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Biomedical subjects

G T Herman

Publications and source records attributed to G T Herman.

At least 37 records · Page 2Linked to original sources
PubMed1986

Dynamic three-dimensional reconstruction of the left ventricle from two-dimensional echocardiograms.

Using an open chest canine model, a method was developed for three-dimensional reconstruction of the contracting left ventricle from two-dimensional echocardiograms, which is applicable to intraoperative studies in humans. A mechanically held 5 MHz transducer was used to record parallel high resolution cross-sectional images with precise spatial registration. Myocardial borders were tracked manually and entered into a computer system. Regional filling and interpolation routines were applied to reconstruct the endocardial and epicardial surfaces of the ventricle. The myocardium can be displayed as a translucent, shaded three-dimensional solid surrounding the ventricular cavity. One or both surfaces can be rotated about any axis, sectioned through any plane and viewed in motion through systole and diastole. Studies before and after left anterior descending coronary artery occlusion showed the three-dimensional extent of abnormal left ventricular cavity and myocardial deformation. Quantitative examination of regions of interest permits the analysis of global and regional volumetric and myocardial thickness changes throughout the cardiac cycle. Thus, open chest three-dimensional echocardiography provides a powerful tool for the quantitative physiologic investigation of the left ventricle.

Animals↗
PubMed1983

Three-dimensional reconstruction of craniofacial deformity using computed tomography.

The computed tomographic studies obtained routinely in the examination of patients with congenital or acquired defects of the skull and facial bones can be utilized as a substrate to provide an accurate three-dimensional representation of osseous abnormalities. The total dose of x-irradiation is reduced as other means of radiological examination are eliminated. Osseous structures are faithfully reproduced. Complete inspection of the reproduced structure can be made from any viewpoint, including internal inspection.

Abnormalities, Multiple↗
PubMed1982

Reconstruction algorithms for nonstandard CT scanner designs.

Data collected by a CT scanner provide estimates of line integrals of the X-ray attenuation distribution in a cross section of the human body. The lines along which integrals are collected are determined by the positions of the source-detector pairs during the data collection. Since only the lines are important (and not the positions of the source and the detector on the line), essentially the same data may be collected by scanners of very different design. In this article we illustrate that in certain situations the problem of reconstruction from data collected by a CT scanner of a new (and nonstandard) design can be "reduced" to the problem of reconstruction from data collected by a CT scanner for which the problem has already been solved. The "reduction" involves identifying values of free parameters in the old design (such as the radius of the circle in which the source rotates), which would make the geometry of data collection essentially identical to that of the proposed new design. Since reconstruction algorithms for the old design already exist, they can be applied without any change to the data collected by the new scanner. In other words, the problem of finding a reconstruction algorithm for a nonstandard mode of data collection can sometimes be solved by describing a (virtual) machine of standard design whose reconstruction algorithms are immediately applicable to the data collected by the nonstandard machine. The method is demonstrated on a recently proposed concept for transforming a radiotherapy simulator into a CT scanner.

Data Display↗
PubMed1982

Reconstruction and imaging of the beating heart.

Computer methods are discussed which have been developed by the Medical Image processing Group (formerly at SUNY/Buffalo, now at the University of Pennsylvania) for the reconstruction of the beating human heart from x-ray projections. Two data collection modes are emphasized: the dynamic spatial reconstructor and gated cardiac scanning with a rotate-only (third-generation) computed tomography scanner. How the reconstructed beating heart can be displayed by means of dynamic computer graphics is also illustrated.

Animals↗
PubMed1981

Evaluation of a preprocessing algorithm for truncated CT projections.

A preprocessing algorithm for completing truncated computed tomography (CT) projection data (so that reconstruction methods suitable for complete projection data can be applied) is experimentally investigated. The study is motivated primarily by the problem of patients who are too obese to fit into the fan beam of a rotate-only (third generation) scanner, and secondarily by dose reduction considerations. Four sets of patient data collected by a rotate-only scanner are used, and the reconstructions from the complete and truncated projection data are compared. It is illustrated that the preprocessing algorithm leads to qualitatively good images, since local variations are nearly identical in the reconstruction from the complete and from the truncated data. Quantitatively, the results are less encouraging; the exact values of CT numbers differ in the two reconstructions by a significant (although slowly varying) amount across the two reconstructed images.

Humans↗
PubMed1981

Sampling properties of stationary and half-rotation rings in positron emission tomography.

The aim in positron emission tomography is to provide quantitative information about the uptake, localization, and turnover of labeled molecules in the human body. Instruments designed for this purpose are based on the coincidence detection of the emitted annihilation photons. In this paper, we examine those instruments that use a ring of detectors. We investigate such instruments with respect to their sampling properties in the stationary and half-rotation modes. It is shown that, although the half-rotation motion provides an improvement if the data are treated as a set of parallel projections, there is no improvement when divergent projections are assumed by the reconstruction procedure. The effects on reconstruction quality of the radial and the angular sampling in ring collected data are discussed and illustrated.

Data Collection↗
PubMed1980

Demonstration of a software package for the reconstruction of the dynamically changing structure of the human heart from cone beam x-ray projections.

The Dynamic Spatial Reconstructor (DSR) is a device constructed at the Biodynamics Research Unit of the Mayo Clinic for (among other things) the visualization of the beating heart inside the intact thorax. The device consists of 28 rotating X-ray sources arranged on a circular arc at 6 degrees intervals (total span 162 degrees) and a matching set of 28 imaging systems. The whole thorax of the patient is projected onto the two-dimensional screen of the imaging systems by cone beams of X rays from the sources. All of the X-ray sources are switched on and off within a total period of 10 milliseconds. The Medical Image Processing Group at the State University of New York at Buffalo has developed a software package for the design and evaluation of algorithms to be used by the DSR. In this paper we illustrate the operation of the package and a particular algorithm for the reconstruction of the dynamically changing structure of the heart from data collected by the DSR.

Computers↗
PubMed1980

The use of three-dimensional computer display in the study of disk disease.

We have developed a software system for three-dimensional dynamic display of organs from computed tomograms (CT). We are now beginning to evaluate the clinical usefulness of this software system. We have chosen the spine in general, and disk disease in particular, as the first step in this evaluation. The choice was to a large extent influenced by our belief that surgical planning can be improved if three-dimensional displays of the diseased disk and its surroundings are available. Patients who have been referred to us for CT evaluation were examined in the routine manner. In those cases in which the ordinary CT scans indicated potential usefulness, the softwar system was applied, and movies were produced showing the appearance of appropriate parts of the spine as if they were rotating in front of the user. It appears that the size and relative location of disk herniations are well represented by such displays. Proof of efficacy in surgical planning awaits a more thorough evaluation, but our initial study indicates that the method has great promise.

Adult↗
PubMed1979

Correction for beam hardening in computed tomography.

We investigate how one can estimate from the total attenuation, p, of a polyenergetic X-ray beam what the total attenuation, m, of a monoenergetic beam would have been along the same ray. We find that for beams with typical diagnostic X-ray spectra passing through the human body one can find a simple function f such that f(p) is a sufficiently close estimate of m to allow good reconstructions. We also find that m cannot be accurately estimated from p based on the assumption that the human body consists of water alone. Our results are demonstrated by reconstructions of a mathematical model of a cross-section of the human thorax. This article is self-contained and includes in its Appendices a detailed discussion of the mathematical nature of the problem of bean hardening in computed tomography.

Humans↗
PubMed1979

Data collection for cross-sectional image reconstruction by a moving ring of positron annihilation detectors.

A ring of positron annihilation detectors capable of two independent motions in the plane of the ring is considered. It can rotate around its center, and the whole ring may move so that its center traces a circular path. Provided certain parameters are chosen according to given formulas, data collected by such a detector ring can be reorganized (rebinned), in a computationally very inexpensive fashion, so that the data items in each bin are measurements along parallel lines spaced at small equal intervals. Efficient high resolution reconstruction algorithms that assume such data organization can therefore be applied to data collected collected by a moving positron ring detector. The method is demonstrated on a realistic example.

Computers↗
PubMed1977

Display of three-dimensional information in computed tomography.

From a sequence of computed tomograms of two-dimensional transverse slices of a body one can build up a three-dimensional array of numbers containing spatial rather than cross-sectional information. We have developed computer methods to display a slice at arbitrary orientation through the three-dimensional object. The three-dimensional array of numbers can also be used to display what any particular organ would look like if it were removed from the body. This is done by a computer technique that first detects the surface of the organ of interest and then displays this surface on a screen.

Data Display↗