| 1. |
- Becher, Tobias H., et al.
(författare)
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Prolonged Continuous Monitoring of Regional Lung Function in Infants with Respiratory Failure
- 2022
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Ingår i: Annals of the American Thoracic Society. - : American Thoracic Society. - 2329-6933 .- 2325-6621. ; 19:6, s. 991-999
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Tidskriftsartikel (refereegranskat)abstract
- Rationale: Electrical impedance tomography (EIT) allows instantaneous and continuous visualization of regional ventilation and changes in end-expiratory lung volume at the bedside. There is particular interest in using EIT for monitoring in critically ill neonates and young children with respiratory failure. Previous studies have focused only on short-term monitoring in small populations. The feasibility and safety of prolonged monitoring with EIT in neonates and young children have not been demonstrated yet.Objectives: To evaluate the feasibility and safety of long-term EIT monitoring in a routine clinical setting and to describe changes in ventilation distribution and homogeneity over time and with positioning in a multicenter cohort of neonates and young children with respiratory failure.Methods: At four European University hospitals, we conducted an observational study (NCT02962505) on 200 patients with postmenstrual ages (PMA) between 25 weeks and 36 months, at risk for or suffering from respiratory failure. Continuous EIT data were obtained using a novel textile 32-electrode interface and recorded at 48 images/s for up to 72 hours. Clinicians were blinded to EIT images during the recording. EIT parameters and the effects of body position on ventilation distribution were analyzed offline. Results: The average duration of FAT measurements was 53 +/- 20 hours. Skin contact impedance was sufficient to allow image reconstruction for valid ventilation analysis during a median of 92% (interquartile range, 77-98%) of examination time. EIT examinations were well tolerated, with minor skin irritations (temporary redness or imprint) occurring in 10% of patients and no moderate or severe adverse events. Higher ventilation amplitude was found in the dorsal and right lung areas when compared with the ventral and left regions, respectively. Prone positioning resulted in an increase in the ventilation-related EIT signal in the dorsal hemithorax, indicating increased ventilation of the dorsal lung areas. Lateral positioning led to a redistribution of ventilation toward the dependent lung in preterm infants and to the nondependent lung in patients with PMA > 37 weeks.Conclusions: EIT allows continuous long-term monitoring of regional lung function in neonates and young children for up to 72 hours with minimal adverse effects. Our study confirmed the presence of posture-dependent changes in ventilation distribution and their dependency on PMA in a large patient cohort.
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| 2. |
- Bergström, Per, et al.
(författare)
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Dual-wavelength digital holography : single-shot shape evaluation using speckle displacements and regularization
- 2014
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Ingår i: Applied Optics. - : Optical Society of America. - 1559-128X .- 2155-3165 .- 0003-6935 .- 1539-4522. ; 53:1, s. 123-131
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Tidskriftsartikel (refereegranskat)abstract
- This paper discusses the possibility of evaluating the shape of a free-form object in comparison with its shape prescribed by a CAD model. Measurements are made based on a single-shot recording using dual-wavelength holography with a synthetic wavelength of 1.4 mm. Each hologram is numerically propagated to different focus planes and correlated. The result is a vector field of speckle displacements that is linearly dependent on the local distance between the measured surface and the focus plane. From these speckle displacements, a gradient field of the measured surface is extracted through a proportional relationship. The gradient field obtained from the measurement is then aligned to the shape of the CAD model using the iterative closest point (ICP) algorithm and regularization. Deviations between the measured shape and the CAD model are found from the phase difference field, giving a high precision shape evaluation. The phase differences and the CAD model are also used to find a representation of the measured shape. The standard deviation of the measured shape relative the CAD model varies between 7 and 19 μm, depending on the slope.
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| 3. |
- Bergström, Per, et al.
(författare)
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Single shot shape evaluation using dual-wavelength holographic reconstructions and regularization
- 2014
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Ingår i: Fringe 2013. - Berlin : Encyclopedia of Global Archaeology/Springer Verlag. - 9783642363580 - 9783642363597 ; , s. 103-108
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Konferensbidrag (refereegranskat)abstract
- The aim of this work is to evaluate the shape of a free form object using single shot digital holography. The digital holography results in a gradient field and wrapped phase maps representing the shape of the object. The task is then to find a surface representation from this data which is an inverse problem. To solve this inverse problem we are using regularization with additional shape information from the CAD-model of the measured object.
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| 4. |
- Khodadad, Davood, 1985-, et al.
(författare)
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A nondestructive validation of reverse impact experiment based on shape measurement using high speed photographs
- 2013
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Ingår i: 2013 International Conference on Advanced Optoelectronics and Lasers (CAOL 2013). - Piscataway, NJ : IEEE. ; , s. 322-324, s. 322-324, s. 322-324
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Konferensbidrag (refereegranskat)abstract
- High speed photography of a reverse impact scenario was taken in order to make shape measurement. The results from the shape measurements were then compared with results from numerical simulations in order to evaluate the possibility to use noncontact shape measurement as a validation tool in future simulations.
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| 5. |
- Khodadad, Davood, 1985-
(författare)
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Advancing road safety assessment with digital holography : a study on skid resistance of asphalt pavements
- 2023
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Ingår i: Proceedings of SPIE - The International Society for Optical Engineering. - : SPIE - The International Society for Optics and Photonics. - 9781510666993
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Konferensbidrag (refereegranskat)abstract
- Enhancing road safety through improved skid resistance is a critical endeavor in preventing accidents and promoting secure driving conditions. This study delves into the investigation of skid resistance in asphalt pavements using digital holography, focusing on macro and microtexture attributes. By employing off-axis digital holography, the paper presents a novel method to accurately measure surface profiles and assess friction properties. The experimental setup leverages single-shot dual-wavelength holography, providing precise 3D topographic information. The study demonstrates how the obtained phase information aids in deriving surface profiles and subsequently determining friction coefficients. The approach overcomes limitations of conventional methods, offering micron-level accuracy for surface roughness measurements. Through experimental results, the versatility of adjusting measurement accuracy and range based on requirements is showcased. The paper concludes by highlighting the interplay between surface features and friction characteristics, paving the way for improved road safety assessment.
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| 6. |
- Khodadad, Davood, 1985-, et al.
(författare)
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B-spline based free form deformation thoracic non-rigid registration of CT and PET images
- 2011
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Ingår i: International Conference on Graphic and Image Processing (ICGIP 2011). - : SPIE - International Society for Optical Engineering. ; 8285
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Konferensbidrag (refereegranskat)abstract
- Accurate attenuation correction of emission data is mandatory for quantitative analysis of PET images. One of the main concerns in CT-based attenuation correction(CTAC) of PET data in multimodality PET/CT imaging is misalignment between PET and CT images. The aim of this study, is to proposed a hybrid method which is simple, fast and accurate, for registration of PET and CT data which affected from respiratory motion in order to improve the quality of CTAC. The algorithm is composed of three methods: First, using B-spline Free Form Deformation to describe both images and deformation field. Then applying a pre-filtering on both PET and CT images before segmentation of structures in order to reduce the respiratory related attenuation correction artifacts of PET emission data. In this approach, B-spline using FFD provide more accurate adaptive transformation to align the images, and structure constraints obtained from prefiltering applied to guide the algorithm to be more fast and accurate. Also it helps to reduce the radiation dose in PET/CT by avoiding repetition of CT imaging. These advances increase the potential of the method for routine clinical application.
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| 7. |
- Khodadad, Davood, 1985-, et al.
(författare)
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Breath detection using short-time Fourier transform analysis in electrical impedance tomography
- 2017
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Ingår i: 2017 XXXIInd General Assembly and Scientific Symposium of the International Union of Radio Science (URSI GASS). - : IEEE. - 9789082598704 ; , s. 1-3
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Konferensbidrag (refereegranskat)abstract
- Spectral analysis based on short-time Fourier transform (STFT) using Kaiser window is proposed to examine the frequency components of neonates EIT data. In this way, a simultaneous spatial-time-frequency analysis is achieved.
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| 8. |
- Khodadad, Davood
(författare)
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Combined Digital Holography and Speckle Correlation for Rapid Shape Evaluation
- 2014
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Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- In manufacturing industry there is a high demand for on line quality control to minimize the risk of incorrectly produced objects. Conventional contact measurement methods are usually slow and invasive, meaning that they cannot be used for soft materials and for complex shapes without influencing thecontrolled parts. In contrast, interferometry and digital holography in combination with computers become faster, more reliable and highly accurate as an alternative non-contact technique for industrial shape evaluation. In digital holography, access to the complex wave field and the possibility tonumerically reconstruct holograms in different planes introduce a new degree of flexibility to optical metrology. With digital holography high resolution and precise three dimensional (3D) images of the manufactured parts can be generated. This technique can also be used to capture data in a single exposure,which is important when doing measurements in a disturbed environment.The aim of this thesis is to perform online process control of free-form manufactured objects by measuring the shape and compare it to the CAD-model. To do this, a new technique to measure surface gradients and shape based on single-shot dual wavelength digital holography and image correlation of speckle displacements is demonstrated. Based on an analytical relation between phase gradients and speckle displacements it is shown that an object is retrieved uniquely to shape and position without the unwrapping problems that usually appear in dual wavelength holography. The method is firstdemonstrated using continues wave laser light from two temperature controlled laser diodes operating at 640 nm. Further a specially designed dual core diode pumped fiber laser that produces pulsed light with wavelengths close to 1030 nm is used. One significant problem when using the dual wavelength single-shot approach is that phase ambiguities are built in to the system that needs to be corrected. An automatic calibration scheme is therefore required. The intrinsic flexibility of digital holography gives a possibility to compensate these aberrations and to remove errors, fully numerically without mechanical movements. In this thesis I present a calibration method which allows single-shot online shape evaluation in a disturbed environment. It is shown that phase maps and speckle displacements can be recovered free of chromatic aberrations. This is the first time that a single-shot dual wavelength calibration is reported by defining a criteria to make an automatic procedure.By the results of the presented work, it is experimentally verified that the single-shot dual wavelength digital holography and numerically generated speckle images can be used together with digital speckle correlation to retrieve and evaluate the object shape. The proposed method is also robust to large phasegradients and large movements within the intensity patterns. The advantage of the approach is that, using speckle displacements, the shape measurement can be done even though the synthetic wavelength is out of the dynamic range of the height variation of the object.
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| 9. |
- Khodadad, Davood
(författare)
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Combined Reduced Phase Dual-Directional Illumination Digital Holography and Speckle Displacements for Shape Measurement
- 2019
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Ingår i: International Journal of Optics. - : Hindawi Publishing Corporation. - 1687-9384 .- 1687-9392. ; 2019
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Tidskriftsartikel (refereegranskat)abstract
- We present a digital holographic method to increase height range measurement with a reduced phase ambiguity using a dual-directional illumination. Small changes in the angle of incident illumination introduce phase differences between the recorded complex fields. We decrease relative phase difference between the recorded complex fields 279 and 139 times by changing the angle of incident 0.5° and 1°, respectively. A two cent Euro coin edge groove is used to measure the shape. The groove depth is measured as ≈300 μm . Further, numerical refocusing and analysis of speckle displacements in two different planes are used to measure the depth without a use of phase unwrapping process.
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| 10. |
- Khodadad, Davood, 1985-
(författare)
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Creating a supportive and effective learning environment for engineering students : Pedagogical strategies, engagement, and enhanced outcomes
- 2023
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Ingår i: International Journal of Engineering Pedagogy. - : International Association of Online Engineering. - 2192-4880. ; 13:8, s. 33-50
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Tidskriftsartikel (refereegranskat)abstract
- Engineering education requires a strong emphasis on problem-solving, critical thinking, and practical application of knowledge. To achieve the highest quality of teaching, educators must create a trusting environment that allows students to feel comfortable asking questions and performing to the best of their abilities. This paper outlines the teaching philosophy and prac-tices of an engineering lecturer who has adapted his pedagogical approach across several universities in Sweden and abroad. The author emphasizes the importance of being flexible and responsive to student needs, offering early and constructive feedback, and providing students a safe and supportive learning environment with opportunities to develop program-ming skills. The paper also includes comments from students that reflect the author’s effec-tiveness as an educator in creating a supportive and challenging learning environment for engineering students.
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