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Biomedical subjects

P F Judy

Publications and source records attributed to P F Judy.

17 recordsLinked to original sources
PubMed1992

Practices and attitudes about cathode-ray tube-based and film-based image interpretation.

A questionnaire was mailed to 708 practicing radiologists and 348 members of the Society for Computer applications in Radiology (SCAR) in order to evaluate current practices and attitudes regarding the perceived advantages or disadvantages of film- and CRT-based image interpretation. A total of 27% of the 1,056 questionnaires (137 practicing radiologists; 145 SCAR members were returned. Ninety percent of practicing radiologists used film at least 75% of the time. Advantages of film-based reading listed by more than 75% of the respondents included: film reading is faster, and facilitates viewing multiple images. Advantages of CRT-based reading included: access to the entire dynamic range and potential imaging processing. Desirable attributes of existing displays included: adjustable grey scale, magnification, ability to view multiple images, allow quick review, and viewing by several individuals. Valued potential advances included: multiple higher resolution monitors, image processing and multimodality display. Practicing radiologists and computer applications society members had similar attitudes. Film-based reading is still nearly universal, but radiologists are interested in CRT-based reading if such devices have the proper features and become more available.

Attitude of Health Personnel↗
PubMed1991

Visualization and detection-localization on computed tomographic images.

These studies investigated observers' ability to detect and locate highly visible liver lesions on computed tomographic (CT) images, manipulating both the lesion's location and polarity (brighter or darker than liver background). Visibility of a lesion is not sufficient to guarantee accurate localization. With clinical images, possible confusions between a lesion and coexisting normal structures (like blood vessels) is a serious constraint on observer performance.

Humans↗
PubMed1988

Size discrimination in computed tomographic images. Effects of feature contrast and display window.

Studies show that features on computed tomographic (CT) images in clinical formats become less detectable when the images are produced with wider CT display windows. We studied the effects of feature contrast and the display window on observer performance in higher-order tasks that involved discriminating small size differences between features on CT images. The features to be discriminated were pairs of disks (9.0 or 9.5 mm in diameter) superimposed on CT images of water phantoms. Sets of image stimuli for two different types of size-discrimination tasks were generated with various CT contrasts specified for the superimposed features and were produced on film transparencies with display windows ranging from 90 to 2880 Hounsfield units (HU) in width. Observers' performance improved with increasing CT contrast in both size discrimination tasks. Unlike performance in feature-detection tasks, however, size discrimination was unaffected by changing the CT display window over a factor of 16 (from 90 to 1440 HU). Performance fell only at the widest display window (2880 HU), for which CT noise was essentially invisible. These results suggest that the effect of changing the CT display window may depend on the spatial frequency content of image information required for a given task.

Humans↗
PubMed1987

Gaining insight: improved images enhance understanding.

The past several decades have witnessed dramatic advances in the technology of image acquisition and display. There have been some parallel but less spectacular advances in understanding human acquisition and analysis of visual information. For the first time, imaging devices are available that allow the operator to determine the brightness relationships between normal and pathologic structures. For the first time too, it is becoming possible for the community of scientists interested in medical imaging to marry knowledge of human observer performance with the capabilities of the modern display devices to permit maximum information extraction from medical images.

Adenocarcinoma↗
PubMed1978

Detection of myocardial ischemia in vitro by computed tomography.

The applicability of CT in the delineation of ischemic myocardium is defined. Twenty-six dogs had their left anterior descending coronary artery occluded, and radiolabeled microspheres were injected into the left atrium to measure myocardial blood flow. From 30 minutes to 7 weeks after coronary occlusion the hearts were excised and scanned in a CT head scanner. An unbiased observer divided selected CT scans slices into normal, abnormal, and borderline areas of attenuation coefficients; these were correlated with blood flow measurements and a progressive decrease in flow from normal to borderline and borderline to abnormal segments was found. As early as 2 hours after coronary arterial occlusion, areas of reduced attenuation coefficient, corresponding to regions of reduced blood flow, were seen. Areas of increased attenuation were seen in regions containing microcalcifications and fibrosis in several longer term experiments. Areas of reduced blood flow were visible immediately after coronary arterial occlusion with intravenous iodinated contrast material (1 ml/kg). CT detection of regions of reduced blood flow defined by radiolabeled microsphere is a promising means of detecting and sizing myocardial infarcts.

Animals↗
PubMed1976

Differing attenuation coefficients of normal and infarcted myocardium.

There are significant differences in attenuation coefficients between normal and infarcted myocardium measurable with a computerized transaxial tomographic scanner. Additionally, iodinated contrast material administered prior to killing the tests animals resulted in excellent visualization of the blood-myocardial interface at a time when standard radiographs detected no differences between the ventricular cavity and the myocardial wall. These natural and induced changes in attenuation coefficients offer a new approach to evaluating and understanding the processes of tissue injury and death. Their clinical relevance lies in application to the twin problems of myocardial infarction and the structure and function of the cardiac wall.

Animals↗
PubMed1976

Computed tomography of the normal and infarcted myocardium.

After intravenous administration of contrast agent, in vitro cardiac scanning showed a significant difference between the attenuation coefficients of the intracavitary blood pool and the myocardial wall, permitting clear delineation of the ventricular cavity. A substantial alteration in hematocrit permitted similar visualization of the intracavitary blood pool-myocardial wall interface. The attenuation coefficient of infarcted myocardium differed sufficiently from that of normal myocardium to render computed tomographic distinction feasible. In three hour old infarctions, the differences between normal and ischemic or infarcted tissue were enhanced by prior administration of contrast agent. These differences in attenuation coefficient indicate that a properly gated CT scanner could be utilized as a noninvasive approach to evaluating suspected or known myocardial infarction and other aspects of cardiac structure and function both in man and in experimental animals.

Animals↗
PubMed1975

Malfunction of linear accelerator dose monitoring systems.

Malfunctions of the dose monitoring systems of two linear accelerators were studied. A variation of plus or minus 2.5% over an air density correction factor range from 1.02 to 1.07 was measured, suggesting that the ionization-type monitor chambers were open to the atmosphere. An average variation of minus 2.0% was present between early morning calibrations and those performed later in the day. Any variation caused by changes in control console temperature was within experimental error. This type of malfunction can lead to errors in delivered doses of 5%.

Electrons↗
PubMedDate not supplied

The line spread function and modulation transfer function of a computed tomographic scanner.

A simple method to measure the line spread function of computed tomographic scanners has been developed. The line spread function of the EMI-Scanner was measured and the MTF of the scanner was calculated. The reproducibility of the method indicated this technique could be utilized to compare the spatial resolution of various computed tomographic scanners.

Diagnosis, Computer-Assisted↗
PubMedDate not supplied

Energy absorbed in calcium tungstate x-ray screens.

The energy which must be absorbed in a CaWO4 x-ray intensifying screen to produce unit net opetical density on a film has been evaluated by measurement and calculation for a screen-film system over a range of beam qualities (1.4--7.4 mm A1 HVL) spanning the diagnostic x-ray region. It was found to be constant within experimental error. The absorbed-energy constant for three additional CaWO4 screens is presented for a single beam quality. To correct the estimation of absorbed energy, the fractional escape of tungsten K x rays has been evaluated and the results are presented as a function of phosphor loading. The absorbed-energy constant is useful for predicting optical density for variable beam conditions; a family of characteristic curves based on exposure is reduced to one curve for a particular film-screen system, expressed as optical density as a function of absorbed energy.

Calcium↗
PubMedDate not supplied

Resolution and contrast reduction.

Lack of resolution (unsharpness) can reduce contrast in diagnostic radiography if the proper conditions of magnification and unsharpness are met. To describe this phenomenon, a modification of the contrast reduction factor (CRF) was introduced which used the response function of a semi-opaque edge to predict contrast reduction for small bar-shaped objects. To predict CRF, unsharpness is employed as a single-term description of resolution and is obtained experimentally from the edge response function. The unsharpness term is defined as the distance over which the response goes from 16.5% to 83.5% of the maximum. Measured and predicted CRFs were compared and the CRF concept was found to be an excellent predictor of contrast reduction. The individual components of unsharpness were determined experimentally and the sum-of-squares rule predicted adequately their combination. Three methods to measure unsharpness were compared: (a) the ICRU prescription using pinhole radiographs of the focal spot, (b) one-dimensional integration of the focal-spot pinhole radiograph, and (c) the unsharpness term produced by a semi-opaque edge. The latter two were measured using a microdensitometer.

Mathematics↗
PubMedDate not supplied

Noise characteristics of a microchannel plate x-ray image intensifier.

The noise performance of an experimental microchannel plate x-ray image intensifier has been evaluated. The intensifier, constructed for use with photons of energies between 20 and 150 keV, uses an MCP as the photon-to-electron converter. The influence of noise was determined by analysis of the optical-density fluctuations of a photograph of the viewing screen of the intensifier when the conversion layer was exposed to between 1 and 60 mR. Additionally, the contrast-detail performance of the experimental device was determined. The influence of both stochastic noise, due to quantum mottle and pulse-height variations, and structural noise, due to fluctuations in inherent gain from point to point, have been considered by using a model that adds these components.

Models, Theoretical↗
PubMedDate not supplied

Effect of x-ray filtration on dose and image performance of CT scanners.

X-ray source filtration as a means to reduce patient dose while maintaining image quality was investigated for CT scanners. The CT values, their variances for various materials, and the surface dose to a cylindrical phantom were calculated for different filter thicknesses and composition as well as for different tube potentials. Thermoluminescent dosimetry indicated that the maximum dose could be predicted by calculation with an accuracy of 10% (+/- 2 s.d.). The product of the variance of the CT values times surface dose was used to establish the appropriate thickness and composition of the filter, a figure of merit that was independent of dose and noise when the sole source of noise was Poisson statistics. This analysis indicated that source filter materials with an atomic number from 29 to 40 are optimum, and if aluminum is used, the minimum thickness, at 120 kVp, should be 4 mm.

Humans↗
PubMedDate not supplied

Contrast-detail curves for liver CT.

Contrast-detail curves were constructed for liver computed tomographic (CT) images using an objective method. Stimuli were created by superimposing disks at specified locations on sets of 92 normal liver CT images. Bright and dark disks of 9 sizes and 36 possible image contrasts were used. Sets of 92 stimuli were rendered on film at five window widths (64, 128, 256, 512, and 1024 HU). The contrast-detail (CD) curve flattened substantially for disks larger than 7-mm diameter, and its slope (on a log-log plot) was less than predicted from signal-detection theory. Manipulation of display window manipulation had little impact on this disks' visibility. The results indicate that human observers have difficulty visualizing large, low-contrast details on liver CT scans, and suggest that narrowing the display window will have little effect on this limitation.

Contrast Media↗
PubMedDate not supplied

Evaluation of video gray-scale display.

Setting up and maintaining video display monitors properly will help to reduce display variation and improve overall presentation of the radiological image. Display monitor gray-scale characteristics were examined using the SMPTE test pattern. This test pattern may be used as a standard for adjusting brightness and contrast. The controls should be adjusted to display the full dynamic range so that the 5% and 95% signal levels in the pattern are visible. Measured luminance on a laboratory workstation used for radiological perceptual experiments, and on the Siemens CT gray-scale monitor was determined to range from 0.17 to 76.0 nit, and 0.17 to 24.66 nit, respectively. These were compared with the range of approximately 17 to 514 nit for a typical film-viewbox combination. Characteristic curves were determined for both monitors, and CRT gammas were 3.34 and 2.48 for the perceptual workstation and CT console, respectively. The display gamma was determined from fitting luminance data to a log-log plot of luminance versus input gray level. The usefulness of the SMPTE test pattern for visual presentation as well as photometric measurement is demonstrated.

Computer Terminals↗