Accelerating fully phase‐encoded MRI near metal using multiband radiofrequency excitation

• Published in: Magnetic resonance in medicine 2017-03, Vol.77 (3), p.1223-1230
• Main Authors: Artz, Nathan S., Wiens, Curtis N., Smith, Matthew R., Hernando, Diego, Samsonov, Alexey, Reeder, Scott B.
• Format: Article
• Language: English
• Subjects: Algorithms; fully phase‐encoded; Image Enhancement - methods; Image Interpretation, Computer-Assisted - methods; imaging near metal; magnetic resonance imaging; Magnetic Resonance Imaging - instrumentation; Magnetic Resonance Imaging - methods; metallic prostheses; Metals; multiband radiofrequency excitation; Phantoms, Imaging; Prostheses and Implants; Radio Waves; Reproducibility of Results; Sensitivity and Specificity; Signal Processing, Computer-Assisted; spectrally resolved
• ISSN: 0740-3194; 1522-2594
• DOI: 10.1002/mrm.26209

Purpose To develop a multiband radiofrequency (RF) excitation strategy for simultaneous excitation of multiple RF offsets to accelerate fully phase‐encoded imaging near metallic prostheses. Methods Multiband RF excitation was designed and incorporated into a spectrally resolved fully phase‐encoded (SR‐FPE) imaging scheme. A triband (−6, 0, 6 kHz) acquisition was compared with three separate single‐band acquisitions at the corresponding RF offsets with a phantom containing the head of a hip prosthesis. In vivo multiband data with continuous spectral coverage were acquired in the knee of a healthy volunteer with the head of a hip prosthesis placed posteriorly and in a volunteer with a total knee prosthetic implant. Results Phantom images acquired with triband excitation were essentially identical to the composite of three single‐band excitations, but with an acceleration factor of three. In vivo multiband images of the healthy knee with adjacent metal demonstrated very good depiction of knee anatomy. In vivo images of the total knee replacement were successfully acquired, allowing visualization of native tissue with far less signal dropout than 2D‐FSE. Conclusions FPE imaging with multiband excitation is feasible in the presence of extreme off‐resonance. This approach can reduce scan time and/or increase off‐resonance coverage, enabling in vivo FPE imaging near metallic prostheses over a broad off‐resonance spectrum. Magn Reson Med 77:1223–1230, 2017. © 2016 International Society for Magnetic Resonance in Medicine