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Andrew J Dugmore - One of the best experts on this subject based on the ideXlab platform.
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how does tephra deposit Thickness Change over time a calibration exercise based on the 1980 mount st helens tephra deposit
Journal of Volcanology and Geothermal Research, 2020Co-Authors: Nick A Cutler, Richard Streeter, Samantha Engwell, Matthew S M Bolton, Britta J L Jensen, Andrew J DugmoreAbstract:Abstract Tephra layers are frequently used to reconstruct past volcanic activity. Inferences made from tephra layers rely on the assumption that the preserved tephra layer is representative of the initial deposit. However, a great deal can happen to tephra after it is deposited; thus, tephra layer taphonomy is a crucial but poorly understood process. The overall goal of this research was to gain greater insight into the taphonomy of terrestrial tephra layers, specifically the extent to which deposit Thickness is altered over time, with implications for tephra volume estimation. We approached this by a)conducting a new survey of the tephra layer from the recent, well-studied eruption of Mount St Helens on May 18th, 1980 (MSH1980); b)modelling the tephra layer Thickness using a mathematical technique and c)comparing our results with an equivalent model based on measurements taken immediately after the eruption. In this way, we aimed to quantify any losses and transformations that have occurred. During our study, we collected measurements of tephra layer Thickness from 86 locations ranging from 600 km from the vent. Geochemical analysis was used to identify tephra of uncertain origin. Our results indicated that the extant tephra layer at undisturbed sites was representative of the original deposit: overall, preservation in these locations (in terms of Thickness, stratigraphy and geochemistry) had been remarkably good. However, the isopach maps generated from our measurements diverged from isopachs produced in the same way, but derived from the original survey data. Furthermore, our estimates of the quantity of tephra produced during the eruption greatly exceeded previous estimates of the fallout volume. In our study, inaccuracies in the modelled fallout arose from issues of sampling strategy, rather than taphonomy. Our results demonstrate the sensitivity of volcanological reconstructions to measurement location, and the great importance of reliably measured low/zero values in reconstructing tephra deposits.
F Eckstein - One of the best experts on this subject based on the ideXlab platform.
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predictive and concurrent validity of cartilage Thickness Change as a marker of knee osteoarthritis progression data from the osteoarthritis initiative
Osteoarthritis and Cartilage, 2017Co-Authors: W Wirth, David J Hunter, Michael C Nevitt, Leena Sharma, C K Kwoh, C Ladel, F EcksteinAbstract:Summary Objective To investigate the predictive and concurrent validity of magnetic resonance imaging (MRI)-based cartilage Thickness Change between baseline (BL) and year-two (Y2) follow-up (predictive validity) and between Y2 and Y4 follow-up (concurrent validity) for symptomatic and radiographic knee osteoarthritis (OA) progression during Y2→Y4. Methods 777 knees from 777 Osteoarthritis Initiative (OAI) participants (age: 61.3 ± 9.0 years, BMI: 30.1 ± 4.8 kg/m 2 ) with Kellgren Lawrence (KL) grade 1–3 at Y2 (visit before progression interval) had cartilage Thickness measurements from 3T MRI at BL, Y2 ( n = 777), and Y4 ( n = 708). Analysis of covariance and logistic regression were used to assess the association of pain progression (≥9 WOMAC units [scale 0–100], n = 205/572 with/without progression) and radiographic progression (≥0.7 mm minimum joint space width (mJSW) loss, n = 166/611 with/without progression) between Y2 and Y4 with preceding (BL→Y2) and concurrent (Y2→Y4) Change in central medial femorotibial (cMFTC) compartment cartilage Thickness. Results Symptomatic progression was associated with concurrent (Y2→Y4: −305 ± 470 μm vs −155 ± 346 μm, Odds ratios (OR) = 1.5 [1.2, 1.7]) but not with preceding cartilage Thickness loss in cMFTC (−150 ± 276 μm vs −151 ± 299 μm, OR = 0.9 95% CI: [0.8, 1.1]). Radiographic progression, in contrast, was significantly associated with both concurrent (−542 ± 550 μm vs −98 ± 255 μm, OR = 3.4 [2.6, 4.3]) and preceding cMFTC Thickness loss (−229 ± 355 μm vs −130 ± 270 μm, OR = 1.3 [1.1, 1.5]). Conclusions These results extend previous reports that did not discern predictive vs concurrent associations of cartilage Thickness loss with OA progression. The observed predictive and concurrent validity of cartilage Thickness loss for radiographic progression and observed concurrent validity for symptomatic progression provide an important step in qualifying cartilage Thickness loss as a biomarker of knee OA progression. Clinicaltrials.gov identification NCT00080171.
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five year followup of knee joint cartilage Thickness Changes after acute rupture of the anterior cruciate ligament
Arthritis & Rheumatism, 2015Co-Authors: F Eckstein, W Wirth, M Hudelmaier, L S Lohmander, Richard FrobellAbstract:Objective. Anterior cruciate ligament (ACL) rupture involves an increased risk of osteoarthritis. The purpose of this study was to explore Changes in cartilage Thickness over 5 years after ACL rupture. Methods. A total of 121 young active adults (ages 18-35 years; 26% women) from the Knee ACL, Nonsurgical versus Surgical Treatment (KANON) study, who had acute traumatic rupture of the ACL were studied. Sagittal magnetic resonance images were acquired within 4 weeks of ACL rupture (baseline) and at the 2-year and 5-year followup assessments. Medial and lateral femorotibial cartilage was segmented (with blinding to acquisition order), and the mean cartilage Thickness was computed across 16 femorotibial subregions. Total femorotibial cartilage Thickness Change was the primary analytic focus. Maximal subregional mean cartilage Thickness loss (ordered value 1 [OV1]) and gain (ordered value 16 [OV16]), independent of its specific location in individual knees, were the secondary analytic focus. Results. Overall femorotibial cartilage Thickness increased by 31 mu m/year over 5 years (95% confidence interval 18, 44). The increase was similar in men and women and was significantly greater in those younger, as compared with those older, than the median age (25.3 years). The rate of total cartilage Thickness Change did not differ significantly between the first 2 years and the later 3 years. However, the maximal annualized subregional cartilage loss (OV1) and gain (OV16) were both significantly greater (P < 0.001 and P < 0.05, respectively) during the earlier interval than during the later interval (-115 versus -54 mu m [OV1] and 116 versus 69 mu m [OV16]). Conclusion. Cartilage thickening was observed over 5 years following ACL injury, particularly in the medial femorotibial compartment and in younger subjects. Major perturbations in cartilage homeostasis were seen over the first 2 years after ACL rupture, with simultaneous subregional thinning and thickening occurring within the same cartilage plate or compartment. (Less)
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lateral and medial joint space narrowing predict subsequent cartilage loss in the narrowed but not in the non narrowed femorotibial compartment data from the osteoarthritis initiative
Osteoarthritis and Cartilage, 2014Co-Authors: W Wirth, Michael C Nevitt, M Hellio Le P Graverand, J A Lynch, S Maschek, M Hudelmaier, F EcksteinAbstract:Summary Objective To determine the predictive value of unicompartimental joint space narrowing (JSN) for MRI-based cartilage Thickness loss in the narrowed and the non-narrowed femorotibial compartment. Methods 922 knees from 922 Osteoarthritis Initiative (OAI) participants (62.2 ± 9.0 years, 61% females) with radiographic OA (158 without JSN [noJSN], 175 with lateral JSN [latJSN], 589 with medial JSN [medJSN]) were analyzed using 3 T MRI. One-year cartilage Thickness Change was determined in the lateral (LFTC) and medial femorotibial compartment (MFTC), and in femorotibial subregions. The probability of subsequent cartilage loss was calculated using predefined thresholds. The predictive value of JSN for the probability and magnitude of cartilage loss was compared between latJSN, medJSN and noJSN knees using Fisher's exact and Mann–Whitney- U tests. Results The probability of cartilage loss was greater in the narrowed compartment of latJSN/medJSN knees (34.9%/32.4%) than in noJSN knees (13.3%/12.7%, P ≤ 6.4 × 10 −6 ) and so was the magnitude of cartilage Thickness Change ( P ≤ 8.2 × 10 −6 ). No significant differences were observed between the narrowed compartments of latJSN vs medJSN knees (probability: P = 0.58, magnitude: P = 0.19) or between the non-narrowed compartment of latJSN/medJSN vs noJSN knees (probability: P ≥ 0.35, magnitude: P = ≥0.23). These results were confirmed by the location-independent ordered value (OV) analyses of femorotibial subregions. Conclusion The predictive value of latJSN for lateral compartment cartilage loss was comparable to that of medJSN for medial compartment cartilage loss, whereas cartilage loss in the non-narrowed compartment was similar to that in noJSN knees. These findings provide important clues to predicting progression of knee OA, and in tailoring inclusion criteria for clinical trials.
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frequency and spatial distribution of cartilage Thickness Change in knee osteoarthritis and its relation to clinical and radiographic covariates data from the osteoarthritis initiative
Osteoarthritis and Cartilage, 2013Co-Authors: R Buck, W Wirth, Michael C Nevitt, D Dreher, F EcksteinAbstract:Summary Objective Estimate the frequency and spatial location of rapid femorotibial cartilage thinning or thickening in knees with, or at risk of, osteoarthritis (OA) and examine their association with clinical and radiographic covariates. Design Knee cartilage Thickness Change over 12 months was measured using magnetic resonance imaging in the right knee of 757 Osteoarthritis Initiative (OAI) participants that had radiographic findings of osteophytes or joint space narrowing (JSN). Thickness Changes in individual knees were classified as having rapid thinning or thickening or no detectable OA-related Change when compared to asymptomatic OAI Control cohort knees. Results Cartilage thinning, found in 18.5% of subjects, was more frequent in knees with OAI calculated Kellgren–Lawrence grade (cKLG) > 2 ( P P = 0.047). No link was found between body mass index, sex, and age and cartilage thinning ( P > 0.15). The percent of knees with thickening was small (4.4%), but greater in knees with frequent pain ( P = 0.02). Rapid thinning was most common in the central (36.4%) and external (32.1%) subregions of the medial weight-bearing femur. Mean cartilage loss in rapidly thinning subregions ranged from 11.2%/y to 24.6%/y. Knees with cKLG > 2, but classified as having no detectable OA-related Change had mean cartilage loss rates significantly >0 (0.4%/y–1.3%/y) in 10 subregions. Conclusion Most observed subregional Changes in OA knees were indistinguishable from Changes found in an asymptomatic cohort, but a fraction of subregions showed rapid progression. The relative frequency of rapid thinning increases when cKLG > 2, a classification closely associated with JSN and/or frequent knee pain are present.
Nick A Cutler - One of the best experts on this subject based on the ideXlab platform.
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how does tephra deposit Thickness Change over time a calibration exercise based on the 1980 mount st helens tephra deposit
Journal of Volcanology and Geothermal Research, 2020Co-Authors: Nick A Cutler, Richard Streeter, Samantha Engwell, Matthew S M Bolton, Britta J L Jensen, Andrew J DugmoreAbstract:Abstract Tephra layers are frequently used to reconstruct past volcanic activity. Inferences made from tephra layers rely on the assumption that the preserved tephra layer is representative of the initial deposit. However, a great deal can happen to tephra after it is deposited; thus, tephra layer taphonomy is a crucial but poorly understood process. The overall goal of this research was to gain greater insight into the taphonomy of terrestrial tephra layers, specifically the extent to which deposit Thickness is altered over time, with implications for tephra volume estimation. We approached this by a)conducting a new survey of the tephra layer from the recent, well-studied eruption of Mount St Helens on May 18th, 1980 (MSH1980); b)modelling the tephra layer Thickness using a mathematical technique and c)comparing our results with an equivalent model based on measurements taken immediately after the eruption. In this way, we aimed to quantify any losses and transformations that have occurred. During our study, we collected measurements of tephra layer Thickness from 86 locations ranging from 600 km from the vent. Geochemical analysis was used to identify tephra of uncertain origin. Our results indicated that the extant tephra layer at undisturbed sites was representative of the original deposit: overall, preservation in these locations (in terms of Thickness, stratigraphy and geochemistry) had been remarkably good. However, the isopach maps generated from our measurements diverged from isopachs produced in the same way, but derived from the original survey data. Furthermore, our estimates of the quantity of tephra produced during the eruption greatly exceeded previous estimates of the fallout volume. In our study, inaccuracies in the modelled fallout arose from issues of sampling strategy, rather than taphonomy. Our results demonstrate the sensitivity of volcanological reconstructions to measurement location, and the great importance of reliably measured low/zero values in reconstructing tephra deposits.
Fiona Coutts - One of the best experts on this subject based on the ideXlab platform.
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abdominal muscle function in chronic low back pain patients measurement with real time ultrasound scanning
Physiotherapy, 2002Co-Authors: Duncan Critchley, Fiona CouttsAbstract:Summary Purpose It has been suggested that transversus abdominis acts as an active stabiliser of the lumbar spine and may be dysfunctional in chronic low back pain patients. Low abdominal hollowing in four-point kneeling is a standard clinical test for transversus abdominis, but is difficult to quantify. Change of muscle Thickness may be an indication of transversus abdominis muscle contraction and is measurable with ultrasound scanning. The purpose of this study was to investigate whether there were differences between chronic low back pain and healthy subjects in abdominal muscles' Change of Thickness during low abdominal hollowing using ultrasound scanning. Methods A pilot study established muscle Thickness measurements via scanning as having acceptable short-term repeatability. Twenty chronic low back pain patients and 24 controls were scanned at rest and during low abdominal hollowing in four-point kneeling. The Thickness and Thickness Change of obliquus externus, obliquus internus and transversus abdominis were measured via a standardised procedure. Differences between groups were examined using ANOVA. Results There was a smaller increase in Thickness (mean ± SD) of transversus abdominis in the patients (19.15 ± 24.07%)than controls (49.71 ± 26.76%) (p Conclusion Real-time ultrasound scanning is potentially a practical means of quantifying transversus abdominis performance. A transversus abdominis dysfunction may occur in many chronic low back pain patients and its assessment and rehabilitation should be considered in these people. The validity of using Thickness Change as a measure of muscle function, the correlation of transversus abdominis dysfunction with other clinical features and the effect of specific retraining all require further investigation.
W Wirth - One of the best experts on this subject based on the ideXlab platform.
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predictive and concurrent validity of cartilage Thickness Change as a marker of knee osteoarthritis progression data from the osteoarthritis initiative
Osteoarthritis and Cartilage, 2017Co-Authors: W Wirth, David J Hunter, Michael C Nevitt, Leena Sharma, C K Kwoh, C Ladel, F EcksteinAbstract:Summary Objective To investigate the predictive and concurrent validity of magnetic resonance imaging (MRI)-based cartilage Thickness Change between baseline (BL) and year-two (Y2) follow-up (predictive validity) and between Y2 and Y4 follow-up (concurrent validity) for symptomatic and radiographic knee osteoarthritis (OA) progression during Y2→Y4. Methods 777 knees from 777 Osteoarthritis Initiative (OAI) participants (age: 61.3 ± 9.0 years, BMI: 30.1 ± 4.8 kg/m 2 ) with Kellgren Lawrence (KL) grade 1–3 at Y2 (visit before progression interval) had cartilage Thickness measurements from 3T MRI at BL, Y2 ( n = 777), and Y4 ( n = 708). Analysis of covariance and logistic regression were used to assess the association of pain progression (≥9 WOMAC units [scale 0–100], n = 205/572 with/without progression) and radiographic progression (≥0.7 mm minimum joint space width (mJSW) loss, n = 166/611 with/without progression) between Y2 and Y4 with preceding (BL→Y2) and concurrent (Y2→Y4) Change in central medial femorotibial (cMFTC) compartment cartilage Thickness. Results Symptomatic progression was associated with concurrent (Y2→Y4: −305 ± 470 μm vs −155 ± 346 μm, Odds ratios (OR) = 1.5 [1.2, 1.7]) but not with preceding cartilage Thickness loss in cMFTC (−150 ± 276 μm vs −151 ± 299 μm, OR = 0.9 95% CI: [0.8, 1.1]). Radiographic progression, in contrast, was significantly associated with both concurrent (−542 ± 550 μm vs −98 ± 255 μm, OR = 3.4 [2.6, 4.3]) and preceding cMFTC Thickness loss (−229 ± 355 μm vs −130 ± 270 μm, OR = 1.3 [1.1, 1.5]). Conclusions These results extend previous reports that did not discern predictive vs concurrent associations of cartilage Thickness loss with OA progression. The observed predictive and concurrent validity of cartilage Thickness loss for radiographic progression and observed concurrent validity for symptomatic progression provide an important step in qualifying cartilage Thickness loss as a biomarker of knee OA progression. Clinicaltrials.gov identification NCT00080171.
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five year followup of knee joint cartilage Thickness Changes after acute rupture of the anterior cruciate ligament
Arthritis & Rheumatism, 2015Co-Authors: F Eckstein, W Wirth, M Hudelmaier, L S Lohmander, Richard FrobellAbstract:Objective. Anterior cruciate ligament (ACL) rupture involves an increased risk of osteoarthritis. The purpose of this study was to explore Changes in cartilage Thickness over 5 years after ACL rupture. Methods. A total of 121 young active adults (ages 18-35 years; 26% women) from the Knee ACL, Nonsurgical versus Surgical Treatment (KANON) study, who had acute traumatic rupture of the ACL were studied. Sagittal magnetic resonance images were acquired within 4 weeks of ACL rupture (baseline) and at the 2-year and 5-year followup assessments. Medial and lateral femorotibial cartilage was segmented (with blinding to acquisition order), and the mean cartilage Thickness was computed across 16 femorotibial subregions. Total femorotibial cartilage Thickness Change was the primary analytic focus. Maximal subregional mean cartilage Thickness loss (ordered value 1 [OV1]) and gain (ordered value 16 [OV16]), independent of its specific location in individual knees, were the secondary analytic focus. Results. Overall femorotibial cartilage Thickness increased by 31 mu m/year over 5 years (95% confidence interval 18, 44). The increase was similar in men and women and was significantly greater in those younger, as compared with those older, than the median age (25.3 years). The rate of total cartilage Thickness Change did not differ significantly between the first 2 years and the later 3 years. However, the maximal annualized subregional cartilage loss (OV1) and gain (OV16) were both significantly greater (P < 0.001 and P < 0.05, respectively) during the earlier interval than during the later interval (-115 versus -54 mu m [OV1] and 116 versus 69 mu m [OV16]). Conclusion. Cartilage thickening was observed over 5 years following ACL injury, particularly in the medial femorotibial compartment and in younger subjects. Major perturbations in cartilage homeostasis were seen over the first 2 years after ACL rupture, with simultaneous subregional thinning and thickening occurring within the same cartilage plate or compartment. (Less)
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lateral and medial joint space narrowing predict subsequent cartilage loss in the narrowed but not in the non narrowed femorotibial compartment data from the osteoarthritis initiative
Osteoarthritis and Cartilage, 2014Co-Authors: W Wirth, Michael C Nevitt, M Hellio Le P Graverand, J A Lynch, S Maschek, M Hudelmaier, F EcksteinAbstract:Summary Objective To determine the predictive value of unicompartimental joint space narrowing (JSN) for MRI-based cartilage Thickness loss in the narrowed and the non-narrowed femorotibial compartment. Methods 922 knees from 922 Osteoarthritis Initiative (OAI) participants (62.2 ± 9.0 years, 61% females) with radiographic OA (158 without JSN [noJSN], 175 with lateral JSN [latJSN], 589 with medial JSN [medJSN]) were analyzed using 3 T MRI. One-year cartilage Thickness Change was determined in the lateral (LFTC) and medial femorotibial compartment (MFTC), and in femorotibial subregions. The probability of subsequent cartilage loss was calculated using predefined thresholds. The predictive value of JSN for the probability and magnitude of cartilage loss was compared between latJSN, medJSN and noJSN knees using Fisher's exact and Mann–Whitney- U tests. Results The probability of cartilage loss was greater in the narrowed compartment of latJSN/medJSN knees (34.9%/32.4%) than in noJSN knees (13.3%/12.7%, P ≤ 6.4 × 10 −6 ) and so was the magnitude of cartilage Thickness Change ( P ≤ 8.2 × 10 −6 ). No significant differences were observed between the narrowed compartments of latJSN vs medJSN knees (probability: P = 0.58, magnitude: P = 0.19) or between the non-narrowed compartment of latJSN/medJSN vs noJSN knees (probability: P ≥ 0.35, magnitude: P = ≥0.23). These results were confirmed by the location-independent ordered value (OV) analyses of femorotibial subregions. Conclusion The predictive value of latJSN for lateral compartment cartilage loss was comparable to that of medJSN for medial compartment cartilage loss, whereas cartilage loss in the non-narrowed compartment was similar to that in noJSN knees. These findings provide important clues to predicting progression of knee OA, and in tailoring inclusion criteria for clinical trials.
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frequency and spatial distribution of cartilage Thickness Change in knee osteoarthritis and its relation to clinical and radiographic covariates data from the osteoarthritis initiative
Osteoarthritis and Cartilage, 2013Co-Authors: R Buck, W Wirth, Michael C Nevitt, D Dreher, F EcksteinAbstract:Summary Objective Estimate the frequency and spatial location of rapid femorotibial cartilage thinning or thickening in knees with, or at risk of, osteoarthritis (OA) and examine their association with clinical and radiographic covariates. Design Knee cartilage Thickness Change over 12 months was measured using magnetic resonance imaging in the right knee of 757 Osteoarthritis Initiative (OAI) participants that had radiographic findings of osteophytes or joint space narrowing (JSN). Thickness Changes in individual knees were classified as having rapid thinning or thickening or no detectable OA-related Change when compared to asymptomatic OAI Control cohort knees. Results Cartilage thinning, found in 18.5% of subjects, was more frequent in knees with OAI calculated Kellgren–Lawrence grade (cKLG) > 2 ( P P = 0.047). No link was found between body mass index, sex, and age and cartilage thinning ( P > 0.15). The percent of knees with thickening was small (4.4%), but greater in knees with frequent pain ( P = 0.02). Rapid thinning was most common in the central (36.4%) and external (32.1%) subregions of the medial weight-bearing femur. Mean cartilage loss in rapidly thinning subregions ranged from 11.2%/y to 24.6%/y. Knees with cKLG > 2, but classified as having no detectable OA-related Change had mean cartilage loss rates significantly >0 (0.4%/y–1.3%/y) in 10 subregions. Conclusion Most observed subregional Changes in OA knees were indistinguishable from Changes found in an asymptomatic cohort, but a fraction of subregions showed rapid progression. The relative frequency of rapid thinning increases when cKLG > 2, a classification closely associated with JSN and/or frequent knee pain are present.