Biomedical subjects
M A Simons
Publications and source records attributed to M A Simons.
Ipsilateral duplication of the inferior vena cava.
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Perforated duodenal ulcer after gastric bypass surgery.
Gastric bypass procedures have been used widely in the surgical therapy of morbid obesity. Evidence exists that the bypassed gastric segment retains its ability to secrete acid. Acid-related ulceration and obstruction of the proximal gastric pouch after surgery have been well documented, but duodenal ulceration after gastric bypass has yet to be reported. We present the first reported case of duodenal ulceration and perforation after gastric bypass surgery for morbid obesity. This case demonstrates that acid-related gastroduodenal disease may occur in the bypassed gastrointestinal tract. Consideration should be given to this area in evaluating upper gastrointestinal bleeding and abdominal pain after gastric bypass. Because barium contrast studies may not adequately evaluate bypassed segments, and standard gastroscopes are not long enough to reach these areas, the use of longer endoscopes may be necessary to confirm the presence of gastroduodenal disease after gastric bypass.
The influence of expertise on X-ray image processing.
Observers with four different levels of radiological experience performed a recognition memory task on slides of faces and chest X-ray films. Half of the X-ray films revealed clinically significant abnormalities and half did not. Recognition memory for faces was uniformly high across all levels of radiological experience. Memory for abnormal X-ray films increased with radiological experience and, for the most experienced radiologists, was equivalent to memory for faces. Surprisingly, recognition memory for normal films actually decreased with radiological experience from above chance to a chance level. These results indicate that radiological expertise is associated with selective processing of clinically relevant abnormalities in X-ray images. Expert radiologists appear to process X-ray images the way that we all process faces, by quickly detecting and devoting processing resources to features that distinguish one stimulus from another. However, the selective processing of X-ray films appears to be restricted to clinically relevant abnormalities. As they develop the ability to detect these abnormalities, radiologists appear to lose the ability to detect variations in normal features.
Quantitative digital subtraction coronary angiography using videodensitometry. An in vivo analysis.
A videodensitometric method for measuring absolute cross-sectional area and diameter has been tested in living dogs with coronary artery stenoses created surgically by placement of small Silastic cuffs. Coronary arteriograms were performed using a circular tomographic unit to provide multiple views of each lesion, and measurements were made from logarithmically subtracted digital images. Dimensions of 13 stenoses of cross section 1 to 5 mm2 and adjacent reference segments (2 to 9 mm2) were determined by histologic sectioning of the segments after injection with a rapidly hardening plastic fixative under physiologic pressure. Two different methods were tested for calculating cross-sectional area. On 238 measurements, 102 of normal vessel segments and 135 of stenoses, both methods showed good correlation with histologic measurements, with slopes of 0.929 + (SD) 0.037 (r = 0.8563) and 0.948 + (SD) 0.037 (r = 0.8554). Multiple measurements of each segment produced values within 30% of the true absolute cross sectional area in most cases. The method shows promise as a means for quantitating absolute dimensions of vessels in clinical arteriography.
Comparison of observer and videodensitometric measurements of simulated coronary artery stenoses.
To test the applicability of an automated vessel measurement technique to coronary arteriography, a videodensitometric method with caliper measurements on digital subtraction images of a moving coronary artery phantom was compared. Percent diameter stenosis was determined by both methods, revealing a twofold improvement in reproducibility with the videodensitometric method, with percent stenosis being determined within +/- 10% for two different iodine concentrations injected during continuous flow into the simulated coronary arteries. Absolute diameters were also measured by the videodensitometric method, showing a high degree of correlation between measured and true diameter for vessels between 0.5-3.0 mm.
MR vascular imaging with a fast gradient refocusing pulse sequence and reformatted images from transaxial sections.
The authors present a method for obtaining magnetic resonance (MR) images of intra- and extracranial vessels from thin contiguous transaxial sections. A section-selective gradient refocusing pulse sequence with a short repetition time caused flow-related enhancement from spins that flowed perpendicular to the transaxial sections. The signal was further enhanced by means of flow compensation gradients to rephase any phase shifts resulting from moving spins in the presence of the imaging gradients. Coronal and sagittal sections, reformatted from multiple transaxial sections, are shown to have excellent vessel contrast without the use of contrast material. These images were obtained in 12 minutes of acquisition time from as many as 60 sections of 3-mm thickness. Such a technique shows significant promise for MR angiography.
Cross-sectional area measurements by digital subtraction videodensitometry.
A method for measurement of absolute cross-section areas in digital images of iodine-opacified vessels was tested in phantoms containing "normal" segments of circular cross-section and either circular or noncircular "stenoses" over a wide range of iodine concentrations. Accuracy varied with iodine concentration, with a slight tendency to overestimate the area at high concentration (185 mg I/ml) and to underestimate at low concentration (23 mg I/ml). Reproducibility was improved at the higher concentrations, with standard deviation ranging from 2% to 7% of the measured value, compared with 7% to 27% at the lowest concentration. Accuracy and reproducibility of area measurements on either normal or stenotic segments were unchanged by rotation of the vessel by up to 25 degrees out of the plane of the image. This method is easily implemented using computerized image processing techniques and has advantages over either manual or automated edge detection because it eliminates the need for an edge criterion and is independent of the viewing projection.
Falls in the healthy elderly: predisposing causes.
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Vessel diameter measurement using digital subtraction radiography.
A method for obtaining absolute diameter and cross-sectional area measurements on subtraction digital images is described and tested in phantom vessels from 1.5 to 5.5 mm in diameter filled with iodine contrast at concentrations from 23 to 185 mg I/ml. A highly linear correlation of true vs. calculated diameter is demonstrated, with accuracy and reproducibility of the method varying from +/- 1% to 2% at the highest iodine concentration to +/- 30% in the smallest tube at the lowest concentration. A method is described for correction of the observed video density values to allow for nonlinearity of response of the imaging system to iodine density, and its effect on the measured diameters is demonstrated.
Measurement of gait and balance in the elderly.
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Expression of kappa chain allotypes at the cell surface and in serum immunoglobulins of normal and allotype-suppressed heterozygous rabbits.
The kappa light chain allotypes b4 and b5 were measured in the serum and on the surfaces of peripheral blood lymphocytes of normal and allotype-suppressed heterozygous rabbits. Surface immunoglobulins (sIg) were detected by fluorescence microscopy and additional quantitative data were obtained by flow microfluorometry. Although a few b5-suppressed animals had no b5 in serum or on cell surfaces for years, most b5-suppressed and all b4-suppressed animals studied had some cells with sIg of the suppressed type by 1 year of age. In suppressed animals the level of serum Ig remained depressed throughout life but cells with sIg appeared in disproportionately large numbers. The effect was particularly striking in those animals suppressed for the b4 type.
Insurance of horses and the role of the veterinary surgeon.
Various type of insurance policies covering the risks against mortality, economic slaughter and loss of use, breeding failures and payment of veterinary fees are discussed. The role of the veterinary surgeon in supplying certificates of health and in relation to claims, including those involving destruction on humane grounds, are considered.
Expression of b 4 and b 5 chi light chain allotypes by B and pre-B cells in allotype-suppressed and neutralized b4b5 rabbits.
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Pre-B and B cells in rabbits. Ontogeny and allelic exclusion of kappa light chain genes.
Pre-B cells in developing rabbits were identified by immunofluorescence as cells containing small amounts of cytoplasmic IgM (cIgM) but lacking surface immunoglobulin (sIg). During ontogeny the first pre-B cells appeared in fetal liver at 23 days gestation, 2 days before the appearance of sIgM+ B lymphocytes. Pre-B cells were relatively frequent in fetal and adult bone marrow, but were not found in other tissues except rarely in fetal spleen. Allelic exclusion is apparently established at this early stage of development, because individual pre-B cells and B lymphocytes from heterozygous rabbits expressed only one of the alternative alleles in amounts sufficient for detection. Development of isotype diversity among rabbit B lymphocytes followed the general pattern seen in mouse and man. sIgM+ cells were detected before birth. Expression of sIgG was detected in neonatal rabbits on cells which were also sIgM+ but in older animals most sIgG+ cells lacked sIgM. Cells bearing sIgA were not found until 5-6 days of age, and had no other isotype on their surface.