Confidence Limits For Change Research Articles

Element mobility and spatial zonation associated with the Archean Hamlet orogenic Au deposit, Western Australia: Implications for fluid pathways in shear zones

Mass balance equations can be used to understand metasomatism. Here we use 2726 multi-element chemical analyses to quantify the effect of metasomatism associated with Au mineralisation at the Hamlet Gold Mine (Hamlet), Yilgarn Craton, Western Australia. Principal components analysis is first used to identify covarying elements and six groups of elements are identified: (1) relatively immobile elements, with Zr and Hf providing an appropriate reference frame for mass balance calculations; (2) elements associated with mafic rocks, such as Ca, Co, Fe, Ge, Mg, Mn, and Zn; (3) elements related to potassic alteration, Ba, Cs, K, Rb, and Tl; (4) elements related to sodic alteration, Be, Na, and Sr; (5) chalcophile elements, including Bi, weakly associated with Au; and (6) Au, Te, and S representing the main Au-mineralising event. A statistically-rigorous approach is then used to quantify element addition and depletion and provides 95% confidence limits for changes in mass. To achieve this, the basaltic host rocks are divided into four subunits based on Cr content. Sample subsets are then created to select altered rocks and least-altered protolith rocks, using discrimination diagrams. Pairings of least altered-altered samples from each basalt subunit are used to construct matrices via bootstrapping. Mass balance results from these matrices indicate similar element mobility associated with Au mineralisation across the four basalt subunits, with up to 24% mass loss. Key potassic and sodic group elements are enriched in the Au mineralised zones at the expense of elements with a mafic-association. Spatial patterns of mass change are linear and repetitive within the steeply-dipping Hamlet Shear Zone, interpreted to represent a mesh-like geometry of metasomatism within the plane of the shear zone. Localised enrichment of K, Na, and Bi are related to Au distribution while Ca depletion zones reflect the movement of reactive fluid along the shear plane.

Repeatability of graph theoretical metrics derived from resting-state functional networks in paediatric epilepsy patients.

To measure the repeatability of metrics that quantify brain network architecture derived from resting-state functional MRI in a cohort of paediatric patients with epilepsy. We identified patients with: (1) epilepsy; (2) brain MRI at 3 T; (3) two identical resting-state functional MRI acquisitions performed on the same day. Undirected, weighted networks were constructed based on the resting-state time series using a range of processing parameters including parcellation size and graph threshold. The following topological properties were calculated: degree, strength, characteristic path length, global efficiency, clustering coefficient, modularity and small worldness. Based on repeated measures, we then calculated: (1) Pearson correlation coefficient; (2) intraclass correlation coefficient; (3) root-mean-square coefficient of variation; (4) repeatability coefficient; and (5) 95% confidence limits for change. 26 patients were included (age range: 4-21 years). Correlation coefficients demonstrated a highly consistent relationship between repeated observations for all metrics, and the intraclass correlation coefficients were generally in the excellent range. Repeatability in the data set was not significantly influenced by parcellation size. However, trends towards decreased repeatability were observed at higher graph thresholds. These findings demonstrate the reliability of network metrics in a cohort of paediatric patients with epilepsy. Advances in knowledge: Our results point to the potential for graph theoretical analyses of resting-state data to provide reliable markers of network architecture in children with epilepsy. At the level of an individual patient, change over time greater than the repeatability coefficient or 95% confidence limits for change is unlikely to be related to intrinsic variability of the method.

Prognostic significance of early changes in the apparent diffusion coefficient that occurs after treatment of patients with glioblastoma multiforme with bevacizumab

2058 Background: To determine the prognostic significance of changes in parameters derived from diffusion tensor imaging (DTI) that occur in response to combination chemotherapy with the antiangiogenesis agent bevacizumab (BEV) in patients with recurrent glioblastoma multiforme (GBM). Methods: 16 patients (10 men, 6 women; age range 38–62 years) with recurrent GBM underwent serial 1.5T MR imaging. Axial single-shot echo planar DTI (TR/TE 6000/100; flip angle 90 degrees; voxel: 1.72 x 1.72 x 5mm; b value of 1000 sec/mm2; 12 directions) was obtained on scans performed 3 days and 1 day prior to and 1 day after initiation of therapy with BEV and irinotecan (CPT-11). Clinical follow-up and survival status was documented up to 20 months after the date of initial MR imaging. Apparent diffusion coefficient (ADC) and fractional anisotropy (FA) maps were aligned to whole brain contrast-enhanced 3D FLASH and 3D FLAIR image volumes (1 mm isotropic voxels) using a rigid body normalized mutual information algorithm. Based on two pre-treatment scans, the 95% confidence limits for change (95%CL) in ADC and FA were calculated in volumes of tumor-related contrast-enhancement (TRE) and FLAIR signal abnormality (FSA). A patient was considered to have a change in FA or ADC after therapy if the difference between the pre- and post-treatment values was greater than the 95% CL for that parameter. Progression was defined on contrast-enhanced MRI using MacDonald criteria by neuro-oncologists blinded to the DTI findings. Survival was compared using the log rank test. Results: DTI detected a change in ADC within FSA after therapy in three patients (2 increased, 1 decreased). Patients with a change in ADC within FSA had significantly shorter overall (p < 0.0012) and progression free (p < 0.015) survival than those with no change. Median survival in the patient group with a change in ADC was 24.7 (95% CI [17.3, 39.4]) weeks and 56.4 (95% CI [41.7, 96]) weeks in those patients with no change. Conclusions: In patients with GBM treated with BEV and CPT-11, a change in ADC after therapy in areas of FSA is associated with decreased survival. Parameters derived from DTI may, therefore, potentially serve as early markers of treatment failure in patients with GBM. [Table: see text]

Determination of inter-spinous process distance in the lumbar spine. Evaluation of reference population to facilitate detection of severe trauma.

Fracture of a spinal segment with minimal or no compression of the vertebral body can be highly unstable. Screening for such an injury in the lumbar spine is often obstructed in a multi-injured patient, because of difficulty in obtaining adequate sagittal radiographs. The position of the spinous processes in relation to each other is the key for proper evaluation of the status of the posterior stabilising structures. The amount of separation or axial rotation of the posterior part of the vertebra that can occur before failure of the posterior structures has not been unambiguously defined. Despite this, it can be assumed that severe separation of the spinous processes indicates a more or less pronounced loss of mechanical support. An analysis of how the posterior spinous processes relate to each other on an anteroposterior (AP) radiograph could obviate this problem. A new, simple and reproducible radiographic tool is presented for screening of an eventual rupture of posterior structures of the lumbar spine. This method is based on measurements of the variation in interspinal process distance between adjacent levels in lumbar spine in a normal population. Two hundred normal AP radiographs of non-injured thoracolumbar spine were studied. The interspinal process distance was measured as the distance between the cranial ends of the adjacent projections of spinous processes on AP radiographs. The mean values and 99% confidence limits for changes in the interspinal process distances between adjacent spinal levels were determined and analysed in relation to age, gender and spinal segment level. An upper limit of a normal difference in distance between the spinous processes at two adjacent levels was determined to be 7-10 mm, depending on age and location in the lumbar spine. A difference in interspinal process distance exceeding 7 mm between two adjacent lumbar levels should alert a surgeon to severe and unstable injury.

Reliability of low contrast letter charts in different viewing conditions

Test‐retest scores were obtained under binocular, monocular and monocular in the presence of conditions from 20 healthy older patients using the Pelli‐Robson and Regan (96% and 11% contrast) charts. Data were analysed using two indices: coefficients of repeatability and intra‐class correlation coefficients. Coefficient of repeatability determines the 95% confidence limits for change. The Regan 96% contrast chart showed the highest reliability under all viewing conditions. Comparing the different viewing conditions, binocular viewing showed the smallest coefficient of repeatability and the highest intra‐class correlation. Monocular viewing in the presence of glare showed the largest coefficient of repeatability and the lowest intra‐class coefficient. The results demonstrate the need for measuring reliability criteria under the appropriate viewing conditions when determining whether a significant change has occurred, e.g. with monocular glare scores in cataract or binocular performance in amblyopia.

Reliability of low contrast letter charts in various viewing conditions

Test-retest data were obtained binocularly, monocularly and monocularly in the presence of glare from 20 healthy older patients using the Pelli-Robson and Regan (96% and 11% contrast) charts. Reliability was assessed by means of two indices: intra-class correlation coefficient and coefficient of repeatability which determines the 95% confidence limits for change. Binocular viewing showed the highest intra-class correlation and the smallest confidence interval with all the charts. Monocular viewing in the presence of glare showed the lowest correlation and the largest confidence interval. Results suggest that when assessing the significance of change, the confidence interval should be determined for identical viewing conditions.

A comparison of lateral versus anterior-posterior spine dual energy x-ray absorptiometry for the diagnosis of osteopenia.

Because bone mineral density (BMD) measurements at various sites differ in the relative amounts of cortical and trabecular bone that they assess, they also differ in their sensitivity for detecting osteopenia. Lateral spine dual energy x-ray absorptiometry (DXA) allows measurement of BMD of the vertebral bodies, which contain mainly trabecular bone, without contribution from the posterior vertebral elements, which are rich in cortical bone. Thus, we hypothesized that lateral spine DXA would detect osteopenia more frequently than anterior-posterior (AP) spine DXA. To assess the ability of DXA to estimate trabecular bone mass, we compared AP and lateral DXA spine measurements with trabecular bone measurements by quantitative computed tomography (QCT) in 58 patients. We then compared AP vs. lateral spine DXA measurements in 1) 300 women referred for routine bone densitometry, 2) 30 glucocorticoid-treated women, and 3) 44 women with vertebral compression fractures. To compare short term reproducibility, we performed repeat AP and lateral DXA scans in 50 women. The association between QCT and DXA measurements was stronger when DXA measurements were made in the lateral (r = 0.784) or midlateral (r = 0.823) projection than in the AP (r = 0.571) projection. The association of BMD with age was stronger when DXA measurements were made in the lateral (r = 0.536) or midlateral (r = 0.536) projection than in the AP (r = 0.382) projection. The declines in BMD with age for AP, lateral, and midlateral DXA measurements were 0.48%, 0.60%, and 0.88%/yr, respectively. In the women referred for routine densitometry, lateral DXA measurements were significantly (P < 0.05) more abnormal than AP measurements compared with those in young women. This was also true in the women treated with glucocorticoids and women with vertebral compression fractures. Lateral DXA often detected osteopenia in patients whose AP DXA was normal. The 95% confidence limits for changes in BMD attributable to measurement error for AP, lateral, and midlateral DXA were 0.027, 0.038, and 0.057 g/cm2, respectively. These results indicate that lateral DXA measurements identify patients with osteopenia more often than AP DXA measurements, probably because lateral DXA more accurately estimates trabecular bone mass. Short term reproducibility of lateral DXA is nearly as good as that for AP DXA.