Biomedical subjects

W Li

Publications and source records attributed to W Li.

At least 217 records · Page 12Linked to original sources

PubMed2001

Interactions of iron bleomycin, phosphate or cyanide, and DNA: sequence-dependent conformations and reactions.

The hypothesis was investigated that axial ligands bound to Fe(III)-bleomycin [Fe(III)Blm] are destabilized at specific 5'-guanine-pyrimidine-3' binding sites but are stable at nonselective dinucleotides. DNA oligomers and calf-thymus DNA were used in reactions with L-Fe(III)Blm, where phosphate and cyanide served as examples of large and small ligands (L). Both ligands underwent dissociation when L-Fe(III)Blm was bound to d(GGAAGCTTCC)2 (I) but not d(GGAAATTTCCC)2 (II) and at large ratios of calf-thymus DNA to drug. Fe(III)Blm is high spin in 20 mM phosphate buffer, signifying the presence of a phosphate adduct. In the titration of HPO4-Fe(III)Blm with calf-thymus DNA, a large excess of DNA was needed to reach the low-spin state, consistent with an equilibrium competition between phosphate and DNA for Fe(III)Blm. Equilibrium constants for binding Fe(III)Blm and CN-Fe(III)Blm to calf-thymus DNA (6.8x10(5) M(-1) and 5.9x10(4) M(-1), respectively, in HEPES buffer at 25 degrees C and pH 7.4) showed that the CN- ligand also reduced the affinity of DNA for the drug. The kinetics of dissociation of CN- from CN-Fe(III)Blm-DNA were slow and first order in bound drug. The reversible nature of these dissociation reactions was shown using 1H NMR spectroscopy of Fe(III)Blm-I in the absence and presence of large excesses of CN- or phosphate. The results are discussed in terms of a two-state hypothesis for the binding of L-Fe(III)Blm to specific and nonspecific dinucleotides. It is proposed that steric restrictions at specific sites inhibit binding of these ligands.

Base Pairing↗

PubMed2001

Double orifice right atrioventricular valve in atrioventricular septal defect: morphology and extension of the concept of fusion of leaflets.

A rare observation of a double orifice right atrioventricular valve in a partial form of atrioventricular septal defect is reported. The concept of leaflet fusion along part of their anticipated zones of apposition is used to explain the formation of this anomaly. We show that this concept can account for the different morphologic presentations of atrioventricular septal defect.

Adult↗

PubMed2001

Recombinant proapoA-I(Lys107del) shows impaired lipid binding associated with reduced binding to plasma high density lipoprotein.

In the present study apoA-I (Lys 107del), a naturally occurring human apoA-I variant with a deletion of Lys 107, was expressed in E. coli to examine the effect of this mutation on lipid binding, cholesterol efflux and lecithin:cholesterol acyltranferase (LCAT) activation. Dimyristoyl phosphatidylcholine (DMPC) binding studies revealed slow interaction of proapoA-I(Lys107del) with DMPC relative to normal proapoA-I. After preincubation with human plasma lipoprotein (d<1.225 g/ml) for 1 h at 37 degrees C, 125I-labeled normal proapoA-I chromatographed as a single peak with the high density lipoprotein (HDL) fraction, whereas 125I-labeled proapoA-I(Lys107del) chromatographed with both HDL and free proapoA-I (26% of the radioactivity). Circular dichroism measurements showed that the alpha-helical content of lipid-bound proapoA-I (Lys107del) was reduced to 64 versus 73% of normal proapoA-I. Non-denaturing gradient gel electrophoresis of reconstituted HDL assembled with either proapoA-I(Lys107del) or normal proapoA-I showed that the mutation led to the formation of a second population of smaller rHDL particles. DMPC/proapoA-I(Lys107del) and normal DMPC/proapoA-I complexes exhibited a similar capacity to promote cholesterol efflux from fibroblasts. ProapoA-I (Lys107del) also activated LCAT similar to wild type proapoA-I and human plasma apoA-I. We conclude that deletion of Lys 107 substantially alters the lipid binding properties of the protein, which correlated with reduced binding to plasma HDL in vitro, but did not affect the capacity of the mutant/lipid complex to promote cholesterol efflux or activate LCAT.

Apolipoprotein A-I↗

PubMed2001

Flavonoids from Glycyrrhiza pallidiflora hairy root cultures.

Glycyrrhiza pallidiflora hairy roots were induced from axenic young plants by direct infection with Agrobacterium rhizogenes. The chemical constituents were then investigated after mass culture. The isoflavone, licoagroisoflavone and the coumestan, licoagroside C, were isolated along with seven known flavonoids. Their structures were determined on the basis of spectroscopic evidence.

Flavonoids↗

PubMed2001

Biflavonoids from the aerial part of Stephania tetrandra.

Investigation of the aerial part of Stephania tetrandra led to the isolation of two biflavonoids, stephaflavone A and stephaflavone B, with a 3-6" linkage pattern, together with beta-sitosterol. Their structures were established on the basis of their spectroscopic data and their physicochemical properties.

Flavonoids↗

PubMed2001

Neural model for processing the influence of visual orientation on visually perceived eye level (VPEL).

An individual line or a combination of lines viewed in darkness has a large influence on the elevation to which an observer sets a target so that it is perceived to lie at eye level (VPEL). These influences are systematically related to the orientation of pitched-from-vertical lines on pitched plane(s) and to the lengths of the lines, as well as to the orientations of lines of 'equivalent pitch' that lie on frontoparallel planes. A three-stage model processes the visual influence: The first stage parallel processes the orientations of the lines utilizing 2 classes of orientation-sensitive neural units in each hemisphere, with the two classes sensitive to opposing ranges of orientations; the signal delivered by each class is of opposite sign in the two hemispheres. The second stage generates the total visual influence from the parallel combination of inputs delivered by the 4 groups of the first stage, and a third stage combines the total visual influence from the second stage with signals from the body-referenced mechanism that contains information about the position and orientation of the eyes, head, and body. The circuit equation describing the combined influence of n separate inputs from stage 1 on the output of the stage 2 integrating neuron is derived for n stimulus lines which possess any combination of orientations and lengths; Each of the n lines is assumed to stimulate one of the groups of orientation-sensitive units in visual cortex (stage 1) whose signals converge on to a dendrite of the integrating neuron (stage 2), and to produce changes in postsynaptic membrane conductance (g(i)) and potential (V(i)) there. The net current from the n dendrites results in a voltage change (V(A)) at the initial segment of the axon of the integrating neuron. Nerve impulse frequency proportional to this voltage change signals the total visual influence on perceived elevation of the visual field. The circuit equation corresponding to the total visual influence for n equal length inducing lines is V(A)= sum V(i)/[n+(g(A)/g(S))], where the potential change due to line i, V(i), is proportional to line orientation, g(A) is the conductance at the axon's summing point, and g(S)=g(i) for each i for the equal length case; the net conductance change due to a line is proportional to the line's length. The circuit equation is interpreted as a basis for quantitative predictions from the model that can be compared to psychophysical measurements of the elevation of VPEL. The interpretation provides the predicted relation for the visual influence on VPEL, V, by n inducing lines each with length l: thus, V=a+[k(i) sum theta(i)/n+(k(2)/l)], where theta(i) is the orientation of line i, a is the effect of the body-referenced mechanism, and k(1) and k(2) are constants. The model's output is fitted to the results of five sets of experiments in which the elevation of VPEL measured with a small target in the median plane is systematically influenced by distantly located 1-line or 2-line inducing stimuli varying in orientation and length and viewed in otherwise total darkness with gaze restricted to the median plane; each line is located at either 25 degrees eccentricity to the left or right of the median plane. The model predicts the negatively accelerated growth of VPEL with line length for each orientation and the change of slope constant of the linear combination rule among lines from 1.00 (linear summation; short lines) to 0.61 (near-averaging; long lines). Fits to the data are obtained over a range of orientations from -30 degrees to +30 degrees of pitch for 1-line visual fields from lengths of 3 degrees to 64 degrees, for parallel 2-line visual fields over the same range of lengths and orientations, for short and long 2-line combinations in which each of the two members may have any orientation (parallel or nonparallel pairs), and for the well-illuminated and fully structured pitchroom. In addition, similar experiments with 2-line stimuli of equivalent pitch in the frontoparallel plane were also fitted to the model. The model accounts for more than 98% of the variance of the results in each case.

Humans↗

PubMed2001

Influences of visual pitch and visual yaw on visually perceived eye level (VPEL) and straight ahead (VPSA) for erect and rolled-to-horizontal observers.

Localization within the space in front of an observer can be specified along two orthogonal physical dimensions: elevation ('up', 'down') and horizontal ('left','right'). For the erect observer, these correspond to egocentric dimensions along the long and short axes of the body, respectively. However, when subjects are rolled-to-horizontal (lying on their sides), the correspondence between the physical and egocentric dimensions is reversed. Employing egocentric coordinates, localization can be referred to a central perceptual point-visually perceived eye level (VPEL) along the long axis of the body, and visually perceived straight ahead (VPSA) along the short axis of the body. In the present experiment, measurements of VPEL and of VPSA were made on each of eight subjects who were either erect or rolled-to-horizontal while monocularly viewing a long 2-line stimulus (two parallel, 64 degrees -long lines separated by 50 degrees ) in otherwise complete darkness that was centered on the eye of the observer and was tilted out of the frontoparallel plane by a variable amount and direction (from -30 degrees to +30 degrees in 10 degrees steps). The stimulus tilt was either around an axis through the center of the two eyes (pitch; VPEL was measured) or around the long axis of the body that passed through the center of the viewing eye (yaw; VPSA was measured). Large variations in the localization settings were measured that were systematic with stimulus tilt. The slopes of the functions plouing the deviations from veridicality against the orientation of the 2-line stimulus ('induction functions') were larger for the rolled-to-horizontal observer than for the erect observer for both VPEL and VPSA, and for a given body orientation were larger for the VPEL discrimination than for the VPSA discrimination; the influences of body orientation in physical space and the direction of the discrimination relative to the body were lineraly additive. Both the y-intercepts of the induction functions and the central perceptual point measured in complete darkness were lower when the norm setting by the subject was along the vertical than when it was along the horizontal; this held for both the VPEL and VPSA discriminations. The systematic effects of body orientation on the slopes and of line orientation on the y-intercepts and dark values result from an effect of gravity on the settings and fit well to a general principle: any departure from erect posture increases the induction effects of the visual stimulus. The effect of gravity is consistent with the effect of gravity in previous work in high-g environments with the VPEL discrimination.

Analysis of Variance↗

PubMed2001

Striatal dopaminergic pathways as a target for the insecticides permethrin and chlorpyrifos.

Because insecticide exposure has been linked to both Parkinsons disease and Gulf War illness, the neurotoxic actions of pyrethroid and organophosphate insecticides on behavior and striatal dopaminergic pathways were investigated in C57BL/6 mice treated with permethrin (three i.p. doses at 0.2-200 mg/kg) or chlorpyrifos (three s.c. doses at 25-100 mg/kg) over a 2-week period. Permethrin altered maximal [3H]dopamine uptake in striatal synaptosomes from treated mice, with changes in Vmax displaying a bell-shaped curve. Uptake was increased to 134% of control at a dose of 1.5 mg/kg. At higher doses of PM (25 mg/kg), dopamine uptake declined to a level significantly below that of control (50% of control at 200 mg/kg, P < 0.01). We also observed a small, but statistically significant decrease in [3H]dopamine uptake by chlorpyrifos, when given at a dose of 100 mg/kg. There was no significant effect on the Km for dopamine transport. Evidence of cell stress was observed in measures of mitochondrialfunction, which were reduced in mice given high-end doses of chlorpyrifos and permethrin. Although cytotoxicity was not reflected in decreased levels of striatal dopamine in either 200 mg/kg PM or 100 mg/kg CPF treatment groups, an increase in dopamine turnover at 100 mg/kg CPF was indicated by a significant increase in titers of the dopamine metabolite, 3,4-dihydroxyphenylacetic acid. Both permethrin and chlorpyrifos caused a decrease in open field behavior at the highest doses tested. Although frank Parkinsonism was not observed, these findings confirm that dopaminergic neurotransmission is affected by exposure to pyrethroid and organophosphorus insecticides, and may contribute to the overall spectrum of neurotoxicity caused by these compounds.

3,4-Dihydroxyphenylacetic Acid↗

PubMed2001

Pulmonary ventilation: dynamic MRI with inhalation of molecular oxygen.

We have recently demonstrated a non-invasive technique to visualize pulmonary ventilation in humans with inhalation of molecular oxygen as a paramagnetic contrast agent. In the current study, T1 shortening of lung tissue by inhalation of oxygen was observed (P<0.001). The T1 values of lung tissue were also correlated with arterial blood oxygen pressure (PaO(2)) in a pig, resulting in excellent correlation (r(2)=0.997). Dynamic wash-in and wash-out MR ventilation images as well as dynamic wash-in wash-out signal intensity versus time curves were obtained. The mean wash-in decay constants were 26.8+/-10.5 s in the right lung, and 26.3+/-9.5 s in the left lung. The mean wash-out decay constants were 23.3+/-11.3 s in the right lung, and 20.8+/-10.5 s in the left lung. Dynamic assessment of pulmonary ventilation is feasible using oxygen-enhanced MR imaging, which could provide dynamic MR ventilation-perfusion imaging in combination with recently developed MR perfusion imaging technique, and thus a robust tool for the study of pulmonary physiology and pathophysiology.

Animals↗

PubMed2001

Ion-selective piezoelectric sensor for niacinamide assay in serum and urine.

An ion-selective piezoelectric (ISP) sensor was successfully applied for the determination of niacinamide in serum and urine. By coating a polyvinylchloride membrane containing niacinamide-silicotungstate on one electrode of a thickness-shear mode piezoelectric quartz crystal, the ISP device can adsorb niacinamide selectively. The amount of coating applied to the crystal was calculated from the Sauerbrey equation by monitoring the frequency change. The logarithm of the frequency shift was linear with the logarithm of niacinamide concentration over the range from 1.0 x 10(-9) to 1.0 x 10(-3) M with a detection limit of 1.0 x 10(-9) M at pH 7.0. Influencing factors were investigated and optimized. The results for real samples obtained by the proposed method were in good agreement with those obtained by the conventional methods.

Electrodes↗

PubMed2001

Determination of 24(R)-pseudoginsenoside F(11) in North American ginseng using high performance liquid chromatography with evaporative light scattering detection.

A gradient liquid chromatographic method with evaporative light scattering detection (ELSD) for the determination of 24(R)-pseudoginsenoside F(11) in North American ginseng is described. Samples are analyzed by means of a reverse-phase column (Waters Spherisorb ODS-2, C(18)) using acetonitrile and water under gradient conditions as the mobile phase over 20 min. The evaporative light scattering detector (ELSD) used, was set at an evaporating temperature of 35 degrees C and nitrogen gas pressure of 3.4 bar. The detection limit (S/N>5) of 24(R)-pseudoginsenoside F(11) is 53 ng on column.

Calibration↗

PubMed2001

Reduced hydrolysis of amelogenin may result in X-linked amelogenesis imperfecta.

Amelogenesis imperfecta (AI) is a group of inherited disorders with defective tooth enamel formation caused by various gene mutations. One of the mutations substitutes a cytidine to adenine in exon 6 of the X-chromosomal amelogenin gene, which results in a proline to threonine change in the expressed amelogenin. This transformation is four amino acids N terminal to the proteinase cleavage site in amelogenin for enamel matrix metalloproteinase-20 (MMP-20), also known as enamelysin. MMP-20 effects the release of tyrosine rich amelogenin peptide (TRAP) from amelogenin. This study evaluated the rate MMP-20 hydrolyzes the putative mutated amelogenin cleavage site. The proteolytic site was modeled as a substrate by two synthetic peptides, P1 (SYGYEPMGGWLHHQ) and M1 (SYGYETMGGWLHHQ), selected from residue 36-49 of the amino acid sequence for amelogenin and the respective X-linked amelogenin mutant. Recombinant metalloproteinase-20 (rMMP-20) was used to digest the oligopeptides and the truncated peptides were separated by reversed phase HPLC and identified by mass spectrometry. The results demonstrate that both peptides are cleaved between tryptophan and leucine, matching the TRAP cutting site found in tooth enamel. However, the apparent first order rate of digestion of the mutation containing peptide by rMMP-20 was approximately 25 times slower than that of the non-mutated peptide. This study suggests that the reduced rate of TRAP formation due to a single amino acid substitution may alter enamel formation and consequently result in amelogenesis imperfecta.

Amelogenesis Imperfecta↗

PubMed2001

Molecular analysis of multiple CYP6B genes from polyphagous Papilio species.

Papilio glaucus (eastern tiger swallowtail) and Papilio. canadensis (Canadian tiger swallowtail) are two closely related species with broad but overlapping hostplant ranges. P. glaucus encounters toxic furanocoumarins occasionally in its diet in its rutaceous hostplants, whereas P. canadensis rarely if ever encounters these compounds. Analysis of their furanocoumarin-metabolic profiles indicates that these species induce cytochrome P450 monooxygenases (P450s) capable of metabolizing linear and angular furanocoumarins to varying degrees in response to dietary supplementation with xanthotoxin (a linear furanocoumarin). In P. glaucus, metabolism is induced to a significantly higher level than in P. canadensis. Cloning of multiple P450 genes from each species has revealed that both species contain and express two groups of P450s, designated CYP6B4 and CYP6B17, that are related to the P. glaucus CYP6B4v1 enzyme known to metabolize an array of furanocoumarins. Expression patterns of the CYP6B4 and CYP6B17 group transcripts differ in these species in both their basal and furanocoumarin-inducible levels. In P. glaucus, CYP6B4 transcripts, which are not detectable constitutively, are 311-fold induced by xanthotoxin and CYP6B17 transcripts, which are detectable constitutively, are 3-fold induced by xanthotoxin. In P. canadensis, CYP6B4 transcripts are only 8-fold induced and CYP6B17 transcripts are 13-fold induced. These findings are consistent with the postulated evolutionary history of these two species, according to which P. glaucus maintains its association with rutaceous hostplants and P. canadensis has differentiated to utilize hostplants in other families more extensively.

Amino Acid Sequence↗

PubMed2001

Production of no-carrier-added 186Re via deuteron induced reactions on isotopically enriched 186W.

Rhenium-186 was produced from the reaction induced by 16 MeV deuterons on isotopically enriched 186W metal powder target. Following its separation from 187W, 183Ta and the bulk of target materials 186W through an acid alumina column, the 186Re was converted to HNO3 solution through an anion exchange column, or to ammonia solution by extracting with N-235-dimethylbenzene, and finally the no-carrier-added 186Re saline solution was obtained. The radionuclidic purity of 186Re was >99.9% and the isotopic impurities were mainly 183Re (5.0 x 10(-3)%) and 184gRe (4.6 x 10(-2)%). The experimental thick-target yield of 186Re was determined to be approximately 529 microCi/microA h and the overall chemical recovery yield was > 80%.

Kinetics↗

PubMed2001

Transmyocardial laser revascularization induced angiogenesis correlated with the expression of matrix metalloproteinases and platelet-derived endothelial cell growth factor.

OBJECTIVE: Transmyocardial laser revascularization (TMLR) has been widely evaluated as a treatment for ischemic myocardium. However, its mechanism remains unclear. One mechanism is angiogenesis. This study examines the relationship between TMLR and angiogenesis from the viewpoint of matrix metalloproteinases and platelet-derived endothelial cell growth factor. METHODS: The left anterior descending coronary artery (LAD) was ligated permanently in 12 beagle dogs. TMLR was accomplished in six of the 12 dogs using a carbon dioxide laser. No laser treatment was done in the six control dogs. Two weeks after the initial operation, dogs were euthanized and transmural samples (each of approximately 0.5 g) were cut from the center of the infarcted LAD territory, right ventricular wall, left circumflex artery perfuse area and interventricular septum except the LAD perfuse area. They were snap-frozen in liquid nitrogen for matrix metalloproteinases and platelet-derived endothelial cell growth factor activity analysis. Hematoxylin and eosin staining, double immunohistologic staining with anti-proliferating cell nuclear antigen and von Willebrand factor antibody, and immunohistologic staining with antibody against platelet-derived endothelial cell growth factor were performed for histologic studies. The activities of matrix metalloproteinases were examined by gelatin zymography. The activity of platelet-derived endothelial cell growth factor was examined by a spectrophotometric method. RESULTS: The channels were found to be infiltrated with granulation tissue and fibrosis. In the laser group, the active matrix metalloproteinase-2 and platelet-derived endothelial cell growth factor activity in the area of the left anterior descending coronary artery was significantly higher than in the control group (P<0.0001 and P=0.037, respectively). Within the channel remnants or close to these areas, the number of von Willebrand factor positive microvessels and proliferating cell nuclear antigen with correlating von Willebrand factor positive microvessels were significantly higher than in the control group (P=0.001 and P=0.0006, respectively). These increases in microvessels significantly correlated with the expression of matrix metalloproteinases and platelet-derived endothelial cell growth factor. CONCLUSION: Based on these findings it was concluded that transmyocardial laser revascularization induced angiogenesis correlated with the expression of active matrix metalloproteinases-2 and platelet-derived endothelial cell growth factor.

Animals↗

PubMed2001

5-Aminolaevulinic acid-mediated photodynamic therapy in multidrug resistant leukemia cells.

To verify if photodynamic therapy (PDT) could overcome multidrug resistance (MDR) when it it applied to eradicate minimal residual disease in patients with leukemia, we investigated the fluorescence kinetics of 5-aminolaevulinic acid (ALA)-induced protoporphyrin IX (PpIX) and the effect of subsequent photodynamic therapy on MDR leukemia cells, which express P-glycoprotein (P-gp), as well as on their parent cells. Evaluation of PpIX accumulation by flow cytometry showed that PpIX accumulated at higher levels in mdr-1 gene-transduced MDR cells (NB4/MDR) and at lower levels in doxorubicin-induced MDR cells (NOMO-1/ADR) than in their parent cells. A P-gp inhibitor could not increase PpIX accumulation. Measurement of extracellular PpIX concentration by fluorescence spectrometry showed that P-gp did not mediate the fluorescence kinetics of ALA-induced PpIX production. Assessment of ferrochelatase activity using high-performance liquid chromatography indicated that PpIX accumulation in drug-induced MDR cells was probably regulated by this enzyme. Assessment of phototoxicity of PDT using the 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) assay showed that PDT was effective in NB4, NB4/MDR, NOMO-1 and NOMO-1/ADR cells, which accumulated high levels of PpIX, but not effective in K562 and K562/ADR cell lines, which accumulated relatively low levels of PpIX. These findings demonstrate that P-gp does not mediate the ALA-fluorescence kinetics, and multidrug resistant leukemia cells do not have cross-resistance to ALA-PDT.

ATP Binding Cassette Transporter, Subfamily B, Mem↗

PubMed2001

Intracellular protein scaffold-mediated display of random peptide libraries for phenotypic screens in mammalian cells.

BACKGROUND: Mammalian cell screens of peptide libraries for changes in cellular phenotype may identify novel functional peptides and their cognate binding partners, and allow identification of signal transduction network members or proteins important in disease processes. RESULTS: Green fluorescent protein (GFP) peptide libraries with different structural biases were tested by retroviral expression in A549 carcinoma cells, HUVEC and other cell types. Three different loop replacement libraries, containing 12 or 18 random residues, were compatible with enhanced GFP (EGFP) folding, as was a C-terminally fused random 20-mer library. Library concentrations in A549 cells ranged from ca. 1 to 54 microM. Replacement of loop 3 with known nuclear localization sequence (NLS) peptides, but not with inactive mutants, directed EGFP to the nucleus. Microscopy-based screens of three different libraries for non-uniform localization revealed novel NLS peptides, novel variants of a peroxisomal localization motif, a variety of partial NLS peptides, peptides localized to the nucleolus, and nuclear-excluded peptides. CONCLUSIONS: Peptides can be presented by EGFP in conformations that can functionally interact with cellular constituents in mammalian cells. A phenotypic screen resulting in the discovery of novel localization peptides that were not cell type-specific suggests that this methodology may be applied to other screens in cells derived from diseased organisms, and illustrates the use of intracellular combinatorial peptide chemistry in mammalian cells.

Animals↗

PubMed2001

Statistical test to assess rank-order imaging studies.

RATIONALE AND OBJECTIVES: Rank-order experiments often provide a reasonable method of determining whether a large-scale receiver operating characteristic study can be justified. The authors' purpose was to formalize a proposed method for analyzing rank-order imaging experiments and provide methods that can be used in determining sample sizes for both cases and raters. MATERIALS AND METHODS: Simulations were conducted to determine the adequacy of the normal approximation of a statistic used to test the null hypothesis of random ordering. For a multireader experiment, formulas are presented and guidelines are provided to enable investigators to determine the number of required readers (raters) and cases for a specific study. RESULTS: When there are at least five ordered images per case, 10 cases are sufficient to test a random rank order. When there are only three or four images for a case, 20 cases are required. The authors constructed tables of statistical power for selected numbers of ordered images, numbers of cases, and degrees of trend, and they also provide an approximation for use in situations that are not tabled. CONCLUSION: The statistical methods for analyzing rank-order experiments and estimating sample sizes for study planning are relatively simple to implement. The derived formulas for sample size estimation, when applied to typical imaging experiments, indicate that modest numbers of cases and readers are required for rank-order studies.

Humans↗