Biomedical subjects

Hui Yan

Publications and source records attributed to Hui Yan.

43 records · Page 3Linked to original sources

PubMed2003

Fuzzy logic guided inverse treatment planning.

A fuzzy logic technique was applied to optimize the weighting factors in the objective function of an inverse treatment planning system for intensity-modulated radiation therapy (IMRT). Based on this technique, the optimization of weighting factors is guided by the fuzzy rules while the intensity spectrum is optimized by a fast-monotonic-descent method. The resultant fuzzy logic guided inverse planning system is capable of finding the optimal combination of weighting factors for different anatomical structures involved in treatment planning. This system was tested using one simulated (but clinically relevant) case and one clinical case. The results indicate that the optimal balance between the target dose and the critical organ dose is achieved by a refined combination of weighting factors. With the help of fuzzy inference, the efficiency and effectiveness of inverse planning for IMRT are substantially improved.

Algorithms↗

PubMed2003

A phantom study on the positioning accuracy of the Novalis Body system.

A phantom study was conducted to investigate inherent positioning accuracy of an image-guided patient positioning system-the Novalis Body system for three-dimensional (3-D) conformal radiotherapy. This positioning system consists of two infrared (IR) cameras and one video camera and two kV x-ray imaging devices. The initial patient setup was guided by the IR camera system and the target localization was accomplished using the kV x-ray imaging system. In this study, the IR marker shift and phantom rotation were simulated and their effects on the positioning accuracy were examined by a Rando phantom. The effects of CT slice thickness and treatment sites on the positioning accuracy were tested. In addition, the internal target shift was simulated and its effect on the positioning accuracy was examined by a water tank. With the application of the Novalis Body system, the positioning error of the planned isocenter was significantly reduced. The experimental results with the simulated IR marker shifts indicated that the positioning errors of the planned isocenter were 0.6 +/- 0.3, 0.5 +/- 0.2, and 0.7 +/- 0.2 mm along the lateral, longitudinal, and vertical axes, respectively. The experimental results with the simulated phantom rotations indicated that the positioning errors of the planned isocenter were 0.6 +/- 0.3, 0.7 +/- 0.2, and 0.5 +/- 0.2 mm along the three axes, respectively. The experimental results with the simulated target shifts indicated that the positioning errors of the planned isocenter were 0.6 +/- 0.3, 0.7 +/- 0.2, and 0.5 +/- 0.2 mm along the three axes, respectively. On average, the positioning accuracy of 1 mm for the planned isocenter was achieved using the Novalis Body system.

Equipment Failure Analysis↗

PubMed2003

[The regulatory effect of endogenous hydrogen sulfide on hypoxic pulmonary hypertension].

OBJECTIVE: To study the changes of endogenous H2S and the effect of exogenously applied H2S on hypoxic pulmonary hypertension (HPH). METHODS: Male Wistar rats were randomly divided into control group (n = 6), hypoxia group (n = 7) and hypoxia + NaHS group (n = 6). The rats that received hypoxia were put into a normobaric hypoxic chamber to respire hypoxic gas containing 10% (volume fraction) O2 for 6 hours everyday. NaHS solution was injected to rats of hypoxia + NaHS group at a dosage of 0.78 mg.kg-1 before hypoxic challenge. After 21 days of hypoxia, the mean pulmonary artery pressure (mPAP) was measured. The weight ratio of right ventricle vs left ventricle and septum [RV/(LV + SP)] was measured. The microstructure and ultrastructure changes in pulmonary small arteries were examined using elastin staining and transparent electron microscope respectively. And the activity of H2S generating enzymes in homogenates of the lung tissue and pulmonary artery was measured. The cystathionine gamma--lyase (CSE) mRNA in lung tissue was also measured using quantitative RT-PCR. RESULTS: Compared with rats in the control group, the mPAP increased 45.6% (P < 0.01) and the RV/(LV + SP) ratio increased 41% (P < 0.01) in rats of hypoxia group respectively. The relative medium thickness (RMT) and relative medium areas (RMA) increased 41% and 49% respectively (P all < 0.01) under optical microscope. The ultrastructure of the pulmonary small arteries also changed significantly. The H2S generating enzyme activity in lung tissue and in pulmonary artery decreased 52% and 54% respectively (P < 0.01). There were obviously negative correlations between the mPAP and H2S generating enzymes ativity. Relative CSE mRNA amount in lung tissue also decreased 53% (P < 0.01) in rats of hypoxia group compared with that of control group. The mPAP, and the RV/(LV + SP) ratio of rats in hypoxia + NaHS group decreased 31.2%, and 24% respectively compard with that of hypoxia group (P < 0.01). The RMT and RMA in rats of hypoxia + NaHS group also decreased 36% and 31% respectively (P < 0.01). In hypoxia + NaHS group, the H2S generating enzymes activity and relative CSE mRNA amount in the lung tissue increased 67.7% and 110% respectively compared with those in hypoxia group (P all < 0.01). CONCLUSION: Endogenous H2S was involved in the pathogenesis of rat's HPH. Exogenously applied H2s could exert protective effect during HPH.

Animals↗

PubMed2002

Characterizing closely spaced, complex disulfide bond patterns in peptides and proteins by liquid chromatography/electrospray ionization tandem mass spectrometry.

Identifying the Cys residues involved in disulfide linkages of peptides and proteins that contain complex disulfide bond patterns is a significant analytical challenge. This is especially true when the Cys residues involved in the disulfide bonds are closely spaced in the primary sequence. Peptides and proteins that contain free Cys residues located near disulfide bonds present the additional problem of disulfide shuffling via the thiol-disulfide exchange reaction. In this paper, we report a convenient method to identify complex disulfide patterns in peptides and proteins using liquid chromatography/electrospray ionization tandem mass spectrometry (LC/ESI-MS/MS) in combination with partial reduction by tris(2-carboxyethyl)phosphine (TCEP). The method was validated using well-characterized peptides and proteins including endothelin, insulin, alpha-conotoxin SI and immunoglobulin G (IgG2a, mouse). Peptide or protein digests were treated with TCEP in the presence of an alkylation reagent, maleimide-biotin (M-biotin) or N-ethylmaleimide (NEM), followed by complete reduction with dithiothreitol and alkylation by iodoacetamide (IAM). Subsequently, peptides that contained alkylated Cys were analyzed by capillary LC/ESI-MS/MS to determine which Cys residues were modified with M-biotin/NEM or IAM. The presence of the alkylating reagent (M-biotin or NEM) during TCEP reduction was found to minimize the occurrence of the thiol-disulfide exchange reaction. A critical feature of the method is the stepwise reduction of the disulfide bonds and the orderly, sequential use of specific alkylating reagents.

Alkylation↗

PubMed2002

Malignant transformation of "benign" cystic mesothelioma of the peritoneum.

BACKGROUND AND OBJECTIVES: Peritoneal mesothelioma is being diagnosed with greater accuracy as a result of immunocytochemical analysis. The histological type of peritoneal mesothelioma has a great influence on the natural history of the disease. Benign cystic mesothelioma is a definite clinical entity; however, the absence of a uniform approach to treatment and a lack of long-term follow-up of patients seriously hinders an accurate assessment of the disease process. METHODS: The medical history of a patient with a diagnosis of benign peritoneal cystic mesothelioma followed for 10 years is presented. The medical literature of this disease is reviewed. RESULTS: The patient was a 36-year-old woman initially diagnosed with benign cystic peritoneal mesothelioma; however, after six surgical procedures with the aim of reducing the volume of intraperitoneal fluid and cysts, the disease developed into an aggressive, diffuse malignant mesothelioma. Involvement of abdominal incisions, invasion of lymph nodes, and invasion of the viscera occurred. CONCLUSIONS: Peritoneal cystic mesothelioma is a disease in need of careful longitudinal studies in order to better define the clinical course of these patients. This case report along with a literature review suggests caution in the assessment of cystic mesothelioma as a benign process. This patient had a clear malignant transformation of benign cystic mesothelioma to an invasive and potentially lethal process.

Adult↗

PubMed2002

Dosimetric characteristics of Novalis shaped beam surgery unit.

The dosimetric characteristics of a new dedicated radiosurgical treatment unit are systematically measured in terms of its percent depth dose, beam profile, and relative scatter factor. High-resolution diode detector, mini-ion-chamber detector, and conventional Kodak XV films are used to measure dosimetric data for a range of field sizes from 6x6 mm to 100x100 mm. The effects of collimator size, micro-multileaf collimator shape, and detector type on the dosimetric data are investigated. Results indicate that, with careful design, accurate dosimetric data could be acquired using either a dedicated diode detector or a mini-ion-chamber detector, and film detector. Special attention is required when measuring dosimetric data for small field sizes such as 6x6 mm.

Equipment Failure Analysis↗

PubMed2002

A technique of intensity-modulated radiosurgery (IMRS) for spinal tumors.

This study is to demonstrate the feasibility of spinal radiosurgery using an image-guided intensity-modulated radiosurgical (IMRS) procedure. A dedicated Novalis shaped beam surgery unit equipped with a built-in micro-multileaf collimator (mMLC) with a single 6 MV photon beam was used. Each patient was simulated in the supine position using an AcQsim CT simulator with infrared sensitive markers for localization. A variety of different treatment plans were developed, but the most common plan was the use of seven coplanar intensity-modulated beams to minimize radiation to critical organs such as the spinal cord and kidneys. An automatic localization device based on infrared and video cameras was used to guide the initial patient setup. Two keV x-ray imaging systems were used to identify potential deviations from the planned isocenter. A total of 25 patients with spinal tumors have been treated using this procedure with a single prescription dose ranging from 6 to 12 Gy. The final verification images indicated that the average isocenter deviation from the planned isocenter was within 2 mm. The phantom verification of isocenter doses indicated that the average deviation of measured isocenter doses from the planned isocenter doses for all patients treated with intensity-modulated beams was less than 2%. Film dose measurement in a phantom study demonstrated good agreement of above 50% isodose lines between the planned and measured results. Preliminary experience shows that precision delivery of high dose radiation could be administered to the planned target volume while the dose to the critical organs is kept within tolerable limits.

Computer Simulation↗