Harada, Masafumi

Hayashi, Hiroaki

Ikemitsu, Natsuki

Kanazawa, Yuki

Matsumoto, Yuki

Miyoshi, Mitsuharu

Sasaki, Toshiaki

Usuda, Takatoshi

Tokushima University Institutional Repository

Page 1 of 13T1 dependence of magnetization transfer effect formacromoleculesPoster No.: C-0827Congress: ECR 2017Type: Scientific ExhibitAuthors: T. Sasaki1, Y. Kanazawa1, Y. Matsumoto1, H. Hayashi2, N.Ikemitsu1, T. Usuda1, M. Miyoshi3, M. Harada1; 1Tokushima/JP,2Tokushima, Tokushima/JP, 3Hino/JPKeywords: Molecular, genomics and proteomics, Image verification, Physics,Molecular imaging, Imaging sequences, MR-Functional imaging,MR, Radiation physics, MR physics, Hybrid Imaging, TissuecharacterisationDOI: 10.1594/ecr2017/C-0827Any 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 13Aims and objectivesMagnetization transfer (MT) is a cross relaxation phenomenon in which the proton isable to move freely; known as bulk water and bound water. The MT effect is observedand provides the signal attenuation for the MT pulse; then, a RF pulse is added at anoff-resonance frequency. This method is said to be the off-resonance method. Signalattenuation occurred for MT pulse by interaction between bulk water and bound watere.g., spin exchange, and chemical shift. The magnetization transfer contrast (MTC)method is demonstrated as the above phenomenon [1, 2]. Mainly, the MTC method isused for magnetic resonance angiography (MRA), of which the clinical application to thehead has many advantages; such as signal saturation of the background on a targettissue, e.g., detection of blood. There is one report that the observation of the peripheralartery in the brain had improved by signal-attenuation on the substance of the backgroundby addition of a MT pulse [3]. Additionally, there are some reports about the applicationof MTC to cartilage macromolecules such as the collagen [4].Generally, a magnetization transfer ratio (MTR) is known to be an index to express signalattenuation by the MT effect quantitatively [6]. MTR is calculated by the ratio of theremainder of each image without and with a MT pulse. Spin exchange between bulk waterand bound water is an important attenuation factor. The spin exchange rate depends onT1 which has been reported by Henkelman [5].For T1 calculation methods, there are the inversion recovery (IR) method and variableflip angle (VFA) method. The IR method is used as the gold-standard method for T1calculation. On the other hand, the VFA method is performed using a spoiled gradient-echo (SPGR) sequence in general, which makes it possible to be a faster imaging methodthan the IR method. At high magnetic field strengths, the VFA method is sensitive to B1inhomogeneity [7, 8]. Accordingly, B1 inhomogeneity needs to be corrected.It is important that we evaluate how much effect T1 has on the MT of macromolecules.However, little attention has been given to the direct measurement of T1 and theeffect it has on the MT. To assess the relationship between T1 and the MT effect onmacromolecules, we constructed a T1 map using the variable flip angle (VFA) methodwith a MT pulse.Methods and materialsWe performed a phantom experiment. The phantom was created using a set of sixsamples in a cylindrical vessel. The sample components used were deionized water withPage 3 of 13polyethylene glycol (PEG) macromolecules at different concentrations (0, 10, 20, 30, 40,and 50 wt%). Figure 1 shows the schematics of the phantom used in this study.All imaging analysis were applied using an in-house program, MATLAB (Mathworks,Natick, MA, USA). A chart of the procedure of this study is shown in Fig. 2.1. MR imagingOn a 3.0 T MR scanner system (Discovery MR750, GE Healthcare, Waukesha, WI,USA), MR imaging data of the phantom were acquired with spoiled gradient echo (SPGR)sequence with and without a MT pulse (offset frequency = 800, 1200, 1600 Hz). Table1 shows detailed imaging parameters.2. B1 correctionThe B1 map was derived using the double angle method. The method uses the MRimages at two flip angles (FA) acquired by gradient echo (GRE) sequence. The MRimages for B1 mapping were acquired using 2 second repetition time (TR), 5.8 ms echotime (TE), 40 degrees FA #, 80 degrees FA 2#, and 5 mm slice thickness. Table 2 showsdetailed imaging parameters for B1 mapping. B1 map was constructed using the followingequation [9]Fig. 3: Equation(1).References: - Tokushima/JPwhere S# and S2# are the signal intensities of the # and 2# FA images. Using equation (1),we created a B1 map from the MR images. Then, we applied the B1 map to MR imagingdata, and performed B1 correction.3. T1 mappingPage 4 of 13After B1 correction was performed, T1 maps were derived using the VFA method. TheVFA method uses more than two FA images acquired by SPGR sequence. Signalintensities of SPGR sequence are given by [7,10]Fig. 4: Equation(2).References: - Tokushima/JPwhere TR and FA # are the control parameters varied by the operator, M0 is theequilibrium magnetization, SSPGR is the measured signal values. Then, based onequation (2), we performed T1 fitting as follow:Fig. 5: Equation(3).References: - Tokushima/JPPage 5 of 13where NSPGR is the number of varied FA, arg min f(x) is the function for which f(x) attainsthe smallest value, M0 and T1 are the estimated parameters determined by nonlinearcurve fitting. Initial estimation values M0 and T1 from the curve fitting values were setto the maximum signal intensity in the same pixel of images and 2000 ms, respectively.With fixed TR and variable FAs, the optimization of the parameters M0 and T1 wascalculated according by the relationship between signal intensity and FA. Mean T1 valuesand standard division (SD) of all samples were measured on T1 maps.4. MTR mappingMTR maps were calculated individually using two FA images with and without a MT pulse.MTR is determined by [2]Fig. 6: Equation(4).References: - Tokushima/JPwhere S0 and SSAT are signal values with and without a MT pulse. MTR of all sampleswere measured on MTR maps at each FA and offset frequency.Images for this section:Page 6 of 13Fig. 1: The schematics of the phantom.© - Tokushima/JPPage 7 of 13Fig. 2: Chart of the procedure.© - Tokushima/JPPage 8 of 13Table 1: Imaging parameters for T1 and MTR mappings.© - Tokushima/JPTable 2: Imaging parameters for B1 mappiing© - Tokushima/JPPage 9 of 13ResultsTable 3 shows the relationship between PEG concentrations and mean T1 values of eachsample with and without a MT pulse.Figure 7 shows T1 map derived from the VFA method with and without a MT pulse (Off-set frequency: 800, 1600 Hz).Figure 8 shows a graph of the data, Table. 3. By the addition of MT pulse, the changein T1 values was seen, but there were almost no changes caused by differences inoffset frequency of the MT pulse. In the PEG 30% solution, a change in the T1 value bythe MT pulse addition was not seen. A decreasing tendency in T1 values was seen atlower PEG concentrations, but the T1 values showed an increasing tendency when PEGconcentration exceeded 30%.Figure 9 shows the relationship between PEG concentrations and MTR at each FA (5,20, 40, 60, and 90 degrees). In MTR, the influence of FA and offset frequency wasremarkable.Images for this section:Table 3: The measured T1 values.© - Tokushima/JPPage 10 of 13Fig. 7: T1 map derived from the VFA method with and without a MT pulse (Off-setfrequency: 800, 1600 Hz).© - Tokushima/JPFig. 8: The relationship between PEG concentrations and measured T1 values.Page 11 of 13© - Tokushima/JPFig. 9: The relationship between PEG concentrations and MTR at each FA (5, 20, 40,60, and 90 degrees).© - Tokushima/JPPage 12 of 13ConclusionDetermination of T1 with a MT pulse makes it possible to obtain more detailed informationof macromolecules not provided when using MTR.Personal informationAuthor Names:Toshiaki Sasaki1, Yuki Kanazawa2, Yuki Matsumoto1, Hiroaki Hayashi2, NatsukiIkemitsu1, Takatoshi Usuda1, Mitsuharu Miyoshi3, and Masafumi Harada2Author Affiliations:1. School of Health Sciences, Tokushima University2. Institute of Biomedical Sciences, Tokushima University Graduate School3. MR Applications and Workflow Asia Pacific GE Healthcare Japan CorporationCorresponding Author and Reprint Info:Yuki Kanazawa, PhDInstitute of Biomedical Sciences, Tokushima University Graduate School3-18-15, Kuramoto-Cho, Toksuhima City, Tokushima, 770-8509, JapanE-mail: yk@tokushima-u.ac.jpReferences1. Wolff SD, Balaban RS. Magnetization transfer contrast (MTC) and tissuewater proton relaxation in vivo. Magn Reson Med. 1989;10(1):135-1442. Henkelman RM, Stanisz GJ, Graham SJ. Magnetization transfer in MRI: areview. NMR Biomed. 2001;14(2):57-64.3. Edelman RR, Ahn SS, Chien D, Li W, Goldmann A, Mantello M, KramerJ, Kleefield J. Improved time-of-flight MR angiography of the brain withmagnetization transfer contrast. Radiology. 1992;184(2):395-399.Page 13 of 134. Wolff SD, Chesnick S, Frank JA, Lim KO, Balaban RS. Magnetizationtransfer contrast: MR imaging of the knee. Radiology. 1991;179(3):623-628.5. Henkelman RM, Huang X, Xiang QS, Stanisz GJ, Swanson SD.Quantitative interpretation of magnetization transfer. Magn Reson Imag.1993;29(6):759-766.6. Finelli DA, Reed DR. Flip angle dependence of experimentally determinedT1sat and apparent magnetization transfer rate constants. Magn ResonImag. 1998;8(3):548-553.7. Hurley SA, Yarnykh VL, Johnson KM, Field AS, Alexander AL, SamsonovAA. Simultaneous variable flip angle-actual flip angle imaging methodfor improved accuracy and precision of three-dimensional T1 and B1measurements. Magn Reson Med. 2012;68(1):54-64.8. Collins CM, Li S, Smith MB. SAR and B1 field distributions in aheterogeneous human head model within a birdcage coil. Magn Reson Med.1998;40(6):847-856.9. Sacolick LI, Wiesinger F, Hancu I, Vogel MW. B1 mapping by bloch-siegertshift. Magn Reson Med. 2010;63(5):1315-1322.10. Kanazawa Y, Hayashi H, Harada M. Clinical approach of T1-mapping forhemodynamic analysis. Med Imag & Infor Sci. 2015;32(4).

T1 dependence of magnetization transfer effect for macromolecules

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T1 dependence of magnetization transfer effect for macromolecules

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