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C R Meyer

Publications and source records attributed to C R Meyer.

At least 109 records · Page 6Linked to original sources
PubMed1988

Anisotropic ultrasonic backscatter from the renal cortex.

We have demonstrated a significant, directionally dependent, anisotropic, echogenicity from the cortices of two sheep kidneys and a normal human cadaver kidney. The anisotropy corresponds to the relationship of the sound field to the medullary rays and interlobular arteries. At 7.5 MHz, the backscatter from specimens of cortex of a sheep kidney was 4.7 +/- .7 dB (mean +/- SEM) greater in parts of the cortex where the field was perpendicular to these structures as opposed to where it was parallel to them. In addition, we measured the angular distribution of this anisotropy and compared it to the 5 dB inclusion angle of the 5 MHz linear array that was used in measurements on the whole kidney specimens. The transducer inclusion angle was 10 degrees +/- 2 degrees, while the angular distribution was 34 degrees +/- 22 degrees and 23 degrees +/- 11 degrees (mean +/- SD) for the intact sheep and human kidney, respectively, demonstrating some variation of the medullary rays from perfect specular reflectors. This anisotropy should be visible in standard diagnostic scanning, and its recognition could increase ultrasound's sensitivity for the detection of renal disease.

Animals↗
PubMed1988

Lesion detectability in ultrasonic computed tomography of symptomatic breast patients.

From 95 subjects imaged with both speed of sound and attenuation ultrasonic computed tomography (UCT), analyses were performed on 40 cases for which unequivocal clinical diagnoses were available for correlation. This paper describes the UCT image characteristics and addresses the hypothesis that carcinomas and other lesions can be detected and localized by means of simple visual criteria or lesion characteristics that are quantitative relative to those of other breast tissues in the same patient. The most useful within-patient criterion was selection of the solid mass with the highest speed of sound in either breast (12 of 12 carcinomas). Architectural asymmetry between breasts in the three types of images was a significant contributing factor in visual image interpretation in seven of the eight cancer patients in whom there were comparable images of both breasts. Solid masses were discriminated by attenuation coefficient and pulse echo criteria. Our results did not substantiate the hypothesis that the average speed of sound throughout the cancer containing breast would be higher than in the contralateral breast. These results are better than might be expected from pulse echo imaging alone on this population. However, clinical implementation probably should be deferred until the technique is made more convenient and less expensive, or more accurate with a greater promise for diagnosis of minimal cancers.

Breast↗
PubMed1988

A simple and accurate spectrophotometric assay for phosphoenolpyruvate carboxylase activity.

The rate of phosphoenolpyruvate carboxylase activity measured through the conventional coupled assay with malate dehydrogenase is underestimated due to the instability of oxaloacetate, which undergoes partial decarboxylation into pyruvate in the presence of metal ions. The addition of lactate dehydrogenase to the conventional assay allows the reduction of pyruvate formed from oxaloacetate to lactate with the simultaneous oxidation of NADH. Then, the enzymic determination of substrate and products shows that the combined activities of malate dehydrogenase and lactate dehydrogenase account for all the phosphoenolpyruvate consumed. The net result of the improved assay is a higher V(max) with no apparent effect on K(m). The free divalent cation concentration appears to be the major factor in the control of the rate of oxaloacetate decarboxylation.

Journal Article↗
PubMed1988

Kinetic studies of the form of substrate bound by phosphoenolpyruvate carboxylase.

Phosphoenolpyruvate carboxylase isolated from maize (Zea mays L.) leaves was assayed with varying concentrations of free phosphoenolpyruvate at several fixed-varying concentrations of free magnesium higher than required to saturate the enzyme reaction. These assays produced velocity data which were found to form a family of individual lines when plotted against free phosphoenolpyruvate or against total phosphoenolpyruvate, but not when plotted against the concentration of the complex of phosphoenolpyruvate with magnesium. In this latter case, the points from all the fixed-varying concentrations fell on the same line, which can be fitted to a modified Michaelis-Menten equation with a multiple correlation coefficient R(2) = 0.995. Similar results were obtained when the enzyme from the C(4) plant maize was assayed with manganese rather than magnesium and when phosphoenolpyruvate carboxylase from leaves of the C(3) plant wheat (Triticum vulgare Vill.) was assayed with magnesium. However, at pH 7.0 the enzyme from the Crassulacean acid metabolism plant Crassula argentea did not produce a satisfactory single line when plotted against the complex of metal ion and substrate, but did so when the assay pH was raised to 8.0. It is concluded that in general the preferred form of substrate for phosphoenolpyruvate carboxylase is the complex of phosphoenolpyruvate with the metal ion.

Journal Article↗
PubMed1988

Adaptive histogram equalization in digital radiography of destructive skeletal lesions.

Adaptive histogram equalization, an image-processing technique that distributes pixel values of an image uniformly throughout the gray scale, was applied to 28 plain radiographs of bone lesions, after they had been digitized. The non-equalized and equalized digital images were compared by two skeletal radiologists with respect to lesion margins, internal matrix, soft-tissue mass, cortical breakthrough, and periosteal reaction. Receiver operating characteristic (ROC) curves were constructed on the basis of the responses. Equalized images were superior to nonequalized images in determination of cortical breakthrough and presence or absence of periosteal reaction. ROC analysis showed no significant difference in determination of margins, matrix, or soft-tissue masses.

Bone Neoplasms↗
PubMed1988

Feasibility of high-resolution, intravascular ultrasonic imaging catheters.

A small-aperture, prototype ultrasonic imaging system, typical of the size necessary to be embedded in a catheter, was developed to evaluate the feasibility of intravascular ultrasonic imaging catheters (UICs). The evaluation included in vitro imaging of postmortem samples of human femoral and iliac arteries with the UIC prototype and a high-resolution magnetic resonance (MR) proton imager. Excellent correlations between results from the UIC images, MR images, and tissue specimens were demonstrated. Although the current prototype is too large to be useful in examination of smaller vessels such as coronary arteries, the signal-to-noise ratio and resolution obtained indicate that imaging with intravascular UICs is feasible and may have significant diagnostic value.

Arteries↗
PubMed1987

Flow effects in multislice, spin-echo magnetic resonance imaging. Model, experimental verification, and clinical examples.

Flowing blood is responsible for a number of complex effects on clinical magnetic resonance (MR) images. To help elucidate these effects, a computer model of a conventional multislice spin-echo pulse sequence was developed. Using TR, TE, and direction of slice acquisition, the model calculates and plots a profile of MR signal intensity vs. z-axis velocity. The model predicts complex profiles with multiple segments of MR signal loss depending on TR, TE, direction of flow, sequence and timing of slice excitation, and slice location relative to adjacent slices. Model predictions were verified by imaging a bulk-flow phantom, consisting of a rotating cylinder filled with a manganese chloride solution with T1 = 840 msec and characterized by a velocity-gradient resolution of 0.23 cm/sec/pixel. In conventional spin-echo MRI of medium and large vessels using body coils, in which the velocity gradients exceed 2-5 cm/sec/pixel, most of the flow artifacts are averaged and are difficult to appreciate. However, bright crescents or rings of MR signal occasionally are seen in the inferior vena cava and portal vein, which the model is invoked to explain. The bulk-flow phantom will find use as a tool for calibrating flow-sensitive pulse sequences when these become widely available.

Blood Circulation↗
PubMed1987

Chemical shift-based true water and fat images: regional phase correction of modified spin-echo MR images.

The process of separating water and fat signal in magnetic resonance images with the Dixon pulse sequence is hindered by phase errors in the water-fat opposed image. These errors arise from static field inhomogeneities, varying magnetic susceptibilities of different body tissues, and other causes. Phase correction performed with data from phantom imaging can compensate for static field inhomogeneities but not for the other effects. A regional phase-correction algorithm is presented that removes non-chemical-shift phase effects and produces true water and fat images. The technique has been applied with good results to 21 patients and healthy volunteers. The images include ones of the abdomen, knees, hips, spine, and head. This method of regional phase correction is an efficacious way of producing separate water and fat images with the Dixon pulse sequence.

Adipose Tissue↗
PubMed1984

Sperm count results from 861 American chemical/agricultural workers from 14 separate studies.

This article presents data from 861 men who have participated in 14 separate occupational studies on testicular function. This population represents the largest series taken from occupational studies. The mean and median sperm counts were 107.1 and 83.0 million/ml of semen, respectively. The percentage of men with sperm counts less than 20 million/ml of semen was 8.7%. No significant differences were noted for age or race. A major issue in occupational studies requiring semen samples is how to successfully recruit the target population to participate. The number of semen samples requested can influence willingness to participate. Data from 137 men, each with three separate sperm counts, indicate that a single sample will suffice for an occupational study.

Adult↗
PubMed1984

Ultrasonic computed tomography of the breast. Improvement of image quality by use of cross-correlation time-of-flight and phase-insensitive attenuation measurements.

The authors present two methods of reducing refraction artifacts in ultrasonic computed tomography of the breast. Measuring the time of flight of sonic pulses by cross-correlation instead of leading-edge detection significantly reduces distortion and improves resolution in speed-of-sound images. Phase-insensitive reception of pulse energy across a large aperture array is shown to be superior to a conventional single-element transducer for attenuation imaging.

Breast Diseases↗
PubMed1984

Estimation of ultrasonic attenuation and mean backscatterer size via digital signal processing.

The backscattered rf signals from the lungs of fetal sheep during their last trimester of development were digitized and processed in an attempt to correlate ultrasonic parameters with measured functional parameters related to lung maturation. The broadband, post- TGC , rf signal of a commercial B-mode ultrasonic scanner was digitized at a sampling rate of 25 MHz. Sorting excluded data from regions of rib shadowing and other nonlung structures from analysis. The sorted data were used to estimate the slope of the ultrasonic attenuation coefficient with respect to frequency via linear regression on the average difference of the logarithm of power spectra from separated data segments. The power spectra were also corrected for attenuation, averaged and used to compute the power cepstrum of the backscattered signal which can be related to mean backscatterer radius. Results are presented for eight fetal sheep.

Animals↗
PubMed1984

Critical review of studies relating occupational exposures of males and reproductive capacity.

At this point, DBCP appears to be the chemical agent with the most recognizable effect on the testis of any chemical studied in regard to occupational exposure. The impact DBCP has upon the testis is gross in character, as manifested by markedly decreased sperm counts. With the discovery of new sensitive laboratory analytical techniques and the use of sophisticated epidemiological methods, new studies will help define the impact of occupational exposures to chemical and physical agents on the reproductive potential of man.

Carbon Disulfide↗
PubMed1983

Automatic computer processing of digital 2-dimensional echocardiograms.

Quantitative studies of left ventricular function using 2-dimensional echocardiography have been limited because of a lack of computerized methods to automatically analyze the echocardiographic images. Previous computer efforts have been directed at digitizing the video output of the 2-D echocardiogram, but this digitizing method has significant limitations. A direct digitization method that produces improvement in signal-to-noise ratio and, subsequently, improved automatic detection of endocardial and epicardial borders, was developed. With definition of these edges, left ventricular global and regional analysis is possible frame by frame so that dynamic changes in cardiac function may be assessed throughout the cardiac cycle. Further technologic advances in 2-D echocardiographic acquisition and image processing should allow computer processing of 2-D echocardiographic data in real time.

Computers↗
PubMed1983

Hazardous chemical exposure at a municipal wastewater treatment plant.

The use of municipal wastewater treatment plants for the disposal of industrial wastes creates the potential for the exposure of treatment plant workers to hazardous chemical compounds that may be present in these wastes. Urine from workers and air and wastewater samples from a municipal wastewater treatment plant receiving wastes from a pesticide manufacturer were analyzed on several occasions by electron-capture gas chromatography for the presence of the compounds hexachlorocyclopentadiene (HEX) and hexachlorobicycloheptadiene (HEX-BCH) which are present in the waste stream from this industry. HEX-BCH was detected more frequently in urine from these workers than in urine from workers at another municipal wastewater treatment plant in the same city. Urine concentrations of HEX-BCH were found to be higher in specimens collected late in the work shift than in those collected earlier. The primary rate of exposure is thought to be by inhalation. This is the first known report of these compounds being detected in human urine and it demonstrates the potential for wastewater treatment plant worker exposure to industrial wastes.

Air Pollutants, Occupational↗
PubMed1983

Environmental hazards of interest to the forensic pathologist.

The hazards associated with occupational exposure to various workplace contaminants (lead, silica, etc.) have been known for a number of years. Until recently, the potential toxic effects of exposures on the male reproductive system had not been appreciated. This article not only discusses recent studies in that area, but gives clinical examples of how environmental exposures (water, soil, air, and dwellings) can affect various organs in the human body. Awareness that these injuries can occur without obvious relationship to these environmental exposures may help the forensic pathologist discover previously unsuspected hazards.

Adult↗
PubMed1983

Liver dysfunction in residents exposed to leachate from a toxic waste dump.

It has been estimated that there are some 30,000 chemical waste dumps in the United States. Many of these landfill operations were undertaken in the early 1950s and 1960s, when knowledge regarding the safe and prolonged containment of the waste buried was nonexistent or minimal at best. As a result, many of these dump sites were located in areas that were geologically unsuitable for toxic chemical wastes. The Love Canal area in Niagara Falls, NY, is probably the best known of these dump sites. While a few of these sites have attracted wide media coverage, the availability of objective scientific information regarding the health effects of such sites has been deficient. The present study of a large toxic waste dump located in Hardeman County, TN, its contamination of surface and underground aquifers and the health effects on the area residents exposed via ingestion of contaminated water, offers the first objective evidence of organ dysfunction in such a human population. During this study comprehensive evaluation of that population revealed multiple symptoms, evidence of hepatomegaly and elevated liver function tests apparently caused by ingestion of water contaminated by numerous organic chemicals, many of which are known to be hepatotoxins.

Adolescent↗