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Biomedical subjects

D L Pham

Publications and source records attributed to D L Pham.

12 recordsLinked to original sources
PubMed2000

Current methods in medical image segmentation.

Image segmentation plays a crucial role in many medical-imaging applications, by automating or facilitating the delineation of anatomical structures and other regions of interest. We present a critical appraisal of the current status of semi-automated and automated methods for the segmentation of anatomical medical images. Terminology and important issues in image segmentation are first presented. Current segmentation approaches are then reviewed with an emphasis on the advantages and disadvantages of these methods for medical imaging applications. We conclude with a discussion on the future of image segmentation methods in biomedical research.

Algorithms↗
PubMed2000

Affordability of inhaled corticosteroids as a potential barrier to treatment of asthma in some developing countries.

SETTING: The cost and availability of the medications required for the treatment of asthma may represent potential barriers to effective management. METHOD: A survey of prices and policies for components of asthma treatment in 1998, in Algeria, Burkina Faso, Ivory Coast, Guinea, Mali, Syria, Turkey and Vietnam. RESULTS: Medications were consistently available in only four of the eight countries studied. The cost of essential medications for standard case management varied by over five times for beclomethasone and by over three times for inhaled salbutamol. In all but two countries, the cost of one year of drugs for treatment of a moderate, persistent case exceeded the monthly salary of a nurse in that country. The essential drugs list included inhaled salbutamol in five of eight countries and beclomethasone in three of eight. The costs of medications were lower where generic preparations were available and, to a lesser extent, where the medications are on the essential drugs list. CONCLUSIONS: The cost and availability of medications vary widely, and may represent an important barrier to effective management in some low and middle income countries.

Albuterol↗
PubMed1999

Reconstruction of the human cerebral cortex from magnetic resonance images.

Reconstructing the geometry of the human cerebral cortex from MR images is an important step in both brain mapping and surgical path planning applications. Difficulties with imaging noise, partial volume averaging, image intensity inhomogeneities, convoluted cortical structures, and the requirement to preserve anatomical topology make the development of accurate automated algorithms particularly challenging. In this paper we address each of these problems and describe a systematic method for obtaining a surface representation of the geometric central layer of the human cerebral cortex. Using fuzzy segmentation, an isosurface algorithm, and a deformable surface model, the method reconstructs the entire cortex with the correct topology, including deep convoluted sulci and gyri. The method is largely automated and its results are robust to imaging noise, partial volume averaging, and image intensity inhomogeneities. The performance of this method is demonstrated, both qualitatively and quantitatively, and the results of its application to six subjects and one simulated MR brain volume are presented.

Algorithms↗
PubMed1999

Adaptive fuzzy segmentation of magnetic resonance images.

An algorithm is presented for the fuzzy segmentation of two-dimensional (2-D) and three-dimensional (3-D) multispectral magnetic resonance (MR) images that have been corrupted by intensity inhomogeneities, also known as shading artifacts. The algorithm is an extension of the 2-D adaptive fuzzy C-means algorithm (2-D AFCM) presented in previous work by the authors. This algorithm models the intensity inhomogeneities as a gain field that causes image intensities to smoothly and slowly vary through the image space. It iteratively adapts to the intensity inhomogeneities and is completely automated. In this paper, we fully generalize 2-D AFCM to three-dimensional (3-D) multispectral images. Because of the potential size of 3-D image data, we also describe a new faster multigrid-based algorithm for its implementation. We show, using simulated MR data, that 3-D AFCM yields lower error rates than both the standard fuzzy C-means (FCM) algorithm and two other competing methods, when segmenting corrupted images. Its efficacy is further demonstrated using real 3-D scalar and multispectral MR brain images.

Algorithms↗
PubMed1999

Quality control of smear microscopy for acid-fast bacilli: the case for blinded re-reading.

SETTING: Quality control of sputum smear microscopy, which is essential for ensuring correct tuberculosis (TB) diagnosis, is often performed through the unblinded rereading of all positive slides and a sample of negative slides. OBJECTIVE: To assess misclassification error introduced by knowledge of prior results. METHODS: The Southern Vietnam Regional TB Laboratory prepared three gold-standard sets of 750 slides: an unblinded set, an unblinded set in which 13% of negative slides were replaced by weakly positive slides purposefully mislabelled as negative, and a blinded set. Six provincial technicians who normally perform district quality control each reread 125 slides from each set. RESULTS: In the three sets only one negative slide was misread as positive. In the unblinded set (referent), 2.9% (9/311) positive slides were misread as negative, compared with 18.7% (57/305) in the blinded set (prevalence ratio [PR] = 6.5; 95% confidence interval [CI] 3.3-12.8; P < 0.001), and 11.3% (33/293) in the unblinded set with mislabelled slides (PR = 3.9; 95%CI 1.9-8.0; P < 0.001). CONCLUSIONS: False-negative error was more common than false-positive error. Knowledge of prior reading influences re-reading. Blinded re-reading of systematically selected slides would appear preferable, although this method requires high levels of proficiency among quality control technicians.

False Negative Reactions↗
PubMed1999

The importance of quality control of sputum smear microscopy: the effect of reading errors on treatment decisions and outcomes.

SETTING: Ho Chi Minh City, Vietnam. OBJECTIVE: To evaluate the impact of slide reading errors at peripheral level on case-finding and treatment decisions. DESIGN: Over a 6-month period in 1997, information on date, type of slide, results of other slides from the patient, and treatment status was collected for all slides from district TB centers detected as having reading errors during smear microscopy quality control re-readings. RESULTS: Reading errors were detected in 117 slides: 115 (98.3%) were incorrectly read as negative, and 75 (65.2%) of these errors occurred in case-finding slides. In the 75 falsely negative case-finding slides, re-reading resulted in initiation of treatment in 38 patients (50.7%). The remaining 37 (49.3%) had only one positive slide and were told to return for follow-up after 6 months; the two (5.4%) who did return were both diagnosed with active TB. Detection of errors in the 40 false-negative follow-up slides resulted in treatment changes in four patients (10%). CONCLUSIONS: Quality control plays a critical role in helping to ensure the timely diagnosis and treatment of new TB cases and appropriate management of patients currently on treatment. The usefulness of quality control could be enhanced by focusing greater efforts on case-finding slides initially read as negative.

Evaluation Studies as Topic↗
PubMed1992

Morbidity from congestive and hypertrophic cardiomyopathy in the Minneapolis-St. Paul metropolitan area: 1979-1984.

In order to develop an epidemiologic profile of congestive and hypertrophic cardiomyopathy, we reviewed hospital discharge diagnosis data for the Minneapolis-St. Paul metropolitan area from 1979 to 1984. For congestive cardiomyopathy, we found statistically significant increases in the age-adjusted hospital discharge diagnosis rate for both men (from 63 to 125/100,000 population/year) and women (from 35 to 58/100,000 population/year). We also found that the age-specific rates increased significantly among older men (55-64 years of age, from 86 to 198/100,000 population/year; 65-74 years of age, from 182 to 322/100,000 population/year) and older women (65-74 years of age, from 106 to 196/100,000 population/year). The rates increased with advancing age for both genders. Men had greater rates than women. For hypertrophic cardiomyopathy, no temporal trends could be discerned. Women were observed to have greater age-specific rates than men; the age-adjusted rates were, however, approximately the same for men and women. The hospital discharge diagnosis rate increased with advancing age among both men and women. The possible reasons for these observed patterns, including the major impact of improvements in diagnosis during the observation period, are discussed. Additional research into these disorders is needed.

Adult↗
PubMed1991

Parkinson's and motoneuron disease morbidity in the Twin Cities metropolitan area: 1979-1984.

To better characterize the morbidity from Parkinson's disease and motoneuron disease, we examined hospital discharge diagnosis data for all acute care facilities (except for the Veterans Administration Medical Center) in the Minneapolis-St. Paul area in each year from 1979 to 1984 for persons aged 30-74 years. For each person in whom the discharge diagnosis included either Parkinson's disease or motoneuron disease, the age, gender, and year of admission were recorded. Annual age-gender-specific and age-adjusted gender-specific hospital discharge diagnosis rates were calculated. For Parkinson's disease, for both, men and women, the age-adjusted hospital discharge diagnosis rate declined by 26-27%. Component age-specific data for Parkinson's disease showed more variable temporal changes. For motoneuron disease, no temporal changes were observed, although the number of observations was small. These data suggest that Parkinson's disease is declining in prevalence in the hospitalized population. The implications for motoneuron disease are less clear. Further studies in this area are needed.

Adult↗
PubMed1990

Hospitalization and case fatality for pulmonary embolism in the twin cities: 1979-1984.

To better characterize the morbidity from pulmonary embolism, we examined hospital discharge data for all acute care facilities (except for the Veterans Administration Medical Center) in the Minneapolis-St. Paul metropolitan area in each year from 1979 to 1984 for persons aged 30 to 74 years. For each person in whom the discharge diagnoses included pulmonary embolism, the age, sex, year of admission, and vital status at discharge were recorded. Annual age-sex-specific and age-adjusted sex-specific hospitalization rates were calculated. Similar analyses were undertaken for case fatality. With the exception of men younger than 55 years of age, all groups experienced significant decline in the pulmonary embolism discharge rate. No significant temporal changes were observed in any of the case fatality rates. These data suggest that changes in pulmonary embolism mortality in the United States from 1979 to 1984 may reflect declining occurrence of the disease and are likely not the result of changes in case fatality. Further studies in this area are needed.

Age Factors↗
PubMedDate not supplied

An image-processing system for qualitative and quantitative volumetric analysis of brain images.

In this work, we developed, implemented, and validated an image-processing system for qualitative and quantitative volumetric analysis of brain images. This system allows the visualization and quantitation of global and regional brain volumes. Global volumes were obtained via an automated adaptive Bayesian segmentation technique that labels the brain into white matter, gray matter, and cerebrospinal fluid. Absolute volumetric errors for these compartments ranged between 1 and 3% as indicated by phantom studies. Quantitation of regional brain volumes was performed through normalization and tessellation of segmented brain images into the Talairach space with a 3D elastic warping model. Retest reliability of regional volumes measured in Talairach space indicated errors of < 1.5% for the frontal, parietal, temporal, and occipital brain regions. Additional regional analysis was performed with an automated hybrid method combining a region-of-interest approach and voxel-based analysis, named Regional Analysis of Volumes Examined in Normalized Space (RAVENS). RAVENS analysis for several subcortical structures showed good agreement with operator-defined volumes. This system has sufficient accuracy for longitudinal imaging data and is currently being used in the analysis of neuroimaging data of the Baltimore Longitudinal Study of Aging.

Aged↗