Comparison of the accuracy of invasive and noninvasive registration methods for image-guided oral implant surgery.

PURPOSE: Registration refers to the linkage of coordinates from an image with actual patient coordinates and has been shown to be the most influential factor in the accuracy of image-guided surgery. Invasive bone markers are the gold standard but require surgical placement prior to imaging. In contrast, registration templates or external registration frames are noninvasive, but their repositioning during imaging and surgery can be a source of error. The purpose of the present study was to determine whether noninvasive registration methods can achieve an accuracy similar to that of invasive bone marker registration. MATERIALS AND METHODS: Computed tomographic slices (1 mm each) of a maxillary and mandibular dental stone cast that had been prepared with target markers on the buccal and oral surfaces were registered with an optical-based navigation system simulating invasive bone markers, noninvasive registration templates, and a noninvasive external registration frame. Predicted error of the navigation system, fiducial registration error, and target registration error were evaluated. The use of five and seven registration markers was compared. RESULTS: A total of 696 error measurements was performed. The external registration frame showed significantly worse fiducial registration error compared with the other methods, but there was no significant difference in target registration error between invasive and noninvasive registration methods. The predicted error given by the navigation system significantly underestimated target registration error. Increasing the number of registration markers from five to seven resulted in no significant differences. CONCLUSIONS: Noninvasive registration based on registration templates or external registration frames showed accuracy that was equivalent to that of invasive registration. The use of five registration markers was sufficient. The predicted error given by a navigation system should not be mistaken as "navigation error" during clinical application.

Bone metastases in patients with neuroendocrine tumor: 68Ga-DOTA-Tyr3-octreotide PET in comparison to CT and bone scintigraphy.

UNLABELLED: Somatostatin receptor scintigraphy is an accurate imaging modality for the diagnosis of neuroendocrine tumor. Because detection of distant metastases has a major impact on treatment, early diagnosis of metastatic spread is of great importance. So far, no standard procedure has become established for the early diagnosis of bone metastases from neuroendocrine tumor. We compared the diagnostic value of CT with that of the novel somatostatin analog (68)Ga-1,4,7,10-tetraazacyclododecane-N,N',N'',N'''-tetraacetic acid-d-Phe(1)-Tyr(3)-octreotide ((68)Ga-DOTATOC) in the detection of such metastases. METHODS: Fifty-one patients (22 women and 29 men; age range, 32-87 y) with histologically verified neuroendocrine tumor were included in this study. PET scans were fused with CT scans using a vacuum fixation device. (18)F-NaF or (99m)Tc-dicarboxypropane diphosphonate bone scans or clinical follow-up served as the reference standard. RESULTS: Twelve of the 51 patients had no evidence of bone metastases on any of the available imaging modalities, and 37 patients had (68)Ga-DOTATOC PET results true-positive for bone metastases. (68)Ga-DOTATOC PET results were true-negative for 12 patients, false-positive for one, and false-negative for another, resulting in a sensitivity of 97% and a specificity of 92%. (68)Ga-DOTATOC PET detected bone metastases at a significantly higher rate than did CT (P < 0.001). Furthermore, conventional bone scans confirmed the results of somatostatin receptor PET but did not reveal additional tumors in any patients. CONCLUSION: (68)Ga-DOTATOC PET is a reliable, novel method for the early detection of bone metastases in patients with neuroendocrine tumor. Our results show that CT and conventional bone scintigraphy are less accurate than (68)Ga-DOTATOC PET in the primary staging or restaging of neuroendocrine tumor.

Computer-assisted minimally invasive treatment of osteochondrosis dissecans of the talus.

OBJECTIVE: Revascularization of areas of necrosis in the talus and stimulation of bone regeneration whilst protecting the talar hyaline cartilage using computer-assisted minimally invasive drilling or retrograde cancellous bone relining of the osteochondrotic zone. INDICATIONS: Osteochondrosis dissecans of the talus, Berndt & Harty stages I-III. CONTRAINDICATIONS: Osteochondrosis dissecans of the talus, Berndt & Harty stage IV. General contraindications such as poor skin and soft-tissue conditions or poor general condition. SURGICAL TECHNIQUE: Before the operation: fitting a removable cast for the ankle (ankle fixation cast), then computed tomography of the ankle with the ankle fixation cast fitted. Planning the site of the central Kirschner wire in the talus using a navigation system in the laboratory. Adjusting and locking the aiming device. Intraoperative procedures: fitting the sterilized ankle fixation cast. Retrograde placement of the 2.4-mm Kirschner wire through the locked aiming device. Check on the position of the Kirschner wire using an image intensifier. Arthroscopy of the ankle; further parallel holes may then be drilled depending on the findings or retrograde cancellous bone grafting may be performed by harvesting cancellous bone from the calcaneus. POSTOPERATIVE MANAGEMENT: For retrograde drilling/parallel drilling: 1 week of partial weight bearing at 30 kg. For retrograde cancellous bone grafting: 4 weeks of partial weight bearing at 15 kg, then 2 more weeks of partial weight bearing at 30 kg. Physiotherapy. RESULTS: From December 1999 to January 2005, 41 patients with osteochondrosis dissecans of the talus were selected for computer-assisted treatment by retrograde drilling or retrograde cancellous bone grafting. In 39 of the 41 patients, the osteochondral lesion-as verified by postoperative magnetic resonance imaging (MRI)-was accessed, i.e., the drilled hole led to the lesion. In two cases, irreparable flaws in the materials were discovered intraoperatively, so that the above method was only performed on 39 patients. The 1-year results for the first 15 patients treated with retrograde drilling/parallel drilling and concomitant ankle arthroscopy without retrograde cancellous bone graft are presented here based on the follow-up MRI (position of drill hole, assessment of vitality of the area of osteochondritis) and a clinical score. The four women and eleven men were, on average, 34.1 years old (14-55 years). In the radiologic comparison of the pre- and postoperative stages of the osteochondritis dissecans, 46.7% of patients showed an improvement in the Berndt & Harty stage. 40.0% showed the same osteochondrosis dissecans stage in the postoperative MRI, and in 13.3% it deteriorated by one grade. In the clinical follow-up examination, the AOFAS Score averaged 88.9 points.

Accuracy in computer-aided implant surgery--a review.

The objective of this article was to review the different factors and limitations influencing the accuracy of computer-aided implant surgery. In vitro and in vivo accuracy studies of articles and congress proceedings were examined. Similar results using bur tracking as well as image-guided template production techniques have been reported, and both methods allow for precise positioning of dental implants. Compared to the conventional technique, this sophisticated technology requires substantially more financial investment and effort (computerized tomographic imaging, fabrication of a registration template, intraoperative referencing for bur tracking, or image-guided manufacturing of a surgical template) but appears superior on account of its potential to eliminate possible manual placement errors and to systematize reproducible treatment success. The potential for the protection of critical anatomic structures and the esthetic and functional advantages of prosthodontic-driven implant positioning must also be considered. However, long-term clinical studies are necessary to confirm the value of this strategy and to justify the additional radiation dose, effort, and costs.

In vitro accuracy of a novel registration and targeting technique for image-guided template production.

OBJECTIVES: The objective of this study was to evaluate the accuracy of a novel registration and targeting technique for image-guided template production (IGTP) in a preliminary phantom study. MATERIAL AND METHODS: Registration of four standard dental stone casts with integrated target pellets to the corresponding computed tomography (CT) data was performed via a vacuum mouthpiece and an external reference frame (Medical Intelligence GmbH, Germany). Using the Treon navigation system (Medtronic Inc., Minneapolis, MN, USA) a surgical path with the entry in the centre of the dental crown and the target in the centre of the target pellet was planned on the CT data. An aiming device was adjusted according to the planned trajectory and guided drillings into the dental stone casts. The accuracy was evaluated on postoperative 3D-CT data. RESULTS: The mean fiducial registration error as given by the registration software was 0.4 mm. One hundred and twelve navigated drillings showed a mean accuracy [xy] of 0.42+/-0.26 mm (maximum 1 mm). For the z-axis, a mean accuracy [z] of 0.25+/-0.12 mm (maximum 0.6 mm) was found. CONCLUSIONS: Comparing the presented registration technique to existing registration methods in IGTP and burr tracking, no radiographic and registration templates are needed. The procedure is easy and requires only minimal effort. Navigation-controlled drillings could be performed with an accuracy that approaches the intrinsic navigation system's accuracy, a fact that warrants its use for surgical template production. Further accuracy studies of template-guided drillings are necessary before the presented registration technique can be implemented for patient treatment.