SignificanceAccurate evaluation of consciousness in patients with prolonged disorders of consciousness (DOC) is critical for designing therapeutic plans, determining rehabilitative services, and predicting prognosis. Effective ways for detecting consciousness in patients with DOC are still needed.AimEvaluation of the residual awareness in patients with DOC and investigation of the spatiotemporal differences in the hemodynamic responses between the minimally conscious state (MCS) and the unresponsive wakefulness syndrome (UWS) groups using active command-driven motor imagery (MI) tasks.ApproachIn this study, functional near-infrared spectroscopy (fNIRS) was used to measure the changes of hemodynamic responses in 19 patients with DOC (9 MCS and 10 UWS) using active command-driven MI tasks. The characteristics of the hemodynamic responses were extracted to compare the differences between the MCS and UWS groups. Moreover, the correlations between the hemodynamic responses and the clinical behavioral evaluations were also studied.ResultsThe results showed significant differences in the spatiotemporal distribution of the hemodynamic responses between the MCS and UWS groups. For the patients with MCS, significant increases in task-evoked hemodynamic responses occurred during the “YES” questions of the command-driven MI tasks. Importantly, these changes were significantly correlated with their coma-recovery scale-revised (CRS-R) scores. However, for the patients with UWS, no significant changes of the hemodynamic responses were found. Additionally, the results did not show any statistical correlation between the hemodynamic responses and their CRS-R scores.ConclusionsThe fNIRS-based command-driven MI tasks can be used as a promising tool for detecting residual awareness in patients with DOC. We hope that the findings and the active paradigm used in this study will provide useful insights into the diagnosis, therapy, and prognosis of this challenging patient population.
Digital speckle pattern interferometry (DSPI) is a full-field optical testing technique that can be used to measure tiny deformations and strains. It has been widely used in aerospace, precision manufacturing and other fields. However, the lack of effective calibration method has prevented the wider adoption of this technique. In the measurement process of DSPI, there are phase shift errors, phase noise, phase map processing algorithm errors, geometric sensitivity factors miscalibration, etc., which will lead to the final measurement error. Item-by-item calibration of the aforementioned error sources faces many difficulties in implementation and does not work well. Comprehensive calibration would be a better solution to minimize the measurement error but it is hard to perform due to the lack of suitable references for deformation measurement. In this paper, a comprehensive calibration method based on the theory of three-axis angle motions measurement using DSPI has been proposed. The tiny three-axis angle motions are loaded by Piezoelectric actuators and measured using a DSPI device based on the DSPI three-axis angle motions measurement theory. A multi-axis interferometry is used to measure the three-axis angle motions simultaneously and its output is used as the measurement reference. Because the angle motions of a rigid body instead of the deformations of an elastic body are measured, the measurement reference is readily available, yielding the successful precision calibration of the DSPI.
A method of simultaneous and precision measurement of yaw and pitch based on digital speckle pattern interferometry is proposed. The relationship between the yaw/pitch and phase distribution is analyzed in detail, resulting in the establishment of the yaw and pitch simultaneous measurement model. A plane fitting method is proposed to separate the two angle motions from a single phase map. The proposed method enjoys the advantages of being free of cooperative target, high-resolution measurement, and compact optical setup. Experimental results show the mean absolute error of the measurement is <1 μrad.
A non-contact and non-cooperative method of angle measurement based on digital speckle pattern interferometry (DSPI) was introduced in this paper. Studies have shown that when the illumination angle of the DSPI system was every small, the angle can be determined according to the interferometric phase distribution and the length of the measured object. Thereby a direct relationship between the angle and the phase distribution was established. In our experiments, the resolution of measurement system was 0.00025° ( 0.9”), proving that the proposed method is effective for measuring small angles. Theoretically, this method can achieve higher resolution if the measurement noise can be minimized.
Recently, a non-cooperative method of roll angle measurement using digital speckle pattern interferometry (DSPI) is introduced. Mechanism was deduced and the mathematic model of roll angle measurement was established. The novel method also enjoys some other advantages, such as high-accuracy, stand-off, non-contact, and full-field measurement. However, this method is only used for precise measurement of very small roll angle which is up to a few milliradians due to the limitation of DSPI’s measuring range. In this article, a means of range enlargement for DSPI roll angle measurement is introduced. With this means, large roll angle can be divided into a number of small angles which are measured in sequence. Therefore, the large angle is then determined by calculating the sum of these small angles. The proposed method of roll angle is characterized by high-resolution and large-range measurement.
It is difficult to measure absolute three-dimensional deformation using traditional digital speckle pattern interferometry (DSPI) when the boundary condition of an object being tested is not exactly given. In practical applications, the boundary condition cannot always be specifically provided, limiting the use of DSPI in real-world applications. To tackle this problem, a DSPI system that is integrated by the spatial carrier method and a color camera has been established. Four phase maps are obtained simultaneously by spatial carrier color-digital speckle pattern interferometry using four speckle interferometers with different illumination directions. One out-of-plane and two in-plane absolute deformations can be acquired simultaneously without knowing the boundary conditions using the absolute deformation extraction algorithm based on four phase maps. Finally, the system is proved by experimental results through measurement of the deformation of a flat aluminum plate with a groove.
We present a spatial phase-shift digital speckle patterns interferometry (SPS-DSPI) system with the capability of measuring three-dimensional (3-D) deformations under a dynamic loading condition simultaneously using multiple cameras. The Fourier transform method is utilized to calculate the phase difference. The consistency of different cameras is achieved using digital image correlation (DIC) technology. Calibration and calculation programs are compiled to make sure each subset on the measuring surface is uniform. SPS-DSPI and DIC techniques are combined to provide a direct measurement of the 3-D deformation of the entire surface area simultaneously. The theory, application result, and validation experiment are presented.
Digital speckle pattern interferometry (DSPI) is an important optical tool which is widely used in many sophisticated applications. However, a traditional DSPI system can only be used to investigate the outer surfaces which can be easily observed. Therefore, an endoscopic DSPI was proposed to detect the internal and hidden surfaces. It has a rigid or flexible endoscopic tube to allow a hidden surface being clearly imaged. A fiber-optics-based setup makes the proposed DSPI system compact and robust. The temporal phase-shifting technique is used to help precise extraction of phase distributions from speckle patterns.
Digital shearography has demonstrated great potential in direct strain measurement and, thus, has become an industrial tool for nondestructive testing (NDT), especially for NDT of delaminations and detection of impact damage in composite materials such as carbon fiber reinforced plastics and honeycomb structures. The increasing demand for high measurement sensitivity has led to the need for real-time monitoring of a digital shearographic phase map. Phase maps can be generated by applying a temporal, or spatial, phase shift technique. The temporal phase shift technique is simpler and more reliable for industry applications and, thus, has widely been utilized in practical shearographic inspection systems. This paper presents a review of the temporal phase shift digital shearography method with different algorithms and the possibility for real-time monitoring of phase maps for NDT. Quantitative and real-time monitoring of full-field strain information, using different algorithms, is presented. The potentials and limitations for each algorithm are discussed and demonstrated through examples of shearographic testing.
Access to the requested content is limited to institutions that have purchased or subscribe to SPIE eBooks.
You are receiving this notice because your organization may not have SPIE eBooks access.*
*Shibboleth/Open Athens users─please
sign in
to access your institution's subscriptions.
To obtain this item, you may purchase the complete book in print or electronic format on
SPIE.org.
INSTITUTIONAL Select your institution to access the SPIE Digital Library.
PERSONAL Sign in with your SPIE account to access your personal subscriptions or to use specific features such as save to my library, sign up for alerts, save searches, etc.