• Title, Summary, Keyword: Array Coil

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The Study on Reliability Improvement in Eddy Current Inspection by Signal Characteristic Optimization of Multi-coil Array Probe (다중센서 신호특성 최적화를 통한 와전류검사 신뢰성 개선연구)

  • Ahn, Y.S.;Gil, D.S.;Park, S.G.
    • Journal of the Korea Society For Power System Engineering
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    • v.14 no.2
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    • pp.60-64
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    • 2010
  • This paper introduces reliability improvement and time saving in eddy current inspection by signal characteristic optimization of multi-coil eddy current array probe. In the past, Multi-coil array probe and single probe were used for the gas turbine rotor surface inspection & defect evaluation. The multi-coil array probe was used for the broad area inspection. But the signal deviations among multi-coil array probe are maximum 28% in commercial probe. This differences were considered to impedance differences among coils, so it is very difficult to evaluate exact defect size. The signal deviations among multi-coil array probe are maximum 28% in commercial probe. So, single coil inspection was used for exact defect sizing. The purpose of this study is to improve signal deviations of multi-coil array probe. The introduced new technology can improves this deviation by adjusting input voltage in each coil. At first, apply same voltage in each coil and collect signal amplitude of each coil. And calculate new input voltage based on signal amplitude of each coil. If the signal amplitude deviation is within 5% among multi-coil array probe, the signal amplitude of multi-coil array probe is reliable. The proposed technology gives 2% signal deviation among multi-coil array probe. The proposed new technology gives reliability improvement and inspection time saving in eddy current inspection.

One-Channel Phased-Array Quadrature RF Coil for Spine Magnetic Resonance Imaging (척추 MRI를 위한 One-Channel Phased-Array Quadrature RF 코일)

  • 양윤정;김선경
    • Journal of Biomedical Engineering Research
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    • v.19 no.2
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    • pp.129-132
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    • 1998
  • A new one-channel phased-array quadrature RF coil is developed for spine MR imaging. Quadrature RF coils for MRI have been used to improve the signal-to-noise ratio (SNR) by$"\squt{2}"$ using two orthogonal RF coils in combination. More recently, the phased-array RF coil has been proposed for more improvement of SNR by using an array of reduced-size RF coil elements. Two schemes proposed for the new phased-array quadrature RF coil are:(1) Proper overlapping of two quadrature RF coils thus removing the mutual inductance and (2) Attaching preamplifiers right after the coil section and combining the signal with proper phase delays. The coil has been implemented for receive-only mode, and tested by phantom and volunteer imaging. The experimental results show the utility of the proposed RF coil.d RF coil.

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Usefulness of the Technique of Collecting Signals by Selecting Elements from RF Receive Phase Array Coil in Magnetic Resonance Imaging (자기공명영상검사 시 Array coil에서 element를 선택하여 신호를 수집하는 기법의 유용성)

  • Choi, Kwan-Woo;Son, Soon-Yong
    • The Journal of the Korea Contents Association
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    • v.18 no.6
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    • pp.461-466
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    • 2018
  • In this study, we investigated the signal intensity changes by activating all and partially selected coil elements as a way to increase the SNR in a single region MR imaging. Two cylindrical fluid phantoms were placed side by side in a phase array coil and MRI scans were repeated by turning on the entire elements and selected elements. As a result, on both of the T1 and T2 weighted images signal intensities were significantly increased by 5.49% and 14.64%, respectively. In conclusion, if only a single region was to be imaged, selecting appropriate elements and collecting signals only from them could easily improve image qualities and signal intensities.

Phased-Array Quadrature RF Coil for Magnetic Resonance Imaging (자기공명영상촬영을 위한 Phased-Array Quadrature RF 코일)

  • Kim, S.K.;Yang, Y.J.;Lee, D.R.;Ahn, C.B.;Lee, H.K.;Oh, C.H.
    • Proceedings of the KOSOMBE Conference
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    • v.1997 no.05
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    • pp.227-229
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    • 1997
  • A new phased-array quadrature RF coil for one or two RF acquisition channels is developed for spine MR imaging. Quadrature RF coils for MRI have been useful to improve the signal-to-noise ratio (SNR) by $"\sqrt{2}"$ using two orthogonal RF coils in combination [1]. More recently, the phased-array RF coil has been proposed for more improvement of SNR by using an array of RF coil elements with a reduced size and coverage for each element. Two new schemes are proposed for the new phased-array quadrature RF coil as follows : (1) Proper overlapping of two quadrature RF coils thus removing the mutual inductance and (2) Attaching preamplifiers right after the coil section and combining the signal with proper phase delays. The coil has been implemented for receive- only mode. It has been tested through phantom and volunteer imaging. The experimental results show the utility of the proposed RF coil.

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Preliminary Results of 7-Channel Insertional pTx Array Coil for 3T MRI

  • Ryu, Yeun Chul
    • Journal of Magnetics
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    • v.22 no.2
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    • pp.238-243
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    • 2017
  • In this research, we report the preliminary results of an insertional type parallel transmission (pTx) array that has 7-elements that are placed in the space above a patient table as a transmit (Tx) coil to give an RF transmission ($B_1{^+}$) field for the body object of a 3 Tesla (T) MRI system. In previous research, we have tried to compare the performances of different coil elements and array geometries for a pTx body image. Based on these results, we attempt to obtain a human image with the proposed pTx array. Through the simulation and experimental results, we introduce a possible structure of multi-channel Tx array and verify the utility of a multi-channel Tx body image using $B_1{^+}$ shimming. The insertional pTx array, combined with a receiver (Rx) array coil, provides an enhanced $B_1{^+}$ field homogeneity in a large ROI image as a result of $B_1{^+}$ shimming applied over the full body size object. Through this research, we hope to determine the usefulness of the proposed insertional type RF coil combination for 3 T body imaging.

Comparative assessment of a 1.5T endorectal coil and a 3.0T phased-array coil available for prostate MRI (전립선 MRI에서 사용하는 1.5T 경직장 코일과 3.0T 위상 배열 코일의 성능 비교 평가)

  • Cho, Jae-Hwan
    • Journal of Digital Contents Society
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    • v.11 no.3
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    • pp.283-290
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    • 2010
  • The effectiveness of 3.0T phase array coil images was tested by comparing signal-to-noise ratios for the same coil images relative to 1.5T endorectal coil images. Signal intensities were measured in the three regions of prostate, central and peripheral (right and left) after 40 patients with prostate cancer were imaged during the period between Jan. 2008 and Oct. 2009 with T2 W, T1 W, and DW images obtained respectively using endorectal coil on a 1.5T MR scanner and phase array coil on a 3.0T MR scanner. For quantitative analysis, comparisons of average SNRs for the same ROIs were made between groups scanned with a 1.5T and a 3.0T MR scanner. The signal-to-noise ratios were shown to increase more sharply when using a phase array coil at a 3.0T MR scanner compared to using an endorectal coil at a 1.5T MR scanner.

Eddy Current Signal Analysis for Transmit-Receive Pancake Coil on ECT Array Probe

  • Lee, Hyang-Beom
    • Journal of the Korean Society for Nondestructive Testing
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    • v.26 no.1
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    • pp.25-29
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    • 2006
  • In this paper, the eddy current signals come from a pair oi transmit-receive (T/R) pancake coil on ECT array Probe are analyzed with the variations of the lift-of and of the distance between transmit and receive coils. To obtain the electromagnetic characteristics of the probes, the governing equation describing the eddy current problems is derived from Maxwell's equation and is solved using three-dimensional finite element method. Eddy current signals from T/R coils on ECT array probe have quite different characteristics compared with ones from impedance coil on rotating pancake coil probe. The results in this paper ran be helpful when the field eddy current signals from ECT array probe are evaluated.

Halbach Magnetic Circuit for Voice Coil Motor in Hard Disk Drives

  • Choi, Young-Man;Ahn, Da-Hoon;Gweon, Dae-Gab;Jeong, Jae-Hwa
    • Journal of Magnetics
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    • v.15 no.3
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    • pp.143-147
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    • 2010
  • Rotary-type voice coil motors are widely used as actuators in hard disk drives. The recent trend toward higher density and smaller form factors in data storage devices requires performance improvement of the voice coil motor. In this study, we introduce a Halbach magnet array to the voice coil motor in order to increase the force generation. The Halbach magnetic circuit outperforms the conventional magnetic circuit due to the confined magnetic flux. To investigate the performance of the Halbach magnetic circuit, we analyze air gap flux density with the various shapes and thickness of the magnets using 3-dimensional finite element analysis. Consequently the optimum shape of the Halbach magnetic circuit is proposed. Simulations and experimental results proved effectiveness of the proposed magnet array in the voice coil motor for a commercial hard disk drive.

Time-Multiplexed RF Transmission to Improve $B_1$ Homogeneity in High Field MRI

  • Han, Byung-Hee;Seo, Jeung-Hun;Heo, Hye-Young;Lee, Soo-Yeol
    • Journal of Biomedical Engineering Research
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    • v.29 no.2
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    • pp.99-106
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    • 2008
  • To improve $B_1$ homogeneity in high field MRI, the RF power is applied to the transmit array coil elements sequentially in the time-multiplexed way. Since only a single coil element is activated in a time-multiplexing slot, the global standing wave formation in the human body is greatly suppressed. The time-multiplexing slot width is on the order of micro seconds, hence, high-order-harmonic slices can be placed far from the transmit coil and simultaneous multiple slice selection can be avoided. The $B_1$ homogeneities of a birdcage coil and an eight-channel transmit array coil have been compared through finite difference time domain simulations. The simulation results indicate that the proposed technique can reduce the peak-to-peak $B_1$ inhomogeneity down to one fourth of the transmission with a birdcage coil on the central plane of the human head model at 3 T. The mimicking experiments at 3 T, eight separate experiments with a single coil element activated and image reconstruction by combining the eight images, also show promising results. It is expected that the proposed technique has some advantages over other $B_1$ improving methods in real practice since simple RF switching circuitries are only necessary and electromagnetic coupling between the coil elements is out of concern in its realization.

Signal Intensity Changes according to Coil Position Changes in MRI using 6 Channel SENSE Cardiac Array Coils (6채널 SENSE Cardiac Array 코일을 이용한 검사 시 코일의 위치 변화에 따른 신호강도)

  • Choi, Kwan-Woo;Son, Soon-Yong;Yoo, Beong-Gyu
    • Journal of the Korean Society of Radiology
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    • v.12 no.5
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    • pp.699-706
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    • 2018
  • In this study, we measured signal intensities according to array coil position changes to provide reference data of coil directions and the distances as it deters image quality unless the coils are aligned properly. The multi-purpose MRI phantom was placed in body array coils, and it was moved to the top, bottom, left, and right directions by 2 cm from the center to 10 cm. After obtaining images, signal intensities were measured and compared. The results of this study were as follows: Except for the upward direction, the signal intensities of the reference signal was not significantly different from that of the reference signal intensity within 2cm in both T1 and T2-weighted images. In conclusion, in clinical circumstances which various challenges exist to align the coils exactly on the same lines, array coils should be positioned at least within 2 cm from the center except for the upward direction, on the same line to prevent the image qualities are lowered.