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Results for “Error minimization”

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At least 811 records · Page 45Linked to original sources

PubMed1993

Duplex Doppler measurements of the portal vein in portal hypertension.

In order to assess the validity of quantitative duplex Doppler measurements of portal vein flow, 10 patients with proven diffuse liver disease and portal hypertension were examined serially by two independent observers over a 3 month period. Multiple measurements of the portal vein were made using a consistent technique in an attempt to minimize observer errors. One patient proved unsuitable for ultrasound examination. In the remaining nine patients the intra-observer portal vein measurements for one observer (19 paired examinations) correlated significantly for flow velocity (r = 0.80, P < 0.001) and derived bulk flow (r = 0.54, P < 0.02) but not for cross-sectional area (r = 0.27, P > 0.05). The intra-observer measurements for the second observer (11 paired examinations) were significantly correlated for cross-sectional area (r = 0.64, P < 0.05) and derived bulk flow (r = 0.61, P < 0.05) but not for flow velocity (r = 0.5, P > 0.05). The inter-observer measurements (28 paired examinations) of the portal vein were all highly significantly correlated for cross-sectional area (r = 0.63, P < 0.001), flow velocity (r = 0.79, P < 0.001) and derived bulk flow (r = 0.73, P < 0.001). These results suggest that this quantitative Doppler technique may be valid for the serial study of portal vein flow in selected groups of patients with diffuse liver disease and portal hypertension.

Adult↗

PubMed2000

An adaptive I-PD controller based on frequency domain system identification

This paper presents an approach to auto-tune an I-PD controller for plants with long time delays such as pneumatic cylinders. The proposed control scheme estimates the frequency response of a plant using the sliding discrete Fourier transform (DFT) and employs a modified Smith predictor to reduce the effect of time delay. Controller gains are determined so as to minimize the error between the open-loop frequency response of the reference model and that of the actual system.

Journal Article↗

PubMed1998

An analytical model of the knee for estimation of internal forces during exercise.

An analytical model of the knee joint was developed to estimate the forces at the knee during exercise. Muscle forces were estimated based upon electromyographic activities during exercise and during maximum voluntary isometric contraction (MVIC), physiological cross-sectional area (PCSA), muscle fiber length at contraction and the maximum force produced by an unit PCSA under MVIC. Tibiofemoral compressive force and cruciate ligaments' tension were determined by using resultant force and torque at the knee, muscle forces, and orientations and moment arms of the muscles and ligaments. An optimization program was used to minimize the errors caused by the estimation of the muscle forces. The model was used in a ten-subject study of open kinetic chain exercise (seated knee extension) and closed kinetic chain exercises (leg press and squat). Results calculated with this model were compared to those from a previous study which did not consider muscle length and optimization. Peak tibiofemoral compressive forces were 3134 +/- 1040 N during squat, 3155 +/- 755 N during leg press and 3285 +/- 1927 N during knee extension. Peak posterior cruciate ligament tensions were 1868 +/- 878 N during squat, 1866 +/- 383 N during leg press and 959 +/- 300 N for seated knee extension. No significant anterior cruciate ligament (ACL) tension was found during leg press and squat. Peak ACL tension was 142 +/- 257 N during seated knee extension. It is demonstrated that the current model provided better estimation of knee forces during exercises, by preventing significant overestimates of tibiofemoral compressive forces and cruciate ligament tensions.

Anterior Cruciate Ligament↗

PubMed1999

A probabilistic rule of mixtures for elastic moduli.

A novel approach is developed for mathematically modeling the variability observed in experimentally determined elastic moduli of longitudinally oriented fibrous tissues such as ligaments and tendons. The elastic modulus of these tissues is modeled with a rule of mixtures (ROM) where each parameter (fibril and matrix moduli and fibril volume fraction) is assumed to be an independent random variable. A joint density function formed from the independent densities results in a probabilistic ROM (pROM). This pROM is used to generate a distribution of moduli which agrees well with moduli determined from tests of rabbit medial collateral ligaments (Woo and Ohland, 1994, Unpublished experimental data as gift). Minimizing the error between the pROM and experimental distributions resulted in an integrated error of 9% for a constrained set of independent distribution parameters derived from the literature. This pROM thus incorporates microstructural observations (fibril and matrix moduli and fibril volume fraction) to partially explain the experimentally observed variability in a macroscopic property (tissue modulus).

Animals↗

PubMed1994

Effectiveness and safety of laparoscopic adrenalectomy.

A laparoscopic approach was used to remove the adrenal gland in 7 patients with aldosterone-producing adenoma (Conn's disease), 2 with corticosteroid-producing adenoma (pituitary-independent Cushing's syndrome) and 2 with pheochromocytoma. The affected gland was on the right side in 3 patients and on the left side in 8. Mean operative time was 3 hours 10 minutes (range 140 to 370 minutes). The operation was uneventful in all patients and blood transfusions were never required. Mean postoperative hospitalization was 2.9 +/- 0.8 days (standard error). Only minimal doses of analgesics were used postoperatively. All patients returned to work within 10 days postoperatively (mean 8.4 +/- 1.2 days). Two months postoperatively no patient had clinical, biochemical or hormonal evidence of recurrent or persistent disease. We conclude that laparoscopic adrenalectomy is a safe and effective, minimally invasive approach for patients with benign adrenal neoplasms.

Adrenal Gland Neoplasms↗

PubMed2003

Measurement of the cardiac output in small animals by thermodilution.

Cardiac output (CO) measurements based on indicator dilution, microspheres, thermodilution and ultrasonic sensors are not suitable for small animals, because of limited blood volume, high heart rates and small caliber vessels that do not allow probe placement within the heart. We developed a modified thermodilution method to measure CO in awake animals weighing less than 100 g. Under anesthesia, the animal is instrumented with a jugular vein catheter placed proximal to the subclavian vein and a temperature probe in the carotid artery with the thermocouple positioned at the aortic arch. Two days after implantation, room temperature saline is injected (150 microl) into the jugular catheter and the temperature change recorded. This system uses the temperature probe as a digital feedback control: (1) to minimize recirculation error; (2) to adjust baseline temperature, thereby increasing sensitivity to small changes in temperature; and (3) to stabilize animal core temperature. The system was calibrated using a laboratory bench model with anatomically scaled components. CO was measured (n=29) in 16 hamsters (65-115 g), and was linearly related to body weight. Cardiac index (CI=CO/weight) was 197.0 +/- 18.8 (ml/min)/kg. Repeated measurements were made. This technique allows correlating systemic flow changes to be correlated to those measured in the microcirculation of window chamber preparations.

Animals↗

PubMed2002

Both random and perseverative errors underlie WCST deficits in prefrontal patients.

The specificity of the Wisconsin Card Sorting Test (WCST) as a marker of frontal lobe pathology remains controversial. One problem is the lack of a well established correspondence between WCST errors and specific cognitive or neural processes. The conventional scoring of non-perseverative WCST errors does not discriminate between errors related to the efficient test of hypotheses during set shifting ('efficient errors'), and random failures to maintain set ('random errors'). This inherent confusion in the non-perseverative error score probably minimizes the relative importance of random errors in frontal lobe pathology. In this study, we used a WCST version sensitive to differences between 'efficient' and random errors to examine set shifting deficits in patients with focal lesions to their lateral prefrontal cortex. As expected, patients showed abnormally high rates of perseverative errors. Interestingly, patients also showed enhanced rates of random errors suggesting constant shifts or fluctuations in their choice of sorting principle. These results suggest that more sensitive tests are needed to elucidate the association between a specific type of set shifting error and a particular type of frontal lobe pathology.

Adult↗

PubMed1997

Influence of perceptual and semantic conflicts between the two halves of chimeric stimuli on the expression of visuo-spatial neglect.

We investigated how perceptual and semantic relationships between the left and right half of chimeric stimuli influence overt and covert visual processing by asking eight right brain damaged (RBD) patients with hemispatial neglect to identify complete, half-, and chimeric drawings. Chimeric stimuli belonged in one of four categories defined according to the perceptual and semantic relatedness between the two compounding hemi-figures. Thus, the hemi-figures could be related both perceptually and semantically, only perceptually, only semantically, or neither perceptually nor semantically. Although patients often appeared to base their report on the right part of the chimerics, the number of errors was minimal when conflicts between the two hemi-figures were maximal. Moreover, perceptual conflicts, which mainly affect the perception of the shape, appeared to influence the performance more than semantic conflicts. Since the analysis of shape incongruency is probably accomplished at early levels of information processing, the result suggests that preattentive analysis is largely spared in the experimental patients and that, in our task, bottom-up factors more than top-down factors modulate the expression of left neglect.

Aged↗

PubMed2002

Predicting risk of ovulation in new start oral contraceptive users.

OBJECTIVE: To assess ovarian follicular development and ovulation rates in women starting to take oral contraceptives (OC) on menstrual cycle day 1, 4, or 7. METHODS: One hundred thirty women starting treatment with OC were randomized to begin use of ethinyl estradiol, 30 microg, plus norgestrel, 300 microg, on menstrual cycle day 1 (group 1), 4 (group 2), or 7 (group 3). Follicular development was assessed by vaginal ultrasonography on menstrual cycle days 7, 14, 21, and 28, and serum progesterone levels were measured on menstrual cycle days 21 and 28. At a.05 level of significance (two-tailed) and power of 80%, 84 participants were required to complete the study. Eighty-five women who met study criteria, made minimal dosing errors, and underwent at least three ultrasonographic examinations were analyzed. RESULTS: A follicle-like structure that reached a maximum diameter over 13 mm was observed in three of 29 (10.3%), five of 29 (17.2%), and 12 of 27 (44.4%) women in groups 1, 2 and 3, respectively (P = 0.003). The median maximum follicle size for each group was 9.0 mm, 9.0 mm, and 12.0 mm for start day 1, 4, and 7 respectively (P <.001). Evidence of ovulation based on serum progesterone was present in two, one, and zero women in groups 1, 2, and 3, respectively (P =.2). CONCLUSION: Although a delay in oral contraceptive initiation results in significantly more ovarian follicular development, the postponement does not appear to increase actual ovulation rates.

Adolescent↗

PubMed2001

Asymmetrical masking between radial and parallel motion flow in transparent displays.

Human spatial behavior remains surprisingly accurate and stable, despite the complexities of the concurrent retinal image flow. How does visual motion analysis contribute to behavioral stability? To approach this question, we rely on current knowledge about heading perception and coherent motion extraction from animated random dot displays. This chapter presents psychophysical evidence for an asymmetry in the global visual decomposition of the retinal motion flow. We examined the ability of human observers to identify the radial and the parallel flow component in displays where the two motions were transparently superimposed. Whereas sensitivity to the radial motion remained unaffected by the presence of parallel flow, sensitivity to the latter was greatly degraded in the presence of radial flow. This imbalance was observed within the first 200 ms of motion exposure, prior to the perception of heading (430 ms; Hooge et al. (1999) Exp. Brain Res., 129: 615-628). Although such an asymmetrical masking is well suited to minimize heading errors, whether it really contributes to the extraction of behavioral direction remains an open question.

Animals↗

PubMed1981

An immunofluorescent test for faecal occult blood.

An immunological test for faecal occult blood is described, which is suitable for screening purposes. Fluorescein-labelled rabbit anti-human-haemoglobin serum is mixed with an aqueous faecal suspension, and free antibody is bound to a membrane sampler coated with human haemoglobin. The fluorescence on the membrane sampler is measured in a fluorometer, and the level of haemoglobin in the suspension is estimated. Advantages over chemical tests include absence of cross-reaction with animal haemoglobins, minimal observer error, and an adjustable sensitivity.

Colonic Neoplasms↗

PubMedDate not supplied

Follow-up consultation billing and documentation.

Frequently, bills are not submitted for follow-up visits for patients who have been evaluated psychiatrically on medical-surgical services. There often is confusion regarding which procedure codes are most appropriate to use in billing. To help the consultant understand the documentation requirements for various procedure codes, information from several sources was synthesized and distilled. This paper should help minimize documentation errors and maximize reimbursement for clinical services. The authors have reviewed available billing choices, and clarified the documentation requirements for different procedure codes according to Medicare regulations.

Accounting↗

PubMed2002

Detection of reactive oxygen species by flow cytometry after spinal cord injury.

The monitoring of reactive oxygen species (ROS) levels in injured nervous tissue is critical for both studying the mechanism of secondary damage and evaluating the effectiveness of antioxidants. Flow cytometry is an excellent method to detect ROS in cultured cells and naturally suspended individual cells. However, its use in nervous tissue is limited due to the difficulties in obtaining single cells in suspension. We have developed a new method which minimizes the error during conventional dissociation. Specifically, we introduced a fixation step (with formaldehyde) between the dye loading and dissociation. As a result, the post-injury ROS signals detected by flow cytometry increase significantly when using hydroethidine as superoxide indicator. The injury-induced elevation of ROS obtained from this new method was also in better agreement with the two other standard ROS detection methods, fluorescence microscopy and lipid peroxidation assay. Furthermore, more pronounced decrease of ROS was found in this improved method in response to treatment with a superoxide scavenger, manganese(III)tetrakis(4-benzoic acid)porphyrin. Based on these observations, we suggest that the data obtained from the cells by this new method are more accurate than those from the classic cell dissociation method that dissociates cells directly from fresh tissues.

Animals↗

PubMed2001

Dosimetric consequences of tumor mobility in radiotherapy of stage I non-small cell lung cancer--an analysis of data generated using 'slow' CT scans.

BACKGROUND: The target coverage for radiotherapy of early-stage lung cancer was evaluated using two different CT techniques. MATERIALS AND METHODS: A conventional planning CT scan and two limited scans of the tumor region were performed in seven patients with peripheral tumors. Three 'slow' scans (slice thickness 4mm, index 3mm, revolution time 4s/slice) were then performed, followed by three-dimensional image registration. Planning target volumes (PTV) were generated using these GTV-PTV margins: (a) 1cm (PTV1.0); (b) 1.5 cm (PTV1.5); and (c) 0.9, 1.0, and 0.9 cm ('PTV(clinical)') when set-up errors are avoided. RESULTS: PTVs derived from three 'slow' scans missed 1.9% of the volume derived from three planning scans for an immobile tumor and 9.3% in the case of a mobile tumor. For an immobile tumor, PTV1.5 achieved comparable coverage to that achieved using PTVclinical, which was generated from three 'slow' scans and a planning scan. For a mobile tumor, PTV(1.5) covered only 89% of the volume captured by PTVclinical. PTV1.0 resulted in inadequate target coverage in all the patients. Reductions in potential lung toxicity (V20) were achievable in six patients despite the larger GTVclinical when treatment set-up errors were minimized. CONCLUSIONS: PTVs derived using 'slow' CT scans consistently produce superior target coverage than that using conventional scans. This may account for the poor local control observed in stage I lung cancer.

Carcinoma, Non-Small-Cell Lung↗

PubMed1999

Quantification and predictors of prostate position variability in 50 patients evaluated with multiple CT scans during conformal radiotherapy.

PURPOSE: To determine the extent and predictors for prostatic motion in a large number of patients evaluated with multiple CT scans during radiotherapy, and evaluate the implications of these data on the design of appropriate treatment margins for patients receiving high-dose three-dimensional conformal radiotherapy. MATERIALS AND METHODS: Fifty patients underwent four serial computerized tomography (CT) scans, consisting of an initial planning scan and subsequent scans at the beginning, middle, and end of the treatment course. Each scan was performed with the patient in the prone treatment position within an immobilization device used during therapy. Contours of the prostate and seminal vesicles were drawn on the axial CT slices of each scan, and the scans were matched by alignment of the pelvic bones with a chamfer matching algorithm. Using the contour information, distributions of the displacement of the organ center of mass and organ border from the planning position were determined separately for the prostate and seminal vesicles in each of the three principle directions: anterior-posterior (AP), superior-inferior (SI) and left-right (LR). Each distribution was fitted to a normal (Gaussian) distribution to determine confidence limits in the center of mass and border displacements and thereby evaluate for the optimal margins needed to contain target motion. RESULTS: The most common directions of displacement of the prostate center of mass (COM) were in the AP and SI directions and were significantly larger than any LR movement. The mean prostate COM displacement (+/- 1 standard deviation, SD) for the entire population was -1.2 +/- 2.9 mm, -0.5 +/- 3.3 mm and -0.6 +/- 0.8 mm in the, AP and SI and LR directions respectively (negative values indicate posterior, inferior or left displacement). The mean (+/- 1 SD) seminal vesicle COM displacement for the entire population was - 1.4 +/- 4.9 mm, 1.3 +/- 5.5 mm and -0.8 +/- 3.1 mm in the AP and SI and LR directions, respectively. The data indicate a tendency for the population towards posterior displacements of the prostate from the planning position and both posterior and superior displacements of the seminal vesicles. AP movement of both the prostate and seminal vesicles were correlated with changes in rectal volume (P = 0.0014 and < 0.0001, respectively) more than with changes in bladder volume (P = 0.030 for seminal vesicles and 0.19 for prostate). A logistic regression analysis identified the combination of rectal volume > 60 cm3 and bladder volumes > 40 cm3 as the only predictor of large ( > 3 mm) systematic deviations for the prostate and seminal vesicles (P = 0.05) defined for each patient as the difference between organ position in the planning scan and mean position as calculated from the three subsequent scans. CONCLUSIONS: Prostatic displacement during a course of radiotherapy is more pronounced among patients with initial planning scans with large rectal and bladder volumes. Such patients may require more generous margins around the CTV to assure its enclosure within the prescription dose region. Identification and correction of patients with large systematic errors will minimize the extent of the margin required and decrease the volume of normal tissue exposed to higher radiation doses.

Artifacts↗

PubMed1997

Do quality of life assessments make a difference in the evaluation of cancer treatments?

The question posed by this set of quality of life papers is whether or not quality of life assessments in cancer clinical trials help evaluate the effects of cancer treatment on patient functioning. In this discussion, missing data problems, particularly those commonly found in advanced stage disease trials, are highlighted. Researchers are encouraged to investigate the extent of bias associated with missing data and to select analysis approaches accordingly. In the worst case, it may not be possible to analyze data longitudinally; descriptive or graphical portrayals of the data may be more appropriate. The importance of instrument reliability (minimizing measurement error) is emphasized for clinical trials research, particularly with respect to enhancing a trial's ability to detect quality of life differences by treatment arm. One strategy for addressing missing data is evaluated with respect to its impact on the measurement properties of the quality of life questionnaire. Clinical trials groups have been successful in obtaining quality of life data in multi-site settings and patients, by and large, appreciate the effort to include a systematic and standardized report of the effects of treatment on their functioning.

Bias↗

PubMed1999

Description of hydration free energy density as a function of molecular physical properties.

A method to calculate the solvation free energy density (SFED) at any point in the cavity surface or solvent volume surrounding a solute is proposed. In the special case in which the solvent is water, the SFED is referred to as the hydration free energy density (HFED). The HFED is described as a function of some physical properties of the molecules. These properties are represented by simple basis functions. The hydration free energy of a solute was obtained by integrating the HFED over the solvent volume surrounding the solute, using a grid model. Of 34 basis functions that were introduced to describe the HFED, only six contribute significantly to the HFED. These functions are representations of the surface area and volume of the solute, of the polarization and dispersion of the solute, and of two types of electrostatic interactions between the solute and its environment. The HFED is described as a linear combination of these basis functions, evaluated by summing the interaction energy between each atom of the solute with a grid point in the solvent, where each grid point is a representation of a finite volume of the solvent. The linear combination coefficients were determined by minimizing the error between the calculated and experimental hydration free energies of 81 neutral organic molecules that have a variety of functional groups. The calculated hydration free energies agree well with the experimental results. The hydration free energy of any other solute molecule can then be calculated by summing the product of the linear combination coefficients and the basis functions for the solute.

Journal Article↗

PubMed1982

Quantitative analysis of procarbazine, procarbazine metabolites and chemical degradation products with application to pharmacokinetic studies.

Quantitative analytical methods are described for the analysis of the anticancer drug procarbazine and eight known metabolites including those known to have cytotoxic activity. A direct sample insertion mass spectrometric assay for procarbazine and the urinary excretion product, N-isopropyl-terephthalamic acid, has been developed. This method employs stable isotope labeled variants in a procedure that minimizes analytical errors that may be encountered in the quantitation of the chemically unstable parent drug. a liquid chromatographic method is described for the analysis of seven known procarbazine metabolites. Use of these methods is demonstrated by the analysis of procarbazine metabolism during incubation in a 9000-g rat liver homogenate preparation. Procarbazine disappearance and metabolite appearance are also monitored in rat plasma following intraperitoneal administration of a 150 mg/kg bolus dose. Applications to patient pharmacokinetics is demonstrated using the liquid chromatographic assay to follow the appearance of active procarbazine metabolites on the first and fourteenth day of an oral 250 mg/kg/day course of therapy of a patient being treated for cancer.

Animals↗