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Biomedical subjects

W K Johnson

Publications and source records attributed to W K Johnson.

9 recordsLinked to original sources
PubMed1996

Superparamagnetic iron oxide (SPIO) as an oral contrast agent in gastrointestinal (GI) magnetic resonance imaging (MRI): comparison with state-of-the-art computed tomography (CT).

This study was conducted to compare the sensitivity and specificity of abdominal magnetic resonance imaging using oral superparamagnetic iron oxide with oral contrast-enhanced computed tomography in the detection of GI pathology. Overall sensitivity was calculated to be 83% for OECT compared to 67% by SPIO MRI. Specificity for OECT was 68% compared to 89% for SPIO MRI. The results from imaging with superparamagnetic iron oxide and imaging with oral contrast-enhanced computed tomography were in agreement in 14 subjects who had normal gastrointestinal tracts. In the remaining 16 patients, eight pathologic entities were detected by both modalities whereas 15 abnormalities were seen by only one modality. Superparamagnetic iron oxide magnetic resonance imaging was helpful in discriminating normal bowel from solid lesions and in detecting subtle gastrointestinal tract mass effect. In 30 consecutively studied patients suspected of having GI pathology, OECT was more sensitive than SPIO MRI in detecting abdominal pathology. Conversely, SPIO MRI was more specific than OECT.

Administration, Oral↗
PubMed1994

Primary liver neoplasms: MR imaging with pathologic correlation.

Magnetic resonance (MR) imaging is a powerful tool in the evaluation of primary liver neoplasms. Determination of tumor extent and tissue characterization is provided with standard spin-echo T1- and T2-weighted imaging and is enhanced by the application of advanced sequences such as gradient-echo, fast spin-echo, and fat suppression techniques. Intravenously administered contrast agents, such as gadopentetate dimeglumine and superparamagnetic iron oxide, provide additional opportunities for lesion characterization. Knowledge of the underlying gross and microscopic pathologic features of primary hepatic neoplasms leads to a better understanding of their often complicated MR imaging appearances. The authors correlate the key pathologic features with the most significant MR imaging findings of primary benign and malignant liver neoplasms, including hemangioma, focal nodular hyperplasia, hepatocellular adenoma, infantile hemangioendothelioma, mesenchymal hamartoma, hepatocellular carcinoma, fibrolamellar carcinoma, intrahepatic cholangiocarcinoma, biliary cystadenoma and cystadenocarcinoma, angiosarcoma, hepatoblastoma, and undifferentiated embryonal sarcoma.

Adenoma, Liver Cell↗
PubMed1987

Beta-lactam resistance in Nocardia brasiliensis is mediated by beta-lactamase and reversed in the presence of clavulanic acid.

Forty clinical isolates and the type strain of Nocardia brasiliensis were screened for susceptibility to 20 beta-lactams. Isolates exhibited a single pattern of resistance, with large zones of inhibition by disk diffusion and low MICs by broth and agar dilutions only to cefotaxime, ceftriaxone, ceftizoxime, Augmentin, and Timentin. All strains produced beta-lactamase, with five different enzyme patterns by isoelectric focusing. Despite the differences in their isoelectric points, the enzymes had the same substrate profiles, with equivalent activity against penicillin, ampicillin, cefamandole, cephalothin, and cephalordine. In an in vitro assay, the enzymes were highly susceptible to clavulanic acid. The MIC50 and MIC90 for the combination of amoxicillin and clavulanic acid (Augmentin) was 2 and 4 micrograms/ml, respectively, compared with 16 micrograms/ml for both values for amoxicillin alone. These studies suggest that beta-lactamase is the major mechanism of beta-lactam resistance in this species and that Augmentin is the first oral beta-lactam with good potential for treating infections due to N. brasiliensis.

Amoxicillin↗
PubMed1982

Lung function and morphology of dogs after sublethal exposure to nitrogen dioxide.

The relationship between respiratory function and morphological changes in 10 dogs exposed for 6 h to 69 ppm nitrogen dioxide was studied. Two additional dogs served as controls. Functional assessments included breathing pattern, breathing mechanics, forced expiration, gas exchange, and acid-base status. Gross, microscopic, and ultrastructural evaluations were made of lung tissues from dogs killed at 0.1, 1.0, 2.0, 3.0, 7.0 and 14.0 d after exposure. Functional changes were similar to those reported for man. The principal dysfunction was gas-exchange impairment, apparently resulting from foam in the airways. Breathing-pattern alterations appeared to result from stimulation of neural receptors. Gas-exchange measurements provided the most useful indicators of the pulmonary damage observed in this study.

Animals↗
PubMedDate not supplied

Castleman disease mimicking an aggressive retroperitoneal neoplasm.

A case of Castleman disease of the retroperitoneum in a 26-year-old woman is presented. Sonography, computed tomography, and magnetic resonance imaging demonstrated a large retroperitoneal mass with somewhat heterogeneous imaging characteristics. Although a definitive preoperative diagnosis was not possible, magnetic resonance imaging was useful in delineating the extent of the tumor and defining the characteristics of surrounding soft tissues.

Adult↗
PubMedDate not supplied

Efficacy of hysterosalpingography in evaluating endometriosis.

Endometriosis is a common disease in young women being evaluated for infertility. Although endometriosis may cause tubal abnormalities on hysterosalpingography, efficacy of radiographic evaluation in this disease is not clear. We reviewed the radiographic and laparoscopic examinations in 50 women being studied for infertility. Laparoscopy was normal in 15 women and showed endometriosis in 35 patients. Endometriosis was staged at laparoscopy using the classification of the American Fertility Society. Radiographic examinations were reviewed blindly and tubal status noted in each patient. Criteria for tubal abnormality included incomplete or absent filling and ampullary dilatation or convolution. Radiographic efficacy was determined by correlating the tubal appearance to the severity and location of endometriosis. A total of 98 tubes were correlated but only 10 (10%) were felt to be involved by endometriosis based on laparoscopic findings. Radiologic sensitivity was 40% (4 of 10) and specificity was 83% (73 of 88). Positive predictive value was 21% (4 of 19) due to 15 false-positive diagnoses in tubes uninvolved by endometriosis. In conclusion, endometriosis, regardless of its severity, rarely causes radiographic abnormalities on hysterosalpingography because of the location of disease in the pelvis.

Adult↗
PubMedDate not supplied

Effects of sulfuric acid aerosols on pulmonary function of guinea pigs.

Forty-seven Hartley guinea pigs were exposed for 1 h to approximately 1-micrometer (mass median aerodynamic diameter) sulfuric acid aerosols at concentrations that ranged from 1.2 to 48.3 mg/m3. Ten animals (controls) were exposed to filtered room air only. Eight H2SO4-exposed animals exhibited marked increases in total pulmonary resistance and marked decreases in dynamic compliance. Four of these eight "responsive" animals died during exposure. All other H2SO4-exposed animals exhibited no major difference from controls and were termed nonresponsive. The proportion of responsive to nonresponsive animals increased with exposure concentration, but the magnitude of pulmonary function change was similar for all responsive animals regardless of concentration. Compared to nonresponders, responsive animals had higher preexposure values of tidal transpulmonary pressure excursions and total pulmonary resistance and lower values of dynamic compliance. Preexposure transpulmonary pressure excursions were positively correlated with minute volume only for nonresponsive animals; transpulmonary pressure excursions were positively correlated with total pulmonary resistance in responsive animals. The results suggest that the Hartley guinea pig reacts to inhaled H2SO4 with an essentially all-or-none airway constrictive response and that an animal's sensitivity to this response may be related to its preexposure airway caliber.

Aerosols↗