title: kT -points: short three-dimensional tailored RF pulses for flip-angle homogenization over an extended volume.
abstract: With Transmit SENSE, we demonstrate the feasibility of uniformly exciting a volume such as the human brain at 7T through the use of an original minimalist transmit k-space coverage, referred to as "k(T) -points." Radio-frequency energy is deposited only at a limited number of k-space locations in the vicinity of the center to counteract transmit sensitivity inhomogeneities. The resulting nonselective pulses are short and need little energy compared to adiabatic or other B 1+-robust pulses available in the literature, making them good candidates for short-repetition time 3D sequences at high field. Experimental verification was performed on three human volunteers at 7T by means of an 8-channel transmit array system. On average, whereas the standard circularly polarized excitation resulted in a 33%-flip angle spread (standard deviation over mean) throughout the brain, and a static radio-frequency shim showed flip angle variations of 17% and up, application of k(T) -point-based excitations demonstrated excellent flip angle uniformity (8%) for a small target flip angle and with sub-millisecond durations.
authors: CEA, DSV, I2BM, NeuroSpin, LRMN, Gif-sur-Yvette, France. Martijn.Cloos@cea.fr
authors: M A
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authors: Cloos
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authors: Boulant
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authors: Luong
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authors: Ferrand
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authors: Giacomini
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authors: Le Bihan
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authors: Amadon