The Experts below are selected from a list of 39963 Experts worldwide ranked by ideXlab platform
Oliver Speck - One of the best experts on this subject based on the ideXlab platform.
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prevention of motion induced Signal loss in diffusion weighted echo planar imaging by dynamic restoration of gradient moments
Magnetic Resonance in Medicine, 2014Co-Authors: Kazim Gumus, Brian Keating, Benedikt A Poser, Brian S R Armstrong, Linda Chang, Julian Maclaren, Thomas E Prieto, Oliver SpeckAbstract:PURPOSE: Head motion is a significant problem in diffusion-weighted imaging as it may cause Signal Attenuation due to residual dephasing during strong diffusion encoding gradients even in single-shot acquisitions. Here, we present a new real-time method to prevent motion-induced Signal loss in DWI of the brain. METHODS: The method requires a fast motion tracking system (optical in the current implementation). Two alterations were made to a standard diffusion-weighted echo-planar imaging sequence: first, real-time motion correction ensures that slices are correctly aligned relative to the moving brain. Second, the tracking data are used to calculate the motion-induced gradient moment imbalance which occurs during the diffusion encoding periods, and a brief gradient blip is inserted immediately prior to the Signal readout to restore the gradient moment balance. RESULTS: Phantom experiments show that the direction as well as magnitude of the gradient moment imbalance affects the characteristics of unwanted Signal Attenuation. In human subjects, the addition of a moment-restoring blip prevented Signal loss and improved the reproducibility and reliability of diffusion tensor measures even in the presence of substantial head movements. CONCLUSION: The method presented can improve robustness for clinical routine scanning in populations that are prone to head movements, such as children and uncooperative adult patients.
Michael G Sowa - One of the best experts on this subject based on the ideXlab platform.
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Signal Attenuation and box counting fractal analysis of optical coherence tomography images of arterial tissue
Biomedical Optics Express, 2010Co-Authors: Dan P Popescu, Costel Flueraru, Shoude Chang, Michael G SowaAbstract:The sensitivity of optical coherence tomography images to sample morphology is tested by two methods. The first method estimates the Attenuation of the OCT Signal from various regions of the probed tissue. The second method uses a box-counting algorithm to calculate the fractal dimensions in the regions of interest identified in the images. Although both the Attenuation coefficient as well as the fractal dimension correlate very well with the anatomical features of the probed samples; the Attenuation method provides a better sensitivity. Two types of samples are used in this study: segments of arteries collected from atherosclerosis–prone Watanabe rabbits (WHHL-MI) and healthy segments of porcine coronary arteries.
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added soft tissue contrast using Signal Attenuation and the fractal dimension for optical coherence tomography images of porcine arterial tissue
Physics in Medicine and Biology, 2010Co-Authors: Costel Flueraru, Dan P Popescu, Shoude Chang, Michael G SowaAbstract:Optical coherence tomography (OCT) images of left-descending coronary tissues harvested from three porcine specimens were acquired with a home-build swept-source OCT setup. Despite the fact that OCT is capable of acquiring high resolution circumferential images of vessels, many distinct histological features of a vessel have comparable optical properties leading to poor contrast in OCT images. Two classification methods were tested in this report for the purpose of enhancing contrast between soft-tissue components of porcine coronary vessels. One method involved analyzing the Attenuation of the OCT Signal as a function of light penetration into the tissue. We demonstrated that by analyzing the Signal Attenuation in this manner we were able to differentiate two media sub-layers with different orientations of the smooth muscle cells. The other classification method used in our study was fractal analysis. Fractal analysis was implemented in a box-counting (fractal dimension) image-processing code and was used as a tool to differentiate and quantify variations in tissue texture at various locations in the OCT images. The calculated average fractal dimensions had different values in distinct regions of interest (ROI) within the imaged coronary samples. When compared to the results obtained by using the Attenuation of the OCT Signal, the method of fractal analysis demonstrated better classification potential for distinguishing amongst the tissue ROI.
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assessment of early demineralization in teeth using the Signal Attenuation in optical coherence tomography images
Journal of Biomedical Optics, 2008Co-Authors: Dan P Popescu, Michael G Sowa, Mark Hewko, Linp Ing ChoosmithAbstract:Optical coherence tomography imaging is used to improve the detection of incipient carious lesions in dental enamel. Measurements of Signal Attenuation in images acquired with an 850-nm light source were performed on 21 extracted molars from eight human volunteers. Stronger Attenuation was observed for the optical coherence tomography (OCT) Signal in healthy enamel than in carious lesions. The measured Attenuation coefficients from the two groups form distinct statistical populations. The coefficients obtained from sound enamel fall within the range of 0.70 to 2.14 mm−1 with a mean value of 1.35 mm−1, while those in carious regions range from 0.47 to 1.88 mm−1, with a mean value of 0.77 mm−1. Three values are selected as the lower threshold for Signal Attenuation in sound enamel: 0.99, 0.94, and 0.88 mm−1. These thresholds were selected to provide detection of sound enamel with fixed specificities of 90%, 95%, and 97.5%, respectively. The corresponding sensitivities for the detection of carious lesions are 92.8%, 90.4%, and 87%, respectively, for the sample population used in this study. These findings suggest that Attenuation of OCT Signal at 850 nm could be an indicator of tooth demineralization and could be used as a marker for early caries detection.
Dan P Popescu - One of the best experts on this subject based on the ideXlab platform.
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Signal Attenuation and box counting fractal analysis of optical coherence tomography images of arterial tissue
Biomedical Optics Express, 2010Co-Authors: Dan P Popescu, Costel Flueraru, Shoude Chang, Michael G SowaAbstract:The sensitivity of optical coherence tomography images to sample morphology is tested by two methods. The first method estimates the Attenuation of the OCT Signal from various regions of the probed tissue. The second method uses a box-counting algorithm to calculate the fractal dimensions in the regions of interest identified in the images. Although both the Attenuation coefficient as well as the fractal dimension correlate very well with the anatomical features of the probed samples; the Attenuation method provides a better sensitivity. Two types of samples are used in this study: segments of arteries collected from atherosclerosis–prone Watanabe rabbits (WHHL-MI) and healthy segments of porcine coronary arteries.
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added soft tissue contrast using Signal Attenuation and the fractal dimension for optical coherence tomography images of porcine arterial tissue
Physics in Medicine and Biology, 2010Co-Authors: Costel Flueraru, Dan P Popescu, Shoude Chang, Michael G SowaAbstract:Optical coherence tomography (OCT) images of left-descending coronary tissues harvested from three porcine specimens were acquired with a home-build swept-source OCT setup. Despite the fact that OCT is capable of acquiring high resolution circumferential images of vessels, many distinct histological features of a vessel have comparable optical properties leading to poor contrast in OCT images. Two classification methods were tested in this report for the purpose of enhancing contrast between soft-tissue components of porcine coronary vessels. One method involved analyzing the Attenuation of the OCT Signal as a function of light penetration into the tissue. We demonstrated that by analyzing the Signal Attenuation in this manner we were able to differentiate two media sub-layers with different orientations of the smooth muscle cells. The other classification method used in our study was fractal analysis. Fractal analysis was implemented in a box-counting (fractal dimension) image-processing code and was used as a tool to differentiate and quantify variations in tissue texture at various locations in the OCT images. The calculated average fractal dimensions had different values in distinct regions of interest (ROI) within the imaged coronary samples. When compared to the results obtained by using the Attenuation of the OCT Signal, the method of fractal analysis demonstrated better classification potential for distinguishing amongst the tissue ROI.
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assessment of early demineralization in teeth using the Signal Attenuation in optical coherence tomography images
Journal of Biomedical Optics, 2008Co-Authors: Dan P Popescu, Michael G Sowa, Mark Hewko, Linp Ing ChoosmithAbstract:Optical coherence tomography imaging is used to improve the detection of incipient carious lesions in dental enamel. Measurements of Signal Attenuation in images acquired with an 850-nm light source were performed on 21 extracted molars from eight human volunteers. Stronger Attenuation was observed for the optical coherence tomography (OCT) Signal in healthy enamel than in carious lesions. The measured Attenuation coefficients from the two groups form distinct statistical populations. The coefficients obtained from sound enamel fall within the range of 0.70 to 2.14 mm−1 with a mean value of 1.35 mm−1, while those in carious regions range from 0.47 to 1.88 mm−1, with a mean value of 0.77 mm−1. Three values are selected as the lower threshold for Signal Attenuation in sound enamel: 0.99, 0.94, and 0.88 mm−1. These thresholds were selected to provide detection of sound enamel with fixed specificities of 90%, 95%, and 97.5%, respectively. The corresponding sensitivities for the detection of carious lesions are 92.8%, 90.4%, and 87%, respectively, for the sample population used in this study. These findings suggest that Attenuation of OCT Signal at 850 nm could be an indicator of tooth demineralization and could be used as a marker for early caries detection.
Eric C Wong - One of the best experts on this subject based on the ideXlab platform.
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optimized isotropic diffusion weighting
Magnetic Resonance in Medicine, 1995Co-Authors: Eric C Wong, Allen W SongAbstract:The authors introduce several sets of time-efficient gradient waveforms for applying isotropic diffusion weighting in NMR experiments. This creates Signal Attenuation that depends on the trace of the diffusion tensor and is therefore rotationally invariant. Numerical methods for the calculation of such gradient sets are outlined, and results are shown for isotropic and anisotropic gradient hardware and first order flow moment nulled diffusion weighting gradients. Preliminary experimental results from the human brain validate this new technique.
Mitsuaki Isobe - One of the best experts on this subject based on the ideXlab platform.
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clinical significance of echo Signal Attenuation on intravascular ultrasound in patients with coronary artery disease
Circulation-cardiovascular Interventions, 2009Co-Authors: Shigeki Kimura, Tsunekazu Kakuta, Taishi Yonetsu, Asami Suzuki, Yoshito Iesaka, Hideomi Fujiwara, Mitsuaki IsobeAbstract:Background— Atherosclerotic plaque that shows echo Signal Attenuation (EA) without associated bright echoes is sometimes observed by intravascular ultrasound but its clinical significance remains unclear. We investigated the impact of EA on coronary perfusion and evaluated the pathological features of plaque with EA. Methods and Results— We studied 687 native coronary lesions in 687 consecutive patients (336 with acute coronary syndrome and 351 with stable angina pectoris) who underwent intravascular ultrasound before percutaneous coronary intervention. By subgroup analysis, 60 lesions (30 lesions with EA) treated with directional coronary atherectomy underwent pathological examination. The Thrombolysis in Myocardial Infarction (TIMI) flow grade and myocardial blush grade after percutaneous coronary intervention were compared between lesions with and without EA in 627 lesions except directional coronary atherectomy subgroup. EA was observed in 245 lesions (35.7%), and coronary flow after percutaneous coronary intervention was worse for lesions with EA than without (final TIMI grade of 0 to 2: 15.4% versus 2.4%, P <0.001; final myocardial blush grade of 0 to 2: 45.6% versus 21.4%, P <0.001). Multivariate analysis revealed a significant association between no reflow (TIMI grade 0 to 2) and EA (odds ratio, 5.59; 95% CI, 2.64 to 11.85; P <0.001), a baseline TIMI grade of 0 to 2 (odds ratio, 5.91; 95% CI, 2.79 to 12.5; P <0.001), and a large reference area (odds ratio, 3.08; 95% CI, 1.40 to 6.76; P =0.005) after controlling for other associated factors. Pathological examination revealed a significantly higher frequency of lipid-rich plaque with microcalcification in lesions with EA. Conclusions— Atherosclerotic plaque with EA showed a significant association with no reflow after percutaneous coronary intervention, suggesting the existence of fragile components susceptible to distal embolization. Received September 16, 2008; accepted August 17, 2009.
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clinical significance of echo Signal Attenuation on intravascular ultrasound in patients with coronary artery disease
Circulation-cardiovascular Interventions, 2009Co-Authors: Shigeki Kimura, Tsunekazu Kakuta, Taishi Yonetsu, Asami Suzuki, Yoshito Iesaka, Hideomi Fujiwara, Mitsuaki IsobeAbstract:Background— Atherosclerotic plaque that shows echo Signal Attenuation (EA) without associated bright echoes is sometimes observed by intravascular ultrasound but its clinical significance remains unclear. We investigated the impact of EA on coronary perfusion and evaluated the pathological features of plaque with EA. Methods and Results— We studied 687 native coronary lesions in 687 consecutive patients (336 with acute coronary syndrome and 351 with stable angina pectoris) who underwent intravascular ultrasound before percutaneous coronary intervention. By subgroup analysis, 60 lesions (30 lesions with EA) treated with directional coronary atherectomy underwent pathological examination. The Thrombolysis in Myocardial Infarction (TIMI) flow grade and myocardial blush grade after percutaneous coronary intervention were compared between lesions with and without EA in 627 lesions except directional coronary atherectomy subgroup. EA was observed in 245 lesions (35.7%), and coronary flow after percutaneous coronary intervention was worse for lesions with EA than without (final TIMI grade of 0 to 2: 15.4% versus 2.4%, P <0.001; final myocardial blush grade of 0 to 2: 45.6% versus 21.4%, P <0.001). Multivariate analysis revealed a significant association between no reflow (TIMI grade 0 to 2) and EA (odds ratio, 5.59; 95% CI, 2.64 to 11.85; P <0.001), a baseline TIMI grade of 0 to 2 (odds ratio, 5.91; 95% CI, 2.79 to 12.5; P <0.001), and a large reference area (odds ratio, 3.08; 95% CI, 1.40 to 6.76; P =0.005) after controlling for other associated factors. Pathological examination revealed a significantly higher frequency of lipid-rich plaque with microcalcification in lesions with EA. Conclusions— Atherosclerotic plaque with EA showed a significant association with no reflow after percutaneous coronary intervention, suggesting the existence of fragile components susceptible to distal embolization. Received September 16, 2008; accepted August 17, 2009.
