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Biomedical subjects

W Chew

Publications and source records attributed to W Chew.

13 recordsLinked to original sources
PubMed1991

Tuberculosis in Australia: an analysis of cases identified in reference laboratories in 1986-88.

The Special Interest Group in Mycobacteria within the Australian Society for Microbiology has carried out a collaborative study of cases of tuberculosis diagnosed in Australian reference laboratories in the years 1986, 1987 and 1988. Annual totals of 574, 584 and 613 respectively, suggest that the incidence of bacteriologically-positive tuberculosis is continuing at 3-4 cases per 100,000 population. The highest rates were detected in males over 50 and females over 65 years of age. Three-quarters of the total cases relate to pulmonary disease. Resistance to at least 1 anti-tuberculosis drug was detected in 78 (12.7%) of isolates tested in 1988. The negligible decline in incidence of tuberculosis in Australia, the high prevalence in S.E. Asian countries, and the fact that HIV-infection is an important risk factor, make it imperative that Australia's diagnostic and management programmes be maintained.

Adolescent↗
PubMed1990

Fat-saturation MR imaging of the upper abdomen.

The fat-saturation (fatsat) MR technique decreases the signal intensity of fat, thereby enhancing the definition of upper abdominal organs and reducing artifacts while maintaining the T1 and T2 information available on spin-echo sequences. To evaluate the potential of fatsat in examining the abdomen, we conducted a prospective study involving 30 subjects, including four normal volunteers, 18 patients investigated for liver disease, and eight patients studied for miscellaneous abdominal disease. Short TR, 300-600/15-20 (TR/TE), and long TR, 2000-2500/20-30, 70-80, spin-echo images with and without fatsat were compared. The images were evaluated both qualitatively and quantitatively. Qualitative assessment was made with receiver-operating-characteristic (ROC) curve analysis of the confidence level of observers to detect the presence of disease, comparing fatsat with standard spin-echo sequences. ROC analysis showed greater interpreter confidence and accuracy for fatsat sequences than for standard spin-echo sequences. The measured signal-difference-to-noise (SD/N) ratio comparing upper abdominal organs with surrounding tissue revealed the highest values for short TR/TE regular spin echo, followed by short TR/TE fatsat. The highest SD/N ratio for hepatic masses was with long TR/TE fatsat followed by short TR/TE fatsat. The results of this study suggest that the fatsat technique may improve abdominal MR imaging.

Abdomen↗
PubMed1990

Diabetic retinopathy--results of a two year screening programme in two medical units in Singapore.

Three hundred patients with Diabetes Mellitus from 2 medical units in Singapore were screened for retinopathy over a 24 month period. Prevalence of retinopathy in this population was 38% with sight-threatening retinopathy in 17%. Risk factors associated with retinopathy included a longer duration of disease, the presence of hypertension, nephropathy and poor glycaemic control. Prevalence of retinopathy was higher in females. Malays and Indians had higher prevalence of retinopathy than Chinese.

Diabetic Nephropathies↗
PubMed1989

Nicardipine reduces ischemic brain injury. Magnetic resonance imaging/spectroscopy study in cats.

We investigated whether the calcium channel entry blocker nicardipine would reduce ischemic brain damage in barbiturate-anesthetized cats subjected to permanent unilateral occlusion of the middle cerebral artery. The evolution of cerebral injury was assessed in vivo in 24 cats by a combination of proton magnetic resonance imaging and phosphorus-31 magnetic resonance spectroscopy for 5 hours following occlusion. Immediately thereafter, the volume of histochemically ischemic brain tissue was determined planimetrically in triphenyl tetrazolium chloride-stained serial coronal sections. Nicardipine was initially administered as an intravenous bolus injection of 10 mg/kg/hr 15 minutes before or 15 minutes after occlusion, followed by continuous infusion at 8 mg/kg/hr for the 5 hours of the experiment. Compared with untreated controls, cats that received nicardipine before or after occlusion showed a significant reduction in the extent of edema in the ipsilateral cerebral cortex, internal capsule, and basal ganglia. The results of phosphorus-31 magnetic resonance spectroscopy studies suggest that nicardipine may protect against cerebral ischemic damage by an action on cellular metabolic processes that preserve high-energy phosphates during the ischemic period.

Animals↗
PubMed1987

Localized imaging using stimulated echoes.

Stimulated-echo localized spectroscopy was combined with phase- and frequency-encoding gradients to obtain "zoom" or magnified images of specific organs in situ. The technique requires neither surface coils nor an imaging coil arrangement that exclusively isolates the target organ. This technique can be readily applied to conventional spectrometer imagers that have limited computational capabilities.

Animals↗
PubMed1987

An in vivo study of halothane uptake and elimination in the rat brain with fluorine nuclear magnetic resonance spectroscopy.

A recent NMR study reported the elimination of halothane from the brain of rabbits to be ten times slower than expected, based on known anesthetic solubility and cerebral blood flow. The authors conducted a study in five rats using fluorine nuclear magnetic resonance (NMR) spectroscopy to see if major pharmacokinetic discrepancies are associated with the uptake, maintenance, and elimination of halothane from the brain. The rats underwent a 60-min period of halothane anesthesia. They employed a spatially selective NMR spectroscopy technique known as surface coil "depth-pulsing" to assure that the fluorine NMR signals originated in brain tissue, and not in the scalp, muscle, adipose tissue, and bone marrow that surround the brain. After the inspired anesthetic concentration was decreased to zero, the amplitude of the fluorine NMR signal decreased to 40% of its maximum value within 34 +/- 8.0 minutes (n = 5), rather than after 7 h as in the recent study, where the fluorine signal may have contained substantial contributions from metabolites or tissues outside the brain. Fluorine was barely detectable in all of the animals 90 min after stopping the administration of halothane. The authors' results are in agreement with model calculations and several other investigations.

Anesthesia↗
PubMed1987

An in vivo 19F nuclear magnetic resonance study of isoflurane elimination from the rabbit brain.

19F nuclear magnetic resonance spectroscopy was performed at 2.0 Tesla to evaluate the washout of isoflurane from the adult rabbit brain after 90 min of anesthesia. This investigation reconciles previous in vivo NMR studies of others, which observed a slow anesthetic washout, with invasive non-NMR studies that found a rapid washout, as predicted by perfusion-limited models of anesthetic uptake and elimination. Two NMR surface coil experiments were performed: in the first, a 1-cm surface coil was placed directly over the exposed dura to be certain that the washout was observed only from the brain; in the second, a 3-cm coil was placed noninvasively over the intact scalp to emulate previous NMR experiments. As in previous NMR experiments, a slow washout of isoflurane was observed with the large coil. The NMR signal that is observed with the large coil cannot be attributed solely to brain tissue. Fat surrounding the brain contributes significantly to the fluorine NMR spectra that are observed with the 3-cm coil, and its contributions lengthen the apparent washout time. A rapid washout of isoflurane from the rabbit brain was observed with the small coil, whose signal unambiguously arises only from brain tissue. The observed rapid washout is consistent with previous invasive biochemical measurements of anesthetic washout from the brain.

Anesthesia↗
PubMedDate not supplied

Hyperglycemia augments ischemic brain injury: in vivo MR imaging/spectroscopic study with nicardipine in cats with occluded middle cerebral arteries.

Hyperglycemia is often associated with an increased frequency of cerebrovascular disease and exacerbation of neuronal injury in focal ischemic cerebral infarction. We used a combination of high-field proton MR imaging and 1H and 31P MR spectroscopy to investigate whether hyperglycemia would adversely influence cerebral metabolism and eventual infarct size following unilateral occlusion of the middle cerebral artery (MCA) of cats pretreated with the calcium channel blocker nicardipine. Normoglycemic animals injected with 10 micrograms/kg of nicardipine (8 micrograms.kg-1.hr-1 maintenance dose) manifested only mild disturbances in phosphorus metabolism and cerebral pH regulation compared with untreated controls, and showed a significant reduction in infarct size 7 hr after MCA occlusion. By comparison, hyperglycemic cats (plasma glucose, 200-300 mg/dl) had significantly reduced cerebral high-energy phosphates, elevated lactic acid, and larger ischemic lesions in the occluded MCA territory, irrespective of whether they were treated with nicardipine. These results indicate that moderate hyperglycemia can exaggerate ischemic brain damage by enhancing formation of tissue lactic acid and impairing normal phosphorus metabolism. One implication of this study is that dextrose should not be provided to patients with acute ischemic stroke.

Animals↗