Search PubMed⌕ Search

SEARCH · Search PubMed

Results for “FIRS”

Search indexed PubMed citations on genomics, clinical trials, systematic reviews and public health. Explore titles, authors and supplied subject terms, then open the PubMed record.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 361 records · Page 20Linked to original sources
PubMed2003

Photosynthesis-nitrogen relationships: interpretation of different patterns between Pseudotsuga menziesii and Populus x euroamericana in a mini-stand experiment.

We compared photosynthesis-nitrogen relationships of one broad-leaved (poplar; Populus x euroamericana (Dole) Guinier) and one conifer (Douglas-fir; Pseudotsuga menziesii (Mirb.) Franco) species. Plants were grown in large pots to allow free root development and were kept well watered. We determined effects of low, intermediate and high nitrogen supply rates on area-based leaf nitrogen (Na) and chlorophyll concentrations, leaf mass per area (LMA), light-saturated photosynthesis (Amax), maximum carboxylation (Vcmax) and electron transport rate (Jmax), photosynthetic nitrogen-use efficiency (PNUE), and proportions of leaf N in active Rubisco (PR), bioenergetic pools (PB) and the light-harvesting complex (PLH). Nitrogen supply significantly affected leaf Na. Leaf mass per area did not differ between species and was unaffected by the N treatments. In both species, there was a positive correlation between leaf Na and chlorophyll concentration, and between leaf Na and the photosynthetic parameters Amax, Jmax and Vcmax. At comparable leaf Na, however, poplar showed twofold higher PNUE and a threefold steeper slope of the Amax- nitrogen relationship than Douglas-fir. Leaf Na was negatively correlated with PNUE in Douglas-fir but not in poplar. Leaf Na was also negatively correlated with PR, PB and PLH in Douglas-fir, whereas in poplar, a negative correlation was found only for PLH. Parameter PR was significantly higher in poplar than in Douglas-fir. The ratio of CO2 concentration in the intercellular space to that in ambient air was higher in poplar than in Douglas-fir. Overall, our data suggest that differences in the photosynthesis-nitrogen relationship and PNUE between Douglas-fir and poplar primarily reflect a different investment of N to active Rubisco, and possibly a different constraint to CO2 diffusion.

Carbon Dioxide↗
PubMed2003

Heme oxygenase-1 and the ischemia-reperfusion injury in the rat heart.

Carbon monoxide (CO) is a signaling gas produced intracellularly by heme oxygenase (HO) enzymes using heme as a substrate. During heme breakdown, HO-1 and HO-2 release CO, biliverdin, and Fe(2+). In this study, we investigated the effects of manipulation of the HO-1 system in an in vivo model of focal ischemia-reperfusion (FIR) in the rat heart. Male Wistar albino rats, under general anesthesia and artificial ventilation, underwent thoracotomy, the pericardium was opened, and a silk suture was placed around the left descending coronary artery; ischemia was induced by tightening the suture and was monitored for 30 min. Subsequently, the ligature was released to allow reperfusion lasting for 60 min. The first group of rats was sham operated and injected intraperitoneally (i.p.) with saline. The second group underwent FIR. The third group was treated ip 18 hr before FIR with hemin (4 mg/kg). The fourth group was pretreated ip 24 hr before FIR and 6 hr before hemin with zinc protoporphyrin IX (ZnPP-IX, 50 microg/kg). Specimens of the left ventricle were taken for determination of HO expression and activity, infarct size, malonyldialdehyde (MDA) production, and tissue calcium content. FIR led to a significant increase in the generation of MDA and notably raised tissue calcium levels. Induction of HO-1 by hemin significantly decreased infarct size, incidence of reperfusion arrhythmias, MDA generation, and calcium overload induced by FIR. These effects were prevented by the HO-1 inhibitor ZnPP-IX. The present experiments show that the concerted actions of CO, iron, and biliverdin/bilirubin modulate the FIR-induced myocardial injury.

Animals↗
PubMed2005

Protection from cardiac injury by induction of heme oxygenase-1 and nitric oxide synthase in a focal ischaemia-reperfusion model.

The enzymes heme oxygenase (HO) generate carbon monoxide (CO) in living organisms during heme degradation. Carbon monoxide has recently been shown to dilate blood vessels and to possess anti-inflammatory properties. It is also known that nitric oxide (NO) donors ameliorate cardiac ischaemia-reperfusion injury in experimental models of global or focal ischaemia-reperfusion (FIR). The two gaseous mediators share the same mechanism of action via the stimulation of soluble guanylyl cyclase and the increase in cellular levels of cyclic GMP. We studied the effects of manipulating the HO system and the possible interaction between CO and NO in an experimental in vivo model of FIR in the rat heart. FIR-subjected rats had necrotic area in the left ventricle, ventricular arrhythmias and a shortening of survival time in comparison to sham-operated animals. Resident mast cells underwent a heavy degranulation, malonyldialdehyde was produced by myocardial cell membranes, and tissue calcium levels were increased. High levels of myeloperoxidase were also detected, suggesting a FIR-related inflammatory process. In animals pre-treated with the HO-1 inducer, hemin, all the biochemical and morphometric markers of FIR were minimized or fully abated. Consistently, the biochemical and morphometric markers of FIR were reversed in rats treated with the HO-1 blocker, ZnPP-IX, prior to hemin administration. Pre-treatment with hemin significantly increases the expression and activity of both cardiac HO-1 and iNOS, suggesting that CO and NO cooperate in the cardioprotective effect against FIR-induced damage, and that there is a therapeutic synergism between NO-donors and CO-releasing molecules, via the common stimulation of increase in cGMP levels and decrease in calcium overload.

Animals↗
PubMed2003

Flow cytometric measurement of fluorescence (Förster) resonance energy transfer from cyan fluorescent protein to yellow fluorescent protein using single-laser excitation at 458 nm.

BACKGROUND: Use of distinct green fluorescent protein (GFP) variants permits the study of protein-protein interactions and colocalization in viable transfected cells by fluorescence (Förster) resonance energy transfer (FRET). Flow cytometry is a sensitive method to detect FRET. However, the typical dual-laser methods used in flow cytometric FRET assays are not generally applicable because they require a specialized krypton ultraviolet (UV) laser. The purpose of this work was to develop a flow cytometric method to detect FRET between cyan fluorescent protein (CFP; donor) and yellow fluorescent protein (YFP; acceptor) by using the 458-nm excitation from a single tunable argon-ion laser. METHODS: FUSE-binding protein (FBP) interacting repressor (FIR) and FBP are c-myc transcription factors and are known to interact physically. To examine their interaction within viable cells, FIR and the binding motif of FBP, the FBP central domain (FBPcd), were fused with CFP and YFP, respectively, and this pair of fluorescently-tagged proteins was used to detect FRET in vivo. Cells transfected with expression plasmids encoding a CFP-FIR fusion protein and YFP as a negative control, a CFP-YFP fusion protein as a positive control, or CFP-FIR and YFP-FBPcd fusion proteins were examined for FRET after excitation with a 458-nm line from a tunable argon-ion laser. FRET was measured as the ratio of YFP:CFP emission or as YFP emission at 564-606 nm. Conventional FRET using the 413-nm UV line from a krypton laser was examined for comparison. Fluorescence signals were separated with a customized optical filter configuration using 530-nm shortpass, 500-nm longpass, and 560-nm shortpass dichroics in addition to 488/30 nm (CFP), 530/30 nm (YFP), and 585/42 nm (FRET) bandpass filters. Further, a laser-scanning confocal microscopic photobleach technique was used to document that FRET occurred by showing that the intensity of donor CFP fluorescence increased after its acceptor YFP was photobleached. Steady-state spectrofluorometry was used to confirm and validate the results detected by flow cytometry. RESULTS: Upon excitation with the 458-nm line of the argon-ion laser, the enhancement of the acceptor YFP signal and the decrease of the CFP signal were easily detected in cells transfected with the CFP-YFP construct or CFP-FIR and YFP-FBPcd. Similarly, FRET was detected under these conditions when the YFP emission was assessed at 564-606 nm. A strong correlation was observed between the increase in the YFP:CFP ratio and the YFP emission detected at 564-606 nm, consistent with the conclusion that FRET was detected comparably by both methods. A conventional flow cytometric krypton UV-laser technique was also used to confirm that FRET occurred with the CFP-YFP fusion protein and from CFP-FIR --> YFP-FBPcd. FRET also was confirmed by a confocal photobleaching technique, in which donor CFP intensity was enhanced after its acceptor YFP was photobleached. The flow cytometric and confocal microscopic results were confirmed by spectrofluorometry. CONCLUSION: These results demonstrated the feasibility of flow cytometric detection of FRET signals from CFP to YFP by excitation with the 458-nm line from the tunable argon-ion laser. The method was as efficient as excitation with the krypton UV laser and therefore should make FRET a more generally available flow cytometric technique.

Argon↗
PubMed2006

New demodulation filter in digital phase rotation beamforming.

In this paper, we present a new quadrature demodulation filter to reduce hardware complexity in digital phase rotation beamforming. Due to its low sensitivity to phase delay errors, digital quadrature demodulation is commonly used in ultrasound machines. However, since it requires two lowpass filters for each channel to remove harmonics, the direct use of conventional finite impulse response (FIR) filters in ultrasound machines is computationally expensive and burdensome. In our new method, an efficient multi-stage uniform coefficient (MSUC) filter is utilized to remove harmonic components in phase rotation beamforming. In comparison with the directly implemented FIR (DI-FIR) and the previously-proposed signed-power-of-two FIR (SPOT-FIR) lowpass filters, the proposed MSUC filter reduces the necessary hardware resources by 93.9% and 83.9%, respectively. In simulation, the MSUC filter shows a negligible degradation in image quality. The proposed method resulted in comparable spatial and contrast resolution to the DI-FIR approach in the phantom study. These preliminary results indicate that the proposed quadrature demodulation filtering method could significantly reduce the hardware complexity in phase rotation beamforming while maintaining comparable image quality.

Humans↗
PubMed2000

The FBP interacting repressor targets TFIIH to inhibit activated transcription.

FUSE-binding protein (FBP) binds the single-stranded far upstream element of active c-myc genes, possesses potent transcription activation and repression domains, and is necessary for c-myc expression. A novel 60 kDa protein, the FBP interacting repressor (FIR), blocked activator-dependent, but not basal, transcription through TFIIH. Recruited through FBP's nucleic acid-binding domain, FIR formed a ternary complex with FBP and FUSE. FIR repressed a c-myc reporter via the FUSE. The amino terminus of FIR contained an activator-selective repression domain capable of acting in cis or even in trans in vivo and in vitro. The repression domain of FIR targeted only TFIIH's p89/XPB helicase, required at several stages in transcription, but not factors required for promoter selection. Thus, FIR locks TFIIH in an activation-resistant configuration that still supports basal transcription.

Amino Acid Sequence↗
PubMed2005

Coevolution between nonhomologous but functionally similar proteins and their conserved partners in the Legionella pathogenesis system.

Legionella pneumophila, the causative agent of Legionnaires' disease, and other pathogenic Legionella species multiply inside protozoa and human macrophages by using the intracellular multiplication (Icm)/defect in organelle trafficking (Dot) type-IV secretion system. The IcmQ protein, which possesses pore-forming activity, and IcmR, which regulates the IcmQ activity, are two essential components of this system. Analysis of the region expected to contain these two genes from 29 Legionella species revealed the presence of a conserved icmQ gene and a large hypervariable gene family [functional homologues of icmR (fir) genes], located at the icmR genomic position. Although hypervariable in their sequence, the fir genes from all 29 Legionella species were found, together with their corresponding icmQ genes, to function similarly during infection. In addition, all FIR proteins we examined were found to interact with their corresponding IcmQ proteins. Detailed bioinformatic, biochemical, and genetic analysis of the interaction between the variable FIR proteins and conserved IcmQ proteins revealed that their interaction depends on a variable region located between two conserved domains of IcmQ. This variable region was also found to be critical for IcmQ self-interaction, and the region probably coevolved with the corresponding FIR protein. A FIR-IcmQ pair was also found in Coxiella burnetii, the only known non-Legionella bacterium that contains an Icm/Dot system, indicating the significance of this protein pair for the function of this type-IV secretion system. We hypothesize that this gene variation, which is probably mediated by positive selection, plays an important role in the evolutionary arms race between the protozoan host cell and the pathogen.

Acanthamoeba castellanii↗
PubMed2005

Storage versus substrate limitation to bole respiratory potential in two coniferous tree species of contrasting sapwood width.

Two coniferous tree species of contrasting sapwood width (Pinus ponderosa L., ponderosa pine and Pseudotsuga menziesii Mirb., Douglas-fir) were compared to determine whether bole respiratory potential was correlated with available storage space in ray parenchyma cells and/or respiratory substrate concentration of tissues (total nitrogen content, N; and total non-structural carbohydrate content, TNC). An increment core-based, laboratory method under controlled temperature was used to measure tissue-level respiration (termed respiratory potential) from multiple positions in mature boles (>100-years-old). The most significant tissue-level differences that occurred were that N and TNC were two to six times higher for inner bark than sapwood, TNC was about two times higher in ponderosa pine than Douglas-fir and there was significant seasonal variation in TNC. Ray cell abundance was not correlated with sapwood respiratory potential, whereas N and TNC often were, implying that respiratory potential tended to be more limited by substrate than storage space. When scaled from cores to whole boles (excluding branches), potential net CO2 efflux correlated positively with live bole volume (inner bark plus sapwood), live bole ray volume, N mass, and TNC mass (adjusted R2 > or =0.4). This relationship did not differ between species for N mass, but did for live bole volume, live bole ray volume, and TNC mass. Therefore, N mass appeared to be a good predictor of bole respiratory potential. The differences in net CO2 efflux between the species were largely explained by the species' relative amounts of whole-bole storage space or substrate mass. For example, ponderosa pine's inner bark was thinner than Douglas-fir's, which had the greater concentration of ray cells and TNC compared with the sapwood. This resulted in ponderosa pine boles having 30-60% less ray volume and 10-30% less TNC mass, and caused ponderosa pine net CO2 efflux/ray volume and net CO2 efflux/TNC mass to be 20-50% higher than Douglas-fir. In addition, because inner bark respiratory potential was 2-25 times higher than that of sapwood, ponderosa pine's thinner inner bark and deeper sapwood (relative to Douglas-fir) caused its bole net CO2 efflux/live bole volume to be 20-25% lower than that of similarly-sized Douglas-fir trees.

Carbohydrate Metabolism↗
PubMed2003

Responses of gas exchange to reversible changes in whole-plant transpiration rate in two conifer species.

This study examined the autonomy of branches with respect to the control of transpiration (E) in Douglas-fir (Pseudotsuga menziesii (Mirb.) Franco) and western red cedar (Thuja plicata Donn) seedlings. Experiments were conducted on whole seedlings in a gas exchange system with a dual-cuvette that permitted independent manipulation and measurement of E in the upper and lower cuvettes. The value of E in one cuvette was manipulated by varying vapor pressure deficit (D) between 2.2 and 0.2 kPa, whereas D in the other cuvette was held at 2.2 kPa. Reducing D, while increasing stomatal conductance (gs), resulted in an overall decrease in E. In western red cedar, this decrease was almost threefold, and in Douglas-fir, approximately fourfold. In well-watered western red cedar, a reduction of whole-plant E by 46% (brought about by reducing D in the upper cuvette) resulted in a 12% increase in gs, a 12% increase in E and a 7% increase in net assimilation (A) of untreated foliage in the lower cuvette. Responses of gs, E and A of untreated foliage were similar irrespective of whether foliage was at the top or bottom of the seedling. When D in the treatment cuvette was restored to 2.2 kPa, gs, E and A of foliage in the untreated cuvette returned to pretreatment values. In contrast, in well-watered Douglas-fir, there was almost no change in gs, E or A of untreated foliage in one cuvette when D in the other cuvette was reduced, causing a 52% reduction in whole-plant E. However, similar manipulations on drought-stressed Douglas-fir led to 7-19% increases in gs, E and A of untreated foliage. In well-watered western red cedar, daytime leaf water potential (Psil) was maintained near -0.9 MPa over a wide range of D, whereas Psil of Douglas-fir decreased from -1.2 to -1.5 MPa as D increased. The tighter (isohydric) regulation of Psil in western red cedar may partly explain its greater stomatal response to D and variation in whole-plant E compared with Douglas-fir. In response to a reduction in E, measured increases in Psil and gs of unmanipulated foliage were less than predicted by a model assuming complete hydraulic connectivity of foliage. Our results suggest the foliage of both species is partially autonomous with respect to water.

Photosynthesis↗
PubMed2003

Freezing tolerance of conifer seeds and germinants.

Survival after freezing was measured for seeds and germinants of four seedlots each of interior spruce (Picea glauca x engelmannii complex), lodgepole pine (Pinus contorta Dougl. ex Loud.), Douglas-fir (Pseudotsuga menziesii (Mirb.) Franco) and western red cedar (Thuja plicata Donn ex D. Donn). Effects of eight seed treatments on post-freezing survival of seeds and germinants were tested: dry, imbibed and stratified seed, and seed placed in a growth chamber for 2, 5, 10, 15, 20 or 30 days in a 16-h photoperiod and a 22/17 degrees C thermoperiod. Survival was related to the water content of seeds and germinants, germination rate and seedlot origin. After freezing for 3 h at -196 degrees C, dry seed of most seedlots of interior spruce, Douglas-fir and western red cedar had 84-96% germination, whereas lodgepole pine seedlots had 53-82% germination. Freezing tolerance declined significantly after imbibition in lodgepole pine, Douglas-fir and interior spruce seed (western red cedar was not tested), and mean LT50 of imbibed seed of these species was -30, -24.5 and -20 degrees C, respectively. Freezing tolerance continued to decline to a minimum LT50 of -4 to -7 degrees C after 10 days in a growth chamber for interior spruce, Douglas-fir and lodgepole pine, or after 15 days for western red cedar. Minimum freezing tolerance was reached at the stage of rapid hypocotyl elongation. In all species, a slight increase in freezing tolerance of germinants was observed once cotyledons emerged from the seed coat. The decrease in freezing tolerance during the transition from dry to germinating seed correlated with increases in seed water content. Changes in freezing tolerance between 10 and 30 days in the growth chamber were not correlated with seedling water content. Within a species, seedlots differed significantly in freezing tolerance after 2 or 5 days in the growth chamber. Because all seedlots of interior spruce and lodgepole pine germinated quickly, there was no correlation between seedlot hardiness and rate of germination. Germination rate and freezing tolerance of Douglas-fir and western red cedar seedlots was negatively correlated. There was a significant correlation between LT50 after 10 days in the growth chamber and minimum spring temperature at the location of seedlot origin for interior spruce and three seedlots of western red cedar, but no relationship was apparent for lodgepole pine and Douglas-fir.

Freezing↗
PubMed2000

Time course of c-FOS expression in status epilepticus induced by amygdaloid stimulation.

Decaying of c-FOS immunoreactivity (FIR) was studied in adult rats with 1 h self-sustaining limbic status epilepticus (SSLSE) induced by amygdaloid electrical stimulation. Rats that failed to enter SSLSE showed localized FIR in the ipsilateral limbic cortex, neocortex, and amygdala. FIR became bilaterally extensive, including the hippocampal formation 0.5 h after SSLSE. It decreased gradually between 2 and 6 h and returned to basal levels around 1 day. Neocortical FIR in clonic SSLSE persisted longer than in other types of SSLSE. We demonstrate for the first time that FIR in SSLSE lasts much longer than several hours, its decaying is related to the seizure behavior, and absent or weak FIR at the hippocampal formation is associated with failed SSLSE entry.

Amygdala↗
PubMed2003

Manganese superoxide dismutase-mediated gene expression in radiation-induced adaptive responses.

Antioxidant enzymes are critical in oxidative stress responses. Radioresistant variants isolated from MCF-7 human carcinoma cells following fractionated ionizing radiation (MCF+FIR cells) or overexpression of manganese superoxide dismutase (MCF+SOD cells) demonstrated dose-modifying factors at 10% isosurvival of 1.8 and 2.3, respectively. MCF+FIR and MCF-7 cells (exposed to single-dose radiation) demonstrated 5- to 10-fold increases in MnSOD activity, mRNA, and immunoreactive protein. Radioresistance in MCF+FIR and MCF+SOD cells was reduced following expression of antisense MnSOD. DNA microarray analysis and immunoblotting identified p21, Myc, 14-3-3 zeta, cyclin A, cyclin B1, and GADD153 as genes constitutively overexpressed (2- to 10-fold) in both MCF+FIR and MCF+SOD cells. Radiation-induced expression of these six genes was suppressed in fibroblasts from Sod2 knockout mice (-/-) as well as in MCF+FIR and MCF+SOD cells expressing antisense MnSOD. Inhibiting NF-kappa B transcriptional activity in MCF+FIR cells, by using mutant I kappa B alpha, inhibited radioresistance as well as reducing steady-state levels of MnSOD, 14-3-3 zeta, GADD153, cyclin A, and cyclin B1 mRNA. In contrast, mutant I kappa B alpha was unable to inhibit radioresistance or reduce 14-3-3 zeta, GADD153, cyclin A, and cyclin B1 mRNAs in MCF+SOD cells, where MnSOD overexpression was independent of NF-kappa B. These results support the hypothesis that NF-kappa B is capable of regulating the expression of MnSOD, which in turn is capable of increasing the expression of genes that participate in radiation-induced adaptive responses.

14-3-3 Proteins↗
PubMed1992

First-phase insulin release in adult cystic fibrosis patients: correlation with clinical and biological parameters.

Adult patients with cystic fibrosis (CF) are at high risk for developing insulin-dependent diabetes mellitus. Therefore, the fast insulin release (FIR) to intravenously administered glucose was measured in 23 adult CF patients. The influence of the clinical parameters and type of gene deletion on the amplitude of the FIR, defined by the sum of the 1st- and 3rd-minute insulin concentrations was analyzed. In 11 of the 18 normoglycemic patients with exocrine pancreatic insufficiency and the 3 nontreated diabetic CF patients studied, an FIR value lower than the 3rd percentile was found. The female patients had higher mean FIR values than the male patients (62.8 +/- 39.6 vs. 27.9 +/- 17.9 mU/l; p < 0.05). No influence of age, body mass index, or pulmonary or liver involvement on the FIR was found. Subjects heterozygous for the delta F508 deletion had a similar insulin response as homozygous patients. The FIR level correlated negatively with the basal glucose level (r = 0.4; p < 0.001). In conclusion, 61% of the adult nondiabetic CF patients with exocrine pancreatic insufficiency presented a loss in acute insulin response, which could not be predicted by clinical or genetic parameters.

Adolescent↗
PubMed1988

Stationary and nonstationary spatial domain Metz filtering.

Stationary and nonstationary finite-impulse-response (FIR) implementations of the count-dependent Metz filter were investigated in this study. Filter size was observed to be an important variable controlling image quality. For Metz filtering of 128 X 128 pixel images at least a 15 X 15 term FIR filter was deemed necessary. By using an algorithm which selected between a set of preformed FIR filters based on pixel count, a nonstationary FIR implementation of the Metz filter was developed which required very little increase in execution time to stationary filtering. In a limited comparison of 'tumor' detection with stationary and nonstationary FIR filtering all of the Metz filtering techniques showed a significant improvement in detection when compared to the unprocessed images. However, no significant difference was observed between the stationary and nonstationary Metz filtering techniques. Thus, for Metz filters optimized solely on the basis of count, nonstationary FIR filtering does not seem to offer an advantage when compared to stationary filtering.

Filtration↗
PubMed1995

Face immersion reflex for diagnosis of diabetic cardiovascular autonomic neuropathy.

To evaluate face immersion reflex (FIR) as a diagnostic test for diabetic autonomic neuropathy, we studied 15 patients with diabetic cardiovascular autonomic neuropathy--defined as the presence of at least two other abnormal autonomic tests-and 15 healthy subjects as a control group. All patients underwent six different autonomic tests including deep breathing R-R variation, Valsalva maneuver, heart rate and blood pressure response to standing, intravenous atropine injection and FIR. FIR test was considered positive for autonomic neuropathy if heart rate did not decrease at least 15% of the basal rate after 10 sec of immersion. FIR was positive in all the diabetic patients and negative in the 15 controls. Its sensitivity was higher than any other single autonomic test (p < 0.025). Considering two abnormal autonomic tests as a gold standard for diabetic cardiovascular autonomic neuropathy, sensitivity was 100% for FIR, 66% for deep breathing R-R variation and Valsalva maneuver, 53% for blood pressure (BP) response to standing and 20% for i.v. atropine injection. All the test were highly specific. We conclude FIR test should be considered among diagnostic tests for diabetic cardiovascular autonomic neuropathy.

Adult↗
PubMed1999

Accurate quantification of (1)H spectra: from finite impulse response filter design for solvent suppression to parameter estimation.

A scheme for accurate quantification of (1)H spectra is presented. The method uses maximum-phase finite impulse response (FIR) filters for solvent suppression and an iterative nonlinear least-squares (NLLS) algorithm for parameter estimation. The estimation algorithm takes the filter influence on the metabolites of interest into account and can thereby correctly incorporate a large variety of prior knowledge into the estimation phase. The FIR filter is designed in such a way that no distortion of the important initial samples is introduced. The FIR filter method is compared numerically with the HSVD method for water signal removal in a number of examples. The results show that the FIR method, using an automatic filter design scheme, slightly outperforms the HSVD method in most cases. The good performance and ease of use of the FIR filter method combined with its low computational complexity motivate the use of the proposed method.

Algorithms↗
PubMed1994

An evaluation of the accelerated expectation maximization algorithms for single-photon emission tomography image reconstruction.

We previously reported that brain single-photon emission tomography (SPET) images could be improved by using an attenuation coefficient map constructed with transmission data and the iterative expectation maximization (EM) algorithm. However, the conventional EM algorithm (CEM) typically requires 30-80 iterations to provide acceptable results, limiting its clinical applicability. Several methods have been proposed to accelerate the EM algorithm. The purpose of this study was to search for a practical method for accelerating the EM algorithm. The methods investigated here include the accelerated EM algorithm (ACEM) using additive correction, ACEM using multiplicative correction, and Tanaka's filtered iterative reconstruction method (FIR). These methods were assessed by simulated SPET studies of a phantom incorporating nonuniform attenuation and by reference to clinical brain SPET data. In the simulation studies, the above methods were evaluated by using three parameters (root mean square error, log likelihood value, and contrast recovery coefficient); the results showed that FIR had an advantage over other methods in terms of all parameters. The results obtained using the clinical data demonstrated that FIR could reconstruct acceptable images in only five iterations. These results show that FIR offers significant advantages over CEM or other ACEMs, indicating that FIR can make the EM algorithm practical for clinical use in SPET.

Adult↗
PubMed2006

Influence of realistic inspiratory flow profiles on fine particle fractions of dry powder aerosol formulations.

PURPOSE: The purpose of the study was to determine how air flow profiles affect fine particle fractions (FPF) (<5 microm) from dry powder aerosol formulations and whether laser diffraction (LD) could be used to measure FPF of aerosols generated by variable flows. MATERIALS AND METHODS: Carrier-based formulations containing 1.5% w/w micronized salbutamol base blended with the 63-90 microm fraction of alpha-lactose monohydrate or sorbitol or maltose were aerosolised from a model glass device using either a constant flow rate or a predetermined flow profile. The FPFs of the same aerosolised particles were first measured by LD and then by a liquid impinger. Volunteer inhalation airflow profiles and 3-phase (acceleration, constant flow rate and deceleration) square wave airflow profiles were generated using the Electronic Lung and an Inhalation Profile Recorder. Similar experiments were conducted for a carrier-free formulation from the Bricanyl Turbohaler. RESULTS: Salbutamol FPFs of all carrier-based formulations were found to increase by increasing the initial flow increase rate (FIR) from 200 to 600 l min(-1) s(-1) although they could be placed in an increasing order of maltose blend < sorbitol blend < lactose blend. A significant linear correlation was found between FPFs measured by LD and by inertial impaction (R (2) = 0.95, p < 0.01, ANOVA). For the Bricanyl Turbohaler, increasing FIR from 120 to 600 l min(-1) s(-1) for a constant peak flow rate (PFR) of 60 l min(-1) increased the mean Terbutaline FPF from 18.2% to 45.5%. For the volunteer inhalation profiles, a higher FIR tended to be associated with higher PFR, leading to a marked increase in drug FPF due to the combined effect of FIR and PFR. CONCLUSION: Drug FPF from either carrier-free or carrier-based formulations is determined by both FIR and PFR. LD is a viable technique to measure the performance of dry powder aerosol formulations at realistic inspiratory flow profiles.

Administration, Inhalation↗