooth loss, implant placement and potential grafting procedure.

OBJECTIVES: The purpose of the present study was to explore the maxillary sinus anatomy, its variations and volume in patients with a need for maxillary implant placement. MATERIAL AND METHODS: Maxillary sinus data of 101 consecutive patients who underwent spiral computed tomography (CT) scans for preoperative implant planning in the maxilla at the Department of Periodontology, University Hospital, Catholic University of Leuven, Leuven, Belgium were retrospectively evaluated. The alveolar bone height was measured on serial cross-sectional images between alveolar crest and sinus floor, parallel to the tooth axis. In order to describe the size of the maxillary sinus anteroposterior (AP) and mediolateral (ML) diameters of the sinus were measured. RESULTS: The results indicated that the alveolar bone height was significantly higher in the premolar regions in comparison to the molar region (n = 46, P < 0.01). The age showed negative relation to bone dimension (r = - 0.32, P = 0.04). Anterior and posterior border of the maxillary sinuses were mostly located in the first premolar (49%) and second molar (84%) regions, respectively. Maxillary sinus septa were indentified in 47% of the maxillary antra. Almost 2/3 (66%) of the patients showed major (> 4 mm) mucosal thickening mostly at the level of the sinus floor. The present sample did not allow revealing any significant difference (P > 0.05) in maxillary sinus dimensions for partially dentate and edentulous subjects. CONCLUSIONS: Cross-sectional imaging can be used in order to obtain more accurate information on the morphology, variation, and the amount of maxillary bone adjacent to the maxillary sinus.

Computer-aided detection of colonic polyps using low-dose CT acquisitions.

RATIONALE AND OBJECTIVES: This report proposes an alternative method for the automatic detection of colonic polyps that is robust enough to be directly applicable on low-dose computed tomographic data. MATERIALS AND METHODS: The polyp modeling process takes into account both the gray-level appearance of polyps (intensity profiles) and their geometry (extended Gaussian images). Spherical harmonic decompositions are used for comparison purposes, allowing fast estimation of the similarity between a candidate and a set of previously computed models. Starting from the original raw data (acquired at 55 mA), five patient data sets (prone and supine scans) are reconstructed at different dose levels (to 5 mA) by using different kernel filters, slice overlaps, and increments. Additionally, the efficacy of applying an edge-preserving smoothing filter before detection is assessed. RESULTS: Although image quality decreases when decreasing acquisition milliamperes, all polyps greater than 6 mm are detected successfully, even at 15 mA. Although not important at high doses, smoothing improves detection results for ultra-low-dose (tube current<15 mA) data. CONCLUSION: The advantage of low-dose scans is a significant decrease in effective dose from 4.93 to 1.61 mSv while retaining high detection values, particularly important when thinking of population screening.

Computer aided detection for low-dose CT colonography.

The paper describes a method for automatic detection of colonic polyps, robust enough to be directly applied to low-dose CT colonographic datasets. Polyps are modeled using gray level intensity profiles and extended Gaussian images. Spherical harmonic decompositions ensure an easy comparison between a polyp candidate and a set of polypoid models, found in a previously built database. The detection sensitivity and specificity values are evaluated at different dose levels. Starting from the original raw-data (acquired at 55mAs), 5 patient datasets (prone and supine scans) are reconstructed at different dose levels (down to 5mAs), using different kernel filters and slice increments. Although the image quality decreases when lowering the acquisition mAs, all polyps above 6mm are successfully detected even at 15 mAs. Accordingly the effective dose can be reduced from 4.93mSv to 1.61 mSv, without affecting detection capabilities, particularly important when thinking of population screening.

Age calculation using X-ray microfocus computed tomographical scanning of teeth: a pilot study.

To correlate dental age with an individual's chronological age based on the calculated volume ratio of pulp versus tooth volume measured, an X-ray microfocus computed tomography unit (microCT) with 25 microm spatial resolution was used to non-destructively scan 43 extracted single root teeth of 25 individuals with well-known chronological age. Custom-made analysis software was used by two examiners to obtain numerical values for pulpal and tooth volume. The ratio of both was calculated and statistically processed. No significant intra- or inter-examiner differences were found. In fact, a very strong concordance correlation coefficient was found. Linear regression analysis showed a coefficient of determination (r) of 0.31 which suggests that there is a rather weak correlation between the volume ratio of pulp versus tooth and biological age. Although rather time consuming, this technique shows promising results for dental age estimation in a non-destructive manner using X-ray microfocus computed tomography.

Accuracy of drilling guides for transfer from three-dimensional CT-based planning to placement of zygoma implants in human cadavers.

The accuracy of surgical drilling guides was assessed for placement of zygoma implants. Six zygoma fixtures of length 45 mm (Nobel Biocare, Göteborg, Sweden) were placed in three formalin-fixed human cadavers using surgical drilling guides. The fabrication of these custom-made drilling guides was based on three-dimensional computerized tomography (3D-CT) data for the maxillary-zygomatic complex. The installation of the implants was simulated preoperatively using an adopted 3D-CT planning system. In addition, anatomical measurements of the zygomatic bone were performed on the 3D images. The preoperative CT images were then matched with postoperative ones in order to assess the deviation between the planned and installed implants. The angle between the planned and actually placed implants was < 3 degrees in four out of six cases. The largest deviation found at the exit point of one of the six implants was 2.7 mm. The present study showed that the use of surgical drilling guides should be encouraged for zygoma implant placement because of the lengths of the implants involved and the anatomical intricacies of the region.

A custom template and definitive prosthesis allowing immediate implant loading in the maxilla: a clinical report.

PURPOSE: The purpose of the present investigation was to examine to what extent precision data from 3-dimensional planning software for oral implants can be transferred to the operative field by means of a drilling template, containing high-precision drilling sleeves, fitted on the jawbone. It was investigated whether this procedure would allow advance preparation of a fixed definitive prosthesis that could be placed at the completion of surgery. MATERIALS AND METHODS: This procedure was experimentally carried out in 2 cadavers and later in 8 consecutive human patients. RESULTS: The results indicated a nearly perfect match between the positions and axes of the placed implants and those planned. DISCUSSION: This procedure permitted the placement of a definitive fixed prosthesis with limited freedom of space between the abutments and the metallic cylinders incorporated into the prosthesis. CONCLUSION: These encouraging results of the Leuven information technology-based oral rehabilitation by means of implants (LITORIM) are presently being further investigated at the clinical level.

Image-based planning and validation of C1-C2 transarticular screw fixation using personalized drill guides.

OBJECTIVE: Posterior transarticular spine fusion is a surgical procedure used to stabilize the cervical bodies C1 and C2. Currently, spine screws are used most frequently, according to the procedure of Magerl. As the anatomy is rather complex and the view is limited, this procedure has a high risk factor. We present and validate a planning system for cervical screw insertion based on preoperative CT imaging. MATERIALS AND METHODS: The planning system discussed allowed a neurosurgeon to interactively determine the desired position of the cervical screws, based on appropriate and real-time reslices through the preoperative CT image volume. From the planning, a personalized mechanical drill guide was derived as a means of transferring the plan intraoperatively. Eight cadaver experiments were performed to validate this approach. Postoperative CT was applied, and screw locations were extracted from the postoperative images after registering them to preoperative images. In this way, the deviations of the axes of the planned and inserted screws were determined. RESULTS: From an initial cadaver series, it was observed that the drill guides were not stable enough to cope with the drilling forces, and tended to become displaced. Still, most of the inserted screws were reported to be placed adequately. No vascular compromise or invasion of the spinal canal was observed. For a second cadaver series, the design of the drill guide was altered. In this series, the displacement was no longer present, and all screws were optimally placed. CONCLUSIONS: The preoperative planning system allowed the neurosurgeon to rehearse screw insertion in a way that is closer to surgical reality. The image-based validation technique allowed verification and enhancement of the template design on a cadaver study, giving accuracies comparable to those obtained with transfer by navigation.

Computer-aided diagnosis in virtual colonography via combination of surface normal and sphere fitting methods.

The success of CT colonography (CTC) depends on appropriate tools for quick and accurate diagnostic reading. Current advancements in computer technology have the potential to bring such tools even to personal computer level. In this paper a technique for computed-aided diagnosis (CAD) using CT colonography is described. The method uses a combination of surface normal and sphere fitting methods to label positions in the volume data, which have a strong likelihood of being polyps, and presents them in a user-friendly way. The method was tested on a study group of 18 patients and the detection rate for polyps of 10 mm or larger was 100%, comparable to that of human readers. The price paid for a high detection rate was a large number of approximately eight false-positive findings per case. Our results show that CAD is feasible, and if the number of false positives is further reduced, then this method can be useful for clinical screenings.