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1. chinaXiv:201710.00003 [pdf]

Development and applications of paleontological computed tomography

WANG Yan-Fang; WEI Cun-Feng; QUE Jie-Min; ZHANG Wen-Ding; SUN Cui-Li; SHU Yan-Feng; HOU Ye-Mao; ZHANG Jiu-Chang; SHI Rong-Jian; WEI Long
Subjects: Geosciences >> Geology

The traditional serial grinding method used to investigate the internal structure of fossils cannot be readily applied to valuable fossil specimens due to its destructive and time-consuming nature. Computed tomography (CT) is an ideal non-destructive technique for investigating the internal structure of fossils, in which thousands of serial images are obtained and used to produce an accurate reconstruction of the internal morphology. This paper reviews the design, development and applications of the first CT system in China dedicated exclusively to scanning fossils. The 225 kV three-dimensional (3D) fossil micro-CT (225-3D-μCT) is capable of high-resolution volumetric imaging, with a resolution up to 5 μm, and can accommodate specimens measuring up to 100 mm in diameter and 100 mm in length. The 450 kV ordinary fossil CT (450-TY-ICT) can produce high signal-to-noise ratio (SNR) images of specimens ranging up to 800 mm in diameter and 1000 mm in length, with a resolution up to 200 μm. Two paleontological CT facilities represent a high-performance platform offering the functional diversity needed to meet the demands of studying fossils at a variety of different scales. The two machines have become indispensable for paleontological research in China.

submitted time 2017-10-09 From cooperative journals:《古脊椎动物学报》 Hits2210Downloads852 Comment 0

2. chinaXiv:201703.00588 [pdf]

Effects of thermal aging on Fe ion-irradiated Fe-0.6%Cu alloy investigated by positron annihilation

HU Yuan-Chao; CAO Xing-Zhong; ZHANG Peng; TSUCHIDA Hidetsugu; XU Qiu; JIN Shuo-Xue; LU Er-Yang; LI Yu-Xiao; YU Run-Sheng; WANG Bao-Yi; WEI Long
Subjects: Physics >> Condensed Matter: Structural, Mechanical and Thermal Properties

Thermal aging effects on surface of 2.5 MeV Fe ion irradiated Fe-0.6%Cu alloy were investigated using positron annihilation techniques. The samples were irradiated at 573 K to a dose of 0.1 dpa. Their thermal aging was performed at 573 K for 5, 50, and 100 h. From the results of Doppler broadening measurement, an obvious trough could be seen in near surface region from the S parameters and inflection point form at S-W curves. This indicates changes in the annihilation mechanism of positrons in surface region after thermal aging. Coincident Doppler broadening indicates that the density of Cu precipitates in the thermal aged samples decreased, due to recovery of the vacancies. Keywords Fe-Cu alloy; Positron annihilation; Irradiation; Thermal aging

submitted time 2017-03-26 Hits452Downloads265 Comment 0

3. chinaXiv:201605.01807 [pdf]

7T Transmit/Receive Arrays Using ICE Decoupling for Human Head MR Imaging

Yan, Xinqiang; Feng, Baotong; Ma, ChuangXin; Wei, Long; Yan, Xinqiang; Zhang, Xiaoliang; Zhang, Xiaoliang; Xue, Rong
Subjects: Biology >> Biophysics

In designing large-sized volume type phased array coils for human head imaging at ultrahigh fields, e.g., 7T, minimizing electromagnetic coupling among array elements is technically challenging. A new decoupling method based on induced current compensation or elimination (ICE) for a microstrip line planar array has recently been proposed. In this study, an eight-channel transmit/receive volume array with ICE-decoupled loop elements was built and investigated to demonstrate its feasibility and robustness for human head imaging at 7T. Isolation between adjacent loop elements was better than - 25 dB with a human head load. The worst-case of the isolation between all of the elements was about - 17.5 dB. All of the MRI experiments were performed on a 7T whole-body human MR scanner. Images of the phantom and human head were acquired and g-factor maps were measured and calculated to evaluate the performance of the coil array. Compared with the conventional capacitively decoupled array, the ICE-decoupled array demonstrated improved parallel imaging ability and had a higher SNR. The experimental results indicate that the transceiver array design with ICE decoupling technique might be a promising solution to designing high performance transmit/receive coil arrays for human head imaging at ultrahigh fields.

submitted time 2016-05-18 Hits1433Downloads652 Comment 0

4. chinaXiv:201605.01482 [pdf]

Hybrid Monopole/Loop Coil Array for Human Head MR Imaging at 7 T

Yan, Xinqiang; Wei, Long; Yan, Xinqiang; Wei, Long; Yan, Xinqiang; Xue, Rong; Xue, Rong; Zhang, Xiaoliang; Zhang, Xiaoliang
Subjects: Biology >> Biophysics

The monopole coil and loop coil have orthogonal radiofrequency (RF) fields and thus are intrinsically decoupled electromagnetically if they are laid out appropriately. In this study, we proposed a hybrid monopole/loop technique which could combine the advantages of both loop arrays and monopole arrays. To investigate this technique, a hybrid RF coil array containing four monopole channels and four loop channels was developed for human head magnetic resonance (MR) imaging at 7 T. In vivo MR imaging and g-factor results using monopole-only channels, loop-only channels and all channels of the hybrid array were acquired and evaluated. Compared with the monopole-only and loop-only channels, the proposed hybrid array has the higher signal-to-noise ratio (SNR) and better parallel imaging performance. Sufficient electromagnetic decoupling and diverse RF magnetic field (B-1) distributions of monopole channels and loop channels may contribute to this performance improvement. From experimental results, the hybrid monopole/loop array has low g-factor and excellent SNR at both periphery and center of the brain, which is valuable for human head imaging at ultrahigh fields.

submitted time 2016-05-12 Hits483Downloads240 Comment 0

5. chinaXiv:201605.01425 [pdf]

Design and Test of Magnetic Wall Decoupling for Dipole Transmit/Receive Array for MR Imaging at the Ultrahigh Field of 7T

Yan, Xinqiang; Xue, Rong; Yan, Xinqiang; Wei, Long; Yan, Xinqiang; Wei, Long; Zhang, Xiaoliang; Zhang, Xiaoliang; Xue, Rong
Subjects: Biology >> Biophysics

Radio-frequency coil arrays using dipole antenna technique have been recently applied for ultrahigh field magnetic resonance (MR) imaging to obtain the better signal-noise-ratio (SNR) gain at the deep area of human tissues. However, the unique structure of dipole antennas makes it challenging to achieve sufficient electromagnetic decoupling among the dipole antenna elements. Currently, there is no decoupling methods proposed for dipole antenna arrays in MR imaging. The recently developed magnetic wall (MW) or induced current elimination decoupling technique has demonstrated its feasibility and robustness in designing microstrip transmission line arrays, L/C loop arrays and monopole arrays. In this study, we aim to investigate the possibility and performance of MW decoupling technique in dipole arrays for MR imaging at the ultrahigh field of 7T. To achieve this goal, a two-channel MW decoupled dipole array was designed, constructed and analyzed experimentally through bench test and MR imaging. Electromagnetic isolation between the two dipole elements was improved from about -3.6 dB (without any decoupling treatments) to -16.5 dB by using the MW decoupling method. MR images acquired from a water phantom using the MW decoupled dipole array and the geometry factor maps were measured, calculated and compared with those acquired using the dipole array without decoupling treatments. The MW decoupled dipole array demonstrated well-defined image profiles from each element and had better geometry factor over the array without decoupling treatments. The experimental results indicate that the MW decoupling technique might be a promising solution to reducing the electromagnetic coupling of dipole arrays in ultrahigh field MRI, consequently improving their performance in SNR and parallel imaging.

submitted time 2016-05-12 Hits483Downloads270 Comment 0

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