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Biomedical subjects

S S Winkler

Publications and source records attributed to S S Winkler.

At least 19 recordsLinked to original sources
PubMed1999

A post-processing technique for displaying vessels from routine fast-spin-echo images: MRI-derived angiography.

Fast-spin-echo magnetic resonance (MR) images are routine components of a standard MR brain examination. On these images, blood vessels are visible as black flow void. We report that by applying an enhancement filter to a stack of routine fast-spin-echo MR images, projected angiographic images can be generated. The vascular detail in the projected image is similar to that observed in a phase-contrast image. In addition to its advantage in obtaining vessel information from routine images, the proposed post-processing technique is fast, easy to implement and completely automatic. These images provide additional vessel information that is useful when MR angiography is unavailable or as an aid in planning dedicated MR angiographic studies.

Brain↗
PubMed1996

MR image segmentation using vector decomposition and probability techniques: a general model and its application to dual-echo images.

A general model is developed for segmenting magnetic resonance images using vector decomposition and probability techniques. Each voxel is assigned fractional volumes of q tissues from p differently weighted images (q < or = p + 1) in the presence of partial-volume mixing, random noise, and other tissues. Compared with the eigenimage method, fewer differently weighted images are needed for segmenting the q tissues, and the contrast-to-noise ratio in the calculated fractional volumes is improved. The model can produce composite tissue-type images similar to that of the probability methods, by comparing the fractional volumes assigned to different tissues on each voxel. A three-tissue (p = 2, q = 3) model is illustrated for segmenting three tissues from dual-echo images. It provides statistical analysis to the algebraic method. A three-compartment phantom is segmented for validation. Two clinical examples are presented.

Artifacts↗
PubMed1994

Dual-echo MRI segmentation using vector decomposition and probability techniques: a two-tissue model.

We combined a vector decomposition technique with Gaussian probability thresholding in feature space to segment normal brain tissues, tumors, or other abnormalities on dual-echo MR images. The vector decomposition technique assigns to each voxel a fractional volume for each of two tissues. A probability threshold, based on an assumed Gaussian probability density function describing random noise, isolates a region in feature space for fractional volume calculation that minimizes contamination from other tissues. The calculated fractional volumes are unbiased estimates of the true fractional volumes. The contrast-to-noise ratio (CNR) between tissues on the segmented images is the same as the Euclidean norm of CNRs in the original images. The method is capable of segmenting more than two tissues from a set of dual-echo images by sequentially analyzing different pairs of tissues. The model is analyzed mathematically and in experiments with a phantom. Two clinical examples are presented.

Adenocarcinoma↗
PubMed1990

Sodium-23 magnetic resonance brain imaging.

This is a review of recent work in 23Na MR imaging. The main emphasis of recent papers has been pulse sequences that, with appropriate postprocessing, give images of the fast, slow, and intermediate components of T2 decay. The assignment of compartmental designation to the T2 component remains a problem except for homogeneous structures easily identifiable anatomically (ventricles, superior sagittal sinus, globe of the eye). Compartmental distribution of sodium is described. The predominance of the interstitial and plasma compartment, the invisibility of part of the intracellular sodium, and the difficulty in imaging the very fast T2 component of visible intracellular sodium make the usual Na spin-echo image essentially an image of the interstitial and plasma space. Use of super paramagnetic iron oxide coupled to dextran as a contrast medium may help to identify the plasma compartment. Because the usual Na MR images are essentially interstitial and plasma images, our own interest is in observing functional changes in these compartments. Another proposed application is the detection of the very fast T2 component in brain tumors to aid in defining tumor grade and extent.

Brain↗
PubMed1988

Clinical and experimental sodium magnetic resonance imaging.

In conclusion, sodium MR imaging has potential for providing physiologic information relevant to cell mitosis, cell energy state, rCBV, and seizures. Considerable technical and experimental development is necessary, however, before sodium MRI becomes a routine examination in the clinical setting.

Brain Chemistry↗
PubMed1983

A study of the image discrepancies due to object time-dependence in transmission and emission tomography.

In conventional computed tomography (CT) imaging of a point object, projection filtering causes the back-projected contributions to image positions away from the point to sum to zero. If the point object intensity is time-dependent, and all the projections are not acquired simultaneously, this cancellation cannot be complete and artefacts result. Loss of spatial invariance makes a general linear-systems approach to the problem impossible. We have studied the properties of such artefacts by the computer simulation of decaying exponential time-dependence in three different spatial distributions and four transmission and emission CT geometries. Spatially complex time-dependent objects typically produce artefacts that can be treated as an additional broad-spectrum noise source with a power comparable to that of other CT noises. Artefacts from broad ranges of similar time-dependence can add coherently to cause patches of artefact, particularly in geometries with a strong correlation between projection acquisition time and projection angle. As expected, artefacts are reduced for all geometries as scan duration is reduced. In our model, with a most rapid decay constant of 1.2 min-1, negligible artefacts were observed for a six second scan duration.

Computers↗
PubMed1980

Explanation of metrizamide brain penetration: a review.

The penetration of intrathecally injected metrizamide into brain and spinal cord substance is a phenomenon that has surprised and puzzled radiologists. No suitable explanation has been offered in the radiologic literature. This article reviews the recent literature on the relationship between the cerebrospinal fluid (CSF) space and the extracellular fluid (ECF) space of the brain. Recent evidence has shown that these spaces are in fact one compartment with no diffusion barrier between them. Thus, penetration of metrizamide into the brain is an expected rather than surprising phenomenon. An explanation is offered as to why metrizamide does not penetrate edematous or infarcted portions of brain on the basis of a pressure gradient between damaged brain ECF and CSF spaces.

Brain↗
PubMed1980

Imaging methods in the transmission computed tomographic measurement of regional xenon kinetics in the brain.

The process of an investigation of transmission computed tomographic measurements of the kinetics of stable xenon in the brain is reported. The use of functional imaging methods to generate maps of regional washout rate estimators is introduced in an animal model. Region-of-interest analysis is introduced using regions specified by the functional maps demonstrates the sensitivity of the methods to the rapid components of cerebral xenon washout. Correspondence among the regional distributions of tissue types as demonstrated by tissue attenuation coefficient, xenon solubility, and washout rate estimators supports the validity of characterizing each pixel by a single exponential response function.

Animals↗