Uncertainty contribution of the laser-beam orientation for laser Doppler vibrometer measurements at the carotid artery

Displacement signals acquired at the carotid artery with laser Doppler vibrometry (LDV) present a characteristic waveform that is correlated to the blood pressure inside the vessel. There are different models in literature that relate the displacement amplitude to the pressure. Therefore, a wrong estimation of the displacement amplitude would lead to errors on the extraction of the pressure information. LDV measures the vibration component in the direction of the laser beam. If the laser beam is not parallel to the vibration direction of the target, only a projection of the real vibration amplitude is measured. With a 3D-LDV measurement it is possible to measure the real amplitude of the displacement. For 1D-LDV measurements it is necessary to calculate the contribution of the uncertainty of the laser beam orientation to the displacement. In this paper, we investigate the uncertainty contribution due to the laser beam direction on the displacement amplitude of vibration signals acquired at the carotid artery. We used a multipoint vibrometer for the investigation. Our aim is to quantify this uncertainty for 1D-LDV measurements at the carotid artery. Moreover, we quantify its influence on the detection of the pressure. We derive an uncertainty contribution due to the laser beam direction of 13% for the displacement amplitude. (paper)