Spin‐echo magnetic resonance spectroscopic imaging at 7 T with frequency‐modulated refocusing pulses

Two approaches to high‐resolution SENSE‐encoded magnetic resonance spectroscopic imaging (MRSI) of the human brain at 7 Tesla (T) with whole‐slice coverage are described. Both sequences use high‐bandwidth radiofrequency pulses to reduce chemical shift displacement artifacts, SENSE‐encoding to reduce scan time, and dual‐band water and lipid suppression optimized for 7 T. Simultaneous B₀ and transmit B₁ mapping was also used for both sequences to optimize field homogeneity using high‐order shimming and determine optimum radiofrequency transmit level, respectively. One sequence (“Hahn‐MRSI”) used reduced flip angle (90°) refocusing pulses for lower radiofrequency power deposition, while the other sequence used adiabatic fast passage refocusing pulses for improved sensitivity and reduced signal dependence on the transmit‐B₁ level. In four normal subjects, adiabatic fast passage‐MRSI showed a signal‐to‐noise ratio improvement of 3.2 ± 0.5 compared to Hahn‐MRSI at the same spatial resolution, pulse repetition time, echo time, and SENSE‐acceleration factor. An interleaved two‐slice Hahn‐MRSI sequence is also demonstrated to be experimentally feasible. Magn Reson Med, 2013. © 2012 Wiley Periodicals, Inc.