Changes In Thickness Measurements Research Articles

Quality factor based correction for SD-OCT measurements in cataract patients.

To correct peripapillary retinal nerve fibre layer (pRNFL) measurements performed with spectral domain optical coherence tomography (SD-OCT) for low image quality factor (QF) in patients with cataract, using measurements before and after cataract surgery. SD-OCT (Topcon 3DOCT-2000) volume scans of the optic disc of 13 cataract patients were used. A set of three reflective filters with optical density ranging from 0.11 to 0.54 were used. The correlation was calculated between the change in thickness measurements and the change in image quality factor. Changes before and after cataract surgery were analysed. A correction for scans with a lower QF was calculated using an equation which was formulated based on the relationship between the change in thickness measurements and the change in image quality factor. Thirteen right eyes of thirteen cataract patients were included in this study. pRNFL thickness measurements before and after cataract differed significantly (96 versus 99 micron, p<0.01). Preoperative linear regression lines showed a different slope than postoperative regression lines. Corrected pRNFL thickness measurements of before cataract surgery differed significantly with pRNFL thickness measurements after cataract surgery. The presence of cataract influences the QF-pRNFL relationship. The lower the image QF, the higher the pRNFL thickness underestimation. We found a rather curvilinear relationship between QF and pRNFL. Our corrected measurements of the pRNFL thickness in case of lower image QF due to cataract still differed significantly from the pRNFL thickness measurements after cataract surgery.

The effect of ethanol pre-treatment upon the mechanical, structural and surface modification of ultrafiltration membranes

ABSTRACTThe in situ ethanol pre-treatment of commercially available polysulfone (PSU) ultrafiltration (UF) membranes resulted in a threefold increase in the pure water flux (PWF) values achieved. Techniques that lead to an increase in flux are of both academic and commercial interest. It is postulated that the mechanisms for performance improvement can be attributed to swelling of membrane skin-layers, as demonstrated by changes in thickness measurements, and consideration of polymer solubility parameters, giving a degree of polymer plasticisation. The modification is accompanied by a hydrophobicity increase – this parameter is linked to a greater fouling tendency. Increases in hydrophobicity contrast with the usual effect of ethanol contact, by enhancing the removal of membrane preservatives and polyvinylpyrrolidone (PVP), a common pore-forming agent. Mechanical property changes were not readily detected, whilst the apparently unaltered sub-layer masked more subtle changes occurring within the dense skin-layer. Directing analysis specifically at the skin layer using colloidal AFM probes allowed a decoupling of changes against the support, showing that the elastic modulus was reduced as a consequence of PVP removal and plasticisation. Moreover, regional elasticity probing allowed observation of spatial inhomogeneities in elasticity, occurring due to the removal of the previously unevenly distributed PVP and leading to pitting. Consequently, the effects of pre-treatment with ethanol are shown to offer advantages by maximising the performance of commercial membranes, though such methods must be used with caution. Elasticity changes that occur may be detrimental to performance if carried out at high transmembrane pressures, where compaction could be assisted.

Establishing Immediate Reliability of Sonographic Measurements of the Transversus Abdominis in Asymptomatic Adults Performing Upright Loaded Functional Tasks in a Clinical Context Without Delayed Recorded Measurement.

This study examined the reliability of sonographic measurements of the transversus abdominis of adults without low back pain during upright loaded functional tasks in real time, without relying on delayed recorded images. A single-group repeated-measures reliability study was conducted on 12 healthy participants without low back pain. Six of these adults reported a prior history of abdominal drawing-in maneuver training without sonographic measurement. The participants performed 3 trials of neutral standing, a loaded forward reach, and a loaded box lift under rest and with abdominal drawing-in maneuver instructions; task order was randomized. Transversus abdominis thickness measurements were obtained by an experienced rater using B-mode sonography in real-time via electronic calipers twice on the same static image during all trials by a rater. The rater was masked to group assignment and on-screen measurement output and required to respond to trivia questions between repeated measurements. The participants included 6 male and 6 female adults with a mean age ± SD of 26.3 ± 3.7 years. Intra-rater intraclass correlation coefficients (2,3) were high and precise for the rater's first and second measurements for all tasks and instruction conditions for mean transversus abdominis thickness and percent change in thickness measurements (eg, ranges were 0.968-0.997 for intraclass correlation coefficients, 0.01-0.21 mm for standard errors of the measurement, and 0.01-0.58 mm for minimal detectable changes). Calipers cleared by the rater or a research assistant produced similar findings of excellent reliability and precision. High intra-rater reliability and precision of transversus abdominis thickness measurements were obtained by a physical therapist in real time from asymptomatic adults performing upright loaded functional tasks under rest and with abdominal drawing-in maneuver instructions.

Optical density filters modeling media opacities cause decreased SD-OCT retinal layer thickness measurements with inter- and intra-individual variation.

To assess the effect of media opacities on thickness measurements of the peripapillary retinal nerve fibre layer (pRNFL) and macular inner retinal layer (mIRL) performed with spectral-domain optical coherence tomography (SD-OCT) using a set of filters with known optical density. Spectral-domain optical coherence tomography volume scans of the optic disc and the macular area were performed in 18 healthy volunteers, using Topcon-3DOCT-1000 Mark II. A set of five filters with optical density ranging from 0.04 to 0.69 was used. The correlation was calculated between the percentage change in thickness measurements (%ΔpRNFL and %ΔmIRL) and the change in optical density. All scans and measurements were performed in duplicate by one operator. Eighteen right eyes of 18 healthy volunteers were included in this study. Percentage decrease in pRNFL and mIRL thickness correlated with change in optical density (Spearman's rho r = 0.82; p < 0.001 and r = 0.89; p < 0.001, respectively). The measured decrease in pRNFL thickness differed from the decrease in mIRL thickness, not only between individuals, but also within the same individual. Optical coherence tomography thickness measurements of both pRNFL and mIRL are influenced by image degradation caused by optical density filters as a model for media opacities. An underestimation of the thickness of these layers was observed, caused by a shift of retinal layer boundary placement due to image quality loss. This underestimation is not the same for each individual and also differed between the pRNFL and mIRL thickness measurements. These individual and interindividual differences demonstrate that an individual approach will be necessary to correct for this underestimation per layer.