ABSTRACT
Las microcalcificaciones agrupadas en mamografias son un signo temprano de una lesion maligna en casi la mitad de los canceres de mama. La caracterizacion de las lesiones benignas y malignas representa un problema sumamente complejo aun para un radiologo con experiencia. Esto se refleja en el alto porcentaje de biopsias innecesarias que se llevan a cabo. La deteccion y clasificacion automatica pueden ayudar al radiologo en la evaluacion de las microcalcificaciones agrupadas. Desarrollamos un esquema de diagnostico asistido por computadora, utilizando hardware de PC, que automaticamente detecta, segmenta y clasifica las microcalcificaciones. El proceso de deteccion esta basado en una combinacion de filtros Gaussiano y morfologico. Dos clasificadores estadisticos fueron usados para la diferenciacion entre los casos malignos y los benignos, los cuales se basan en un conjunto seleccionado de caracteristicas cuantitativas. Para una tasa de falsos positivos del 10 por ciento, una tasa de verdaderos positivos del 87 por ciento fue alcanzada con el clasificador que utiliza el metodo de los K vecinos mas proximos
Subject(s)
Breast Neoplasms , Diagnosis, Computer-Assisted , Mammography , StatisticsABSTRACT
Las microcalcificaciones agrupadas en mamografias son un signo temprano de una lesion maligna en casi la mitad de los canceres de mama. La caracterizacion de las lesiones benignas y malignas representa un problema sumamente complejo aun para un radiologo con experiencia. Esto se refleja en el alto porcentaje de biopsias innecesarias que se llevan a cabo. La deteccion y clasificacion automatica pueden ayudar al radiologo en la evaluacion de las microcalcificaciones agrupadas. Desarrollamos un esquema de diagnostico asistido por computadora, utilizando hardware de PC, que automaticamente detecta, segmenta y clasifica las microcalcificaciones. El proceso de deteccion esta basado en una combinacion de filtros Gaussiano y morfologico. Dos clasificadores estadisticos fueron usados para la diferenciacion entre los casos malignos y los benignos, los cuales se basan en un conjunto seleccionado de caracteristicas cuantitativas. Para una tasa de falsos positivos del 10 por ciento, una tasa de verdaderos positivos del 87 por ciento fue alcanzada con el clasificador que utiliza el metodo de los K vecinos mas proximos (AU)
Subject(s)
Breast Neoplasms/diagnosis , Diagnosis, Computer-Assisted , Mammography , StatisticsABSTRACT
We present results from numerical simulations of a dynamic phase-shifting speckle interferometer used in the presence of mechanical vibrations. The simulation is based on a detailed mathematical model of the system, which is used to predict the expected frequency response of the rms measurement error, in the time-varying phase difference maps, as a result of vibration. The performance of different phase-shifting algorithms is studied over a range of vibrational frequencies. Phase-difference evaluation is performed by means of temporal phase shifting and temporal phase unwrapping. It is demonstrated that longer sampling windows and higher framing rates are preferred in order to reduce the phase-change error that is due to vibration. A numerical criterion for an upper limit on the length of time window for the phase-shifting algorithm is also proposed. The numerical results are finally compared with experimental data, acquired with a phase-shifting speckle interferometer of 1000 frames/s.
ABSTRACT
We describe a phase-shifting out-of-plane speckle interferometer operating at 1 kHz for studying dynamic events. The system is based on a Pockels cell that is synchronized to a high-speed video camera to ensure that the phase shifting occurs between frames. Phase extraction is performed by use of a standard four-frame algorithm, and temporal phase unwrapping allows sequences of several hundred absolute (rather than relative) displacement maps to be obtained fully automatically. The maximum theoretical surface velocity of 67 microm s(-1) is a factor of 40 greater than can be achieved with a speckle interferometer based on a conventional video camera. We test the system using a target that is displaced with constant speed in a direction normal to its surface by means of a piezoelectric transducer. The system's performance in a practical situation is illustrated with measurements on a thin plate undergoing out-of-plane deformation.
ABSTRACT
Inasmuch as current fringe analysis techniques used in digital speckle-pattern interferometry (DSPI) yield a phase map modulo 2pi, phase unwrapping is the final step of any data evaluation process. The performance of a recently published algorithm used to unwrap DSPI phase maps is investigated. The algorithm is based on a least-squares minimization technique that is solvable by the discrete cosine transform. When phase inconsistencies are present, they are handled by exclusion of invalid pixels from the unwrapping process through the assignment of zero-valued weights. Then the weighted unwrapping problem is solved in an iterative manner by a preconditioned conjugate-gradient method. The evaluation is carried out with computer-simulated DSPI phase maps, an approach that permits the generation of phase fields without inconsistencies, which are then used to calculate phase deviations as a function of the iteration number. Real data are also used to illustrate the performance of the algorithm.
ABSTRACT
The introduction of a pulsed laser into an electronic speckle-shearing pattern interferometer allows high-speed transient deformations to be measured. We report on a computerized system that permits automatic data reduction by introducing carrier fringes through the translation of a diverging lens. The quantitative determination of the phase map that is due to deformation is carried out by the spatial synchronous detection method. Experimental results obtained for a metal plate transiently deformed by an electromagnetic hammer illustrate the advantages of the proposed system.
ABSTRACT
We describe an electronic speckle-pattern interferometry system for analyzing addition fringes generated by the transient deformation of a test object. The system is based on a frequency-doubled twin Nd:YAG laser emitting dual pulses at a TV camera field rate (50 Hz). The main advance has been the automatic, quantitative analysis of dual-pulse addition electronic speckle-pattern interferometry data by the introduction of carrier fringes and the application of Fourier methods. The carrier fringes are introduced between dual pulses by a rotating mirror that tilts the reference beam. The resulting deformation-modulated addition fringes are enhanced with a deviation filter, giving fringe visibility close to that of subtraction fringes. The phase distribution is evaluated with a Fourier-transform method with bandpass filtering. From the wrapped phase distribution, a continuous phase map is reconstructed with an iterative weighted least-squares unwrapper. Preliminary results for a thin plate excited by an acoustic shock show the suitability of the system for the quantitative evaluation of transient deformation fields.
ABSTRACT
The performance of a minimum L(0)-norm unwrapping algorithm is investigated by use of synthetic digital speckle-pattern interferometry (DSPI) wrapped phase maps that simulate experimentally obtained data. This algorithm estimates its own weights to mask inconsistent pixels. Particular features usually included in DSPI wrapped phase distributions, such as shears, speckle noise, fringe cuts, object physical limits, and superimposed phase maps, are analyzed. Some adequate approaches to solving these features are discussed. Finally, it is shown that a complex case in which shears and fringe cuts coexist in the wrapped phase cannot be solved satisfactorily with the minimum L(0)-norm algorithm by itself. To cope with this problem, we propose a new scheme.
ABSTRACT
Current whole-field interferometric techniques yield a phase distribution in modulo 2π. Removal of the resulting cyclic discontinuities is a process known as unwrapping, which must be performed before the data can be interpreted. We investigate an iterative unwrapping technique recently published by Ghiglia and Romero [J. Opt. Soc. Am. A 11, 107 (1994)], which is based on least-squares minimization, obtained by the discrete cosine transform. We apply this technique to remove phase wraps from electronic speckle pattern interferometry data, using modest personal computer hardware. The algorithm is shown to be fast, easy to implement, robust in the presence of noise, and able to handle phase inconsistencies without propagating local errors.
ABSTRACT
A digital image-processing method for analyzing double-pulsed electronic speckle pattern interferometry addition fringes is described. The procedure consists of three steps, forming a combination particularly suited to addressing some important practical limitations of the measurement system. In the first step it is shown that in certain cases fringe visibility may be enhanced by subtraction of a reference interferogram, so that a pattern with a quality similar to that of a subtraction one is obtained. In the second step noise is reduced by the application of a spectral subtraction image-restoration method. The third step concerns the calculation of the wrapped phase by means of a Fourier transform method with bandpass filtering. Preliminary experimental results that illustrate the performance of this approach are presented.
ABSTRACT
Dual-plate speckle photography provides a technique for canceling rigid body displacements of an object by recording the images that correspond to the two deformation states on separate photographic plates. When both plates are positioned with a glass base between the emulsions and illuminated by a laser beam, a pattern of circular fringes is formed. Speckle displacement can be determined by measuring the distance between the fringe pattern center and the undiffracted laser beam. The performance of an algorithm for automatic analysis of these fringes is evaluated by using computer-generated fringe patterns. Accuracy is determined for different values of speckle displacements and fringe visibilities.
ABSTRACT
New developments of a phase-shifting readout system for the analysis of whole-field fringes in dual-plate speckle photography are presented.
ABSTRACT
A new use of holographic interferometry to investigate the residual deformations induced in nitrogen implanted specimens by a plasma focus device is reported. The method is simple and nondestructive. Experimental results obtained for AISI 304 stainless steel specimens are presented.
ABSTRACT
This paper reports on the application of phase shifting interferometry to comparative holography. The method here enables the measurement of phase distributions corresponding to the difference in displacements of two nominally identical specimens subjected to similar loading steps. Different aspects of the method are discussed, and experimental results are presented to demonstrate the feasibility and versatility of the technique in flaw detection.
ABSTRACT
A phase shifting readout system is used to analyze whole field fringes in dual plate speckle photography and preliminary results obtained with a first prototype are presented.
ABSTRACT
Two algorithms for analyzing speckle photography fringes for spacing and orientation using a digital image processing system are compared. Each algorithm was tested for accuracy and computer run-time through a computer simulation which includes the degradation of data by noise.
ABSTRACT
The performance of a previously published algorithm for the determination of the direction of speckle photography fringes is evaluated through computer simulation. Numerical results indicate that even in the extreme cases of patterns with very low fringe densities and visibilities contaminated with high noise levels, fringe direction can be determined with a fair degree of accuracy (0.5 degrees ).
ABSTRACT
The propagation of long thermal waves induced in thin aluminum plates by a slowly modulated heat source was investigated by stroboscopic holographic interferometry. The effect of different modulation frequencies on the visualization of such waves is shown. Experimental results confirm analytical thermoelastic predictions. The application of long thermal waves to holographic nondestructive testing is demonstrated.
