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Biomedical subjects

S C Liew

Publications and source records attributed to S C Liew.

16 recordsLinked to original sources
PubMed1999

Anterior ischaemic optic neuropathy in a patient with optic disc drusen.

BACKGROUND: Although visual field defects are well-known complications of optic disc drusen, reduction in visual acuity with this condition is rare. METHOD/RESULTS: We report on a 68-year-old male with bilateral optic disc drusen who presented with monocular loss of vision in the right eye associated with an inferior altitudinal visual field defect and signs consistent with acute anterior ischaemic optic neuropathy, confirmed on fluorescein angiography. He also had a left inferior nasal step, but no evidence of glaucomatous cupping. The disc drusen were documented clinically and on B scan ultrasound and computed tomography. CONCLUSIONS: The diagnosis of acute anterior ischaemic optic neuropathy should be considered in patients with optic disc drusen who present with reduced visual acuity, particularly when the visual loss has been acute and non-progressive and is associated with altitudinal field loss and characteristic fluorescein angiography signs.

Aged↗
PubMed1997

Modulation of major histocompatibility complex class II expression in retinas with age-related macular degeneration.

PURPOSE: To investigate antigenic and morphologic features of microglial and vascular elements in the neural retina associated with age-related macular degeneration (ARMD) compared with those features in age-matched normal and young adult retinas. METHODS: Adult eyes (n = 97) were classified histopathologically into normal and ARMD-associated groups. Peroxidase imunohistochemical examination of retinal flatmounts was used to visualize major histocompatibility complex class II (MHC-II) immunoreactivity; the intensity and distribution of labeling were quantified by image analysis. In histochemical investigation, reduced nicotinamide-adenine dinucleotide phosphate diaphorase and glial fibrillary acidic protein or MHC-II double labeling were used to detect vascular changes in some preparations. RESULTS: An increase in the proportion of the retina (percentage of total area) expressing MHC-II immunoreactivity was observed in age-matched retinas compared with that seen in normal retinas. A significant increase (P < 0.05) in the percentage of area immunoreactive for MHC-II was observed, primarily on vascular elements, in retinas with incipient ARMD compared with the area affected in the age-matched group. Increased MHC-II immunoreactivity on vessels in the normal-aged group observed with confocal microscopy was associated with irregularities in the organization of astrocytes. Hypertrophy of retinal microglia was also apparent, although the intensity of microglial MHC-II immunoreactivity was not significantly different between groups. CONCLUSIONS: The results indicate that an increase in MHC-II immunoreactivity on retinal vascular elements is associated with normal aging. A further increase in MHC-II immunoreactivity on vascular elements and morphologic changes in microglia was associated with incipient ARMD. Immunologic responses in neural retinal microglia and vascular elements appear to be related to early pathogenetic changes in retinal pigment epithelium pigmentation and drusen formation.

Adult↗
PubMed1996

Retrieval of organs for transplantation: experience of the Australian National Liver Transplantation Unit.

The Australian National Liver Transplantation Unit carried out 251 multiple organ-retrieval procedures between January 1986 and December 1994: 53% were in the Sydney metropolitan area, 22% in country New South Wales and the Australian Capital Territory, 21% interstate and 4% in New Zealand; mean total procurement times were, respectively, 4 hours 57 minutes, 6 hours 58 minutes, 9 hours 20 minutes and 12 hours 20 minutes. Donor operation times steadily decreased over the nine years. One-year patient and graft survival rates were 77.1% and 70.3%, respectively; primary non-function occurred in only one case. The importance of coordination of donor organ procurement and efficient organ retrieval to the success of transplantation programs is discussed.

Adolescent↗
PubMed1995

Early outcome and intermediate follow-up of vascular stents in the femoral and popliteal arteries without long-term anticoagulation.

PURPOSE: The role of arterial stenting in the treatment of femoral and popliteal arterial disease is controversial and has been hampered by recommendations for patients to be given anticoagulants (oral warfarin) for several months or more. This study was undertaken to evaluate the immediate and midterm outcomes of vascular stents implanted percutaneously in the femoral and popliteal arteries, without long-term anticoagulation. METHODS: Over a 3-year period, 32 patients admitted to a vascular surgery service had arterial stents implanted in the femoral (n = 22) or popliteal (n = 10) artery for the following indications: recurrent stenosis after angioplasty (n = 13), suboptimal result after angioplasty of occluded (n = 12) or calcified stenotic arteries (n = 2), percutaneous transluminal angioplasty-induced thrombosis or dissection (n = 5). Access to the artery was gained by percutaneous insertion of a hemostatic sheath into the ipsilateral common femoral artery. Systemic heparin was given at the time of stent insertion, and patients were prescribed daily low-dose aspirin. RESULTS: Successful stent implantation was achieved in 31 of the 32 patients. Acute thrombosis (< 30 days) occurred in two patients. There was no incidence of false aneurysm formation, acute leg ischemia, or vessel perforation. All patients were monitored by Doppler scanning index and duplex scanning within 24 hours, and thereafter at 3- to 6-month intervals. The mean ankle-brachial systolic pressure index improved from 0.60 (before treatment) to 0.88 (3 to 6 months after stenting). Stent occlusion has occurred in six patients; two stents were successfully salvaged with urokinase infusion. In follow-up to date (range 3 to 33 months) the primary patency rate by life-table analysis was 75% at 18 months, whereas the secondary patency rate was 89% at the same interval. Restenosis (> 50% lumen diameter) was detected by duplex ultrasonography in seven of 25 patent stents (28%) at a mean interval of 9.5 months (range 4 to 15 months); of these, four patients remained clinically symptom-free despite the ultrasound findings. CONCLUSIONS: We conclude that vascular stents can be implanted into the femoropopliteal arteries with few complications and with acceptable early and intermediate patency rates, without the need for long-term anticoagulation. Restenosis is not prevented by stents, and the main value of stenting at this site appears to be in salvaging acute complications of percutaneous transluminal angioplasty, or to correct suboptimal results after recanalization of occluded arteries.

Aged↗
PubMed1995

Laparoscopic splenectomy.

The innovations in laparoscopic technology have expanded the variety of general surgical procedures amenable to laparoscopic approach. An initial experience with eight cases of laparoscopic splenectomy is presented. The indications for splenectomy were immune thrombocytopenic purpura (ITP, n = 6), hereditary spherocytosis (n = 1) and enlarged spleen with filling defects (n = 1). There were six females and two males, aged 27 to 46 years. Seven patients had the spleen removed laparoscopically and one had laparoscopically assisted splenectomy. The operations took from 2 h 15 min to 3 h 30 min (mean 2 h 45 min). The spleens removed varied from 70 to 563 g (mean = 250). Blood loss ranged from insignificant to 1400 mL. Significant bleeding was encountered in three patients with moderate splenomegaly (240, 350, 563 g). Two patients received autologous blood transfusion. The average narcotic required was three doses. The patients were discharged after a mean postoperative stay of 3 days (range 2-4). One patient developed a below knee deep venous thrombosis. Laparoscopic splenectomy is possible and promises to provide the advantages associated with other laparoscopic procedures. Patients with an enlarged spleen can present a technical challenge, and there is a potential for significant blood loss. The current technology and laparoscopic expertise means that this procedure should probably be limited to patients whose spleens are not palpable clinically.

Adult↗
PubMed1994

Modulation of MHC class II expression in the absence of lymphocytic infiltrates in Alzheimer's retinae.

This study describes the expression of MHC class II antigens in retinal flat mounts from normal donors and patients with Alzheimer's disease (AD). We confirm previous observations of MHC class II immunoreactivity on microglia in normal retinae, while observing insignificant levels of reactivity on endothelial cells (EC). A significantly increased level of MHC class II expression was detected in AD retinae. This increased immunoreactivity was found to occur in the absence of lymphocytic infiltrates, suggesting that the pathogenesis of AD in the retina may be distinct from that reported to occur in some regions of the brain. MHC class II expression, measured using computerized optical densitometry, appeared to be increased principally as a result of induced MHC class II immunoreactivity on EC. Ramified microglia and perivascular macrophages, although hypertrophied, appeared to show unchanged levels of MHC class II expression. These findings are consistent with earlier suggestions that both aberrant MHC class II expression and suppressor activity of resident macrophages may restrict immune responses.

Adult↗
PubMed1994

Day-only admission for varicose vein surgery.

Day-only admissions for surgery are strongly encouraged, in an effort to keep costs down. Varicose vein surgery has been considered too major for day-only management despite the fact that there have been studies from overseas showing that it can be done with a morbidity comparable to inpatient surgery. The morbidity of day-only surgery for varicose veins (both long and short saphenous procedures) was assessed and compared with the results of inpatient surgery. Patients were also asked whether they were satisfied with the surgery being done this way. There were 165 consecutive patients available for study, 64 day-only and 101 inpatient. All patients attending Shellharbour Hospital. Shellharbour, had surgery done as day-only (as it was a morning list and allowed adequate time for recovery). Patients attending Bulli Hospital, Bulli, had surgery done as an inpatient (afternoon list). All surgery was performed by one surgeon. There was no difference (Chi-squared) in the age distribution (mean 48 years for day-only, 51 years for inpatient) or sex proportion in either group (Chi-squared test of proportions with continuity correction). Assessment of the results was done by review of the surgeon's notes, as well as telephone interviews for day-only subjects. The complication rate in both groups was similar. Wound problems represented the main complication with an incidence of 10.5% in each group. There was one deep venous thrombosis (DVT) in each group (diagnosed by duplex scan). Response to the telephone interview suggested that most patients were happy to have the surgery done as a day-only procedure.(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗
PubMed1994

Complication of hard cervical collars in multi-trauma patients.

All multi-trauma patients with suspected cervical spine injury should have their cervical spine protected while other life-threatening injuries are being managed. The application of a hard cervical collar is an acceptable method of temporarily immobilizing the cervical spine. Two cases of significant occipital pressure ulceration associated with the use of hard cervical collar are presented.

Adult↗
PubMed1994

Mesenteric cyst.

Mesenteric cyst is one of the rarest abdominal tumours, with approximately 820 cases reported since 1507. The incidence varies from 1 per 100,000 to 250,000 admissions. The lack of characteristic clinical features and radiological signs may present great diagnostic difficulties. The cyst may present in one of three ways: (i) non-specific abdominal features; (ii) an incidental finding; or (iii) an acute abdomen. Abdominal pain is the major presenting symptom. Abdominal mass is found in more than 50% of cases and 40% of cases are discovered incidentally. More than one aetiological mechanism is probably involved in the development of mesenteric cysts. Mesenteric cysts have been reported from the duodenum to the rectal mesentery but are most commonly located in the ileal mesentery. Malignant cysts occur in less than 3% of cases. Enucleation of the cyst is the treatment of choice. Knowledge of these tumours is important due to the various complications associated with suboptimal surgical management. Two cases of mesenteric cysts are presented including a recurrent mesenteric cyst in a post-partum woman demonstrating the inferior technique of internal marsupialization. The association of mesenteric cyst with pregnancy is discussed.

Abdomen, Acute↗
PubMed1993

Human retinal microglia express phenotypic characteristics in common with dendritic antigen-presenting cells.

Neural tissue has been considered to be immunologically privileged and major histocompatibility complex (MHC) class II antigens not expressed in normal human brain grey matter and retina. In the present study we compare phenotypic characteristics of human retinal microglia and dendritic Langerhans cells, including their morphologies and distribution, MHC class II and CD45 antigen expression and nucleotidase reactivity. Levels of class II expression were measured using optical densitometry in combination with standard immunohistochemical techniques applied to retinal flatmounts. The results indicate that ramified retinal microglia have features in common with dendritic antigen presenting cells of cornea and conjunctivum, including the constitutive expression of MHC class II antigens.

Adult↗
PubMed1993

Noise propagation in SPECT images reconstructed using an iterative maximum-likelihood algorithm.

The effects of photon noise in the emission projection data and uncertainty in the attenuation map on the image noise in attenuation-corrected SPECT images reconstructed using a maximum-likelihood expectation-maximization algorithm were investigated. Emission projection data of a physical Hoffman brain phantom and a thorax-like phantom were acquired from a prototype emission-transmission computed tomography (ETCT) scanner being developed at UCSF. Computer-simulated emission projection data from a head-like phantom and a thorax-like phantom were also obtained using a fan-beam geometry consistent with the ETCT system. The simulation assumed a 99Tcm source, included collimator blurring but ignored photon scatter. For each phantom, a region of interest (ROI) at the centre of the reconstructed image was chosen for the purpose of noise analysis. In all cases, the mean value (m) in the ROI approached a constant value after approximately 20 iterations. The standard deviation (sigma) generally increased with the number of iterations. The ratio (sigma/m) was found to be inversely proportional to the square root of the total detected counts and proportional to the relative uncertainty in the attenuation maps. These two noise components contributed independently towards the noise in the reconstructed image. In the ETCT system employing an x-ray tube for attenuation map acquisition, the uncertainty in the reconstructed radionuclide distribution is limited mainly by photon noise in the emission projection data. Our results are expected to be generally applicable to other emission-transmission systems, including those using external radionuclide sources for the acquisition of attenuation maps.

Algorithms↗
PubMed1992

Description of a prototype emission-transmission computed tomography imaging system.

We have developed a prototype imaging system that can perform simultaneous x-ray transmission CT and SPECT phantom studies. This system employs a 23-element high-purity-germanium detector array. The detector array is coupled to a collimator with septa angled toward the focal spot of an x-ray tube. During image acquisition, the x-ray fan beam and the detector array move synchronously along an arc pivoted at the x-ray source. Multiple projections are obtained by rotating the object, which is mounted at the center of rotation of the system. The detector array and electronics can count up to 10(6) cps/element with sufficient energy-resolution to discriminate between x-rays at 100-120 kVp and gamma rays from 99mTc. We have used this device to acquire x-ray CT and SPECT images of a three-dimensional Hoffman brain phantom. The emission and transmission images may be superimposed in order to localize the emission image on the transmission map.

Algorithms↗
PubMed1985

Anisotropic elasticity of bovine pericardial tissues.

Artificial heart valves fashioned from bovine pericardial tissues appear to perform favourably when compared to those fashioned from other biological materials. Tissue mechanical properties have been implicated as a possible factor in determining the success or failure of the materials used for constructing tissue valve substitutes. In this study, strips of bovine pericardial tissues, cut in three different directions (along the base-apex axis of the heart, perpendicular to this axis and at an angle of 45 degrees to this axis), were subjected to uniaxial tensile tests using an Instron machine, at strain rates of 666.7, 166.7, 66.7, and 6.7% X min-1. The pericardial tissues were found to have non-linear stress-strain curves. Anisotropy was also observed, in that the tissue was most extensible when stretched along the vertical direction and least extensible when stained along the horizontal direction. The tissues also exhibited viscoelastic properties, as the extensibility was found to decrease with the increasing strain-rate. The strain at rupture for these tissues, however, were found to be independent of the strain rates and the direction in which they were stretched. On the other hand the stress at rupture was largest when stretched in the horizontal direction and least when stretched in the vertical direction. Stresses at rupture also increase with the strain rate. The implications of the observed tissue properties, when these are used in the fashioning of tissue valve substitutes, will be discussed.

Animals↗
PubMedDate not supplied

Noise, resolution, and sensitivity considerations in the design of a single-slice emission-transmission computed tomographic system.

A prototype Emission-Transmission Computed Tomography (ETCT) system is being developed that will acquire single-slice x-ray transmission CT images simultaneously with single photon emission computed tomography (SPECT) images. This system will permit the correlation of anatomical information from x-ray CT with functional information from SPECT images. The patient-specific attenuation map derived from the x-ray CT images can be used to perform attenuation correction of the SPECT images, so that accurate quantitative information can be obtained. The fan-beam scanning geometry and the use of a segmented HPGe detector array impose special constraints on the design of the collimator for the system. Based on a signal detection model, an efficiency-resolution figure of merit (ERFM) as a function of the collimator geometric efficiency, system resolution width, and object diameter is defined. The ERFM is proportional to the square of the detection signal-to-noise ratio. The collimator design parameters can then be optimized by optimizing the ERFM for an anticipated object diameter. The collimator point-spread function, geometric efficiency, and resolution are calculated. The collimator optimized for the detection of a 1-cm object will have a single-slice point source efficiency of 1.2 X 10(-4), and a FWHM of 6.5 mm at the center of the reconstruction circle, at 12 cm from the collimator face. The minimum object contrast which will give a detection SNR of 5 is 74%, for a total accumulated count per slice of 2 X 10(6).

Humans↗