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Biomedical subjects

W K Chu

Publications and source records attributed to W K Chu.

At least 19 recordsLinked to original sources
PubMed2006

The role of phospholipase D and phosphatidic acid in the mechanical activation of mTOR signaling in skeletal muscle.

Signaling by the mammalian target of rapamycin (mTOR) has been reported to be necessary for mechanical load-induced growth of skeletal muscle. The mechanisms involved in the mechanical activation of mTOR signaling are not known, but several studies indicate that a unique [phosphotidylinositol-3-kinase (PI3K)- and nutrient-independent] mechanism is involved. In this study, we have demonstrated that a regulatory pathway for mTOR signaling that involves phospholipase D (PLD) and the lipid second messenger phosphatidic acid (PA) plays a critical role in the mechanical activation of mTOR signaling. First, an elevation in PA concentration was sufficient for the activation of mTOR signaling. Second, the isozymes of PLD (PLD1 and PLD2) are localized to the z-band in skeletal muscle (a critical site of mechanical force transmission). Third, mechanical stimulation of skeletal muscle with intermittent passive stretch ex vivo induced PLD activation, PA accumulation, and mTOR signaling. Finally, pharmacological inhibition of PLD blocked the mechanically induced increase in PA and the activation of mTOR signaling. Combined, these results indicate that mechanical stimuli activate mTOR signaling through a PLD-dependent increase in PA. Furthermore, we showed that mTOR signaling was partially resistant to rapamycin in muscles subjected to mechanical stimulation. Because rapamycin and PA compete for binding to the FRB domain on mTOR, these results suggest that mechanical stimuli activate mTOR signaling through an enhanced binding of PA to the FRB domain on mTOR.

1-Butanol↗
PubMed1999

Inhibition of vascular endothelial cell morphogenesis in cultures by limbal epithelial cells.

PURPOSE: To study the in vitro angiogenic activity of human conjunctival and limbal epithelial cells and conjunctival, limbal, and corneal fibroblasts in a three-cell-type coculture model. METHODS: Human umbilical vein endothelial cells (EC) were cocultured with epithelial cells, fibroblasts, or epithelial cells and fibroblasts to test their effect on EC morphogenesis. Neutralizing antibodies to some known angiogenic factors were added to the culture to see whether the EC morphogenesis may be blocked by a particular antibody. RESULTS: Conjunctival and limbal epithelial cells exhibited very little or no stimulatory effect on EC tube formation when examined in an EC- epithelial cell coculture system. In contrast, conjunctival, limbal, and corneal fibroblasts all promoted EC morphogenesis when examined under the same culture conditions. Fibroblast-induced EC morphogenesis was inhibited by addition of anti-vascular endothelial growth factor (VEGF) and/or anti-basic fibroblast growth factor (bFGF) antibodies to the culture medium. In the three-cell-type coculture system consisting of ECs, fibroblasts, and epithelial cells, limbal epithelial cells (but not conjunctival epithelial cells) exhibited a strong inhibitory effect on fibroblast-induced EC tube formation. CONCLUSIONS: The proangiogenic activity of ocular surface fibroblasts is probably mediated through a paracrine mechanism by VEGF and bFGF. Limbal epithelial cells, but not conjunctival epithelial cells, inhibit fibroblast-stimulated angiogenesis.

Adolescent↗
PubMed1998

A review of digital image networking technologies for radiation oncology treatment planning.

Dosimetrists, physicists, and physicians rely heavily upon digital imaging modalities in their daily work. In the current healthcare marketplace, many radiotherapy facilities operate satellite centers or may be undergoing mergers with other service providers in their community. As a consequence, the development of network-based radiotherapy image communication may yield a significant impact on the clinical operation of such centers. Digital image networking will become an everyday tool in radiotherapy treatment planning in the near future. As responsible users of this technology, an accurate perception of what the network does is essential and enhances our ability to utilize it. This article presents a review of the network architecture and transmission standards necessary for understanding and developing a radiotherapy image network.

Computer Communication Networks↗
PubMed1998

An examination of radiation exposure to clinical staff from patients implanted with 137Cs and 192Ir for the treatment of gynecologic malignancies.

The treatment of cancers by placement of radioactive materials within or adjacent to a tumor is clinically known as brachytherapy. Although the intracavitary treatment of gynecologic cancers using 137Cs has been in widespread use for nearly a century, interstitial techniques using 192Ir have developed within the last decade. Both procedures are performed as temporary implants and typically require a hospital stay of approximately 48 h. Significant differences in source strengths, loading conditions, and patient care requirements are visible between the intracavitary and interstitial techniques. Facilities that are experienced in the use of intracavitary techniques may lack clinical experience in the use of newer interstitial procedures. An examination of radiation exposure to the radiation oncology staff administering the treatment, exposure rate at frequently occupied points in the patient room, and exposure to the nursing staff will be of value to those institutions considering integration of interstitial brachytherapy techniques into their department.

Body Burden↗
PubMed1997

An application of digital network technology to medical image management.

With the advent of network technology, there is considerable interest within the medical community to manage the storage and distribution of medical images by digital means. Higher workflow efficiency leading to better patient care is one of the commonly cited outcomes [1,2]. However, due to the size of medical image files and the unique requirements in detail and resolution, medical image management poses special challenges. Storage requirements are usually large, which implies expenses or investment costs make digital networking projects financially out of reach for many clinical institutions. New advances in network technology and telecommunication, in conjunction with the decreasing cost in computer devices, have made digital image management achievable. In our institution, we have recently completed a pilot project to distribute medical images both within the physical confines of the clinical enterprise as well as outside the medical center campus. The design concept and the configuration of a comprehensive digital image network is described in this report.

Computer Communication Networks↗
PubMed1996

An analysis of the elements essential in the development of a customized TBI program.

Bone marrow transplant, once a procedure carried out at a relatively small number of large medical centers, is being employed at an increasing number of non-academic hospitals. The use of total body photon irradiation for the purpose of marrow ablation and immunosuppression can be expected to accompany the outward growth of bone marrow transplantation at these same hospitals. An analysis of the fundamental physical factors associated with total body photon irradiation (TBI) should be of value to facilities considering the incorporation of a total body irradiation program into an existing radiation oncology department. By examining the existing resources of a radiotherapy center and the clinical objectives of the treatment, a facility considering TBI may determine whether or not their center already fulfills the necessary criteria, in addition to the avoidance of potential pitfalls in project implementation.

Bone Marrow Purging↗
PubMed1995

Proton spectroscopy of brain glutamine in acute liver failure.

Evidence indicates that the accumulation of glutamine in the brain plays an important role in the pathogenesis and severity of the encephalopathy of acute liver failure (ALF). This study uses in vivo proton magnetic resonance spectroscopy (1H MRS) to assess brain glutamine (GLN) in five cases of acute liver failure. The findings are consistent with prior investigations and suggest that the alpha 1H of the GLN molecule can be used for noninvasive spectroscopic quantitation of brain GLN in patients with ALF.

Acute Disease↗
PubMed1994

Prospective utility of cerebral proton magnetic resonance spectroscopy in monitoring HIV infection and its associated neurological impairment.

Neurological manifestations of HIV disease occur in most adults and children with AIDS. Many of those affected will inevitably suffer clinical neurological deficits involving mental function, movement, and sensation. Surprisingly, there are not as yet adequate monitoring systems to predict the onset and/or progression of HIV infection of the CNS. Neurological, neuropsychological, CSF, and magnetic resonance imaging (MRI) analyses cannot accurately detect mental deterioration during advancing HIV disease. Reports suggest that in vivo proton MR spectroscopy (1H MRS) of the brain could be a predictor of virus-induced neurological deterioration. H MRS can measure N-acetylaspartate (NAA), a metabolite present only in neurons. Decreased NAA reflects neuronal loss seen during HIV infection of brain. To uncover possible associations between NAA levels and HIV-induced neurological disease we performed serial 1H MRS brain tests in HIV-infected patients with or at risk for encephalopathy. Serial testing, for 1 year, of 10 patients showed that brain NAA levels decreased in all HIV-infected subjects. The most severe NAA reductions were associated with progressive neurological impairment. These findings suggest that NAA can be used as a noninvasive measure of neuronal loss in patients with HIV disease. Most important, the results suggest that 1H MRS could be used to monitor therapeutics directed against HIV infection within the CNS.

AIDS Dementia Complex↗
PubMed1993

Role of brachytherapy in the management of the skull base meningioma. Treatment of skull base meningiomas.

BACKGROUND: The treatment of primary and recurrent skull base meningiomas presents a formidable surgical problem. METHODS: Fifteen patients with primary and recurrent skull base meningiomas were treated by means of interstitial irradiation with iodine 125 (125I) seed implantation. The physical characteristics of 125I enabled the authors to administer a minimum tumor dose ranging from 100 to 500 Gy at a low dose rate of 0.05-0.25 Gy per hour. RESULTS: All 15 patients are alive at a median follow-up of 29 months. Of the 15 patients, 2 with calcification and 2 without calcification achieved only partial responses. The remaining 11 patients achieved a complete response. No early or late complications were observed. CONCLUSIONS: From these data, the authors conclude that interstitial irradiation with 125I seeds is an effective, safe, and simple method in the treatment of both recurrent and primary skull base meningiomas.

Adult↗
PubMed1993

Continuous low dose rate brachytherapy with high activity iodine-125 seeds in the management of meningiomas.

The purpose of this study was to evaluate if meningiomas can be effectively treated with brachytherapy using permanent implantation of high activity I-125 seeds. Thirteen patients with intracranial meningiomas were treated by means of permanent stereotactic implantation of one or more high-activity I-125 seeds. The physical characteristics of I-125 enabled us to deliver a minimum tumor dose ranging from 100 Gy to 500 Gy at a low dose rate of 5 cGy to 25 cGy per hr. Indications for this procedure included recurrence after initial surgery or as primary modality of treatment in patients who were not candidates for surgery. All 13 patients are alive at a median follow-up of 25 months. Nine of 13 patients achieved complete resolution of the tumor and in the remaining four, more than 50% reduction in tumor volume was noted at the last follow-up. No late complications were observed. We conclude from this initial data that localized high dose irradiation delivered at a low dose rate using I-125 permanent implantation is an effective, safe, and simple method in the treatment of both recurrent and primary intracranial meningiomas.

Adult↗
PubMed1992

Estimation of the mean effective organ doses for total body irradiation from Rando phantom measurements.

For the total body irradiation (TBI) procedure, it is necessary to compare the mean dose obtained from the tissue or organs and the estimated dose equivalent value from the computer program. Due to the easy-access of the Rando phantom and repeatability of TLDs and its output, the results from the experiment are quite encouraging for the verification of the dose distributions from total body irradiation at the given prescribed monitor units. The estimation of effective dose equivalent particularly across the lung sections was studied by combinations of using arms as the scatter volume to compensate for the inhomogeneity across the breast portion, as well as using the spoiler for skin-sparing purposes. The results were based upon various beam quality such as 4 MV, 6 MV, and 10 MV X rays. One series of experiments performed for this survey to ascertain the dose equivalent of the tissues was conducted. This paper describes the method and procedure for comparison between the measured data and computed data as a reference in the dosimetry of total body irradiation. Comparison of the measured and computed data for the largest collimated field shows that the calculated dose rates do not differ by more than 2% from the measured data. Because uncertainty is inherent in non-patient-like phantoms, the calculated data may be served as a reference for the dosimetry. For the total body irradiation setup, considering the radiation field size and treatment distances commonly employed, we conclude that the best combination of the patient setup will be (1) laying both arms down as compensation for lung inhomogeneity, and (2) the spoiler, which is made of acrylic about 8 mm thick and functions like a bolus, is needed to reduce the skin sparing effects and contribute the uniform dose distribution. The beam spoiler with the frame stands near the patient during the treatment.

Humans↗
PubMed1992

Hypertrophic response to unilateral concentric isokinetic resistance training.

The purposes of this study were to 1) determine the effect of concentric isokinetic training on strength and cross-sectional area (CSA) of selected extensor and flexor muscles of the forearm and leg, 2) examine the potential for preferential hypertrophy of individual muscles within a muscle group, 3) identify the location (proximal, middle, or distal level) of hypertrophy within an individual muscle, and 4) determine the effect of unilateral concentric isokinetic training on strength and hypertrophy of the contralateral limbs. Thirteen untrained male college students [mean age 25.1 +/- 6.1 (SD) yr] volunteered to perform six sets of 10 repetitions of extension and flexion of the nondominant limbs three times per week for 8 wk, using a Cybex II isokinetic dynamometer. Pretraining and posttraining peak torque and muscle CSA measurements for both the dominant and nondominant limbs were determined utilizing a Cybex II isokinetic dynamometer and magnetic resonance imaging scanner, respectively. The results indicated significant (P less than 0.0008) hypertrophy in all trained muscle groups as well as preferential hypertrophy of individual muscles and at specific levels. None of the muscles of the contralateral limbs increased significantly in CSA. In addition, significant (P less than 0.0008) increases in peak torque occurred for trained forearm extension and flexion as well as trained leg flexion. There were no significant increases in peak torque, however, for trained leg extension or for any movement in the contralateral limbs. These data suggest that concentric isokinetic training results in significant strength and hypertrophic responses in the trained limbs.

Adult↗
PubMed1991

Brachytherapy: a viable alternative in the management of basal meningiomas.

Thirteen patients with intracranial meningiomas of the skull base were treated with one or more high-activity iodine-125 seeds. In 11 patients, the seeds were implanted stereotactically under local anesthesia. A minimum dose of 100 to 500 Gy was delivered to the tumor at a dose rate of 5 to 25 cGy/h. Indications for this procedure included recurrence after initial surgery or as the primary modality of treatment in patients who were not candidates for surgery. All 13 patients are alive at a median follow-up of 15 months. Nine of 11 patients (82%) without calcification in their meningiomas achieved complete response. The remaining 4 patients-2 with calcification and 2 without--achieved partial response. No early or late complications were observed. We conclude from our experience that both recurrent and primary meningiomas of the skull base can be treated effectively with permanent iodine-125 brachytherapy.

Adult↗
PubMed1991

An image analysis on MR imaging of the brain for hepatic encephalopathy.

Through the Magnetic Resonance Imaging (MRI) sequences with T1 weighting (TR 600 msec/TE 20 msec) of the brain, the high intensity lesions due to hepatic encephalopathy have been demonstrated markedly. The data have been collected were based upon eleven patients with clinically proven hepatic encephalopathy. Three sets of normal brain MRI which were identified with no evidence of brain or liver diseases were also included in this study. After the brain MRI slices have been identified, it showed that the affected regions of interest (ROI) were around the largest third ventricle. The histogram which was generated out of that particular slice is composed of two distinguished peaks lumped together. After the decomposition and curve fitting procedures, the Gaussian distributions were identified with the mean value and the standard deviation. One was assumed to be gray index region for gray and white matter, the other with higher gray index value was the contribution of hepatic encephalopathy. Once the range of the distribution has been determined, the affected portion can be marked and highlighted. This mechanism of histogram decomposition and curve fitting techniques shows the valuable correlation with the clinical status of MR findings.

Brain↗
PubMed1990

Magnetic resonance imaging of the brain in infants and children before and after cardiac surgery. A prospective study.

We assessed the morphologic findings of the brain prospectively before and after cardiac surgery using magnetic resonance imaging. There were 12 patients with acyanotic and 6 with cyanotic heart disease. There were 2 deaths, and 1 patient did not have to undergo postoperative magnetic resonance imaging. The study group consisted of 15 patients completing both the preoperative and postoperative magnetic resonance imagings. All patients in the study group underwent moderate hypothermic cardiopulmonary bypass using a nonpulsatile membrane oxygenator. The mean (+/- SD) cardiopulmonary bypass time was 100 +/- 55 minutes. Ten of the preoperative studies were interpreted as normal. One third (5 of 15) of the patients showed ventriculomegaly and dilatation of the subarachnoid spaces on preoperative magnetic resonance images. Measurements of the preoperative and postoperative magnetic resonance images showed a postoperative increase in the bicaudate and third ventricular diameters. Four patients in the study group developed postoperative subdural hematomas. The subdural hematomas were small and caused no demonstrable mass effect on magnetic resonance imaging. One patient had a preoperative white matter infarction. There was 1 patient with a postoperative infarction.

Brain↗
PubMed1990

A microcomputer-based system for measurement of ultrasound imaging.

A microcomputer-based imaging system for acquisition and analysis of ultrasound has become available. In order to fulfill the clinical demands, the more complete and detailed examinations required, the more sophisticated ultrasound instrumentation costs. This paper demonstrates the simplicity of a personal computer to provide an inexpensive method for measurement on video images from a real-time ultrasound scanner. The process data obtained on ATL 600 and found acoustic intensity histograms to be of value in differential diagnostic purposes. It includes spatial filtering, gray scale expansion, contrast enhancement, color index shifting and histogram analysis, etc. It allows the computer graphics to be superimposed on the ultrasound video images and permits subsequent analysis. To perform the manipulations and programming one of commercially available software and hardware are outlined and encouraged.

Computer Graphics↗
PubMed1989

Comparison of omnipaque with hypaque in temporomandibular arthrography.

Decreasing or alleviating pain experienced by some patients during or after temporomandibular arthrography would make this relatively inexpensive and highly accurate technique more attractive. This is particularly true for those patients without access to MR or those whose referring physicians prefer arthrography to other techniques for diagnosing internal derangements. Ionic and nonionic contrast agents were compared in a randomized, double-blind trial to determine if pain could be decreased by using a nonionic contrast material. Forty patients received either Omnipaque 300 (nonionic, iohexol) or Hypaque 60 (ionic, diatrizoate meglumine). Radiographs were assessed for diagnostic quality, and patients were asked to note their level of discomfort. No significant differences between the agents were detected. Maximal discomfort was noted at 24 hr. Discomfort was classified as none, mild, or moderate, with no patients describing marked discomfort. This study does not support the use of nonionic contrast agents over the less expensive ionic agents for decreasing pain or improving film quality in temporomandibular joint arthrography.

Adult↗