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Biomedical subjects

H M Lai

Publications and source records attributed to H M Lai.

At least 19 recordsLinked to original sources
PubMed2006

Nonspecular effects on reflection from absorbing media at and around Brewster's dip.

We show that, for a TM (or p-state) Gaussian beam incident onto an absorbing medium at and around Brewster's dip, the reflected beam always remains Gaussian and undergoes a Goos-Hänchen-like (GH) shift, an angular shift, a focal shift, and a beam-waist modification, provided that the beam is sufficiently collimated that the third-order change of the (logarithmic) reflection coefficient can be ignored in the angular range of beam divergence. For weak absorption, not only are a large negative GH shift and an odd-functioned-like focal shift with greater magnitude found but also the angular shift, though small by itself, is shown to give an even larger lateral net shift at a distance beyond the Rayleigh range.

Journal Article↗
PubMed2004

Extinction paradox and actual power scattered in light beam scattering: a two-dimensional study.

The extinction paradox is examined by applying partial-wave analysis to a two-dimensional light beam interacting with a long transverse cylinder without absorption, assuming always short wavelengths. We show that the (conventional) power scattered, Psca, except for a very narrow beam hitting a transparent cylinder on axis, is always double the power directly intercepted by the scatterer, Pitc, including a zero result for Psca when the incident beam is basically off the material surface. This contradicts the interpretation that attributes one half of Psca to edge diffraction by the scatterer. Furthermore, we identify the shadow-forming wave (SFW) from the partial-wave sum in the forward direction and show that the actual power scattered or, equivalently, the power depleted from the incident beam is equal to one unit of Pitc for a narrow beam, gets larger for a broader beam, and approaches 2Pitc for a very broad beam. The larger value in the latter cases is due to the extent of divergence of the SFW beam out of the incident beam at distances well beyond the Rayleigh range.

Journal Article↗
PubMed2001

Unusual 1/r-dependent radiation intensity in any biaxial crystal.

Lighthill's prediction of an unusual 1/r-dependent radiation intensity from a small monochromatic source is found to exist in any homogeneous and lossless biaxial crystal along the two optical ray axes, where r is the radial distance from the source. This is a consequence of the special shape of the wave-vector surface on which there is, around each singular point of self-intersection (or "dimple"), a circular locus of points all having the same surface normal direction and thus sharing a common tangent plane. A heuristic derivation of the result is given and a simple optical experiment is proposed to detect such an unusual distance dependence.

Journal Article↗
PubMed2000

Overwhelming septic cavernous sinus thrombosis in a woman after combination of high-dose steroid and intravenous cyclophosphamide therapy for lupus nephritis.

There are many treatment methods for lupus nephritis, including high-dose steroids, pulse methylprednisolone, and cyclophosphamide therapy. In cyclophosphamide therapy, there can be some side effects such as nausea, vomiting, and infection. We report on a case receiving a combination of high dose steroid and intravenous cyclophosphamide. Following this, she developed a fever and a protruding right eye, and septic cavernous sinus thrombosis was diagnosed. This complication had never been reported in a patient with systemic lupus erythematosus, and related literature is reviewed.

Adult↗
PubMed2000

The effect of fluvastatin on fibrinolytic factors in patients with hypercholesterolemia.

Several studies have shown cardiovascular benefit in treating hypercholesterolemia with HMG-CoA reductase inhibitor. However, in addition to the lowering of cholesterol, the beneficial effects of this inhibitor reflect other pharmacological activities. Whether these beneficial effects are partly mediated by changes in fibrinolytic factors remains to be proven, since clinical studies on the effects of HMG-CoA reductase inhibitors on fibrinolytic factors have not yielded consistent results. The purpose of this study was to evaluate the effects of fluvastatin on fibrinolytic factors in hypercholesterolemic patients. After 6 weeks on a low-fat, low-cholesterol diet, 23 outpatients known to have primary hypercholesterolemia with low density lipoprotein cholesterol (LDL-C) > or = 130 mg/dl with at least 2 risk factors or fasting LDL-C > or = 160 mg/dl were selected for the study. Venous blood samples were collected at baseline and at 8 weeks after fluvastatin therapy (40 mg/day) to measure of tissue plasminogen activator (t-PA), plasminogen activators inhibitor-1 (PAI-1), fibrinogen, D-dimer and lipid profile. After 8 weeks of therapy, fluvastatin reduced serum cholesterol by 11% (261.9 mg/dl vs 233.2 mg/dl, P < 0.01) and LDL-C by 22% (191.9 mg/dl vs 149.3 mg/dl, P < 0.01). D-dimer was significantly decreased (0.38 ng/L vs 0.28 ng/L, P = 0.02) and tPA, PAI-1 and fibrinogen tended to decrease after therapy. Fluvastatin therapy improved fibrinolytic profile; the result of this study may in part explain the benefit of HMG-CoA reductase inhibitor on cardiovascular system other than lipid lowering.

Aged↗
PubMed1998

Correlations between monthly enhanced MRI lesion rate and changes in T2 lesion volume in multiple sclerosis.

Magnetic resonance imaging (MRI) provides a powerful tool for assessing disease activity in multiple sclerosis (MS), and its role as a surrogate marker for monitoring treatment efficacy is now becoming established. The most commonly used MRI parameters in treatment trials are (1) monthly gadolinium-enhanced MRI, with the number of active lesions serving as the outcome measure, and (2) annual lesion load quantification, in which change in MS lesion volume provides the MRI endpoint. We evaluated clinical/MRI correlations and the relationship between these two markers of disease activity in 73 patients with clinically definite MS. Quantification of T2 lesion load was performed at study entry and exit, with a median study duration of 11 months (range, 9 to 14 months). Monthly postgadolinium T1-weighted images were acquired between these time points. Lesion load at study entry was significantly correlated with the baseline Expanded Disability Status Scale (EDSS) score, but no significant longitudinal correlation was demonstrated. The number of enhancing lesions on the entry scan was predictive of subsequent relapse rate over the study duration and also correlated with the subsequent enhancing lesion activity over the study period. A significant correlation was found between change in lesion load and disease activity on the monthly scans. Our results suggest that annual lesion load quantification provides an efficient measure of ongoing disease activity, and this supports its application as a surrogate marker of disease evolution in phase III treatment trials.

Adolescent↗
PubMed1998

Correction for variations in MRI scanner sensitivity in brain studies with histogram matching.

Quantitative comparisons of abnormalities in MRI scans between patients or within patients serially are affected by variations in MR scanner performance. A histogram matching method is proposed to correct for variation in scanner sensitivity. It is demonstrated that this histogram matching method reduced the variation in white matter intensities across normal subjects from 7.5 to 2.5% and provided a method to remove the threshold dependency in lesion volume measurement with global thresholding in patients with multiple sclerosis (MS). The effectiveness of the method was compared with three other possible correction schemes. The histogram matching method was shown to be 2 to 5 times better.

Algorithms↗
PubMed1998

The saturation characteristics of glucose transport in bovine retinal pigment epithelium.

PURPOSE: To study the saturation characteristics of the glucose transport across the bovine retinal pigment epithelium(RPE). METHODS: The bovine RPE preparations were munted with a modified Ussing chamber. The L-[3H]-glucose and 3-O-methyl-D-[14C]-glucose fluxes across the RPE from the choroid to retina were studied at different glucose concentrations. RESULTS: The glucose transport was found to be stereospecific, with 3-O-methyl-D-glucose (MDG) being transported about three times faster than L-glucose. The glucose transport showed typical saturation characteristics in Michaelis-Menten fashion. The Vmax and the Km of corrected MDG were 2452 nmol cm-2h-1 and 30.8 mM respectively. It was shown that the glucose transport system was saturated at 61.6 mM. CONCLUSIONS: The saturation characteristics of the corrected MDG flux suggested that the capacity of glucose transport through the bovine RPE is immense.

3-O-Methylglucose↗
PubMed1997

Serial magnetisation transfer ratios in gadolinium-enhancing lesions in multiple sclerosis.

The magnetisation transfer (MT) ratio of eight multiple sclerosis lesions has been studied serially. Initially, when the lesions showed gadolinium enhancement, there was a marked reduction in their MT ratio compared with normal white matter. Follow-up a mean of 11 months later (range 3-23 months), when the lesions no longer enhanced, revealed a consistent and usually marked recovery of the MT ratios towards normal. The MT ratio is thought to reflect the structural integrity of tissues with an important contribution from myelin and axons. MT imaging is a promising tool for elucidating pathophysiology and monitoring treatment in multiple sclerosis.

Adult↗
PubMed1997

CT findings at lupus mesenteric vasculitis.

PURPOSE: To describe the spectrum of early CT findings of lupus mesenteric vasculitis (LMV) and to assess the utility of CT in the management of this uncommon entity. METHODS: Abdominal CT was performed within 1-4 days (average 2.2 days) of the onset of severe abdominal pain and tenderness in 15 women with systemic lupus erythematosus. Prompt high-dose i.v. corticosteroid was administered in 11 patients after the CT diagnosis of LMV was made. CT was performed after abdominal symptoms subsided. RESULTS: Eleven cases revealed CT features suggestive of LMV including conspicuous prominence of mesenteric vessels with palisade pattern or comb-like appearance (CT comb sign) supplying focal or diffuse dilated bowel loops (n = 11), ascites with slightly increased peritoneal enhancement (n = 11), small bowel wall thickening (n = 10) with double halo or target sign (n = 8). Follow-up CT before high-dose steroid therapy revealed complete or marked resolution of the abnormal CT findings. CONCLUSION: CT is helpful for confirming the diagnosis of LMV, especially the comb sign which may be an early sign. Bowel ischemia due to LMV is less ominous than previously expected, and the abnormal CT findings were reversible when early diagnosis and prompt i.v. steroid therapy could be achieved.

Abdominal Pain↗
PubMed1997

Therapeutic effect of mitoxantrone combined with methylprednisolone in multiple sclerosis: a randomised multicentre study of active disease using MRI and clinical criteria.

OBJECTIVE: To evaluate the efficiency of mitoxantrone in multiple sclerosis. METHODS: Forty two patients with confirmed multiple sclerosis, selected as having a very active disease on clinical and MRI criteria were randomised to receive either mitoxantrone (20 mg intravenously (IV) monthly) and methylprednisolone (1 g iv monthly) or methylprednisolone alone over six months. In the steroid alone group five patients dropped out due to severe exacerbation. RESULTS: Blinded analysis of MRI data showed significantly more patients with no new enhancing lesions in the mitoxantrone group compared with the steroid alone group, (90% v 31%, P < 0.001). In the mitoxantrone group there was a month by month decrease almost to zero in the number of new enhancing lesions, and in the total number of enhancing lesions, whereas both remained high in the steroid alone group. The differences were significant for both indices at all months from 1-6. Unblinded clinical assessments showed a significant improvement in change in EDSS at months 2-6 in the mitoxantrone group, with a final mean improvement of more than one point (-1.1 v + 0.3; P < 0.001). There was a significant reduction in the number of relapses (7 v 31; P < 0.01), and an increase in the number of patients free of exacerbation (14 v 7; P < 0.05). CONCLUSION: In this selected group of patients with multiple sclerosis with very active disease, mitoxantrone combined with methylprednisolone was effective in improving both clinical and MRI indices of disease activity over a period of six months whereas methylprednisolone alone was not. Further double blinded long term studies are needed to properly evaluate the effect of mitoxantrone on progression in disability.

Adjuvants, Immunologic↗
PubMed1997

Survey of the distribution of lesion size in multiple sclerosis: implication for the measurement of total lesion load.

OBJECTIVES: Quantitative measurement of lesion load on proton density or T2 weighted brain MRI in multiple sclerosis is a widely used marker of disease progression in treatment trials and natural history studies. However, it has proved difficult to obtain highly reproducible measurements. Several factors account for this, one of which is uncertainties in lesion identification, particularly very small white matter abnormalities. This paper aims to ascertain the significance of very small white matter abnormalities in the measurement of lesion load in multiple sclerosis. METHODS: All visible lesion areas identified by an experienced observer on proton density weighted spin echo brain MRI with 5 mm thick slices were measured by using a contouring technique in 15 patients with secondary progressive multiple sclerosis (SPMS) and 13 with relapsing remitting multiple sclerosis (RRMS). The size distribution of these lesions was analysed. RESULTS: 80% of the number of the lesions were smaller than 80 mm2. Lesions that were smaller than 10 mm2 (equivalent diameter <3.5 mm) made up nearly 20% of all lesions; their relative contribution to the total lesion load varied from 0.0-5.7% (mean=1.1%, median=0.65%) in individual patients, and was larger when the total lesion load was smaller (r = -0.65, P<0.001). Median lesion size was significantly smaller in the SPMS group than the RRMS group. CONCLUSIONS: The results suggest that it is prudent to identify and measure small lesions in evaluating treatment effects, and that measures are undertaken (for example, using thinner slices such as 3 mm) to improve their detection.

Adult↗
PubMed1997

Transcription termination by bacteriophage T3 and SP6 RNA polymerases at Rho-independent terminators.

Transcription termination of T3 and SP6 DNA-dependent RNA polymerases have been studied on the DNA templates containing the threonine (thr) attenuator and its variants. The thr attenuator is from the regulatory region of the thr operon of Escherichia coli. The DNA template, encoding the thr attenuator, contains specific features of the rho-independent terminators. It comprises a dG + dC rich dyad symmetry, encoding a stem-and-loop RNA, which is followed by a poly(U) region at the 3'-end. Thirteen attenuator variants have been analyzed for their ability to terminate transcription and the results indicated that the structure as well as the sequence in the G + C rich region of RNA hairpin affect termination of both RNA polymerases. Also, a single base change in the A residues of the hairpin failed to influence termination, whereas changes in the poly(U) region significantly reduced the termination of both T3 and SP6 RNA polymerases. The requirement of a poly(U) region for termination by T3 and SP6 RNA polymerases was studied with nested deletion mutants in this region. The minimum number of U residues required for termination of SP6 and T3 RNA polymerases was five and three, respectively. However, both RNA polymerases needed at least eight U residues to reach a termination efficiency close to that achieved by wild-type thr attenuator encoding nine U residues. In addition, the orientation of the loop sequences of the RNA hairpin did not affect the transcription termination of either of the bacteriophage RNA polymerases.

Bacteriophage T3↗
PubMed1996

Progressive cerebral atrophy in multiple sclerosis. A serial MRI study.

Recent studies of the spinal cord and cerebellum have highlighted the importance of atrophy in the development of neurological impairment in multiple sclerosis. We have therefore developed a technique to quantify the volume of another area commonly involved pathologically in multiple sclerosis: the cerebral white matter. The technique we describe extracts the brain from the skull on four contiguous 5 mm periventricular slices using an algorithm integrated in an image analysis package, and quantifies their volume. Intra-observer scan-rescan reproducibility was 0.56%. We have applied this technique serially to 29 patients with multiple sclerosis selected for an 18-month treatment trial with a monoclonal antibody against CD4+ lymphocytes (deemed clinically ineffective). A decrease in volume beyond the 95% confidence limits for measurement variation was seen in 16 patients by the end of the 18-month period. The rate of development of atrophy was significantly higher in those who had a sustained deterioration in their Kurtzke expanded disability status scale (EDSS) score compared with those who did not (respective means: -6.4 ml year-1 and -1.8 ml year-1, P < 0.05) but in both groups these changes differed significantly from baseline (P < 0.05). Baseline T2 lesion load, change in T2 lesion load over 18 months and the volume of new gadolinium enhancing lesions on monthly scans for the first 10 months showed no correlation with the development of atrophy. This study demonstrates that progressive cerebral atrophy can be detected in individual patients with multiple sclerosis, correlates with worsening disability and gives additional information to that obtained with conventional MRI. The effect of putative therapies aimed at preventing disability could be objectively assessed by this measure.

Adult↗
PubMed1993

Pseudotumour cerebri associated with arteriovenous malformations.

The association of intracranial hypertension and arteriovenous malformations is described in two patients. Both patients had the typical clinical features of pseudotumour cerebri and were found to have intracranial arteriovenous malformations on arteriography. The mechanism of raised intracranial pressure in patients with arteriovenous malformations is discussed.

Adult↗
PubMed1991

Use of NMR and MRI to study water relations in foods.

Water is the most important component of a food system, because it influences so many process variables, product characteristics, and stability attributes. Some of the most successful techniques used to probe the behavior of water in food systems are Nuclear Magnetic Resonance (NMR) spectroscopy and, more recently, pulsed-field gradient NMR and Magnetic Resonance Imaging (MRI). The purpose of this chapter is to review the theory underlying these techniques and to present several examples of how they have been applied to study water relations in foods.

Carbohydrates↗
PubMed1991

Is sick sinus syndrome an adenosine-mediated disease? Effects of intravenous aminophylline on sick sinus node function after pharmacologic autonomic blockade.

To assess the effects of intravenous aminophylline on the sinus node, 12 patients with clinical and Holter monitor-documented sick sinus syndrome were studied (1) during the control state, (2) after pharmacologic autonomic blockade and (3) 5 min after intravenous administration of aminophylline. The effects of aminophylline on sinus node function were compared with those after pharmacologic autonomic blockade. No significant improvement of sinus node function was found after intravenous aminophylline administration with a mean sinus cycle length and a mean maximum CSRT of 968 +/- 218 and 1832 +/- 1036 ms, respectively. The mean serum theophylline level was 10.9 +/- 1.7 micrograms/ml. Since aminophylline is an adenosine receptor antagonist, these findings suggest that intrinsic adenosine may not play an important role in pathogenesis in patients with chronic and advanced sick sinus syndrome.

Adenosine↗