Each scout image requires less than 0.1 s to capture therefore, patients can present their own NHP freely and negative effects from patient’s head movements are not significant. Scout images are necessary before each full CBCT scan to verify the patient’s position thus, this operation does not introduce extra radiation exposure to patients. Based on this result, we used scout images of a calibrated CBCT to record patient’s NHP. We firstly investigated the orientation reproducibility in the field-of-view (FOV) of a CBCT scanner, as presented in the next section. The aim of this study was to investigate direct NHP recording in CBCT without extra hardware and procedures. This limits its application in daily practice. IMU systems deliver very high accuracy in recording NHP however, additional equipment and operations are required. Orientation readings recorded by the IMU can be used to orientate patients’ heads when they are in an NHP. Therefore, NHP posture has sometimes been recorded using a patented inertial motion unit (IMU). In cone beam computerized tomography (CBCT), the image acquisition times are long the patient’s head may move, resulting in motion artifacts during scanning. The accuracies achieved by traditional and stereophotogrammetry (SPNHP) methods are around ☑ and greater than ☐.1 degrees, respectively. ![]() In stereophotogrammetry (SP), a physical reference board has been proposed for calibrating the SP system and to capture the 3D facial mesh surface with reference to the true horizontal plane. In traditional 2D photographs/radiographs, pictures are taken of the subject, along with a hanging plumb bob as reference for reproducing patients’ NHP. ![]() Clinical methods have been developed to record this head position in various imaging modalities. The mirror serves as a reference for defining the patient’s head orientation. In clinical settings, patients reproduce their own NHP by looking straight into a hanging mirror at their own eyes in a balanced position. Natural head position (NHP) is a reproducible head position in an upright posture, with the subject focusing on a distant point at eye level.
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