Curtis N Wiens1, Nathan S Artz1,2, Hyungseok Jang1, Alan B McMillan1, Kevin M Koch3, Scott B Reeder1,4,5,6,7. 1. Department of Radiology, University of Wisconsin, Madison, Wisconsin, USA. 2. Department of Diagnostic Imaging, St. Jude Children's Research Hospital, Memphis, Tennessee, USA. 3. Department of Radiology, Medical College of Wisconsin, Milwaukee, Wisconsin, USA. 4. Department of Biomedical Engineering, University of Wisconsin, Madison, Wisconsin, USA. 5. Department of Medical Physics, University of Wisconsin, Madison, Wisconsin, USA. 6. Department of Medicine, University of Wisconsin, Madison, Wisconsin, USA. 7. Department of Emergency Medicine, University of Wisconsin, Madison, Wisconsin, USA.
Abstract
PURPOSE: To develop a fully phase-encoded MRI method for distortion-free imaging near metallic implants, in clinically feasible acquisition times. THEORY AND METHODS: An accelerated 3D fully phase-encoded acquisition with broadband excitation and ultrashort echo times is presented, which uses a broadband radiofrequency pulse to excite the entire off-resonance induced by the metallic implant. Furthermore, fully phase-encoded imaging is used to prevent distortions caused by frequency encoding, and to obtain ultrashort echo times for rapidly decaying signal. RESULTS: Phantom and in vivo acquisitions were used to describe the relationship among excitation bandwidth, signal loss near metallic implants, and T1 weighting. Shorter radiofrequency pulses captured signal closer to the implant by improving spectral coverage and allowing shorter echo times, whereas longer pulses improved T1 weighting through larger maximum attainable flip angles. Comparisons of fully phase-encoded acquisition with broadband excitation and ultrashort echo times to T1 -weighted multi-acquisition with variable resonance image combination selective were performed in phantoms and subjects with metallic knee and hip prostheses. These acquisitions had similar contrast and acquisition efficiency. CONCLUSIONS: Accelerated fully phase-encoded acquisitions with ultrashort echo times and broadband excitation can generate distortion free images near metallic implants in clinically feasible acquisition times. Magn Reson Med 79:2156-2163, 2018.
PURPOSE: To develop a fully phase-encoded MRI method for distortion-free imaging near metallic implants, in clinically feasible acquisition times. THEORY AND METHODS: An accelerated 3D fully phase-encoded acquisition with broadband excitation and ultrashort echo times is presented, which uses a broadband radiofrequency pulse to excite the entire off-resonance induced by the metallic implant. Furthermore, fully phase-encoded imaging is used to prevent distortions caused by frequency encoding, and to obtain ultrashort echo times for rapidly decaying signal. RESULTS: Phantom and in vivo acquisitions were used to describe the relationship among excitation bandwidth, signal loss near metallic implants, and T1 weighting. Shorter radiofrequency pulses captured signal closer to the implant by improving spectral coverage and allowing shorter echo times, whereas longer pulses improved T1 weighting through larger maximum attainable flip angles. Comparisons of fully phase-encoded acquisition with broadband excitation and ultrashort echo times to T1 -weighted multi-acquisition with variable resonance image combination selective were performed in phantoms and subjects with metallic knee and hip prostheses. These acquisitions had similar contrast and acquisition efficiency. CONCLUSIONS: Accelerated fully phase-encoded acquisitions with ultrashort echo times and broadband excitation can generate distortion free images near metallic implants in clinically feasible acquisition times. Magn Reson Med 79:2156-2163, 2018.
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