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Biomedical subjects

W K Chong

Publications and source records attributed to W K Chong.

At least 55 records · Page 3Linked to original sources
PubMed1998

Intraoperative ultrasonographically guided cryoablation of renal masses: initial experience.

The purpose of this study was to evaluate the feasibility of intraoperative ultrasonography to guide cryoablation of renal masses. Renal cryoablation was performed on six patients with solid renal tumors. Under ultrasonographic guidance, cryoprobes measuring 3 mm in diameter were placed into the renal tumor parenchyma or into surrounding normal parenchyma. Intraoperative ultrasonography accurately delineated tumor size, cryoprobe placement, and depth of freezing. An echogenic interface was generated by the marked impedance differences at the junction of the normal renal parenchyma and frozen tissue. In addition, intraoperative ultrasonography identified a total of nine additional lesions in three patients that were not detected by preoperative imaging. These lesions also were treated cryosurgically during the same operation. There were no deaths. The patients have been followed with clinical and laboratory assessments as well as with MR imaging or CT scanning, and all have remained tumor free 3 to 22 months postoperatively. Ultrasonographically guided renal cryoablation is a feasible technique for treating malignant renal tumors while preserving renal parenchyma. Long-term follow-up studies in a larger series of patients are required to determine the true efficacy and safety of this procedure.

Aged↗
PubMed1997

Diffusion weighted magnetic resonance imaging of compromised tissue in stroke.

Diffusion weighted imaging (DWI) and T2 weighted magnetic resonance imaging were performed on at least two occasions in 28 children presenting with stroke. In previous reports of DWI in human stroke, eventual infarction was observed (with only one exception) in all regions in which early DWI hyperintensity occurred. In the present report, two children had regions of DWI hyperintensity which did not progress to infarction. One patient who presented with right hemiplegia showed extensive high signal on DWI, with T2 evidence of tissue swelling but without hyperintensity. DWI changes persisted over weeks, with no imaging indication of infarction. This child recovered completely. A second child who had a major vessel infarct with concomitant regions of hyperintensity on T2 weighted imaging and DWI, also had DWI hyperintensity in an adjacent territory which did not develop any subsequent evidence of infarction. Thus in clinical practice DWI can demonstrate tissue which is compromised but not irreversibly so.

Brain↗
PubMed1997

Correlation of MRI and neuropathology in AIDS.

OBJECTIVE: To assess the correlation between findings on radiological and neuropathological examinations of the brain. METHODS: The formalin fixed brains of 19 patients who had died of AIDS were examined by MRI and neuropathology. RESULTS: The rate of identification of cerebral atrophy was similar radiologically and neuropathologically. However, only in half of these cases were the two examinations concordant in the diagnosis. Furthermore, in the 15 brains which had radiological diffuse white matter lesions, the underlying pathology was heterogeneous. CONCLUSIONS: The possible reasons for the inconsistencies, and their relevance to the interpretation of imaging studies, are discussed. The study suggests that the qualitative identification of atrophy in the postmortem brain is problematical and that diffuse white matter lesions seen on MRI are not indicative of a specific pathological process.

Acquired Immunodeficiency Syndrome↗
PubMed1997

Proton Spectroscopy in a Cross-Section of HIV-Positive Asymptomatic Patients Receiving Immediate Compared with Deferred Zidovudine (Concorde Study).

The purpose of this study was to examine by proton spectroscopy for any difference in cerebral metabolites in patients taking part in the Concorde study (comparing the efficacy of immediate versus deferred treatment with zidovudine on asymptomatic HIV infected individuals). Forty seven HIV positive male patients [29 immediate, 18 deferred zidovudine] were examined in the last 9 months of the therapeutic trial. Magnetic resonance imaging and proton spectroscopy were performed at 1.5 Tesla using a single voxel placed in the parieto-occipital white matter. No significant difference was found in metabolite ratios comparing immediate versus deferred zidovudine (NA/NA+Cho+Cr 0.52 vs. 0.52). High quality spectra were acquired in relatively large numbers of patients and logistically spectroscopy may be applied to clinical therapeutic studies.

HIV Infections↗
PubMed1996

A multicenter proton magnetic resonance spectroscopy study of neurological complications of AIDS.

Human immunodeficiency virus (HIV) infection as seen in Europe and the United States has predominantly been contracted through male homosexual sex or intravenous drug abuse. In infected subjects, the brain is frequently affected both clinically and neuropathologically. The aim of this multicenter study has been to evaluate the value of single-voxel proton magnetic resonance spectroscopy (MRS) in the assessment of the neurological complications of acquired immunodeficiency syndrome (AIDS). MRS (voxel size = 8 ml, TR/TE = 1600/135 msec) was performed in 137 HIV-1-seropositive patients and 64 healthy controls without risk factors at three clinical MR sites operating at 1.5 T. The first result of this multicenter trial is that good reproducibility of results among participating sites was found. This demonstrates the reliability and robustness of MRS in the study of in vivo brain metabolism. In HIV patients, there was no significant correlation between metabolite ratios of brain detected by MRS and CDC grouping of patients or CD4 count. In contrast, the variations of brain metabolite ratios (NA/Cr, NA/Cho, and Cho/Cr) were related to the occurrence of encephalopathy, brain atrophy, or diffuse white matter lesions. There was no significant difference in brain metabolites between male homosexual AIDS patients and male intravenous drug user AIDS patients, whatever their neurological status (neurosymptomatic or neuroasymptomatic). Thus, the mode of transmission of HIV infection does not appear to affect the cerebral changes observed in the proton spectra from AIDS patients. Because of its ease of implementation and high information content, single-voxel proton MRS is likely to play a significant role in the evaluation of HIV-related encephalopathies.

Acquired Immunodeficiency Syndrome↗
PubMed1996

Cerebral magnetic resonance relaxometry in HIV infection.

A prospective, cross-sectional study was designed to determine the magnetic resonance relaxation times of cerebral white matter in human immunodeficiency virus (HIV) infected individuals. T1 and T2 were estimated at 1.5 T using four-point methods. Seventy-five HIV-1 seropositive subjects, 48 seronegative blood donors, and 17 seronegative homosexual men were studied. Associations between relaxometry and clinical classification, neurological status, immunological status, and qualitative MRI were investigated. Statistically significant differences in white matter T1 relaxation time were found comparing low-risk control and AIDS groups (p < .005), seropositive subjects with neurological signs and those without (p < .005), and subjects with low (CD4 < or = 200 x 10(6)/l) and high (CD4 > 200 x 10(6)/1) CD4 cell counts (p < .05). These findings add to the body of information that reveals no HIV-related change in the brain before the onset of symptomatic immunosuppression and go someway to validating the previous visually rated, qualitative findings. Statistically significant difference in white matter T2 relaxation time were also found comparing the two control groups (p < .005) highlighting the need for appropriate controls.

AIDS Dementia Complex↗
PubMed1996

The effectiveness of papilledema as an indicator of raised intracranial pressure in children with craniosynostosis.

Craniosynostosis management partially depends on the detection and treatment of elevated intracranial pressure (ICP). Examination for papilledema is considered to be the most reliable screening method for identifying raised ICP, but its effectiveness has not been defined. One hundred and twenty-two children with craniosynostosis who underwent funduscopic examinations and then Camino ICP monitoring were studied. All eye examinations were performed by an ophthalmologist after pharmacological pupillary dilation. Fifteen patients (12%) had papilledema. Subsequent ICP monitoring showed that the median ICP was 12.7 mm Hg, with 41 patients (34%) having elevated ICPs (> 15 mm Hg). Those with papilledema had higher ICPs (17.5 +/- 3.2 versus 12.7 +/- 5.5 mm Hg), were older (5.9 +/- 4.7 versus 1.9 +/- 2.6 years), and were more likely to have craniofacial syndromes (73 versus 41%) than those without papilledema (P < 0.05). Patients with both elevated ICPs and papilledema were older (5.9 +/- 4.7 versus 1.6 +/- 1.4 years) and more likely to have multiple-suture synostosis (92 versus 61%) than those with elevated ICPs and no papilledema (P < 0.05). The presence of papilledema was a specific (98%) indicator of raised ICP, but its sensitivity was age-dependent. It was 100% sensitive in children older than 8 years, but it indicated elevated ICP in only 22% of younger patients. These results suggest that ICP monitoring to document elevated ICP is unnecessary in children older than 8 years who have detailed ophthalmological examinations. In the younger child, the presence of papilledema reliably indicates elevated ICP but its absence does not rule out elevated ICP; formal ICP measurement has a greater role in detecting elevated ICP in these patients.

Adolescent↗
PubMed1996

The beaten copper cranium: a correlation between intracranial pressure, cranial radiographs, and computed tomographic scans in children with craniosynostosis.

OBJECTIVE: The beaten copper appearance of the cranium, as well as other cranial radiographic and computed tomographic findings in children with craniosynostosis, is often interpreted by clinicians as evidence of elevated intracranial pressure (ICP). However, a correlation between radiological findings and ICP measurements has not been previously demonstrated, and their usefulness in detecting elevated ICP has not been defined. METHODS: To address those issues, 123 children with craniosynostosis who had cranial radiographs and ICP monitoring were studied. To assess the specificity of certain radiological findings to patients with craniosynostosis, cranial radiographs of patients with craniosynostosis were compared to those of age- and sex-matched controls. In patients with craniosynostosis, findings on cranial radiographs were compared to computed tomographic scans of the brain. Radiographic findings were then correlated with ICP measurements obtained while the patient was sleeping, which was measured using a Camino fiberoptic ICP monitor (Camino Laboratories, San Diego, CA). All radiographs were independently analyzed by two radiologists who were blinded to clinical and ICP data. RESULTS: A diffuse beaten copper pattern, erosion of the dorsum sellar, and suture diastasis were seen more commonly in patients with craniosynostosis than in controls (P < 0.05), but the presence of the beaten copper pattern was no more common in children with craniosynostosis. ICP was greater when a diffuse beaten copper pattern, dorsum sellar erosion, suture diastasis, or narrowing of basal cisterns was present (P < 0.05). CONCLUSION: Although this study demonstrates that some cranial radiographic and computed tomographic findings do correlate with elevated ICP, the sensitivity of radiological methods for detecting elevated ICP is universally low and they are not recommended to screen for elevated ICP in children with craniosynostosis.

Child↗
PubMed1996

Painful and painless ophthalmoplegia with cavernous sinus pseudotumour.

Acquired isolated ophthalmoplegia in childhood has many potential causes. Although other ophthalmological or clinical features may aid lesion localisation, the absence of these does not preclude structural pathology. Two cases of cavernous sinus pseudotumour presented as ophthalmoplegia with and without pain. Magnetic resonance imaging of the cavernous sinus revealed the presence of enhancing tissue consistent in appearance with pseudotumour in both cases, and they responded well to steroid treatment. These cases emphasise the importance of detailed imaging of the cavernous sinus in the investigation of these symptoms in order to exclude this treatable condition.

Adolescent↗
PubMed1996

Blood-Brain Barrier Integrity in HIV Infection:Evaluation by Contrast-Enhanced Magnetic Resonance Imaging.

This study assesses the integrity of the blood-brain barrier (BBB) in human immunodeficiency virus (HIV) seropositive individuals to magnetic resonance imaging (MRI) contrast agent Gd-DTPA. Twelve HIV seropositive patients and six control subjects had T2-weighted and serial pre- and post-contrast TI-weighted MRI. Ten of the twelve seropositive patients demonstrated white matter hyperintensity with or without atrophy on T2-weighted MRI and 8/10 who underwent neurological examination demonstrated neurological abnormalities. No statistically significant differences of trends in white matter pixel values were observed between pre- and post-contrast scans in any of the patients or controls. Serial T1-weighted MRI does not demonstrate any change in the integrity of the BBB to Gd-DTPA in HIV seropositive patients, regardless of the presence or absence of white matter hyperintensity with or without atrophy on T2-weighted MRI or clinical signs of HIV-I associated with cognitive/motor complex.

Blood-Brain Barrier↗
PubMed1995

Structure-activity relationships of the antimalarial agent artemisinin. 2. Effect of heteroatom substitution at O-11: synthesis and bioassay of N-alkyl-11-aza-9-desmethylartemisinins.

A novel class of artemisinin analogs, N-alkyl-11-aza-9-desmethylartemisinins 17-29, were synthesized via ozonolysis and acid-catalyzed cyclization of precursor amides 5-16. These amides were prepared through condensation of an activated ester of the known intermediate acid 2 with the corresponding primary amine. The analogs were tested in vitro against W-2 and D-6 strains of Plasmodium falciparum and found in some cases to be more active than artemisinin. A comparison of the in vitro testing methods of Milhous and Makler was conducted and gave similar relative antimalarial activities for these artemisinin analogs. Log P values were determined for most of the compounds, but no apparent correlation between log P and in vitro activity was found.

Animals↗
PubMed1995

Spatial data analysis in the quantitative assessment of cerebral white matter pathology on MRI in HIV infection.

This study was carried out using MRI (proton density--and T2-weighted) on 16 HIV-negative controls, 9 symptom-free HIV-positive patients and 25 with CDC IV HIV disease. The studies from this last group had previously been allocated by a radiologist to the following categories: 8 with focal mass lesions and normal-appearing white matter; 9 with diffuse encephalopathy (high signal on T2-weighted images, affecting most or all of the white matter) and 8 with patchy encephalopathy (high signal affecting only one or two areas within the white matter). Moran's I, a statistic of spatial autocorrelation, was calculated for the grey-scale values of a sampled pixel array from a central white matter region of each of the images. All values of Moran's I calculated in this study showed a large positive excess over the expected value under randomisation, indicating highly significant positive auto-correlation in the spatial arrangement of the grey-scale values. On T2-weighted images a statistically significant increase in the mean value of Moran's I, compared with controls, was found in the diffuse encephalopathy group, indicating that quantifiable changes in the spatial autocorrelation of pixel data can be related to recognised qualitative changes in the appearance of white matter in subjects with HIV disease. A lesser, but significant, rise in the mean value of Moran's I was also found in the focal mass lesion group, suggesting that changes in spatial autocorrelation may indicate pathological change in advance of qualitative MRI changes.

AIDS Dementia Complex↗
PubMed1995

Short echo time proton spectroscopy of the brain in HIV infection/AIDS.

Short echo time proton spectra have been acquired from the brains of 30 male homosexual Acquired Immunodeficiency Syndrome (AIDS) patients and 12 age-matched control subjects on a 1.5 T MR system. The acquisition protocol used stimulated acquisition voxel localisation with a voxel size of 8 ml and repeat, echo, and mixing times of 5000, 20, and 30 ms, respectively. A single 25.6-ms Gaussian water suppression pulse was used with 128 spectral acquisitions and the data were eddy current corrected using a water reference. Baseline-corrected spectra were nonlinearly least squares fitted to a model function consisting of Gaussian functions representing the major metabolites reported in short echo proton spectra. Results indicate that the N-acetyl/creatine (NA/Cr) ratio is significantly reduced by 20% in AIDS patients [NA/Cr = 1.91 (0.51)] compared to control subjects [NA/Cr = 2.37 (0.25)] at short echo times.

AIDS Dementia Complex↗
PubMed1995

Sonography of transjugular intrahepatic portosystemic shunts.

Transjugular intrahepatic portosystemic shunting (TIPS) is an effective procedure for relieving portal hypertension. Sonography can usefully assist portal vein puncture. Color and duplex sonography after TIPS demonstrates changes in hepatic vascular hemodynamics, detects complications, and confirms shunt patency. A large proportion of shunts will develop progressive stenosis over 12 months. Stenosis occurs because of pseudointimal hyperplasia in the stent or in the hepatic vein. Patent shunts are characterized by velocities in excess of 70 cm/s and hepatofugal flow in the portal circulation distal to the shunt. Although the cause of the stenosis can rarely be seen, velocities of less than 50 cm/s indicate shunt stenosis. Loss of cardiac pulsatility is another useful sign of shunt stenosis. Regular sonographic monitoring reliably detects stenosis, allowing stent revision and preventing recurrence of bleeding.

Blood Flow Velocity↗
PubMed1994

Incidence of shunt occlusion or stenosis following transjugular intrahepatic portosystemic shunt placement.

BACKGROUND/AIMS: Transjugular intrahepatic portosystemic shunt (TIPS) placement has been used for the treatment of recurrent variceal hemorrhage. The 1-year incidence of shunt stenosis or occlusion after TIPS placement was prospectively assessed, and the accuracy of Doppler ultrasonography to predict TIPS stenosis was evaluated. METHODS: Twenty-two patients with recurrent variceal hemorrhage were selected for TIPS placement between April 1991 and May 1992. Preoperative and postoperative evaluation included clinical assessment, upper gastrointestinal endoscopy, portal angiography with pressure measurements, and Doppler ultrasonography. Follow-up was performed at 3 and 12 months post-TIPS and when patients developed recurrent bleeding. RESULTS: Twenty-one of 22 patients (Child-Pugh class A-1, B-11, C-9) had successful TIPS placement. Seventeen of 21 patients have completed follow-up for at least 12 months. Of these 17 patients, 2 of 17 (12%) developed TIPS occlusion, 7 of 17 (41%) developed shunt stenosis, and 8 of 17 (47%) showed no stenosis on follow-up angiography. Doppler ultrasonographic assessment of the TIPS predicted shunt stenosis or occlusion with 100% sensitivity, 98% specificity, and 90% positive predictive value. CONCLUSIONS: Shunt occlusion or stenosis develops frequently within 12 months after TIPS placement, and Doppler ultrasonography is accurate in the noninvasive assessment of shunt stenosis. TIPS placement without careful follow-up and shunt revision cannot be considered a long-term treatment of variceal hemorrhage.

Adult↗
PubMed1994

Proton spectroscopy in HIV infection: relaxation times of cerebral metabolites.

In vivo proton spectroscopy has demonstrated abnormalities in the cerebral metabolite ratios from subjects with acquired immunodeficiency syndrome (AIDS). Some of the sequences employed are subject to T1 or T2 weighting, which may affect spectroscopic interpretation. The relaxation times of choline (Cho), creatine (Cr), and N-acetyl (NA) resonances have been estimated at 1.5 T in 21 patients infected with the human immunodeficiency virus (HIV) and 8 controls using gradient localised, spin-echo spectroscopic sequences of varying echo and repetition times. A statistically significant increase in the T2 of NA was found in the HIV seropositive patients who had diffuse abnormalities on MR imaging consistent with HIV encephalopathy (493 +/- 199 ms) when compared to controls (292 +/- 118 ms; p < .05). No other statistically significant differences were found in the relaxation times between patients and control subjects. These results demonstrate that signals from the NA resonance obtained using long echo time sequences in subjects who are HIV seropositive are not solely indicative of metabolite concentration.

Adult↗
PubMed1994

Cyst formation of the craniopharyngeal duct.

The craniopharyngeal duct is the route by which the adenohypophysis ascends from the pharynx to the pituitary fossa. Rathke's cleft cyst represents an expansion of primitive vesicles that lie between the pars intermedia and the pars anterior. These cysts are rare but have been detected more frequently with the more widespread use of CT and MRI. Three cases are described which illustrate the variety of positions that a cystic lesion of the craniopharyngeal duct can occupy. These cases provide a basis for the discussion of the embryological formation of the pituitary, cyst formation of the duct, and CT and MRI appearances of the cysts.

Adult↗