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Results for “parameter optimization”

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PubMed2026

Technical note: reconstructing dose distributions from manually planned electron boosts in breast radiotherapy.

PURPOSE: In breast radiotherapy, delivery of manually-calculated electron boosts limits retrospective dose-response analyses as dose distribution is unavailable. This work evaluates the feasibility of reconstructing dose distributions from manually planned electron boosts in breast-conserving radiotherapy. METHODS: Only 72 out of 198 breast cancer patients had complete stored dose distributions from sequential electron boosts in the REQUITE study. Arbitrary data from 70/72 patients were used to develop and validate dose reconstruction method. Twenty patients were used to determine optimal parameters for Monte-Carlo-based (MC) electron dose reconstruction on RayStation (v.11B-R), considering CT-calibration curve, MC-history number, andcalculation grid resolution. Remaining 50 patients were used to quantify dose reconstruction accuracy. The similarity between reconstructed and stored dose was evaluated using 3D-gamma index and dosimetric parameters extracted from breast and tumour bed contours. Dose difference location was evaluated using dose-location histogram. RESULTS: Calculation grid resolution significantly impacted electron dose distribution (p < 0.01), where the finest grid (0.15 cm) showed highest similarity to stored doses. CT-calibration curve and MC-history number had a negligible influence on dose reconstruction. Dosimetric difference between reconstructed and stored doses was < 1 Gy for breast and tumour bed. Reconstructed dose was achieved > 90% gamma passing rate in the validation set. However, around 2.5 Gy dose differences were observed at the skin and tissue interface regions. CONCLUSIONS: Retrospective electron boost dose reconstruction is feasible with acceptable accuracy, and could increase data completeness in large cohort studies. Caution is advised when assessing dose near tissue interface and further validation is needed outside the REQUITE dataset.

Electrons↗

PubMed2004

Single-step granulation/tabletting of different grades of lactose: a comparison with high shear granulation and compression.

The influence of the particle size, particle morphology and crystallinity of lactose on the extrusion properties and on the quality of tablets were investigated using single-step granulation/tabletting as a tabletting technique. Results showed that particle size and type of lactose (alpha-lactose monohydrate, anhydrous beta-lactose and spray dried lactose) affected the powder feeding, the process performance as well as the process capacity. Different grades of lactose yielded tablets with similar tensile strength, but significantly different disintegration time. Single-step granulation/tabletting always yielded tablets with a significantly higher tensile strength and similar or significantly lower disintegration time compared to high shear granulation and compression. The tensile strength of alpha-lactose monohydrate tablets (without and with PVP) did not change during one year of storage at 60% RH-25 degrees C and at 75% RH-40 degrees C, whereas a significant increase in disintegration time was observed. It can be concluded that although the lactose grade affected the performance and the optimal parameters of single-step granulation/tabletting, all lactose grades can be efficiently processed using this technique.

Compressive Strength↗

PubMed2005

Performance of a seizure warning algorithm based on the dynamics of intracranial EEG.

During the past decade, several studies have demonstrated experimental evidence that temporal lobe seizures are preceded by changes in dynamical properties (both spatial and temporal) of electroencephalograph (EEG) signals. In this study, we evaluate a method, based on chaos theory and global optimization techniques, for detecting pre-seizure states by monitoring the spatio-temporal changes in the dynamics of the EEG signal. The method employs the estimation of the short-term maximum Lyapunov exponent (STL(max)), a measure of the order (chaoticity) of a dynamical system, to quantify the EEG dynamics per electrode site. A global optimization technique is also employed to identify critical electrode sites that are involved in the seizure development. An important practical result of this study was the development of an automated seizure warning system (ASWS). The algorithm was tested in continuous, long-term EEG recordings, 3-14 days in duration, obtained from 10 patients with refractory temporal lobe epilepsy. In this analysis, for each patient, the EEG recordings were divided into training and testing datasets. We used the first portion of the data that contained half of the seizures to train the algorithm, where the algorithm achieved a sensitivity of 76.12% with an overall false prediction rate of 0.17h(-1). With the optimal parameter setting obtained from the training phase, the prediction performance of the algorithm during the testing phase achieved a sensitivity of 68.75% with an overall false prediction rate of 0.15h(-1). The results of this study confirm our previous observations from a smaller number of patients: the development of automated seizure warning devices for diagnostic and therapeutic purposes is feasible and practically useful.

Adult↗

PubMed2004

Sequential injection spectrophotometric determination of etilefrine hydrochloride.

A simple, fast, economical and automated sequential injection spectrophotometric method for the determination of etilefrine hydrochloride is developed. The method is based on the condensation reaction of etilefrine hydrochloride with 4-aminoantipyrine in the presence of alkaline potassium hexacyanoferrate and the absorbance of the colored product measured at 503 nm. Aspiration order, flow rate, reaction coil diameter, reaction coil length, concentration of 4-aminoantipyrine and potassium ferricyanide, as well as aspiration volume of reagents and sample has been optimized. Using these optimized parameters, a linear relationship between the relative peak height and concentration was obtained in the range 1-20 mg l(-1). The detection limit (as 3sigma value) was 0.1 mg l(-1) and precision was 2.7% and 1.5% at 1 and 2 mg l(-1), respectively. This method is superior over previously reported ones in terms of linear range, short analysis time, high sample throughput, excellent reagent economy and minimum waste generation.

Etilefrine↗

PubMed2005

Radiation pneumonitis and pulmonary fibrosis in non-small-cell lung cancer: pulmonary function, prediction, and prevention.

Although radiotherapy improves locoregional control and survival in patients with non-small-cell lung cancer, radiation pneumonitis is a common treatment-related toxicity. Many pulmonary function tests are not significantly altered by pulmonary toxicity of irradiation, but reductions in D(L(CO)), the diffusing capacity of carbon monoxide, are more commonly associated with pneumonitis. Several patient-specific factors (e.g. age, smoking history, tumor location, performance score, gender) and treatment-specific factors (e.g. chemotherapy regimen and dose) have been proposed as potential predictors of the risk of radiation pneumonitis, but these have not been consistently demonstrated across different studies. The risk of radiation pneumonitis also seems to increase as the cumulative dose of radiation to normal lung tissue increases, as measured by dose-volume histograms. However, controversy persists about which dosimetric parameter optimally predicts the risk of radiation pneumonitis, and whether the volume of lung or the dose of radiation is more important. Radiation oncologists ought to consider these dosimetric factors when designing radiation treatment plans for all patients who receive thoracic radiotherapy. Newer radiotherapy techniques and technologies may reduce the exposure of normal lung to irradiation. Several medications have also been evaluated for their ability to reduce radiation pneumonitis in animals and humans, including corticosteroids, amifostine, ACE inhibitors or angiotensin II type 1 receptor blockers, pentoxifylline, melatonin, carvedilol, and manganese superoxide dismutase-plasmid/liposome. Additional research is warranted to determine the efficacy of these medications and identify nonpharmacologic strategies to predict and prevent radiation pneumonitis.

Antineoplastic Agents↗

PubMed2004

Treatment of silica effluents: ultrafiltration or coagulation-decantation.

In the electronics industry, the preparation of silicon plates generates effluents that contain a great amount of colloidal silica. Two processes--decantation and ultrafiltration--are studied with in view the treatment of the effluents released by the firm Rockwood Electronic Materials. The feasibility of each of the two processes is studied separately and their operating parameters optimized. Both processes allow the recovery of a great proportion of the initial effluent (over 89%) as transparent and colorless water that can be reused at the start of a line. In view of the results and of the compared advantages and disadvantages of the two processes, ultrafiltration will be selected for the industrial unit.

Colloids↗

PubMed2006

Processing of spent NiMo and CoMo/Al2O3 catalysts via fusion with KHSO4.

This work describes a route for processing spent commercial hydrorefining (HDR) catalysts (CoMo and NiMo/Al2O3), containing support additives, for recovering active phase and support components. Samples were used as catalysts in diesel hydrotreaters. They had neither been submitted to mechanical stresses nor overheating while under operation. The route is based on fusion of samples with KHSO4. Four experimental parameters were optimized: reaction time, sample/flux mass ratio, temperature, and sample physical characteristics (ground/non-ground). After fusion, the solid was dissolved in water (90-100 degrees C); the insoluble matter presented low crystallization. Several phases were identified: silicates, spinel-like compounds and aluminosilicates. Cobalt, nickel, molybdenum and aluminum were recovered by conventional precipitation techniques or selective solvent-extraction procedures, with at least 85 wt.% yield. Final liquid colorless effluents are obtained as neutral solutions of alkali sulfates or chlorides and a water insoluble solid after fusion, which can be either sent to industrial dumps or co-processed. Fusion with KHSO4 was shown to be applicable to the catalysts of the present study, and the optimized experimental parameters are much less drastic than the conventional pyrometallurgical routes proposed in the literature.

Aluminum↗

PubMed2005

The single basis filter diagonalization method: a rapid multidimensional data processing scheme.

A new way to apply the filter diagonalization method (FDM) that results in a large increase in the speed of calculation of multidimensional NMR spectra is presented. The speed increase is accompanied by slight differences in spectral lineshapes, although frequency estimates remain essentially identical. For contoured spectra, the method does not result in appreciable differences from the full FDM calculation. Optimal parameter sets for an FDM calculation can be estimated far more rapidly, which makes the FDM more straightforward to employ in practice. The performance of the method versus the full FDM was investigated for both model and experimental signals. The effect of noise on the method was also studied.

Algorithms↗

PubMed2005

Effective rotational correlation times of proteins from NMR relaxation interference.

Knowledge of the effective rotational correlation times, tauc, for the modulation of anisotropic spin-spin interactions in macromolecules subject to Brownian motion in solution is of key interest for the practice of NMR spectroscopy in structural biology. The value of tauc enables an estimate of the NMR spin relaxation rates, and indicates possible aggregation of the macromolecular species. This paper reports a novel NMR pulse scheme, [15N,1H]-TRACT, which is based on transverse relaxation-optimized spectroscopy and permits to determine tauc for 15N-1H bonds without interference from dipole-dipole coupling of the amide proton with remote protons. [15N,1H]-TRACT is highly efficient since only a series of one-dimensional NMR spectra need to be recorded. Its use is suggested for a quick estimate of the rotational correlation time, to monitor sample quality and to determine optimal parameters for complex multidimensional NMR experiments. Practical applications are illustrated with the 110 kDa 7,8-dihydroneopterin aldolase from Staphylococcus aureus, the uniformly 15N-labeled Escherichia coli outer membrane protein X (OmpX) in 60 kDa mixed OmpX/DHPC micelles with approximately 90 molecules of unlabeled 1,2-dihexanoyl-sn-glycero-3-phosphocholine (DHPC), and the 16 kDa pheromone-binding protein from Bombyx mori, which cover a wide range of correlation times.

Aldehyde-Lyases↗

PubMed2005

Fitting of random tessellation models to keratin filament networks.

The role of specific structural patterns in keratin filament networks for regulating biophysical properties of epithelial cells is poorly understood. This is at least partially due to a lack of methods for the analysis of filament network morphology. We have previously developed a statistical approach to the analysis of keratin filament networks imaged by scanning electron microscopy. The segmentation of images in this study resulted in graph structures, i.e. tessellations, whose structural characteristics are now further investigated by iteratively fitting geometrical statistical models. An optimal model as well as corresponding optimal parameters are detected from a given set of possible random tessellation models, i.e. Poisson-Line tessellations (PLT), Poisson-Voronoi tessellations (PVT) and Poisson-Delaunay tessellations (PDT). Using this method, we investigated the remodeling of keratin filament networks in pancreatic cancer cells in response to transforming growth factor alpha (TGFalpha), which is involved in pancreatic cancer progression. The results indicate that the fitting of random tessellation models represents a suitable method for the description of complex filament networks.

Algorithms↗

PubMed2006

Contrast enhanced ultrasound for radio frequency ablation of canine prostates: initial results.

PURPOSE: We determined the feasibility of contrast enhanced ultrasound for radio frequency ablation of the entire prostate as a method of minimally invasive treatment for prostate cancer in a canine model. MATERIALS AND METHODS: Approval of the Institutional Animal Use and Care committee was obtained. Initially 5 dogs (group 1) were tested using variable power (5 to 30 W), time (4 to 12 minutes), bolus (0.01 to 0.04 ml/kg) and infusion (3 to 11 ml per minute at 0.015 microl/kg) injections of an ultrasound contrast agent with conventional grayscale power Doppler and pulse inversion harmonic imaging to establish optimal parameters. Subsequently 4 dogs (group 2) underwent entire prostate ablation using parameters based on group 1. The size of the thermal lesions and residual viable tissue was measured with ImageJ software (National Institutes of Health, Bethesda, Maryland) on ultrasound and pathological study. Linear regression and Student's t test were used for statistical analysis. RESULTS: A bolus of 0.04 ml/kg, an infusion of 11 ml per minute at 0.015 microl/kg and the contrast enhanced pulse inversion harmonic imaging mode were ranked best for guiding ablation. Thermal lesion volume was proportional to ablation power and time. There was no significant difference in measured thermal lesion size in group 1 between ultrasound and pathological findings (mean +/- SD 1.51 +/- 0.74 and 1.46 +/- 0.74 cm3, p = 0.56) or in residual viable tissue in group 2 (0.43 +/- 0.043 and 0.41 +/- 0.291 cm3, p = 0.21). The average volume of prostate ablation achieved in group 2 was 96.3%. CONCLUSIONS: Contrast enhanced pulse inversion harmonic imaging is able to guide, monitor and control radio frequency ablation of the entire prostate.

Animals↗

PubMed2005

Dosimetric advantage and clinical implication of a micro-multileaf collimator in the treatment of prostate with intensity-modulated radiotherapy.

This paper investigates the dosimetric benefits of a micro-multileaf (4-mm leaf width) collimator (mMLC) for intensity-modulated radiation therapy (IMRT) treatment planning of the prostate cancer and its potential application for dose escalation and hypofractionation. We compared treatment plans for IMRT delivery using 2 different multileaf collimator (MLC) leaf widths (4 vs. 10 mm) for 10 patients with prostate cancer. Treatment planning was performed on the XknifeRT2 treatment planning system. All beams and optimization parameters were identical for the mMLC and MLC plans. All of the plans were normalized to ensure that 95% of the planning target volume (PTV) received 100% of the prescribed dose (74 Gy). The differences in dose distribution between the 2 groups of plans using the mMLC and the MLC were assessed by dose-volume histogram (DVH) analysis of the target and critical organs. Significant reductions in the volume of rectum receiving medium to higher doses were achieved using the mMLC. The average decrease in the volume of the rectum receiving 40, 50, and 60 Gy using the mMLC plans was 40.2%, 33.4%, and 17.7%, respectively, with p-values less than 0.0001 for V40 and V50 and 0.012 for V60. The mean dose reductions for D17 and D35 for the rectum were 20.0% (p < 0.0001) and 18.3% (p < 0.0002), respectively, when compared to those with the MLC plans. There were consistent reductions in all dose indices studied for the bladder. The target dose inhomogeneity was improved in the mMLC plans by an average of 32%. In the high-dose range, there was no significant difference in the dose deposited in the "hottest" 1 cc of the rectum between the 2 MLC plans for all cases (p > 0.78). Because of the reduction of rectal volume receiving medium to higher doses, dose to the prostate target can be escalated by about 20 Gy to over 74 Gy, while keeping the rectal dose (either denoted by D17 or D35) the same as those with the use of the MLC. The maximum achievable dose, derived when the rectum is allowed to reach the tolerance level, was found to be in the range of 113-172 Gy (using the tolerance value of D17). We conclude that the use of the mMLC for IMRT of the prostate may facilitate dose hypofractionation due to its dosimetric advantage in significantly improving the DVH parameters of the prostate and critical organs. When used for conventional fractionation scheme, mMLC for IMRT of the prostate may reduce the toxicity to the critical organs.

Equipment Design↗

PubMed2006

Segmentation of anatomical structures in chest radiographs using supervised methods: a comparative study on a public database.

The task of segmenting the lung fields, the heart, and the clavicles in standard posterior-anterior chest radiographs is considered. Three supervised segmentation methods are compared: active shape models, active appearance models and a multi-resolution pixel classification method that employs a multi-scale filter bank of Gaussian derivatives and a k-nearest-neighbors classifier. The methods have been tested on a publicly available database of 247 chest radiographs, in which all objects have been manually segmented by two human observers. A parameter optimization for active shape models is presented, and it is shown that this optimization improves performance significantly. It is demonstrated that the standard active appearance model scheme performs poorly, but large improvements can be obtained by including areas outside the objects into the model. For lung field segmentation, all methods perform well, with pixel classification giving the best results: a paired t-test showed no significant performance difference between pixel classification and an independent human observer. For heart segmentation, all methods perform comparably, but significantly worse than a human observer. Clavicle segmentation is a hard problem for all methods; best results are obtained with active shape models, but human performance is substantially better. In addition, several hybrid systems are investigated. For heart segmentation, where the separate systems perform comparably, significantly better performance can be obtained by combining the results with majority voting. As an application, the cardio-thoracic ratio is computed automatically from the segmentation results. Bland and Altman plots indicate that all methods perform well when compared to the gold standard, with confidence intervals from pixel classification and active appearance modeling very close to those of a human observer. All results, including the manual segmentations, have been made publicly available to facilitate future comparative studies.

Algorithms↗

PubMed2004

Effects of echo time variation on perfusion assessment using dynamic susceptibility contrast MR imaging at 3 tesla.

The implications of changing the echo time of a gradient-echo echo planar imaging sequence applied to dynamic susceptibility contrast magnetic resonance imaging (DSC-MRI) for perfusion imaging at 3T were investigated. Four echo times in the range of 21 to 45 ms were examined in a total of 17 patients who received a dose of 0.1 mmol/kg bodyweight Gadobutrol (Gadovist, 1.0 mmol/ml). As the primary optimization parameter, the concentration-to-noise ratio (SNRc) was selected as it takes effects of variations in baseline as well as in signal drop into account. In an analysis of gray matter, white matter and arterial regions of interest, SNRc showed the highest values for the shortest applied echo time in all cases. Maps of regional cerebral blood volume (rCBV) and blood flow (rCBF) were calculated using deconvolution based on singular value decomposition. The quality of rCBF and rCBV images was judged to be good or excellent in all cases, independent of the echo time. Calculated gray matter/white matter ratios of rCBF and rCBV displayed no significant dependence on the applied echo time. Considering the better SNRc and arterial signal saturation aspects, we found that the shortest investigated echo time was the superior one. We thus suggest that short echo times should be applied, taking technical limitations and clinical demands into consideration.

Adult↗

PubMed2006

Extracranial carotid MR imaging at 3T.

Some controversy exists over the accuracy and optimal parameters for carotid CE MR angiography at 1.5T. Spatial resolution remains more important than does temporal resolution to address the key question of vessel stenosis, based upon a review of the available literature that compares CE MR angiography with DSA. Specifically, CE MR angiograms with 0.9- to 1.2-mm resolution in all three planes before interpolation have a high reported sensitivity and specificity compared with DSA. To achieve this type of spatial resolution, cover the entire course of the carotid arteries from the aortic arch through the skull base, and achieve an absence of venous signal usually requires an elliptic-centric phase encoding CE MR angiogram that lasts for 50 to 60 seconds without the use of parallel imaging techniques. This near-millimeter resolution requires an accurate timing of the gadolinium bolus arrival to maximize intra-arterial SNR and to minimize venous contamination. Parallel imaging techniques can decrease the imaging time, but at a cost of some SNR. Initial experience with eight-channel or higher neurovascular coils at 3T indicates an increase in SNR/CNR compared with 1.5T. This should allow more consistent submillimeter-resolution carotid CE MR angiography with adequate SNR to maintain good IQ in a wide variety of clinical patients. Although a definite, prospective comparison of various CE MR angiography techniques,including a 20- to 30-second scan with 1.2- to 1.4-mm(3) voxel resolution and 50- to 60-second scan with 0.9- to 1.1-mm(3) voxel resolution at 1.5T, as well as 0.5- to 0.6-mm(3) voxel resolution with scan time of 50 to 60 seconds at 3T versus rotational DSA does not exist, the expectation is that the higher resolution and increased SNR that has resulted from 3T carotid CE MR angiography will have high sensitivity and specificity in detecting severe carotid stenosis. The most exciting application of 3T for carotid artery imaging may not be the higher resolution CE MR angiogram, however. Early work has demonstrated the potential of 3T, combined with sensitive surface coils, to depict carotid plaque with sufficient SNR to identify important plaque components consistently in most patients. This could help move MR imaging of the carotid arteries away from a strict evaluation of luminal narrowing to a focused evaluation of plaque morphology. Much work needs to be done. Although there is a growing body of literature to support the contention that plaque morphology is a predictor of subsequent thrombo-embolic disease, the natural history of these various plaque components in a large number of patients needs to be elucidated. If plaque characterization proves to be an independent risk factor that predicts stroke, more aggressive clinical treatment option strategies may be devised for patients who are at the highest risk. Currently, plaque characterization at 3T requires a different set of coils compared with the global assessment of the entire course of the carotid arteries. Future generations of 16- to 32-channel carotid coils should be able to combine the best features of current 4- to 8-channel surface carotid coils and neurovascular coils. These will enable a comprehensive evaluation of the entire course of the carotid artery and detailed carotid bifurcation plaque characterization at 3T within a clinically acceptable 1-hour time frame. This comprehensive carotid artery evaluation with 3T MR imaging would be far superior to that which is possible with US or CT.

Artifacts↗

PubMed2005

Functional multi-layer perceptron: a non-linear tool for functional data analysis.

In this paper, we study a natural extension of multi-layer perceptrons (MLP) to functional inputs. We show that fundamental results for classical MLP can be extended to functional MLP. We obtain universal approximation results that show the expressive power of functional MLP is comparable to that of numerical MLP. We obtain consistency results, which imply that the estimation of optimal parameters for functional MLP is statistically well defined. We finally show on simulated and real world data that the proposed model performs in a very satisfactory way.

Algorithms↗

PubMed2006

3D MTR measurement: from 1.5 T to 3.0 T.

This study investigates some of the issues involved in magnetization transfer ratio (MTR) acquisition, and in particular aims to determine whether high quality in vivo MTR measurements can be made at 3.0 T. The dependency of the MTR white-to-grey matter contrast to noise ratio (CNR) on MT pulse characteristics at 1.5 T and at 3.0 T was investigated using an established two-pool model for MT. The simulations showed that MT pulse parameters optimizing the CNR can be derived for both field strengths. Both the SNR and the CNR of MTR maps at 3.0 T were increased compared to 1.5 T. Images obtained using a safe in vivo MTR acquisition protocol based on results of simulations at 3.0 T are presented.

Artifacts↗

PubMed2005

Erbium: yttrium-aluminum-garnet laser application in stapedotomy.

OBJECTIVE: To assess clinical safety and efficacy of the erbium: yttrium-aluminum-garnet (Er:YAG) laser in the stapes surgery; to define and optimize parameters that render the procedure safe for the inner ear. STUDY DESIGN: Retrospective study. MATERIAL AND METHODS: A microscope-integrated Er:YAG laser stapedotomy was performed on 29 patients and a conventional stapedotomy on 41 patients. An early (within 1 to 3 days after stapes surgery) and late (at least 6 weeks) pure-tone bone-conduction threshold audiogram was obtained. RESULTS: No statistically significant differences were found by Student's t test over all measured frequencies between pre- and postoperative bone-conduction thresholds in each group. There was no statistically significant difference for all frequencies between early (3 days) and late postoperative mean bone-conduction thresholds. CONCLUSIONS: The results of our preliminary clinical study showed that erbium laser poses no risk to inner ear function. However, the lack of standardization obliges further investigation to establish safe clinical parameters of the Er:YAG laser.

Adult↗