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Biomedical subjects

H H Liu

Publications and source records attributed to H H Liu.

At least 37 records · Page 2Linked to original sources

Prevalence and predictors of highly active antiretroviral therapy use in patients with HIV infection in the united states. HCSUS Consortium. HIV Cost and Services Utilization.

BACKGROUND: Highly active antiretroviral therapy (HAART) became standard for HIV in 1996. Studies at that time showed that most people infected with HIV had initiated HAART, but that members of minority groups and poor people had lower HAART use. It is not known whether high levels of HAART use have been sustained or whether socioeconomic and racial disparities have diminished over time. OBJECTIVES: To determine the proportion of patients who had received and were receiving HAART by January 1998, and to evaluate predictors of HAART receipt. DESIGN AND PARTICIPANTS: Prospective cohort study of a national probability sample of 2267 adults receiving HIV care who completed baseline, first follow-up, and second follow-up interviews from January 1996 to January 1998. MAIN OUTCOME VARIABLES: Proportion currently using HAART at second follow-up (August 1997 to January 1998), contrasted with the cumulative proportions using HAART at any time before January 1998 and before December 1996. ANALYSES: Bivariate and multiple logistic regression analysis of population characteristics predicting current use of HAART at the time of the second follow-up interview. RESULTS: The proportion of patients ever having received HAART increased from 37% in December 1996 to 71% by January 1998, but only 53% of people were receiving HAART at the time of the second follow-up interview. Differences between sociodemographic groups in ever using HAART narrowed after 1996. In bivariate analysis, several groups remained significantly less likely to be using HAART at the time of the second follow-up interview: blacks, male and female drug users, female heterosexuals, people with less education, those uninsured and insured by Medicaid, those in the Northeast, and those with CD4 counts of >/=500 cells/microl (all p <.05). Using multiple logistic regression analysis, low CD4 count (for CD4 <50 cells/microl: odds ratio [OR], 3.20; p <.001) remained a significant predictor of current HAART use at the time of the second follow-up interview, but lack of insurance (OR, 0.71; p <.05) predicted not receiving HAART. CONCLUSIONS: The proportion of persons under HIV care in the United States who had ever received HAART increased to over 70% of the affected population by January 1998 and the disparities in use between groups narrowed but did not disappear. However, nearly half of those eligible for HAART according to the U.S. Department of Health and Human Services guidelines were not actually receiving it nearly 2 years after these medications were first introduced. Strategies to promote the initiation and continuation of HAART are needed for those without contraindications and those who can tolerate it.

Adolescent↗

Backscatter towards the monitor ion chamber in high-energy photon and electron beams: charge integration versus Monte Carlo simulation.

In some linear accelerators, the charge collected by the monitor ion chamber is partly caused by backscattered particles from accelerator components downstream from the chamber. This influences the output of the accelerator and also has to be taken into account when output factors are derived from Monte Carlo simulations. In this work, the contribution of backscattered particles to the monitor ion chamber response of a Varian 2100C linac was determined for photon beams (6, 10 MV) and for electron beams (6, 12, 20 MeV). The experimental procedure consisted of charge integration from the target in a photon beam or from the monitor ion chamber in electron beams. The Monte Carlo code EGS4/BEAM was used to study the contribution of backscattered particles to the dose deposited in the monitor ion chamber. Both measurements and simulations showed a linear increase in backscatter fraction with decreasing field size for photon and electron beams. For 6 MV and 10 MV photon beams, a 2-3% increase in backscatter was obtained for a 0.5 x 0.5 cm2 field compared to a 40 x 40 cm2 field. The results for the 6 MV beam were slightly higher than for the 10 MV beam. For electron beams (6, 12, 20 MeV), an increase of similar magnitude was obtained from measurements and simulations for 6 MeV electrons. For higher energy electron beams a smaller increase in backscatter fraction was found. The problem is of less importance for electron beams since large variations of field size for a single electron energy usually do not occur.

Electrons↗

Acute rhabdomyolysis and renal failure in HIV-infected patients: risk factors, presentation, and pathophysiology.

Rhabdomyolysis is a common cause of acute renal failure and may be related to a variety of predisposing factors. This entity has been increasingly recognized in HIV-infected individuals and is an important cause of morbidity and mortality. We present a series of seven HIV-positive patients admitted with rhabdomyolysis over a 5-year period; three developed acute renal failure. Infections and substance abuse were the most common risk factors identified; an average of three predisposing factors was present in each case. All patients showed resolution of creatinine phosphokinase (CPK) elevation and serum creatinine returned to the normal range in the three patients who developed renal insufficiency; however, all patients required prolonged hospitalization and one patient died of sepsis. The pathophysiological mechanisms of muscle injury in our patients are reviewed and their bearing on prognosis discussed. It is concluded that clinicians should have a high index of suspicion for the development of rhabdomyolysis in HIV-infected patients with a combination of noncompliance with medical therapy and/or substance abuse and acute infection. With comprehensive supportive care, the prognosis of acute rhabdomyolysis in this population may be reasonably good.

Acute Kidney Injury↗

Modeling photon output caused by backscattered radiation into the monitor chamber from collimator jaws using a Monte Carlo technique.

Dose per monitor unit in photon fields generated by clinical linear accelerators can be affected by the backscattered radiation into the monitor chamber from collimator jaws. Thus, it is necessary to account for the backscattered radiation in computing monitor unit setting for a treatment field. In this work, we investigated effects of the backscatter from collimator jaws based on Monte Carlo simulations of a clinical linear accelerator. The backscattered radiation scored within the monitor chamber was identified as originating either from the upper jaws (Y jaws), or from the lower jaws (X jaws). From the results of Monte Carlo simulations, ratios of the monitor-chamber-scored dose caused by the backscatter to the dose caused by the forward radiation, R(x,y), were modeled as functions of the individual X and Y jaw positions. The amount of the backscattered radiation for any field setting was then computed as a compound contribution from both the X and Y jaws. The dose ratios of R(x,y) were then used to calculate the change in photon output caused by the backscatter, Scb(x,y). Results of these calculations were compared with available measured data based on counting the electron pulses or charge from the electron target of an accelerator. Data from this study showed that the backscattered radiation contributes approximately 3% to the monitor-chamber-scored dose. A majority of the backscattered radiation comes from the upper jaws, which are located closer to the monitor chamber. The amount of the backscatter decreases approximately in a linear fashion with the jaw opening. This results in about a 2% increase of photon output from a 10 cm x 10 cm field to a 40 cm x 40 cm field. The off-axis location of the jaw opening does not have a significant effect on the magnitude of the backscatter. The backscatter effect is significant for monitor chambers using kapton windows, particularly for treatment fields using moving jaws. Applying the backscatter correction improves the accuracy of monitor-unit calculation using a model-based dose calculation algorithm such as the convolution method.

Algorithms↗

Crown diameters of the deciduous teeth of Taiwanese.

The purposes of this study were (1) to characterize the crown diameters of the deciduous teeth of Taiwanese; (2) to compare the differences in the deciduous crown diameters between different populations. The results might provide odontometric information in making preformed stainless steel crowns of the Chinese population. Study casts of 90 children (51 boys and 39 girls) of aged 3 to 6 years were used in this study. The maximum mesiodistal crown diameter (the greatest distance between the contact points of the approximal surfaces) and the buccolingual crown diameter (the greatest distance at a right angle to the mesiodistal measurement) were obtained by using an electronic digital caliper. Significant differences between antimeres were found in the mesiodistal diameters of maxillary canine and maxillary molars (p < 0.001) as well as in the buccolingual diameters of mandibular molars (p < 0.05). Excellent correlations between the antimeres of the corresponding teeth were found (r = 0.70 to 0.96). Boys generally had larger crown diameters than girls with the exception of mesiodistal diameters of maxillary and mandibular canines, and mandibular lateral incisor, whereas the statistically significant gender difference was only found in the buccolingual diameter of mandibular second molar (p < 0.05). The higher the percentage of sexual dimorphism, the larger the gender differences. The percentage of sexual dimorphism ranged from 0.09 to 1.94 for mesiodistal diameters and 0.04 to 2.86 for buccolingual diameters. The mandibular second molar was the most dimorphic tooth. Variations in the crown diameters of the deciduous teeth existed among and within different populations. Deciduous mesiodistal crown diameters of Taiwanese were, in general, smaller than those of Australian aborigines, Taiwan Chinese aborigines, and Hong Kong Chinese, but larger than those of American whites. When considering the buccolingual crown diameters, our data were significantly smaller than those of Icelanders, western Indians, and whites.

Child↗

[A study on dental and cranioficial structure of normal shanghai adults occlusion-I the craniofacial structure analysis with posterioanterior cephalometric roentgenography]

OBJECTIVE: To evaluate the characteristics of normal transverse craniofacial structure in Shanghai area and to establish the database of normal Shanghai adults occlusion for posterioanterior cephalometric roentgenography.METHODS:Posterioanterior-cephalometric of the 92 adults subjects with normalocclusion were measured and analysed by Jiffy orthodontic evaluation 5.0 software package.RESULTS:The database of normal Shanghai adults occlusion for posterioanterior cephalometric roentgenography was established. Transverse measurements were intercorrelated, no statistically significant gender differences were demonstrated in craniofacial width, while the molar overjet of male was larger than that of female.CONCLUSION:The normal transverse cranioficial structure in Shanghai area has its own characteristics. The established database would provide a foundation for the diagnosis and treatment of malocclusion.

Journal Article↗

Optimization of beam orientations and weights for coplanar conformal beams in treating pancreatic cancer.

In treating pancreatic cancer with external-beam radiotherapy, radiation dose given to the tumor volume is largely limited by the tolerance of the normal structures near the disease site, including the kidneys, liver, stomach, small bowel, and spinal cord. The purpose of this work was to investigate whether a coplanar conformal therapy technique with beam optimization could reduce dose to the normal tissues compared to the conventional 4-field technique; and if this was true, whether other beam arrangements were more effective than the 4-field technique in treating pancreatic cancer. In this study, 9 patients who were treated previously for T3N0 or T3N1 pancreatic cancer with external-beam therapy of 30 Gy in 10 fractions were selected. Beam orientations and weights were optimized for 4 to 6 coplanar conformal beams using a simulated annealing algorithm to minimize the kidney volume receiving more than 20 Gy. Optimized plans were compared with standard plans using a 4-field technique with respect to the isodose distributions and dose volume histograms. For the standard 4-field plans giving 30 Gy to the tumor volume, the total kidney volume above 20 Gy ranged from 10% to 35%, with a mean of 22% and a standard deviation of 7%. Optimization of the beam orientations and weights reduced this volume by approximately 2 times without a significant increase of dose to the liver, stomach, and small bowel. This indicated that the radiation toxicity to the kidneys could be reduced substantially by a careful selection of oblique beam angles and weights. Analysis of the optimized plans showed that beam arrangements which involved left and right anterior oblique beams were superior to the conventional 4-field technique for reducing the kidney dose in treating pancreatic cancer.

Adenocarcinoma↗

Antibiotic resistance in bacteria. A current and future problem.

Bacterial pathogens have become increasingly resistant to commonly used antibiotics. In some cases, there are no remaining first-line options for therapy. Problem pathogens which may cause dermatologic and rheumatologic infections will be discussed, including vancomycin-resistant staphylococci and enterococci as well as the multiply-resistant Gram-negative bacilli. Risk factors for acquisition of these organisms and diagnostic studies available for their detection will be reviewed. The underlying mechanisms of resistance, geographic prevalence, potential for continued spread, and proposed strategies for prevention and control are examined. Finally, information on the newer topical and systemic antimicrobial agents, including investigational therapies, will be presented.

Bacillus↗

Calculating dose distributions and wedge factors for photon treatment fields with dynamic wedges based on a convolution/superposition method.

A convolution/superposition based method was developed to calculate dose distributions and wedge factors in photon treatment fields generated by dynamic wedges. This algorithm used a dual source photon beam model that accounted for both primary photons from the target and secondary photons scattered from the machine head. The segmented treatment tables (STT) were used to calculate realistic photon fluence distributions in the wedged fields. The inclusion of the extra-focal photons resulted in more accurate dose calculation in high dose gradient regions, particularly in the beam penumbra. The wedge factors calculated using the convolution method were also compared to the measured data and showed good agreement within 0.5%. The wedge factor varied significantly with the field width along the moving jaw direction, but not along the static jaw or the depth direction. This variation was found to be determined by the ending position of the moving jaw, or the STT of the dynamic wedge. In conclusion, the convolution method proposed in this work can be used to accurately compute dose for a dynamic or an intensity modulated treatment based on the fluence modulation in the treatment field.

Humans↗

[Study on the relationship among ossification of finger's bone, maxillary and mandibular lengths and body height for Shanghai adolescents aged between 11-15 years old]

OBJECTIVE:To research the intrinsic relationship in the growth and development progress of adolescents and to provide scientific basis for orthodontic diagnosis and treatment.METHODS:Sample included 125 Shanghai adolescents between 11-15 years old, and the relationship among maxillary length, mandibular length, ossification of finger's bone, body height and the age of first coming of menstruation on female was studied.RESULTS:The ossification of finger's bone, the increase of maxilla and mandibular lengths and the body height of Shanghai adolescents between 11-15 years old keep the same pace tendency. Female goes into the young quick growing period 2 years earlier than male, but from about 13 years old the growing speed of male is apparently more quick than that of female. When the ossification of finger's bone is nearly 100%, the body height and the mandibular length of male still possesses great growing capacity. The age of sesamoid bone appearance for both male and female and the age of first coming menstruation for female are getting earlier when comparing with others regions.CONCLUSION: There is a close relationship among ossification of finger's bone, maxilla and mandibular lengths and body height of adolescents. Understanding the intrinsic rule correctly has the guiding significance to early diagnosis and treatment in clinical orthodontics.

Journal Article↗

[A correlate study on the first cervical vertebra and mandibular growth:A comparison of Shanghai females between 12 and 15 years old]

OBJECTIVE:To study the correlation between the cervical vertebra and mandibular growth and to reveal the intrinsic rule of the progress of individual growth, especially the trend of craniofacial development.METHODS:The morphological features of the first cervical vertebra and certain variables of craniofacial in lateral cephalometric radiographs from Shanghai females between 12 and 15 years old were measured and correlated. A set of normal values of the atlas vertebra shape of Shanghai 12 and 15 years old females were established.RESULTS:There was a significant correlation between D1 and AP of the first cervical vertebra and the direction of mandibular growth at the age of 12. But the association between atlas size ratio (AP/D1) and the mandibular growth is more notable than either AP or D1. When the atlas size ratio increased, a reduction of the amount of mandibular horizontal growth was showed, and the mandibular rotated backward; on the contrary, when the atlas size ratio decreased, the amount of mandibular horizontal growth increased and the mandibular rotated forward. CONCLUSION: The first cervical vertebra can be used as an indicator to predict the mandibular growth.

Journal Article↗

[Study on the maturation of cervical vertebra for 208 cases Shanghai adolescents growth]

OBJECTIVE:To establish a set of normal values of maturation stages of cervical vertebra for Shanghai adolescents and to provide valid reference index for assessing skeletal age while making diagnosis and treatment plan.METHODS:208 Shanghai adolescents from 11 to 15 years of age were investigated by lateral cephalometric radiographs. The growth status and the relationship of C2-C5 cervical vertebra were observed. RESULTS:The anterior and posterior vertical heights and areas of C2-C5 cervical vertebra increased progressively along with the age, the shapes of cervical vertebra bodies varied regularly. Although female goes into the young quick growing period 2 years earlier than male, the shape changes have no difference between gender. The established standard values of maturation stages of cervical vertebra for Shanghai 11-15 years old adolescents revealed that the growth and development of Shanghai adolescents are getting earlier when comparing with that of GuangDong province. CONCLUSION: The morphological variation of cervical vertebra can be used as an indicator of skeletal age to determine adolescents' growth and development status.

Journal Article↗

Calculating dose and output factors for wedged photon radiotherapy fields using a convolution/superposition method.

We have developed a convolution/superposition method to calculate dose distributions in photon treatment fields with beam modifiers such as physical wedges. The dose component due to wedge generated radiation was accounted for by using an extended phantom model, which integrated a wedge, an air gap, and a patient phantom as the calculation phantom. The inhomogeneities in the extended phantom and the effect of beam hardening by the wedge were both corrected for in the convolution dose calculation. The calculated dose was verified by Monte Carlo simulation of the same extended phantom. A new dual photon source model was also used in the convolution method to account for both primary photons from the target and extra-focal photons from the primary collimator and flattening filter. Thus, realistic photon energy fluence distributions in the extended phantom were used for the dose calculation. The calculated dose distributions and the wedge factors agreed with the measured data within 2% for a variety of treatment fields including asymmetric fields. Our results showed that the wedge-generated radiation could contribute a significant fraction of the total dose in patients. This dose component depends on a specific field configuration, thus wedge factor changes with photon energy, wedge angle, field size, depth, and patient phantom SSD. The variation of the wedge factor can be predicted accurately by our convolution approach with the extended phantom model, which allows for more accurate dose or monitor unit computation for photon fields with beam modifiers.

Algorithms↗

Correcting kernel tilting and hardening in convolution/superposition dose calculations for clinical divergent and polychromatic photon beams.

To account for clinical divergent and polychromatic photon beams, we have developed kernel tilting and kernel hardening correction methods for convolution dose calculation algorithms. The new correction methods were validated by Monte Carlo simulation. The accuracy and computation time of the our kernel tilting and kernel hardening correction methods were also compared to the existing approaches including terma divergence correction, dose divergence correction methods, and the effective mean kernel method with no kernel hardening correction. Treatment fields of 10 x 10-40 x 40 cm2 (field size at source to axis distance (SAD)) with source to source distances (SSDs) of 60, 80, and 100 cm, and photon energies of 6, 10, and 18 MV have been studied. Our results showed that based on the relative dose errors at a depth of 15 cm along the central axis, the terma divergence correction may be used for fields smaller than 10 x 10 cm2 with a SSD larger than 80 cm; the dose divergence correction with an additional kernel hardening correction can reduce dose error and may be more applicable than the terma divergence correction. For both these methods, the dose error increased linearly with the depth in the phantom; the 90% isodose lines at the depth of 15 cm were shifted by about 2%-5% of the field width due to significant underestimation of the penumbra dose. The kernel hardening effect was less prominent than the kernel tilting effect for clinical photon beams. The dose error by using nonhardening corrected kernel is less than 2.0% at a depth of 15 cm along the central axis, yet it increased with a smaller field size and lower photon energy. The kernel hardening correction could be more important to compute dose in the fields with beam modifiers such as wedges when beam hardening is more significant. The kernel tilting correction and kernel hardening correction increased computation time by about 3 times, and 0.5-1 times, respectively. This can be justified by more accurate dose calculations for the majority of clinical treatments.

Algorithms↗

Measuring dose distributions for enhanced dynamic wedges using a multichamber detector array.

This paper investigates measuring dose distributions for enhanced dynamic wedges (EDWs) using a commercial multichamber detector array. The technical aspects of using the chamber array, including chamber calibration, selection of measurement parameters, and use of the reference chamber, have been fully investigated. The measurement results from the chamber array were also confirmed by those from the single chamber and radiographic film measurements. The results reported here showed that proper operation of the chamber array is essential to measure dose accurately for the EDW fields; the chamber detector array can be used more efficiently than a single chamber without compromising the dose measurement accuracy.

Biophysical Phenomena↗