Coefficient Of Variation For Volume Research Articles

Asymmetric information and the distribution of trading volume

We propose the Volume Coefficient of Variation (VCV), the ratio of the standard deviation to the mean of trading volume, as a new and simple measure of information asymmetry in security markets. We use a microstructure model to demonstrate that VCV is strictly increasing in the proportion of informed trade. Empirically, we obtain VCV from daily observations of trading volume and provide extensive evidence supporting the hypothesis that VCV indicates information asymmetry, by studying return reversals, institutional ownership, and extant firm-level measures of asymmetric information in the cross-section of US stocks. Moreover, VCV increases following exogenous reductions in analyst coverage induced by brokerage closures, and steeply decreases around earnings announcements and other information disclosures.

Patient-Ventilator Synchrony in Neurally-Adjusted Ventilatory Assist and Variable Pressure Support Ventilation.

Neurally-adjusted ventilatory assist (NAVA) improves patient-ventilator synchrony and reduces the risk of respiratory over-assistance. Variable pressure support ventilation (PSV) is a recently introduced mode of assisted ventilation that has also shown reduction in patient-ventilator asynchronies. We hypothesized that NAVA would reduce patient-ventilator asynchronies and inspiratory effort compared to variable PSV because breathing variability was intrinsically determined by the patient and not by the ventilator. This study aimed to evaluate patient-ventilator asynchronies and inspiratory effort pressure-time product (PTP) between NAVA and variable PSV in subjects with mild ARDS. After 24 h of controlled mechanical ventilation, subjects (PaO2 /FIO2 200-300 and PEEP level < 10 cm H2O) were randomized in sequence 1:1 by using a web-based encrypted platform and assigned to NAVA or variable PSV groups. Both modes of ventilation were consecutively kept for 24 h unless there were clinical changes. The primary aim of this study was to evaluate differences in asynchrony index (AI) between variable PSV and NAVA. Our secondary aims were to evaluate the coefficient of variation (CV) of breathing patterns and inspiratory effort between the groups. Thirteen subjects were randomized in the NAVA group and 13 subjects in the variable PSV group. AI over time and minute PTP (PTPmin) were not different between NAVA and variable PSV groups (AI t0P = .52, AI t12P = .27, AI t24P = .12; and PTPmin-t0P = .60, PTPmin-t12P = .57, PTPmin-t24P = .85, respectively). CV for tidal volume (VT) and pressure support (PS) was lower in variable PSV group over time compared with NAVA group (P < .05). In this randomized controlled trial including subjects with mild ARDS, NAVA and variable PSV had comparable effects on patient-ventilator synchronies and PTP. However, variable PSV reduced the variability of VT and PS when compared with NAVA.

Heart atlas for retrospective cardiac dosimetry: a multi-institutional study on interobserver contouring variations and their dosimetric impact

PurposeCardiac effects after breast cancer radiation therapy potentially affect more patients as survival improves. The heart’s heterogeneous radiation exposure and composition of functional structures call for establishing individual relationships between structure dose and specific late effects. However, valid dosimetry requires reliable contouring which is challenging for small volumes based on older, lower-quality computed tomography imaging. We developed a heart atlas for robust heart contouring in retrospective epidemiologic studies.Methods and materialsThe atlas defined the complete heart and geometric surrogate volumes for six cardiac structures: aortic valve, pulmonary valve, all deeper structures combined, myocardium, left anterior myocardium, and right anterior myocardium. We collected treatment planning records from 16 patients from 4 hospitals including dose calculations for 3D conformal tangential field radiation therapy for left-sided breast cancer. Six observers each contoured all patients. We assessed spatial contouring agreement and corresponding dosimetric variability.ResultsContouring agreement for the complete heart was high with a mean Jaccard similarity coefficient (JSC) of 89%, a volume coefficient of variation (CV) of 5.2%, and a mean dose CV of 4.2%. The left (right) anterior myocardium had acceptable agreement with 63% (58%) JSC, 9.8% (11.5%) volume CV, and 11.9% (8.0%) mean dose CV. Dosimetric agreement for the deep structures and aortic valve was good despite higher spatial variation. Low spatial agreement for the pulmonary valve translated to poor dosimetric agreement.ConclusionsFor the purpose of retrospective dosimetry based on older imaging, geometric surrogate volumes for cardiac organs at risk can yield better contouring agreement than anatomical definitions, but retain limitations for small structures like the pulmonary valve.

Improving priors for human monoclonal antibody linear pharmacokinetic parameters by using half-lives from non-human primates

Obtaining a good prior for the linear pharmacokinetics of new monoclonal antibodies (mAbs) would be an advantage not only for designing first-in-human (FIH) studies but also for stabilizing fitting of data with non-linear target-mediated disposition models. We estimated the pharmacokinetics from FIH studies for five mAbs using a two-compartment model, both separately and together, using a simple pool, a third hierarchical level of random effects for between mAb differences and non-human-primate half-lives as a predictor covariate for said differences. There was good agreement between compounds for the rapidly accessible central volume of 2.9L (70kg human), but clearances and peripheral volumes differed with terminal half-lives ranging from 15 to 28 days. The simple pool of human studies gave inter-individual variability estimates of 32% coefficient of variation (CV) for clearance and 33% CV for peripheral volume, larger than for separate fits (13-26% CV and 15-35% CV for clearance and volume respectively). Using third level hierarchical random effects gave inter-individual variability estimates close to those of separate fits (24% and 16% CV respectively). The between-mAb differences became predictable if non-human primate body weight scaled terminal half-life estimates were included as covariates on clearance and peripheral volume. In conclusion, ignoring inter-mAb variation leads to inflated estimates of inter-individual variability and unrealistic simulations for FIH studies. However, by using 70kg body weight scaled terminal half-life estimates from non-human primates one can account for between-mAb differences and provide non-inflated priors for the linear pharmacokinetic parameters of new mAbs.

The Impact of Automated Information Acquisition on the Stock Market

Does collecting regulatory financial information with the help of automated computer algorithms (robots) affect the stock market? Using the EDGAR Server Log data set, I construct firm-level measures of information acquisition by robots and non-robots and show that robots are extensively used for information acquisition when new information becomes available. The SEC's mandate regarding interactive data leads to a notable increase in information demand, consistent with decreased information acquisition costs for standardised regulatory financial information in XBRL-format. A higher relative importance of robots acquiring information about a firm combined with the XBRL adoption is associated with a consequent increase in trading volume, smaller bid-ask spreads, lower volatility, positive cumulative abnormal return and increased volume coefficient of variation. The findings are consistent with the idea that automation and standardisation bene fits informed investors disproportionately more than uninformed traders.

Variations in tree sparrow (Passer montanus) egg characteristics under environmental metal pollution

Environmental metal pollution is known to adversely affect bird reproduction, for which the variations of egg characteristics are considered very important. Our study explored whether variations in egg characteristics, such as egg volume, eggshell spotting pattern, eggshell coloration, and eggshell thickness, were correlated with heavy metal levels (Cu, Zn, Pb, and Cd) and Ca levels in the eggshells of tree sparrows (Passer montanus), a widespread passerine species. Eggs were collected from a long-term heavy metal polluted area (Baiyin, BY, northwest China) and a relatively unpolluted area (Liujiaxia, LJX, northwest China). Our results showed that the embryonated (eggshell: Cu: p = 0.003, Pb: p = 0.002) and non-embryonated (egg contents: Pb: p = 0.044, Ca: p = 0.045) eggs collected from BY contained relatively higher metal concentrations than those from LJX. Eggs from BY were smaller in volume (p < 0.01) and thinner in eggshell thickness (p < 0.01) than those from LJX. Mean egg volume increased with clutch size in BY (p = 0.017), which was also accompanied by an increase in the within-clutch coefficient of variation (CV) for egg volume (p = 0.045). Clutches with a higher CV for egg volume tended to contain higher concentrations of Zn and Pb (Zn: p = 0.084; Pb: p = 0.081) in the eggshells from BY. No differences were found in the eggshell spotting coverage ratio of eggs; however, eggshells were much darker in BY than in LJX. A more aggregated eggshell spotting distribution indicated higher eggshell Zn and Pb levels (BY: Zn: p = 0.040, Pb: p = 0.076; LJX: Pb: p = 0.066). The results demonstrate that the egg characteristics of tree sparrows can be used as indicators of metal pollution, especially for the within-clutch CV for egg volume, eggshell spotting pattern and eggshell coloration.

Penicillamine as radiation protector against gamma radiation effect on complete blood count parameters of guinea pigs

Background and aim The increasing use of nuclear technology has increased the risk of exposure to radiation. Exposure to radiation induces harms to human beings. The blood and blood-forming organs are one of the most sensitive to radiation. People exposed to high radiation doses had blood count changes, and death may occur owing to acute radiation syndromes. Therefore, radioprotective compounds are very important in clinical radiotherapy. The aim of this study was to examine the effect of penicillamine as a radiation protector agent against gamma radiation effects on complete blood count parameters of guinea pigs. Materials and methods Thirty healthy male guinea pigs were divided into three equal groups: treated irradiated (n=10), irradiated (n=10), and control (n=10) groups. The treated irradiated and irradiated groups were exposed to acute gamma radiation dose (9 kGy). The treated irradiated group received penicillamine (10 mg/kg) 1 h before exposure to radiation. Blood samples were collected soon after radiation and immediately placed in tubes containing EDTA, and these samples were used in the assessment of blood profile. Results Treated irradiated guinea pigs had significant higher red blood cell count, white blood cell count, hemoglobin concentration, hematocrit, mean corpuscular volume, mean corpuscular hemoglobin, and mean corpuscular hemoglobin concentration (P≤0.05). The treated irradiated guinea pigs had significant lower relative distribution width of red blood cells by volume coefficient of variation (%) and platelet count (P≤0.05). Relative width of the distribution of platelets in volume index of the heterogeneity of platelets (%) had no significant difference between the two groups (P>0.05). Conclusion Administration of penicillamine reduced radiation damage to red blood cell count, white blood cell count, hemoglobin concentration, hematocrit, mean corpuscular volume, mean corpuscular hemoglobin, and mean corpuscular hemoglobin concentration.

Asymmetric Information and the Distribution of Trading Volume

We propose the Volume Coefficient of Variation (VCV), the ratio of the standard deviation to the mean of trading volume, as a new and easily computable measure of information asymmetry in security markets. We use a simple microstructure model to demonstrate that VCV is strictly increasing in the proportion of informed trade. Empirically, we find that firm-year observations of VCV, computed from daily trading volumes, are correlated with extant firm-level measures of asymmetric information in the cross-section of US stocks. Moreover, VCV increases following exogenous reductions in analyst coverage induced by brokerage closures, and steeply decreases around earnings announcements.

Asymmetric Information and the Distribution of Trading Volume

We use the Kyle (1985) model to characterize the distribution of trading volume as a function of the proportion of informed trade. If most orders are submitted by uninformed traders and are hence uncorrelated, order imbalance is small compared to observed trading volume, and the distribution of trading volume resembles a Normal distribution. On the other hand, if most orders are correlated because they are submitted by informed traders, the order imbalance is large and needs to be absorbed by market makers. The trading volume distribution is in this case more skewed and has a higher coefficient of variation (ratio of standard deviation to mean). We find that the volume coefficient of variation (VCV) is highly correlated to alternative measures indicative of informed trading in the cross section of stocks. Moreover, the VCV sharply decreases after earnings announcements, which resolve information asymmetries. Finally, the post earnings announcement drift is stronger for stocks with a low VCV prior to the announcement.

Multi-subject atlas-based auto-segmentation reduces interobserver variation and improves dosimetric parameter consistency for organs at risk in nasopharyngeal carcinoma: A multi-institution clinical study

Background and purposeTo assess whether consensus guideline-based atlas-based auto-segmentation (ABAS) reduces interobserver variation and improves dosimetric parameter consistency for organs at risk (OARs) in nasopharyngeal carcinoma (NPC). Materials and methodsEight radiation oncologists from 8 institutes contoured 20 OARs on planning CT images of 16 patients via manual contouring and manually-edited ABAS contouring. Interobserver variation [volume coefficient of variation (CV), Dice similarity coefficient (DSC), three-dimensional isocenter difference (3D-ICD)] and dosimetric parameters were compared between the two methods of contouring for each OAR. ResultsInterobserver variation was significant for all OARs in manual contouring, resulting in significant dosimetric parameter variation (P<0.05). Edited ABAS significantly improved multiple metrics and reduced dosimetric parameter variation for most OARs; brainstem, spinal cord, cochleae, temporomandibular joint (TMJ), larynx and pharyngeal constrictor muscle (PCM) obtained most benefit (range of mean DSC, volume CV and main ICD values was 0.36–0.83, 12.1–84.3%, 2.2–5.0mm for manual contouring and 0.42–0.86, 7.2–70.6%, 1.2–3.5mm for edited ABAS contouring, respectively; range of dose CV reduction: 1.0–3.0%). ConclusionSubstantial objective interobserver differences occur during manual contouring, resulting in significant dosimetric parameter variation. Edited ABAS reduced interobserver variation and improved dosimetric parameter consistency, particularly for brainstem, spinal cord, cochleae, TMJ, larynx and PCM.

Intraobserver variability in fibroid size measurements: estimated effects on assessing fibroid growth.

To evaluate intraobserver variability of fibroid sonographic measurements and apply this factor to fibroid growth assessment. Study participants were African American women aged 23 to 34 years who had never had a diagnosis of uterine fibroids. All participants underwent transvaginal sonography to screen for the presence of previously undiagnosed fibroids (≥0.5 cm in diameter). The diameters of up to 6 fibroids were measured in 3 perpendicular planes at 3 separate times during the examinations by experienced sonographers. Intraobserver variability as measured by the coefficient of variation (CV) for fibroid diameter and volume was calculated for each fibroid, and factors associated with the CV were assessed by regression models. The impact of variability on growth assessment was determined. Ninety-six of 300 women screened were found to have at least 1 fibroid, yielding a total of 174 fibroids for this analysis. The mean CV for the 3 measurements of fibroid maximum diameter was 5.9%. The mean CV for fibroid volume was 12.7%. Fibroid size contributed significantly to intraobserver variability (P = .04), with greater variability for smaller fibroids. Fibroid type (submucosal, intramural, or subserosal) was not important. Fibroids from the same woman tended to have similar measurement variability when assessed for volume but not for maximum diameter. Calculations showed that when following up fibroids, as much as a 20% increase in diameter could be due to measurement error, not "true growth." A small fibroid must have a greater change in size than a large fibroid to conclude that it is growing, but even for small fibroids an increase in diameter of greater than 20% is likely to indicate true growth, not measurement variability.

Dosimetric Consequences of Interobserver Variability in Delineating the Organs at Risk in Gynecologic Interstitial Brachytherapy

To investigate the dosimetric variability associated with interobserver organ-at-risk delineation differences on computed tomography in patients undergoing gynecologic interstitial brachytherapy. The rectum, bladder, and sigmoid of 14 patients treated with gynecologic interstitial brachytherapy were retrospectively contoured by 13 physicians. Geometric variability was calculated using κ statistics, conformity index (CIgen), and coefficient of variation (CV) of volumes contoured across physicians. Dosimetric variability of the single-fraction D0.1cc and D2cc was assessed through CV across physicians, and the standard deviation of the total EQD2 (equivalent dose in 2 Gy per fraction) brachytherapy dose (SD(TOT)) was calculated. The population mean ± 1 standard deviation of κ, CIgen, and volume CV were, respectively: 0.77 ± 0.06, 0.70 ± 0.08, and 20% ± 6% for bladder; 0.74 ± 06, 0.67 ± 0.08, and 20% ± 5% for rectum; and 0.33 ± 0.20, 0.26 ± 0.17, and 82% ± 42% for sigmoid. Dosimetric variability was as follows: for bladder, CV = 31% ± 19% (SD(TOT) = 72 ± 64 Gy) for D0.1cc and CV = 16% ± 10% (SD(TOT) = 9 ± 6 Gy) for D2cc; for rectum, CV = 11% ± 5% (SD(TOT) = 16 ± 17 Gy) for D0.1cc and CV = 7% ± 2% (SD(TOT) = 4 ± 3 Gy) for D2cc; for sigmoid, CV = 39% ± 28% (SD(TOT) = 12 ± 18 Gy) for D0.1cc and CV = 34% ± 19% (SD(TOT) = 4 ± 4 Gy) for D2cc. Delineation of bladder and rectum by 13 physicians demonstrated substantial geometric agreement and resulted in good dosimetric agreement for all dose-volume histogram parameters except bladder D0.1cc. Small delineation differences in high-dose regions by the posterior bladder wall may explain these results. The delineation of sigmoid showed fair geometric agreement. The higher dosimetric variability for sigmoid compared with rectum and bladder did not correlate with higher variability in the total brachytherapy dose but rather may be due to the sigmoid being positioned in low-dose regions in the cases analyzed in this study.

A Novel Radio-Opaque Hydrogel Marker Can Be Used to Decrease Interobserver Variability in the Delineation of the Lumpectomy Cavity

Accurate lumpectomy cavity (LC) delineation is necessary to define a target for cavity boost or partial breast irradiation (PBI), but the LC is not always well visualized on CT. Surgical clips mark discrete points along the cavity margin, leaving the majority of the LC border undefined. We introduced a novel radio-opaque hydrogel marker to lumpectomy cavities of female cadavers to assess the effect on inter-observer variability in defining the lumpectomy cavity during CT-based treatment planning. Three refrigerated, unfixed female cadaveric specimens underwent lumpectomy procedures with oncoplastic closures by breast surgeons. Saline was introduced via an indwelling catheter to eliminate air. Baseline simulation CT images were performed, and the saline was replaced by the hydrogel marker via the catheter. The hydrogel marker used in this cadaveric series is an FDA-approved injectable polyethylene glycol-based hydrogel designed to be visible under CT, MR and ultrasound imaging for several months after implantation. LC contouring was performed on the axial slices of the simulation CT data sets by three breast radiation oncologists. To assess change in visibility of the LC with the addition of hydrogel, a cavity visualization score (CVS) of 1-5 was assigned to each LC by each physician observer, and the median CVS was compared for each cavity with and without the hydrogel. LC volume variability was assessed by Vmax/Vmin and the coefficient of variation for volume (COVvol), defined as the standard deviation of the mean divided by the mean. A conformity index (CI) was used to evaluate variability of the LC shape, defined as the sum of the intersections of all possible pairs of delineations divided by the sum of unions of all possible pairs. Paired-samples (repeated measures) t tests were used to compare differences between groups. The median CVS increased in 7/9 cavities with the hydrogel. For all cavities, the median change in CVS when hydrogel was introduced was +2 (range, 0 to +2). The mean LC volume decreased from 17.8 cm3 to 7.0 cm3 with the addition of the hydrogel (p = 0.002). Mean COVvol decreased from 0.41 to 0.28 (p = 0.025) and Vmax/Vmin decreased from 2.6 to 1.8 (p = 0.023). The mean CI increased from 0.30 to 0.47 (p = 0.009). The addition of a radio-opaque hydrogel marker to lumpectomy cavities with oncoplastic closure at the time of surgery may increase cavity visualization and decrease inter-observer variability of volume and shape when delineating the cavity for adjuvant radiation therapy. In addition, there is a significant decrease in the delineated LC volume, which could potentially have dosimetric benefits. Further study is warranted.

Reliability of Cycling Gross Efficiency Using the Douglas Bag Method

The aim of this study was to establish the reliability of gross efficiency (GE) measurement (the ratio of mechanical power input to metabolic power output, expressed as a percentage) using the Douglas bag method. The experiment was conducted in two parts. Part 1 examined the potential for errors in the Douglas bag method arising from gas concentration analysis, bag residual volume, and bag leakage or gas diffusion rates. Part 2 of this study examined the within-subject day-to-day variability of GE in 10 trained male cyclists using the Douglas bag method. Participants completed three measurements of GE on separate days at work rates of 150, 180, 210, 240, 270, and 300 W. The results demonstrate that the reliability of gas sampling is high with a coefficient of variation (CV) <0.5% for both O2 and CO2. The bag residual volume CV was ∼15%, which amounts to +0.4 L. This could cause the largest error, but this can be minimized by collecting large gas sample volumes. For part 2, a mean CV of 1.5% with limits of agreement of +0.6% in GE units, around a mean GE of 20.0%, was found. The Douglas bag method of measuring expired gases and GE was found to have very high reliability and could be considered the gold-standard approach for evaluating changes in GE. Collecting larger expired gas samples minimizes potential sources of error.

Spinning Disk Platform for Microfluidic Digital Polymerase Chain Reaction

An inexpensive plastic disk disposable was designed for digital polymerase chain reaction (PCR) applications with a microfluidic architecture that passively compartmentalizes a sample into 1000 nanoliter-sized wells by centrifugation. Well volumes of 33 nL were attained with a 16% volume coefficient of variation (CV). A rapid air thermocycler with aggregate real-time fluorescence detection was used, achieving PCR cycle times of 33 s and 94% PCR efficiency, with a melting curve to validate product specificity. A CCD camera acquired a fluorescent image of the disk following PCR, and the well intensity frequency distribution and Poisson distribution statistics were used to count the positive wells on the disk to determine the number of template molecules amplified. A 300 bp plasmid DNA product was amplified within the disk and analyzed in 50 min with 58-1000 wells containing plasmid template. Target concentrations measured by the spinning disk platform were 3 times less than that predicted by absorbance measurements. The spinning disk platform reduces disposable cost, instrument complexity, and thermocycling time compared to other current digital PCR platforms.

Three-dimensional and thermal surface imaging produces reliable measures of joint shape and temperature: a potential tool for quantifying arthritis

IntroductionThe assessment of joints with active arthritis is a core component of widely used outcome measures. However, substantial variability exists within and across examiners in assessment of these active joint counts. Swelling and temperature changes, two qualities estimated during active joint counts, are amenable to quantification using noncontact digital imaging technologies. We sought to explore the ability of three dimensional (3D) and thermal imaging to reliably measure joint shape and temperature. MethodsA Minolta 910 Vivid non-contact 3D laser scanner and a Meditherm med2000 Pro Infrared camera were used to create digital representations of wrist and metacarpalphalangeal (MCP) joints. Specialized software generated 3 quantitative measures for each joint region: 1) Volume; 2) Surface Distribution Index (SDI), a marker of joint shape representing the standard deviation of vertical distances from points on the skin surface to a fixed reference plane; 3) Heat Distribution Index (HDI), representing the standard error of temperatures. Seven wrists and 6 MCP regions from 5 subjects with arthritis were used to develop and validate 3D image acquisition and processing techniques. HDI values from 18 wrist and 9 MCP regions were obtained from 17 patients with active arthritis and compared to data from 10 wrist and MCP regions from 5 controls. Standard deviation (SD), coefficient of variation (CV), and intraclass correlation coefficients (ICC) were calculated for each quantitative measure to establish their reliability. CVs for volume and SDI were <1.3% and ICCs were greater than 0.99. ResultsThermal measures were less reliable than 3D measures. However, significant differences were observed between control and arthritis HDI values. Two case studies of arthritic joints demonstrated quantifiable changes in swelling and temperature corresponding with changes in symptoms and physical exam findings. Conclusion3D and thermal imaging provide reliable measures of joint volume, shape, and thermal patterns. Further refinement may lead to the use of these technologies to improve the assessment of disease activity in arthritis.

Importance of intra-individual variation in tumour volume of hepatic colorectal metastases

Aims The efficacy of surgical resection for multiple colorectal hepatic metastases (MCHM) has been controversial. We examined the survival of patients who received surgery for MCHM and examined the factors associated with survival. Methods A retrospective analysis was performed of 50 consecutive patients who received hepatic resections for MCHM, defined as four or more metastatic lesions of colorectal cancer. Results Overall survival after hepatic resection for MCHM was 48% at 3 years and 43% at 5 years (median survival, 22.3 months). Multivariate analyses revealed that a coefficient of variation (CV) in volume of hepatic metastases in each individual patient above 1.8 ( P = 0.01, HR = 4.08, 95% CI = 1.33–12.5) was the only poor prognostic factor after resection of MCHM. Conclusions A CV in volume of hepatic metastases in each individual patient above 1.8 predicts poor survival after hepatectomy of MCHM. Thus, the CV in volume of hepatic metastases in each individual patient might be useful in planning the therapeutic strategy for patients with MCHM.

Low variation and high reproducibility in plaque volume with intravascular ultrasound

Background: Intravascular ultrasound (IVUS) has several advantages compared to angiography when evaluating coronary atherosclerosis in the vessel wall. Methods: The accuracy, reproducibility, and short-time spontaneous variation in volume of vessel, plaque and lumen were studied by electrocardiographic-gated three-dimensional (3D) IVUS in 20 male patients with ischaemic heart disease (IHD). Results: The study lesions were angiographically insignificant, with a length of the analysed segment on 11.4±5.9 mm. At baseline the mean minimal lumen diameter was 2.41±0.59 mm, minimal lumen area 4.82±2.38 mm 2, and maximal plaque burden 65.61±9.57%. Mean reference diameter was 3.1±0.6 mm. No significant changes were observed in volumes of total vessel, lumen or plaque. The coefficient of variation (CV) for two volume measurements at baseline was: vessel 0.8%, plaque 1.3%, and lumen 1.4%. For measurements recorded at baseline and after 12.6±1.5 weeks, CV was respectively 3.5%, 3.3% and 6.6%. Reproducibility and interobserver and intraobserver variation showed very high correlations. A linear correlation was present in percent changes over 12.6±1.5 weeks between vessel volume and lumen volume ( r=0.804; p<0.001) and between percent changes in plaque volume and vessel volume ( r=0.581; p=0.007). No correlation was found between changes in plaque volume and lumen volume ( r=0.015; p=0.950). Conclusion: ECG-gated 3D IVUS is a highly reproducible method when applied on coronary artery atherosclerosis. CV for lumen volume over 12.6±1.5 weeks is twice that of plaque volume indicating the superiority of the 3D IVUS compared to coronary angiography (CAG).

Errors in Determination of the Water Content of a Trickle Irrigated Soil Volume

AbstractA short review of the possible methods of measuring soil water content under high frequency trickle irrigation suggested that the gravimetric method was most appropriate. Three sources of errors in this method have been evaluated and discussed. The sources are those of water content by weight, bulk density, and integration based on the sampling grid. Furthermore, as the sampling mesh became coarser the results became unstable because the differences in volume of water became larger than the defined standard deviation (SD). Error analysis of measurements on uniform Bet Dagan grumusol and sandy soils of Nahal Sinai (Israel) and Yuma (Arizona) showed that coefficient of variation in volume of water within an irrigated volume element may be reduced if the sampling grid is taken properly. The analysis suggests that for a given coefficient of variation and interval of sampling depth, an optimum distance between lateral samples can be evaluated from a mathematical reorganization of the coefficient of variation.

Early and late volume changes during erythroid differentiation of cultured friend leukemic cells

Friend erythroleukemic cells (FLC) can be induced to differentiate in vitro by addition of dimethylsulfoxide (DMSO). We have studied the kinetics of induction by measuring cell volume, volume coefficient of variation and cell doubling time. Two distinct volume changes (early and late) are observed after the addition of the inducing agent. The early change occurs after ten hours and consist of a 10-20% decrease in volume compared to an untreated control population. This shift persists for two days and its magnitude is proportional to both the concentration of DMSO and the number of differentiated cells seen on day 5. FLC lines which induce weakly or not all with DMSO exhibit a reduced or absent early volume shift. Inclusion of a local anaesthetic in the culture prevents the appearance of differentiated cells and also counteracts the early volume shift. The exact time of the early volume change is a function of cell growth rate and appears to be cell cycle related. Synchronized cell populations exposed to DMSO during G2 and S phase undergo one round of mitosis before expression of the volume change whereas cells in G2-M express the change only after a second mitosis. A later, more gradual decrease in volume is observed in those cultures which begin to produce hemoglobin. It occurs after approximately five doubling times and coincides with the first appearance of hemoglobin-containing cells. Volume distribution parameters indicate that only a proportion of the population becomes smaller in size.