Biomedical subjects

Tieh-Chi Chu

Publications and source records attributed to Tieh-Chi Chu.

15 recordsLinked to original sources

PubMed2006

Analytical separation of Au/Ag core/shell nanoparticles by capillary electrophoresis.

This paper demonstrates that capillary electrophoresis (CE) can be employed for characterizing the sizes of a series of Au/Ag core/shell nanoparticles (NPs). We effected the CE separation of Au/Ag core/shell NPs using a mixed buffer of sodium dodecyl sulphate (SDS) (40 mM) and 3-(cyclohexylamino)propanesulfonic acid (10 mM) at pH 9.7 and an applied voltage of 20 kV. A linear relationship (R(2)>0.99) existed between the electrophoretic mobilities and the sizes of the Au/Ag core/shell NPs within the diameter range from 25 to 90 nm; the relative standard deviations of these electrophoretic mobilities were <0.9%. From the good correlation between the results obtained by CE and those provided by scanning electron microscopy, we confirmed that this CE method is a valid one for characterizing the sizes of Au/Ag core/shell NP samples. In addition, when the Au/Ag core/shell NPs were separated through CE and detected using an on-line photodiode array detector, this approach allowed the chemical characterization of the NP species. This CE approach should allow the rapid and cost-effective characterization of a number of future nanomaterials.

Electrophoresis, Capillary↗

PubMed2005

Combining optical lithography with rapid microwave heating for the selective growth of Au/Ag bimetallic core/shell structures on patterned silicon wafers.

We demonstrate a novel approach for the production of patterned films of nanometer-sized Au/Ag bimetallic core/shell nanoparticles (NPs) on silicon wafers. In this approach, we first self-assembled monodisperse Au NPs, through specific Au...NH(2) interactions, onto a silicon substrate whose surface had been modified with a pattern of 3-aminopropyltrimethoxysilane (APTMS) groups to form a sandwich structure having the form Au NPs/APTMS/SiO(2). These Au NPs then served as seeds for growing the Au/Ag bimetallic core/shell NPs: we reduced silver ions to Ag metal on the surface of Au seeds under rapid microwave heating in the presence of sodium citrate. Energy-dispersive X-ray analysis confirmed that the Au/Ag bimetallic core/shell NPs grew selectively on the regions of the surface of the silicon wafer that had been patterned with the Au seeds. Scanning electron microscopy images revealed that we could synthesize well-scattered, high-density (>82%) thin films of Au/Ag bimetallic core/shell NPs through the use of this novel strategy. The patterned structures that can be formed are simple to produce, easily controllable, and highly reproducible; we believe that this approach will be useful for further studies of nanodevices and their properties.

Journal Article↗

PubMed2005

Studying the size/shape separation and optical properties of silver nanoparticles by capillary electrophoresis.

This paper describes the feasibility of employing capillary electrophoresis (CE) to separate silver particles in nanometer regimes. We have found that the addition of an anionic surfactant, sodium dodecyl sulphate (SDS), to the running electrolyte prevents coalescence of the silver particles during the process, which improves the separation performance; the concentration of SDS required for optimal silver nanoparticle separation is ca. 20 mM. By monitoring the electropherograms using a diode-array detection (DAD) system, we have also investigated the separation of suspended silver nanorods with respect to their shapes. Our results demonstrate that the combination of CE and DAD is a powerful one for the separation and characterization of various silver nanoparticles.

Electrophoresis, Capillary↗

PubMed2005

A positron emission tomography/computed tomography (PET/CT) acquisition protocol for CT radiation dose optimization.

BACKGROUND: In current combined positron emission tomography/computed tomography (PET/CT) systems, high-quality CT images not only increase diagnostic value by providing anatomic delineation of hyper- and hypometabolic tissues, but also shorten the acquisition time for attenuation correction compared with standard PET imaging. However, this technique potentially introduces more radiation burden to patients as a result of the higher radiation exposure from CT. METHODS: In this study, the radiation doses delivered from typical germanium-based and CT-based transmission scans were measured and compared using an anthropomorphic Rando Alderson phantom with insertions of thermoluminescent dosimeters. Image geometric distortion and quantified uptake values in PET images with different manipulating CT acquisition protocols for attenuation correction were also evaluated. RESULTS: It was found that radiation doses during germanium-based transmission scans were almost negligible, while doses from CT-based transmission scans were significantly higher. Using a lower radiation dose, the CT acquisition protocol did not significantly affect attenuation correction and anatomic delineation in PET. CONCLUSIONS: This study revealed the relation between image information and dose. The current PET/CT imaging acquisition protocol was improved by decreasing the radiation risks without sacrificing the diagnostic values.

Body Burden↗

PubMed2004

Correlation between temporal response of fMRI and fast reaction time in a language task.

Correlation between behavioral parameters and fMRI responses can provide an advanced understanding of the neuronal processes. A lexical decision task was employed to examine the correlation between the reaction time (RT) and the temporal parameters in event-related BOLD responses. Word frequency was manipulated in the experiment. RTs for high-frequency, low-frequency and pseudowords were measured during fMRI (417 +/- 9 ms, 631 +/- 22 ms and 658 +/- 15 ms, respectively). For high-frequency words, RTs were significantly shorter than that for low-frequency and pseudowords (p < 0.0005). In the left inferior frontal region, the FWHM of the fMRI responses was significantly correlated with RT (p < 0.001), which may correspond to areas with sustained activation during the whole processing.

Adult↗

PubMed2004

Three-dimensional conformal radiation therapy for unresectable hepatocellular carcinoma patients who had failed with or were unsuited for transcatheter arterial chemoembolization.

BACKGROUND: The purpose of our study was to evaluate the outcome of unresectable hepatocellular carcinoma (HCC) patients, who had either failed with or were unsuited for transcatheter arterial chemoembolization (TACE), treated with three-dimensional conformal radiation therapy (3DCRT) and to determine the prognostic outcome factors. METHODS: From September 1999 to March 2003, 44 patients with unresectable HCC underwent 3DCRT. Thirty-seven patients were male and seven female. Mean age was 62 years, ranging from 34 to 88. Eastern Cooperative Oncology Group (ECOG) performance status was 0 in 10 patients, 1 in 19 patients, and 2 in 15 patients. According to Child-Pugh classification for cirrhosis of the liver, 32 patients were in class A and 12 patients in class B. There were 14 patients with main portal vein thrombosis. Twenty patients had alpha-fetoprotein (AFP) level >400 ng/ml. Tumor size was <5 cm in 16 patients, 5-10 cm in 16 patients, and >10 cm in 12 patients. Thirty-two patients had tumors of confluent type, the remaining patients presented a single hepatic tumor. Serum hepatitis antigen markers were positive for type B in 35 patients and type C in nine patients. Twenty-one patients had Okuda Stage I, 22 patients Stage II, and one patient Stage III. According to the AJCC staging system (5th edition), eight patients were in Stage II (T2N0M0), 19 in Stage IIIA (T3N0M0) and 17 in Stage IVA (T4N0M0). RESULTS: An objective response was observed in 27 of 44 patients, giving a response rate of 61.4%. The survival rates at 1, 2 and 3 years were 60.5%, 40.3% and 32.0%, respectively. In the analysis of prognostic factors, Okuda stage, AJCC stage, portal vein thrombosis, pretreatment AFP level, and total dose of radiotherapy all had significant impact on survival. CONCLUSIONS: 3DCRT induced a substantial tumor response rate of 61.4% with survival rates at 1, 2 and 3 years of 60.5%, 40.3% and 32.0%, respectively, and a median survival time of 15.2 months in patients with unresectable HCC who had either failed with or were unsuited for TACE. The complications are acceptable and can be managed with conservative treatment. Although we do not know whether there is a survival benefit through the use of this treatment, 3DCRT seems to be a practical method of salvage for this subset of patients. Further study is warranted to evaluate the survival of such patients with and without this treatment.

Adult↗

PubMed2004

Temporal resolving power of perfusion- and BOLD-based event-related functional MRI.

Functional magnetic resonance imaging (fMRI) based on both perfusion and blood oxygenation level-dependent (BOLD) contrasts has been widely applied in spatiotemporal mapping of the human brain function. Temporal resolving power of fMRI is limited by the smoothed hemodynamic response function dispersed from the neuronal activity. In this study, temporal modulation transfer functions were utilized to quantify the resolving powers of perfusion and BOLD fMR signals in time domain. The impulse response function was determined using brief visual stimulations and event-related image acquisition schemes. An important feature of arterial spin labeling techniques is that quantitative perfusion and BOLD signals could be simultaneously acquired. This simultaneous BOLD response may arise from signals that are more proximal to capillary beds, and its temporal resolution may be different from that of the typical BOLD response. Therefore, we assessed and compared the temporal resolving capabilities of perfusion, simultaneous BOLD, and the typical BOLD response obtained from the gradient echo EPI pulse sequence. Full-width-at-half-maximums of perfusion and simultaneous BOLD measurements were significantly smaller than that of BOLD ones (4.3+/- 0.6 s vs 5.5 +/- 0.9 s, p<0.02 and 4.7 +/- 1.3 s vs 5.5 +/- 0.9 s, p<0.01, respectively). The corresponding temporal resolving powers of perfusion and simultaneous BOLD signals were statistically better than that of BOLD signals (0.23 +/- 0.03 Hz vs 0.17 +/- 0.02 Hz, p<0.01 and 0.21 +/- 0.04 Hz vs 0.17 +/- 0.02 Hz, p<0.01, respectively). Our results showed that the typical BOLD response was significantly smoothed from the perfusion response, thus resulting in a degraded temporal resolving power. However, results from the simultaneous BOLD and perfusion measurements were not significantly different. Biophysical implications of the experimental outcomes were further investigated using a computer simulation based on the Balloon model. By fitting the measured data into the model, an apparently longer transit time was obtained for the typical BOLD signal (1.7 s), comparing to that for the simultaneous BOLD one (1.2 s). Therefore, the simultaneous BOLD signal was regarded as less susceptible to the variations from local draining veins. Combining the simulation result with the significantly discrepant resolving powers between the two BOLD signals, we speculated that the blurred effects from large vessels played a predominant role that further reduced the temporal resolution of the BOLD-based fMRI from the perfusion response.

Cerebrovascular Circulation↗

PubMed2003

Radiation exposure during transmission measurements: comparison between CT- and germanium-based techniques with a current PET scanner.

In positron emission tomographic (PET) scanning, transmission measurements for attenuation correction are commonly performed by using external germanium-68 rod sources. Recently, combined PET and computed tomographic (CT) scanners have been developed in which the CT data can be used for both anatomical-metabolic image formation and attenuation correction of the PET data. The purpose of this study was to evaluate the difference between germanium- and CT-based transmission scanning in terms of their radiation doses by using the same measurement technique and to compare the doses that patients receive during brain, cardiac and whole-body scans. Measurement of absorbed doses to organs was conducted by using a Rando Alderson phantom with thermoluminescent dosimeters. Effective doses were calculated according to the guidelines in the International Commission on Radiation Protection Publication Number 60. Compared with radionuclide doses used in routine 2-[fluorine-18]-fluoro-2-deoxy-D-glucose PET imaging, doses absorbed during germanium-based transmission scans were almost negligible. On the other hand, absorbed doses from CT-based transmission scans were significantly higher, particularly with a whole-body scanning protocol. Effective doses were 8.81 mSv in the high-speed mode and 18.97 mSv in the high-quality mode for whole-body CT-based transmission scans. These measurements revealed that the doses received by a patient during CT-based transmission scanning are more than those received in a typical PET examination. Therefore, the radiation doses represent a limitation to the generalised use of CT-based transmission measurements with current PET/CT scanner systems.

Body Burden↗

PubMed2003

Indoor light on thermoluminescence of CVD diamond film used as a high-energy photon dosimeter.

The effect of light on polycrystalline diamond film that was produced by chemical vapor deposition and is used as a thermoluminescent dosimeter should be considered, although some researchers have indicated that such an effect was theoretically unlikely to happen. A 15 min exposure to a normal desk light bulb induces significant thermoluminescence (TL) comparable to a 0.5 Gy exposure to high-energy photons. This light-induced TL will be saturated within 2 h. The saturated TL intensity depends on the frequency of the light and the blue light dominates. The TL peak area at a temperature of 605 K is insensitive to light but is sensitive to high-energy photons. Another peak at about 410 K is caused by light only, because the TL from the ionization radiation at the same location is bleached. The effect of light could be easily distinguished by a numerical or an experimental method. Lamps with a green lampshade or pure red lights are suggested for use as indoor light sources. To reduce the effect of light, pre-heating treatment before readout is also suggested.

Diamond↗

PubMed2003

Study of induced thermoluminescence in CVD diamond film by low-energy X-rays.

For diamond film the one-hit model that is used to interpret low-energy X-ray thermoluminescence (TL) will require some modifications. After the films were irradiated with a superficial X-ray machine with different peak voltages, a two-compartment model with three parameters, the target size, the microscopic saturation factor and the high-LET saturation factor, was used to more precisely describe the TL response to X-ray with energies down to 10 kV. The microdosimetric distribution was calculated using single-event Monte Carlo code developed by authors together with EEDL cross-section data library. Some mechanistic insight into the physical aspect of radiation interaction with solid detectors can be obtained. The sensitive size in diamond was found to be about 15 nm. The saturation of one group of sublevels combined with the activation of another group of sublevels caused the relative efficiency to have a local minimum near 20 keV. The relative efficiency becomes higher below 10 keV, which is similar to the increasing relative biological effectiveness when the linear energy transfer passing through a biological system increases. The similarity made this material to be a molecular-scale dosimeter in the future.

Cobalt Radioisotopes↗

PubMed2002

Fabry-perot-type antireflective coating for deep-ultraviolet binary photomask applications.

We demonstrate an antireflective coating structure, which is based on the three-layer metal interference called the Fabry-Perot structure, for a deep-ultraviolet binary mask. The antireflective coating structure is composed of a metal-oxide-metal stack. By addition of different optimized structures, reflectances of less than 1.5% at both 248 and 193 nm have been achieved. At the three-layer Fabry-Perot structure, the bottom chrome layer provides suitable absorption. By controlling the thickness of the intermediate silicon oxide layer, we can tune the minimum-reflection regime to the desired exposure wavelength. The top metal layer can prevent charge accumulation during e-beam writing.

Journal Article↗

PubMed2002

Surface dose with grids in electron beam radiation therapy.

This investigation attempts to solve the problem of the lack of skin-sparing effect in electron radiation therapy and to increase the tolerance of skin to radiation using the grid technique. Electron grid therapy involves the mounting of a Cerrobend grid in the electron cone. Film dosimetry was employed to measure the relative surface dose and the percentage depth dose profile of electron grid portals. Various grid hole diameters (d = 0.45, 1.0, 1.5 cm) and grid hole spacings (s = 0.4, 0.2 cm) were considered for electron beams from 6 to 14 MeV. Experimental results indicate that the electron grid technique can reduce the relative surface dose in electron radiation therapy. Degradations of the relative surface dose depend on the percentage of open area in the grid portal. A proper grid design allows the surface dose to be reduced and the range of nonhomogeneous doses to be limited to a depth at which the target volume can receive a homogeneous dose. The grid technique can lower the surface dose in electron radiation therapy.

Electrons↗

PubMed2002

Monte Carlo simulation of surface percent depth dose.

This work studied the surface percent depth dose of 6 and 15 MV X-rays, 10 x 10 cm2 and 20 x 20 cm2 fields by Monte Carlo simulation. The OMEGA/BEAM code, an EGS4 user code developed by the NRCC, was used. The linac, Siemens PRIMUS, was accurately modeled according to the ion chamber and CEA film measurement, and the phase space data generated from this linac were collected to simulate dose distribution in water. The water phantom had radius 30 cm and thickness 10 cm. The percent depth doses at zero depth, PDDsurface, for 6 MV X-rays were 13.85 +/- 0.11% and 23.21 +/- 0.20% for the 10 x 10 cm2 and 20 x 20 cm2 fields, respectively. For 15 MV X-rays, PDDsurface values were 8.83 +/- 0.07% and 18.60 +/- 0.12% for the 10 x 10 cm2 and 20 x 20 cm2 fields, respectively.

Humans↗

PubMed2002

The effect of a metal hip prosthesis on the radiation dose in therapeutic photon beam irradiations.

Prostate and cervical cancer patients are often treated with external X-ray beams of bi-lateral incidence. Such treatment may incur some dose effect that cannot be predicted precisely in commercial treatment planning systems (TPS) for patients having undergone total hip replacement. This study performs a Monte Carlo (MC) simulation and an analytical calculation (convolution superposition algorithm which is implemented in ADAC TPS) of a 6 MV, 5 x 5 cm2 X-ray beam incident into water with the existence of hip prosthesis, e.g. Ti6A14V and CoCrMo alloy. The results indicate that ADAC TPS cannot precisely account for the scatter and backscatter radiation that a metal hip prosthesis causes. For percent depth dose (PDD) curves, the maximum underdosage of ADAC TPS up to 5mm above the interface between dense material and water is 5%, 20% and 27% for PDD(Bone), PDD(Ti) and PDD(Co), respectively. The dose re-buildup, which occurs behind the hip region, becomes more and more obvious for denser medium existed in water. Increasing inhomogeneity also enhances the underdosage of ADAC for greater depth (> 10cm), as the figures of nearly 2% in PDD(Bone), PDD(Ti) and 4-5% in PDD(Co) reveal. Overestimating the attenuated power of high-density non-water material in ADAC TPS causes this underdosage. For dose profiles, no significant differences were found in Profile(Bone) at any depth. Profile(Ti) reveals that MC slightly exceeds ADAC at off-axis position 1.0-2.0 cm. Profile(Co) reveals this more obviously. This finding means that scatter radiation from these denser materials is significant and cannot be predicted precisely in ADAC.

Algorithms↗

PubMed2002

Accuracy of the convolution/superposition dose calculation algorithm at the condition of electron disequilibrium.

Using Monte Carlo simulation and the convolution/superposition algorithm, this work examines percent depth dose curves of the central axis in an acrylic phantom (20 x 20 x 20 cm(3)) with variously sized air cavities (20 x 20 x 1.0, 20 x 20 x 2.0, 20 x 20 x 3.0, 20 x 20 x 4.0 and 20 x 20 x 4.95 cm(3) for study of longitudinal electron disequilibrium (ED) and 3.6 x3.6 x 4.95, 4.5 x 4.5 x 4.95, 5.4 x 5.4 x 4.95 and 20 x 20 x 4.95 cm(3) for study of lateral ED). Radiochromic film samples are also measured to verify the Monte Carlo results. The Monte Carlo simulation is performed using OMEGA/BEAM and DOSXYZ codes, and the convolution/superposition calculation relies on an ADAC commercial treatment planning system. Underestimating the dose kernel expansion leads to overestimating the dose of what was found in the air cavity of ED using the convolution/superposition algorithm. Consequently, the dose in the rebuild-up region is influenced. The influenced region is on the acrylic phantom surface to a depth of about 0.5 cm. The density scaling method of the convolution/superposition algorithm, applied to heterogeneous media, should be enhanced to account for the over-expansion of the dose kernel in the cavity of ED.

Journal Article↗