[Recommendations for a QA program for digital mammography].
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Humans↗
Biomedical subjects
P Heid
Publications and source records attributed to P Heid.
[Digital mammography and computer assisted diagnosis].
Until recently, the film has remained the only medium of information in mammography. The film is used to record, to exploit, to store and to transmit the image. Computerization of images allows to dissociate and to optimize these different functions. Among classical factors of image quality (spatial resolution, contrast, noise), new factors should be added like the detective quantum efficiency and the conversion factor. Radioluminescent screens, then digital sensors for breast stereotactic imaging have been marketed. Manufacturers are now testing full field digital mammographs. Digital imaging allows many applications (computed-aided diagnostic, 3D imaging.) and permits the easy transfer of images for diagnosis and teaching. Three parts are presented in this chapter. The first one describes the different imaging modalities and gives a reminder of the different elements related to image quality. The second one is related to the practical aspects of full field mammography, the reading of mammograms on a review station, ergonomy in full field mammography and to possible changes for screening mammography. The third part is devoted to computed aided diagnosis and its possible application in screening.
Diagnosis, Computer-Assisted↗
The internal phosphodiesterase RegA is essential for the suppression of lateral pseudopods during Dictyostelium chemotaxis.
Dictyostelium strains in which the gene encoding the cytoplasmic cAMP phosphodiesterase RegA is inactivated form small aggregates. This defect was corrected by introducing copies of the wild-type regA gene, indicating that the defect was solely the consequence of the loss of the phosphodiesterase. Using a computer-assisted motion analysis system, regA(-) mutant cells were found to show little sense of direction during aggregation. When labeled wild-type cells were followed in a field of aggregating regA(-) cells, they also failed to move in an orderly direction, indicating that signaling was impaired in mutant cell cultures. However, when labeled regA(-) cells were followed in a field of aggregating wild-type cells, they again failed to move in an orderly manner, primarily in the deduced fronts of waves, indicating that the chemotactic response was also impaired. Since wild-type cells must assess both the increasing spatial gradient and the increasing temporal gradient of cAMP in the front of a natural wave, the behavior of regA(-) cells was motion analyzed first in simulated temporal waves in the absence of spatial gradients and then was analyzed in spatial gradients in the absence of temporal waves. Our results demonstrate that RegA is involved neither in assessing the direction of a spatial gradient of cAMP nor in distinguishing between increasing and decreasing temporal gradients of cAMP. However, RegA is essential for specifically suppressing lateral pseudopod formation during the response to an increasing temporal gradient of cAMP, a necessary component of natural chemotaxis. We discuss the possibility that RegA functions in a network that regulates myosin phosphorylation by controlling internal cAMP levels, and, in support of that hypothesis, we demonstrate that myosin II does not localize in a normal manner to the cortex of regA(-) cells in an increasing temporal gradient of cAMP.
3',5'-Cyclic-AMP Phosphodiesterases↗
Hormone replacement therapy and screening mammography: analysis of the results in the Bouches du Rhône programme.
OBJECTIVE: To evaluate the effectiveness of a mass screening programme for breast cancer in a French population where hormone replacement therapy (HRT) is common and where mammography is prescribed outside the programme for asymptomatic women. METHODS: From 1993 to 1996 inclusive, 41,062 women underwent a first test and 48,275 a second or third test in the Bouches du Rhône programme. Their HRT status was ascertained at the time of the test. False positive and false negative tests were identified at one year follow up. The incidence of interval cancers was estimated up to three years after the screening test. RESULTS: The odds of being detected at screening rather than as an interval cancer within one year of the test was five times greater among non-users of HRT than among users (odds ratio (OR) 5.14 (confidence interval 2.5 to 11.8)). This high reduction in sensitivity among users (71% v 92%) was associated with a very small reduction in specificity at the incident screen only. The incidence of interval cancers among HRT users was 3.5 times that of non-users within the first year after the test and 1.7 times during the following two years. CONCLUSIONS: When the early results of a programme have been used to measure its effectiveness they should be reassessed in populations where HRT is in widespread use. As interval cancers had better prognostic factors in HRT users than in non-users, the efficacy of a screening programme in such populations should be the subject of further studies.
Aged↗
Kinetic analysis of the hydrodynamic transition accompanying protein folding using size exclusion chromatography. 1. Denaturant dependent baseline changes.
Size exclusion profiles of proteins with persistent conformations exhibit broad asymmetric peaks whose shape and elution times are dependent on denaturant concentration. The collective elution profiles were precisely simulated by an apparent binding model that treats the denaturant dependence in terms of an apparent matrix binding. The model requires three experimentally measurable parameters: the elution time for the unbound protein, an apparent association equilibrium constant for binding, and an apparent exchange time for binding. The denaturant dependence for each of these parameters is related to the accessible surface area of the protein.
Amino Acid Sequence↗
A kinetic study of the folding of staphylococcal nuclease using size-exclusion chromatography.
The kinetics of the hydrodynamic volume change accompanying the reversible unfolding of staphylococcal nuclease have been observed by size-exclusion chromatography at 4 degrees C and pH 7.0 using the denaturant guanidine hydrochloride. The observed chromatographic profiles have been simulated by a six-component unfolding/refolding mechanism using a consistent set of equilibrium and kinetic parameters. The native protein is an equilibrium mixture of the cis and trans isomers of the peptide bond preceding proline-117. The native conformation containing the cis isomer dominates the equilibrium mixture, is more stable, and unfolds more slowly at its transition midpoint. The denatured protein is an equilibrium mixture of at least four components, the cis/trans isomers of proline-117 and one of the five remaining prolines. The dominant refolding pathway is initiated from the denatured component containing the trans isomer of proline-117. The six-component mechanism is consistent with tryptophan fluorescence kinetic measurements of the wild-type protein and with chromatographic measurements of a mutant P117G protein.
Chromatography, Gel↗