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At least 109 records · Page 6Linked to original sources
PubMed2000

Polar organic phase liquid chromatography with packed capillary columns using a vancomycin chiral stationary phase

Vancomycin immobilized on silica served as the chiral stationary phase (CSP) in this investigation with polar organic solvents as the mobile phase in liquid chromatography (LC). It was shown that trace amounts of water were beneficial for improving peak shape and efficiency. To regulate the retention and selectivity an acid and/or base were added to the mobile phase where an excess of acid was shown to be preferential for enantioseparation. An unusual increase in selectivity with increasing temperature was shown for the acidic drug, thalidomide. Additionally, nonlinear van't Hoff plots were obtained for metoprolol enantiomers that showed increased retention with increasing temperature. Metoprolol also showed unusual behavior in the polar organic phase when water was added to resemble reversed-phase chromatography, with minimum retention observed at high water or high methanol concentrations. In both instances a high degree of electrostatic interaction between metoprolol and vancomycin was concluded. Metoprolol and ten of its analogs were examined on this CSP to evaluate the enantiorecognition process. A comparison in enantioselectivity for a number of acidic and basic drugs using this CSP was also carried out using the polar organic phase, reversed phase, and normal phase LC which were all compared to the results obtained in supercritical fluid chromatography (SFC). Polar organic phase LC offered a better separation of basic molecules while reversed phase LC was preferred for the resolution of acids. SFC showed the broadest enantioselectivity overall and normal phase LC indicated similar properties, as expected, to SFC but with lower column efficiency. Copyright 2000 Wiley-Liss, Inc.

Journal Article↗
PubMedDate not supplied

Optimal phases of dynamic CT for detecting hepatocellular carcinoma: evaluation of unenhanced and triple-phase images.

BACKGROUND: To determine the optimal phases of dynamic computed tomography (CT) for detecting hepatocellular carcinoma (HCC). METHODS: Fifty-two patients with 85 HCC nodules were examined by means of unenhanced and triple-phase CT images of the whole liver. The time for obtaining the arterial-phase images was 25-55 s after intravenous bolus injection of contrast material, the time for obtaining the portal venous-phase images was 65-100 s, and the time for obtaining late-phase images was 145 s to 4 min. Detectability of the HCC nodules for all phases was statistically compared. RESULTS: The detection rates for the arterial- and late-phase images were significantly higher than for the unenhanced and portal venous-phase images (p < 0.01). The combination of arterial- and late-phase images showed the same number of HCC nodules in the same number of patients as did the combination of unenhanced and triple-phase images. CONCLUSION: The combination of the arterial- and late-phase imagings was best for detecting HCC nodules.

Adult↗
PubMed1987

Phase separation and hexagonal HII phase formation by gramicidins A, B and C in dioleoylphosphatidylcholine model membranes. A study on the role of the tryptophan residues.

The role of the tryptophan-residues in gramicidin-induced HII phase formation was investigated in dioleoylphosphatidylcholine (DOPC) model membranes. 31P-NMR and small angle X-ray diffraction measurements showed, that gramicidin A and C (in which tryptophan-11 is replaced by tyrosine) induce a similar extent of HII phase formation, whereas for gramicidin B and synthetic analogs in which one tryptophan, either at position 9 or 11 is replaced by phenylalanine, a dramatic decrease of the HII phase inducing activity can be observed. Modification of all four tryptophans by means of formylation of the indole NH group leads to a complete block of HII phase formation. Sucrose density centrifugation experiments on the various peptide/lipid samples showed a quantitative incorporation of the peptide into the lipid. For all samples in a 1/10 molar ratio of peptide to lipid distinct bands were found, indicative of a phase separation. For the gramicidin A'/DOPC mixture these bands were analyzed and the macroscopic organization was determined by 31P-NMR and small-angle X-ray diffraction. The results demonstrate that a quantitative phase separation had occurred between a lamellar phase with a gramicidin/lipid ratio of 1/15 and a hexagonal HII phase, which is highly enriched in gramicidin. A study on the hydration properties of tryptophan-N-formylated gramicidin in mixtures with DOPC showed that this analog has a similar dehydrating effect on the lipid headgroup as the unmodified gramicidin. In addition both the hydration study and sucrose density centrifugation experiments showed that, like gramicidin also its analogs have a tendency to aggregate, but with differences in aggregation behaviour which seemed related to their HII phase inducing activity. It is proposed that the main driving force for HII phase formation is the tendency of gramicidin molecules to self-associate and organize into tubular structures such as found in the HII phase and that whether gramicidin (analogs) form these or other types of aggregates depends on their tertiary structure, which is determined by intra- as well as intermolecular aromatic-aromatic stacking interactions.

Gramicidin↗
PubMed1988

Cell cycle phase-specific cDNA libraries reflecting phase-specific gene expression of Ehrlich ascites cells growing in vivo.

Asynchronous populations of Ehrlich ascites tumor cells grown in vivo were separated by centrifugal elutriation into fractions of G1-, S-, and G2/M-phase cells with less than 10% cross-contamination. Cytoplasmic mRNA from phase-synchronous cells was used to prepare cDNA which was ligated with bacteriophage lambda gt10 arms and amplified in Escherichia coli C600 hfl-. EcoRI digests of DNA isolated from the sublibraries (G1, S, G2/M) were submitted to Southern hybridizations with radiolabeled probes either (a) for genes whose phase-specific expression is clearly documented, thymidine kinase, dihydrofolate reductase, and thymidylate synthase, or (b) for genes whose change of expression during the cell cycle is likely, lamin C, beta-actin, alpha- and beta-tubulin, c-myc, c-fos, p53. The cDNA sequences for genes of group (a) were found to be significantly enriched in DNA of the S-phase library indicating that the cell cycle phase-specific patterns of the respective mRNA levels are conserved in the sublibraries. Sequences belonging to group (b) were also found to be enriched in DNA isolated from the sublibraries: c-fos in G1 phase, lamin C, beta-actin, tubulins, c-myc in S phase, and p53 in G1/S phase. The unexpected prevalence of c-myc and alpha-tubulin in the S-phase library is supported by Northern analysis of RNA from phase-synchronous cells. Non-phase-specific, randomly chosen sequences hybridized equally strong with DNA isolated from the different sublibraries. No significant changes of the patterns of hybridization signals were observed with DNA from different amplifications of the sublibraries when analyzed with the same DNA probe indicating that the cDNA complexities are well conserved during amplifications. Consequently, the sublibraries are useful to obtain information about the cell cycle phase-specific expression of mRNAs for other genes of interest. Since the sublibraries reflect mRNA levels of the cells growing in vivo they supply data on the physiological in vivo pattern of gene expression undisturbed by potentially unphysiological in vitro conditions.

Animals↗
PubMed1992

Cubic phases of lipid-containing systems. The structure of phase Q223 (space group Pm3n). An X-ray scattering study.

The hexagonal (H) and the cubic (Q223) phases of the systems dodecyltrimethylammonium chloride-water and palmitoyllysophosphatidy choline-water have been studied by X-ray scattering techniques. The signs of the reflections of phase H were determined by a systematic study as a function of the water content, those of phase Q223 were assessed using a pattern recognition approach based upon the axiom that the histograms of the electron density maps of phases Q223 and H, extrapolated to the same concentration and properly normalized in scale and shape, are very similar to each other. In the case of phase Q223, all the sign combinations (the phi-sets) compatible with the observed reflections were generated, and each of the corresponding histograms was compared with the histogram of the map of phase H. One novelty of this work is the use of a highly sensitive criterion to estimate the similarity of the histograms, namely the distance in the six-dimensional space of the moments [mean value of (delta rho)n]1/n, for 3 greater than or equal to n greater than or equal to 8. In the two systems, the use of this criterion has led to the unambiguous choice of one electron density map. The maps show that the structure of phase Q223 consists of disjointed micelles (of type I), belonging to two different classes: those of one class are quasi-spherical in shape and are centered at the points a, those of the other class are disc-shaped and are centred at the points c. The results of this work rule out a structure formed by a cage-like distribution of rods enclosing a set of quasi-spherical micelles and is consistent with previous proposals. This is the second example, after that of phase Q227, of a micellar cubic phases in lipid-containing systems; all the known examples of phase Q223 are of type I, those of phase Q227 of type II.

Freeze Fracturing↗
PubMed2000

Partitioning of amphiphiles between coexisting ordered and disordered phases in two-phase lipid bilayer membranes.

The partition coefficients (K(P)) of a series of single-chain and double-chain fluorescent amphiphiles, between solid ordered (P(beta') and L(beta)) and liquid disordered (L(alpha) of the type l(d)) lipid phases coexisting in the same lipid bilayer, was studied using steady-state fluorescence emission anisotropy. The single-chain amphiphiles were N-(7-nitrobenzoxa-2, 3-diazol-4-yl)-alkylamines, and the double-chain amphiphiles were N-(7-nitrobenzoxa-2, 3-diazol-4-yl)-phosphatidylethanolamines with chain lengths of 12-18 carbon atoms. Saturated 18-carbon alkyl/acyl chain compounds were also compared with Delta(9)-cis unsaturated chains of the same chain length. The fluorescence anisotropy of the probes was examined in lipid bilayers (multilamellar vesicles) prepared from an equimolar mixture of dilauroylphosphatidylcholine and distearoylphosphatidylcholine and studied as a function of temperature through the entire temperature range of coexistence of ordered gel phases and a disordered fluid phase in this system. The unsaturated chain amphiphiles partitioned exclusively into the fluid phase whenever this phase was present, as did the saturated chain amphiphiles with the shortest chains (C(12:0)), while K(P) ranges between 1 and 2, in favor of the L(beta) solid phase, for the amphiphiles with long saturated (C(18:0)) alkyl/acyl chains, with intermediate behavior for the intermediate chain lengths. All probes appeared to be totally excluded from P(beta') solid (gel) phases. The technique was also used to determine partitioning of some of the probes between coexisting liquid ordered (cholesterol-containing) (l(o)) and liquid disordered (l(d)) L(alpha) phases. In this case the ratio of signal amplitude to noise allowed us to obtain a qualitative, but not quantitative, measure of the phase partitioning of the probes. We conclude that the partitioning behavior of the probes examined between coexisting l(o) and l(d) phases is qualitatively similar to that observed between solid ordered and liquid disordered phases.

Fluorescence Polarization↗
PubMed1995

Forced coalescence phasing: a method for ab initio determination of crystallographic phases.

A method has been developed for ab initio determination of crystallographic phases. This technique, called forced coalescence phasing (FCP), is implemented on a computer and uses an automated iterative procedure that combines real space filtering with numerically seeded Fourier transforms to solve the crystallographic phase problem. This approach is fundamentally different from that of traditional direct methods of phasing, which rely on structure invariant probabilistic phase relationships. In FCP, the process begins with an appropriate set of atoms randomly distributed throughout the unit cell. In subsequent cycles of the program, these atoms undergo continual rearrangements ultimately forming the correct molecular structure(s) consistent with the observed x-ray data. In each cycle, the molecular rearrangement is directed by an electron density (Fourier) map calculated using specially formulated numerical seed coefficients that, along with the phase angles for the map, are derived from the arrangement of atoms in the preceding cycle. The method has been tested using actual x-ray data from three organic compounds. For each data set, 100 separate phase determination trials were conducted, each trial beginning with a different set of randomly generated starting phases. Correct phase sets were successfully determined in all of the trials with most trials requiring fewer than 50 cycles of the FCP program. In addition to its effectiveness in small molecule phase determination, FCP offers unexplored potential in the application of real-space methods to ab initio phasing of proteins and other macromolecule structures.

Journal Article↗
PubMed2001

An improved phase-extension procedure for isomorphous replacement phases.

A new phase-extension procedure has been applied to isomorphous replacement data and shown to yield improved phases and maps compared with standard solvent flattening operating on a full set of centroid phases. In this procedure, a starting subset of core phases is selected based on the sharpness of the phase-probability curves. Phase extension using solvent flattening as the density-modification procedure is then carried out, gradually adding additional phases. In tests with known protein structures, the mean phase errors for the output expanded phase sets were reduced by 3-9 degrees and the corresponding map correlation coefficients were increased by 0.05-0.18 relative to phase sets from standard solvent-flattening procedures. With SIR data, the lowest final mean phase errors were approximately 58 degrees and the corresponding map correlation coefficients were in the range 0.53-0.68.

Protein Conformation↗
PubMed1981

Fate of phase I and phase II Coxiella burnetii in several macrophage-like tumor cell lines.

Several macrophage-like tumor cell lines of murine origin were exposed to phase I and phase II Coxiella burnetii, and the subsequent fate of the parasites was determined by electron and bright-field microscopy. Phase I C. burnetii proliferated within and established a persistent infection of P388D1, J774, and PU-5-IR cell lines but not of WEHI-3 and WEHI-274 cell lines. Phase II C. burnetii, however, entered into and persistently infected all five cell lines. The parasites proliferated within vacuoles. Macrophage cell lines persistently infected with phase I and phase II C. burnetii were maintained for over 200 and 100 days, respectively. Within P388D1 cells, the phase I C. burnetii converted, in part, to phase II; phase II organisms remained in the phase II state. The differential fate of the two rickettsial phases after exposure to the WEHI-3 and WEHI-274 cells may be attributable to surface differences such as lipopolysaccharide content.

Animals↗
PubMed1996

Two-phase helical CT for pancreatic tumors: pancreatic versus hepatic phase enhancement of tumor, pancreas, and vascular structures.

PURPOSE: To quantitatively evaluate and validate a two-phase helical computed tomographic (CT) protocol for evaluation of pancreatic tumors. MATERIALS AND METHODS: Twenty-seven patients with pathologically proved pancreatic adenocarcinomas prospectively underwent two-phase CT examination with helical acquisition during the pancreatic phase (40-70 seconds after infusion of intravenous contrast material at 3 mL/sec) and the hepatic phase (70-100 seconds after infusion). Mean CT attenuation values of tumor, bordering pancreas, and all major peripancreatic vessels were obtained for both time intervals. RESULTS: Mean tumor-pancreas contrast was significantly greater during the pancreatic phase (67 HU +/- 19) than the hepatic phase (39 HU +/- 16) (P < .001) This was the result of both greater enhancement of normal pancreas and lower tumor enhancement during the pancreatic phase. Opacification of all vascular structures, including the portal vein, was also greater during the pancreatic phase (P < .001). CONCLUSION: Two-phase helical CT with pancreatic phase acquisition provides statistically significantly better pancreatic, arterial, and portal venous enhancement than that of hepatic phase imaging, with improved tumor-pancreas contrast.

Adenocarcinoma↗
PubMed1992

Biomechanical properties of duodenal wall and duodenal tone during phase I and phase II of the MMC.

We used a new method, impedance planimetry, to look at variations in compliance, tone, and distension-induced peristaltic activity during phase I and phase II of the migrating myoelectric complex (MMC) in the human duodenum. A balloon was inflated stepwise with pressures up to 30 cmH2O in the duodenum, while the pressure and balloon cross-sectional area (CSA) were measured simultaneously. The biomechanical wall parameters were calculated from these measurements. Nine duodenal phase IIIs were recorded in six subjects. A balloon pressure of 20 cmH2O induced a smaller CSA in early phase I [266 (236-324) mm2] than in late phase II [385 (276-474) mm2] (P < 0.05). Balloon distensions elicited no contractions in phase I, whereas they increased contractile activity 60% (P < 0.05) proximal to the balloon and 4% distal to the balloon in late phase II. Step distensions in phase I with balloon pressures between 10 and 30 cmH2O increased the CSA from 40 (30-81) to 645 (603-704) mm2. It increased circumferential wall tension from 35 (28-63) to 429 (402-466) mm x cmH2O and the pressure elastic modulus from 9.7 (9.0-14.7) to 33.8 (27.6-33.8) cmH2O, respectively. Thus compliance differs from phase I to phase II. This is most likely caused by increased smooth muscle tone during phase I. Duodenal wall stiffness increases with the balloon pressure applied.

Adult↗
PubMed2000

Photic phase response curve in Octodon degus: assessment as a function of activity phase preference.

Light exposure during the early and late subjective night generally phase delays and advances circadian rhythms, respectively. However, this generality was recently questioned in a photic entrainment study in Octodon degus. Because degus can invert their activity phase preference from diurnal to nocturnal as a function of activity level, assessment of phase preference is critical for computations of phase reference [circadian time (CT) 0] toward the development of a photic phase response curve. After determining activity phase preference in a 24-h light-dark cycle (LD 12:12), degus were released in constant darkness. In this study, diurnal (n = 5) and nocturnal (n = 7) degus were randomly subjected to 1-h light pulses (30-35 lx) at many circadian phases (CT 1-6: n = 7; CT 7-12: n = 8; CT 13-18: n = 8; and CT 19-24: n = 7). The circadian phase of body temperature (Tb) onset was defined as CT 12 in nocturnal animals. In diurnal animals, CT 0 was determined as Tb onset + 1 h. Light phase delayed and advanced circadian rhythms when delivered during the early (CT 13-16) and late (CT 20-23) subjective night, respectively. No significant phase shifts were observed during the middle of the subjective day (CT 3-10). Thus, regardless of activity phase preference, photic entrainment of the circadian pacemaker in Octodon degus is similar to most other diurnal and nocturnal species, suggesting that entrainment mechanisms do not determine overt diurnal and nocturnal behavior.

Activity Cycles↗
PubMedDate not supplied

Comparison of temperature-phased and two-phase anaerobic co-digestion of primary sludge and municipal solid waste.

Characterization of the similarities and differences between two-phase and temperature-phased systems treating primary wastewater sludge (PS) and the organic fraction of municipal solid waste (OFMSW) as substrate was performed by comparing the rates of key steps, including hydrolysis and methanogenesis. Aceticlastic methanogenic rates were determined using batch respirometric tests with inocula from operating two-phase and temperature-phased systems. The initial methane production rates ranged from 0.32 to 0.93 mL methane/g volatile solids (VS)h for all systems, with the greatest rates observed from the first stage of the temperature-phased system. Hydrolysis rates were determined from particulate chemical oxygen demand destruction. The first stage of the temperature-phased system had greater specific hydrolysis rates than the first stage of the two-phase system at each operating condition. The temperature-phased system outperformed the two-phase system in terms of methane production and VS destruction when treating a mixed OFMSW-PS stream at OFMSW-to-PS ratios of 0:100, 20:80, and 40:60. When the feed ratios were 60:40 and 80:20 OFMSW-PS, there was no significant difference in the performance of the two systems. The overall methane yield and VS destruction of the temperature-phased system ranged from 0.299 to 0.418 L/g VS fed and 47.5 to 71.6%, respectively. The overall methane yield and VS destruction of the two-phase system ranged from 0.281 to 0.332 L/g VS fed and 39.6 to 69.3%, respectively.

Bacteria, Anaerobic↗
PubMed2001

Phase-inversion sonography during the liver-specific late phase of contrast enhancement: improved detection of liver metastases.

OBJECTIVE: The purpose of our study was to assess whether phase-inversion sonography during the late, liver-specific phase of contrast enhancement using Levovist improves the detection of hepatic metastases relative to unenhanced conventional B-mode sonography. SUBJECTS AND METHODS: Sixty-two patients were studied with unenhanced B-mode sonography and phase-inversion sonography 2.5 min after the injection of Levovist. All patients underwent one reference examination (CT, MR imaging, or intraoperative sonography). The conspicuity, number, size, and distribution of metastases before and after contrast administration as judged by a sonographer (who was unaware of other imaging findings) were compared with each other and with reference imaging. RESULTS: The conspicuity of metastases was improved by contrast-enhanced phase inversion in 94% of patients. Thirty-nine patients showed metastases on reference imaging; 36 of these were positive on baseline sonography and 38 on phase-inversion sonography. Phase-inversion sonography showed more reference imaging-confirmed metastases than baseline sonography in 28 patients (45%). The average number of confirmed metastases per patient was 3.06 for baseline sonography and 5.42 for contrast-enhanced phase-inversion sonography (p < 0.01). The average sensitivity for detecting individual metastases improved from 63% to 91%. Metastases of less than 1 cm were shown in 14 patients on baseline sonography, in 24 patients on phase-inversion sonography, and in 26 on reference imaging. Both sonographic techniques showed false-positive lesions in six patients. CONCLUSION: Contrast-enhanced phase-inversion sonography in the liver-specific phase of contrast enhancement using Levovist provides a marked improvement in the detection of hepatic metastases relative to unenhanced conventional sonography, without loss of specificity. Phase-inversion sonography was particularly advantageous in detecting small metastases and may be a competitive alternative to CT and MR imaging.

Adult↗
PubMed2002

Coordinated regulation of M phase exit and S phase entry by the Cdc2 activity level in the early embryonic cell cycle.

In the early embryonic cell cycle, exit from M phase is immediately followed by entry into S phase without an intervening gap phase. To understand the regulatory mechanisms for the cell cycle transition from M to S phase, we examined dependence on Cdc2 inactivation of cell-cycle events occurring during the M-S transition period, using Xenopus egg extracts in which the extent of Cdc2 inactivation at M phase exit was quantitatively controlled. The result demonstrated that MCM binding to and the initiation of DNA replication of nuclear chromatin occurred depending on the decrease of Cdc2 activity to critical levels. Similarly, we found that Cdc2 inhibitory phosphorylation and cyclin B degradation were turned on and off, respectively, depending on the decrease in Cdc2 activity. However, their sensitivity to Cdc2 activity was different, with the turning-on of Cdc2 inhibitory phosphorylation occurring at higher Cdc2 activity levels than the turning-off of cyclin B degradation. This means that, when cyclin B degradation ceases at M phase exit, Cdc2 inhibitory phosphorylation is necessarily activated. In the presence of constitutive synthesis of cyclin B, this condition favors the occurrence of the Cdc2 inactivation period after M phase exit, thereby ensuring progression through S phase. Thus, M phase exit and S phase entry are coordinately regulated by the Cdc2 activity level in the early embryonic cell cycle.

Animals↗
PubMed1996

Pediatric phase I drug tolerance: a review and comparison of recent adult and pediatric phase I trials.

PURPOSE: We evaluated the ratio of pediatric to adult maximum tolerated doses (MTDs) from 70 Phase I studies conducted between 1975 and 1995. The aim of this study was to determine whether previously observed differences in drug tolerance between adult and pediatric Phase I patients have persisted over the 20-year period of this analysis. PATIENTS AND METHODS: Phase I trials of pediatric and adult patients with solid tumors as the predominant diagnosis and sharing similar dosing regimens were evaluated. For consistent comparison between Phase I studies, the MTD was defined as the drug dose one level below that yielding dose-limiting toxicity in >30% of patients. The ratio of pediatric to adult MTDs was calculated and plotted chronologically by year of pediatric study closure. Statistical evaluation of MTD ratios included regression and correlation analysis. The extent of therapy before Phase I study entry was also examined. RESULTS: Ninety-three Phase I studies were reviewed. Twenty-one drugs (70 studies) met our criteria for paired review of MTDs and analysis of the variation of ratio with time. The pediatric to adult MTD ratios ranged from 0.4 to 2.8, with a median of 1.2. Regression analysis of the ratio of MTD versus date of pediatric study closure supports a linear relationship of decreasing ratio with time (p<0.01). Analysis of the regression line predicts MTD ratios of 2.02 and 0.76 for 1974 and 1995, respectively. Of patients included in this analysis, 37.1% and 68.6% of adult and pediatric patients, respectively, were considered to have been heavily pretreated before study entry. A significant (p<0.001) downward trend with time was observed in the proportion of adult patients entering Phase I studies who had received both radiation and chemotherapy. CONCLUSIONS: The results of this review continue to show an equal or greater drug tolerance in the pediatric population when compared with adult patients for most drugs studied during Phase I trials. However, there appears to be significant trend of decreasing differences in drug tolerance between pediatric and adult Phase I patients with time, as defined by the descent of the MTD ratio toward values <1.0. Mechanisms to explain greater drug tolerance in children and the observation of decreasing maximum tolerated dose ratios with time are discussed. Limited data suggest that changes in degree of therapy before Phase I study entry may be influencing the MTD ratio.

Adult↗
PubMedDate not supplied

Multistep phase difference phase contrast imaging.

A new technique for multistep phase-contrast image processing is presented. The N-step method consists of simply forming the linear average of the N-1 adjacent phase-difference signals. It has similar noise reduction properties as other multistep techniques, but the simplicity of the noise variance of the N-step technique allows intuitive insight into phase-difference phase-contrast processing and noise reduction, which can aid in the design of efficient and improved phase-contrast imaging sequences. As well, the computational simplicity of the N-step phase-difference technique compared with any other known multistep technique is advantageous. Like other multistep techniques, it has far more efficient noise reduction properties than simple two-step, multiple average phase-contrast imaging, even when normalized for total scan time. A three-step phase-difference velocity image has 50% less variance than an image acquired with two steps and two scans averaged but is obtained in 25% less scan time. Given its advantages, it should now be the chosen technique for increasing velocity-to-noise and contrast-to-noise ratios in all phase-difference phase-contrast clinical applications.

Blood Flow Velocity↗
PubMed1990

Signal-to-noise in phase angle reconstruction: dynamic range extension using phase reference offsets.

The dynamic range of phase-reconstructed magnetic resonance images is compared to that of magnitude-reconstructed images. From analysis of propagation of errors, the phase angle noise is phase-independent and given in radians by sigma ([I])/[I], the noise-to-signal ratio of the corresponding magnitude-reconstructed image. As the phase can range from minus pi to pi, the phase angle dynamic range is 2 pi times that of the signal magnitude. These results agree with experiment, verifying that the noise in the two receiver channels is uncorrelated. An artifact-free technique is presented for correcting phase spillover, which further extends the phase angle dynamic range. The reconstruction-based reference phase is adjusted on a local basis so that the boundary of phase wraparound is reconstructed near the center of the [- pi, pi] interval. For a particular flow study, the phase signal-to-noise was extended over twofold by spillover correction, to a value 15 times that of the magnitude signal-to-noise.

Algorithms↗