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Results for “Measuring algorithm”

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PubMed1991

Calculation of pulse-wave velocity using cross correlation--effects of reflexes in the arterial tree.

The need to investigate the elastic properties of arterial vessels in situ for the early recognition of degenerative disorders in arteries has long been apparent. Pulse-wave diagnostics has been used in traditional medicine, but only in a qualitative way. By measuring the vessel diameter change, simultaneously at two levels along an artery, it should be possible to calculate the pulse-wave velocity (PWV). A newly developed ultrasonic instrument, DIAMOVE, was designed to provide a two-dimensional, real time, B-mode image for display of the exact position of two measurement sites; a computer-controlled digital phased-locked loop detector for the measurement of diameter changes; and a personal computer for the display of the momentary displacement of the artery walls. The cross-correlation technique was used on the information from the vessel wall movements to calculate the resulting PWV. Early measurements on healthy patients showed some unexpected artifacts, which were found to be due to reflected waves, affecting the shape of the pulse-wave at the sites of measurement. A modified PWV estimation algorithm, where only the foot of the pulse-wave in every beat is utilized, seems to have solved this problem and now makes the method suitable for clinical use.

Algorithms↗

PubMed1989

Evaluation of lung dose correction methods for photon irradiations of thorax phantoms.

Radiation absorbed dose in lung is measured and calculated using several algorithms available on commercial treatment planning systems. Phantoms resembling the human thorax are used and irradiated with small and large photon beams of 60Co, 4, 6, and 10 MV X ray energies. The applicability and usefulness of the different calculation methods in clinical situations is discussed.

Lung↗

PubMed2004

Effects of geriatric evaluation and management on adverse drug reactions and suboptimal prescribing in the frail elderly.

PURPOSE: To determine if inpatient or outpatient geriatric evaluation and management, as compared with usual care, reduces adverse drug reactions and suboptimal prescribing in frail elderly patients. METHODS: The study employed a randomized 2 x 2 factorial controlled design. Subjects were patients in 11 Veterans Affairs (VA) hospitals who were > or =65 years old and met criteria for frailty (n = 834). Inpatient geriatric unit and outpatient geriatric clinic teams evaluated and managed patients according to published guidelines and VA standards. Patients were followed for 12 months. Blinded physician-pharmacist pairs rated adverse drug reactions for causality (using Naranjo's algorithm) and seriousness. Suboptimal prescribing measures included unnecessary and inappropriate drug use (Medication Appropriateness Index), inappropriate drug use (Beers criteria), and underuse. RESULTS: For serious adverse drug reactions, there were no inpatient geriatric unit effects during the inpatient or outpatient follow-up periods. Outpatient geriatric clinic care resulted in a 35% reduction in the risk of a serious adverse drug reaction compared with usual care (adjusted relative risk = 0.65; 95% confidence interval: 0.45 to 0.93). Inpatient geriatric unit care reduced unnecessary and inappropriate drug use and underuse significantly during the inpatient period (P <0.05). Outpatient geriatric clinic care reduced the number of conditions with omitted drugs significantly during the outpatient period (P <0.05). CONCLUSION: Compared with usual care, outpatient geriatric evaluation and management reduces serious adverse drug reactions, and inpatient and outpatient geriatric evaluation and management reduces suboptimal prescribing, in frail elderly patients.

Aged↗

PubMed2003

Monitoring cytochrome redox changes in the mitochondria of intact cells using multi-wavelength visible light spectroscopy.

We have developed an optical system based on visible light spectroscopy for the continuous study of changes in the redox states of mitochondrial cytochromes in intact mammalian cells. Cells are suspended in a closed incubation chamber in which oxygen and nitric oxide (NO) concentrations can be monitored during respiration. Simultaneously the cells are illuminated with a broad-band tungsten-halogen light source. Emergent light in the visible region (from 490-650 nm) is detected using a spectrophotometer and charge-coupled device camera system. Intensity spectra are then converted into changes in optical attenuation from a 'steady-state' baseline. The oxidised-minus-reduced absorption spectra of the mitochondrial cytochromes are fitted to the attenuation spectra using a multi-wavelength least-squares algorithm. Thus, the system can measure changes in the redox states of the cytochromes during cellular respiration. Here we describe this novel methodology and demonstrate its validity by monitoring the action of known respiratory chain inhibitors, including the endogenous signalling molecule NO, on cytochrome redox states in human leukocytes.

Cytochromes↗

PubMed2006

Development and temporal organization of compulsive checking induced by repeated injections of the dopamine agonist quinpirole in an animal model of obsessive-compulsive disorder.

Rats treated chronically with the dopamine D2/D3 receptor agonist quinpirole develop locomotor sensitization and exhibit compulsive checking of specific places in an open-field arena, a behavioral profile that may represent an animal model of obsessive-compulsive disorder. However, it is not known how compulsive checking develops across quinpirole injections nor whether checking behavior possesses a particular temporal structure. Male rats received quinpirole (0.5mg/kg, twice weekly x 10) or an equivalent regimen of saline and were placed in a large open field for 55 min where their behavior was digitally tracked for subsequent analysis of checking behavior using existing and newly developed computer software. Results showed that the measures of compulsive checking did not follow a singular profile across injections: some remained constant and others changed monotonically reaching their near-maximum levels after about 5-7 quinpirole injections. Moreover, results showed that checking behavior was organized into bouts of checking, with the number of bouts, as well as the rate of checking within a bout, increasing across injections to reach near maximal levels after about 5-7 administrations of quinpirole. Finally, quinpirole-treated rats showed a paucity of long inter-bout intervals. These results suggest that (a) compulsive checking emerges from the operation of at least two underlying processes: a regulated process and a process of sensitization that intensifies the performance of checking behavior; and (b) quinpirole treatment may attenuate a sense of satiety that could underlie the compulsive nature of checking. Finally, because key variables measured using the newly developed algorithms showed the expected profile, the present study provides validation for the use of this methodology for the analysis of checking behavior.

Analysis of Variance↗

PubMed2006

Active sensation: insights from the rodent vibrissa sensorimotor system.

Rats sweep their vibrissae through space to locate objects in their immediate environment. In essence, their view of the proximal world is generated through pliable hairs that tap and palpate objects. The texture and shape of those objects must be discerned for the rat to assess the value of the object. Furthermore, the location of those objects must be specified with reference to the position of the rat's head for the rat to plan its movements. Recent in vivo and in vitro electrophysiological measurements provide insight into the algorithms and mechanisms that underlie these behavioral-based computations.

Action Potentials↗

PubMed2005

Peak pressure curve: an effective parameter for early detection of foot functional impairments in diabetic patients.

A clinical investigation was conducted on 61 diabetic patients and 22 healthy volunteers. Joint mobility, muscular function of the foot-ankle complex and plantar pressure measurements were characterised. A clustering algorithm was applied to obtain patient classification based on the shape and amplitude of the time curve of the instantaneous maximum pressure the foot experienced during gait. Results indicate that a screening test based on the peak pressure curve might be an effective way to detect diabetic patients at risk of foot ulceration.

Algorithms↗

PubMed2004

A new type of model-based Roentgen stereophotogrammetric analysis for solving the occluded marker problem.

Roentgen stereophotogrammetric analysis (RSA) measures micromotion of an orthopaedic implant with respect to its surrounding bone. A problem in RSA is that the markers are sometimes overprojected by the implant itself. This study describes the so-called Marker Configuration Model-based RSA (MCM-based RSA) that is able to measure the pose of a rigid body in situations where less than three markers could be detected in both images of an RSA radiograph. MCM-based RSA is based on fitting a Marker Configuration model (MC-model) to the projection lines from the marker projection positions in the image to their corresponding Roentgen foci. An MC-model describes the positions of markers relative to each other and is obtained using conventional RSA. We used data from 15 double examinations of a clinical study of total knee prostheses and removed projections of the three tibial component markers, simulating occlusion of markers. The migration of the tibial component with respect to the bone, which should be zero, for the double examination is a measure of the accuracy of algorithm. With the new algorithm, it is possible to estimate the pose of a rigid body of which one or two markers are occluded in one of the images of the RSA radiograph with high accuracy as long as a proper MC-model of the markers in the rigid body is available. The new algorithm makes RSA more robust for occlusion of markers. This improves the results of clinical RSA studies because the number of lost RSA follow-up moments is reduced.

Biomechanical Phenomena↗

PubMed2006

A comparison of the abuse liability of tramadol, NSAIDs, and hydrocodone in patients with chronic pain.

Concern about abuse/dependence in chronic pain patients taking opioid analgesics may lead to undertreatment of pain, yet little is known about the prevalence of abuse/dependence in these patients and how it differs among analgesic agents. The objective of this study was to assess the prevalence of tramadol abuse compared to nonsteroidal anti-inflammatory drugs (NSAIDs) and hydrocodone-containing analgesics in patients with chronic noncancer pain (CNP). The study had three arms. The first arm consisted of subjects prescribed tramadol alone; the second of subjects randomized to either NSAIDs or tramadol; and the third of subjects randomized to hydrocodone or tramadol. Each investigator received two boxes of prescriptions randomized so that one in every four prescriptions was for tramadol. Upon deciding on the therapeutically appropriate arm, the physician selected the appropriate box, opened the next envelope and completed the enclosed prescription. After the initial randomization, physicians could prescribe whatever medication was therapeutically appropriate. A total of 11,352 subjects were enrolled. Up to nine interviews using a structured questionnaire were conducted over a 12-month period. An algorithm called the "Abuse Index" was developed to identify subjects who were abusing the drug. The primary components of the index were increasing dose without physician approval, use for purposes other than intended, inability to stop its use, and withdrawal. The percent of subjects who scored positive for abuse at least once during the 12-month follow-up were 2.5% for NSAIDs, 2.7% for tramadol, and 4.9% for hydrocodone. When more than one hit on the algorithm was used as a measure of persistence, abuse rates were 0.5% for NSAIDs, 0.7% for tramadol, and 1.2% for hydrocodone. Thus, the results of this study suggest that the prevalence of abuse/dependence over a 12-month period in a CNP population that was primarily female was equivalent for tramadol and NSAIDs, with both significantly less than the rate for hydrocodone.

Adolescent↗

PubMed2006

Diagnostics and therapy of lymphoceles after kidney transplantation.

Lymphocele incidence after kidney transplantation is as high as 18%. We retrospectively studied the therapy of 42 lymphoceles that occurred in our clinic between 1990 and 2005, focusing on possible predisposing factors for their formation and the results of several therapy variants: conservative, operative, percutaneous puncture, and laparoscopic or open marsupialization. There was no connection between lymphocele formation and the following parameters: the extent to which the iliac vessels had been prepared, the materials used for the preparation, or whether clips or ligatures were applied. Lymphoceles may originate either from the lymphatic system of the recipient or the transplanted kidney. The most sensible measures to prevent their occurrence therefore seems to be to restrict the transplant bed to the smallest permissible level with careful ligature of the lymphatic vessels in the area of the kidney hilus. Treatment for lymphoceles should start with minimally invasive measures. We use the following algorithm in our clinic: puncture to differentiate between urinoma/lymphocele and to test for bacterial infection, sclerotization (200 mg doxycyclin), and finally marsupialization if persistent. The choice of operative technique depends on the location. This algorithm resulted in a relapse rate of 9.5% during the postoperative observation period of up to 15 years.

Diagnosis, Differential↗

PubMed1996

Neural networks to identify glaucoma with structural and functional measurements.

PURPOSE: Neural networks can recognize patterns and classify complex variables. We assessed the ability of neural networks to discriminate between normal and glaucomatous eyes by using structural and functional measurements. METHODS: Several neural network algorithms were tested with a database of 185 eyes of patients with early glaucomatous visual field loss (average mean defect, 4.5 dB) and 54 eyes of age-matched normal control subjects. The information used included automated visual field indices (mean defect, corrected loss variance, and short-term fluctuation) and structural data (cup/disk ratio, rim area, cup volume, and nerve fiber layer height) from computerized image analysis. RESULTS: A back propagation network with two intermediate layers assigned an estimated probability of being glaucomatous to each eye and correctly identified 88% of all eyes with 90% sensitivity and 84% specificity. The same neural network trained with only structural data correctly identified 80% of the eyes with 87% sensitivity and 56% specificity, and when trained with functional data only, it correctly identified 84% of the eyes with 84% sensitivity and 86% specificity. CONCLUSION: Analysis of several optic nerve and visual field variables by neural networks can help identify early glaucomatous damage and assign an estimated probability that early damage is present in individual patients.

Algorithms↗

PubMed2000

Quantitative analysis of cell columns in the cerebral cortex.

We present a quantified imaging method that describes the cell column in mammalian cortex. The minicolumn is an ideal template with which to examine cortical organization because it is a basic unit of function, complete in itself, which interacts with adjacent and distance columns to form more complex levels of organization. The subtle details of columnar anatomy should reflect physiological changes that have occurred in evolution as well as those that might be caused by pathologies in the brain. In this semiautomatic method, images of Nissl-stained tissue are digitized or scanned into a computer imaging system. The software detects the presence of cell columns and describes details of their morphology and of the surrounding space. Columns are detected automatically on the basis of cell-poor and cell-rich areas using a Gaussian distribution. A line is fit to the cell centers by least squares analysis. The line becomes the center of the column from which the precise location of every cell can be measured. On this basis several algorithms describe the distribution of cells from the center line and in relation to the available surrounding space. Other algorithms use cluster analyses to determine the spatial orientation of every column.

Algorithms↗

PubMed2001

Extraction of full absorption peaks in airborne gamma-spectrometry by filtering techniques coupled with a study of the derivatives. Comparison with the window method.

In this paper, an adaptation of a spectral profile analysis method, currently used in high-resolution spectrometry, to airborne gamma measurements is presented. A new algorithm has been developed for extraction of full absorption peaks by studying the variations in the spectral profile of data recorded with large-volume NaI detectors (16 l) with a short sampling time (2 s). The use of digital filters, taking into consideration the characteristics of the absorption peaks, significantly reduced the counting fluctuations, making detection possible based on study of the first and second derivatives. The absorption peaks are then obtained by modelling, followed by subtraction of the Compton continuum in the detection window. Compared to the conventional stripping ratio method, spectral profile analysis offers similar performance for the natural radioelements. The 137Cs 1SD detection limit is approximately 1200 Bq/m2 in a natural background of 200 Bq/kg 40K, 33 Bq/kg 238U and 33 Bq/kg 232Th. At low energy the very high continuum leads to detection limits similar to those obtained by the windows method, but the results obtained are more reliable. In the presence of peak overlaps, however, analysis of the spectral profile alone is not sufficient to separate the peaks, and further processing is necessary. Within the framework of environmental monitoring studies, spectral profile analysis is of great interest because it does not require any assumptions about the nature of the nuclides. The calculation of the concentrations from the results obtained is simple and reliable, since only the full absorption contributions are taken into consideration. A quantitative estimate of radioactive anomalies can thus be obtained rapidly.

Air Pollution, Radioactive↗

PubMed2003

A noninvasive eye fixation and computer-aided eye monitoring system for linear accelerator-based stereotactic radiotherapy of uveal melanoma.

PURPOSE: To introduce a noninvasive eye fixation and computer-aided eye monitoring system for linear accelerator-based stereotactic radiotherapy for uveal melanoma. METHODS AND MATERIALS: At the Department of Radiotherapy and Radiobiology, University of Vienna, stereotactic radiotherapy is offered to patients with uveal melanoma considered unsuitable for (106)Ru brachytherapy or local resection. For the present feasibility study, 8 patients were carefully selected according to their ability to fixate a small light source with the diseased eye and whether they had a rather small head to meet the limited geometric space available. A polymethyl methacrylate tube was attached to a stereotactic mask system in craniocaudal orientation supporting a 45 degrees mirror, which was placed in front of the diseased eye. At the other end of the tube, the patient was given a small fixation light, and a small camera was positioned beneath, which was shielded for use during MRI. A computer interface calculated and visualized the spatial difference of the actual and a given reference pupil position, which was defined before CT scanning, during the MRI sequences, and during treatment delivery at the linear accelerator. RESULTS: The described system can be attached to a conventional stereotactic mask system with minor modifications. Because of the large distance between the eye and the fixation light, the optical fixation system was well tolerated by all patients, and a stable position of the eye was obtained. The camera system can be used during CT and MRI without interference. Absorption of the 6-MV photon beam by the mirror and the polymethyl methacrylate tube was negligible. The computer interface designed to determine the pupil position uses an image-processing algorithm that correlates a template of the reference image with the actual image of the eye. Provided sufficient illumination of the pupil, the correlation function showed a pronounced minimum at the reference position. The precision of the algorithm was tested by phantom measurements. For a given 1 mm or 2 mm displacement, the interface reported a mean shift of 0.96 +/- 0.18 mm or 2.07 +/- 0.11 mm, respectively. CONCLUSION: The results of this study demonstrated the feasibility of a new optical fixation system for linear accelerator-based stereotaxis. The artifact-free application of the camera system during image acquisition and irradiation and the use of the computer interface, which automatically monitored eye movements with submillimeter precision, provided large improvements compared with existing techniques. Given well-defined interruption criteria and accelerated image processing, the described system has a high potential to perform automatically gated treatment beam delivery in the near future.

Humans↗

PubMed2001

Improving storage efficiency of vector quantization codebook for physiological quasi-periodic signals.

A quasi-periodic signal is a periodic signal with period and amplitude variations. The electrocardiogram (ECG) and several physiological signals can be treated as quasi-periodic. Vector quantization (VQ) is a valuable and universal tool for signal compression. However, the periodicity of a quasi-periodic signal causes data redundancy in the VQ codebook, where many codevectors are highly correlated. This paper explores the codebook (CB) redundancy in order to increase storage efficiency for physiological quasi-periodic signals. A quantitative CB redundancy measure and two redundancy reducing algorithms are proposed. Both algorithms use a mixed CB structure containing one and two-dimensional CBs. The first algorithm is applied to a CB directly, and the second one uses an LBG-like training algorithm to obtain a storage-efficient CB from a set of training vectors. With the MIT/BIH ECG database, the experimental results show that both algorithms can reduce the CB redundancy effectively with essentially no loss of signal quality. For comparison, the mean-shape VQ (MSVQ) proposed by Cárdenas-Barrera and Lorenzo-Ginori for ECG compression is implemented and the resulting average percent of the root-mean-square difference (PRD) is 10.78%. By using the first algorithm, the CB storage space is reduced by 40% and the resulting average PRD is 10.87%. The second algorithm can reduce the CB storage space by 75% and the average PRD is 10.27%, which is even better than the original MSVQ.

Algorithms↗

PubMed2004

Performance of a digital PCO2/SPO2 ear sensor.

OBJECTIVE: For determining the adequacy of ventilation, conventional pulse oximetry should be amended by PaCO2 (= arterial carbon dioxide partial pressure). This study investigates the precision of carbon dioxide measurements of the first digital ear-clip sensor providing continuous non-invasive monitoring of PaCO2, SpO2 (= functional arterial oxygen saturation as estimated with a pulse oximeter) and pulse rate and compares it to two conventional analog oximeters. METHODS: 30 hypoxemia episodes in 6 adult volunteers were investigated in a standardized protocol. EQUIPMENT: Masimo analog finger sensor, Nellcor analog ear sensor, SenTec digital ear sensor. RESULTS: The difference between PCO2 data (= PaCO2 estimated from the measured PcCO2 based on an algorithm by Severinghaus) (PcCO2 = cutaneous carbon dioxide pressure) and the PaCO2 is clinically unimportant. Therefore, we suggest, the two methods of estimating patient's carbon dioxide status can be used interchangeably. CONCLUSIONS: Combined digital SpO2/ PcCO2 ear sensors are very promising to allow for a fast and reliable monitoring of patient's oxygenation, hyper-/hypocapnia and ventilation with one single non-invasive probe. Optimal primary signal processing--amplification and digitalisation within the probe--allow for fast and reliable downstream signal processing algorithms. The resulting short SpO2 response times give the medical staff more time to take appropriate actions.

Adult↗

PubMed1987

Effects of cognitive training on primary mental ability structure.

We report results of the first empirical test, as far as we know, of the assumption of structural invariance of latent constructs from pretest to posttest in cognitive training research on the elderly. In all, 401 participants in the Seattle Longitudinal Study, over 62 years old, received a 5-hr test battery at pre- and posttest that included 16 ability tests, marking the five primary abilities of Spatial Orientation, Inductive Reasoning, Numerical Ability, Verbal Ability, and Perceptual Speed. A total of 229 of our subjects received 5 hr of individual training on either Spatial Orientation or Inductive Reasoning. Restricted factor analysis with the LISREL algorithm tested the hypothesis of measurement equivalence across test occasions, separately for the control subjects and for each of the training groups. When ability-specific cognitive training intervenes, no structural change is observed for abilities not subject to intervention. However, slight shifts occurred in the optimal regression weights for the different markers for the training target abilities.

Aged↗

PubMed2003

Circadian rhythm of the corrected QT interval: impact of different heart rate correction models.

A reduced circadian pattern in the QTc interval has been repeatedly reported to provide prognostic information in cardiac patients. However, the results of studies in healthy subjects in which different heart rate correction formulas were used are inconsistent regarding the presence and extent of diurnal variations in QTc. This study compared the diurnal variations in QTc obtained with four frequently used heart rate correction models with those based on individually optimized heart rate correction. In 53 subjects (25 men aged 27 +/- 7 years and 28 women aged 27 +/- 9 years) 12-lead digital ECGs were obtained every 30 seconds during 24 hours. The QT interval was measured automatically by six different algorithms provided by a commercially available device. The QT/RR relation was estimated by four common heart rate correction models and by an individually optimized correction model, QTc = QT/RR alpha. In each 24-hour recording, RR, QT, and WTc intervals of separate ECG samples were averaged over 10-minute intervals. Marked differences were found in the extent of the circadian pattern of QTc obtained with different formulas for heart rate correction. Under and overcorrection of the QT interval resulted in significant over- or underestimation of the circadian pattern. Thus, the extent of circadian variation in QTc depends highly on the heart rate correction formula used. To obtain proper insight regarding diurnal variation in QTc prolongation during pharmacologic therapy and/or to assess higher risk due to impaired autonomic regulation of ventricular repolarization, individualized heart rate correction is necessary.

Adolescent↗