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S M Pizer

Publications and source records attributed to S M Pizer.

36 records · Page 2Linked to original sources
PubMed1989

Medical image work stations: functions and implementation.

Electronic work stations are becoming a standard means of presenting medical images for diagnosis and consultation, and they will become more wide-spread as picture archiving and communication systems (PACS) come into use. These work stations must allow the user both to perceive the patterns necessary for accurate diagnosis and to "navigate" efficiently within large sets of related images, ie, quickly find and compare desired images. The work stations must operate without a feeling of "fraction" and have an affordable cost. In this report we survey the tasks and system objectives, first regarding the perceptual needs and second with respect to the navigational needs. We then survey the technology available to satisfy these needs and conclude with a list of needed research and technology that can be expected or should be provided in the future.

Data Display↗
PubMed1989

Three-dimensional display techniques in radiation therapy treatment planning.

Good radiation treatment planning requires that the target volume be treated with a high and uniform dose of radiation while irradiating normal tissue as little as possible. Even if the merits of a given treatment plan are judged only on the appearance of isodose lines in one or a few planes it can sometimes be difficult for the experienced radiation oncologist to select the best of several alternative plans. If consideration is given to the entire spatial distribution of dose, however, the problem becomes far more difficult because of the enormous amount of data that must be evaluated. We believe that the lack of suitable methods to display these data has greatly contributed to the slow incorporation of 3D considerations into routine radiation treatment planning. In the past few years there have been great advances in both the theory of how to produce effective 3D displays and in the display hardware itself. In this paper we survey some of the methods used at the University of North Carolina, and show specific examples of how these displays can be used in radiation therapy treatment planning.

Computer Graphics↗
PubMed1987

Automatic digital contrast enhancement of radiotherapy films.

The practice of radiotherapy involves the precise geometric localization of both anatomic and non-anatomic structures using radiographs which are typically of very low contrast. Portal and verification films suffer from poor contrast as a result of the dominance of Compton interactions at therapeutic energies, and implant localization films often are degraded by extreme patient thickness (lateral pelvis) or projection of bony structures (head and neck). Automatic contrast enhancement techniques developed and proven for optimization of the display of digitally produced images such as CT have been applied to radiotherapy films to improve contrast and augment readability. This approach has become viable only recently with the advent of high speed, high resolution film digitizers and laser cameras and the evolution of sufficiently powerful computer hardware.

Brachytherapy↗
PubMed1987

Effective presentation of medical images on an electronic display station.

In summary, the following should be parts of a useful system for electronic medical image display. 1. All display scales should be linearized. 2. Contrast Limited Adaptive Histogram Equalization should be applied to all slices as they arrive at display. 3. A screen or portion thereof should be dedicated to a low-sampled index of all slices, and navigation among the slices should be accomplished by reference to this index. 4. One second access to any slice or group of slices from the index should be provided.

Diagnostic Imaging↗
PubMed1987

Effect of ambient light on electronically displayed medical images as measured by luminance-discrimination thresholds.

The effect of ambient light on linearization of gray scales was studied in two experiments by measuring brightness-discrimination thresholds for stimuli as a function of ambient-light level. The luminance and contrast levels of stimuli were chosen to include typical instances encountered in electronically displayed medical images. Three ambient-light levels were used: 4 and 40 lx, which span the range that we found in well-controlled radiologic reading rooms set up with electronic displays, and 148 lx, which represents the low end of the ambient-light range found in light-box reading rooms. In the first experiment, discriminability of some test stimuli was found to change as ambient light increased. The pattern of results suggests that a single linearization function would be clinically acceptable in a reading room with ambient light ranging from 4 up to, at least, 40 lx. At 148 lx, however, the just-noticeable-difference versus intensity function is different enough to require a gray-scale linearization function other than our standard one, which is based on 4-lx ambient light. We attribute these changes in stimulus discriminability to changes in the displayed image produced by ambient light, not to changes in the visual sensitivity of the observer. In the second experiment, which controlled for the display changes produced by ambient light, we found no change in stimulus discriminability as a function of ambient light.

Adaptation, Physiological↗
PubMed1984

Adaptive grey level assignment in CT scan display.

The normal method of assigning grey levels to computed tomographic (CT) numbers in CT scan display involves interactive selection of an intensity window. This method often results in the inability to visualize different types of tissue in a single image and sometimes results in unnecessary loss of contrast sensitivity. A method is described that solves these problems by automatically adapting the assignment of displayable grey levels to CT numbers in a way that varies smoothly across the image according to local needs for the presentation of contrast. The adaptation is based on local histogram equalization implemented using interpolation so as to operate on a minicomputer in a few tens of seconds. This contrast enhancement is followed by a mapping that causes the viewer's perceptual response to be linear across the display scale.

Data Display↗
PubMed1978

Improvement of scintigrams by computer processing.

Computer processing can improve the quality of scintigrams in several ways. It can increase the accuracy with which the image approximates the activity distribution by reversing degradation. It can selectively enhance normal or abnormal structures of interest. It can optimize the use of the display system presenting the image. The usefulness of computer processing must be determined by observer testing and clinical experience. The need to correct distortion in both intensity (nonuniformity) and space can be avoided by attention to calibration and to the setup of the imaging device employed and by use of the sliding energy window technique. Nonuniformity correction, especially for quantitative studies, should not be done using a flood field as this may actually decrease accuracy. Instead, any necessary correction should employ the sensitivity matrix, which measures the variation of sensitivity to a point source with the position of the source. Statistical fluctuations (noise) and degradation of resolution are commonly corrected using linear, stationary techniques [concepts which are defined and developed in the text], but nonstationary techniques appear to be frequently more successful at the expense of increased processing time. Techniques of choice for pure smoothing are nine-point binomial smoothing and variable shape averaging, and those for both sharpening and smoothing (preferred for most modern, high-count scintigrams) are unsharp masking, Metz or Wiener filtering, and bi-regional sharpening. Structures of interest can be enhanced by methods which detect and emphasize changes in local distributions of slope and curvature of intensity. High quality display devices are essential to reap any benefits from degradation correction. Those devices, which must have appropriately high sensitivity and must avoid display artifacts, have become available only recently. Use of the display should be matched to the processing done. Contrast enhancement, e.g. by histogram qualization, for optimal use for each image of the display intensity range, is often helpful. Most scintigram processing is done using computers with about 32K 16-bit words. Floating point hardware is often useful. Most processing methods require 1-30 seconds on such computers and usually under 15 seconds. Processing time tends to be negligible compared to time for user specification of the processing to be done, so the quality of command languages should be of concern. Careful observer studies using phantoms have shown processing to improve detectability of lesions when a single display is used for both processed and unprocessed images, but not when unprocessed images on standard analog displays are compared to processed images on common computer displays...

Computers↗
PubMed1976

An ultrasonogram display system using a natural color scale.

The gray scale display used in B scan ultrasonography limits the perceptibility of clinically useful information. Presentation in color can increase perceptibility, but current color displays have no natural scale and may have the fault of a discrete color spectrum. The continuous heated-object color spectrum solves these problems. To produce a display using this spectrum, we have built an inexpensive system to adapt the scan converter output of a gray scale ultrasonograph to a commercial color television.

Adult↗
PubMed1975

NUMEDICS: a system for on-line data processing in nuclear medicine.

A multiterminal system --NUMEDICS--has been developed to study the problems of on-line acquisition, processing, and display of scintigraphic data. The hardware-software configuration of NUMEDICS permits simultaneous and independent operation of terminals in the Division of Nuclear Medicine, the Physics Research Laboratory, and the Cyclotron Laboratory of the Massachusetts General Hospital. This paper describes the hardware and software developments in NUMEDICS which have been proven to be of value in clinical and research applications. These features are illustrated by applications to the evaluation of left ventricular performance, three-dimensional imaging, and functional imaging of rCBF.

Nuclear Medicine↗
PubMedDate not supplied

Color display in ultrasonography.

Color display is useful in medical ultrasonography to increase sensitivity to contrast, to improve quantitative comparability between image regions, and to allow multiparameter display. In its first section this paper expands upon these objectives, sets forth the concepts of color definition, and discusses the criteria that should be used to select a pseudocolor display scale. The second section surveys the published work applying color display in ultrasonography, and the final section presents some of our recent results on (1) producing continuous pseudocolor scales with a natural order and with the property that equal changes in driving signal produce equally perceptible changes along the pseudocolor scale; and (2) applying these scales to ultrasound images.

Color↗
PubMedDate not supplied

Image processing algorithms for digital mammography: a pictorial essay.

Digital mammography systems allow manipulation of fine differences in image contrast by means of image processing algorithms. Different display algorithms have advantages and disadvantages for the specific tasks required in breast imaging-diagnosis and screening. Manual intensity windowing can produce digital mammograms very similar to standard screen-film mammograms but is limited by its operator dependence. Histogram-based intensity windowing improves the conspicuity of the lesion edge, but there is loss of detail outside the dense parts of the image. Mixture-model intensity windowing enhances the visibility of lesion borders against the fatty background, but the mixed parenchymal densities abutting the lesion may be lost. Contrast-limited adaptive histogram equalization can also provide subtle edge information but might degrade performance in the screening setting by enhancing the visibility of nuisance information. Unsharp masking enhances the sharpness of the borders of mass lesions, but this algorithm may make even an indistinct mass appear more circumscribed. Peripheral equalization displays lesion details well and preserves the peripheral information in the surrounding breast, but there may be flattening of image contrast in the nonperipheral portions of the image. Trex processing allows visualization of both lesion detail and breast edge information but reduces image contrast.

Algorithms↗
PubMedDate not supplied

Examination of the extracranial carotid bifurcation by thin-section dynamic CT: direct visualization of intimal atheroma in man (Part 1).

Because carotid angiography has been shown to have limitations in the detection of intimal disease at the bifurcation, a new method of examination of the extracranial carotid artery has been developed using thin-section dynamic computed tomographic (CT) scanning. Carotid atheroma and thrombi can be imaged directly on these sections. The intimal lesions are uniformly hypodense with respect to the carotid arterial wall. Radiologic-pathologic correlation studies using human carotid arteries in a neck phantom confirm that these hypodense lesions are atheromas or thrombi. There is good correlation between CT cross-sectional images and cross-sectional postmortem artery sections. While a number of new computer-based methods of reformation of the carotid artery have been developed, consecutive thin slices through the carotid bifurcation display the pathologic lesions satisfactorily.

Carotid Arteries↗