Mean Standard Deviation Difference Research Articles

Differences and Limits of Agreement among Pentacam, Corvis-ST, and IOL-Master 700 Optical Biometric Devices regarding Central Corneal Thickness Measurements.

Purpose:To investigate the differences and limits of agreement in measuring corneal thickness using Pentacam, Corvis, and intraocular lens (IOL)-Master 700 devices.Methods:This study was conducted on 37 right eyes of 21 males and 16 females (n = 37) with a mean age of 52.11 ± 6.30 years. The central corneal thickness was measured using three optical biometric devices, including Pentacam, Corvis, and IOL-Master 700. The inclusion criteria were normal eyes without any ophthalmological abnormalities, history of ocular pathology, or ocular surgery. The data obtained from these three devices were compared two by two. The correlation and agreement limits among them were analyzed using statistical techniques.Results:The mean standard deviation differences between Pentacam and Corvis, Pentacam and IOL-Master 700, as well as Corvis and IOL-Master 700 regarding the corneal thickness measurement, were 22.13 ± 8.05, 7.91 ± 8.02, and 14.21 ± 9.85 μm, respectively, which were statistically significant (P < 0.0001). Based on the investigation of the limits of agreement according to the Bland Altman method, the corresponding values between Pentacam and Corvis, Pentacam and IOL-Master 700, and Corvis and IOL-Master 700 were -16.2 to +15.4, -15.8 to +16.3, and -20.1 to +20.0 μm, respectively. Furthermore, the correlation coefficients of the measurements obtained by Pentacam and Corvis, Pentacam and IOL-Master 700, as well as Corvis and IOL-Master 700 were determined 0.957, 0.964, and 0.948, respectively (P < 0.0001).Conclusion:The results from this study indicate that the interchangeable use of these three devices is not appropriate due to statistically significant differences and broad limits of agreement among the three devices, especially between Corvis and IOL-Master 700.

Development of a simple numerical model for trabecular bone structures.

Advances in additive manufacturing processes are enabling the fabrication of surrogate bone structures for applications including use in high-resolution anthropomorphic phantoms. In this research, a simple numerical model is proposed that enables the generation of microarchitecture with similar statistical distribution to trabecular bone. A human humerus, radius, ulna, and several vertebrae were scanned on the Imaging and Medical beamline at the Australian Synchrotron and the proposed numerical model was developed through the definition of two complex functions that encode the trabecular thickness and position-dependant spacing to generate volumetric surrogate trabecular structures. The structures reproduced those observed at 19 separate axial locations through the experimental bone volumes. The applicability of the model when incorporating a two-material approximation to absorption- and phase-contrast CT was also investigated through simulation. The synthetic structures, when compared with the real trabecular microarchitecture, yielded an average mean thickness error of 2μm, and a mean difference in standard deviation of 33μm for the humerus, 24μm for the ulna and radius, and 15μm for the vertebrae. Simulated absorption- and propagation-based phase contrast CT projection data were generated and reconstructed using the derived mathematical simplifications from the two-material approximation, and the phase-contrast effects were successfully demonstrated. The presented model reproduced trabecular distributions that could be used to generate phantoms for quality assurance and validation processes. The implication of utilizing a two-material approximation results in simplification of the additive manufacturing process and the generation of synthetic data that could be used for training of machine learning applications.

The effect of proton pump inhibitors on cognition and brain volume in the Rhineland study

Introduction Proton pump inhibitors (PPI) are one of the most widely used drug classes in the world. Several studies have found that users of PPIs had an increased risk of cognitive decline and dementia. This could however not be confirmed by others. Protopathic bias, in which early signs and symptoms of the disease influence drug exposure, could be a reason for these conflicting results. Given that alterations in brain volume can be seen years before the occurrence of cognitive symptoms, examining the association between PPI use and brain volume in non-demented persons would eliminate the potential of protopathic bias. Therefore, we aimed to assess the associations between PPI use and cognition and brain volume. Methods We performed a cross-sectional study based on the first 1306 participants in the Rhineland Study. The Rhineland Study is a population-based cohort study in Bonn Germany that includes people aged ≥ 30 years. Information on medication use is collected in an interview in which regularly and as needed used medication is registered. PPI use was classified as regular use of PPIs (ATC code A02BC). Participants who reported using PPIs as needed were excluded. We assessed the following cognitive domains: processing speed [Trail Making Test (TMT) A], executive functioning (TMT B - A), working memory (Digit Span Forward), and long-term memory [Verbal Learning and Memory Test (VLMT); delayed loss]. Measures for TMT and VLMT were inverted so that higher values represent better test performance for all tests. All eligible participants were scanned on Siemens 3 Tesla Prisma MRI scanners. We assessed the effect of PPI use on total brain volume, cortical grey matter volume, and ventricle volume. Processing speed and ventricle volume were log transformed. All outcome measures were z-standardized. We examined the association between PPI use and cognition using multivariable linear regression models. Within the first model we only controlled for age (m1: age). Because PPI use strongly increased with increasing age, we included variables that were a determinant for PPI use after controlling for age in the fully adjusted model (m2: age, body mass index, diabetes, hypertension, antithrombotic use, statin use and NSAID use). We subsequently examined the association between PPI use and brain volume outcomes in the same way but with additional control for head size in all models. Results We included 1130 participants [mean age 55, standard deviation (SD) 13.5; 57% women; 81 PPI users] to determine the effect of PPI use on cognition. We excluded 176 participants, 25 for missing drug information, 89 for as needed PPI use and 62 for missing cognition data. We observed no effect on processing speed with a mean SD difference [95% confidence interval (95% CI)] for m1 of 0.00 (−0.19; 0.19) and for m2 of 0.02 (−0.18; 0.22). We observed a trend towards a negative effect of PPI use with a mean SD difference (95% CI) for executive functioning, working memory and long-term memory for m1 of −0.18 (−0.40; 0.03), −0.17 (−0.40; 0.05), and −0.29 (−0.51; −0.07) and for m2 of −0.13 (−0.35; 0.10), −0.12 (−0.36; 0.11), and −0.17 (−0.39; 0.06). Effect sizes were comparable to a 5-year increase in age for executive functioning and a 9-year increase in age for working memory and long-term memory. We had MRI data in a subset of 640 participants (mean age 54, SD 13.2; 56% women; 28 PPI users). Brain volume measures were smaller in PPI users compared to non-users, but these effects were far from significant, mean SD difference (95% CI) for total brain volume, cortical grey matter volume, and ventricle volume for m1 was −0.07 (−0.23; 0.09), −0.07 (−0.26; 0.12), and 0.02 (−0.27; 0.31), and for m2 was −0.05 (−0.21; 0.12), −0.03 (−0.23; 0.16) and −0.06 (−0.36; 0.24). Conclusions Given our small sample size and relatively young population, these results suggest a possible effect of PPI use on brain structure and function and warrant further investigation in larger samples.

Sea–air CO2 fluxes in the Southern Ocean for the late spring and early summer in 2009

Abstract The Southern Ocean is an important sink of atmospheric carbon dioxide (CO 2 ). However, the magnitude of the CO 2 sink is uncertain because of the scarcity of in-situ observations due to its remote and rough waters. Empirical relationships were deduced based on the in-situ partial pressure of carbon dioxide ( p CO 2 ) in surface seawater and its main controls including Chlorophyll a (Chl-a) and Sea Surface Temperature (SST) obtained during the 26th CHINARE cruise in late spring (November) and early summer (December) 2009. An extrapolation method based on multiple linear regressions was set up for combining the empirical relationship with satellite data to compute the sea–air carbon fluxes and carbon uptake in the Southern Ocean (south of 50°S). The empirical relationships are validated with independent measurements from SOCATv2 database. The mean standard deviation differences (Std) between extrapolated and measured p CO 2 from SOCATv2 database (13.8 to 18.1 μatm) are consistent with the precision of our regressions (13.6 to 21.3 μatm). Including the effects of sea ice, we estimate a Southern Ocean CO 2 source to the atmosphere in November 2009 about 1.65 Tg C with an uncertainty of ± 0.73 Tg C by uncertainty propagation formula. While in December 2009, we estimated a CO 2 sink of − 2.34 Tg C with an uncertainty of ± 1.03 Tg C. The carbon source and sink of the South Atlantic Ocean, the South Indian Ocean and the South Pacific Ocean were estimated. For the austral summer, the South Atlantic Ocean and the South Pacific Ocean are still strong carbon sink. When compared to the climatological monthly results of Takahashi et al. (2012), our results showed a similar distribution of sea–air carbon flux.

A voxel-based finite element model for the prediction of bladder deformation

A finite element (FE) bladder model was previously developed to predict bladder deformation caused by bladder filling change. However, two factors prevent a wide application of FE models: (1) the labor required to construct a FE model with high quality mesh and (2) long computation time needed to construct the FE model and solve the FE equations. In this work, we address these issues by constructing a low-resolution voxel-based FE bladder model directly from the binary segmentation images and compare the accuracy and computational efficiency of the voxel-based model used to simulate bladder deformation with those of a classical FE model with a tetrahedral mesh. For ten healthy volunteers, a series of MRI scans of the pelvic region was recorded at regular intervals of 10 min over 1 h. For this series of scans, the bladder volume gradually increased while rectal volume remained constant. All pelvic structures were defined from a reference image for each volunteer, including bladder wall, small bowel, prostate (male), uterus (female), rectum, pelvic bone, spine, and the rest of the body. Four separate FE models were constructed from these structures: one with a tetrahedral mesh (used in previous study), one with a uniform hexahedral mesh, one with a nonuniform hexahedral mesh, and one with a low-resolution nonuniform hexahedral mesh. Appropriate material properties were assigned to all structures and uniform pressure was applied to the inner bladder wall to simulate bladder deformation from urine inflow. Performance of the hexahedral meshes was evaluated against the performance of the standard tetrahedral mesh by comparing the accuracy of bladder shape prediction and computational efficiency. FE model with a hexahedral mesh can be quickly and automatically constructed. No substantial differences were observed between the simulation results of the tetrahedral mesh and hexahedral meshes (<1% difference in mean dice similarity coefficient to manual contours and <0.02 cm difference in mean standard deviation of residual errors). The average equation solving time (without manual intervention) for the first two types of hexahedral meshes increased to 2.3 h and 2.6 h compared to the 1.1 h needed for the tetrahedral mesh, however, the low-resolution nonuniform hexahedral mesh dramatically decreased the equation solving time to 3 min without reducing accuracy. Voxel-based mesh generation allows fast, automatic, and robust creation of finite element bladder models directly from binary segmentation images without user intervention. Even the low-resolution voxel-based hexahedral mesh yields comparable accuracy in bladder shape prediction and more than 20 times faster in computational speed compared to the tetrahedral mesh. This approach makes it more feasible and accessible to apply FE method to model bladder deformation in adaptive radiotherapy.

Whole-body and multi-joint kinematic control strategy variability during backward rotating dismounts from beam

The aim of this study was to develop insight into the whole-body and multi-joint kinematic control strategy variability associated with the execution of fundamental backward rotating dismounts from beam. Two-dimensional joint centre coordinate data were obtained for ten backward piked and backward tucked somersault dismount skills performed by four female gymnasts (N = 80 trials). Gymnast-specific and group variability in whole-body and multi-joint discrete kinematic measures were compared for the aerial and impact phase of backward piked and backward tucked skills. The backward tucked skill was executed using a more variable knee joint angular velocity at take-off (mean difference in standard deviation ± SD: −2.6 ± 1.0 rad · s−1; P < 0.01) than the backward piked skill. The variability in the whole-body and multi-joint kinematic responses produced between the impact phases of each skill was gymnast-specific. The greater variability in the localized knee joint action at take-off was considered indicative of the diverse shape element demands and key performance outcomes of the two skills. Self-selected modulations to the multi-joint kinematic strategy used in the impact phase suggested customization of the joint loading adjustments in executing the fundamental dismount skills.

Sind mit der Mehrschicht-Computertomografie Dichtemessungen auch bei geringer Schichtdicke und niedrigem Röhrenstrom verlässlich? Ergebnisse einer Phantomstudie

To test whether CT with low slice thickness and low tube current provides reliable attenuation measurements. Using multi-slice CT and a phantom, we measured the attenuation values of thrombi with different proportions of erythrocytes, using a slice thickness of 1.25 mm, 2.5 mm, and 5 mm with tube currents of 200 mA, 300 mA, and 400 mA and a slice thickness of 0.625 mm with tube currents of 150 mA, 175 mA, and 200 mA. Differences in attenuation values and pixel noise between the three thrombi for tube current and slice thickness were statistically analyzed. The attenuation values of all thrombi increased (p<0.05) when the slice thickness decreased using a tube current of 200 mA or when the tube current decreased using a slice thickness of 1.25 mm. With higher tube currents and thicker slices, the CT values depended on the type of thrombus and the slice thickness. In slices with a thickness of 0.625 mm, the CT values decreased with the tube current in the mixed thrombus with a low proportion of erythrocytes and in the red thrombus (p<0.05). The maximal difference in mean attenuation values was 4.3 HU with a slice thickness of 0.625 mm and 2.2 HU with a slice thickness of 1.25 mm. The pixel noise increased as the slice thickness decreased (p<0.05) with the exception of the red thrombus, if reduced to 0.625 mm. The pixel noise also increased as the tube current decreased (p<0.05) except in mixed thrombi measured with 0.625 mm. The maximal difference in mean standard deviation was 1.8 HU with a slice thickness of 1.25 mm. The accuracy of attenuation values as determined by CT with low slice thickness and low tube current with a maximal difference of 4.3 HU suffices for the purposes of clinical routine. A reduction of slice thickness from 1.25 mm to 0.625 mm yields the greatest differences in CT values.

Decreasing Variability in Faculty Ratings of Student Case Presentations: A Faculty Development Intervention Focusing on Reflective Practice

Background: Faculty perceptions of medical student knowledge are often based on case presentations, but their assessment of student performance can vary significantly based on content, presentation skill, and interpersonal characteristics. Purpose: To determine if a brief faculty development intervention could significantly decrease (≥ 20%) faculty members' variability in rating student case presentations in the ambulatory setting. Methods: During the 1998–99 academic year, we videotaped 10 third-year medical students during one well-child presentation. Seven general pediatric faculty rated the videotapes using a validated scoring instrument measuring content: History of Present Illness (HPI), Past Medical History, and Physical Exam (PE); and communication skill: Precision of Language, Fluency, and Economy. Baseline ratings were from June to September 1999 and then repeated in October to –November 2000 following a workshop where faculty reflected on the rating process and decreasing rating variance. The change in mean faculty ratings of the student's overall performance and for each item and the change in the mean difference in standard deviation before and after the workshop were analyzed. Results: Internal consistency of the scoring instrument using Cronbach's alpha was 0.88. The mean faculty rating for overall presentation performance and the PE did not significantly change after the workshop, whereas for all other items it did. The mean standard deviation of faculty ratings decreased significantly for the overall performance and all other items except HPI. Conclusion: Despite using a validated scoring instrument to rate student case presentations significant variability exists among faculty, with rating inflation likely. A brief faculty development intervention using “reflection-on-action” was associated with more congruent ratings in the short term.

Effects of Atherosclerosis on Capacity of Barorefles System in WHHL Rabbits

The aim of this experiment was to study the effects of atherosclerosis on the cardiovascular hemodynamics in conscious condition and in response to hemorrhagic hypotension. Arterial pressure was monitored, via a catheter chronically inserted into the aortic arch, for six hours in seven normal and eight WHHL (Watanabe-Heritable Hyperlipidemic) conscious rabbits, sampled at one sec intervals using AD-converter and stored in a digital computer. Percentage frequency distribution curve, mean and standard deviation of the mean arterial pressure for six hours (21, 600 data points) were calculated for each string of pressure data. Mean and standard deviation were pooled for the seven normal rabbits and the eight WHHL rabbits, respectively. Mean and standard deviation of mean values were 117±10 mmHg in the WHHL rabbits, and 87±7 mmHg in the normal rabbits. They showed significant difference (p<0.05) . Mean and standard deviation of standard deviations were 9.5±1.8 mmHg in the WHHL rabbits and 6.5±1.4 mmHg in the normal rabbits. Difference in mean standard deviation between the normal and WHHL rabbits was significant (p<0.05) . Thus, the WHHL rabbits were slightly but significantly hypertensive and their systemic pressure was less controlled. This suggests that the pressure control capacity of the rapidly acting arterial pressure control system, i.e., the baroreflex system, deteriorates. In order to quantify the capacity of the rapidly acting arterial pressure control system, the open-loop gain (G) of the system was estimated in fifteen WHHL rabbits, aged 3 to 31 months. Twenty-five normal Japanese white rabbits, aged 6 to 30 months, were used as a control. After being anesthetized by intravenous injection of Nembutal, the rabbits were bled by 2 ml /kg body weight within 1 to 2 sec through a catheter inserted into the aortic arch. The arterial pressure change after this quick hemorrhage was monitored via a catheter placed in the aortic arch for more than 2 min. G was calculated as (ΔAPI/ΔAPs) -1, where dAPI was the immediate fall and ΔAPs the steady-state fall. The pulse pressure, ΔAPI and ΔAPs increased and G decreased with aging in the WHHL rabbit. These results indicate that the progress of atherosclerosis with aging in the WHHL rabbit decreases the vascular compliance and impairs the arterial pressure restoring function of the rapidly acting arterial pressure control system.