Biomedical subjects

J Xuan

Publications and source records attributed to J Xuan.

11 recordsLinked to original sources

PubMed2001

Magnetic resonance image analysis by information theoretic criteria and stochastic site models.

Quantitative analysis of magnetic resonance (MR) images is a powerful tool for image-guided diagnosis, monitoring, and intervention. The major tasks involve tissue quantification and image segmentation where both the pixel and context images are considered. To extract clinically useful information from images that might be lacking in prior knowledge, we introduce an unsupervised tissue characterization algorithm that is both statistically principled and patient specific. The method uses adaptive standard finite normal mixture and inhomogeneous Markov random field models, whose parameters are estimated using expectation-maximization and relaxation labeling algorithms under information theoretic criteria. We demonstrate the successful applications of the approach with synthetic data sets and then with real MR brain images.

Algorithms↗

PubMed2001

Economic evaluation of major selective serotonin-reuptake inhibitors in a managed care population.

This study evaluated pharmaceutical charges and economic outcomes related to therapy with the three leading selective serotonin-reuptake inhibitors. Patient treatment episodes of major depression occurring between July 1, 1995 and June 30, 1996 were included for analysis (patient age range, 18-64 yr). Results showed no significant differences among direct and related medical charges for fluoxetine, paroxetine, and sertraline. Direct and related pharmaceutical charges were significantly lower for paroxetine and sertraline compared with fluoxetine. The higher drug charges observed for fluoxetine resulted in higher total treatment charges compared with paroxetine and sertraline.

Adolescent↗

PubMed2000

Automatic detection of foreign objects in computed radiography.

This paper presents an effective two-step scheme for automatic object detection in computed radiography (CR) images. First, various structure elements of the morphological filters, designed by incorporating available morphological features of the objects of interest including their sizes and rough shape descriptions, are used to effectively distinguish the foreign object candidates from the complex background structures. Second, since the boundaries of the objects are the key features in reflecting object characteristics, active contour models are employed to accurately outline the morphological shapes of the suspicious foreign objects to further reduce the rate of false alarms. The actual detection scheme is accomplished by jointly using these two steps. The proposed methods are tested with a database of 50 hand-wrist computed radiographic images containing various types of foreign objects. Our experimental results demonstrate that the combined use of morphological filters and active contour models can provide an effective automatic detection of foreign objects in CR images achieving good sensitivity and specificity, and the accurate descriptions of the object morphological characteristics.

Algorithms↗

PubMed2000

The economic burden of congestive heart failure in a managed care population.

OBJECTIVE: To examine the economic burden of and treatment patterns for congestive heart failure (CHF) in a managed care population. STUDY DESIGN: Retrospective review of medical and pharmacy claims. PATIENTS AND METHODS: We reviewed integrated medical and pharmacy claims data from 6 independent-practice-association model health maintenance organizations to identify patients diagnosed with CHF. Of the approximately 1.4 million people enrolled in these managed care plans during the study period (January through December 1994), a total of 2777 patients (mean age, 56.9 years) met the study criteria, which included diagnostic codes for CHF and claims eligibility of at least 1 year. We reviewed the charges incurred by patients diagnosed with CHF for the 6 months after the initial CHF medical claim. We also examined the treatment received by each of these patients. RESULTS: During the study period, 378 of the 2777 patients with CHF (14%) were admitted to the hospital at a cost of almost $3 million (an average of $7863 per hospitalized patient). Seventy-eight percent of the study population received prescription drugs, at an average per-patient cost of $942. The most commonly prescribed drug class was angiotensin-converting enzyme inhibitors, prescribed for 38% of patients. Calcium channel blockers were prescribed for 33% of patients, but beta-blockers were prescribed for only 18% of patients. Hospitalization accounted for 54% of the total cost for CHF treatment, with prescription drugs accounting for 38%. CONCLUSION: Congestive heart failure represents a significant financial burden within a non-elderly managed care population. Improved management of the condition is needed to reduce the morbidity and mortality, as well as the costs of treatment, associated with CHF. Considerable data indicate that drugs such as beta-blockers and angiotensin-converting enzyme inhibitors can significantly decrease the morbidity and mortality of CHF. Further investigation is needed into whether increased use of prescription pharmaceuticals may reduce hospitalization rates and overall costs for CHF in this setting.

Aged↗

PubMed1999

Effects of comorbidity on health-related quality-of-life scores: an analysis of clinical trial data.

Coexisting diseases may have unforeseen yet clinically significant effects on patients' well-being. Both generic and disease-specific measures are frequently used to assess health-related quality of life (QOL). The present study assessed the effects of comorbidity on the results of QOL measures through an analysis of longitudinal data from 3 double-masked, randomized, placebo-controlled clinical trials dealing with heartburn, asthma, and ulcer. Patients were assigned to subgroups by comorbidity status: those with no comorbid diseases and those whose principal disease was heartburn, asthma, or ulcer and whose comorbid condition was chronic obstructive pulmonary disease, asthma, or chronic bronchitis; hypertension; migraine, coronary artery disease, or varicose veins; chronic gastrointestinal conditions; arthritis or back pain; diabetes; or depression. Multivariate analysis of covariance was used to test the study hypotheses. The study results suggest that comorbid conditions significantly and extensively affect patients' scores on generic QOL measures and estimation of treatment effect, whereas their influence on disease-specific QOL scores and estimation of treatment effect is considerably smaller. Further, the most important comorbidities in the 3 trial populations were arthritis or back pain and depression, which respectively accounted for 17% and 5% of the patient population. These findings have significant practical implications for the estimation of true treatment effects, control of comorbidity effects, and design of QOL trials.

Asthma↗

PubMed1998

Sequence of a 131-kb region of 5q13.1 containing the spinal muscular atrophy candidate genes SMN and NAIP.

The spinal muscular atrophies (SMA), which are characterized by motor neuron loss and progressive paralysis, are among the most common autosomal recessive disorders. The SMA region of chromosome 5q13.1 is distinguished by variable amplification of genomic sequence incorporating a number of genes and pseudogenes. Recently, two SMA candidate genes mapping to this area were identified: survival motor neuron (SMN) and neuronal apoptosis inhibitory protein (NAIP). The telomeric copy of SMN (SMNtel) is deleted in over 95% of cases of SMA, with NAIP deletions primarily seen in type I SMA. We present here 131 kb of genomic sequence from 5q13.1 incorporating both NAIP and SMNtel in addition to revisions of the original NAIP cDNA sequence. The Alu-rich NAIP-SMNtel interval contains the microsatellite polymorphisms that are deleted in as many as 80% of type I SMA chromosomes, focusing attention on this region in the pathogenesis of type I SMA.

Amino Acid Sequence↗

PubMed1998

Crystal structure of glycosylasparaginase from Flavobacterium meningosepticum.

The crystal structure of recombinant glycosylasparaginase from Flavobacterium meningosepticum has been determined at 2.32 angstroms resolution. This enzyme is a glycoamidase that cleaves the link between the asparagine and the N-acetylglucosamine of N-linked oligosaccharides and plays a major role in the degradation of glycoproteins. The three-dimensional structure of the bacterial enzyme is very similar to that of the human enzyme, although it lacks the four disulfide bridges found in the human enzyme. The main difference is the absence of a small random coil domain at the end of the alpha-chain that forms part of the substrate binding cleft and that has a role in the stabilization of the tetramer of the human enzyme. The bacterial glycosylasparaginase is observed as an (alphabeta)2-tetramer in the crystal, despite being a dimer in solution. The study of the structure of the bacterial enzyme allows further evaluation of the effects of disease-causing mutations in the human enzyme and confirms the suitability of the bacterial enzyme as a model for functional analysis.

Aspartylglucosylaminase↗

PubMed1996

Corneal topography research of myopia in Chinese.

PURPOSE: To determine corneal topography parameters of myopia in Chinese and help for studies of causes of myopia, distingiush other corneal diseases (such as early keratoconus), further explore the accurateness and safeness of the clinical effects of radil keratotomy (RK) or photorefractive keratectomy (PRK). METHODS: Fifty-eight eyes with mild or moderate myopia were examined by computer-assisted photokeratography. (TMS-1 Computed Anatomy Inc. New York. NY) RESULTS: The corneal topography of most (68%) of the examined eyes showed symmetric bowtie pattern: the corneal surface of most (75%) of the examined eyes showed positive aspheric shape (steeper centrally, flatter peripherally); the refractive power of central cornea is at mean 44.165 +/- 1.429 D; the refractive difference between 1 to 25 ring in keratoscpe was at mean 1.655 +/- 0.785D; the mean SRI was 0.558 +/- 0.768, the mean SAI was 0.296 +/- 0.149; the mean Smik was 44.209 +/- 1.515D. The apex and visual axis were dislocation in all the cornea examined. CONCLUSIONS: The corneal surface refractive characterization of myopia might be relative to the clinical effects of RK or PRK.

Adolescent↗

PubMed1995

Corneal topography analysis before and after radial keratotomy.

Corneal topographic analyses were conducted on 58 eyes of 42 cases with mild or moderate myopia by computer-assisted photokeratography before and after radial keratotomy (RK). The results indicate that the corneal surfaces of most examined eyes (76%) are positive aspheric shape before RK, while after RK they are changed to negative aspheric shape. Before RK, the corneal topography of most examined eyes (67%) is symmetric bow tie pattern or asymmetric bow tie pattern; after RK, the forms of central flattened regions are mainly round or approximately round, dumbbell and belt-shaped. Before and after RK there is no significant change in surface regularity index (SRI), but surface asymmetry index (SAI) is changed significantly. RK makes the central and central peripheral parts of the cornea flattened. The most significant RK effect is found at the region 1.140 +/- 0.090 mm away from the corneal optical center. Examination and analysis on the corneal topography before and after RK not only provide an accurate and objective basis for RK operational plan, but also make it possible to objectively and quantitatively evaluate the RK effect, to accurately predict the RK clinical effects, and to effectively improve the RK clinical quality.

Adolescent↗

PubMed1994

[The comparative study of pattern visual evoked potential in the normal infants and adults].

This paper presents the pattern visual evoked potential (PVEP) results and comparative study between the two groups of 65 normal infants at the age of 3, 6, 9, 12 months and 18 normal adults. The different pattern spatial frequency stimulations (74', 25', 6') were given to the infants and adults. In the infant group, the latencies of P1 components of PVEP delayed significantly and amplitudes of PVEP decreased significantly between 74' and 6' spatial frequency with the spatial frequency of stimulation increasing. In the same spatial frequency stimulation, when 3 months infant group was compared with the 6, 9, 12 months infant and adult groups, the latencies of N1 and P1 waves showed significant difference, but no difference was found in the amplitudes of P1 wave. Our results might indicate that the visual function expressed by low, medium, and high spatial frequency in infants from 6 to 12 months could reach the level in adults, and in 3 months infants, not maturely develop.

Adult↗

PubMed1994

[Corneal topography of patients with unsatisfactory visual acuity after epikeratophakia for aphakia].

Corneal topographic characteristics of 5 patients who obtained unsatisfactory vision after aphakic epikeratophakia, with at least nine months follow-up, were reported. All grafts were apparently decentered relative to visual axis. The contour of cornea showed highly irregular pattern of power distribution. These findings suggest that to mark visual axis before surgery, lathe corneal lenses carefully and do standard operation should be the basis of successful epikeratophakia.

Adolescent↗