Papers by Albert Macovski
Lecture Notes in Computer Science, 2018
ICASSP '83. IEEE International Conference on Acoustics, Speech, and Signal Processing
An operator framework for image reconstruction from limited line integral data is presented in th... more An operator framework for image reconstruction from limited line integral data is presented in this paper. From this framework we derive iterative limited data reconstruction algorithms. The framework applies to arbitrary scanning geometries and arbitrary patterns of missing data. All available a priori information is incorporated by constraint operators. We show how a priori knowledge of the density in part of the object improves the quality of the reconstructed image. The technique is demonstrated with real x-ray data collected on a clinical CT scanner.
IEEE Transactions on Acoustics, Speech, and Signal Processing, 1986
An algebraic limitation on the maximum number of directions of arrival of plane waves that can be... more An algebraic limitation on the maximum number of directions of arrival of plane waves that can be resolved by a uniform linear sensor array is studied. Achievable lower and upper bounds are derived on that number as a function of the number of elements in the array, number of snapshots, and the rank of the source sample-correlation matrix. The signals are assumed narrow-band and of identical and known center frequency. The results are also applicable in the coherent signal case and when directions of arrival are estimated from few snapshots. While in the multiple snapshot case the lower bounds coincide with known asymptotic results, the upper bounds indicate the potential for resolving more signals than by present methods of array processing.
Images of the Twenty-First Century. Proceedings of the Annual International Engineering in Medicine and Biology Society
ABSTRACT
Images of the Twenty-First Century. Proceedings of the Annual International Engineering in Medicine and Biology Society
This paper describes a new approach to the problem of reconstructing a 3-D arterial tree model fr... more This paper describes a new approach to the problem of reconstructing a 3-D arterial tree model from a few angiographic projections. We first develop a natural optimality criterion that defines the globally best reconstruction, and then outline an algorithm that maximizes this criterion. The criterion is a compromise between the conflicting goals of measurement likelihood and object smoothness. Our approach uses a parametric model for the arterial tree, with a new, more accurate model for bifurcations. The algorithm is demonstrated on simulated projections and on magnetic resonance (MR) images.
SPIE Proceedings, 1978
Preliminary results have been obtained with a non-linear filter system for projection data in com... more Preliminary results have been obtained with a non-linear filter system for projection data in computed tomography imaging. The non-linear filter system consists of a sequence of three filters: a non-linear median smoother, a linear smoother and a non-linear correction filter. The non-linear correction filter is a modified Kalman filter. Both patient data and simulated phantom data have been used in evaluating and designing the non-linear filter system. There are six parameters to be adjusted to the type of projection data considered. Additional work is required to optimize the filter system. Our preliminary results show a significant improvement in image resolution for a noise reduction comparable to what is obtained with conventional linear filtering techniques. However, this is at the cost of enhancing the streak artifacts.
IEEE Transactions on Acoustics, Speech, and Signal Processing, 1986
gorithm for the maximization of this criterion is presented. The algorithm is equally applicable ... more gorithm for the maximization of this criterion is presented. The algorithm is equally applicable in the case of signal coherence in the array problem. Simulation shows the estimator to be capable of providing more accurate frequency estimates than currently existing techniques. The algorithm is similar to those independently derived by Kumaresan et aE. In addition to its practical value, the present formulation is used to interpret previous methods such as Prony's, Pisarenko's, and modifications thereof.
Physics in Medicine and Biology, 1976
All X-ray computerized tomography systems that are available or proposed base their reconstructio... more All X-ray computerized tomography systems that are available or proposed base their reconstructions on measurements that integrate over energy. X-ray tubes produce a broad spectrum of photon energies and a great deal of information can be derived by measuring changes in the transmitted spectrum. We show that for any material, complete energy spectral information may be summarized by a few constants which are independent of energy. A technique is presented which uses simple, low-resolution, energy spectrum measurements and conventional computerized tomography techniques to calculate these constants at every point within a cross-section of an object. For comparable accuracy, patient dose is shown to be approximately the same as that produced by conventional systems. Possible uses of energy spectral information for diagnosis are presented.
ICASSP '84. IEEE International Conference on Acoustics, Speech, and Signal Processing
An estimation approach to three dimensional reconstruc-tion from projections, with incomplete and... more An estimation approach to three dimensional reconstruc-tion from projections, with incomplete and very noisy data, is suggested. Using a stochastic dynamic model for the object of interest in the probed domain, the reconstruction problem is, reformulated as a nonlinear state ...
ICASSP '85. IEEE International Conference on Acoustics, Speech, and Signal Processing
ABSTRACT A unified framework for the exact Maximum Likelihood esti-mation of the parameters of su... more ABSTRACT A unified framework for the exact Maximum Likelihood esti-mation of the parameters of superimposed exponential signals in noise, encompassing both the single and the multi-experiment cases (respectively the time series and the array problems), is presented. An exact ...
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Papers by Albert Macovski