Virtual pointer projection of the central sulcus to the outside of the skull using frameless neuronavigation - Accuracy and applications

Background. The purpose of this prospective study was to localize the centr al sulcus by frameless neuronavigation and to project this anatomical struc ture to the outside of the skull on the skin. This method was analyzed in r espect to its practicability, accuracy, and potential applications. Method. In 27 patients investigated (28 unaffected hemispheres), the centra l sulcus was virtually projected to the outside of the skull using frameles s neuronavigation and a virtual pointer elongation of 15 or 20 mm. The foll owing parameters were measured on the scalp: 1. the distance between the br egma and the midline junction of the central sulcus, and 2, the angle betwe en the central sulcus and the midline. These dada were compared with measur ements based on the original axial MR images of these patients. Finally. a laboratory phantom study was designed in analogy to a patient's examination for estimation of the overall accuracy of the neuronavigation system in th e experimental setup used in this study. Findings. Virtual pointer projection of the central sulcus to the outside o f the skull using frameless neuronavigation was found to be easily possible . The distance between the bregma and the midline junction of the central s ulcus amounted to a mean of 55 mm on the left and 56 mm on the right. The a ngle between the central sulcus and the midline reached a mean of 63 degree s on the left and 60 degrees on the right. These data confirmed results of other studies with no frameless neuronavigation devices. The phantom study revealed a mean overall inaccuracy of 0.9 mm at a virtual pointer elongatio n of 15 mm, At a virtual pointer elongation of 20 mm, the mean overall inac curacy of our study was 1.1 mm. These results correspond to the inaccuracy of frame based stereotaxy. Interpretation. It is easily possible, valid, and reliable to virtually pro ject the central sulcus to the outside of the skull with an acceptably low inaccuracy using frameless neuronavigation. This is important for research studies that correlate and integrate different functional imaging methods w ith the aid of frameless neuronavigation.