Harada, Masafumi

Hayashi, Hiroaki

Ikemitsu, Natsuki

Kanazawa, Yuki

Matsumoto, Yuki

Miyoshi, Mitsuharu

Sasaki, Toshiaki

Usuda, Takatoshi

Tokushima University Institutional Repository

Page 1 of 19An improvement of signal-to- noise ratio for phase imagePoster No.: C-0803Congress: ECR 2017Type: Scientific ExhibitAuthors: N. Ikemitsu1, Y. Kanazawa1, Y. Matsumoto1, H. Hayashi2, T.Usuda1, T. Sasaki1, M. Miyoshi3, M. Harada1; 1Tokushima/JP,2Tokushima, Tokushima/JP, 3Hino/JPKeywords: MR physics, Computer applications, Contrast agents, MR,Experimental investigations, Computer Applications-General,Physics, Biological effectsDOI: 10.1594/ecr2017/C-0803Any information contained in this pdf file is automatically generated from digital materialsubmitted to EPOS by third parties in the form of scientific presentations. Referencesto any names, marks, products, or services of third parties or hypertext links to third-party sites or information are provided solely as a convenience to you and do not inany way constitute or imply ECR's endorsement, sponsorship or recommendation of thethird party, information, product or service. ECR is not responsible for the content ofthese pages and does not make any representations regarding the content or accuracyof material in this file.As per copyright regulations, any unauthorised use of the material or parts thereof aswell as commercial reproduction or multiple distribution by any traditional or electronicallybased reproduction/publication method ist strictly prohibited.You agree to defend, indemnify, and hold ECR harmless from and against any and allclaims, damages, costs, and expenses, including attorneys' fees, arising from or relatedto your use of these pages.Please note: Links to movies, ppt slideshows and any other multimedia files are notavailable in the pdf version of presentations.www.myESR.orgPage 2 of 19Aims and objectivesTransverse relaxation time (T2) is a time constant which includes only nuclear-nuclearinteractions. T2* is a time constant including nuclear-nuclear interactions and staticmagnetic field (B0) inhomogeneity, which is affected by susceptibility. Setting of T2 or T2*is generally applied to long echo time (TE). It is generally known that the T2* decay is afaster process than the T2 decay. If a material has strong susceptibility, e.g., blood, FeO,and MR contrast media, the T2* decay is faster.In magnetic resonance (MR) imaging, a magnitude image takes an absolute value fromreal and imaginary parts and is used normally in clinical. A phase image made from phasedifferences of real and imaginary parts which are a reflection of variable information ofa local magnetic field. A phase image has good contrast and reveals detail structuresthat are not visible on the corresponding magnitude image, e.g., it obtains informationconcerning iron deposit as phase in blood vessels and tissue [1, 2]. The phase image hascontrast depending on the susceptibility and TE of each tissue. Moreover, it is used tomake a susceptibility weighted image (SWI) [3]. Accordingly, signal-to-noise ratio (SNR)of a phase image is an important factor.Fig. 1: How to make a phase imageReferences: Tokushima University - Tokushima/JPWu B et al., have been reported that the SNR of image phase depends on TE, eachmaterial's T2*, and offset frequency [4]. Here, we are concerned with the indication ofmaximum SNR of the image phase when TE is equal to T2*. Therefore, the purpose ofthis study is to investigate temporal characteristics of the phase SNR, and make a phaseimage with high SNR by using phase data at the optimized TE. Accordingly, we improvethe SNR of the phase image by focusing T2*.Page 3 of 19Images for this section:Fig. 1: How to make a phase image© Tokushima University - Tokushima/JPPage 4 of 19Methods and materials1. Phase SNRIn general, theoretical formula of T2* decay is described as follows,Fig. 2References: Tokushima University - Tokushima/JPwhere is the MR signal, is the transverse magnetization, and is the TE. When the noisevariance of real and imaginary channel are equal, noise power in the phase is describedby the following equation,Fig. 3References: Tokushima University - Tokushima/JPwhere represent the noise variance in real or imaginary parts with the noise power. Then,the phase SNR (SNR#) at is shown as [4],Page 5 of 19Fig. 4References: Tokushima University - Tokushima/JPwhere is the frequency offset. The above equation is differentiated by,Fig. 5References: Tokushima University - Tokushima/JPthe phase becomes maximum when the TE is equal to the T2*. In other words, the T2* isthe optimal TE when considering the best .Page 6 of 19Fig. 6: Relationship between TE and phase SNRReferences: Tokushima University - Tokushima/JP2. MR imagingOn a 3.0T MRI system, both phantom was acquired with three-dimensional fast spoiledgradient-echo (3D-SPGR). The other imaging parameters are shown in Fig7.Fig. 7: Image parameterReferences: Tokushima University - Tokushima/JPPage 7 of 19We made a phantom using six tubes of gadopentetate dimeglumine (Gd-DTPA;Magnevist, Bayer Pharma AG, Germany) at different concentrations (0.1, 0.5, and 1.0 wt%) and Gd-DTPA (0.1, 0.5, 1.0 wt%) and with agar (1.0 wt%). The six tubes were fixedin agar (1.0 wt%) and placed within a cylindrical container.Fig. 8: Phantom componentReferences: Tokushima University - Tokushima/JPPage 8 of 19Fig. 9: Chart of this experimentsReferences: Tokushima University - Tokushima/JP3. Data analysisWe determined regions of interest (ROIs) for each sample and calculated mean T2*and SD. SNRs were performed normalization at maximum phase SNR on each TE.We determined TE at maximum phase SNR and T2*. Coefficient of determination wascalculated to confirm accuracy of T2* curve fitting. We applied iPhase image to SWI andcalculated SNR defining using the following equation (5) :Page 9 of 19Fig. 10References: Tokushima University - Tokushima/JPAll statistical analysis was performed using MATLAB (MathWorks, Inc., Natick, MA,USA). SMV and SHARP algorisms were used with our custom-written codes at http://weill.cornell.edu/mri/pages/qsm.html. We performed our analysis on a MacBook Pro (4cores, Corei7 2.4 GHz with 16 GB RAM).Images for this section:Page 10 of 19Fig. 6: Relationship between TE and phase SNR© Tokushima University - Tokushima/JPFig. 9: Chart of this experiments© Tokushima University - Tokushima/JPPage 11 of 19ResultsFigure 11 shows measured T2* values for each sample of the phantom. The T2* fluctuationcalculation was only high for the Gd-DTPA 0.1% sample when compared to the othersamples.Fig. 11: T2* values at each sample of a phantomReferences: Tokushima University - Tokushima/JPFigure 12 shows SNR values for each sample of the phantom. SWIs were derived fromthe conventional method and our method. SWI derived from iPhase showed in higherSNR than conventional SWI.Fig. 12: Comparison of SWIs derived from the conventional method and our methodReferences: Tokushima University - Tokushima/JPPage 12 of 19Fig. 13: Relationship between TE and normalized phase SNRReferences: Tokushima University - Tokushima/JPFigure 13 shows the relationship between TE and normalized phase SNR in the phantomexperiment. It is shown that the TE at maximum phase SNR values are close to the T2* ofeach sample. T2* values of each sample indicate closely at the peak of the curve betweenTE and phase SNR values.Page 13 of 19Fig. 14: Relationship between TE and SIReferences: Tokushima University - Tokushima/JPFigure 14 shows the relationship between TE and signal intensity (SI). Each plot SI andTE indicate a good fit with the data. With increase in echo number, SNR of iPhase showeda high value and good T2* curve fit. Our method requires accurate T2* curve fitting touse the T2* map. Then, we measured coefficient of determination. The coefficient ofdetermination was high in value and T2* curve fitting was highly accurate.Page 14 of 19Fig. 15: T2* map and iPhase imageReferences: Tokushima University - Tokushima/JPFigure 15 shows each image derived from multi-echo 3D-SPGR of the phantom. Left,shows the T2* map (Fig.15a). Right, shows the iPhase image using phase data atoptimized TE at each pixel (Fig.15b).Fig. 16: Conventional SWI and iPhase method SWIPage 15 of 19References: Tokushima University - Tokushima/JPFigure 16 shows a comparison of two phantom images. The conventional SWI (Fig.16a),and the SWI derived from iPhase image in our method (Fig.16b). The conventional SWIis only able to emphasize the susceptibility in each pixel [3]; it is reconstructed afterthe phase images are high-pass-filtered and transformed to a phase mask that variesin amplitude between zero and one. This method differs vastly from our method in agreat deal in physical concept of T2* decay. Here, to evaluate the improvement of phaseSNR, we compared the SNR of SWI applied iPhase method and conventional SWI in aphantom experiment. The results showed that five of the six samples significantly wereimproved in each SNR, and one sample (at agar + Gd-DTPA 1.0%) was had a low-SNR(Fig. 12 and Fig 16).Images for this section:Fig. 13: Relationship between TE and normalized phase SNR© Tokushima University - Tokushima/JPPage 16 of 19Fig. 14: Relationship between TE and SI© Tokushima University - Tokushima/JPPage 17 of 19Fig. 15: T2* map and iPhase image© Tokushima University - Tokushima/JPFig. 16: Conventional SWI and iPhase method SWI© Tokushima University - Tokushima/JPPage 18 of 19ConclusionWe developed the iPhase image method for correction for SNR using a T2* phase cycleof multi-echo SPGR data. The iPhase image was able to improve the image phase SNR.Moreover, our method makes it possible to obtain a phase image at a good SNR for animage affected by susceptibility, e.g., susceptibility weighted image (SWI).Personal informationAuthor Names:Natsuki Ikemitsu1, Yuki Kanazawa2, Yuki Matsumoto1, Hiroaki Hayashi2, TakatoshiUsuda1, Toshiaki Sasaki1, Mitsuharu Miyoshi3, and Masahumi Harada2Author Affiliations:1School of Health Sciences, Tokushima University2Institute of Biomedical Sciences, Tokushima University Graduate School3MR Applications and Workflow Asia Pacific GE Healthcare Japan CorporationCorresponding Author and Reprint Info:Yuki Kanazawa, PhDInstitute of Biomedical Sciences, Tokushima University Graduate School 3-18-15,Kuramoto-Cho, Toksuhima City, Tokushima, 770-8509, Japan E-mail: yk@tokushima-u.ac.jpReferences1. Bock J, Kreher BW, Hennig J, and Markl M. Optimized pre-processing of time-resolved2D and 3D Phase Contrast MRI data. Proc. Intl. Soc. Mag. Reson. Med. 15 (2007).2. Sood S, Urriola J, Reutens D, O'Brien K, Bollmann S, Barth M, Vegh V. EchoTime-Dependrnt Quantitative Susceptibility Mapping Contains Information on Tissueproperties. Magn Reson Med. 2016 May 25.Page 19 of 193. Haacke EM, Xu Y, Cheng YC, Reichenbach JR. Susceptibility Weighted Imaging(SWI). Magnetic Resonance in Medicine 52:612-618 (2004).4. Wu B, Li W, Avram AV, Gho SM, Liu C. Fast and tissue-optimized mapping of magneticsusceptibility and T2* with multi-echo and multi-shot spirals. Neuroimage. 2012 Jan2;59(1):297-305.

An improvement of signal-to- noise ratio for phase image

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An improvement of signal-to- noise ratio for phase image

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