Background: Knowing the orientation of the head is important in many fields,\r\nincluding medicine. Many methods and measuring systems exist, but usually they\r\nuse different markers or sensors attached to the subjectâ��s head for head orientation\r\ndetermination. In certain applications these attachments may represent a burden or\r\na distraction to the subject under study which may have an unfavourable impact on\r\nthe measurement. We propose a non-contact optical method for head-to-trunk\r\norientation measurement that does not require any attachments to the subject\r\nunder study.\r\nMethods: An innovative handheld 3D apparatus has been developed for non-invasive\r\nand fast 3D shape measurements. It is based on the triangulation principle in\r\ncombination with fringe projection. The shape of the subjectâ��s upper trunk and head is\r\nreconstructed from a single image using the Fourier transform profilometry method.\r\nTwo shape measurements are required to determine the head-to-trunk orientation\r\nangles: one in the reference (neutral) position and the other one in the position of\r\ninterest. The algorithm for the head-to-trunk orientation angle extraction is based on\r\nthe separate alignment of the shape of the subjectâ��s upper trunk and head against the\r\ncorresponding shape in the reference pose. Single factor analysis of variance (ANOVA)\r\nwas used for statistical characterisation of the method precision.\r\nResults: The method and the 3D apparatus were verified in-vitro using a mannequin\r\nand a reference orientation tracker. The uncertainty of the calculated orientation was\r\n2�°. During the in-vivo test with a human subject diagnosed with cervical dystonia\r\n(aged 60), the repeatability of the measurements was 3�°. In-vitro and in-vivo comparison\r\nwas done on the basis of an experiment with the mannequin and a healthy male\r\n(aged 29). These results show that only the difference between flexion/extension\r\nmeasured angles was statistically significant. The differences between means were less\r\nthan 1�° for all ranges.\r\nConclusions: The new non-contact method enables the compensation of the\r\nmovement of the measuring instrument or the subjectâ��s body as a whole, is non-invasive,\r\nrequires little additional equipment and causes little stress for the subject and operator.\r\nWe find that it is appropriate for measurements of the head orientation with respect to\r\nthe trunk for the characterization of the cervical dystonia.
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