title: Gradient-Modulated PETRA MRI.
abstract: Image blurring due to off-resonance and fast T2*signal decay is a common issue in radial ultrashort echo time MRI sequences. One solution is to use a higher readout bandwidth, but this may be impractical for some techniques like pointwise encoding time reduction with radial acquisition (PETRA), which is a hybrid method of zero echo time and single point imaging techniques. Specifically, PETRA has severe specific absorption rate (SAR) and radiofrequency (RF) pulse peak power limitations when using higher bandwidths in human measurements. In this study, we introduce gradient modulation (GM) to PETRA to reduce image blurring artifacts while keeping SAR and RF peak power low. Tolerance of GM-PETRA to image blurring was evaluated in simulations and experiments by comparing with the conventional PETRA technique. We performed inner ear imaging of a healthy subject at 7T. GM-PETRA showed significantly less image blurring due to off-resonance and fast T2*signal decay compared to PETRA. In in vivo imaging, GM-PETRA nicely captured complex structures of the inner ear such as the cochlea and semicircular canals. Gradient modulation can improve the PETRA image quality and mitigate SAR and RF peak power limitations without special hardware modification in clinical scanners.
authors.affiliation: Center for Magnetic Resonance Research, Department of Radiology, University of Minnesota, MN, USA.
authors.forename: Naoharu
authors.initials: N
authors.lastname: Kobayashi
authors.affiliation: Center for Magnetic Resonance Research, Department of Radiology, University of Minnesota, MN, USA.
authors.forename: Ute
authors.initials: U
authors.lastname: Goerke
authors.affiliation: Center for Magnetic Resonance Research, Department of Radiology, University of Minnesota, MN, USA.
authors.forename: Luning
authors.initials: L
authors.lastname: Wang
authors.affiliation: Center for Magnetic Resonance Research, Department of Radiology, University of Minnesota, MN, USA.
authors.forename: Jutta
authors.initials: J
authors.lastname: Ellermann
authors.affiliation: Center for Magnetic Resonance Research, Department of Radiology, University of Minnesota, MN, USA.
authors.forename: Gregory J
authors.initials: GJ
authors.lastname: Metzger
authors.affiliation: Center for Magnetic Resonance Research, Department of Radiology, University of Minnesota, MN, USA.
authors.forename: Michael
authors.initials: M
authors.lastname: Garwood
keywords: image blurring; magnetic resonance imaging; off-resonance; pointwise encoding time reduction with radial acquisition; ultrashort echo time