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Clinical Magnetic Resonance Imaging of the Knee at 7 T

Optimization of Fat Suppression

Wyss, Michael, BSc*; Manoliu, Andrei, MD, PhD†,‡; Marcon, Magda, MD; Spinner, Georg, MSc*; Luechinger, Roger, PhD*; Pruessmann, Klaas P., PhD*; Andreisek, Gustav, MD, MBA†,§,∥

doi: 10.1097/RLI.0000000000000523
Original Articles

Purpose The aim of this study was to evaluate the efficiency and performance of different fat suppression techniques for clinical 7 T knee magnetic resonance imaging including the slice-selective gradient reversal (SSGR) technique.

Materials and Methods This article is an ethical board–approved prospective study with written informed consent from 8 volunteers (mean, 31 ± 4 years). It included fat phantom and knee magnetic resonance imaging at 3 T (Magnetom Skyra; Siemens Healthcare) and at 7 T (Achieva, Philips Healthcare). At 3 T, an axial proton density-weighted turbo spin echo sequence with spectral adiabatic inversion recovery (SPAIR) was acquired. At 7 T, a series of 5 proton density-weighted turbo spin echo sequences was acquired: (a) without fat suppression, (b) with spectral presaturation with inversion recovery (SPIR), (c) with SPAIR, (d) with SSGR, and (e) with the combination of SSGR + SPIR. Additional noise scans allowed pixelwise calculation of signal-to-noise ratio and contrast-to-noise ratio maps. Quantitative data at 7 T were compared with each other but not to 3 T. Two independent radiologists evaluated overall image quality, homogeneity and grade of fat suppression, and the delineation between 2 adjacent structures. Results were compared using Wilcoxon signed rank and paired sample t tests.

Results Relative signal-to-noise ratios of fat demonstrated that the SPIR technique reduced the fat signal to 45% ± 5.4%; SPAIR, 18% ± 1.2%; SSGR, 14% ± 1.1%; and SSGR + SPIR, 11% ± 0.3%. Contrast-to-noise ratio showed superior contrast between muscle-fat (P < 0.001) and fluid-fat (P ≤ 0.001) for SSGR and SSGR + SPIR. The radiologists rated the overall image quality higher at 7 T than 3 T. The homogeneity and grade of fat suppression as well as the delineation between 2 different (adjacent) structures were rated best for SSGR + SPIR.

Conclusions At 7 T, fat saturation for clinical knee imaging using SSGR and the combination of SSGR + SPIR was superior compared with standard methods based on spectrally selective radiofrequency pulses.

From the *Institute for Biomedical Engineering, ETH Zurich and University of Zurich;

Institute for Diagnostic and Interventional Radiology, University Hospital of Zurich;

Department of Psychiatry, Psychotherapy and Psychosomatics, Psychiatric University Hospital, University of Zurich, Zurich;

§Radiologie, Spital Thurgau, Munsterlingen; and

University of Zurich, Zurich, Switzerland.

Received for publication January 30, 2018; and accepted for publication, after revision, September 9, 2018.

Conflicts of interest and sources of funding: none declared.

Correspondence to: Gustav Andreisek, MD, MBA, Department of Radiology, Spital Thurgau AG, Spitalcampus 1, 8596 Munsterlingen, Switzerland. E-mail: gustav@andreisek.de.

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