Application of the limited-memory quasi-Newton algorithm for multi-dimensional, large flip-angle RF pulses at 7T

TY - JOUR

T1 - Application of the limited-memory quasi-Newton algorithm for multi-dimensional, large flip-angle RF pulses at 7T

AU - Vinding, Mads Sloth

AU - Brenner, Daniel

AU - Tse, Desmond H. Y.

AU - Vellmer, Sebastian

AU - Vosegaard, Thomas

AU - Suter, Dieter

AU - Stöcker, Tony

AU - Maximov, Ivan

PY - 2017/2/1

Y1 - 2017/2/1

N2 - Objective: Ultrahigh field MRI provides great opportunities for medical diagnostics and research. However, ultrahigh field MRI also brings challenges, such as larger magnetic susceptibility induced field changes. Parallel-transmit radio-frequency pulses can ameliorate these complications while performing advanced tasks in routine applications. To address one class of such pulses, we propose an optimal-control algorithm as a tool for designing advanced multi-dimensional, large flip-angle, radio-frequency pulses. We contrast initial conditions, constraints, and field correction abilities against increasing pulse trajectory acceleration factors. Materials and methods: On an 8-channel 7T system, we demonstrate the quasi-Newton algorithm with pulse designs for reduced field-of-view imaging with an oil phantom and in vivo with scans of the human brain stem. We used echo-planar imaging with 2D spatial-selective pulses. Pulses are computed sufficiently rapid for routine applications. Results: Our dataset was quantitatively analyzed with the conventional mean-square-error metric and the structural-similarity index from image processing. Analysis of both full and reduced field-of-view scans benefit from utilizing both complementary measures. Conclusion: We obtained excellent outer-volume suppression with our proposed method, thus enabling reduced field-of-view imaging using pulse trajectory acceleration factors up to 4.

AB - Objective: Ultrahigh field MRI provides great opportunities for medical diagnostics and research. However, ultrahigh field MRI also brings challenges, such as larger magnetic susceptibility induced field changes. Parallel-transmit radio-frequency pulses can ameliorate these complications while performing advanced tasks in routine applications. To address one class of such pulses, we propose an optimal-control algorithm as a tool for designing advanced multi-dimensional, large flip-angle, radio-frequency pulses. We contrast initial conditions, constraints, and field correction abilities against increasing pulse trajectory acceleration factors. Materials and methods: On an 8-channel 7T system, we demonstrate the quasi-Newton algorithm with pulse designs for reduced field-of-view imaging with an oil phantom and in vivo with scans of the human brain stem. We used echo-planar imaging with 2D spatial-selective pulses. Pulses are computed sufficiently rapid for routine applications. Results: Our dataset was quantitatively analyzed with the conventional mean-square-error metric and the structural-similarity index from image processing. Analysis of both full and reduced field-of-view scans benefit from utilizing both complementary measures. Conclusion: We obtained excellent outer-volume suppression with our proposed method, thus enabling reduced field-of-view imaging using pulse trajectory acceleration factors up to 4.

KW - MRI

KW - Parallel transmit

KW - RF pulse design

KW - Ultrahigh field MRI

UR - http://www.scopus.com/inward/record.url?scp=84982794712&partnerID=8YFLogxK

U2 - 10.1007/s10334-016-0580-1

DO - 10.1007/s10334-016-0580-1

M3 - Journal article

C2 - 27485854

SN - 0968-5243

VL - 30

SP - 29

EP - 39

JO - Magnetic Resonance Materials in Physics, Biology and Medicine

JF - Magnetic Resonance Materials in Physics, Biology and Medicine

IS - 1

ER -