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At least 919 records · Page 51Linked to original sources
PubMed1993

The use of agarose gels for quantitative determination of fluid saturations in porous media.

The use of agarose gel reference standards for quantifying petrophysical properties in porous media is described. The specific interest is to determine the values of fluid saturations and porosity in oil bearing rocks; the MRI methodology for estimating these properties is discussed. It is shown that the relaxation times of the gel reference standard and the relaxation times of the fluid contained in the porous media affect the estimation process. The determination of porosity and fluid saturations can be greatly simplified if the relaxation times of the reference standard and the relaxation times of the fluid are closely matched. Gel concentration of paramagnetic impurities in the form of copper ions is used to control the longitudinal relaxation properties. The relaxation properties of agarose gels, as a function of agarose and paramagnetic impurity concentrations, have been measured at 2.0 T. The data are well fitted by a simple polynomial in agarose concentration and paramagnetic impurity concentration. Finally, a one-dimensional imaging example of use of agarose gels as reference phantoms is discussed.

Engineering↗
PubMed2006

Systematic review of methods to diagnose infection in foot ulcers in diabetes.

AIM: To undertake a systematic review of the diagnostic performance of clinical examination, sample acquisition and sample analysis in infected foot ulcers in diabetes. METHODS: Nineteen electronic databases plus other sources were searched. To be included, studies had to fulfil the following criteria: (i) compare a method of clinical assessment, sample collection or sample analysis with a reference standard; (ii) recruit diabetic individuals with foot ulcers; (ii) present 2 x 2 diagnostic data. Studies were critically appraised using a 12-item checklist. RESULTS: Three eligible studies were identified, one each on clinical examination, sample collection and sample analysis. For all three, study groups were heterogeneous with respect to wound type and a small proportion of participants had foot ulcers due to diabetes. No studies identified an optimum reference standard. Other methodological problems included non-blind interpretation of tests and the time lag between index and reference tests. Individual signs or symptoms of infection did not prove to be useful tests when assessed against punch biopsy as the reference standard. The wound swab did not perform well when assessed against tissue biopsy. Semiquantitative analysis of wound swab might be a useful alternative to quantitative analysis. The limitations of these findings and their impact on recommendations from relevant clinical guidelines are discussed. CONCLUSION: Given the importance of this topic, it is surprising that only three eligible studies were identified. It was not possible to describe the optimal methods of diagnosing infection in diabetic patients with foot ulceration from the evidence identified in this systematic review.

Biopsy↗
PubMed2000

Power Doppler imaging: initial evaluation as a screening examination for carotid artery stenosis.

PURPOSE: To evaluate power Doppler imaging as a possible screening examination for carotid artery stenosis. MATERIALS AND METHODS: In the principal pilot study, a prospective, blinded comparison of power Doppler imaging with duplex Doppler imaging, the reference-standard method, was conducted in 100 consecutive patients routinely referred for carotid artery imaging at a large, private multispecialty clinic. In the validation pilot study, a prospective, blinded comparison of power Doppler imaging with digital subtraction angiography, the reference-standard method, was conducted in 20 consecutive patients routinely referred at a teaching hospital. Using conservative assumptions, the authors performed cost-effectiveness analysis. RESULTS: Power Doppler imaging produced diagnostic-quality images in 89% of patients. When the images of the patients with nondiagnostic examinations were regarded as positive, power Doppler imaging had an area under the receiver operating characteristic curve, A(z), of 0.87, sensitivity of 70%, and specificity of 91%. The validation study results were very similar. The cost-effectiveness of screening and, as indicated, duplex Doppler imaging as the definitive diagnostic examination and endarterectomy was $47,000 per quality-adjusted life-year. CONCLUSION: The A(z) value for power Doppler imaging compares well with that for mammography, a generally accepted screening examination, and with most other imaging examinations. Power Doppler imaging is likely to be a reasonably accurate and cost-effective screening examination for carotid artery stenosis in asymptomatic populations.

Adult↗
PubMed2004

Systematic review of radiological imaging for hepatocellular carcinoma in cirrhotic patients.

We systematically reviewed the evidence for determining the best radiological imaging for characterizing hepatocellular carcinoma (HCC) in cirrhotic patients in 997 articles between 1995 and 2001. We selected only prospective and retrospective cohorts of patients, excluding both case reports and studies without separate data on HCC. Only 29 studies, comprising 918 patients, fulfilled the inclusion criteria: 10 used the explanted liver as the reference standard of diagnosis. All except one, either found no statistically significant difference between imaging modalities or had no direct comparison of sensitivity between different modalities of imaging; 16 studies evaluated HCC among cirrhotic patients and had biopsy or imaging as the reference standard for diagnosis. However, no one imaging technique was shown to be superior. In two studies, data of a HCC subgroup was derived from the studies evaluating different kinds of focal hepatic lesions. No conclusion could be drawn because of the small sample size. One study addressed the issue of therapeutic impact. The evidence for choosing the best modality of imaging for characterizing HCC in cirrhotic patients is inadequate. Large multicentre studies with defined reference standards for diagnosis, and studies evaluating therapeutic impact are needed.

Carcinoma, Hepatocellular↗
PubMed1996

The transferability of a candidate reference method for determination of creatinine in serum.

We developed a candidate reference method for the determination of creatinine in serum. For the acceptance of a reference method it is important that it be rigorously validated against a definitive method and that the method can be transferred from one laboratory to another. This study focussed on the transferability and consisted of two parts: introduction and familiarization with the method in four clinical chemistry laboratories in the Netherlands, followed by independent measurements of Standard Reference Material 909a2 and several commercial quality control materials provided with reference method values according to the protocol of the German Quality Assessment Organisation. The criterion for judging transferability was the mean total error (%) of the five sera used in the accuracy experiment. For creatinine we used a total error of < 2.2%. For Standard Reference Material 909a2 all four laboratories were able to comply with this demand, while only two laboratories met this requirement for the other four sera. The results for the Standard Reference Material 909a2 from the collaborating laboratories demonstrate that this candidate reference method can be successfully transferred without loss of precision and accuracy.

Chromatography, High Pressure Liquid↗
PubMed2000

Microwave assisted extraction of polycyclic aromatic hydrocarbons from atmospheric particulate samples.

For several years, microwave assisted extraction (MAE) was applied to extract organic compounds such as polycyclic aromatic hydrocarbons (PAHs), polychlorinated biphenyls, etc., from soils, sediments and standard reference materials. Very few authors applied this methodology for the extraction of PAHs from atmospheric particulate matter. In the present study, MAE of polycyclic aromatic hydrocarbons with hexane/acetone (1:1) from real atmospheric particulate samples was investigated and the effect of microwave energy and irradiation time studied. The yields of extracted compounds obtained by microwave irradiation were compared with those obtained using traditional Soxhlet extraction. MAE was evaluated using spiked real atmospheric particulate samples and two standard reference materials. Analytical determinations of PAHs were carried out by high performance liquid chromatography (HPLC) with ultraviolet and fluorescence detection. The best recoveries were achieved with a microwave energy of 400 W and an irradiation time of 20 min.

Air Pollutants↗
PubMed2006

Automated sonographic evaluation of testicular perfusion.

Contrast-enhanced ultrasound (US) imaging is potentially applicable to the investigation of vascular disorders of the testis. We investigated the ability of two automated computer algorithms to analyse contrast-enhanced pulse inversion US data in a rabbit model of unilateral testicular ischaemia and to correctly determine relative testicular perfusion: nonlinear curve fitting of the US backscatter intensity as a function of time; and spectral analysis of the intensity time trace. We compared (i) five metrics based on the algorithmic data to testicular perfusion ratios obtained with radiolabelled microspheres, a reference standard; (ii) qualitative assessment of the US images by two independent readers blinded to the side of the experimental and control testes to the radiolabelled microsphere perfusion ratios; and (iii) results of the algorithmically-derived metrics to the qualitative assessments of the two readers. For the curve fit method, the algorithmically-derived metrics agreed with the reference standard in 54% to 68% of all cases. For the spectral method, the results agreed in 70% of all cases. The two readers agreed with the reference standard in 40% and 35% of all cases, respectively. These results suggest that automated methods of analysis may provide useful information in the assessment of testicular perfusion.

Algorithms↗
PubMed1984

A comparative evaluation of glycosylated haemoglobin assays: feasibility of references and standards.

Four assays, high pressure liquid chromatography, colorimetric with thiobarbituric acid, affinity columns, and microcolumn cation exchange were compared for ability to discriminate between samples taken from diabetic and normal subjects; correlation with each other; stability over time at different temperatures; and reproducibility between laboratories. The most discriminatory (10 samples from a diabetic and 10 samples from a normal group) was the microcolumn cation exchange method (t = 5.25; p less than 0.001), but all were significantly different at p less than 0.005. The intra-assay coefficient of variation was 1%-6%, except for the affinity column method which was 13% in normal subjects. High pressure liquid chromatography was used as a reference and the other assays correlated well (r = 0.93-0.99). Storage at -80 degrees C, -20 degrees C, 4 degrees C, and 24 degrees C showed marked differences. The thiobarbituric acid method results were stable except for 24 degrees C. Microcolumn cation exchange was labile under all conditions. Affinity column was stable for up to 15 days, only if samples were stored as whole blood. High pressure liquid chromatography showed an increase in haemoglobin A1a + b and a decrease in the haemoglobin A1c. Haemoglobin A1c was reproducible for 4 days when stored at 4 degrees C and up to 11 days when stored at -80 degrees C. Samples exchanged between centres at 4 degrees C and performed within 5 days by high pressure liquid chromatography for haemoglobin A1 and haemoglobin A1c correlated well (r = 0.98 and 0.99). Samples exchanged between centres after storage (up to 40 days -80 degrees C) correlated (r = 0.99) by the thiobarbituric acid method.(ABSTRACT TRUNCATED AT 250 WORDS)

Chromatography, Affinity↗
PubMed1999

Inter-observer variation. An alternative method of assessing the role of ultrasonic imaging in clinical decision-making in lower limb arterial disease.

BACKGROUND: The aim of the study is to determine the role of duplex scanning in deciding on the final treatment for patients with lower limb arterial disease compared to intra-arterial digital subtraction arteriography (IA DSA). METHODS: Eighty-two patients (55 males, 27 females, mean age 68 years) with lower limb arterial disease had both duplex and arteriography performed. The findings of both modalities were reported by sonographer and radiologist in 164 anonymous reports. Five vascular surgeons (consultant grade) were asked to plan their treatment on the data provided in these reports. For the purposes of statistical analysis, the actual treatment the patient received was used as the reference standard. Both reports and treatment decisions were coded (double blinded). RESULTS: The overall accuracy of duplex scanning to assess arterial disease of the lower limbs showed a sensitivity of 92%, and specificity of 99%. The accuracy of the decisions based on duplex was 84% and kappa with k of 0.62 (95% CI+0.14) compared to the reference standard, while the accuracy of the decision based on arteriography was 85% and kappa 0.63 (95% CI+0.14). The accuracy of decisions based on duplex compared to those based on arteriography (arteriography used as reference standard) was 91% and a kappa of 0.77 (95% CI+0.14). CONCLUSIONS: Duplex scanning is an accurate diagnostic modality, and clinical decisions can be safely based on its findings.

Aged↗
PubMed1993

Cholesterol-lowering therapy: what patients expect in return.

OBJECTIVE: To assess variability in patients' values and preferences regarding cholesterol-lowering therapy. DESIGN: A descriptive study. Patients currently receiving cholesterol-lowering therapy were interviewed using the time tradeoff and standard reference gamble techniques of utility assessment. SETTING: Internal medicine clinics of a military medical center. PARTICIPANTS: Thirty-five patients, clinically free of coronary disease, receiving cholesterol-lowering therapy for at least three months. RESULTS: When the time tradeoff method was applied, 12 (34%) of the patients indicated that less than one month of additional life would be a fair return for adhering to their current therapy for the rest of their lives, while 13 (37%) patients required more than one additional year of life, and four (11%) required at least five years. By the standard reference gamble method, 18 (51%) patients would not have accepted a risk of one in a thousand of imminent death (in 30 days) in hopes of obtaining a normal life expectancy off therapy, while 14 (40%) would have agreed to a 1% or greater risk in order to avoid therapy. CONCLUSIONS: While many patients apparently expected very little in return for adhering to therapy, many others may not be getting "what they bargained for."

Adult↗
PubMed1994

Comparison of three in vitro assays for serum IgE with skin testing in asthmatic children.

The diagnostic performance of three commercial assay kits [Phadezym RAST (PhRAST), Pharmacia CAP system (CAP), and multiple chemiluminescent assay (CLA-MAST)] for measuring serum-specific IgE was evaluated and compared using intradermal skin testing or skin prick testing as reference standards. Serum samples were obtained from allergic patients who were tested with either intradermal skin tests or skin prick tests (96 and 49 subjects, respectively). Six different allergen extracts were tested: Dermatophagoides pteronyssinus, Candida albicans, Aspergillus, short ragweed, Bermuda grass, and cockroach mix. Results showed that when using intradermal skin testing as a reference standard, the CLA-MAST had the lowest sensitivity (75%), specificity (80%), and efficiency (85%) but the Pharmacia CAP system achieved the highest sensitivity, specificity, and efficiency (86%, 94%, and 91%, respectively). When compared with these two relatively new assays, the Phadezym RAST had medium sensitivity (80%), specificity (92%), and efficiency (88%). In contrast, when using skin prick testing as a reference standard, the highest specificity was achieved by Phadezym RAST (95%), followed by Pharmacia CAP system (90%), and MAST (81%). As for the sensitivity of each test, the Phadezym RAST was the lowest (60%) and Pharmacia CAP system reached the highest sensitivity (79%); and for the efficiency test, the score was 87% for CAP, 83% for Phadezym RAST, and 75% for MAST. These results suggest, therefore, that the CAP system is the preferred test and provides a useful guide for prescription of environmental control and immunotherapy in unselected patients.

Adolescent↗
PubMedDate not supplied

Bioavailability, absorption mechanism, and toxicity of microencapsulated iron (I) sulfate: studies in mice.

The iron compounds used for food fortification have to meet certain requisites related to their bioavailability, absorption mechanism, and toxicity, since they will be consumed by a massive population group. With these purposes, we evaluated a new product used for the iron fortification of milk and lacteous derivatives, called SFE-171, which is a ferrous sulfate, microencapsulated with phospholipids. The bioavailability studies were carried out using four groups of 30 female mice each. In two groups, we studied the absorption of ferrous ascorbate and ferrous sulfate, both in water as reference standards, which show absorptions of 13.1+/-4.9% and 13.2+/-4.3%, respectively. With the third group, we studied the absorption of ferrous sulfate in milk; its value, 7.9+/-3.2%, is significantly lower than that of the remaining groups, with a p < 0.01. The studies with SFE-171 in milk, were performed on the fourth group, with a result of 11.6+/-4.5%, demonstrating that its absorption does not differ significantly from that of the reference standards. The absorption mechanism was determined by means of in vivo self-displacement studies of the ferrous ion and the SFE-171, taking ferrous sulfate as the reference compound. For this study, 210 female mice were used, and no significant difference between the absorption mechanism of both products could be observed. Toxicity studies of the new product with regard to ferrous sulfate were carried out with two groups of 70 female mice each and two groups of 70 male mice each. The lethal dose 50% LD50 for SFE-171 and for ferrous sulfate was 1200 and 680 mg/kg for female mice and 1230 and 670 mg/kg for male mice, respectively, demonstrating that the toxicity of the first product is substantially lower than that of the reference standard. We conclude that the iron product under study has a high bioavailability, an absorption mechanism equal to that of nonhemic iron, and lower toxicity than ferrous sulfate.

Analysis of Variance↗
PubMed1987

Characterization of a monoclonal antibody which detects luteinizing hormone from diverse mammalian species.

The present study describes the development and characterization of a monoclonal antibody (518B7) generated against bovine LH (bLH). Although 518B7 was extremely specific for LH, very low species specificity was observed. A RIA using this antibody and radioiodinated equine LH (eLH) showed good sensitivity for all mammalian LH preparations tested, with the exception of human LH (15%, relative to the eLH reference standard). Activities of most mammalian LH's ranged between approximately 50-200%. Much less activity was detected with reptilian LH (less than 1.5%). Amphibian and avian LH fractions were essentially inactive. The reactivities of LH alpha and beta subunits from a variety of mammals clearly showed that the antibody reacts with the beta subunit. Sensitive RIAs were also developed utilizing 125I-bovine and 125I-rat LH. Interestingly, all hormone preparations which showed sufficient reactivity for statistical analysis within the dose ranges used in the present study (0.01-1000 ng/tube) produced a displacement curve parallel to the reference standard. We have also validated the use of 518B7 in detecting LH in serum. Parallel dilution curves relative to purified LH reference standards were observed with equine and bovine serum samples and equine pituitary extract. High (average 94%) recoveries were also seen with bovine serum with known amounts of exogenously added bLH. Similar patterns of LH secretion were detected with a RIA based upon 125I-bLH and 518B7 and a previously described polyclonal antibody-based RIA in bovine serum samples during estrus. Thus, a monoclonal antibody for LH has been produced which can be used to develop sensitive and specific RIAs in many different mammalian species.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed2002

Quality assurance in screening for sight-threatening diabetic retinopathy.

AIMS: There is a need for continuous evaluation of screening services for diabetic retinopathy against agreed performance standards. We describe a quality assurance programme implemented in Newcastle in January 1999 and report on outcomes at 18 months. METHODS: Annual retinal screening is performed using combined retinal photography and direct ophthalmoscopy in two streams. Diabetologists perform screening in the Hospital Screening Programme, which serves patients whose diabetes is managed in specialist clinics, and trained retinal screeners perform screening in the District Screening Programme, which serves patients whose diabetes is managed in the community. Reference standard examination of dilated fundoscopy with a slit-lamp and condensing lens was performed by an ophthalmologist at periodic sessions on consecutive patients attending for screening. RESULTS: Six hundred and nine (6.4%) of 9468 patients screened underwent reference standard examination. The sensitivity and specificity of detection of sight-threatening diabetic retinopathy (STDR) was 82.5% and 98%, respectively, for the Hospital Screening Programme; 85.7% and 95.7%, respectively, for the District Screening Programme; and 83.3% and 96.8% for both services combined. One hundred and ten (18.1%) of 609 patients audited were referred to ophthalmology as a result of screening, and this led to 16 patients (2.6%) receiving laser photocoagulation for STDR. Reference standard examination identified a further four patients (0.7%) who required laser photocoagulation. CONCLUSIONS: Preliminary data indicate that satisfactory performance standards are being achieved. The National Service Framework for Diabetes requires that all units institute quality assurance for retinal screening, and we report the practical implementation of this in one district.

Diabetic Retinopathy↗
PubMed1997

Doppler sonography evaluation of superior mesenteric artery flow to assess Crohn's disease activity: correlation with clinical evaluation, Crohn's disease activity index, and alpha 1-antitrypsin clearance in feces.

OBJECTIVE: This study was undertaken to investigate the value of Doppler flow measurements of the superior mesenteric artery (SMA) as a marker for disease activity in patients with Crohn's disease. SUBJECTS AND METHODS: Duplex Doppler sonography measurements of SMA blood flow volume were obtained in 29 consecutive patients with suspected Crohn's disease. We prospectively sought a correlation between the independent assessment of Doppler flow measurements and markers for disease activity: Crohn's disease activity index and fecal alpha 1-antitrypsin clearance and our reference standard based on clinical history, physical examination, laboratory values, endoscopy, surgery, and follow-up. RESULTS: In 27 of 29 patients, adequate measurements of SMA blood flow were obtained. In 15 patients no disease activity was judged to be present or no Crohn's disease (n = 2) was found at follow-up (group 1). In 12 patients, activity of Crohn's disease was diagnosed (group 2) on the basis of the reference standard. In group 2 the Doppler SMA blood flow values were significantly higher (p < .05) than those for group 1 (826 +/- 407 ml/min versus 323 +/- 103 ml/min). Of the other parameters investigated, only the alpha 1-antitrypsin value correlated with the reference standard but to a lesser degree than the values for SMA blood flow measurement. CONCLUSION: This prospective study shows that SMA Doppler blood flow measurements can be used to assess disease activity in patients with Crohn's disease. This approach may be of value in the diagnosis and follow-up of patients with Crohn's disease, providing directly available, quantifiable, noninvasive information on disease activity.

Adult↗
PubMed2006

The use of slurry sampling for the determination of manganese and copper in various samples by electrothermal atomic absorption spectrometry.

Manganese and copper in multivitamin-mineral supplements and standard reference materials were determined by slurry sampling electrothermal atomic absorption spectrometry. Slurries were prepared in an aqueous solution containing Triton X-100. The effects of different parameters such as ratio of solid to liquid phase volume, total slurry volume and addition of Triton X-100 as a dispersant on the analytical results were investigated. The graphite furnace programs were optimized for slurry sampling depending on the analytes and their concentrations in the samples. The linear calibration method with aqueous standard solutions was used for the quantification. At optimum experimental conditions, R.S.D. values were below 5%. The analytes were determined in the limits of 95% confidence level with respect to certified values in coal and soil standard reference materials and to those found by wet-digestion in multivitamin-mineral supplements. Detection limits (3delta) for Mn and Cu were 0.10 microg L(-1) and 1.82 microg L(-1) for 10 microL coal standard reference material slurry, respectively.

Copper↗
PubMed1987

Pulmonary function testing in children.

This article concentrates on those factors that are particularly important for performing and interpreting lung function tests in children. Specifically, technical considerations such as equipment, personnel, test performance, and bronchoprovocation procedures are discussed. Changes in lung function with growth and appropriate use of race-specific reference standards are emphasized, and references for standard and experimental pulmonary function tests are provided. Several examples illustrating the utility of pulmonary function testing in clinical situations in children with lung disease are provided as well.

Blood Gas Analysis↗
PubMed2006

Commercial reference shape standards use in the study of particle shape effect on laser diffraction particle size analysis.

The purpose of this paper is to describe the use of LGC Promochem AEA 1001 to AEA 1003 monosized fiber-analog shape standards in the study of the effect of particle shape on laser diffraction (LD) particle size analysis (psa). The psa of the AEA standards was conducted using LD psa systems from Beckman Coulter, Horiba, and Malvern Instruments. Flow speed settings, sample refractive index values, and sample cell types were varied to examine the extent to which the shape effect on LD psa results is modified by these variables. The volume and number probability plots resulting from these measurements were each characterized by a spread in the particle size distribution that roughly extended from the breadth to the longest dimension of the particles. For most of the selected sample refractive index values, the volume probability plots were characterized by apparent bimodal distributions. The results, therefore, provide experimental verification of the conclusions from theoretical studies of LD psa system response to monosized elliptical particles in which this apparent bimodality was the predicted result in the case of flow-oriented particles. The data support the findings from previous studies conducted over the past 10 years that have called into question the verity of the tenets of, and therefore the value of the application of, the equivalent spherical volume diameter theory and the random particle orientation model to the interpretation of LD psa results from measurements made on nonspherical particles.

Drug Evaluation, Preclinical↗