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[Is telemammography an option for screening programs?--A phantom study].

Abstract

PURPOSE: To show that it is possible to proceed a 20-fold JPEG 2000 wavelet compression of radiographs of a CDMAM phantom without data loss and the usefulness of this technique in telemammography for screening. MATERIAL AND METHODS: After digitizing and a 20-fold data compression, four radiographs of a CDMAM phantom were transferred via ISDN to a PACS archive. Using a soft copy work station, the contrast detail detectability of these data sets was compared to the contrast detail detectability of the original radiographs. RESULTS: The contrast detail detectability showed no difference for the original radiographs and the data sets. CONCLUSION: It is possible to digitize radiographs of a contrast detail mammography phantom, to compress the data sets, to transfer them to a soft copy station and to decompress them without negative influence on the contrast detail detectability.

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BibTeXRIS

T Wollenweber, M Freund. 2005. [Is telemammography an option for screening programs?--A phantom study].. https://doi.org/10.1055/s-2005-858373

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Contrast Sensitivity↗

Bayesian adaptive estimation of threshold versus contrast external noise functions: the quick TvC method.

External noise paradigms, measuring contrast threshold as a function of external noise contrast (the "TvC" function), provide a valuable tool for studying perceptual mechanisms. However, measuring TvC functions at the multiple performance criteria needed to constrain observer models has previously involved demanding data collection (often>2000 trials). To ease this task, we developed a novel Bayesian adaptive procedure, the "quick TvC" or "qTvC" method, to rapidly estimate multiple TvC functions, by adapting a strategy originally developed to estimate psychometric threshold and slope [Cobo-Lewis, A. B. (1996). An adaptive method for estimating multiple parameters of a psychometric function. Journal of Mathematical Psychology, 40, 353-354; Kontsevich, L. L., and Tyler, C. W. (1999). Bayesian adaptive estimation of psychometric slope and threshold. Vision Research, 39(16), 2729-2737]. Exploiting the regularities observed in empirical TvC functions, the qTvC method estimates three parameters: the optimal threshold c(0), the critical noise level N(c), and the common slope, eta, of log-parallel psychometric functions across external noise conditions. Before each trial, the qTvC uses a one-step-ahead search to select the stimulus (jointly defined by signal and noise contrast) that minimizes the expected entropy of the three-dimensional posterior probability distribution, p(N(c),c(0),eta). The method's accuracy and precision, for estimating TvC functions at three performance criteria (65%, 79%, and 92% correct), were evaluated using Monte-Carlo simulations and a psychophysical task. Simulations showed that less than 300 trials were needed to estimate TvC functions at three widely separated criteria with good accuracy (bias<5%) and precision (mean root mean square error <1.5 dB). Using an orientation identification task, we found excellent agreement (weighted r(2)>.95) between TvC estimates obtained with the qTvC and the method of constant stimuli, although the qTvC used only 12% of the data collection (240 vs 1920 trials). The qTvC may hold considerable practical value for applying the external noise method to study mechanisms of observer state changes and special populations. We suggest that the same adaptive strategy can be applied to directly estimate other classical functions, such as the contrast sensitivity function, elliptical equi-discrimination contours, and sensory memory decay functions.

Contrast Sensitivity↗

The perceived contrast of texture patches embedded in natural images.

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