Scalp Marking For Superficial Intracranial Lesions Using A Laser Pointer During Preoperative Computed Tomographic Imaging

Department of Neurosurgery College of medicine, Zhejiang UniversityPostgraduate: YiLi Chen Tutor: Professor WeiGuo Liu Professor HaiPeng GanOBJECTIVE: For neurosurgery patients, preoperative scalp markings are often required for the placement of the burr holes or for the craniotomy siting. However pinpoint localization of the superficially located brain lesion is not always achieved easily on the basis of computed tomography or magnetic resonance images alone. Stereotactic craniotomy and navigator-based craniotomy have been used increasingly because they provide accurate localization and are minimally invasive. These systems and devices are, however, very expensive and somewhat cumbersome to use for simply determining the placement of a burr hole or craniotomy for superficial intracranial lesions.Scalp marking for superficial intracranial lesions using a laser pointer during preoperative computed tomographic imaging was firstly described by Kubo in 2000. In our country, it has not been reported until now. But in Kubo's article, the accuracy of this method was not mentioned.We devised a simple device on the basis of Kubo's one for accurately marking the scalp. In its entirety, our new system uses a laser pointer and the measurement software included with the scanner, without the need for any additional software or costly hardware.The aim of this study was to know the clinical value of the method after using it for preoperative localization of 20s superfical intracranial lesions.METHODS: Between June 2001 and April 2002, we used the device preoperatively for marking the craniotomy site in 21 patients with superficial cranial or brain lesions.Introduction of the device: The device is basically a projector ,which consists of a carrier and a laser pointer. The carrier ,modeled from polystyrene plastic foam and plastic plates ,is arc shaped,its curvature matching that of the aperture of the gantry .The carrier base ,opposite the arch,serves as a horizontal on which a pencil-shaped laser pointer is mounted,perpendicular to the base .With this configuration,the laser pointer is always aimed at the center of the circular area of the scanning plane when the carrier is aligned at any point on the circular slit window in the gantry through which the X-ray beam passes(circular x-ray window).Its configuration is based on a simple geometrical rule:the vertical from the midpoint of any chord passes throug the center of the circle that encompasses the chord. A scale is marked parallel to the arc shaped side, representing the angle (in degrees, 450 totally). The cross point of laser beam and arc shaped side was marked as 0?Procedures: Transaxial images are obtained at the level of the lesion. On a selected image on the monitor, two points are chosen on the scalp, so as to include the lesion between them. The software is used to draw a line between the points through the center of the image, the coordinates of which are in pixels on theimage matrix, Corresponding to the center of the gantry. The angle formed by this line and the vertical to the center of the image is measured by the software.The laser beam projector is then brought in and aligned on the circular x-ray window in the gantry, at the same angle as the line on the image . When the beam is emitted, the point illuminated on the patient's head represents the predetermined point on the image. We place the radiopaque marker on this scalp point. The procedure may be repeated for each point on each slice sequentially. Finally, the lesion was rescanned.Patients were divided into 5 groups according to lesion's position. Patient's general data, the time and cost of marking, coordinates of marked points and predetermined points and operator's experiences were recorded. We evaluated accuracy of this method using the coordinates' differences between marked points and predetermined points on the image.RESULTS :No case had to be abandoned because of marking failure. ISmales and 8 females were involved in the study with a mean age of 49.4 years (ra...