PMID- 29993630
OWN - NLM
STAT- MEDLINE
DCOM- 20190624
LR  - 20190624
IS  - 1558-254X (Electronic)
IS  - 0278-0062 (Linking)
VI  - 37
IP  - 8
DP  - 2018 Aug
TI  - Squeezed Trajectory Design for Peak RF and Integrated RF Power Reduction in 
      Parallel Transmission MRI.
PG  - 1809-1821
LID - 10.1109/TMI.2018.2828112 [doi]
AB  - High peak RF amplitude and excessive specific absorption rate (SAR) are two 
      critical concerns for hardware implementation and patient safety in scientific 
      and clinical research for high field MRI using parallel transmissions (pTX). In 
      this paper, we introduce a squeezing strategy to reduce peak RF amplitude and 
      integrated RF power via direct reshaping of the k-space trajectory. In the 
      existing peak RF / integrated RF power optimization methods gradient amplitude or 
      slew rate is reduced, but the k-space trajectory remains unchanged. Unlike these 
      traditional methods, we worked directly in the excitation k-space to reshape 
      k-space traversal by a squeezing vector in order to achieve peak RF and total RF 
      power optimization, using a particle swarm optimization algorithm. The squeezing 
      strategy was applied to the conventional variable density spiral (CVDS) and the 
      variable rate selective excitation (VERSE) trajectories, dubbed SVDS (squeezed 
      variable density spiral) and SVERSE (squeezing trajectory with VERSE), 
      respectively, for different excitation profiles of small or large tip angles. 
      Pulse acceleration and off-resonance effects were evaluated for an 8-ch pTX via 
      Bloch simulation. CVDS, VERSE, SVDS, and SVERSE pulses were implemented on a 3T 
      scanner with a 2-ch pTX. Phantom and in vivo experiments were performed for 
      reduced FOV (rFOV) imaging. The results show that SVDS pulses simultaneously 
      reduce integrated RF power and peak RF by about 30% on average compared to CVDS 
      pulses for a square pattern ( $80\times80$ mm2) with flip angles of 30 degrees , 90 degrees , and 
      180 degrees . Compared with the VERSE method under the same peak RF constraints, the SVDS 
      method reduces integrated RF power by an average of 20% for small tip excitations 
      for profiles of slice, rectangular, square, and circle, and has slightly reduced 
      excitation accuracy slightly (about 0.6%, from 6.8% to 7.4%). The SVERSE method 
      shortens the duration of the VERSE pulse by 12.8% at large ti p angle (180 degrees ). 
      Feasibility for rFOV imaging was demonstrated with phantom and in vivo 
      experiments with squeezed pulses.
FAU - Li, Qing
AU  - Li Q
FAU - Liao, Congyu
AU  - Liao C
FAU - Ye, Huihui
AU  - Ye H
FAU - Chen, Ying
AU  - Chen Y
FAU - Cao, Xiaozhi
AU  - Cao X
FAU - Yuan, Lisha
AU  - Yuan L
FAU - He, Hongjian
AU  - He H
FAU - Zhong, Jianhui
AU  - Zhong J
LA  - eng
PT  - Journal Article
PT  - Research Support, Non-U.S. Gov't
DEP - 20180418
PL  - United States
TA  - IEEE Trans Med Imaging
JT  - IEEE transactions on medical imaging
JID - 8310780
SB  - IM
MH  - Algorithms
MH  - Brain/diagnostic imaging
MH  - Humans
MH  - Image Processing, Computer-Assisted/*methods
MH  - Magnetic Resonance Imaging/*methods
MH  - Phantoms, Imaging
EDAT- 2018/07/12 06:00
MHDA- 2019/06/25 06:00
CRDT- 2018/07/12 06:00
PHST- 2018/07/12 06:00 [pubmed]
PHST- 2019/06/25 06:00 [medline]
PHST- 2018/07/12 06:00 [entrez]
AID - 10.1109/TMI.2018.2828112 [doi]
PST - ppublish
SO  - IEEE Trans Med Imaging. 2018 Aug;37(8):1809-1821. doi: 10.1109/TMI.2018.2828112. 
      Epub 2018 Apr 18.