Biomedical subjects

Tong Xu

Publications and source records attributed to Tong Xu.

26 records · Page 2Linked to original sources

PubMed2004

Area beam equalization: optimization and performance of an automated prototype system for chest radiography.

RATIONALE AND OBJECTIVES: To evaluate the feasibility and performance of an x-ray beam equalization system for chest radiography using anthropomorphic phantoms. MATERIALS AND METHODS: Area beam equalization involves the process of the initial unequalized image acquisition, attenuator thickness calculation, mask generation using a 16 x 16 piston array, and final equalized image acquisition. Chest radiographs of three different anthropomorphic phantoms were acquired with no beam equalization and equalization levels of 4.8, 11.3, and 21. Six radiologists evaluated the images by scoring them from 1-5 using 13 different criteria. The dose was calculated using the known attenuator material thickness and the mAs of the x-ray tube. RESULTS: The visibility of anatomic structures in the under-penetrated regions of the chest radiographs was shown to be significantly (P < .01) improved after beam equalization. An equalization level of 4.8 provided most of the improvements with moderate increases in patient dose and tube loading. Higher levels of beam equalization did not show much improvement in the visibility of anatomic structures in the under-penetrated regions. CONCLUSION: A moderate level of x-ray beam equalization in chest radiography is superior to both conventional radiographs and radiographs with high levels of beam equalization. X-ray beam equalization can significantly improve the visibility of anatomic structures in the under-penetrated regions while maintaining good image quality in the lung region.

Feasibility Studies↗

PubMed2004

Scanning-slit photon counting x-ray imaging system using a microchannel plate detector.

An experimental prototype of a novel photon counting x-ray imaging system was evaluated. This system is based on an "edge-on" microchannel plate (MCP) detector and utilizes scanning slit imaging configuration. The detector is capable of photon counting, direct conversion, high spatial resolution, controllable physical charge amplification, quantum limited and scatter free operation. The detector provides a 60 mm wide field of view (FOV) and its count rate is 200 kHz for the entire FOV. The count rate of the current system is limited by the position encoding electronics, which has a single input for all events from the entire detector, and incorporates a single channel ADC with 1 micros conversion time. It is shown that the count rate can potentially be improved to clinically acceptable levels using multichannel application specific integrated circuit (ASIC) electronics and multi-slit image acquisition geometry. For a typical acquisition time used in this study, the image noise was measured to be less than the typically acceptable noise level for medical x-ray imaging. It is anticipated that the noise level will be also low after the implementation of the ASIC electronics. The quantum efficiency of the detector was measured to be 40%-56% for an energy range of 50-90 kVp for MCPs used in this study and can be improved to > 80% using MCPs with the optimized parameters. Images of resolution and anthropomorphic phantoms were acquired at an x-ray tube voltage of 50 kVp. The value of contrast transfer function for the detector was measured to be 0.5 at a spatial frequency of 5 lp/mm. The intrinsic spatial resolution of the system is 28 microm FWHM and was limited by the accuracy of the time-to-digital conversion of the position encoding electronics. Given the advantages of the edge-on MCP detector such as direct conversion and physical charge amplification, it can potentially be applied to mammography and chest radiography.

Equipment Design↗

PubMed2004

Treatment planning considerations of reshapeable automatic intensity modulator for intensity modulated radiation therapy.

As compared with multi-leaf collimator based intensity modulated radiation therapy (IMRT) techniques, physical modulators have the major advantage of temporally invariant intensity map delivery which makes it more flexible with monitor unit rate, simpler resolution of interrupted treatment and easier implementation and use with respiratory gating. However, traditional physical modulator techniques require long fabrication time and operator intervention during treatments. It has been previously proposed [Xu et al., Med. Phys. 29, 2222-2229 (2002)] that a reshapeable automatic intensity modulator (RAIM) can automatically produce physical modulators by molding a deformable high x-ray attenuation material using a matrix of computer-controlled pistons. RAIM can potentially eliminate the limitations of traditional physical modulators. The present study addresses the treatment planning considerations of RAIM for IMRT. In this study, a 3D treatment-planning system (PLUNC) was modified to include the capability of providing treatment planning using RAIM. Two clinically representative cases were studied: nasopharyngeal and prostate tumors. First, the RAIM system with two different spatial resolutions at isocenter, 1 x 1 cm2 and 0.5 x 0.5 cm2, were evaluated. The treatment planning results of RAIM were then compared with other IMRT techniques such as smooth modulator with ideal (100%-2%) and limited (100%-13%) intensity modulation ranges, segmental multi-leaf collimator (SMLC) with ten intensity levels, 1 cm leaf width and 0.5 cm step size and serial tomotherapy using the Peacock system. Bringing the spatial resolution of RAIM down to 0.5 x 0.5 cm2 did not show improvement due to the effect of penumbra. The RAIM system with 1 x 1 cm2 proved slightly inferior as compared to the ideal smooth physical modulator but better than the SMLC technique and the smooth modulator with limited modulation range. When compared to serial tomotherapy, RAIM is only inferior in brain stem sparing for the nasopharynx case. Furthermore, the RAIM system with 1 x 1 cm2 resolution required significantly lower monitor units as compared to the other IMRT techniques for the two cases studied.

Algorithms↗

PubMed2003

Diverse effects of methylseleninic acid on the transcriptional program of human prostate cancer cells.

Methylseleninic acid (MSA) has been shown to have potent anticancer activity and is an excellent compound for studying the anticancer effects of selenium in vitro. To gain insights into the effects of MSA in prostate cancer, we characterized the global transcriptional response of LNCaP, an androgen-sensitive human prostate cancer cell line, to MSA by using high-density cDNA microarrays. We identified 951 genes whose expression shows striking dose- and time-dependent changes in response to 3-30 microM MSA over the time course of 48 h. Transcript levels of many cell cycle-regulated genes change in response to MSA, suggesting that MSA inhibits proliferation. Consistent with these gene expression changes, cell proliferation, monitored by carboxyfluoroscein succinimidyl ester staining, was decreased after MSA treatment, and an accumulation of cells at G0/G1 phase was detected by flow cytometry. Surprisingly, MSA also modulated expression of many androgen-regulated genes, suppressed androgen receptor (AR) expression at both mRNA and protein level, and decreased levels of prostate specific antigen secreted into the medium. Low concentrations of MSA also induced significant increases in transcript levels of phase 2 detoxification enzymes and induced NADPH dehydrogenase, quinone 1 enzymatic activity, a surrogate marker of global phase 2 enzyme activity. Our results suggest that MSA may protect against prostate cancer by inhibiting cell proliferation, by modulating the expression of AR and AR-regulated genes and by inducing carcinogen defenses.

Adenocarcinoma↗

PubMed2003

Patient-specific region-of-interest fluoroscopy device for X-ray dose reduction.

A region-of-interest (ROI) fluoroscopy device that provides an automatically generated ROI filter with an arbitrary shape, as well as digitally compensated images, was built and evaluated. ROI filters were generated by using a deformable attenuation material. Images were compensated by using a compensation ratio and a running average interpolation method. Image compensation parameters were predicted on the basis of the x-ray tube potential used. The image quality with and without an ROI filter was evaluated. This ROI fluoroscopic technique was shown to substantially reduce patient and operator radiation exposure without degrading image quality within the ROI.

Filtration↗

PubMed2002

Reshapable physical modulator for intensity modulated radiation therapy.

A new method of generating beam intensity modulation filters for intensity modulated radiation therapy (IMRT) is presented. The modulator was based on a reshapable material, which is not compressible but can be deformed under pressure. A two-dimensional (2D) piston array was used to repeatedly shape the attenuating material. The material is a mixture of tungsten powder and a silicon-based binder. The linear attenuation coefficient of the material was measured to be 0.409 cm(-1) for a 6 MV x-ray beam. The maximum thickness of the physical modulator is 10.2 cm, allowing a transmission of 1.5%. A 16 x 16 square piston array was used to generate a depth pattern in the deformable attenuating material. Each piston has a cross section of 6.37 x 6.37 mm2. The modulator was placed 65 cm from the radiation source of the linear accelerator in the position of the shielding tray. At this position, each piston projects to a 1.0 x 1.0 cm2 area at the isocenter, giving a treatment field of 16 x 16 cm2. The percent depth dose curve and output factor measurement show a slight beam hardening and a 1%-4% increase in scatter fraction when 2.2-4.4 cm uniform thickness filters are in the beam. The surface dose was decreased with the filter in the beam. Ion chamber and verification films were used to verify the entrance dose. The measured absolute and relative doses were compared with the calculated dose. The agreement of measurements and calculations is within 3%. In order to verify the spatial modulation of dose, 1-D dose profiles were obtained using dose calculations. Calculated and measured profiles were compared. The 20%-80% penumbra of the modulator was measured to be 5.5-10 mm. The results show that a physical modulator formed using a 16 x 16 piston array and a deformable attenuation material can provide intensity modulation for IMRT comparable with those provided by currently available commercial MLC techniques.

Biophysical Phenomena↗

PubMed2002

Detecting K-ras and p53 gene mutation from stool and pancreatic juice for diagnosis of early pancreatic cancer.

OBJECTIVE: To explore new methods for the early diagnosis of pancreatic cancer through detection of K-ras and p53 mutations in pancreatic juice and stool. METHODS: 201 patients in PUMC Hospital from 1994 - 2000 and 60 control individuals were enrolled in this study. K-ras point mutation was detected by PCR-RFLP while p53 mutation was detected by PCR-SSCP. RESULTS: K-ras mutation was found in pancreatic juice in 87.8% (36/41) of pancreatic cancer patients and 23.5% (4/17) of benign pancreatic disease patients. In 261 stool specimens, amplification found mutations successfully in 235 patients (90%). K-ras mutation was found in stool in 88% (66/75) of pancreatic cancer patients, 51.1% (24/47) of benign pancreatic disease patients and 19.6% (9/46) of normal individuals. p53 mutation was found in pancreatic juice in 47.4% (18/38) of pancreatic cancer patients and 12.5% (2/16) of benign pancreatic disease patients. p53 mutation was found in stool in 37.1% (23/62) and 19.1% (4/21) of chronic pancreatitis patients. CONCLUSION: K-ras mutation in pancreatic juice has higher diagnosis sensitivity and specificity, and therefore may be used as a supplement in the diagnosis of pancreatic cancer. Detection of K-ras mutation combined with p53 mutation in stool can aid in the screening of pancreatic cancer.

Feces↗

PubMedDate not supplied

Multivalent poly(ethylene glycol)-containing conjugates for in vivo antibody suppression.

Poly(ethylene glycol) (PEG) was incorporated into multivalent conjugates of the N-terminal domain of beta(2)GPI (domain 1). PEG was incorporated to reduce the rate of elimination of the conjugates from plasma and to putatively improve their efficacy as toleragens for the suppression of anti-beta(2)GPI antibodies and the treatment of antiphospholipid syndrome (APS). Three structurally distinct types of multivalent platforms were constructed by incorporating PEG into the platform structures in different ways. The amount of PEG incorporated ranged from about 5000 g per mole to about 30000 g per mole. The platforms were functionalized with either four or eight aminooxy groups. The conjugates were prepared by forming oxime linkages between the aminooxy groups and N-terminally glyoxylated domain 1 polypeptide. The plasma half-life of each conjugate, labeled with (125)I, was measured in both mice and rats. The half-lives of the conjugates ranged from less than 10 min to about 1 h in mice, and from less than 3 h to about 19 h in rats. The ability of five tetravalent conjugates to suppress anti-domain 1 antibodies in immunized rats was also measured. Incorporation of PEG in the conjugates significantly reduced the doses required for suppression, and the amount of reduction correlated with the amount of PEG incorporated.

Animals↗