Pentafrequency Resonator based on a CRLH Microstrip for Multinuclear MRI and MRS at 7 T

Daniel Hernandez 한국자기학회 2020 Journal of Magnetics Vol.25 No.4

In this study, we present a transmission-line design based on the concept of composed right- and left-hand microstrip (CRLHTL) that is able to produce a uniform B1 field at five different frequencies. The design uses the same conductor line for all five frequencies, and maintains a uniform field along the Z axis. The CRLH concept is used to ensure that the line is operating with a uniform propagation constant in a lossless scenario. We performed electromagnetic simulations to validate the design.

Optimizing Radio-Frequency Coils for Ultra-High Field MRI: Importance of Electromagnetic Simulations using Biological Virtual Models

Daniel Hernandez,Donghyuk Kim,Taewoo Nam,Yonghwa Jeong,Minyeong Seo,Eunwoo Lee,Kyoung-Nam Kim 한국자기학회 2023 한국자기학회 학술연구발표회 논문개요집 Vol.33 No.1

A head motion estimation algorithm for motion artifact correction in dental CT imaging

Hernandez, Daniel,Eldib, Mohamed Elsayed,Hegazy, Mohamed A A,Cho, Myung Hye,Cho, Min Hyoung,Lee, Soo Yeol Institute of Physics in association with the Ameri 2018 Physics in medicine & biology Vol.63 No.6

<P>A small head motion of the patient can compromise the image quality in a dental CT, in which a slow cone-beam scan is adopted. We introduce a retrospective head motion estimation method by which we can estimate the motion waveform from the projection images without employing any external motion monitoring devices. We compute the cross-correlation between every two successive projection images, which results in a sinusoid-like displacement curve over the projection view when there is no patient motion. However, the displacement curve deviates from the sinusoid-like form when patient motion occurs. We develop a method to estimate the motion waveform with a single parameter derived from the displacement curve with aid of image entropy minimization. To verify the motion estimation method, we use a lab-built micro-CT that can emulate major head motions during dental CT scans, such as tilting and nodding, in a controlled way. We find that the estimated motion waveform conforms well to the actual motion waveform. To further verify the motion estimation method, we correct the motion artifacts with the estimated motion waveform. After motion artifact correction, the corrected images look almost identical to the reference images, with structural similarity index values greater than 0.81 in the phantom and rat imaging studies.</P>

A Review on the RF Coil Designs and Trends for Ultra High Field Magnetic Resonance Imaging

Hernandez, Daniel,Kim, Kyoung-Nam Korean Society of Magnetic Resonance in Medicine 2020 Investigative Magnetic Resonance Imaging Vol.24 No.3

In this article, we evaluated the performance of radiofrequency (RF) coils in terms of the signal-to-noise ratio (S/N) and homogeneity of magnetic resonance images when used for ultrahigh-frequency (UHF) 7T magnetic resonance imaging (MRI). High-quality MRI can be obtained when these two basic requirements are met. However, because of the dielectric effect, 7T magnetic resonance imaging still produces essentially a non-uniform magnetic flux (|B₁|) density distribution. In general, heterogeneous and homogeneous RF coils may be designed using electromagnetic (EM) modeling. Heterogeneous coils, which are surface coils, are used in consideration of scalability in the |B₁| region with a high S/N as multichannel loop coils rather than selecting a single loop. Loop coils are considered state of the art for their simplicity yet effective |B₁|-field distribution and intensity. In addition, combining multiple loop coils allows phase arrays (PA). PA coils have gained great interest for use in receiving signals because of parallel imaging (PI) techniques, such as sensitivity encoding (SENSE) and generalized autocalibrating partial parallel acquisition (GRAPPA), which drastically reduce the acquisition time. With the introduction of a parallel transmit coil (pTx) system, a form of transceiver loop arrays has also been proposed. In this article, we discussed the applications and proposed designs of loop coils. RF homogeneous coils for volume imaging include Alderman-Grant resonators, birdcage coils, saddle coils, traveling wave coils, transmission line arrays, composite right-/left-handed arrays, and fusion coils. In this article, we also discussed the basic operation, design, and applications of these coils.

A Review on the RF Coil Designs and Trends for Ultra High Field Magnetic Resonance Imaging

Jose Daniel Hernandez Chang,김경남 대한자기공명의과학회 2020 Investigative Magnetic Resonance Imaging Vol.24 No.3

In this article, we evaluated the performance of radiofrequency (RF) coils in terms of the signal-to-noise ratio (S/N) and homogeneity of magnetic resonance images when used for ultrahigh-frequency (UHF) 7T magnetic resonance imaging (MRI). Highquality MRI can be obtained when these two basic requirements are met. However, because of the dielectric effect, 7T magnetic resonance imaging still produces essentially a non-uniform magnetic flux (|B1|) density distribution. In general, heterogeneous and homogeneous RF coils may be designed using electromagnetic (EM) modeling. Heterogeneous coils, which are surface coils, are used in consideration of scalability in the |B1| region with a high S/N as multichannel loop coils rather than selecting a single loop. Loop coils are considered state of the art for their simplicity yet effective |B1|-field distribution and intensity. In addition, combining multiple loop coils allows phase arrays (PA). PA coils have gained great interest for use in receiving signals because of parallel imaging (PI) techniques, such as sensitivity encoding (SENSE) and generalized autocalibrating partial parallel acquisition (GRAPPA), which drastically reduce the acquisition time. With the introduction of a parallel transmit coil (pTx) system, a form of transceiver loop arrays has also been proposed. In this article, we discussed the applications and proposed designs of loop coils. RF homogeneous coils for volume imaging include Alderman-Grant resonators, birdcage coils, saddle coils, traveling wave coils, transmission line arrays, composite right-/left-handed arrays, and fusion coils. In this article, we also discussed the basic operation, design, and applications of these coils.

Fermented Non-Digestible Fraction of Andean Berry (Vaccinium meridionale Swartz) Juice Induces Apoptosis in Colon Adenocarcinoma Cells

Carlos Daniel Agudelo,Ivan Luzardo-Ocampo,Angelica Maria Hernandez-Arria,Julio Cesar Rendon,Rocio Campos-Vega,Maria Elena Maldonado-Celis 한국식품영양과학회 2020 Preventive Nutrition and Food Science Vol.25 No.3

Vaccinium meridionale Swartz, known as Andean berry, has a high content of anthocyanins, phenolic acids, and other flavonoids due to their putative anticancer activity. However, after consumption, the structures and function of these molecules may be altered. The purpose of this study was to evaluate the pro-apoptotic effect of fermented non-digestible fraction (FNDF) of Andean berry juice (ABJ) on colon adenocarcinoma HT29 cells. HT29 cells were treated by FNDF-ABJ obtained by in vitro gastrointestinal fermentation. We determined the proapoptotic capacity by terminal deoxynucleotidyl transferase dUTP nick end labeling (TUNEL) assays, oxidative stress by analyzing superoxide dismutase and catalase activity, lipid peroxidation by measuring 8-iso-prostaglandin F2α, and measured lactate dehydrogenase. Our results show that FNDF-ABJ inhibited cell growth [lethal dose 50(%)=26% v/v]. In addition, FNDF-ABJ increased the number of TUNEL positive cells 2-fold compared with untreated cells without altering the release of lactate dehydrogenase. However, superoxide dismutase activity was reduced in HT29 cells treated with FNDF-ABJ, catalase activity was not affected and 8-iso-prostaglandin F2α levels were increased. These results support that the anti-proliferative effects of FNDF-ABJ on HT29 cells can be explained by apoptotic mechanisms.

Denoising of B1? field maps for noise-robust image reconstruction in electrical properties tomography.

Michel, Eric,Hernandez, Daniel,Cho, Min Hyoung,Lee, Soo Yeol Published for the American Association of Physicis 2014 Medical physics Vol.41 No.10

<P>To validate the use of adaptive nonlinear filters in reconstructing conductivity and permittivity images from the noisy B1(+) maps in electrical properties tomography (EPT).</P>

Computational Analysis of a Dual Loop Dipole Antenna and Its Interleaving Array for Improving Transceiver |B1|-field for MRI

Hyunwoo Song,Daniel Hernandez,Kyoung-Nam Kim 한국물리학회 2020 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.76 No.4

This article intends to present the electromagnetic (EM) insight of the operation of a double loop shaped dual loop dipole (DLD) antenna as a single-channel transceiver coil and in an array configuration of multi-channel transceiver coil, designed to provide high signal-to-noise ratio (SNR) by using numerical simulations for 300 MHz magnetic resonance imaging (MRI). Thus, this section includes the comparison of DLD antenna and commonly used loop coils through EM simulations. The use of a DLD antenna is proposed to address the length issue that traditional straight dipole have by making a spiral type in a loop style, while having the same effective physical length of the straight dipole. The magnetic flux density (|B1|)-fields of the DLD antenna and the traditional loop coil are compared by field maps acquired by EM simulations. In addition, the DLD antenna has been extended to a 7-channels array, for which the magnetic field coupling between each coil is analyzed and presented through the noise correlation matrix. The use of the DLD antenna exhibits higher |B1|-field intensity while keeping the similar uniformity than a surface loop coil. We use the DLD antenna 7-channel array to observe its utility as multi-channel with short distance overlap between elements; each element is approximately 37 mm away from neighboring element. Transceiver array arrangements also show improved coil performance, especially the interleaving configuration with loop coil indicates lowered mutual inductance coupling at calculated noise correlation matrix. The proposed DLD antenna is expected to induce rapid imaging and high |B1|-field, when expanded to multi-channel planar or volume configuration since it can maximize the number of configuring coil elements within limited imaging area leading effective parallel imaging and deeper penetration depth due to the traveling wave.

A Tool Box to Evaluate the Phased Array Coil Performance Using Retrospective 3D Coil Modeling

Marlon Perez,Daniel Hernandez,Eric Michel,조민형,이수열 대한자기공명의과학회 2014 Investigative Magnetic Resonance Imaging Vol.18 No.2

Purpose : To efficiently evaluate phased array coil performance using a software tool box with which we can make visualcomparison of the sensitivity of every coil element between the real experiment and EM simulation. Materials and Methods: We have developed a C++- and MATLAB-based software tool called Phased Array Coil Evaluator(PACE). PACE has the following functions: Building 3D models of the coil elements, importing the FDTD simulation results,and visualizing the coil sensitivity of each coil element on the ordinary Cartesian coordinate and the relative coil positioncoordinate. To build a 3D model of the phased array coil, we used an electromagnetic 3D tracker in a stylus form. Aftermaking the 3D model, we imported the 3D model into the FDTD electromagnetic field simulation tool. Results: An accurate comparison between the coil sensitivity simulation and real experiment on the tool box platform hasbeen made through fine matching of the simulation and real experiment with aids of the 3D tracker. In the simulationand experiment, we used a 36-channel helmet-style phased array coil. At the 3D MRI data acquisition using the spoiledgradient echo sequence, we used the uniform cylindrical phantom that had the same geometry as the one in the FDTDsimulation. In the tool box, we can conveniently choose the coil element of interest and we can compare the coil sensitivitieselement-by-element of the phased array coil. Conclusion: We expect the tool box can be greatly used for developing phased array coils of new geometry or for periodicmaintenance of phased array coils in a more accurate and consistent manner.

Dual-Tuned Monopole/Loop Coil Array for Concurrent RF Excitation and Reception Capability for MRI

한상덕,송정현,Daniel Hernandez,김경남 한국물리학회 2019 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.75 No.8

Radiofrequency (RF) coils based on two operating frequencies, or dual-tuned (DT) coils, for magnetic resonance imaging (MRI) in parallel with MR spectroscopy (MRS) and MR spectroscopy imaging (MRSI) are used to obtain morphological and metabolic information for early diagnosis of diseases. However, this method suffers from serious problems such as the extremely low signal sensitivity of X-nuclei and the long image acquisition time required for the two measurements. In this study, a single-channel DT coil was proposed for RF excitation/reception (Tx/Rx) of hydrogen (1H) and phosphorous (31P) by using a monopole antenna and a loop coil, and it was extended to an eight-channel volume coil at 7 T. To verify the DT coil performance, we compared the single RF port of the DT coil with monopole/loop geometry to the individual coil of the 1H monopole antenna and the 31P loop coil with a cylindrical phantom. The monopole/loop coil shows no magnetic flux interaction between individual coils despite the superimposed positions owing to the single RF port. The study results demonstrated that the proposed DT monopole/loop (DTML) coil can be extended to multiple RF Tx/Rx systems and can reduce the acquisition time with a single measurement.