1H MRS assessment of lipid composition at 3T and 7

Guruprasad P. Aithal (7239569)

Hannah Williams (5559683)

James King (1252200)

Penny Gowland (615649)

Scott Willis (3124653)

Stephen Bawden (7241105)

English

Loughborough University Institutional Repository

08/11/2018 https://submissions.mirasmart.com/ISMRM2019/ViewSubmissionPublic.aspx?sei=a90jFdQuEhttps://submissions.mirasmart.com/ISMRM2019/ViewSubmissionPublic.aspx?sei=a90jFdQuE 1/31H MRS assessment of lipid composition at 3T and 7TStephen Bawden , Scott Willis , Hannah Williams , James King , Guruprasad P Aithal , and Penny Gowland NIHR Nottingham Digestive Diseases Biomedical Research Centre, Nottingham University hospitals NHS trust and University of Nottingham,Nottingham, United Kingdom, Sir Peter Mansfield Imaging Centre, School of Physics, University of Nottingham, Nottingham, United Kingdom, School ofSport, Exercise and Health Sciences, Loughborough University, Louhgborough, United KingdomSynopsisMRI and MRS provides a powerful tool to non-invasively assess lipid deposition in vivo. In addition to fat fraction measurements, recent studieshave shown that lipid composition may play an important role in health outcomes. H MRS at high field strength provides good SNR ofindividual fat peaks and can be used to asses lipid composition (saturation, poly-unsaturation etc.). In this study a number of edible oils werescanned at 3T and 7T and MR spectra used to compare measurements of lipid composition with predicted values. An in vivo dataset was alsoacquired for comparison.IntroductionEctopic lipid deposition leads to a number of poor health outcomes and is an increasing burden on health care services globally . Whilst most research hasfocused on the quantity of lipid accumulation, recent studies indicate that lipid composition also plays a key role . Advanced MR techniques have beendeveloped to evaluate fat deposits in vivo and used in many patient studies. MRS in particular offers high SNR of individual fatty acid protons which allowsfor a non-invasive measure of composition  in addition to proton density fat fraction (PDFF).In this study, various edible oils with known lipid profiles were scanned and H MRS used to analyse fatty acid composition at 3T and 7T, with the aim touse these measurements in future studies.MethodsFat emulsions were produced at 4 different fat fractions (5, 10, 20 and 40%) using 5 different edible oils with varying fatty acid composition (figure 1).Emulsions were injected in spherical phantoms which were laid out in a grid and submersed in water.Phantoms were scanned at room temperature using a 3T Philips Ingenia MRI system with XL body coil. Single Voxel Spectroscopy was acquired for eachemulsion (STEAM, 10x10x10mm, TE=15, 30, 45, 80ms,TR=2000ms, PB shim). Spectra were pre-processed using jMRUI and peaks fitted using AMARESwith prior knowledge from previous studies . T  correction was applied to the water peak, and the T  corrected peak amplitudes were used to calculatePDFF%. Data were also acquired using the same protocol from the liver in one subject withelevated liver fat. For preliminary comparisons at higher field strength, the most and leastsaturated oil (coconut and linseed respectively) were scanned on a 7T Philips system using an 8channel multi-transmit body coil (MR Coils, Utrecht).Saturated fat indices (SI) and poly-unsaturated fat indices (UI) were calculated as previously described . In addition, a novel short-chain fat acid index(SCI) was introduced by taking the ratio of end (methyl) to mid-chain hydrogens whilst also considering the number of carbons associated with eachhydrogen as follows: [1/3 Methyl] / [1/3 Methyl + 1/2 (Methylene + β-Carboxyl + α-Olenfinic) + α-Carboxyl + Diacyl].PDFF values were compared with expected values using linear regression. Fat T  values were also measured and compare across oils. SI, PUI and SCIwere calculated for each oil at each fat fraction, and compared with previously published fatty acid compositions  (figure 1).ResultsFigure 2 shows the spectra of the varying oils acquired at 3Tand 7T and in vivo data, which were well shimmed and showed good resolution for lipid indexdetermination.SI, PUI and SCI calculated for each oil at each PDFF is shown in figure 3 (some values could not be calculated at small PDFFs due to low SNR). At 7T, SIwas 0.57 and 0.91; PUI was 0.07 and 0.02; and SCI was 0.11 and 0.08 for linseed and coconut oil respectively. The in vivo lipid indices were SI = 0.91, PUI= 0, SCI = 0.78 and no Diacyl peak was detected.The measured and actual PDFFs were well correlated (R2 > 0.9) across all oils (figure 4), with a gradient close to unity for all except coconut(gradient=1.24). The total fat T  values (measured at 40% fat fraction) were 46, 31, 35, 31 and 33 ms for coconut, linseed, palm, peanut and sunflower oilsrespectively.DiscussionSI, PUI and SCI were as expected from figure 1 , and appear to give stronger agreement for 40% emulsion. Values at 5% were more variability due topoor individual peak SNR, indicating that in vivo studies of lipid composition below 5% are not viable. SCI results were as expected with coconut oil alonehaving shorter chain (carbon < 16) fatty acids, and Introducing this term may also prove useful, as medium and short chain fatty acids are considered tohave more health benefits.PDFF remained stable across different lipid compositions, although coconut oil PDFF was slightly elevated. The T of fat in coconut oil was also greaterthan the other oils.In vivo lipid is stored as triglycerides and can be made up of saturated or unsaturated fats. The subject in this study had lipid indices that indicate highlysaturated, long-chain triglyceride content. The 7T spectra from this study provided pilot data that should be developed in future work.Conclusion1,2 3 2 3 1 212 311  23 4141 2526,7,826,7,82 08/11/2018 https://submissions.mirasmart.com/ISMRM2019/ViewSubmissionPublic.aspx?sei=a90jFdQuEhttps://submissions.mirasmart.com/ISMRM2019/ViewSubmissionPublic.aspx?sei=a90jFdQuE 2/3This study showed the potential of using high field MRS to measure varying lipid composition. MRS provides unique insight into fatty acid composition, andmay have a range of applications in liver fat, adipose tissue and stomach content measurements.AcknowledgementsNo acknowledgement found.References1. Zelber-Sagi, S., V. Ratziu, and R. Oren. Nutrition and physical activity in NAFLD: An overview of the epidemiological evidence. WorldJournal of Gastroenterology, 2011, 17(29), 3377-3389;2. Luukkonen, P.K., et al., Saturated Fat Is More Metabolically Harmful for the Human Liver ThanUnsaturated Fat or Simple Sugars. Diabetes Care, 2018. 41(8): p. 1732-1739.3. Reeder, S.B., H.C.H. Hu, and C.B. Sirlin, Proton density fat-fraction: A standardized mr-based biomarker of tissue fat concentration. Journal of MagneticResonance Imaging, 2012. 36(5): p. 1011-10144. Hamilton, G., et al., In vivo characterization of the liver fat H-1 MR spectrum. Nmr in Biomedicine, 2011. 24(7): p. 784-790.5. Johnson, N.A., et al., Noninvasive assessment of hepatic lipid composition: Advancing understanding and management of fatty liverdisorders. Hepatology, 2008. 47(5): p. 1513-1523.6. Orsavova, J., et al., Fatty Acids Composition of Vegetable Oils and Its Contribution to Dietary Energy Intake and Dependence ofCardiovascular Mortality on Dietary Intake of Fatty Acids. International Journal of Molecular Sciences, 2015. 16(6): p. 12871-12890.7. Lewinska, A., et al., Fatty Acid Profile and Biological Activities of Linseed and Rapeseed Oils. Molecules, 2015. 20(12): p. 22872-22880.8. Taufik, M., H.N. Lioe, and N.D. Yuliana, Evaluation of Major Fatty Acids Determination in Palm Oil by Gas Chromatography-Flame IonizationDetection. Agritech-Jurnal Teknologi Pertanian, 2016. 36(3): p. 308-316.FiguresTable showing literature values of fatty acid composition of edible oils analysed in this study H MRS of lipids at 3T, 7T, and in vivo as labelled 6,7,8108/11/2018 https://submissions.mirasmart.com/ISMRM2019/ViewSubmissionPublic.aspx?sei=a90jFdQuEhttps://submissions.mirasmart.com/ISMRM2019/ViewSubmissionPublic.aspx?sei=a90jFdQuE 3/3Plot of Saturation Index (SI), Poly-Unsaturated Index (PUI) and Short Chain Index (SCI) for each oil at each fat fraction, compared with known values ofdouble bond ratio (1 - double bond / carbon), Poly-unsaturated ratio (fraction of fatty acids with >1 multiple bonds) and Short chain ratio (fraction of fattyacids with <18 carbons) Plot of measured H MRS PDFF% compared with actual fat fraction for each oil used in this study 1

1H MRS assessment of lipid composition at 3T and 7T

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1H MRS assessment of lipid composition at 3T and 7T

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