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Biomedical subjects

K C Li

Publications and source records attributed to K C Li.

88 records · Page 5Linked to original sources
PubMed1979

The collection of arsenic oxide vapor in water-filled impingers.

The efficiency of water as a collection medium for arsenic oxide vapor was investigated. The vapor was generated by passing air over arsenolite (As2O3, s) at various flow rates and temperatures, passed through a particulate filter and then was collected in a series of chilled Greenburg-Smith impingers. It was found that the first impinger always collected at least 90% of the vapor while the remainder, within the limit of detection, was collected in the second impinger. No differences were found between water and 2% sodium hydroxide when used as a collection medium. Up to 15% of the collected arsenic may be absorbed on the walls of the impinger train; this amount will not dissolve in water and will be lost unless the train is thoroughly washed with hydroxide.

Air Pollutants, Occupational↗
PubMed1973

Bimodal effect of insulin on hormone-stimulated lipolysis: relation to intracellular 3',5'-cyclic adenylic acid and free fatty acid levels.

The present study was undertaken to determine the relationship between the antilipolytic and lipolytic effects of insulin on hormone-stimulated lipolysis and the mechanisms of these reactions. The dose-response curve of norepinephrine-stimulated lipolysis in rat adipocytes was not sigmoidal but biphasic in nature. Intracellular free fatty acid levels were linearly related to lipolytic rate and also described a biphasic profile in response to increments in norepinephrine concentration. Intracellular 3',5'-cyclic AMP levels measured 10 min after addition of increasing concentrations of norepinephrine showed a rise and a plateau followed by a secondary rise. Insulin was antilipolytic at low concentrations of norepinephrine and distinctly lipolytic at high concentrations. The combined antilipolytic and lipolytic effect of insulin is termed the "bimodal" effect of insulin on hormone-stimulated lipolysis. The bimodal effect of insulin correlated positively with changes in peak intracellular 3',5'-cyclic AMP levels. In the presence of glucose, insulin invariably enhanced lipolysis. It is suggested that the antilipolytic effect of insulin is achieved by both inhibition of adenyl cyclase activity and activation of low-K(m) 3',5'-cyclic AMP phosphodiesterase, the net effect being a low accumulation of 3',5'-cyclic AMP. On the other hand, the lipolytic effect of insulin probably reflects enhancement of adenyl cyclase activity to an extent that overrides any activation of low-K(m) 3',5'-cyclic AMP phosphodiesterase activity, resulting in an increase in peak adipocyte 3',5'-cyclic AMP levels.

Adenosine Triphosphate↗
PubMedDate not supplied

Power Doppler imaging and resistance index measurement in the evaluation of acute renal transplant rejection.

PURPOSE: This study was designed to test the hypotheses that power Doppler imaging has a predictive value in the assessment of acute renal allograft rejection and that the information garnered from the combination of resistance index (RI) determination and power Doppler imaging has an even greater predictive value in this assessment. METHODS: Power Doppler images obtained prior to 96 sequential renal allograft biopsies in 92 patients with suspected renal transplant rejection were retrospectively graded for parenchymal vascularity on a scale of 1 to 4: 1, normal, uniform cortical flow; 2, mild peripheral cortical hypoperfusion; 3, vascular pruning in cortex and medulla; and 4, no visible parenchymal flow, with flow seen only in central vessels. Power Doppler grades and RIs for these cases were compared to graft biopsy results. RESULTS: No statistically significant association was observed between parenchymal vascularity as graded by power Doppler imaging, RI, and the presence of acute transplant rejection. CONCLUSIONS: Neither grading of vascularity on power Doppler images, RI measurement, nor the combination of these methods is an accurate means of detecting renal allograft rejection.

Acute Disease↗
PubMedDate not supplied

Paramagnetic polymerized liposomes as new recirculating MR contrast agents.

We describe a well-tolerated blood pool contrast agent with extended recirculatory half-life based on paramagnetic polymerized liposomes (PPLs). PPLs were constructed from a new type of polymerizable lipid molecule that has a derivative of gadopentetate dimeglumine as the hydrophilic head group and diacetylene groups in the hydrophobic acyl chains, which cross-link when irradiated with ultraviolet (UV) light. Biodistribution, blood pool half-life, and MR image enhancement were determined for PPLs composed of 10% of the gadopentetate dimeglumine lipid and 90% of ditricosadiynoyl tricosadiynayl phosphatidylcholine (DAPC) at a dose of 0.015 mmol Gd+3/kg in rats. In T1-weighed MR images (TR/TE = 400/18 msec), an average signal enhancement of 34% in the kidneys and 20% in the liver was observed, which persisted for at least 90 minutes after administration of the PPLs. Biodistribution studies using radiolabeled PPLs confirmed that 80% of the injected dose remained in the blood pool after 2 hours. The half-life of elimination from the blood pool was 19 hours. The preparation was well tolerated in rats and produced similar MR contrast enhancement of the blood pool as produced by other liposome contrast agents. However, the half-life of PPL elimination from the blood pool was prolonged relative to other liposome systems.

Animals↗
PubMedDate not supplied

Placenta accreta: MRI antenatal diagnosis and surgical correlation.

We describe a case of a placenta previa accreta that was diagnosed antenatally by MRI with subsequent surgical confirmation. We show the advantages of ultrafast MRI single shot (SS) fast spin echo (FSE) techniques for accurate diagnosis with minimal scan time and fetal motion artifacts.

Adult↗
PubMedDate not supplied

Benign liver tumors.

This article discusses the most important benign liver tumors, both in adult and pediatric patients. A pathologic discussion of each neoplasm is included to provide a basis for understanding the radiologic-pathologic correlation that is used throughout the monograph. The benign liver tumors are presented according to their frequency. Therefore, hemangioma, the most common primary benign liver neoplasm, is discussed first, followed by focal nodular hyperplasia, hepatocellular adenoma, and the benign primary pediatric tumors--infantile hemangioendothelioma and mesenchymal hamartoma. Finally, a brief discussion of nodular regenerative hyperplasia and other rare hepatic masses is included. Bile duct cyst (simple, non-parasitic cyst of the liver) is not included since it is not a neoplasm. Likewise, cystadenoma is not discussed since it originates from the biliary duct cell and is appropriately included in the biliary neoplasms category.

Carcinoma, Hepatocellular↗
PubMedDate not supplied

Sensitivity and specificity of MRI in detecting malignant spinal cord compression and in distinguishing malignant from benign compression fractures of vertebrae.

The accuracy of magnetic resonance (MR) imaging in the detection of metastatic compression of the spinal cord and the cauda equina (MCCE) in 75 patients with known primary malignancy outside the central nervous system is determined retrospectively by comparing the MR results with findings of myelography, surgery, clinical follow-up and autopsy. The sensitivity is 93%, the specificity 97% and the overall accuracy 95%. The signal intensity measured in the sagittal MR images of a collapsed vertebral body is divided by that of an average of three adjacent normal vertebrae to form a signal intensity ratio (SIR). The SIRs of 41 metastatic and 15 post-traumatic collapsed vertebrae are calculated. A ratio of 0.8 has the most differentiating power. All benign and one malignant compressed vertebrae have SIRs greater than 0.8.

Cauda Equina↗
PubMedDate not supplied

MRI in osteoarthritis of the hip: gradations of severity.

In a prospective study, 10 patients with well-documented osteoarthritis (O.A.) of the hips were imaged using spin-echo pulse sequences (TR = 0.5 to 1.5 s and TE = 28 to 60 ms). After analyzing the changes observed, an MR grading system for assessing severity of O.A. in the hips was developed. Using this grading system and an established grading system for osteoarthritis using roentgenograms (both systems use grades 0-4), two radiologists independently graded the MR studies and plain films separately, twice. The roentgenogram grading system was more accurate in predicting symptoms in the more severe cases, whereas the MR grading system was slightly more useful in the less severe cases. Our results show that MR can demonstrate a spectrum of changes of O.A. in the hips. Its ability to directly image articular cartilage makes it a powerful research and clinical tool.

Adult↗
PubMedDate not supplied

Normal variations of pelvic fat distribution implications on CT staging of pelvic tumors.

In order to determine the normal variations of pelvic fat distribution, 25 men and 25 women normal pelvic computer tomography (CT) scans were reviewed. No distinct fat planes were demonstrated between the prostate and pelvic side walls, bladder and seminal vesicles, and prostate and rectum in 69%, 81%, and 86% of the men patients, respectively. Similarly, there were no distinct fat planes between the uterus and pelvic side walls, and uterus and rectum in 86% and 96% of the women patients, respectively. We conclude that there are no distinct fat planes around pelvic organs in the majority of normal people and this may be a major source of error in the CT staging of pelvic tumors.

Adipose Tissue↗
PubMedDate not supplied

Polymeric contrast agents for magnetic resonance imaging: synthesis and characterization of gadolinium diethylenetriaminepentaacetic acid conjugated to polysaccharides.

The synthesis and characterization of polysaccharides esterified with gadolinium diethylenetriaminepentaacetic acid (GdDTPA) are described. The results of several synthetic methods are presented for esterification of dextrans and inulin with DTPA. One method results in highly conjugated products labeled with an average of 0.4 mol of GdDTPA/mol of glucopyranose unit in dextrans of up to 70,800 average molecular weight and 0.5 mol of GdDTPA/mol of fructofuranose unit in inulin. Chromatographic and potentiometric evidence supporting the absence of significant chelate cross-linking of the conjugated polysaccharides is presented. The thermodynamic stability constant, log K (Gd3+ + L4(-)----GdL-), of the complexes was 18.0 +/- 0.2 based on an independent chelate model. In vitro ester hydrolysis of the GdDTPA-dextran 70,800 (at 37 degrees C, pH = 7.4 phosphate buffer) occurs with a half-life of 21 h. The agents exhibit T1 relaxivities ranging from 1.5 to 2.3 times that of GdDTPA at 100 MHz, and decreasing in vitro relaxivity with increasing molecular weight of the dextran carrier was observed. Phantom MRI studies indicate that the T1 and T2 effects of the complexes differ from those of GdDTPA, with the polysaccharide-bound complexes exhibiting a considerably faster drop in relative signal intensity with increased concentration in T1 and T2 weighted pulse sequences.

Chemical Phenomena↗
PubMedDate not supplied

MR imaging of Pelizaeus-Merzbacher disease.

Pelizaeus-Merzbacher disease (PMD) is a rare, slowly progressive, sex-linked demyelinating disorder generally classified with the sudanophilic leukodystrophies. The onset is most often in the pediatric age group and may be diagnosed as cerebral palsy because of the subtle onset. Cranial magnetic resonance (MR) imaging of two patients with PMD showed reversal of the normal gray/white matter signal relationships, consistent with dysmyelination, as well as low intensity lentiform nuclei and thalami possibly suggesting pathologic iron deposition. Magnetic resonance also better demonstrated low volume brain without the beam hardening limitations of X-ray CT. Although our MR findings correlate well with the pathophysiology of PMD, the MR characteristics are not specific. The diagnosis of PMD remains one of clinical and laboratory exclusion.

Adolescent↗
PubMedDate not supplied

Do arterial phase helical CT images improve detection or characterization of colorectal liver metastases?

Our goal was to determine if arterial phase images from dual phase helical CT improve either the detection or the characterization of hepatic metastases in patients with colorectal carcinoma. Sixty-two patients with known colorectal cancer underwent 65 dual phase helical CT examinations to evaluate for possible liver metastases. Three blinded reviewers independently evaluated the portal venous phase images alone to determine if hepatic metastases were present or absent. Arterial phase images were then analyzed to determine if they identified additional lesions or aided in characterizing small hepatic lesions. Scores of the two methods for diagnosing metastases were compared with the "gold standard" established by a consensus panel of three other radiologists who reviewed all images together with clinical, pathologic, and other imaging data. The addition of arterial phase imaging did not detect any new metastases. However, in 6 of the 64 technically adequate examinations, hepatic arterial phase images increased lesion conspicuity and significantly increased diagnostic confidence when compared with portal vein phase scans alone. In patients with colorectal cancer, the addition of arterial phase imaging does not increase sensitivity, but improves the specificity in diagnosing liver metastases in a small number of cases. Dual phase helical CT does not appear to be indicated in the evaluation of liver metastases from colorectal cancer.

Adult↗
PubMedDate not supplied

Conventional and CT metrizamide myelography in Arnold-Chiari I malformation and syringomyelia.

Four normal controls and 26 cases of Arnold-Chiari I malformations and/or syringomyelia were reviewed. The pathologic cases included five isolated Arnold-Chiari I malformations, nine communicating syringomyelia, five idiopathic syringomyelia, four posttraumatic syringomyelia, one syringomyelia with hemangioblastoma, and two postshunt syringomyelia. The objectives of this study were to compare the accuracy of conventional metrizamide myelography with CT metrizamide myelography and to study indirectly the hydrodynamics of CSF flow in syringomyelia by comparing the sequential enhancement patterns of the spinal cords and cord cavities in the different groups of patients. Twenty-five patients underwent conventional metrizamide myelography immediately before CT metrizamide myelography, and one patient underwent CT metrizamide myelography only. Scans were obtained 1-2 hr, 4-8 hr, and 12-24 hr after injection of metrizamide, but not all patients were scanned during all three intervals. CT metrizamide myelography was found to be more sensitive than conventional metrizamide myelography in the diagnosis of both Arnold-Chiari I malformation and syringomyelia. Performing just an immediate and a delayed scan was found to be more cost-effective than doing all three scans. Contrary to previous reports, it was found that delayed (12-24 hr) scans demonstrated more syrinx cavities than intermediate ones. In studying the sequential enhancement patterns of the spinal cords and cord cavities, some interesting trends were observed that tend to support the theories of Aboulker and of Ball and Dayan of transneural passage of CSF into cord cavities in syringomyelia.

Adult↗
PubMedDate not supplied

Acquired hepatocerebral degeneration: MR similarity with Wilson disease.

Acquired hepatocerebral degeneration (AHD) is a neurologic syndrome occurring in the presence of chronic hepatic disease, which results in permanent neurologic aberrations. The syndrome shares many of the clinical manifestations of Wilson disease, however, distinction can be made with slit lamp examination and biochemical studies. Cranial magnetic resonance (MR) imaging of a patient with AHD revealed increased signal intensity in the dentate nuclei bilaterally on T2-weighted images indistinguishable from Wilson disease. The MR findings of Wilson disease as described in the literature are not specific and further investigation with slit lamp examination and biochemical studies is warranted to distinguish between the two entities.

Adult↗