A critical inventory of preoperative skull replicas

Physical replicas of organs are used increasingly for preoperative planning. The quality of these models is generally accepted by surgeons. In view of the strong trend towards minimally invasive and personalised surgery, however, the aim of this investigation was to assess qualitatively the accuracy of such replicas, using skull models as an example

Evaluating Preoperative Models: A Methodologic Contribution.

Three-dimensional (3D) printed models of the human skull and parts of it are being increasingly used for surgical education and customized preoperative planning. This study, using the calvaria as a model, provides a methodologic analysis with regard to future investigations aimed at evaluating patient-specific skull replicas. Postmortem computed tomography was used for 3D reconstruction of a skull. The digital model obtained was converted to a physical replica by 3D printing. This copy was compared qualitatively and quantitatively with the original, using both a classical anthropometric and a 3D surface scanning approach. Qualitatively, the replica and the original displayed good qualitative concordance. The quantitative deviations, as measured by osteometric tools, lay partly in the submillimetric area, partly between 1 and 2 mm. The maximum difference was 3.7 mm. On the basis of the surface scans, a mean deviation of 0.2930 mm (±0.2677 mm) and a median difference of 0.2125 mm (0.0000-1.5509 mm) were observed for the inner surface. For the whole object, corresponding figures amounted to 0.9101 mm (±0.5390 mm) and 0.8851 mm (0.000-3.2647 mm). Qualitatively flawless replicas of the skull region investigated are feasible, subject to extensive manual CT image editing. However, neurosurgeons should be aware that models of one and the same patient will vary according to the production chain used by the 3D printing laboratory in charge. Methodologically, both classic anthropological and light-stripe-based comparisons are justified for use in future studies. For trials aimed at assessing mean deviations and topographic distribution patterns, optical 3D scanning technologies can be recommended

Landmark-based surgical navigation

Navigational support is a widely adopted technique in surgery that has become a part of the clinical routine. This navigation support either comes in the form of an abstract display that shows for example the distance and direction to the target position or in the form of augmented reality where segmented anatomical structures of interest are overlaid onto a visual image sequence in real-time. In this paper we propose a cost-effective real-time augmented reality approach using an off-the-shelf tablet PC in combination with a novel 2D/3D point correspondence mapping technique. The proposed point pattern matching algorithm is tailored towards moderate projective distortions and suitable for computational low-power devices. Experiments and comparisons were done on synthetic images and accuracy was measured on real scenes. The excellent performance is demonstrated by an Android 3D guidance application for a relevant medical intervention