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Biomedical subjects

X L Xu

Publications and source records attributed to X L Xu.

44 records · Page 3Linked to original sources
PubMed1986

[DNA transformation activity of a human gastrocarcinoma cell line].

DNAs of three cell lines of human gastrocarcinoma (MGC-803, BGC-823 and PACM-82) and two fresh solid tumors of human stomach cancer were used to transfect NIH3T3 and Rat-1 cells. The transformed cells were selected with high concentration of glucose and low concentration of serum, or with medium containing Geneticin (G418) after co-transfection of pSVneo and DNAs of stomach cancer cell line or primary transformants. From the second round transfection, we had obtained transformants which could grow with high colony forming efficiency in soft agarose and were tumorigenic in nude mice. The southern blot analysis showed that the cellular DNA of the transformants contained human Alu repeat sequence and the transformed gene from stomach cancer cell line (BGC-823) and was homologous to proto-oncogene c-Ha-ras. The transforming gene is able to induce neoplastic transformation of NIH3T3 and Rat-1 cells.

Animals↗
PubMed1985

[Argon laser trabeculoretraction in chronic open-angle glaucoma. Personal results based on 100 eyes].

Argon laser trabeculoplasty (or trabeculoretraction) was used following WISE's technique in 100 cases of open angle glaucoma. The patients, all of different ages, presented with various forms of open angle glaucoma. In some cases, the intraocular pressure had not been normalized by the medical treatment, and in some others, the patients showed drug intolerance. We eliminated the patients whose angle was too narrow to allow photocoagulation. They were examined at regular intervals of 1 week, 2 weeks, 1 month, 3 months, 6 months and 12 months after therapy. Pressure figures only were considered in the therapeutic follow-up. After 12 months, the mean pressure drop was 7.3 mmHg after 180 degrees trabeculoplasty and 11.43 mmHg after 360 degrees trabeculoplasty, the latter consequently entailing a more considerable drop. Older subjects however showed a greater pressure decrease. We obtained less satisfactory results in cases of exfoliative syndrome glaucoma and pigmentary glaucoma. The important point is that pressure normalization was obtained--in most cases--only if the prior medical treatment was maintained either without any change or lightly reduced. The trabeculoplasty alone reduced ocular pressure in only 3.57% and in 9.09% respectively after 180 degrees and 360 degrees trabeculoplasty. We can therefore conclude from these observations that this technique is only an auxiliary method in open angle glaucomas that do not sufficiently respond to medical treatment.

Adult↗
PubMedDate not supplied

Time delay estimation using wavelet transform for pulsed-wave ultrasound.

The windowed cross-correlation (WCC) technique has recently attracted attention in pulsed-wave (PW) ultrasound for measurement of tissue motion and blood flow velocity because of its performance advantages over the conventional Doppler method. The WCC measures tissue motion and blood flow velocity via estimation of time delays of backscattered signals in two consecutive echoes. In this paper, we propose a wavelet transform-based cross-correlation (WTCC) technique for the time delay estimation in PW ultrasound. The WTCC consists of three steps: (i) computing wavelet transforms (WTs) of received echoes, (ii) computing cross-correlations in the wavelet domain, and (iii) estimating the time delays by maximizing the estimated cross-correlations. Dyadic or continuous wavelets may be used in the proposed approach. The WTCC has a unique feature of using varying time-frequency windows in processing compared with the WCC which only uses a single fixed window. Our computer simulations show that, compared with the WCC, the WTCC provides a better estimation of time delays (lower failure rate and lower estimate error) and its performance is more consistent under various conditions, and more robust with window size. In the simulations, we also tested a specific continuous wavelet for the WTCC that was the emitted pulse itself and found the corresponding WTCC outperforms the WTCC with a regular dyadic wavelet.

Bias↗
PubMedDate not supplied

Quantitative comparisons of image registration techniques based on high-resolution MRI of the brain.

OBJECTIVE: A variety of methods for matching intrasubject MRI-MRI, PET-PET, or MRI-PET image pairs have been proposed. Based on the rigid body transformations needed to align pairs of high-resolution MRI scans and/or simulated PET scans (derived from these MRI scans), we obtained general comparisons of four intrasubject image registration techniques: Talairach coordinates, head and hat, equivalent internal points, and ratio image uniformity. In addition, we obtained a comparison of stereotaxic Z frames with a customized head mold for MRI-MRI image pairs. MATERIALS AND METHODS AND RESULTS: Each technique was quantitatively evaluated using the mean and maximum voxel registration errors for matched voxel pairs within the brain volumes being registered. CONCLUSION: We conclude that fiducial markers such as stereotaxic Z frames that are not rigidly fixed to a patient's skull are inaccurate compared with other registration techniques, Talairach coordinate transformations provide surprisingly good registration, and minimizing the variance of MRI-MRI, PET-PET, or MRI-PET ratio images provides significantly better registration than all other techniques tested. Registration optimization based on measurement of the similarity of spatial distributions of voxel values is superior to techniques that do not use such information.

Algorithms↗
PubMedDate not supplied

Iterative algebraic reconstruction algorithms for emission computed tomography: a unified framework and its application to positron emission tomography.

In this paper, a unified framework of iterative algebraic reconstruction for emission computed tomography (ECT) and its application to positron emission tomography (PET) is presented. The unified framework is based on an algebraic image restoration model and contains conventional iterative algebraic reconstruction algorithms: ART, SIRT, Landweber iteration (LWB), the generalized Landweber iteration (GLWB), the steepest descent method (STP), as well as iterative filtered backprojection (IFBP) reconstruction algorithms: Chang's method, Walters' method, and a modified iterative MAP. The framework provides an effective tool to systematically study conventional iterative algebraic algorithms and IFBP algorithms. Based on this framework, conventional iterative algebraic algorithms and IFBP algorithms are generalized. It is shown from the algebraic point of view that IFBP algorithms are not only excellent methods for correction of attenuation (either uniform or nonuniform) but are also good general iterative reconstruction algorithms (they can be applied to either attenuated or attenuation-free projections and converge very fast). The convergence behavior of iterative algebraic algorithms is discussed and insight is drawn into the fast convergence property of IFBP algorithms. A simulated PET system is used to evaluate IFBP algorithms and LWB in comparison with the maximum likelihood estimation via expectation maximization algorithm (MLE-EM) and the filtered backprojection (FBP) algorithm. The simulation results indicate that for both attenuation-free projection and attenuated projection cases IFBP algorithms have a significant computational advantage over LWB and MLE-EM, and have performance advantages over FBP in terms of contrast recovery and/or noise-to-signal ratios (NSRs) in regions of interest.

Algorithms↗