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X G Xu

Publications and source records attributed to X G Xu.

At least 19 recordsLinked to original sources
PubMed2006

X-ray imaging optimization using virtual phantoms and computerized observer modelling.

This study develops and demonstrates a realistic x-ray imaging simulator with computerized observers to maximize lesion detectability and minimize patient exposure. A software package, ViPRIS, incorporating two computational patient phantoms, has been developed for simulating x-ray radiographic images. A tomographic phantom, VIP-Man, constructed from Visible Human anatomical colour images is used to simulate the scattered portion using the ESGnrc Monte Carlo code. The primary portion of an x-ray image is simulated using the projection ray-tracing method through the Visible Human CT data set. To produce a realistic image, the software simulates quantum noise, blurring effects, lesions, detector absorption efficiency and other imaging artefacts. The primary and scattered portions of an x-ray chest image are combined to form a final image for computerized observer studies and image quality analysis. Absorbed doses in organs and tissues of the segmented VIP-Man phantom were also obtained from the Monte Carlo simulations. Approximately 25,000 simulated images and 2,500,000 data files were analysed using computerized observers. Hotelling and Laguerre-Gauss Hotelling observers are used to perform various lesion detection tasks. Several model observer tasks were used including SKE/BKE, MAFC and SKEV. The energy levels and fluence at the minimum dose required to detect a small lesion were determined with respect to lesion size, location and system parameters.

Computer Simulation↗
PubMed2004

Fluence-to-dose conversion coefficients for monoenergetic proton beams based on the VIP-Man anatomical model.

A new set of fluence-to-absorbed dose and fluence-to-effective dose conversion coefficients has been calculated for high-energy protons using the whole-body anatomical model VIP-Man, which was developed from the high-resolution transverse colour photographic images of the National Library of Medicine's Visible Human Project. For 10 monoenergetic proton beams between 20 and 10,000 MeV, organ dose calculations were performed using the Monte Carlo code MCNPX under six different irradiation geometries: anterior-posterior, posterior-anterior, left lateral, right lateral, isotropic and rotational. The absorbed dose results for 24 major organs of VIP-Man are presented and compared with those based on mathematical phantoms reported in the literature. The discrepancies (generally within 40%) in organ dose and effective dose estimates are attributed to the use of different transport models employed by different Monte Carlo codes.

Adult↗
PubMed2004

Specific absorbed fractions for internal photon emitters calculated for a tomographic model of a pregnant woman.

Specific absorbed fractions are essential for calculation of radiation dose from internal emitters. Existing specific absorbed fractions for pregnant women were calculated using the stylized models; in this work, a partial-body tomographic model for a pregnant woman was constructed from a rare set of CT images. Based on this tomographic model, the Monte Carlo code, EGS4-VLSI, was used to derive specific absorbed fractions. Monoenergetic, isotropic photon emitters from 15 keV to 4 MeV were distributed in different source organs, and doses were calculated to many target regions in the body. Even though the results showed general agreement with previous studies for higher energies, significant differences were also found, especially for lower energies. The main reasons for the differences are due to the variation of mass, geometry, and organ distances, and they demonstrate the influence of more realistic body models on dose calculations.

Adult↗
PubMed2003

Calculations of specific absorbed fractions of the gastrointestinal tract using a realistic whole body tomographic model.

Assessment of organ doses from internally deposited radionuclides involves the use of predetermined specific absorbed fractions (SAFs). Many tabulations of SAFs have been derived from Monte Carlo transport simulations using stylized computational models that are not fully realistic of human internal organ anatomy. This paper presents the results of a study to calculate SAFs in the gastrointestinal (GI) tract using a recently developed tomographic model VIP-Man and the EGS4 Monte Carlo radiation transport code. Results show that, for some energies and source-target combinations, considerable discrepancies exist between these results and those from earlier studies, suggesting a need to evaluate existing data carefully by comparison with realistic models.

Digestive System↗
PubMed2003

Estimating the depth of embedded contaminants from in-situ gamma spectroscopic measurements.

The depth of radiological contamination is information required for decontamination and decommissioning of nuclear facilities. This paper proposes and tests a simple technique for measuring the depth of contamination. The method uses measurements with an HPGe detector at two distances (or heights) from the surface on the same side of the medium. The ratio of the photopeak areas easily can be used to yield the depth of an embedded source. The calculational algorithm was verified by simulations with the MCNP4C code and laboratory experiments for a point source and other special sources. Predictions of the depth for shallowly embedded sources have relatively large uncertainties (approximately 18%) but improve as depth increases. This technique provides a very easy way for a user to quickly estimate the depth of the subsurface contamination on site.

Algorithms↗
PubMed2001

Specific absorbed fractions from the image-based VIP-Man body model and EGS4-VLSI Monte Carlo code: internal electron emitters.

VIP-Man is a whole-body anatomical model newly developed at Rensselaer from the high-resolution colour images of the National Library of Medicine's Visible Human Project. This paper summarizes the use of VIP-Man and the Monte Carlo method to calculate specific absorbed fractions from internal electron emitters. A specially designed EGS4 user code, named EGS4-VLSI, was developed to use the extremely large number of image data contained in the VIP-Man. Monoenergetic and isotropic electron emitters with energies from 100 keV to 4 MeV are considered to be uniformly distributed in 26 organs. This paper presents, for the first time, results of internal electron exposures based on a realistic whole-body tomographic model. Because VIP-Man has many organs and tissues that were previously not well defined (or not available) in other models, the efforts at Rensselaer and elsewhere bring an unprecedented opportunity to significantly improve the internal dosimetry.

Bone Marrow↗
PubMed2001

Conversion coefficients based on the VIP-Man anatomical model and EGS4.

A new set of conversion coefficients from kerma free-in-air to absorbed dose and kerma free-in-air to "effective VIP-Man dose" has been calculated for external monoenergetic photon beams from 10 keV to 10 MeV using an image-based whole-body anatomical model. This model, called VIP-Man, was recently developed at Rensselaer from the high-resolution color images of the National Library of Medicine's Visible Human Project. An EGS4-based Monte Carlo user code, named EGS4-VLSI, was developed to efficiently process the extremely large image data in VIP-Man. Irradiation conditions include anterior-posterior, posterior-anterior, right lateral, left lateral, rotational, and isotropic geometries. Conversion coefficients from this study are compared with those obtained from two mathematical models, ADAM and EVA. "Effective VIP-Man doses" differ from the previously reported effective dose results by 10%-50% for photons between 100 keV and 10 MeV. Discrepancies are more significant at lower energies and for individual organ doses. Since VIP-Man is a realistic model that contains several tissues that were not previously defined well (or not available) in other models, the reported results offer an opportunity to improve the existing dosimetric data and the mathematical models.

Air Pollutants, Radioactive↗
PubMed2001

Fluence-to-dose conversion coefficients based on the VIP-Man anatomical model and MCNPX code for monoenergetic neutrons above 20 MeV.

A new set of fluence-to-absorbed dose and fluence-to-effective dose conversion coefficients has been calculated for high-energy neutrons using a whole-body anatomical model, VIP-Man, developed from the high-resolution transversal color photographic images of the National Library of Medicine's Visible Human Project. Organ dose calculations were performed using the Monte Carlo code MCNPX for 20 monoenergetic neutron beams between 20 MeV and 10,000 MeV under 6 different irradiation geometries: anterior-posterior, posterior-anterior, left lateral, right lateral, isotropic, and rotational. For neutron Monte Carlo calculations, results based on an image-based whole-body model were not available in the literature. The absorbed dose results for 24 major organs of VIP-Man are presented in the form of tables and selected figures that compare with those based on simplified mathematical phantoms reported in the literature. VIP-Man yields up to 40% larger values of effective dose and many organ doses, thus suggesting that the results reported in the past may not be conservative.

Humans↗
PubMed2001

Organ dose conversion coefficients for 0.1-10 MeV electrons calculated for the VIP-Man tomographic model.

A whole-body tomographic model, called VIP-Man, was recently developed at Rensselaer Polytechnic Institute from the high-resolution color photographic images of the National Library of Medicine's Visible Human Project. An EGS4-based Monte Carlo user code, named EGS4-VLSI, was developed to efficiently transport electrons using the large image data set for VIP-Man. VIP-Man has been used to calculate doses for neutrons and photons. This paper presents a new set of fluence-to-absorbed-dose conversion coefficients for monoenergetic electron beams between 100 keV and 10 MeV for VIP-Man. Irradiation conditions include anterior-posterior, posterior-anterior, right lateral, left lateral, rotational, and isotropic source geometries. Comparisons between organ doses from VIP-Man, which is taller and heavier than the Reference Man, and existing data from mathematical models show significant discrepancies. It appears that even slight differences between body models can cause dramatic dosimetric deviations for low penetrating electron irradiation. This suggests that a single standard body model may poorly represent a large population and may not be acceptable for electron dosimetry.

Electrons↗
PubMed2000

Effects of des-aspartate-angiotensin I on angiotensin II-induced incorporation of phenylalanine and thymidine in cultured rat cardiomyocytes and aortic smooth muscle cells.

Des-aspartate-angiotensin I, a pharmacologically active nine-amino acid angiotensin peptide, and losartan, an AT(1) angiotensin receptor antagonist, but not angiotensin-(1-7), another active angiotensin peptide, completely attenuated the angiotensin II-induced incorporation of [3H]phenylalanine in cultured rat cardiomyocytes. The attenuation by des-aspartate-angiotensin I but not that of losartan was inhibited by indomethacin. The data support an earlier suggestion that the nonapeptide attenuates cardiac hypertrophy in rats via an indomethacin-sensitive angiotensin AT(1) receptor subtype. In rat aortic smooth muscle cells, both des-aspartate-angiotensin I and angiotensin-(1-7) had no effect on the angiotensin II-induced [3H]phenylalanine incorporation. However, the two peptides significantly attenuated the angiotensin II-induced [3H]thymidine incorporation in the smooth muscle cells. The attenuation by angiotensin-(1-7) but not by des-aspartate-angiotensin I was inhibited by (D-Ala(7))-angiotensin-(1-7), a specific angiotensin-(1-7) antagonist. Des-aspartate-angiotensin I also attenuated FCS-stimulated [3H]thymidine incorporation. This attenuation was inhibited by the peptide angiotensin receptor antagonist, (Sar(1), Ile(8))-angiotensin II, but not by losartan. These data indicate that des-aspartate-angiotensin I and angiotensin-(1-7) do not participate in the process of protein synthesis in vascular smooth muscle cells and that the nonapeptide and heptapeptide act on different non-AT(1) receptors to mediate their anti-hyperplasic action. Although the exact mechanisms of action remain to be elucidated, the findings indicate that des-aspartate-angiotensin I acts as an agonist on angiotensin AT(1) and non-AT(1) receptor subtypes and induces responses that oppose the actions of angiotensin II.

1-Sarcosine-8-Isoleucine Angiotensin II↗
PubMed2000

Fluence-to-dose conversion coefficients from monoenergetic neutrons below 20 MeV based on the VIP-man anatomical model.

A new set of fluence-to-absorbed dose and fluence-to-effective dose conversion coefficients have been calculated for neutrons below 20 MeV using a whole-body anatomical model, VIP-Man, developed from the high-resolution transverse colour photographic images of the National Library of Medicine's Visible Human Project. Organ dose calculations were performed using the Monte Carlo code MCNP for 20 monoenergetic neutron beams between 1 x 10(-9) MeV and 20 MeV under six different irradiation geometries: anterior-posterior, posterior-anterior, right lateral, left lateral, rotational and isotropic. The absorbed dose for 24 major organs and effective dose results based on the realistic VIP-Man are presented and compared with those based on the simplified MIRD-based phantoms reported in the literature. Effective doses from VIP-Man are not significantly different from earlier results for neutrons in the energy range studied. There are, however, remarkable deviations in organ doses due to the anatomical differences between the image-based and the earlier mathematical models.

Algorithms↗
PubMed2000

VIP-Man: an image-based whole-body adult male model constructed from color photographs of the Visible Human Project for multi-particle Monte Carlo calculations.

Human anatomical models have been indispensable to radiation protection dosimetry using Monte Carlo calculations. Existing MIRD-based mathematical models are easy to compute and standardize, but they are simplified and crude compared to human anatomy. This article describes the development of an image-based whole-body model, called VIP-Man, using transversal color photographic images obtained from the National Library of Medicine's Visible Human Project for Monte Carlo organ dose calculations involving photons, electron, neutrons, and protons. As the first of a series of papers on dose calculations based on VIP-Man, this article provides detailed information about how to construct an image-based model, as well as how to adopt it into well-tested Monte Carlo codes, EGS4, MCNP4B, and MCNPX.

Adult↗
PubMed1999

Experience of urgent reconstruction of electrical injuries.

Although there have been great advances in the treatment of electrical injuries in the last 20 years, the extremity loss ratio in electrical injuries remains at an unacceptably high level. The primary reason for this is the progressive tissue necrosis and enlargement of the necrosis in the wound. The goal in this study is to examine possible ways to break the necrotic malignancy circle and save the form and function of damaged extremities. As a result of systematic experimental and clinical research, a comprehensive urgent reconstruction alternative for electrical injuries has been proposed. The alternative includes the following principles: debriding the wound as early as possible after injury; preserving as much as possible the vital tissue structures, such as nerve, vessels, joints, tendons, and bone, even when they have undergone devitalization or local necrosis; transplanting these vital tissues during the first surgery if the functional reconstruction requires; nourishing the wound bed by covering with tissue flaps that have rich blood supply; improving flap survival by continuous irrigations with a compound medicine beneath the flaps for a 24- to 72-hour period after surgery; providing general treatment with vasoactive agents and antibiotics. This paper summarizes our experience of using this method in the treatment of 105 electrical injury patients (a total of 309 wounds) in the time period from 1 January 1986 to 31 December 1996. Satisfying results were obtained, with the extremity loss ratio decreasing to 7% as compared to 41.5% during the 10 years preceding 1984 at the same hospital. Thus, the urgent comprehensive reconstruction alternative presented here is an effective and workable method to manage electrical injuries.

Adolescent↗
PubMed1999

A non-destructive method to determine the depth of radionuclides in materials in-situ.

A non-destructive method based on in-situ gamma spectroscopy is developed to determine the depth of radiological contamination in media. An innovative algorithm, Gamma Penetration Depth Unfolding Algorithm (GPDUA), uses point kernel techniques to predict the depth of contamination based on the results of the uncollided peak information from the in-situ gamma spectroscopy. The GPDUA is designed and verified through extensive Monte Carlo simulations and validated through laboratory experiments. This innovative tool promises to be "better, faster, safer, and cheaper" than the current practice in decontamination and decommissioning. The method requires the a priori knowledge of the contaminant source distribution. The applicable radiological contaminants of interest are any isotopes that emit two or more gamma rays per disintegration or isotopes that emit a single gamma ray but have gamma-emitting progeny in secular equilibrium with its parent (e.g., 60Co, 235U, and 137Cs to name a few). The predicted depths from the GPDUA algorithm using Monte Carlo N-Particle Transport Code simulations and laboratory experiments using 60Co have consistently produced predicted depths within 20% of the actual or known depth.

Gamma Rays↗
PubMed1996

Sex-specific tissue weighting factors for effective dose equivalent calculations.

The effective dose equivalent was defined in the International Commission on Radiological Protection Publication 26 in 1977 and later adopted by the U.S. Nuclear Regulatory Commission. To calculate organ doses and effective dose equivalent for external exposures using Monte Carlo simulations, sex-specific anthropomorphic phantoms and sex-specific weighting factors are always employed. This paper presents detailed mathematical derivation of a set of sex-specific tissue weighting factors and the conditions which the weighting factors must satisfy. Results of effective dose equivalent calculations using female and male phantoms exposed to monoenergetic photon beams of 0.08, 0.3, and 1.0 MeV are provided and compared with results published by other authors using different sex-specific weighting factors and phantoms. The results indicate that females always receive higher effective dose equivalent than males for the photon energies and geometries considered and that some published data may be wrong due to mistakes in deriving the sex-specific weighting factors.

Female↗
PubMed1996

Exacerbation of cold restraint-induced gastric ulcer by GABA in mice.

AIM: To study the effect of GABA on cold restraint-induced gastric ulcer (CRGU) and its mechanism. METHODS: CRGU was produced in adult male mice at 1 degree C in cold room under restraint for 1 h. The ulcer index indicated the severity of gastric mucosa lesion. Gastric mucin was determined with alcian blue dye. RESULTS: GABA 2 mumol (i.c.v.) accelerated CRGU, Bicuculline (Bic) 0.2 mumol (i.c.v.) did not affect CRGU, whereas Baclofen (Bac) 4 mumol (i.c.v.) exacerbated CRGU. Bic did not modify the exacerbation of CRGU by GABA and Bac. Atropine (Atr) 0.2 mg.kg-1 (s.c.) and Phentolamine (Phen) 2.5 mg.kg-1 inhibited CRGU, and abolished the exacerbation of CRGU by GABA. Cold restraint (CR) decreased the amount of the gastric mucin, but GABA 2 mumol had no effect on CR gastric mucin. CONCLUSION: While GABA-B receptor in brain was activated, exogenous GABA exacerbated CRGU via vagal and sympathetic nerves, bearing no relation to decrease of the gastric mucin or weakening of the gastric mucosal barrier.

Adrenergic alpha-Antagonists↗
PubMed1995

A study of the angular dependence problem in effective dose equivalent assessment.

The newly revised American National Standard N13.11 (1993) includes measurements of angular response as part of personnel dosimeter performance testing. However, data on effective dose equivalent (HE), the principle limiting quantity defined in International Commission on Radiological Protection (ICRP) Publication 26 and later adopted by U.S. Nuclear Regulatory Commission (NRC), for radiation incident on the body from off-normal angles are little seen in the literature. The absence of scientific data has led to unnecessarily conservative approaches in radiation protection practices. This paper presents a new set of fluence-to-HE conversion factors as a function of radiation angles and sex for monoenergetic photon beams of 0.08, 0.3, and 1.0 MeV. A Monte Carlo transport code (MCNP) and sex-specific anthropomorphic phantoms were used in this study. Results indicate that Anterior-posterior (AP) exposure produces the highest HE per unit photon fluence in all cases. Posterior-anterior (PA) exposure produces the highest HE among beams incident from the rear half-plane of the body. HE decreases dramatically as one departs from the AP and PA orientations. The results also indicate that overestimations caused by using isotropic dosimeters in assessing effective dose equivalent from near-overhead and near-underfoot exposures are 550%, 390%, and 254% for 0.08, 0.3, and 1.0 MeV, respectively. Comparisons of the angular dependence of HE with those based on the secondary quantities defined in International Commission on Radiation Units and Measurements (ICRU) Reports 39, 43, and 47 show significant differences. This paper discusses why more accurate assessments of HE are necessary and possible. An empirical equation is proposed which can be used as the optimum dosimeter angular response function for radiation angles ranging from 0 degrees to 90 degrees for dosimeter calibration, performance testing, and design.

Dose-Response Relationship, Radiation↗